Chapter3 transport layer

1

Transport Layer 3-1

Chapter 3Transport Layer

Computer Networking A Top Down Approach 5th edition Jim Kurose Keith RossAddison-Wesley April 2009

Transport Layer 3-2

Chapter 3 Transport LayerOur goals understand principles

behind transport layer services multiplexingdemultipl

exing reliable data transfer flow control congestion control

learn about transport layer protocols in the Internet UDP connectionless

transport TCP connection-oriented

transport TCP congestion control

2

Transport Layer 3-3

Chapter 3 outline

31 Transport-layer services

32 Multiplexing and demultiplexing

33 Connectionless transport UDP

34 Principles of reliable data transfer

35 Connection-oriented transport TCP segment structure reliable data transfer flow control connection management

36 Principles of congestion control

37 TCP congestion control

Transport Layer 3-4

Transport services and protocols provide logical communication

between app processes running on different hosts

transport protocols run in end systems send side breaks app

messages into segments passes to network layer

rcv side reassembles segments into messages passes to app layer

more than one transport protocol available to apps Internet TCP and UDP

applicationtransportnetworkdata linkphysical


3

Transport Layer 3-5

Transport vs network layer

network layer logical communication between hosts

transport layer logical communication between processes relies on enhances

network layer services

Household analogy12 kids sending letters to

12 kids processes = kids app messages = letters

in envelopes hosts = houses transport protocol =

Ann and Bill network-layer protocol

= postal service

Transport Layer 3-6

Internet transport-layer protocols

reliable in-order delivery (TCP) congestion control flow control connection setup

unreliable unordered delivery UDP no-frills extension of

ldquobest-effortrdquo IP services not available

delay guarantees bandwidth guarantees


networkdata linkphysical







4

Transport Layer 3-7

Chapter 3 outline








Transport Layer 3-8

Multiplexingdemultiplexing

application

transport

network

link

physical

P1 application

transport

network

link

physical

application

transport

network

link

physical

P2P3 P4P1

host 1 host 2 host 3

= process= socket

delivering received segmentsto correct socket

Demultiplexing at rcv hostgathering data from multiplesockets enveloping data with header (later used for demultiplexing)

Multiplexing at send host

5

Transport Layer 3-9

How demultiplexing works host receives IP datagrams

each datagram has source IP address destination IP address

each datagram carries 1 transport-layer segment

each segment has source destination port number

host uses IP addresses amp port numbers to direct segment to appropriate socket

source port dest port

32 bits

applicationdata

(message)

other header fields

TCPUDP segment format

Transport Layer 3-10

Connectionless demultiplexing

Create sockets with port numbers

DatagramSocket mySocket1 = new DatagramSocket(12534)


UDP socket identified by two-tuple

(dest IP address dest port number)

When host receives UDP segment checks destination port

number in segment directs UDP segment to

socket with that port number

IP datagrams with different source IP addresses andor source port numbers directed to same socket

6


Connectionless demux (cont)DatagramSocket serverSocket = new DatagramSocket(6428)

ClientIPB

P2

clientIP A

P1P1P3

serverIP C

SP 6428DP 9157

SP 9157DP 6428

SP 6428DP 5775

SP 5775DP 6428

SP provides ldquoreturn addressrdquo


Connection-oriented demux

TCP socket identified by 4-tuple source IP address source port number dest IP address dest port number

receiving host uses all four values to direct segment to appropriate socket

Server host may support many simultaneous TCP sockets each socket identified by

its own 4-tuple Web servers have

different sockets for each connecting client non-persistent HTTP will

have different socket for each request

7


Connection-oriented demux (cont)

ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B


Connection-oriented demux Threaded Web Server

ClientIPB

P1

clientIP A

P1P2

serverIP C

SP 9157DP 80

SP 9157DP 80

P4 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

8


Chapter 3 outline









UDP User Datagram Protocol [RFC 768]

ldquono frillsrdquo ldquobare bonesrdquo Internet transport protocol

ldquobest effortrdquo service UDP segments may be lost delivered out of order

to app connectionless

no handshaking between UDP sender receiver

each UDP segment handled independently of others

Why is there a UDP no connection

establishment (which can add delay)

simple no connection state at sender receiver

small segment header no congestion control UDP

can blast away as fast as desired

9


UDP more often used for streaming

multimedia apps loss tolerant rate sensitive

other UDP uses DNS SNMP

reliable transfer over UDP add reliability at application layer application-specific

error recovery


32 bits

Applicationdata

(message)

UDP segment format

length checksumLength in

bytes of UDPsegmentincluding

header


UDP checksum

Sender treat segment contents

as sequence of 16-bit integers

checksum addition (1rsquos complement sum) of segment contents

sender puts checksum value into UDP checksum field

Receiver compute checksum of

received segment check if computed checksum

equals checksum field value NO - error detected YES - no error detected

But maybe errors nonetheless More later hellip

Goal detect ldquoerrorsrdquo (eg flipped bits) in transmitted segment

10


Internet Checksum Example Note

When adding numbers a carryout from the most significant bit needs to be added to the result

Example add two 16-bit integers

1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


Chapter 3 outline








11


Principles of Reliable data transfer important in app transport link layers top-10 list of important networking topics

characteristics of unreliable channel will determine complexity of reliable data transfer protocol (rdt)




12





Reliable data transfer getting started

sendside

receiveside

rdt_send() called from above (eg by app) Passed data to

deliver to receiver upper layer

udt_send() called by rdtto transfer packet over

unreliable channel to receiver

rdt_rcv() called when packet arrives on rcv-side of channel

deliver_data() called by rdt to deliver data to upper

13


Reliable data transfer getting startedWersquoll incrementally develop sender receiver sides of

reliable data transfer protocol (rdt) consider only unidirectional data transfer

but control info will flow on both directions use finite state machines (FSM) to specify

sender receiver

state1

state2

event causing state transitionactions taken on state transition

state when in this ldquostaterdquo next state

uniquely determined by next event

eventactions


Rdt10 reliable transfer over a reliable channel

underlying channel perfectly reliable no bit errors no loss of packets

separate FSMs for sender receiver sender sends data into underlying channel receiver read data from underlying channel

Wait for call from above packet = make_pkt(data)

udt_send(packet)

rdt_send(data)

extract (packetdata)deliver_data(data)

Wait for call from

below

rdt_rcv(packet)

sender receiver

14


Rdt20 channel with bit errors

underlying channel may flip bits in packet checksum to detect bit errors

the question how to recover from errors acknowledgements (ACKs) receiver explicitly tells sender

that pkt received OK negative acknowledgements (NAKs) receiver explicitly

tells sender that pkt had errors sender retransmits pkt on receipt of NAK

new mechanisms in rdt20 (beyond rdt10) error detection receiver feedback control msgs (ACKNAK) rcvr-gtsender


rdt20 FSM specification

Wait for call from above

snkpkt = make_pkt(data checksum)udt_send(sndpkt)

extract(rcvpktdata)deliver_data(data)udt_send(ACK)

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt)

rdt_rcv(rcvpkt) ampamp isACK(rcvpkt)

udt_send(sndpkt)

rdt_rcv(rcvpkt) ampampisNAK(rcvpkt)

udt_send(NAK)

rdt_rcv(rcvpkt) ampamp corrupt(rcvpkt)

Wait for ACK or

NAK

Wait for call from

belowsender

receiverrdt_send(data)

15


rdt20 operation with no errors






udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)


rdt20 error scenario






udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16


rdt20 has a fatal flaw

What happens if ACKNAK corrupted

sender doesnrsquot know what happened at receiver

canrsquot just retransmit possible duplicate

Handling duplicates sender retransmits current

pkt if ACKNAK garbled sender adds sequence

number to each pkt receiver discards (doesnrsquot

deliver up) duplicate pkt

Sender sends one packet then waits for receiver response

stop and wait


rdt21 sender handles garbled ACKNAKs

Wait for call 0 from

above

sndpkt = make_pkt(0 data checksum)udt_send(sndpkt)

rdt_send(data)

Wait for ACK or NAK 0 udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||isNAK(rcvpkt) )


rdt_send(data)

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp isACK(rcvpkt)

udt_send(sndpkt)



Wait forcall 1 from

above

Wait for ACK or NAK 1

17


rdt21 receiver handles garbled ACKNAKs

Wait for 0 from below

sndpkt = make_pkt(NAK chksum)udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp not corrupt(rcvpkt) ampamphas_seq0(rcvpkt)

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp has_seq1(rcvpkt)

extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(ACK chksum)udt_send(sndpkt)




rdt_rcv(rcvpkt) ampamp (corrupt(rcvpkt)

sndpkt = make_pkt(ACK chksum)udt_send(sndpkt)






rdt21 discussion

Sender seq added to pkt two seq rsquos (01) will

suffice Why must check if received

ACKNAK corrupted twice as many states

state must ldquorememberrdquo whether ldquocurrentrdquo pkt has 0 or 1 seq

Receiver must check if received

packet is duplicate state indicates whether

0 or 1 is expected pkt seq

note receiver can notknow if its last ACKNAK received OK at sender

18


rdt22 a NAK-free protocol

same functionality as rdt21 using ACKs only instead of NAK receiver sends ACK for last pkt

received OK receiver must explicitly include seq of pkt being ACKed

duplicate ACK at sender results in same action as NAK retransmit current pkt


rdt22 sender receiver fragments


above


rdt_send(data)

udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||

isACK(rcvpkt1) )

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp isACK(rcvpkt0)

Wait for ACK

0

sender FSMfragment



extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(ACK1 chksum)udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp (corrupt(rcvpkt) ||

has_seq1(rcvpkt))

udt_send(sndpkt)

receiver FSMfragment

19


rdt30 channels with errors and loss

New assumptionunderlying channel can also lose packets (data or ACKs) checksum seq ACKs

retransmissions will be of help but not enough

Approach sender waits ldquoreasonablerdquo amount of time for ACK

retransmits if no ACK received in this time

if pkt (or ACK) just delayed (not lost) retransmission will be

duplicate but use of seq rsquos already handles this

receiver must specify seq of pkt being ACKed

requires countdown timer


rdt30 sendersndpkt = make_pkt(0 data checksum)udt_send(sndpkt)start_timer

rdt_send(data)

Wait for

ACK0

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||isACK(rcvpkt1) )


above

sndpkt = make_pkt(1 data checksum)udt_send(sndpkt)start_timer

rdt_send(data)




stop_timerstop_timer

udt_send(sndpkt)start_timer

timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21


Performance of rdt30

rdt30 works but performance stinks ex 1 Gbps link 15 ms prop delay 8000 bit packet

U sender utilization ndash fraction of time sender busy sending

U sender =

00830008

= 000027 L R RTT + L R

=

1KB pkt every 30 msec -gt 33kBsec thruput over 1 Gbps link network protocol limits use of physical resources

dsmicrosecon8bps10

bits80009

R

Ldtrans


rdt30 stop-and-wait operation

first packet bit transmitted t = 0

sender receiver

RTT

last packet bit transmitted t = L R

first packet bit arriveslast packet bit arrives send ACK

ACK arrives send next packet t = RTT + L R

U sender =

00830008

= 000027 L R RTT + L R

=

22


Pipelined protocolsPipelining sender allows multiple ldquoin-flightrdquo yet-to-

be-acknowledged pkts range of sequence numbers must be increased buffering at sender andor receiver

Two generic forms of pipelined protocols go-Back-N selective repeat


Pipelining increased utilization


sender receiver

RTT

last bit transmitted t = L R



last bit of 2nd packet arrives send ACKlast bit of 3rd packet arrives send ACK

U sender =

02430008

= 00008 3 L R RTT + L R

=

Increase utilizationby a factor of 3

23


Pipelining Protocols

Go-back-N overview sender up to N

unACKed pkts in pipeline

receiver only sends cumulative ACKs doesnrsquot ACK pkt if

therersquos a gap sender has timer for

oldest unACKed pkt if timer expires

retransmit all unACKed packets

Selective Repeat overview sender up to N unACKed

packets in pipeline receiver ACKs individual

pkts sender maintains timer

for each unACKed pkt if timer expires retransmit

only unACKed packet


Go-Back-NSender k-bit seq in pkt header ldquowindowrdquo of up to N consecutive unACKed pkts allowed

ACK(n) ACKs all pkts up to including seq n - ldquocumulative ACKrdquo may receive duplicate ACKs (see receiver)

timer for each in-flight pkt timeout(n) retransmit pkt n and all higher seq pkts in window

24


GBN sender extended FSM

Wait start_timerudt_send(sndpkt[base])udt_send(sndpkt[base+1])hellipudt_send(sndpkt[nextseqnum-1])

timeout

rdt_send(data)

if (nextseqnum lt base+N) sndpkt[nextseqnum] = make_pkt(nextseqnumdatachksum)udt_send(sndpkt[nextseqnum])if (base == nextseqnum)

start_timernextseqnum++

elserefuse_data(data)

base = getacknum(rcvpkt)+1If (base == nextseqnum)

stop_timerelsestart_timer


base=1nextseqnum=1



GBN receiver extended FSM

ACK-only always send ACK for correctly-received pkt with highest in-order seq may generate duplicate ACKs need only remember expectedseqnum

out-of-order pkt discard (donrsquot buffer) -gt no receiver buffering Re-ACK pkt with highest in-order seq

Wait

udt_send(sndpkt)

default

rdt_rcv(rcvpkt)ampamp notcurrupt(rcvpkt)ampamp hasseqnum(rcvpktexpectedseqnum)

extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(expectedseqnumACKchksum)udt_send(sndpkt)expectedseqnum++

expectedseqnum=1sndpkt = make_pkt(expectedseqnumACKchksum)

25


GBN inaction


Selective Repeat

receiver individually acknowledges all correctly received pkts buffers pkts as needed for eventual in-order delivery

to upper layer sender only resends pkts for which ACK not

received sender timer for each unACKed pkt

sender window N consecutive seq rsquos again limits seq s of sent unACKed pkts

26


Selective repeat sender receiver windows


Selective repeat

data from above if next available seq in

window send pkttimeout(n) resend pkt n restart timerACK(n) in [sendbasesendbase+N]

mark pkt n as received if n smallest unACKed pkt

advance window base to next unACKed seq

senderpkt n in [rcvbase rcvbase+N-1]

send ACK(n) out-of-order buffer in-order deliver (also

deliver buffered in-order pkts) advance window to next not-yet-received pkt

pkt n in [rcvbase-Nrcvbase-1]

ACK(n)otherwise ignore

receiver

27


Selective repeat in action


Selective repeatdilemma

Example seq rsquos 0 1 2 3 window size=3

receiver sees no difference in two scenarios

incorrectly passes duplicate data as new in (a)

Q what relationship between seq size and window size

28


Chapter 3 outline









TCP Overview RFCs 793 1122 1323 2018 2581

full duplex data bi-directional data flow

in same connection MSS maximum segment

size connection-oriented

handshaking (exchange of control msgs) initrsquos sender receiver state before data exchange

flow controlled sender will not

overwhelm receiver

point-to-point one sender one receiver

reliable in-order byte steam no ldquomessage boundariesrdquo

pipelined TCP congestion and flow

control set window size send amp receive buffers

socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment

applicationwrites data

applicationreads data

29


TCP segment structure


32 bits

applicationdata

(variable length)

sequence numberacknowledgement number

Receive windowUrg data pointerchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)


TCP seq rsquos and ACKsSeq rsquos

byte stream ldquonumberrdquo of first byte in segmentrsquos data

ACKs seq of next byte

expected from other side

cumulative ACKQ how receiver handles

out-of-order segments A TCP spec doesnrsquot

say - up to implementer

Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt

of echoedlsquoCrsquo

host ACKsreceipt oflsquoCrsquo echoes

back lsquoCrsquo

timesimple telnet scenario

30


TCP Round Trip Time and Timeout

Q how to set TCP timeout value

longer than RTT but RTT varies

too short premature timeout unnecessary

retransmissions too long slow reaction

to segment loss

Q how to estimate RTT SampleRTT measured time from

segment transmission until ACK receipt ignore retransmissions

SampleRTT will vary want estimated RTT ldquosmootherrdquo average several recent

measurements not just current SampleRTT



EstimatedRTT = (1- )EstimatedRTT + SampleRTT

Exponential weighted moving average influence of past sample decreases exponentially fast typical value = 0125

31


Example RTT estimationRTT gaiacsumassedu to fantasiaeurecomfr

100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)

SampleRTT Estimated RTT



Setting the timeout EstimtedRTT plus ldquosafety marginrdquo

large variation in EstimatedRTT -gt larger safety margin first estimate of how much SampleRTT deviates from

EstimatedRTT

TimeoutInterval = EstimatedRTT + 4DevRTT

DevRTT = (1-)DevRTT +|SampleRTT-EstimatedRTT|

(typically = 025)

Then set timeout interval

32


Chapter 3 outline









TCP reliable data transfer

TCP creates rdt service on top of IPrsquos unreliable service

pipelined segments cumulative ACKs TCP uses single

retransmission timer

retransmissions are triggered by timeout events duplicate ACKs

initially consider simplified TCP sender ignore duplicate ACKs ignore flow control

congestion control

33


TCP sender eventsdata rcvd from app create segment with

seq seq is byte-stream

number of first data byte in segment

start timer if not already running (think of timer as for oldest unACKed segment)

expiration interval TimeOutInterval

timeout retransmit segment

that caused timeout restart timerACK rcvd if acknowledges

previously unACKed segments update what is known to

be ACKed start timer if there are

outstanding segments


TCP sender(simplified)

NextSeqNum = InitialSeqNumSendBase = InitialSeqNum

loop (forever) switch(event)

event data received from application above create TCP segment with sequence number NextSeqNum if (timer currently not running)

start timerpass segment to IP NextSeqNum = NextSeqNum + length(data)

event timer timeoutretransmit not-yet-acknowledged segment with

smallest sequence numberstart timer

event ACK received with ACK field value of y if (y gt SendBase)

SendBase = yif (there are currently not-yet-acknowledged segments)

start timer

end of loop forever

Commentbull SendBase-1 last cumulatively ACKed byteExamplebull SendBase-1 = 71y= 73 so the rcvrwants 73+ y gt SendBase sothat new data is ACKed

34


TCP retransmission scenariosHost A

timepremature timeout

Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100


TCP retransmission scenarios (more)Host A

loss

tim

eout

Cumulative ACK scenario

Host B

X

time

SendBase= 120

35


TCP ACK generation [RFC 1122 RFC 2581]

Event at Receiver

Arrival of in-order segment withexpected seq All data up toexpected seq already ACKed

Arrival of in-order segment withexpected seq One other segment has ACK pending

Arrival of out-of-order segmenthigher-than-expect seq Gap detected

Arrival of segment that partially or completely fills gap

TCP Receiver action

Delayed ACK Wait up to 500msfor next segment If no next segmentsend ACK

Immediately send single cumulative ACK ACKing both in-order segments

Immediately send duplicate ACK indicating seq of next expected byte

Immediate send ACK provided thatsegment starts at lower end of gap


Fast Retransmit

time-out period often relatively long long delay before

resending lost packet detect lost segments

via duplicate ACKs sender often sends

many segments back-to-back

if segment is lost there will likely be many duplicate ACKs for that segment

If sender receives 3 ACKs for same data it assumes that segment after ACKed data was lost fast retransmit resend

segment before timer expires

36


Host A

tim

eout

Host B

time

X

seq x1seq x2seq x3seq x4seq x5

ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer

else increment count of dup ACKs received for yif (count of dup ACKs received for y = 3)

resend segment with sequence number y

Fast retransmit algorithm

a duplicate ACK for already ACKed segment

fast retransmit

37


Chapter 3 outline









TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching send rate to receiving applicationrsquos drain rate

app process may be slow at reading from buffer

sender wonrsquot overflowreceiverrsquos buffer by

transmitting too muchtoo fast

flow control

IPdatagrams

TCP data(in buffer)

(currently)unused buffer

space

applicationprocess

38


TCP Flow control how it works

(suppose TCP receiver discards out-of-order segments)

unused buffer space= rwnd

= RcvBuffer-[LastByteRcvd -LastByteRead]

receiver advertises unused buffer space by including rwnd value in segment header

sender limits of unACKed bytes to rwnd guarantees receiverrsquos

buffer doesnrsquot overflow

IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39


TCP Connection ManagementRecall TCP sender receiver

establish ldquoconnectionrdquo before exchanging data segments

initialize TCP variables seq s buffers flow control

info (eg RcvWindow) client connection initiator

Socket clientSocket = new Socket(hostnameport

number)

server contacted by clientSocket connectionSocket = welcomeSocketaccept()

Three way handshakeStep 1 client host sends TCP

SYN segment to server specifies initial seq no data

Step 2 server host receives SYN replies with SYNACK segment server allocates buffers specifies server initial

seq Step 3 client receives SYNACK

replies with ACK segment which may contain data


TCP Connection Management (cont)

Closing a connection

client closes socketclientSocketclose()

Step 1 client end system sends TCP FIN control segment to server

Step 2 server receives FIN replies with ACK Closes connection sends FIN

client server

close

close

closed

tim

ed w

ait

40



Step 3 client receives FIN replies with ACK

Enters ldquotimed waitrdquo -will respond with ACK to received FINs

Step 4 server receives ACK Connection closed

Note with small modification can handle simultaneous FINs

client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline









Principles of Congestion Control

Congestion informally ldquotoo many sources sending too much

data too fast for network to handlerdquo different from flow control manifestations

lost packets (buffer overflow at routers) long delays (queueing in router buffers)

a top-10 problem

42


Causescosts of congestion scenario 1

two senders two receivers

one router infinite buffers

no retransmission

large delays when congested

maximum achievable throughput

unlimited shared output link buffers

Host Ain original data

Host B

out



one router finite buffers sender retransmission of lost packet

finite shared output link buffers

Host A in original data

Host B

out

in original data plus retransmitted data

43


Causescosts of congestion scenario 2 always (goodput) ldquoperfectrdquo retransmission only when loss

retransmission of delayed (not lost) packet makes larger (than perfect case) for same

in

out

=

in

out

gt

in

out

ldquocostsrdquo of congestion more work (retrans) for given ldquogoodputrdquo unneeded retransmissions link carries multiple copies of pkt

R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3


Causescosts of congestion scenario 3 four senders multihop paths timeoutretransmit

in

Q what happens as and increase

in



Host B

out


44



another ldquocostrdquo of congestion when packet dropped any ldquoupstream transmission

capacity used for that packet was wasted

Host A

Host B

ou

t


Approaches towards congestion control

end-end congestion control

no explicit feedback from network

congestion inferred from end-system observed loss delay

approach taken by TCP

network-assisted congestion control

routers provide feedback to end systems single bit indicating

congestion (SNA DECbit TCPIP ECN ATM)

explicit rate sender should send at

two broad approaches towards congestion control

45


Case study ATM ABR congestion control

ABR available bit rate ldquoelastic servicerdquo if senderrsquos path

ldquounderloadedrdquo sender should use

available bandwidth if senderrsquos path

congested sender throttled to

minimum guaranteed rate

RM (resource management) cells

sent by sender interspersed with data cells

bits in RM cell set by switches (ldquonetwork-assistedrdquo) NI bit no increase in rate

(mild congestion) CI bit congestion

indication RM cells returned to sender by

receiver with bits intact



two-byte ER (explicit rate) field in RM cell congested switch may lower ER value in cell senderrsquo send rate thus maximum supportable rate on path

EFCI bit in data cells set to 1 in congested switch if data cell preceding RM cell has EFCI set sender sets CI

bit in returned RM cell

46


Chapter 3 outline









TCP congestion control goal TCP sender should transmit as fast as possible

but without congesting network Q how to find rate just below congestion level

decentralized each TCP sender sets its own rate based on implicit feedback ACK segment received (a good thing) network not

congested so increase sending rate lost segment assume loss due to congested

network so decrease sending rate

47


TCP congestion control bandwidth probing

ldquoprobing for bandwidthrdquo increase transmission rate on receipt of ACK until eventually loss occurs then decrease transmission rate continue to increase on ACK decrease on loss (since available

bandwidth is changing depending on other connections in network)

ACKs being received so increase rate

X

X

XX

X loss so decrease ratese

ndin

g ra

te

time

Q how fast to increasedecrease details to follow

TCPrsquosldquosawtoothrdquobehavior


TCP Congestion Control details

sender limits rate by limiting number of unACKed bytes ldquoin pipelinerdquo

cwnd differs from rwnd (how why) sender limited by min(cwndrwnd)

roughly

cwnd is dynamic function of perceived network congestion

rate = cwndRTT bytessec

LastByteSent-LastByteAcked cwnd

cwndbytes

RTT

ACK(s)

48


TCP Congestion Control more details

segment loss event reducing cwnd

timeout no response from receiver cut cwnd to 1

3 duplicate ACKs at least some segments getting through (recall fast retransmit) cut cwnd in half less

aggressively than on timeout

ACK received increase cwnd

slowstart phase increase exponentially

fast (despite name) at connection start or following timeout

congestion avoidance increase linearly


TCP Slow Start when connection begins cwnd =

1 MSS example MSS = 500 bytes

amp RTT = 200 msec initial rate = 20 kbps

available bandwidth may be gtgt MSSRTT desirable to quickly ramp up

to respectable rate increase rate exponentially

until first loss event or when threshold reached double cwnd every RTT done by incrementing cwnd

by 1 for every ACK received

Host A

RTT

Host B

time

49


Transitioning intoout of slowstartssthresh cwnd threshold maintained by TCP on loss event set ssthresh to cwnd2

remember (half of) TCP rate when congestion last occurred when cwnd gt= ssthresh transition from slowstart to congestion

avoidance phase

slow start timeout

ssthresh = cwnd2cwnd = 1 MSS

dupACKcount = 0retransmit missing segment

timeoutssthresh = cwnd2

cwnd = 1 MSSdupACKcount = 0

retransmit missing segment

cwnd gt ssthresh

cwnd = cwnd+MSSdupACKcount = 0transmit new segment(s)as allowed

new ACKdupACKcount++

duplicate ACK

cwnd = 1 MSS

ssthresh = 64 KBdupACKcount = 0 congestion

avoidance


TCP congestion avoidance

when cwnd gt ssthreshgrow cwnd linearly increase cwnd by 1

MSS per RTT approach possible

congestion slower than in slowstart

implementation cwnd = cwnd + MSScwndfor each ACK received

ACKs increase cwnd by 1 MSS per RTT additive increase

loss cut cwnd in half (non-timeout-detected loss ) multiplicative decrease

AIMD

AIMD Additive IncreaseMultiplicative Decrease

50


TCP congestion control FSM overview

slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout


TCP congestion control FSM details

slow start

congestionavoidance

fastrecovery



retransmit missing segmenttimeout

ssthresh = cwnd2 cwnd = 1 MSS


cwnd gt ssthresh


new ACKcwnd = cwnd + MSS (MSScwnd)

dupACKcount = 0transmit new segment(s)as allowed

new ACK

dupACKcount++

duplicate ACK

ssthresh= cwnd2cwnd = ssthresh + 3retransmit missing segment

dupACKcount == 3

dupACKcount++

duplicate ACK

ssthresh= cwnd2cwnd = ssthresh + 3


dupACKcount == 3

timeoutssthresh = cwnd2cwnd = 1 dupACKcount = 0retransmit missing segment

cwnd = cwnd + MSStransmit new segment(s) as allowed

duplicate ACK

cwnd = ssthreshdupACKcount = 0

New ACK

cwnd = 1 MSS

ssthresh = 64 KBdupACKcount = 0

51


Popular ldquoflavorsrdquo of TCP

ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)


Summary TCP Congestion Control

when cwnd lt ssthresh sender in slow-startphase window grows exponentially

when cwnd gt= ssthresh sender is in congestion-avoidance phase window grows linearly

when triple duplicate ACK occurs ssthresh set to cwnd2 cwnd set to ~ ssthresh

when timeout occurs ssthresh set to cwnd2 cwnd set to 1 MSS

52


TCP throughput

Q whatrsquos average throughout of TCP as function of window size RTT ignoring slow start

let W be window size when loss occurswhen window is W throughput is WRTTjust after loss window drops to W2

throughput to W2RTT average throughout 75 WRTT


TCP Futures TCP over ldquolong fat pipesrdquo

example 1500 byte segments 100ms RTT want 10 Gbps throughput

requires window size W = 83333 in-flight segments

throughput in terms of loss rate

L = 210-10 Wow new versions of TCP for high-speed

LRTT

MSS221

53


fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness


Why is TCP fairTwo competing sessions Additive increase gives slope of 1 as throughout increases multiplicative decrease decreases throughput proportionally

R

R

equal bandwidth share

Connection 1 throughput

congestion avoidance additive increaseloss decrease window by factor of 2


54


Fairness (more)Fairness and UDP multimedia apps often

do not use TCP do not want rate

throttled by congestion control

instead use UDP pump audiovideo at

constant rate tolerate packet loss

Fairness and parallel TCP connections

nothing prevents app from opening parallel connections between 2 hosts

web browsers do this example link of rate R

supporting 9 connections new app asks for 1 TCP gets

rate R10 new app asks for 11 TCPs

gets R2


Chapter 3 Summary principles behind transport

layer servicesmultiplexing

demultiplexing reliable data transfer flow control congestion control

instantiation and implementation in the Internet UDP TCP

Next leaving the network

ldquoedgerdquo (application transport layers)

into the network ldquocorerdquo

2

Transport Layer 3-3

Chapter 3 outline








Transport Layer 3-4

Transport services and protocols provide logical communication

between app processes running on different hosts

transport protocols run in end systems send side breaks app

messages into segments passes to network layer

rcv side reassembles segments into messages passes to app layer

more than one transport protocol available to apps Internet TCP and UDP



3

Transport Layer 3-5









= postal service

Transport Layer 3-6














4

Transport Layer 3-7

Chapter 3 outline








Transport Layer 3-8


application

transport

network

link

physical

P1 application

transport

network

link

physical

application

transport

network

link

physical

P2P3 P4P1


= process= socket




5

Transport Layer 3-9







32 bits

applicationdata

(message)

other header fields













6



ClientIPB

P2

clientIP A

P1P1P3

serverIP C

SP 6428DP 9157

SP 9157DP 6428

SP 6428DP 5775

SP 5775DP 6428










7



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2

serverIP C

SP 9157DP 80

SP 9157DP 80

P4 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

8


Chapter 3 outline




















9






error recovery


32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum










10





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


Chapter 3 outline








11







12






sendside

receiveside







13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









3

Transport Layer 3-5









= postal service

Transport Layer 3-6














4

Transport Layer 3-7

Chapter 3 outline








Transport Layer 3-8


application

transport

network

link

physical

P1 application

transport

network

link

physical

application

transport

network

link

physical

P2P3 P4P1


= process= socket




5

Transport Layer 3-9







32 bits

applicationdata

(message)

other header fields













6



ClientIPB

P2

clientIP A

P1P1P3

serverIP C

SP 6428DP 9157

SP 9157DP 6428

SP 6428DP 5775

SP 5775DP 6428










7



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2

serverIP C

SP 9157DP 80

SP 9157DP 80

P4 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

8


Chapter 3 outline




















9






error recovery


32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum










10





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


Chapter 3 outline








11







12






sendside

receiveside







13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









4

Transport Layer 3-7

Chapter 3 outline








Transport Layer 3-8


application

transport

network

link

physical

P1 application

transport

network

link

physical

application

transport

network

link

physical

P2P3 P4P1


= process= socket




5

Transport Layer 3-9







32 bits

applicationdata

(message)

other header fields













6



ClientIPB

P2

clientIP A

P1P1P3

serverIP C

SP 6428DP 9157

SP 9157DP 6428

SP 6428DP 5775

SP 5775DP 6428










7



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2

serverIP C

SP 9157DP 80

SP 9157DP 80

P4 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

8


Chapter 3 outline




















9






error recovery


32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum










10





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


Chapter 3 outline








11







12






sendside

receiveside







13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









5

Transport Layer 3-9







32 bits

applicationdata

(message)

other header fields













6



ClientIPB

P2

clientIP A

P1P1P3

serverIP C

SP 6428DP 9157

SP 9157DP 6428

SP 6428DP 5775

SP 5775DP 6428










7



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2

serverIP C

SP 9157DP 80

SP 9157DP 80

P4 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

8


Chapter 3 outline




















9






error recovery


32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum










10





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


Chapter 3 outline








11







12






sendside

receiveside







13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









6



ClientIPB

P2

clientIP A

P1P1P3

serverIP C

SP 6428DP 9157

SP 9157DP 6428

SP 6428DP 5775

SP 5775DP 6428










7



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2

serverIP C

SP 9157DP 80

SP 9157DP 80

P4 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

8


Chapter 3 outline




















9






error recovery


32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum










10





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


Chapter 3 outline








11







12






sendside

receiveside







13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









7



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2

serverIP C

SP 9157DP 80

SP 9157DP 80

P4 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

8


Chapter 3 outline




















9






error recovery


32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum










10





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


Chapter 3 outline








11







12






sendside

receiveside







13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









8


Chapter 3 outline




















9






error recovery


32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum










10





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


Chapter 3 outline








11







12






sendside

receiveside







13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









9






error recovery


32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum










10





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


Chapter 3 outline








11







12






sendside

receiveside







13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









10





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum


Chapter 3 outline








11







12






sendside

receiveside







13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









11







12






sendside

receiveside







13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









12






sendside

receiveside







13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









13





sender receiver

state1

state2




eventactions






udt_send(packet)

rdt_send(data)


Wait for call from

below

rdt_rcv(packet)

sender receiver

14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









14















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









15








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









16











stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









17


















rdt21 discussion









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









18









above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0

sender FSMfragment





has_seq1(rcvpkt))

udt_send(sndpkt)


19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









19













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)

20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









20


rdt30 in action


rdt30 in action

21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









21





U sender =

00830008

= 000027 L R RTT + L R

=


dsmicrosecon8bps10

bits80009

R

Ldtrans




sender receiver

RTT




U sender =

00830008

= 000027 L R RTT + L R

=

22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









22








sender receiver

RTT





U sender =

02430008

= 00008 3 L R RTT + L R

=


23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









23













only unACKed packet





24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









24




timeout

rdt_send(data)







base=1nextseqnum=1






Wait

udt_send(sndpkt)

default




25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









25


GBN inaction


Selective Repeat





26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









26




Selective repeat










receiver

27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









27









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









28


Chapter 3 outline















overwhelm receiver





socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment



29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









29




32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)









Host A Host B

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo


30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









30







to segment loss









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









31



100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

isec

onds

)






EstimatedRTT



(typically = 025)


32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









32


Chapter 3 outline















congestion control

33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









33






















start timer

end of loop forever


34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









34




Host B

Seq=

92 t

imeo

ut

Host A

loss

tim

eout

lost ACK scenario

Host B

X

timeSe

q=92

tim

eout

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



loss

tim

eout


Host B

X

time

SendBase= 120

35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









35



Event at Receiver





TCP Receiver action






Fast Retransmit








36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









36


Host A

tim

eout

Host B

time

X


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit

37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









37


Chapter 3 outline









TCP Flow Control






flow control

IPdatagrams

TCP data(in buffer)


space

applicationprocess

38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









38









IPdatagrams

TCP data(in buffer)


space

applicationprocess

rwndRcvBuffer


Chapter 3 outline








39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









39







number)













client server

close

close

closed

tim

ed w

ait

40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









40







client server

closing

closing

closedti

med

wai

t

closed



TCP clientlifecycle

TCP serverlifecycle

41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









41


Chapter 3 outline













a top-10 problem

42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









42





no retransmission





Host B

out






Host B

out


43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









43




in

out

=

in

out

gt

in

out


R2

R2in

out

b

R2

R2in

out

a

R2

R2in

out

c

R4

R3



in


in



Host B

out


44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









44





Host A

Host B

ou

t












45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









45



















46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









46


Chapter 3 outline














47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









47






X

X

XX


ndin

g ra

te

time







roughly




cwndbytes

RTT

ACK(s)

48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









48



















Host A

RTT

Host B

time

49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









49




avoidance phase

slow start timeout






cwnd gt ssthresh



duplicate ACK

cwnd = 1 MSS


avoidance









AIMD


50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









50



slow start

congestionavoidance

fastrecovery

cwnd gt ssthresh

losstimeout

losstimeout

new ACK loss3dupACK

loss3dupACK

losstimeout



slow start

congestionavoidance

fastrecovery






cwnd gt ssthresh




new ACK

dupACKcount++

duplicate ACK


dupACKcount == 3

dupACKcount++

duplicate ACK



dupACKcount == 3



duplicate ACK


New ACK

cwnd = 1 MSS


51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









51



ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









52


TCP throughput










LRTT

MSS221

53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









53



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness



R

R





54












gets R2









54












gets R2









Documents

Chapter3 transport layer