Upload
others
View
6
Download
0
Embed Size (px)
Citation preview
Ethernet architecturePoint-to-point architecture
Computer Networks (ComNet) 5/5 :Data link and physical layers
Olivier Fourmaux ([email protected])
Version 6.3
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
ComNet: course 5/5 outline
1 Ethernet architecturetechnologyhardwareIEEE standards
2 Point-to-point architectureHDLCPPP: basic mechanismsPPP: usages
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
Underlying technologies and OSI model
Presentation
Application
Session
Transport
Network
Data link
Physical
7
6
5
4
3
2
1
Interface Interface
Host A
APDU
Presentation
Application
Session
Transport
Network
Data link
Physical
Host B
Network Network
Data link Data link
Physical Physical
Router Router
Application protocol
Presentation protocol
Transport protocol
Session protocol
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
OSI: the data link layer
The data link layer carries bits over a medium using a particulartransmission technique. The associated functions are:
framing and error controlsequencing, reliability, and flow controlthree technology types for the data link layer:
point-to-pointmultipoint without broadcast à U.E. RTELmultipoint with broadcast (shared medium)
Routing process
Router
Frames here
Packets here
2 2 2 3
2
3
Data link layer process
Transmission line to a router
Data link protocol
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
OSI: physical layer
The physical layer is associated with signal transmission:specification of the medium and the signaling
bit encoding, baseband or passband transmissioncharacteristics of the electrical, optical, radio, signals. . .characteristics of the media:
impedance of electrical cables, attenuation, max. length. . .multimode, monomode fiber optics. . .connector shapes, conduit colors. . .
Copper core
Insulating material
Braided outer conductor
Protective plastic covering
erehpsonoI
Earth's surface Earth's surface
(a) (b)
Ground wave
Jacket (plastic) Core Cladding
Sheath Jacket
Cladding (glass)
Core (glass)
(a) (b)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
Underlying technologies and TCP/IP
Ethernet
HTTP
TCP UDP
PPP
DNSSNMP
ATM MPLS
SMTP
IP
OSI data link + physical layers ∼ layers underlying TCP/IP
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
ComNet: course 5/5 outline
1 Ethernet architecturetechnologyhardwareIEEE standards
2 Point-to-point architectureHDLCPPP: basic mechanismsPPP: usages
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: introduction
Until the 1990’s: many LAN technologies
Ethernet, Token Ring, FDDI, ATM...
Today (for wired networks): LAN = Ethernet
Ethernet is to local networks what Internet is toplanetary-scale networks
why?
appeared first (mid-1970’s)simpledecentralizedautoconfigurable
à economical and adaptable
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: where?
...
... ... ...
... ...
......
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: various flavors
Different types of Ethernet. . .
two topologies:
bus, star
various media:
coaxial cables, twisted pair, fiber optics
wide range of bandwidths:
10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps, 40 Gbps, 100 Gbps
. . . but all on the same basis:
LAN addresses
frame structure
connectionless service with no reliability guarantees
generally, baseband (digital) transmission
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: LAN addresses
Interface addresses (6 bytes, hexadecimal notation) à identifier
also called:
Ethernet addressesphysical addressesMAC (Media Access Control) addresses
flat address space, administered by the IEEE
h
00:10:A4:87:BF:1A
00:04:76:21:25:EA
00:04:76:21:27:8E
00:20:ED:87:FD:E6
00:10:A4:86:2D:0B
00:78:77:0A:91:84
00:19:78:27:94:1A
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: frame structure (1)
Delimiting the frame:beginning
preambledetecting the sending of a framesynchronization to the sender’s clockmark the start of the frame (8th byte)
endno current during the interframe gap: IFS (Inter FrameSpacing)
8 octets 6 octets 6 octets 2 46 − 1500 max octets 4 octets
101010101010....1011Préambule Adresse
sourceType Données CRC
Adressedestination
3 octets 3 octets
Codeunique
Codeconstructeur
1: Diffusion ou multipoint0: Adresse individuelle
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: frame structure (2)
Destination and source addresses
an interface only accepts frames that are addressed to it
Ethernet type (Ethertype) > 1500:
0x0800 = DoD Internet 0x0806 = ARP
0x0801 = X.75 Internet 0x8035 = RAP
0x0802 = NBS Internet 0x8098 = Appletalk
0x0803 = ECMA Internet 0x86DD = IPv6...
Data:
MTU (Maximum Transfer Unit) = 1500 bytes
minimum size = 46 bytes plus with, if necessary, the additionof padding bytes (sent at the network layer)
CRC-32 (Cyclic Redundancy Check), generator polynomial:G(x) = x32 +x26 +x23 +x22 +x16 +x12 +x11 +x10 +x8 +x7 +x5 +x4 +x2 +x +1
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: service
Service offered to the network layer:
connectionlessdatagram service (just like IP or UDP)no setup exchange prior to sending data
no reliability guaranteeserror control (and discard without warning)no error correctionno acknowledgements
the sender does not know if the data has been deliveredno flow control (except in switches)no receiver windowloss detection at the higher layers (e.g., TCP)
à simplicity
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: transmission
Baseband
direct sending of digital signals
Manchester coding for 10 Mbps bandwidth
20 Mhz bandwidth required (1B/2B)
for higher bandwidths, 4B/5B (FDDI), 8B/10B (FiberChannel), 64B/66B and various encapsulations (FR, ATM,SONET...)
Bit stream 1 0 0 0 0 1 0 1 1 1 1
Binary encoding
Manchester encoding
(a)
(b)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Medium access protocole
Direct sender-receiver connections à see following slidesShared links:
channel sharing protocolsstatic bandwidth share (R/N per sender)
frequency division multiplexing (FDM)time division multiplexing (TDM)
resource sharing protocols (taking-turns protocols)deterministinc bandwidth share (R per sender)
pollingtoken-passing
random access protocolsstatistical bandwidth sharing (R per sender) but collisions arepossible
ALOHACSMA à Ethernet
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
ALOHA
University of Hawaii, 1970
datagram based radio networkrandom access protocol, completely decentralizedif collision, retransmission after a random wait time
User
Time
A
B
C
D
E
picture from Tanenbaum A. S. Computer Networks 3rd edition
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
CSMA
Improvement over the random approach
carrier sensing: CSMA (Carrier Sense Multiple Access)à wait before sendingcollision detection: CSMA/CD (CSMA with CollisionDetection) à retransmissions
example with a mini frame size of 64 bytesT detection: 64 bytes at 10 Mbps = 512/107 = 51, 2µsecT prop. max: 2 * 2500m at 2.108ms−1 = 25µsec + 8 ∗ trepet
Packet starts at time 0A B A B
Packet almost at B at τ - ∋
Collision at time τ
A B
Noise burst gets back to A at 2τ
A B
(a) (b)
(c) (d)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet access protocol (1)
How interfaces function:
start sending at any moment: time not discretized
no sending if activity is detected on the channel: CSMA
stop sending if other activity is detected: /CD
wait a (growing) random amount of time beforeretransmission: TBEB (Truncated Binary ExponentialBackoff)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet access protocol (2)
Protocol steps carried out by interfaces:
1 build and store the frame
2 if activity detected, wait for end of signal
3 wait for 96 bit IFS (without detecting a signal)
4 start transmission
1 if collision is detected
1 stop transmitting2 32 bit jam sequence3 exponential backoff (for the nth consecutive collision) of
int(rand()*2min(10,n))* 512 bits (exponential backoff phase)then return to step 2.
2 if not, continue transmitting until the end
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: 10Base5
bandwidth: 10 Mbps
topology: extended bus, with hosts connected viatransceivers that are attached to a coaxial cable by a bluecable (51.2µs max between 2 hosts à 4 repeaters + 2500mmax.)
medium: yellow coax., 500m max., and 2 50Ω terminatingresistors
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: 10Base2
bandwidth: 10 Mbps
topology: extended bus (51.2µs max à 4 repeaters and 925mmax. between 2 stations)
medium: black coaxial cable of 200m (185m max) and 30hosts max per segment, BNC T-Connecters and 50Ωterminating resistors
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: 10BaseT
bandwidth: 10 Mbpstopology: star based at a hubmedium: twisted pair, 100m max. (UTP3), RJ45connectorsaccess:
half duplex à CSMA/CDmultiple cascading hubs possible (51.2µs max)
full duplex à point-to-point bidirectional simultaneous(without collisions)
activity detection (Link Pulse every 16±8 ms)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: 100BaseTX (Fast Ethernet, 1995)
bandwidth: 100 Mbps
topology: hub based star
medium: twisted pair, 100m max (UTP5), RJ45 connectors
coding: 4B/5B (FDDI)access:
half duplex à CSMA/CD, minimum 64 bytes2 hubs can be linked (but 5.12µs max: 210m max)length limits and corporate networks... see switches
full duplex à point-to-point simultaneous bidirectional
activity detection (Fast Link Pulse: 33 pulses/∼16 ms)FLP consists of 16 bits for autonegotiation
detection of possible speeds, modes, and available mechanisms
many variants:100BaseT4: 4 UTP3 twisted pairs (no full duplex)100BaseFX: 2 optical fibers (400m MMF, 20km SMF)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: 1000BaseT (Gigabit Ethernet, 1998)
bandwidth: 1000 Mbps (1 Gbps)
topology: hub based star
medium: twisted pair, 100m max., UTP5+ (4 pairs)
coding: 8B/10B (= Fiber Channel 1G)
access:half duplex à CSMA/CD, min. 512 bytes (extend themedium if necessary) à 4.01µs rather than 0.512µs!
2 hubs can be connected (still 210m max)performance? carrier extension plus burst
full duplex à point-to-point simultaneous bidirectional
many variants:
1000BaseCX : 2 shielded twisted pairs (STPs): 25m1000BaseSX : 850nm multimode optical fiber (MMF): 500m1000BaseLX : 1300nm MMF and singlemode fiber (SMF): 5km
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: 10GBaseT (10Gigabit Ethernet, 2002)
bandwidth: 10 Gbps
topology: switch based star
medium:optical fiber:
MMF and SMF (from 65m to 40km max.)multiplex SONET/SDH : OC192 (10Gbit/s)
twisted pair:
100m max. on Cat. 6e (FTP 500MHz), 6a (UTP 500MHz)and 7 (STP 600MHz)
access: full duplex only (no more CSMA/CD)
coding: 64B/66B (= Fiber Channel 10G)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet: 40/100G (100Gigabit Ethernet, 2009)
bandwidth: 40/100 Gbps
topology: switch based star
medium:optical fiber:
100m on OM3 MMF40km max. on SMFmultiplexed SONET/SDH: OC768 (40Gbit/s)
twisted pair:
a few meters (backplane)
access: only full duplex
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Broadcast networks
IP transport:
address resolution
encapsulation format
Multiple access on a shared medium: implicit broadcast
A
B
C
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
ARP: Address Resolution Protocol
Explicit broadcast (use of a broadcast address)
@IP−A
@IP−B
@IP−C@H−A
@H−C
@H−B
Broadcast @H (@IP−B)?
? ?
?
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
ARP over Ethernet
ARP messages are transported directly in Ethernet frames:
ARP request: destination address = broadcast(FF:FF:FF:FF:FF:FF), source = requester
ARP response: destination address = requester,source = responder
6 octets 6 octets 2 46 − 1500 max octets 4 octets
Adressesource
Type CRCAdresse
destinationARP
2 octets 2 octets 2 octets
HWtype
Prototype
Plen
1 1 Hlen octets Plen octets Hlen octets Plen octets
Sender HA Target HASender PA Target PAOper−ation
Hlen
1: request2: response
1: ethernet0x0800 : IP
(ethernet=6)(IP=4)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
IP over Ethernet
Ethertype > 1500:
0x0800 = DoD Internet
Data:
MTU: maximum IP packet size = 1500 bytes
minimum size = 46 bytes (the IP packet can be smaller)
if necessary, add padding bytes8 octets 6 octets 6 octets 2 46 − 1500 max octets 4 octets
101010101010....1011Préambule
sourceCRC
destinationAdr. MAC Adr. MAC
Entête IP Données IP (bourrage)
08 00
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
ComNet: course 5/5 outline
1 Ethernet architecturetechnologyhardwareIEEE standards
2 Point-to-point architectureHDLCPPP: basic mechanismsPPP: usages
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet hub
physical layer entity (bit level)
multiport repeatera bit arriving on one interface is broadcast to the others
administration through SNMP, RMON...
interconnecting hubs
linearlyhierarchically with a federating hub...
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Interconnecting hubs
in a multilevel system (several hubs)
LAN = the entire local network (collision domain)segment = the equipment connected to a hub
benefits:
4 increases connectivity4 increases redundancy (in case hubs break down)8 physical limitations (distance, number of machines. . . )8 reduces the bandwidth per host8 increases collisions (and so reduces overall bandwidth)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet bridge
link layer entity (frame level)
frame switchingfilters on the basis of destination addressan arriving frame is sent out on the destination port onlyrecord + CSMA/CD (entities without address)
benefits:
4 separation of collision domains4 multi-technology (10Base2 with 100BaseTX...)4 no more physical limitations
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Bridge: filtering and forwarding
Filtering
determining whether to accept or reject a frame
Forwarding
choosing the output interface
à table:
LAN address Interface Time
00:10:A4:86:2D:0B 1 09: 32: 5500:04:76:21:27:8E 3 09: 32: 5500:04:76:21:1B:95 3 09: 32: 55... ... ...
algorithm, using the table:when a frame with @LAN dest arrives on If x, the table showsoutput port IF y:
if IF x = IF y then the frame comes from the destinationsegment à filterotherwise, send the frame on IF y à forwarding
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Transparent bridging
Autonomous learning
table creation algorithm:1 table initially empty2 upon frame reception, insertion into the table of:
1 its @LAN source
2 its arrival interface3 its arrival time
3 the entry remains valid for a limited time only
note:
if @LAN dest is not in the table then broadcast (copy to theother interfaces, record + CMSA/CD)such bridges are called:
plug and play (no configuration required)transparent (they do not themselves have addresses)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Bridge: redundancy
multiple paths
4 backup path4 autoconfiguration8 loops (duplicate frames)
spanning tree protocol (STP)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Bridges: STP (Spanning Tree Protocol)
bridged LAN with redundancy ∼ graph (nodes = bridges)graph without loop = tree à construction of a spanning tree
each bridge has an ID number: the smallest becomes the rootexchange of BPDUs <id root, dst root, id snd,
num port>
disable the ports that are not on the shortest path to the root
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Bridge or router
Bridge (layer 2): forwards frames
4 autoconfigurable4 forwarding performance8 all frames follow the same tree (SPF)8 global broadcasting
limited network size (→100 machines)simple functionality
Router (layer 3): forwards packets
4 no loops (TTL-limited forwarding)4 calculation of the best path (routing)8 manual configuration8 slower treatment of each PDU
large networks (1000→ machines)“intelligent” functionality: traffic isolation,filtering. . .
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet switch
high performance bridge (layer 2)
many interfaces (∼ hub)high aggregate bandwidth à switching fabric
multi-bandwidth
10 Mbps, 100 Mbps, 1 Gbps...
full duplexpossible to avoid CSMA/CD (∼ point-to-point links)
100
1001000
10Workgroup Switch
Catalyst
CiscoSystems
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
“Store and forward” switching
Storing prior to forwarding the frame
∼ bridge functionality
storage of the complete frame (and CRC-32 calculation)
minimum latency LF/Ri (LF frame size, Ri output bandwidth)
Workgroup Switch
Catalyst
CiscoSystems
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
“Cut-through” switching
Direct transmission
∼ hub functionality
send as soon as the output buffer is empty
minimum latency = time to read the destination address
example: 100Mbps, 1518 frame à gain ∼ 120µs
no integrity check on the frame (CRC-32)
Workgroup Switch
Catalyst
CiscoSystems
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet hierarchy (1)
Router
WAN
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
Ethernet hierarchy (2)
Additional functionality associated with full duplex:
flow control (back pressure)
avoid frame loss due to switch overloaddirect a PAUSE frame to the sender (IEEE 802.3x)
link aggregation (Ethernet trunk, NIC teaming, portchannel, port teaming, port trunking, link bundling,EtherChannel, Multi-link trunking, NIC bonding, networkbonding, Network Fault Tolerance...)
parallel use of several cables/ports to increase bandwidth andredundancysame switches, identical link bandwidthslate standardisation (IEEE 802.3ad in 2000, 802.1ax in 2008with the Link Aggregation Control Protocol)
virtualisation ...
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
VLAN (1)
Generic cabling infrastructureà logical LAN configuration: Virtual LAN
Twisted pairto a hub
Office
Switch
Hub
Hub
Corridor
Cableduct
picture from Tanenbaum A. S. Computer Networks 4rd edition
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
VLAN (2)
Configuration table in bridges and switches
assigns VLANsby portby LAN addressby protocol or layer 3 network
several VLANs per port for transit (Virtual STP)
E F G H
A B C D
I
J
K
L
M
N
O
E F G H
A B C D
I
J
K
L
M
N
OB1 B2 S1 S2
GW GW
GW
GW
W
G
G
G
G
W
WWWG
G W G G
W
WG
31
4
2
picture from Tanenbaum A. S. Computer Networks 4rd edition
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
ComNet: course 5/5 outline
1 Ethernet architecturetechnologyhardwareIEEE standards
2 Point-to-point architectureHDLCPPP: basic mechanismsPPP: usages
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
IEEE 802 standardization
Definition de l’architecture de standardisation:80
2 O
verv
iew
& A
rchi
tect
ure
802.3MAC
802.3
802.5MAC
802.5
802.11MAC
802.11
802.16MAC MAC
CSMA/CD Token ring WLAN WPAN WMAN
802.15
802.15
802.16PHY PHY PHY PHY PHY
802.1 Bridging
802.2 LLC
802.
10 S
ecur
ity
802.
1 M
anag
emen
t
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
802.1x
Some interesting standards:
802.1d MAC Bridges
STP...
802.1f MIB IEEE 802
802.1g MAC distant bridging
LAN interconnection of LAN with WAN technologies
802.1h MAC Bridging of Ethernet V2 in IEEE 802 LAN
802.1q Virtual Bridged LAN...
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
802.1q (1)
Adds a VLAN identifier to the frame:
Switching doneusing tags
Legacyframe
Taggedframe
Taggedframe
VLAN−awareswitch
VLAN−awareend domain
Legacyend domain
LegacyPC
VLAN−awarecore domain
VLAN−aware
PCpicture from Tanenbaum A. S. Computer Networks 4rd edition
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
802.1q (2)
Evolution of the Ethernet frame structure: 1522 bytes max!
only 802.1q enabled equipment exchanges the new frames
possibility to identify 4096 VLANs
3 pirority bits
802.3 Data PadCheck−
sumDestination
addressSourceaddress
802.1Q Data Pad
VLAN protocolID (0x8100)
Check−sum
Destinationaddress
Sourceaddress
Length
LengthTag
VLAN IdentifierCFI
Pri
picture from Tanenbaum A. S. Computer Networks 4rd edition
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
802.2 bridging
Subdivision into two sublayers of the OSI link layer
LLC (Logical Link Control) sublayer
MAC (Medium Access Control) sublayer
à allows direct bridging of different IEEE 802 networks:Host A
Network
LLC
MAC
Physical
Pkt
Pkt
Pkt802.3
802.3 Pkt
Host B
BridgePkt
Pkt
Pkt802.4
802.4 Pkt802.3
802.3 Pkt
Pkt
802.3 Pkt
802.4 Pkt
802.4 Pkt
802.4 PktPkt
CSMA/CD LAN Token bus LANpicture from Tanenbaum A. S. Computer Networks 3rd edition
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
IEEE 802.2
Datalink
layer
Network layer
Physical layer Network
LLC
MAC
LLC
LLC
Packet
Packet
Packet MAC MAC
802.3 Length Data PadCheck−
sumDestination
addressSourceaddress
802.11 Seq. DataCheck−
sumAddress
1Address
2Address
3Address
4Framecontrol
Dur−ation
802.16 DataCheck−
sumLength Connection ID Header
CRCType EK0 E
CCI
picture from Tanenbaum A. S. Computer Networks 4rd edition
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
IEEE 802.3: CSMA/CD
SNAP/LLC encapsulation:
8 octets 6 octets 6 octets 2 46 − 1500 max octets 4 octets
101010101010....1011Préambule
sourceCRC
destination
Données
Code
3 octets
AA AA
SNAP
DSAP SSAP
LLC
Type
2 octets1 1 1
Ctrl Organisation (Eth)03 00 00 00
TailleAdr. MAC Adr. MAC
Sous couche MAC
Sous couche LLC
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
IEEE 802.3: naming
802.3 1985 10Base5 thick coax 50Ω
802.3a 1988 10Base2 thin coax 50Ω
802.3b 1985 10Broad36 coaxial TV 75Ω
802.3i 1990 10BaseT on 2 UTP3 pairs
802.3j 1993 10BaseF on MM/SM fibers
802.3u 1995 100BaseT4 on 4 UTP3 pairs
802.3x/y 1997 100BaseT2 on 2 UTP5 pairs802.3z 1998 1000BaseX GBIC module
802.3ab 1999 1000BaseT on 4 UTP5 pairs
802.3ac 1998 VLAN for 802.3
802.3ad 2000 Trunking
802.3ae 2002 10GBaseX on MM/SM fibers
802.3af 2003 Power-over-Ethernet
802.3ah 2004 Ethernet in the First Mile
802.3an 2006 10GBASE-T on FTP6e or UTP7
802.3ap 2007 Backplane Ethernet
802.3av 2009 10 Gbits/s PHY EPON
802.3ba 2009 Ethernet 40 and 100 Gbits/s
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
IEEE 802.5: Token RingRing
interfaceStation
Unidirectional ring
1 bit delay
Ring interface
To station
From station
To station
From station
(a) (b) (c)
Destination address
Source address
ChecksumData
No limit 4Bytes 2 or 6 2 or 6
Starting delimiter
Access controlFrame control Ending delimiter
Frame status
SD AC ED FS
1 1
FC
1 1 1
SD AC ED
1 1 1
(a)
(b)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
technologyhardwareIEEE standards
IEEE802.11: WLAN (Wireless Ethernet)
service zone: cell or BSS (Basic Service Set)
wireless stationsbase station or AP (Access Point) acting as an 802 bridge
MAC: CSMA/CA
...
BSS
AP
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
ComNet: course 5/5 outline
1 Ethernet architecturetechnologyhardwareIEEE standards
2 Point-to-point architectureHDLCPPP: basic mechanismsPPP: usages
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
Direct communication between two entities
Basic functionalities of point-to-point communications:
framing
functionalities similar to those found in the transport layer arealso possible (except congestion control):
error controlflow controlsequencing (numbering)sliding windowreliability (acknowledgements and retransmissions)
For transporting data:
no address resolution
encapsulation format
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
Point-to-point data link layer
Point-to-point service defined in the OSI data link layer
Characteristics:homogeneous interface technology
Routing process
Router
Frames here
Packets here
2 2 2 3
2
3
Data link layer process
Transmission line to a router
Data link protocol
various transmission unitsbits, bytes, cells...
various neighboring layerscan have layers between this layer and the physical layercan have multiple active elements (multiplexers, modems,bridges, switches, routers, application gateways. . . )
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
Point-to-point data link: where?
...
... ... ...
... ...
......
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
ComNet: course 5/5 outline
1 Ethernet architecturetechnologyhardwareIEEE standards
2 Point-to-point architectureHDLCPPP: basic mechanismsPPP: usages
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
HDLC: protocol family
Most protocols from the data link layer are related to HDLC:
SDLC (Synchronous Data Link Control) from IBM for SNA
ADCCP (Advance Data Communication Control Procedure)ANSI version of SDLC
HDLC (High-level Data Link Control) ISO version of SDLC
LAP (Link Access Procedure) ITU version of HDLC
LAP-B for X25LAP-D for ISDNLAP-F for Frame Relay ...
PPP (Point-to-Point Protocol) IETF standard
These protocols function over a wide variety of physical mediathat enable transmission of bits (or other signals) between twohosts.
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
HDLC: structure
Breakdown into bits or bytes
a (flag) used for delimitation à (01111110)2
series of bits: 01111110 (bit stuffing protection)byte of value 0x7E (byte stuffing protection)
3 frame types (control):
Information: data transmission with a sliding window (max.7 unacknowledged frames)
Supervisory: flow control, non-piggybacked ACK, NACK,request for selective retransmission. . .
Unumbered: for internal control in the data link layer
0 1 1 1 1 1 1 0 0 1 1 1 1 1 1 0Address Control Data Checksum
Bits 8 8 8 > 0 16 8
picture from Tanenbaum A. S. Computer Networks 3rd edition
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
IP over serial line
SLIP (Serial Line Internet Protocol)
character oriented, delimited with the character 0xC0basic: no control, no negotiation
PPP ...
PC
Routing process
Router
Modems
Internet provider's office
User's home
Client process using TCP/IP
Modem
Dial-up telephone line
TCP/IP connection using SLIP or PPP
picture from Tanenbaum A. S. Computer Networks 3rd edition
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
ComNet: course 5/5 outline
1 Ethernet architecturetechnologyhardwareIEEE standards
2 Point-to-point architectureHDLCPPP: basic mechanismsPPP: usages
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPP: (Point-to-Point Protocol, RFC 1661)
General protocol à many features
multi-protocol
transports a variety of layer 3 traffic, not just IPoperates over a variety of technologies, not just serial lines
negotiation
adaptation to the medium (detection and correction of errors,protection of modems’ control codes, header compression. . . )automatic client configuration
Couche réseau (3)
PAP
CHAPCouche liaison (2)
Compression d’entete
PPP
IP
Adaptation au support
Couche physique (1) ou assimilée...
authentification données négociation
LCP
NCP
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPP: protocol structure
Simple encapsulation: adds 2 bytes (compressible to 1)Protocol: indicates the type of information transported
LCP: control protocol at the link layernegotation of parameters of the underlying medium(compression, frame size. . . )
PAP and CHAP: authentication protocolsNCP: control protocol at the network layer
negotation of parameters of the protocol being transported(addressing. . . ) à specific to each network layer protocol thatis supported
IP, AppleTalk, IPX, IPv6...Payload: contains the frame data
MRU (Maximum Receive Unit) negotiable (default: 1500 B)padding if the underlying medium requires it
Flag01111110
Flag01111110
Address11111111
ProtocolControl00000011
Payload Checksum
Bytes 1 1 2 (1)1 Variable 2 1
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPP: protocols carried
Valeur Description
0x0001 Padding protocol
0x0021 IP
0x0029 AppelTalk
0x002B IPX
0x002D/2F TCP/IP w/ Van Jacobson header compression
0x0057 IPv6
0x0281 MPLS
0x8021 IPCP: IP configuration
0x8029 ATCP: AppleTalk configuration
0x802B IPXCP: IPX configuration
0x8057 IPV6CP: IPv6 configuration
0x8281 MPLS configuration
0xC021 LCP: Link Control Protocol
0xC023 PAP: Password Authentification Protocol
0xC025 LQR: Link Quality Report
0xC223 CHAP: Challenge Handshake Authentification Protocol
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPP: classical encapsulation
Similar to an HDLC frame for a bytestream:
a binary flag: 0111 1110 (0x7E)address (1 byte): 1111 1111 (0xFF, broadcast)
there is only one receiver (point-to-point)control (1 octet):
reliable link à no control: 0000 0011 (0x03, UI frame, seeRFC 1662)
optimisation: field suppression Address and Control
unreliable link à sequencing control (see HDLC, UA andSABME frames, see RFC 1663)
Protocol and Payload: PPP encapsulation
Checksum (2 bytes): CRC 16 bits
another binary flag: 0111 1110
Flag01111110
Flag01111110
Address11111111
ProtocolControl00000011
Payload Checksum
Bytes 1 1 2 (1)1 Variable 2 1
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPP: flag protection
Deux types de liaison point-a-point:
synchronous (bits: the flag is the sequence 0111 1110)bit stuffing protection
a 0 bit is added after every five 1 bits01111110111110 à 0111110101111100
asynchronous (bytes, the flag has the value 0x7E)byte stuffing protection
escape byte with value 0x7D:0x7E à 0x7D 0x5E
0x7D à 0x7D 0x5D
special byte values for active control of the asynchronousconnection (correspond to ASCII codes < 32), same protectionprinciple:
0x11 (XON: restart the transfer) à 0x7D 0x31
0x13 (XOFF: stop the transfer) à 0x7D 0x33
à The available bandwidth is variable!
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPP: negotiation
Structure of a typical PPP negotiation frame:
0 7 15 bit 31code identifier length
data
code: indicates the type of negotiation
identifier: associates queries with responses
length: total frame size, with the LCP header
allows one to eliminate eventual padding bytes
data: parameters of the negotiation
Negotiation begins at the start of the connection
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPP: negotiation frames
Val. Code Description LCP NCP
1 Configure-Request change default values [4] [4]
2 Configure-Ack receiver accepts all changes [4] [4]
3 Configure-Nak values refused, others proposed [4] [4]
4 Configure-Reject values nonnegotiable [4] [4]
5 Terminate-Request a host wishes to terminate [4] [4]
6 Terminate-Ack confirm termination [4] [4]
7 Code-Reject code unknown [4] [4]
8 Protocol-Reject protocol unknown [4]
9 Echo-Request request link state test [4]
10 Echo-Reply link state test reply [4]
11 Discard-Request silently discarded by the receiver [4]
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
LCP (Link Control Protocol)
Oversee the state of the link
PPP frame protocol field: 0xC021
initial negotiation when connection is opened
TLV style option definition
see RFC 1570 and RFC 1661format:
1 byte 1 byte (Length - 2) bytes
Type Length Value
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
LCP: option types
Val. Code Length Description
1 MRU 4 maximum size of received frames
2 ACCM 6 table of transcoding values
3 authentification 4 type of auth. protocol
4 qualite 6 type of QoS mgt. protocol
5 Magic Number 6 negotiation of this value
7 compression protocol 2 1 byte protocol field
8 compression address 2 suppression of these fieldsand control
10 self-describing padding 3 padding parameter that can beautomatically eliminated
13 callback 3+ ...
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PAP (Password Authentication Protocol, RFC 1334)
Once the connection is established and the LCP parametersnegotiatedà identity verification
protocol field of the PPP frame: 0xC023cleartext transmission of the identifier and password4 types of negotiation frame (Configure-Request,Configure-Ack, Configure-Nak ou Configure-Reject)format identical to LCP, code value:
1: authentication request:1 B (IdLgth) bytes 1 B (PassLgth) bytes
IdLgth Identifier PassLgth Password
2: positive acknowledgement:1 B (IdLgth) bytes
IdLgth Client message
3: negative acknowledgement (retransmission required):1 B (IdLgth) bytes
IdLgth Client message
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
CHAP (CHallenge Authentication Protocol, RFC 1334)
After LCP negotiation and during communicationà identity verification
PPP frame protocol field: 0xC223
the 2 endpoints share a secret key
4 types of negotiation frames (Configure-Request,Configure-Ack, Configure-Nak or Configure-Reject)format identical to LCP, value of the code field:
1: challenge (binary sequence sent):1 B (FieldLgth) bytes
FieldLgth binary sequence
2: response (sequence returned encrypted with the key
à certificate):1 B (CCLgth) bytes
CCLgth encrypted binary sequence
3: success: the received encrypted sequence and the onecalculated locally are identical4: failure (retransmission necessary)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
RADIUS (Remote Auth. Dial-In User Service, RFC 2865)
Centralization of the information regarding a user:
AAA functions: Authentication, Authorization, andAccounting
identity verificationknowing one’s rights and access configurationtracking the user’s actions
client/server modelclient can connect to different access points of an ISP
client: access point of an ISP (PPP endpoint, or other proto.)server: supports a database of ISP users
ADSL
PPPoA PPP
CHAPPAP
RTC
Serveur RADIUS
FAI
10
1010
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
RADIUS: message
Connectionless service (UDP port 1812)
reliability handled at the application layer
format:
0 7 16 bit 31
code identifier length
authentifierdigest = MD5(code+id.+lgth.+auth req+param+secret)
parameters
typical exchange:Access-Request client message
username, encrypted passwordIP address of the access point, UDP portsession type (PPP, rlogin, telnet...)
Access-Accept RADIUS server resonselist of session attributes (address, servers. . . )
Access-Reject RADIUS server responsethe user is not in the database, or does not have access rights
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
NCP (Network Control Protocol)
After link configuration (LCP) and optional authentication (PAPor CHAP), configuration of the layer 3 protocols
one NCP per protocol that is carried:
IPCP for IPv4 configuration (RFC 1332)IPV6CP for IPv6 configuration (RFC 2472)ATCP for AppleTalk configuration (RFC 1378)IPXCP for IPX configuration (RFC 1552)OSINLCP for OSI protocol configuration (RFC 1377)...
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
IPCP (Internet Protocol Control Protocol)
PPP frame protocol field: 0x8021
4 types of negotiation frames (Configure-Request,Configure-Ack, Configure-Nak or Configure-Reject)
format identical to LCP, value of code field:2: header compression
2 bytes for the type of compression (0x002d for VanJacobson; 0x0061 for extended, RFC 2507; 0x0003 forROHC, RObust Header Compression, RFC 3241)1 byte for the max number of compressed connections1 byte to indicate the presence of a connection number
3: 4 byte client IP address4: permanent IP address (home address)129: primary DNS server IP address130: primary NBNS server IP address131: secondary DNS server IP address132: secondary NBNS server IP address
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
TCP/IP header compression
PPP must make efficient use of low bandwidth links
interactive TCP/IP connection (telnet...)
Nagle’s algorithmlarge headersexample:
0020 ea 14 81 cf 00 15 52 40 18 65 52 65 10 0e 50 10
0010 00 28 b5 8f 40 00 40 06 0d be 84 e3 3d 7a cb 10
trame 1 (A−>B)
trame 2 (A−>B)
0000 45 00
0000 45 00
0010 00 29 b5 8e 40 00 40 06 0f 78 84 e3 3d 7a cb 10
0020 ea 14 81 cf 00 15 52 40 18 64 52 65 10 0d 50 18
0030 ff ff bb 7b 00 00 64
0030 ff ff aa 5f 00 00
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
Differences between two segments
32 bits (4 octets)
D F
M F
HlenVer TOS Packet Lenght
Identifier Frag. offset
TTL Protocol Header checksum
IP source address
IP destination address
Destination portSource port
Sequence number
Acknowledgment number
Checksum Urgent data ptr
Rcv window sizeHlen
P S H
F I N
S Y N
R S T
U R G
A C K
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
Van Jacobson algorithm
TCP/IP header compression algorithm (RFC 1144)
classic headers preserved for SYN, RST, and FIN (protocolfield value 0x0021)then, compression:
entire packet sent with a connection identifier (0x002F):for synchronization (first complete packet)for negative ACK or sequence numbers (error)
difference between two headers (0x002D):connection identifierstate maintained at each endpointonly the fields that have changed are sentthe difference is usually encoded with one byte
SYNFINRST
Emetteur Récepteur
inef.
Comp.
0x002D
UDP/IP
TCP/IP
UDP/IP
TCP/IP 0x002F
0x0021
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
Compressed IP header
données
8 bits
C I P S A W U
delta fenetredelta acquittement
id. connexion
pointeur urgent
delta séquencedelta id. IP
checksum TCP
Only the first byte and theTCP checksum are required(3 B min.)
1st byte: presence of fieldsC bit: connection ID present
not sent if same as previous
U bit: copyW bit: window delta
negative two’s complement
S/A bits: seq./acq. delta
no negative values
I bit: IP ID delta
absent = +1
P bit: copy PUSH TCP bit
deltas encoded in 1 to 2 B
1 byte:0x01 to 0xFF3 B: 0x000100 to 0x00FFFF
TCP checksum: copy
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
Error detection
TCP checsum used to validate the reconstituted packet:
checksum TCPnon valide
Hôte A Hôte B
RTOrejet
S=10
S=10
S=12
S=17
S=15
S=15
S=12
S reconstitué
002F| S=12......
002D|S+3
002D|S+3
002D|S+2
002D|S+2
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
ComNet: course 5/5 outline
1 Ethernet architecturetechnologyhardwareIEEE standards
2 Point-to-point architectureHDLCPPP: basic mechanismsPPP: usages
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
POS (Packet Over SONET)
PPP Over SONET/SDH (RFC 2615)
PPP initially for low bandwidth PSTN links
also adapted to telecom high bandwidth linkshierarchy of SONET/SDH multiplexing
OC-3c/STM-1 (155 Mbps)OC-12c/STM-4c (622 Mbps)OC-48c/STM-16c (2.5 Gbps)OC-192c/STM-64c (10 Gbps)OC-768c/STM-256c (40 Gbps)
PPP over synchronous byte-based links
∼ byte-oriented serial connections
goal: closeness to the fiberPOS simplifies the IP/ATM/SONET approach
MPLS/POS more flexible (Traffic Eng.)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
POS (2)
POS
ATM
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPPoA (PPP Over ATM/AAL5, RFC 2364)
Telecom operators’ last mile is usually ATM
Use of AAL 5 ATM connections
no more HDLC framingadaptation of CPCS PDU AAL 5 frames
padding (multiples of 48 bytes)
two RFC 1483 encapsulations:VC-multiplexed PPP
the endpoints know that they are transporting PPP
LLC encapsulated PPP
protocol identification for each PDU
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPPoA: encapsulations
VCMUX
Protocol Identifier(8 or 16 bits)
...PPP information field PPP payload
...
PAD ( 0 - 47 bytes)
CPCS-UU (1 byte)CPI (1 byte)
Length (2 bytes) CPCS-PDUCRC (4 bytes) Trailer
SNAP/LLC
Destination SAP (0xFE)Source SAP (0xFE) LLC header
Frame Type = UI (0x03)
NLPID = PPP (0xCF)
Protocol Identifier(8 or 16 bits)
...PPP information field PPP payload
...
PAD ( 0 - 47 bytes)
CPCS-UU (1 byte)CPI (1 byte)
Length (2 bytes) CPCS-PDUCRC (4 bytes) Trailer
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPPoA: remarks
Avantages:
dissociates the ADSL/ATM provider from the ISPper-session authentication (PAP and CHAP)user supervision (RADIUS)
per-session billing of usersoverbooking and timed disconnections
attribution of an IP address to the clientsecuring access without ATM-level management
ATM signaling too complex: use of PVCVPNs handled by PPP tunnels (no end-to-end PVC)
adaptable to network evolutionaggregation routers (high density of PPP terminations)
Disadvantages:
one connection per PVCoverall coplexity of the solution (IP, PPP, AAA, ATM...)1 IP address à NPAT limits the applications
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPPoA over ADSL
Client
Multiplexer
OF OF OF OF
DSL Access
ATMATM ATMATM
PPP
IP
TCP
HTTP
IP
HTTP
TCP
IP
PPP
TelTel
?
? ?
?
Server
Telephone Company
ATM Switch
modem DSL
PPPoA
ISP
Internet
1 0
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPPoE (PPP Over Ethernet, RFC 2516)
Point-to-point over a shared link:
Ethernet has self-configuration: ARP, DHCP. . .... but no remote handling, nor AAA
Putting in place a point-to-point connection over EthernetEthertype values
0x8863 for discovery frames0x8864 for data frames
payload format for these Ethernet phase:0 4 7 16 bit 31
Ver Type Code Session id
Length
PPPoE payload...
Ver and Type = 0x01Code = 0x00 (data) and ... (discovery)Session id = flow identifier (with MAC addr.)Length = data length (remove padding)
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPPoE: discovery messages
Encapsulated in PPPoE frames (Ethertype = 0x8863)
Code field:
0x09: PADI (PPPoE Active Discovery Initiation) à broadcast0x07: PADO (PPPoE Active Discovery Offer) à proposition(with Session id)0x19: PADR (PPPoE Active Discovery Request) à selection0x65: PADS (PPPoE Active Discovery Session-confirmation)0xA7: PADT (PPPoE Active Discovery Terminate)
champ PPPoE payload (TLV avec caracteres codees UTF-8):0 16 bit 31
Tag type Tag length
Tag value ...
IRC name, name of last mile company, session identifier,validation cookie, error type
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPPoE: remarks
Avantages:
similar to those of PPPoAper-session authentification (PAP and CHAP)
in a LAN-type network type
user monitoring (RADIUS)billing session usersoverbooking and connections timing out
uuser without direct access ATM (briding)
many connections per PVCgiving an IP address to the client
maintain the point-to-point model on a shared medium
Drawbacks:
LAN technology subject to broadcast bursts
solution complexity (IP, PPP, AAA, ATM, LAN...)
1 IP address à NPAT still limits applications
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPPoE over ADSL
OFOF
DSL AccessMultiplexer
Client
ATMATM ATM
Brigde /
ATM
OFOF
IP
PPP
TCP
HTTP
IP
HTTP
TCP
IP
PPP
Tel Tel
TPTP
Eth Eth/LLC LLC
ISP
SNAP/LLC over ATM
PPPoE
modem DSL
Server
Telephone Company
ATM Switch
?
Internet
??
?
1 0
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
PPP tunnels
Carrying PPP frames
L2F (Layer 2 Forwarding)
proprietary to Cisco, Northern Telecom, and Shivafrom a Home Gateway to a Network Access Server
PPTP (Point-to-Point Tunneling Protocol)
proprietary to Microsoft, 3Com, Ascend, US Robotics, and ECITelematicsfrom a concentrator to an access server (software)
L2TP (Layer 2 Tunneling Protocol)
IETF standard
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
L2TP: architecture
Example: ADSL access
the ADSL access provider (AAP) manages the link up to anaccess concentrator (AC)how to reach the Internet service provider (ISP)?
AC at the ISP (serving a single ISP)the AAP manages IP configuration (delegated by the ISP)the ISP has access to each AC (too heavy)
creating of an tunnel from the AC to the ISPcarrying PPP across the network between the AAP and theISP
LAC LNSTelecomInternet
L2TP Acces Concentrator
ISP
L2TP Network Server
PPP L2TP
IP
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
L2TP (Layer 2 Tunneling Protocol, RFC 2661)
Two communication channels:
Control Channel: exchange of tunnel control messages,with a dedicated reliability and flow control protocolData Channel: PPP frames encapsulated in unreliable,unsecured L2TP messages
telecom networks (ATM, FR...)Internet (UDP port 1702)
+----------------------------+
| PPP Frames |
+----------------------------+ +---------------------------------+
| L2TP Data Messages | | L2TP Control Messages |
+----------------------------+ +---------------------------------+
| L2TP Data Channel (unrel.) | | L2TP Control Channel (reliable) |
+-----------------------------------------------------------------+
| Packet Transport (UDP, FR, ATM, etc.) |
+-----------------------------------------------------------------+
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
ADSL and L2TP
Brigde /
DSL Access
ATMATM
Client
Multiplexer
OF OF
ATM
TCP
L2TP
PPP
Eth/LLCEth
TP TP
Tel
IP
L2TP
IPTel IP
HTTP
IP
TCP
IP
PPP
LLC
UDP UDP
PPP
HTTP
ISP
Internet
?
?
?
?
?
?
Telephone Company
SNAP/LLC over ATM
PPPoE
modem DSL
Server
?
?
1 0
1 0
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers
Ethernet architecturePoint-to-point architecture
HDLCPPP: basic mechanismsPPP: usages
VPN (Virtual Private Network)
Virtual links between several entities
inexpensive private networks (shared infrastructure)generally Internet
can carry other protocolscan concatenate several technologies (ATM-TCP/IP. . . )
based on tunnels between different endpoints
no network accessisolated machine
security
IPSEC à U.E. ING
Olivier Fourmaux ([email protected]) Computer Networks (ComNet) 5/5 : Data link and physical layers