Chapter 1: roadmap - Universitetet i Bergenmatthew/INF14213/LectureSlides/SummaryCh1To7.pdf · Chapter 1: roadmap 1.1 what is the ... guided media: signals propagate in solid media:

Introduction

Chapter 1: roadmap1.1 what is the Internet?1.2 network edge

end systems, access networks, links1.3 network core

packet switching, circuit switching, network structure1.4 delay, loss, throughput in networks1.5 protocol layers, service models1.6 networks under attack: security1.7 history

1-3

Introduction

Internet: “network of networks” Interconnected ISPs

protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, 802.11

Internet standards RFC: Request for comments IETF: Internet Engineering Task Force

What’s the Internet: “nuts and bolts” view

mobile network

global ISP

regional ISP

home network

institutional network

1-6

What’s the Internet: a service view

Infrastructure that provides services to applications: Web, VoIP, email, games, e-

commerce, social nets, … provides programming

interface to apps hooks that allow sending

and receiving app programs to “connect” to Internet

provides service options, analogous to postal service

mobile network

global ISP

regional ISP

home network


Introduction 1-7

Introduction




1-10

Introduction

A closer look at network structure:

network edge: hosts: clients and servers servers often in data

centers

access networks, physical media: wired, wireless communication links

network core: interconnected routersnetwork of networks

mobile network

global ISP

regional ISP

home network


1-11

Introduction

Access net: digital subscriber line (DSL)

central office

ISP

telephonenetwork

DSLAM

voice, data transmittedat different frequencies over

dedicated line to central office

use existing telephone line to central office DSLAM data over DSL phone line goes to Internet voice over DSL phone line goes to telephone net

< 2.5 Mbps upstream transmission rate (typically < 1 Mbps) < 24 Mbps downstream transmission rate (typically < 10 Mbps)

DSLmodem

splitter

DSL access multiplexer

1-13

Introduction

Access net: cable network

cablemodem

splitter

…

cable headend

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

frequency division multiplexing: different channels transmittedin different frequency bands

1-14

Introduction

Access net: home network

to/from headend or central office

cable or DSL modem

router, firewall, NAT

wired Ethernet (100 Mbps)

wireless access point (54 Mbps)

wirelessdevices

often combined in single box

1-16

Introduction

Enterprise access networks (Ethernet)

typically used in companies, universities, etc 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates today, end systems typically connect into Ethernet switch

Ethernet switch

institutional mail,web servers

institutional router

institutional link to ISP (Internet)

1-17

Introduction

Wireless access networks

shared wireless access network connects end system to router via base station aka “access point”

wireless LANs: within building (100 ft) 802.11b/g (WiFi): 11, 54 Mbps

transmission rate

wide-area wireless access provided by telco (cellular)

operator, 10’s km between 1 and 10 Mbps 3G, 4G: LTE

to Internet

to Internet

1-18

Introduction

Physical media

bit: propagates betweentransmitter/receiver pairs

physical link: what lies between transmitter & receiver

guided media: signals propagate in solid

media: copper, fiber, coax unguided media:

signals propagate freely, e.g., radio

twisted pair (TP) two insulated copper

wires Category 5: 100 Mbps, 1

Gpbs Ethernet Category 6: 10Gbps

1-20

Introduction

Physical media: coax, fiber

coaxial cable: two concentric copper

conductors bidirectional broadband:

multiple channels on cable HFC

fiber optic cable: glass fiber carrying light

pulses, each pulse a bit high-speed operation:

high-speed point-to-point transmission (e.g., 10’s-100’s Gpbs transmission rate)

low error rate: repeaters spaced far apart immune to electromagnetic

noise

1-21

Introduction

Physical media: radio

signal carried in electromagnetic spectrum

no physical “wire” bidirectional propagation environment

effects: reflection obstruction by objects interference

radio link types: terrestrial microwave

e.g. up to 45 Mbps channels LAN (e.g., WiFi)

11Mbps, 54 Mbps wide-area (e.g., cellular)

3G cellular: ~ few Mbps satellite

Kbps to 45Mbps channel (or multiple smaller channels)

270 msec end-end delay geosynchronous versus low

altitude

1-22

Introduction


end systems, access networks, links

1.3 network core packet switching, circuit switching, network structure

1.4 delay, loss, throughput in networks1.5 protocol layers, service models1.6 networks under attack: security1.7 history

1-23

Introduction

mesh of interconnected routers

packet-switching: hosts break application-layer messages into packets forward packets from one

router to the next, across links on path from source to destination

each packet transmitted at full link capacity

The network core

1-24

Network Layer 4-27

Two key network-core functionsforwarding: move packets from router’s input to appropriate router output

routing: determines source-destination route taken by packets

routing algorithms

routing algorithm

local forwarding table

header value output link

0100010101111001

3221

1

23

0111

dest address in arrivingpacket’s header

Introduction

Alternative core: circuit switchingend-end resources allocated

to, reserved for “call” between source & dest:

In diagram, each link has four circuits. call gets 2nd circuit in top

link and 1st circuit in right link.

dedicated resources: no sharing circuit-like (guaranteed)

performance circuit segment idle if not used

by call (no sharing) Commonly used in traditional

telephone networks1-28

Internet structure: network of networks

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnetaccess

net

accessnet

…

………

…

…

… and content provider networks (e.g., Google, Microsoft, Akamai ) may run their own network, to bring services, content close to end users

ISP B

ISP A

ISP B

IXP

IXP

regional net

Content provider network

Introduction




1-42

Introduction

Four sources of packet delay

dproc: nodal processing check bit errors determine output link typically < msec

A

B

propagation

transmission

nodalprocessing queueing

dqueue: queueing delay time waiting at output link

for transmission depends on congestion

level of router

dnodal = dproc + dqueue + dtrans + dprop

1-44

Introduction

Packet loss queue (aka buffer) preceding link in buffer has finite

capacity packet arriving to full queue dropped (aka lost) lost packet may be retransmitted by previous node, by

source end system, or not at all

A

B

packet being transmitted

packet arriving tofull buffer is lost

buffer (waiting area)

1-51* Check out the Java applet for an interactive animation on queuing and loss

Introduction

Throughput throughput: rate (bits/time unit) at which bits

transferred between sender/receiver instantaneous: rate at given point in time average: rate over longer period of time

server, withfile of F bits

to send to client

link capacity Rs bits/sec

link capacity Rc bits/sec

server sends bits (fluid) into pipe

pipe that can carryfluid at rate Rs bits/sec)

pipe that can carryfluid at rate Rc bits/sec)

1-52

Introduction




1-55

Introduction

Internet protocol stack application: supporting network

applications FTP, SMTP, HTTP

transport: process-process data transfer TCP, UDP

network: routing of datagrams from source to destination IP, routing protocols

link: data transfer between neighboring network elements Ethernet, 802.111 (WiFi), PPP

physical: bits “on the wire”

application

transport

network

link

physical

1-60

Introduction

source

applicationtransportnetwork

linkphysical

HtHn M

segment Ht

datagram

destination

applicationtransportnetwork

linkphysical

HtHnHl M

HtHn M

Ht M

M

networklink

physical

linkphysical

HtHnHl M

HtHn M

HtHn M

HtHnHl M

router

switch

Encapsulationmessage M

Ht M

Hn

frame

1-62

Introduction




1-63

Introduction




1-69

Application Layer 2-2

Chapter 2: outline

2.1 principles of network applications

2.2 Web and HTTP2.3 FTP 2.4 electronic mail

SMTP, POP3, IMAP2.5 DNS

2.6 P2P applications2.7 socket programming

with UDP and TCP


Chapter 2: application layer

our goals: conceptual,

implementation aspects of network application protocols transport-layer

service models client-server

paradigm peer-to-peer

paradigm

learn about protocols by examining popular application-level protocols HTTP FTP SMTP / POP3 / IMAP DNS

creating network applications socket API


Application architectures

possible structure of applications: client-server peer-to-peer (P2P)


Sockets process sends/receives messages to/from its socket socket analogous to door

sending process shoves message out door sending process relies on transport infrastructure on

other side of door to deliver message to socket at receiving process

Internet

controlledby OS

controlled byapp developer

transport

application

physical

link

network

process

transport

application

physical

link

network

processsocket


Internet transport protocols services

TCP service: reliable transport between

sending and receiving process

flow control: sender won’t overwhelm receiver

congestion control: throttle sender when network overloaded

does not provide: timing, minimum throughput guarantee, security

connection-oriented: setup required between client and server processes

UDP service: unreliable data transfer

between sending and receiving process

does not provide: reliability, flow control, congestion control, timing, throughput guarantee, security, orconnection setup,

Q: why bother? Why is there a UDP?


Chapter 2: outline

2.1 principles of network applications app architectures app requirements




with UDP and TCP


HTTP connections

non-persistent HTTP at most one object

sent over TCP connection connection then

closed downloading multiple

objects required multiple connections

persistent HTTP multiple objects can

be sent over single TCP connection between client, server


Method types

HTTP/1.0: GET POST HEAD

asks server to leave requested object out of response

HTTP/1.1: GET, POST, HEAD PUT

uploads file in entity body to path specified in URL field

DELETE deletes file specified in

the URL field


Cookies: keeping “state” (cont.)

client server

usual http response msg

usual http response msg

cookie file

one week later:

usual http request msgcookie: 1678 cookie-

specificaction

access

ebay 8734usual http request msg Amazon server

creates ID1678 for user create

entry

usual http response set-cookie: 1678

ebay 8734amazon 1678

usual http request msgcookie: 1678 cookie-

specificaction

access

ebay 8734amazon 1678

backenddatabase


Web caches (proxy server)

user sets browser: Web accesses via cache

browser sends all HTTP requests to cache object in cache: cache

returns object else cache requests

object from origin server, then returns object to client

goal: satisfy client request without involving origin server

client

proxyserver

client

HTTP request

HTTP response

HTTP request HTTP request

origin server

origin server

HTTP response HTTP response

institutionalnetwork

1 Gbps LAN


Caching example: install local cache

originservers

1.54 Mbps access link

local web cache

assumptions: avg object size: 100K bits avg request rate from browsers to

origin servers:15/sec avg data rate to browsers: 1.50 Mbps RTT from institutional router to any

origin server: 2 sec access link rate: 1.54 Mbps

consequences: LAN utilization: 15% access link utilization = 100% total delay = Internet delay + access

delay + LAN delay = 2 sec + minutes + usecs

??

How to compute link utilization, delay?

Cost: web cache (cheap!)

public Internet


Chapter 2: outline





with UDP and TCP


Chapter 2: outline





with UDP and TCP


Electronic mail

Three major components: user agents mail servers simple mail transfer

protocol: SMTP

User Agent a.k.a. “mail reader” composing, editing, reading

mail messages e.g., Outlook, Thunderbird,

iPhone mail client outgoing, incoming

messages stored on server

user mailbox

outgoing message queue

mailserver

mailserver

mailserver

SMTP

SMTP

SMTP

useragent

useragent

useragent

useragent

useragent

useragent


Mail access protocols

SMTP: delivery/storage to receiver’s server mail access protocol: retrieval from server

POP: Post Office Protocol [RFC 1939]: authorization, download

IMAP: Internet Mail Access Protocol [RFC 1730]: more features, including manipulation of stored msgs on server

HTTP: gmail, Hotmail, Yahoo! Mail, etc.

sender’s mail server

SMTP SMTPmail access

protocol

receiver’s mail server

(e.g., POP, IMAP)

useragent

useragent


Chapter 2: outline





with UDP and TCP


Root DNS Servers

com DNS servers org DNS servers edu DNS servers

poly.eduDNS servers

umass.eduDNS servers

yahoo.comDNS servers

amazon.comDNS servers

pbs.orgDNS servers

DNS: a distributed, hierarchical database

client wants IP for www.amazon.com; 1st approx: client queries root server to find com DNS server client queries .com DNS server to get amazon.com DNS server client queries amazon.com DNS server to get IP address for

www.amazon.com

… …


45

6

3

recursive query: puts burden of name

resolution on contacted name server

heavy load at upper levels of hierarchy?

requesting hostcis.poly.edu

gaia.cs.umass.edu

root DNS server

local DNS serverdns.poly.edu

1

27

authoritative DNS serverdns.cs.umass.edu

8

DNS name resolution example

TLD DNS server


Chapter 2: outline





with UDP and TCP


P2P file distribution: BitTorrent

tracker: tracks peers participating in torrent

torrent: group of peers exchanging chunks of a file

Alice arrives …

file divided into 256Kb chunks peers in torrent send/receive file chunks

… obtains listof peers from tracker… and begins exchanging file chunks with peers in torrent

Distributed Hash Table (DHT)

DHT: a distributed P2P database database has (key, value) pairs; examples:

key: ss number; value: human name key: movie title; value: IP address

Distribute the (key, value) pairs over the (millions of peers)

a peer queries DHT with key DHT returns values that match the key

peers can also insert (key, value) pairsApplication 2-85

Circular DHT with shortcuts

each peer keeps track of IP addresses of predecessor, successor, short cuts.

reduced from 6 to 2 messages. possible to design shortcuts so O(log N) neighbors, O(log N)

messages in query

1

3

4

5

810

12

15

Who’s responsible

for key 1110?

Application 2-91

Peer churn

example: peer 5 abruptly leavespeer 4 detects peer 5 departure; makes 8 its immediate successor; asks 8 who its immediate successor is; makes 8’s immediate successor its second successor.what if peer 13 wants to join?

1

3

4

5

810

12

15

handling peer churn:peers may come and go (churn)each peer knows address of its two successors each peer periodically pings its two successors to check alivenessif immediate successor leaves, choose next successor as new immediate successor

Application 2-92


Chapter 2: outline





with UDP and TCP


Socket programming

goal: learn how to build client/server applications that communicate using sockets

socket: door between application process and end-end-transport protocol

Internet

controlledby OS

controlled byapp developer

transport

application

physical

link

network

process

transport

application

physical

link

network

processsocket

Transport Layer 3-3

Chapter 3 outline

3.1 transport-layer services

3.2 multiplexing and demultiplexing

3.3 connectionless transport: UDP

3.4 principles of reliable data transfer

3.5 connection-oriented transport: TCP segment structure reliable data transfer flow control connection management

3.6 principles of congestion control

3.7 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

logical end-end transportapplicationtransportnetworkdata linkphysical

Transport Layer 3-7

Chapter 3 outline








Transport Layer 3-11

Connectionless demux: exampleDatagramSocket serverSocket = new DatagramSocket

(6428);

transport

application

physical

link

network

P3transport

application

physical

link

network

P1

transport

application

physical

link

network

P4

DatagramSocket mySocket1 = new DatagramSocket (5775);

DatagramSocket mySocket2 = new DatagramSocket (9157);

source port: 9157dest port: 6428

source port: 6428dest port: 9157

source port: ?dest port: ?

source port: ?dest port: ?


Connection-oriented demux: example

transport

application

physical

link

network

P3transport

application

physical

link

transport

application

physical

link

network

P2

source IP,port: A,9157dest IP, port: B,80

source IP,port: B,80dest IP,port: A,9157

host: IP address A

host: IP address C

server: IP address B

network

P3

source IP,port: C,5775dest IP,port: B,80

source IP,port: C,9157dest IP,port: B,80

P4

threaded server


Chapter 3 outline









UDP: User Datagram Protocol [RFC 768]

“no frills,” “bare bones” Internet transport protocol

“best effort” 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

UDP use: streaming multimedia

apps (loss tolerant, rate sensitive)

DNS SNMP

reliable transfer over UDP: add reliability at

application layer application-specific error

recovery!


Chapter 3 outline









Reliable data transfer: getting started

sendside

receiveside

rdt_send(): called from above, (e.g., by app.). Passed data to deliver to receiver upper layer

udt_send(): called by rdt,to 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


rdt3.0 sendersndpkt = make_pkt(0, data, checksum)udt_send(sndpkt)start_timer

rdt_send(data)

Wait for

ACK0

rdt_rcv(rcvpkt) && ( corrupt(rcvpkt) ||isACK(rcvpkt,1) )

Wait for call 1 from

above

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

rdt_send(data)

rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) && isACK(rcvpkt,0)

rdt_rcv(rcvpkt) && ( corrupt(rcvpkt) ||isACK(rcvpkt,0) )

rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) && isACK(rcvpkt,1)

stop_timerstop_timer

udt_send(sndpkt)start_timer

timeout

udt_send(sndpkt)start_timer

timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


rdt3.0 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0

(d) premature timeout/ delayed ACK

pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0

send pkt0rcv ack1 pkt0

rcv pkt0send ack0ack0

rcv pkt0

send ack0(detect duplicate)


Pipelined protocols: overviewGo-back-N: sender can have up to

N unacked packets in pipeline

receiver only sends cumulative ack doesn’t ack packet if

there’s a gap sender has timer for

oldest unacked packet when timer expires,

retransmit all unacked packets

Selective Repeat: sender can have up to N

unack’ed packets in pipeline

rcvr sends individual ack for each packet

sender maintains timer for each unacked packet when timer expires,

retransmit only that unacked packet


Go-Back-N: sender k-bit seq # in pkt header “window” of up to N, consecutive unack’ed pkts allowed

ACK(n): ACKs all pkts up to, including seq # n - “cumulative ACK” may receive duplicate ACKs (see receiver)

timer for oldest in-flight pkt timeout(n): retransmit packet n and all higher seq # pkts in

window


Selective repeat: sender, receiver windows


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) inits 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 “message

boundaries” pipelined:

TCP congestion and flow control set window size


Chapter 3 outline









TCP reliable data transfer TCP creates rdt service

on top of IP’s unreliable service pipelined segments cumulative acks single retransmission

timer retransmissions

triggered by: timeout events duplicate acks

let’s initially consider simplified TCP sender: ignore duplicate acks ignore flow control,

congestion control


Chapter 3 outline









TCP flow controlapplication

process

TCP socketreceiver buffers

TCPcode

IPcode

application

OS

receiver protocol stack

application may remove data from

TCP socket buffers ….

… slower than TCP receiver is delivering(sender is sending)

from sender

receiver controls sender, so sender won’t overflow receiver’s buffer by transmitting too much, too fast

flow control


Chapter 3 outline









TCP 3-way handshake

SYNbit=1, Seq=x

choose init seq num, xsend TCP SYN msg

ESTAB

SYNbit=1, Seq=yACKbit=1; ACKnum=x+1

choose init seq num, ysend TCP SYNACKmsg, acking SYN

ACKbit=1, ACKnum=y+1

received SYNACK(x) indicates server is live;send ACK for SYNACK;

this segment may contain client-to-server data

received ACK(y) indicates client is live

SYNSENT

ESTAB

SYN RCVD

client state

LISTEN

server state

LISTEN


FIN_WAIT_2

CLOSE_WAIT

FINbit=1, seq=y

ACKbit=1; ACKnum=y+1

ACKbit=1; ACKnum=x+1 wait for server

close

can stillsend data

can no longersend data

LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2*max

segment lifetime

CLOSED

TCP: closing a connection

FIN_WAIT_1 FINbit=1, seq=xcan no longersend but can receive data

clientSocket.close()

client state server state

ESTABESTAB


Chapter 3 outline









four senders multihop paths timeout/retransmit

Q: what happens as in and in’

increase ?

finite shared output link buffers

Host A out

Causes/costs of congestion: scenario 3

Host B

Host CHost D

in : original data

'in: original data, plus

retransmitted data

A: as red in’ increases, all arriving

blue pkts at upper queue are dropped, blue throughput 0


Case study: ATM ABR congestion control

ABR: available bit rate: “elastic service” if sender’s path

“underloaded”: sender should use

available bandwidth if sender’s 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 (“network-assisted”) NI bit: no increase in rate

(mild congestion) CI bit: congestion

indication RM cells returned to sender

by receiver, with bits intact


Chapter 3 outline









TCP congestion control: additive increase multiplicative decrease

approach: sender increases transmission rate (window size), probing for usable bandwidth, until loss occurs additive increase: increase cwnd by 1 MSS every

RTT until loss detectedmultiplicative decrease: cut cwnd in half after loss cwnd:

TC

P s

ende

r co

nges

tion

win

dow

siz

e

AIMD saw toothbehavior: probing

for bandwidth

additively increase window size ……. until loss occurs (then cut window in half)

time


Summary: TCP Congestion Control

timeoutssthresh = cwnd/2

cwnd = 1 MSSdupACKcount = 0

retransmit missing segment

cwnd > ssthresh

congestionavoidance

cwnd = cwnd + MSS (MSS/cwnd)dupACKcount = 0

transmit new segment(s), as allowed

new ACK.

dupACKcount++

duplicate ACK

fastrecovery

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

duplicate ACK

ssthresh= cwnd/2cwnd = ssthresh + 3


dupACKcount == 3

timeoutssthresh = cwnd/2cwnd = 1 dupACKcount = 0retransmit missing segment

ssthresh= cwnd/2cwnd = ssthresh + 3retransmit missing segment

dupACKcount == 3cwnd = ssthreshdupACKcount = 0

New ACK

slow start

timeoutssthresh = cwnd/2

cwnd = 1 MSSdupACKcount = 0


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

new ACKdupACKcount++

duplicate ACK

cwnd = 1 MSSssthresh = 64 KBdupACKcount = 0

NewACK!

NewACK!

NewACK!

Network Layer 4-3

4.1 introduction4.2 virtual circuit and

datagram networks4.3 what’s inside a router4.4 IP: Internet Protocol

datagram format IPv4 addressing ICMP IPv6

4.5 routing algorithms link state distance vector hierarchical routing

4.6 routing in the Internet RIP OSPF BGP

4.7 broadcast and multicast routing

Chapter 4: outline

Network Layer 4-6

1

23

0111

value in arrivingpacket’s header

routing algorithm

local forwarding tableheader value output link

0100010101111001

3221

Interplay between routing and forwarding

routing algorithm determinesend-end-path through network

forwarding table determineslocal forwarding at this router

Network Layer 4-10







Chapter 4: outline

Network Layer 4-14

VC forwarding table12 22 32

12

3

VC numberinterfacenumber

Incoming interface Incoming VC # Outgoing interface Outgoing VC #

1 12 3 222 63 1 18 3 7 2 171 97 3 87… … … …

forwarding table innorthwest router:

VC routers maintain connection state information!

Network Layer 4-17

1

23

Datagram forwarding table

IP destination address in arriving packet’s header

routing algorithm

local forwarding tabledest address output

linkaddress-range 1address-range 2address-range 3address-range 4

3221

4 billion IP addresses, so rather than list individual destination addresslist range of addresses(aggregate table entries)

Network Layer 4-21







Chapter 4: outline

Network Layer 4-22

Router architecture overviewtwo key router functions: run routing algorithms/protocol (RIP, OSPF, BGP) forwarding datagrams from incoming to outgoing link

high-seed switching

fabric

routing processor

router input ports router output ports

forwarding data plane (hardware)

routing, managementcontrol plane (software)

forwarding tables computed,pushed to input ports

Network Layer 4-32







Chapter 4: outline

Network Layer 4-33

The Internet network layer

forwardingtable

host, router network layer functions:

routing protocols• path selection• RIP, OSPF, BGP

IP protocol• addressing conventions• datagram format• packet handling conventions

ICMP protocol• error reporting• router “signaling”

transport layer: TCP, UDP

link layer

physical layer

networklayer

Network Layer 4-37







Chapter 4: outline

Network Layer 4-42

how many? 223.1.1.1

223.1.1.3

223.1.1.4

223.1.2.2223.1.2.1

223.1.2.6

223.1.3.2223.1.3.1

223.1.3.27

223.1.1.2

223.1.7.0

223.1.7.1223.1.8.0223.1.8.1

223.1.9.1

223.1.9.2

Subnets

Network Layer 4-46

DHCP client-server scenario

223.1.1.0/24

223.1.2.0/24

223.1.3.0/24

223.1.1.1

223.1.1.3

223.1.1.4 223.1.2.9

223.1.3.2223.1.3.1

223.1.1.2

223.1.3.27223.1.2.2

223.1.2.1

DHCPserver

arriving DHCPclient needs address in thisnetwork

Network Layer 4-56

NAT: network address translation

10.0.0.1

10.0.0.2

10.0.0.3

10.0.0.4

138.76.29.7

local network(e.g., home network)

10.0.0/24

rest ofInternet

datagrams with source or destination in this networkhave 10.0.0/24 address for source, destination (as usual)

all datagrams leaving localnetwork have same single

source NAT IP address: 138.76.29.7,different source

port numbers

Network Layer 4-64







Chapter 4: outline

Network Layer 4-71

Tunneling

physical view:

IPv4 IPv4

A B

IPv6 IPv6

E

IPv6 IPv6

FC D

logical view:

IPv4 tunnel connecting IPv6 routers

E

IPv6 IPv6

FA B

IPv6 IPv6

Network Layer 4-72

flow: Xsrc: Adest: F

data

A-to-B:IPv6

Flow: XSrc: ADest: F

data

src:Bdest: E

B-to-C:IPv6 inside

IPv4

E-to-F:IPv6

flow: Xsrc: Adest: F

data

B-to-C:IPv6 inside

IPv4

Flow: XSrc: ADest: F

data

src:Bdest: E

physical view:A B

IPv6 IPv6

E

IPv6 IPv6

FC D

logical view:

IPv4 tunnel connecting IPv6 routers

E

IPv6 IPv6

FA B

IPv6 IPv6

Tunneling

IPv4 IPv4

Network Layer 4-73







Chapter 4: outline

Network Layer 4-78







Chapter 4: outline

Network Layer 4-81

w3

4

v

x

u

5

37 4

y

8

z2

7

9

Dijkstra’s algorithm: example

Step N'D(v)

p(v)

012345

D(w)p(w)

D(x)p(x)

D(y)p(y)

D(z)p(z)

u ∞ ∞ 7,u 3,u 5,uuw ∞ 11,w 6,w 5,u

14,x 11,w 6,wuwxuwxv 14,x 10,v

uwxvy 12,y

notes: construct shortest path tree by

tracing predecessor nodes ties can exist (can be broken

arbitrarily)

uwxvyz

Network Layer 4-85







Chapter 4: outline

Network Layer 4-87

Bellman-Ford example

u

yx

wv

z2

2

13

1

1

2

53

5clearly, dv(z) = 5, dx(z) = 3, dw(z) = 3

du(z) = min { c(u,v) + dv(z), c(u,x) + dx(z), c(u,w) + dw(z) } = min {2 + 5, 1 + 3, 5 + 3} = 4

node achieving minimum is nexthop in shortest path, used in forwarding table

B-F equation says:

Network Layer 4-96







Chapter 4: outline

Network Layer 4-99

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

forwarding table configured by both intra- and inter-AS routing algorithm intra-AS sets entries

for internal dests inter-AS & intra-AS

sets entries for external dests

Network Layer 4-104







Chapter 4: outline

Network Layer 4-108

w x yz

A

C

D B

destination subnet next router # hops to dest

w A 2y B 2

z B 7x -- 1…. …. ....

routing table in router D

A 5

dest next hops w - 1 x - 1 z C 4 …. … ...

A-to-D advertisement

RIP: example

Network Layer 4-113

Hierarchical OSPFboundary router

backbone router

area 1

area 2

area 3

backboneareaborderrouters

internalrouters

Network Layer 4-116

BGP basics

when AS3 advertises a prefix to AS1: AS3 promises it will forward datagrams towards that prefix AS3 can aggregate prefixes in its advertisement

AS3

AS2

3b

3c

3a

AS1

1c1a

1d1b

2a2c

2b

othernetworks

othernetworks

BGP session: two BGP routers (“peers”) exchange BGP messages: advertising paths to different destination network prefixes (“path vector”

protocol) exchanged over semi-permanent TCP connections

BGP message

Network Layer 4-124







Chapter 4: outline

Link Layer 5-3

Link layer, LANs: outline

5.1 introduction, services5.2 error detection,

correction 5.3 multiple access

protocols5.4 LANs

addressing, ARP Ethernet switches VLANS

5.5 link virtualization: MPLS5.6 data center networking5.7 a day in the life of a web

request

Link Layer 5-6

Link layer services framing, link access:

encapsulate datagram into frame, adding header, trailer channel access if shared medium “MAC” addresses used in frame headers to identify source,

dest • different from IP address!

reliable delivery between adjacent nodes we learned how to do this already (chapter 3)! seldom used on low bit-error link (fiber, some twisted pair) wireless links: high error rates• Q: why both link-level and end-end reliability?

Link Layer 5-7

flow control: pacing between adjacent sending and receiving nodes

error detection: errors caused by signal attenuation, noise. receiver detects presence of errors:

• signals sender for retransmission or drops frame error correction:

receiver identifies and corrects bit error(s) without resorting to retransmission

half-duplex and full-duplex with half duplex, nodes at both ends of link can transmit, but not at

same time

Link layer services (more)

Link Layer 5-10




protocols5.4 LANs



request

Link Layer 5-12

Parity checkingsingle bit parity: detect single bit

errors

two-dimensional bit parity: detect and correct single bit errors

0 0

Link Layer 5-16




protocols5.4 LANs



request

Link Layer 5-17

Multiple access links, protocolstwo types of “links”: point-to-point

PPP for dial-up access point-to-point link between Ethernet switch, host

broadcast (shared wire or medium) old-fashioned Ethernet upstream HFC 802.11 wireless LAN

shared wire (e.g., cabled Ethernet)

shared RF (e.g., 802.11 WiFi)

shared RF(satellite)

humans at acocktail party

(shared air, acoustical)

Link Layer 5-22

FDMA: frequency division multiple access channel spectrum divided into frequency bands each station assigned fixed frequency band unused transmission time in frequency bands go idle example: 6-station LAN, 1,3,4 have pkt, frequency bands 2,5,6

idle

freq

uenc

y ba

nds

time

FDM cable

Channel partitioning MAC protocols: FDMA

Link Layer 5-23

Random access protocols when node has packet to send

transmit at full channel data rate R. no a priori coordination among nodes

two or more transmitting nodes ➜ “collision”, random access MAC protocol specifies:

how to detect collisions how to recover from collisions (e.g., via delayed

retransmissions) examples of random access MAC protocols:

slotted ALOHA ALOHA CSMA, CSMA/CD, CSMA/CA

Link Layer 5-25

Pros: single active node can

continuously transmit at full rate of channel

highly decentralized: only slots in nodes need to be in sync

simple

Cons: collisions, wasting slots idle slots nodes may be able to detect

collision in less than time to transmit packet

clock synchronization

Slotted ALOHA1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C CS S SE E E

Link Layer 5-32

CSMA/CD (collision detection)

spatial layout of nodes

Link Layer 5-37

token passing: control token passed from

one node to next sequentially.

token message concerns:

token overhead latency single point of failure

(token)

T

data

(nothingto send)

T

“Taking turns” MAC protocols

Link Layer 5-40

Summary of MAC protocols channel partitioning, by time, frequency or code

Time Division, Frequency Division random access (dynamic),

ALOHA, S-ALOHA, CSMA, CSMA/CD carrier sensing: easy in some technologies (wire), hard in

others (wireless) CSMA/CD used in Ethernet CSMA/CA used in 802.11

taking turns polling from central site, token passing bluetooth, FDDI, token ring

Link Layer 5-41




protocols5.4 LANs



request

R

1A-23-F9-CD-06-9B222.222.222.220

111.111.111.110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D

111.111.111.112

111.111.111.11174-29-9C-E8-FF-55

A

222.222.222.22249-BD-D2-C7-56-2A

222.222.222.22188-B2-2F-54-1A-0F

B

Link Layer 5-50

Addressing: routing to another LAN

IP src: 111.111.111.111 IP dest: 222.222.222.222

R forwards datagram with IP source A, destination B R creates link-layer frame with B's MAC address as dest, frame contains A-

to-B IP datagram

MAC src: 1A-23-F9-CD-06-9B MAC dest: 49-BD-D2-C7-56-2A

IPEthPhy

IPEthPhy

Link Layer 5-53




protocols5.4 LANs



request

Link Layer 5-55

Ethernet: physical topology bus: popular through mid 90s

all nodes in same collision domain (can collide with each other) star: prevails today

active switch in center each “spoke” runs a (separate) Ethernet protocol (nodes do not

collide with each other)

switch

bus: coaxial cablestar

Link Layer 5-60




protocols5.4 LANs



request

A

A’

B

B’ C

C’

1 2

345

6

Link Layer 5-66

Self-learning, forwarding: exampleA A’

Source: ADest: A’

MAC addr interface TTL

switch table (initially empty)

A 1 60

A A’A A’A A’A A’A A’

frame destination, A’, location unknown: flood

A’ A

destination A location known:

A’ 4 60

selectively send on just one link

Link Layer 5-68

Self-learning multi-switch exampleSuppose C sends frame to I, I responds to C

Q: show switch tables and packet forwarding in S1, S2, S3, S4

A

B

S1

C D

E

FS2

S4

S3

H

I

G

Link Layer 5-72

VLANsport-based VLAN: switch ports grouped

(by switch management software) so that single physical switch ……

switch(es) supporting VLAN capabilities can be configured to define multiple virtual LANS over single physical LAN infrastructure.

Virtual Local Area Network

1

8

9

16102

7

…

Electrical Engineering(VLAN ports 1-8)

Computer Science(VLAN ports 9-16)

15

…

Electrical Engineering(VLAN ports 1-8)

…

1

82

7 9

1610

15

…

Computer Science(VLAN ports 9-16)

… operates as multiple virtual switches

Link Layer 5-76




protocols5.4 LANs



request

Link Layer 5-77

Multiprotocol label switching (MPLS)

initial goal: high-speed IP forwarding using fixed length label (instead of IP address) fast lookup using fixed length identifier (rather than

shortest prefix matching) borrowing ideas from Virtual Circuit (VC) approach but IP datagram still keeps IP address!

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

Link Layer 5-80

R2

D

R3R4R5

A

R6

MPLS versus IP paths

IP-onlyrouter

IP routing: path to destination determined by destination address alone

MPLS and IP router

MPLS routing: path to destination can be based on source and dest. address fast reroute: precompute backup routes in

case of link failure

entry router (R4) can use different MPLS routes to A based, e.g., on source address

Link Layer 5-83




protocols5.4 LANs



request

Link Layer 5-85

Server racks

TOR switches

Tier-1 switches

Tier-2 switches

Load balancer

Load balancer

B

1 2 3 4 5 6 7 8

A C

Border router

Access router

Internet

Data center networks load balancer: application-layer routingreceives external client requestsdirects workload within data centerreturns results to external client (hiding data center internals from client)

Link Layer 5-87




protocols5.4 LANs



request

Wireless, Mobile Networks 6-3

Chapter 6 outline

6.1 Introduction

Wireless6.2 Wireless links,

characteristics CDMA

6.3 IEEE 802.11 wireless LANs (“Wi-Fi”)

6.4 Cellular Internet Access architecture standards (e.g., GSM)

Mobility6.5 Principles: addressing and

routing to mobile users6.6 Mobile IP6.7 Handling mobility in

cellular networks6.8 Mobility and higher-layer

protocols

6.9 Summary


Characteristics of selected wireless links

Indoor10-30m

Outdoor50-200m

Mid-rangeoutdoor

200m – 4 Km

Long-rangeoutdoor

5Km – 20 Km

.056

.384

1

4

5-11

54

2G: IS-95, CDMA, GSM

2.5G: UMTS/WCDMA, CDMA2000

802.15

802.11b

802.11a,g

3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO

4G: LTWE WIMAX

802.11a,g point-to-point

200 802.11n

Dat

a ra

te (

Mbp

s)


Chapter 6 outline

6.1 Introduction








protocols

6.9 Summary


Wireless network characteristicsMultiple wireless senders and receivers create additional

problems (beyond multiple access):

AB

C

Hidden terminal problem B, A hear each other B, C hear each other A, C can not hear each other

means A, C unaware of their interference at B

A B C

A’s signalstrength

space

C’s signalstrength

Signal attenuation: B, A hear each other B, C hear each other A, C can not hear each other

interfering at B


Chapter 6 outline

6.1 Introduction








protocols

6.9 Summary


802.11: passive/active scanning

AP 2AP 1

H1

BBS 2BBS 1

1

23

1

passive scanning: (1) beacon frames sent from APs(2) association Request frame sent: H1 to

selected AP (3) association Response frame sent from

selected AP to H1

AP 2AP 1

H1

BBS 2BBS 1

122

3 4

active scanning: (1) Probe Request frame broadcast

from H1(2) Probe Response frames sent

from APs(3) Association Request frame sent:

H1 to selected AP (4) Association Response frame sent

from selected AP to H1


Collision Avoidance: RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer


802.11: advanced capabilities

Rate adaptation base station, mobile

dynamically change transmission rate (physical layer modulation technique) as mobile moves, SNR varies

QAM256 (8 Mbps)QAM16 (4 Mbps)

BPSK (1 Mbps)

10 20 30 40SNR(dB)

BE

R

10-1

10-2

10-3

10-5

10-6

10-7

10-4

operating point

1. SNR decreases, BER increase as node moves away from base station

2. When BER becomes too high, switch to lower transmission rate but with lower BER


Chapter 6 outline

6.1 Introduction




6.4 Cellular Internet access architecture standards (e.g., GSM)




protocols

6.9 Summary


Mobile Switching

Center

Public telephonenetwork

Mobile Switching

Center

Components of cellular network architecture

connects cells to wired tel. net. manages call setup (more later!) handles mobility (more later!)

MSC

covers geographical region base station (BS) analogous to 802.11 AP mobile users attach to network through BS air-interface: physical and link layer protocol between mobile and BS

cell

wired network


radionetwork controller

MSC

SGSN

Public telephonenetwork

GatewayMSC

G

Public Internet

GGSN

G

radio access networkUniversal Terrestrial Radio Access Network (UTRAN)

core networkGeneral Packet Radio Service

(GPRS) Core Network

publicInternet

radio interface(WCDMA, HSPA)

3G (voice+data) network architecture


Chapter 6 outline

6.1 Introduction








protocols

6.9 Summary


Mobility via indirect routing

wide area network

homenetwork

visitednetwork

3

2

41

correspondent addresses packets using home address of mobile

home agent intercepts packets, forwards to foreign agent

foreign agent receives packets, forwards to mobile

mobile replies directly to correspondent

1 23

4


Mobility via direct routing

homenetwork

visitednetwork

correspondent requests, receives foreign address of mobile

correspondent forwards to foreign agent

foreign agent receives packets, forwards to mobile

mobile replies directly to correspondent


Chapter 6 outline

6.1 Introduction








protocols

6.9 Summary


Mobile IP: indirect routing

Permanent address: 128.119.40.186

Care-of address: 79.129.13.2

dest: 128.119.40.186

packet sent by correspondent

dest: 79.129.13.2 dest: 128.119.40.186

packet sent by home agent to foreign agent: a packet within a packet

dest: 128.119.40.186

foreign-agent-to-mobile packet


Public switched telephonenetwork

mobileuser

homeMobile

Switching Center

HLR home network

visitednetwork

correspondent

Mobile Switching

Center

VLR

GSM: indirect routing to mobile

1 call routed to home network

2

home MSC consults HLR,gets roaming number ofmobile in visited network

3

home MSC sets up 2nd leg of callto MSC in visited network

4

MSC in visited network completescall through base station to mobile


home network

Home MSC

PSTN

correspondent

MSC

anchor MSC

MSCMSC

(a) before handoff

GSM: handoff between MSCs

anchor MSC: first MSC visited during call call remains routed

through anchor MSC new MSCs add on to end of

MSC chain as mobile moves to new MSC

optional path minimization step to shorten multi-MSC chain

Multimedia networking: outline

7.1 multimedia networking applications7.2 streaming stored video7.3 voice-over-IP7.4 protocols for real-time conversational

applications7.5 network support for multimedia

Multmedia Networking 7-2





constant bit rate videotransmission

Cum

ulat

ive

data

time

variablenetwork

delay

client videoreception

constant bit rate video playout at client

client playoutdelay

buff

ered

vid

eo

client-side buffering and playout delay: compensate for network-added delay, delay jitter


Streaming stored video: revisted

Client-side buffering, playout


variable fill rate, x(t)

client application buffer, size B

playout rate,e.g., CBR r

buffer fill level, Q(t)

video server

client

Streaming multimedia: HTTP multimedia file retrieved via HTTP GET send at maximum possible rate under TCP

fill rate fluctuates due to TCP congestion control, retransmissions (in-order delivery)

larger playout delay: smooth TCP delivery rate HTTP/TCP passes more easily through firewalls


variable rate, x(t)

TCP send buffer

videofile

TCP receive buffer

application playout buffer

server client

CDN: “simple” content access scenario


Bob (client) requests video http://netcinema.com/6Y7B23Vvideo stored in CDN at http://KingCDN.com/NetC6y&B23V

netcinema.com

KingCDN.com

1

1. Bob gets URL for for video http://netcinema.com/6Y7B23Vfrom netcinema.com web page 2

2. resolve http://netcinema.com/6Y7B23Vvia Bob’s local DNS

netcinema’sauthorative DNS

3

3. netcinema’s DNS returns URL http://KingCDN.com/NetC6y&B23V

4

4&5. Resolve http://KingCDN.com/NetC6y&B23via KingCDN’s authoritative DNS, which returns IP address of KIingCDN server with video

56. request video fromKINGCDN server,streamed via HTTP

KingCDNauthoritative DNS

Case study: Netflix


1

1. Bob manages Netflix account

Netflix registration,accounting servers

Amazon cloud

Akamai CDN

Limelight CDN

Level-3 CDN

22. Bob browsesNetflix video

3

3. Manifest filereturned for requested video

4. DASH streaming

upload copies of multiple versions of video to CDNs





constant bit ratetransmission

Cum

ulat

ive

data

time

variablenetwork

delay(jitter)

clientreception

constant bit rate playout at client

client playoutdelay

buff

ered

data

Delay jitter

end-to-end delays of two consecutive packets: difference can be more or less than 20 msec (transmission time difference)


packets

time

packetsgenerated

packetsreceived

loss

r

p p'

playout schedulep' - r

playout schedulep - r

sender generates packets every 20 msec during talk spurt. first packet received at time r first playout schedule: begins at p second playout schedule: begins at p’


VoIP: fixed playout delay

interleaving to conceal loss: audio chunks divided into

smaller units, e.g. four 5 msec units per 20 msec audio chunk

packet contains small units from different chunks

if packet lost, still have most of every original chunk

no redundancy overhead, but increases playout delay


VoiP: recovery from packet loss (3)


supernode overlay network

Voice-over-IP: Skype proprietary application-

layer protocol (inferred via reverse engineering) encrypted msgs

P2P components:

Skype clients (SC)

clients: skype peers connect directly to each other for VoIP call

super nodes (SN): skype peers with special functions

overlay network: among SNs to locate SCs

login server

Skype login server supernode (SN)



applications: RTP, SIP7.5 network support for multimedia


RTP runs on top of UDP

RTP libraries provide transport-layer interface that extends UDP:

• port numbers, IP addresses• payload type identification• packet sequence numbering• time-stamping


SIP: Session Initiation Protocol [RFC 3261]

long-term vision: all telephone calls, video conference calls take

place over Internet people identified by names or e-mail addresses,

rather than by phone numbers can reach callee (if callee so desires), no matter

where callee roams, no matter what IP device callee is currently using


SIP services SIP provides

mechanisms for call setup: for caller to let

callee know she wants to establish a call

so caller, callee can agree on media type, encoding

to end call

determine current IP address of callee: maps mnemonic

identifier to current IP address

call management: add new media

streams during call change encoding

during call invite others transfer, hold calls


SIP example: [email protected] calls [email protected]


1

1. Jim sends INVITEmessage to UMass SIP proxy.

2. UMass proxy forwards request to Poly registrar server

2 3. Poly server returns redirect response,indicating that it should try [email protected]

3

5. eurecom registrar forwards INVITE to 197.87.54.21, which is running keith’s SIP client

5

4

4. Umass proxy forwards request to Eurecom registrar server

86

76-8. SIP response returned to Jim

9

9. Data flows between clients

UMass SIP proxy

Poly SIPregistrar

Eurecom SIPregistrar

197.87.54.21

128.119.40.186





Scenario 1: mixed HTTP and VoIP example: 1Mbps VoIP, HTTP share 1.5 Mbps link.

HTTP bursts can congest router, cause audio loss want to give priority to audio over HTTP

packet marking needed for router to distinguish between different classes; and new router policy to treat packets accordingly

Principle 1

R1R2


Principles for QOS guarantees (more) what if applications misbehave (VoIP sends higher

than declared rate) policing: force source adherence to bandwidth allocations

marking, policing at network edge

provide protection (isolation) for one class from othersPrinciple 2

R1 R2

1.5 Mbps link

1 Mbps phone

packet marking and policing


allocating fixed (non-sharable) bandwidth to flow: inefficient use of bandwidth if flows doesn’t use its allocation

while providing isolation, it is desirable to use resources as efficiently as possible

Principle 3

R1R2

1.5 Mbps link

1 Mbps phone

1 Mbps logical link

0.5 Mbps logical link


Principles for QOS guarantees (more)

Weighted Fair Queuing (WFQ): generalized Round Robin each class gets weighted amount of service in

each cycle real-world example?


Scheduling policies: still more

Policing mechanisms: implementation

token bucket: limit input to specified burst size and average rate

bucket can hold b tokens tokens generated at rate r token/sec unless bucket

full over interval of length t: number of packets admitted

less than or equal to (r t + b)Multmedia Networking 7-78

Policing and QoS guarantees

token bucket, WFQ combine to provide guaranteed upper bound on delay, i.e., QoS guarantee!

WFQ

token rate, r

bucket size, b

per-flowrate, R

D = b/Rmax

arrivingtraffic


arrivingtraffic

edge router: per-flow traffic management

marks packets as in-profile and out-profile

core router:

per class traffic management

buffering and scheduling based on marking at edge

preference given to in-profile packets over out-of-profile packets

Diffserv architecture


r

b

marking

scheduling

...

Classification, conditioningmay be desirable to limit traffic injection rate of

some class: user declares traffic profile (e.g., rate, burst size) traffic metered, shaped if non-conforming


Documents

Chapter 1: roadmap - Universitetet i Bergenmatthew/INF14213/LectureSlides/SummaryCh1To7.pdf · Chapter 1: roadmap 1.1 what is the ... guided media: signals propagate in solid media: