Introduction1-1 Chapter 1 Introduction All material copyright 1996-2007 J.F Kurose and K.W. Ross, All Rights Reserved.

Introduction 1-1

Chapter 1Introduction

All material copyright 1996-2007J.F Kurose and K.W. Ross, All Rights Reserved

Introduction 1-2

Chapter 1: IntroductionOur goal: get “feel” and

terminology more depth, detail

later in course approach:

use Internet as example

Overview: what’s the Internet? what’s a protocol? network edge; hosts, access

net, physical media network core: packet/circuit

switching, Internet structure

Introduction 1-3

Chapter 1: roadmap

1.1 What is the Internet?1.2 Network edge

end systems, access networks, links

1.3 Network core circuit switching, packet switching, network

structure

1.4 Delay, loss and throughput in packet-switched networks

1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History

Introduction 1-4

What is the Internet

internetwork (internet) A network of networks: a network that connects many

heterogeneous networks Internet

An internet that connects various networks by using TCP/IP protocol.

An end system considers the whole network as a single global network.

Introduction 1-5

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

millions of connected computing devices: hosts = end systems running network

apps Home network

Institutional network

Mobile network

Global ISP

Regional ISP

router

PC

server

wirelesslaptop

cellular handheld

wiredlinks

access points

communication links fiber, copper,

radio, satellite transmission rate

= bandwidth

routers: forward packets (chunks of data)

Introduction 1-6

“Cool” internet appliances

World’s smallest web serverhttp://www-ccs.cs.umass.edu/~shri/iPic.html

IP picture framehttp://www.ceiva.com/

Web-enabled toaster +weather forecaster

Internet phones

Introduction 1-7

What’s the Internet: “nuts and bolts” view protocols control sending,

receiving of msgs e.g., TCP, IP, HTTP, Skype,

Ethernet

Internet: “network of networks” loosely hierarchical public Internet versus

private intranet

Internet standards RFC: Request for comments IETF: Internet Engineering

Task Force

Home network

Institutional network

Mobile network

Global ISP

Regional ISP

Introduction 1-8

What’s the Internet: a service view communication

infrastructure enables distributed applications: Web, VoIP, email,

games, e-commerce, file sharing

communication services provided to apps: reliable data delivery

from source to destination

“best effort” (unreliable) data delivery

Introduction 1-9

What’s a protocol?human protocols: “what’s the time?” “I have a question” introductions

… specific msgs sent… specific actions

taken when msgs received, or other events

network protocols: machines rather than

humans all communication

activity in Internet governed by protocols

protocols define format, order of msgs sent and

received among network entities, and actions taken on msg transmission, receipt

Introduction 1-10

What’s a protocol?a human protocol and a computer network protocol:

Q: Other human protocols?

Hi

Hi

Got thetime?

2:00

TCP connection request

TCP connectionresponseGet http://www.awl.com/kurose-ross

<file>time

Introduction 1-11

Chapter 1: roadmap

1.1 What is the Internet?1.2 Network edge

end systems, access networks, links

1.3 Network core circuit switching, packet switching, network

structure

Introduction 1-12

A closer look at network structure:

network edge: applications and hosts

access networks, physical media: wired, wireless communication links network core: interconnected

routers network of networks

Introduction 1-13

The network edge: end systems (hosts):

run application programs e.g. Web, email at “edge of network”

client/server

peer-peer

client/server model client host requests, receives

service from always-on server e.g. Web browser/server;

email client/server peer-peer model:

minimal (or no) use of dedicated servers

e.g. Skype, BitTorrent

Introduction 1-14

Access Networks The traditional telephone network doesn’t have

such access networks. It has simple pt-to-pt subscriber lines.

CoreBuilderCoreBuilder 9000 9000

subscriber line(loop) transport networkCustomerPremisesNetwork(CPN)

Introduction 1-15

Access networks for Internet

Today the ways of connecting customers to the core network are complex due to the need for high-speed internet access service. Customers have access to the core network in several ways through which is often called access networks. xDSL HFC FTTHx Ethernet Wireless

Introduction 1-16

ADSL

Asymmetric Digital Subscriber Line It uses the same TP as used in POTS. But data is transferred using over different

frequency bandwidth.

ADSLRT UnitADSL

RT Unit

EndUser

PSTNPOTS

TP 1pair

1.5 ~ 8 Mbps

16 ~ 640kbps

HeadendADSL

COUnit

Introduction 1-17

HFC

Hybrid fiber coax

Head end ONU

분배점

케이블 모뎀 PC

Set topbox TV

Introduction 1-18

Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes

Introduction 1-19

Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

Introduction 1-20

Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

FDM (more shortly):

Introduction 1-21

Company access: local area networks

company/univ local area network (LAN) connects end system to edge router

Ethernet: 10 Mbs, 100Mbps,

1Gbps, 10Gbps Ethernet

modern configuration: end systems connect into Ethernet switch

LANs: chapter 5

Introduction 1-22

Wireless access networks

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

point”

wireless LANs: 802.11b/g (WiFi): 11 or 54

Mbps

wider-area wireless access provided by telco operator ~1Mbps over cellular system

(EVDO, HSDPA) next up (?): WiMAX (10’s Mbps)

over wide area

basestation

mobilehosts

router

Introduction 1-23

Physical media

guided media(wired): signals propagate in solid media Twisted pair(TP)

• Unshielded TP(UTP)– Category 3

– Category 5

• Shielded TP(STP)

Introduction 1-24

Coaxial cable two concentric copper conductors bidirectional baseband

• Single channel on cable• Ethernet

broadband• Multiple channel on cable• HFC

Introduction 1-25

Fiber optic cable glass fiber carrying light pulses, each pulse

a bit high-speed operation low error rate: repeaters spaced far apart ;

immune to electromagnetic noise

Introduction 1-26

Figure 7-21

Radio Communication Band

Infrared Light wave

400 900

Introduction 1-27

Chapter 1: roadmap

1.1 What is the Internet?1.2 Network edge

end systems, access networks, links

1.3 Network core circuit switching, packet switching, network

structure

Introduction 1-28

The Network Core

mesh of interconnected routers

the fundamental question: how is data transferred through net? circuit switching:

dedicated circuit per call: telephone net

packet-switching: data sent thru net in discrete “chunks”

Introduction 1-29

Switching networks

There should be transmission links to connect between network end systems.

Switches(or routers) help to reduce the number of transmission link when we construct a large network.

switched networkpoint-to-point links(dedicated links)

Introduction 1-30

Network Core: Circuit Switching

End-end resources reserved for “call”

link bandwidth, switch capacity

dedicated resources: no sharing

circuit-like (guaranteed) performance

call setup required

Introduction 1-31

Network Core: Circuit Switching

network resources (e.g., bandwidth) divided into “pieces”

pieces allocated to calls

resource piece idle if not used by owning call (no sharing)

dividing link bandwidth into “pieces” frequency division time division

Introduction 1-32

Circuit Switching: FDM and TDM

FDM

frequency

time

TDM

frequency

time

4 users

Example:

Introduction 1-33

Numerical example

How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? All links are 1.536 Mbps Each link uses TDM with 24 slots/sec 500 msec to establish end-to-end circuit

Let’s work it out!

Introduction 1-34

Network Core: Packet Switching

each end-end data stream divided into packets

user A, B packets share network resources

each packet uses full link bandwidth

resources used as needed

resource contention: aggregate resource

demand can exceed amount available

congestion: packets queue, wait for link use

store and forward: packets move one hop at a time Node receives complete

packet before forwarding

Bandwidth division into “pieces”Dedicated allocationResource reservation

Introduction 1-35

Packet Switching: Statistical Multiplexing

Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand statistical multiplexing.

TDM: each host gets same slot in revolving TDM frame.

A

B

C100 Mb/sEthernet

1.5 Mb/s

D E

statistical multiplexing

queue of packetswaiting for output

link

Introduction 1-36

Packet-switching: store-and-forward

takes L/R seconds to transmit (push out) packet of L bits on to link at R bps

store and forward: entire packet must arrive at router before it can be transmitted on next link

delay = 3L/R (assuming zero propagation delay)

Example: L = 7.5 Mbits R = 1.5 Mbps transmission delay =

15 sec

R R RL

more on delay shortly …

Introduction 1-37

Packet switching versus circuit switching

1 Mb/s link each user:

100 kb/s when “active”

active 10% of time

circuit-switching: 10 users

packet switching: with 35 users,

probability > 10 active at same time is less than .0004

Packet switching allows more users to use network!

N users

1 Mbps link

Q: how did we get value 0.0004?

Introduction 1-38

Packet switching versus circuit switching

great for bursty data resource sharing simpler, no call setup

excessive congestion: packet delay and loss protocols needed for reliable data transfer,

congestion control Q: How to provide circuit-like behavior?

bandwidth guarantees needed for audio/video apps

still an unsolved problem (chapter 7)

Is packet switching a “slam dunk winner?”

Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?

Introduction 1-39

Internet structure: network of networks

roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T,

Cable and Wireless), national/international coverage treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1 providers interconnect (peer) privately

Introduction 1-40

Tier-1 ISP: e.g., Sprint

…

to/from customers

peering

to/from backbone

….

………

POP: point-of-presence

Introduction 1-41

Internet structure: network of networks

“Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer oftier-1 provider

Tier-2 ISPs also peer privately with each other.

Introduction 1-42

Internet structure: network of networks

“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet

Introduction 1-43

Internet structure: network of networks

a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Introduction 1-44

Internet Structure in Korea

http://isis.nida.or.kr/