Introduction1-1 Part of slides provided by J.F Kurose and K.W. Ross, All Rights Reserved Chapter 1...

Introduction 1-1

Part of slides provided by J.F Kurose and K.W. Ross, All Rights Reserved

Chapter 1Computer Networksand the Internet

Computer networking -A top-down approach featuring the internet4th Edition, 2008Addison WesleyJames F. Kurose, Keith W. RossISBN 0-321-49770-8

Communication NetworksP. Demeester

Introduction 1-2

Chapter 1: Introduction

Our goal: Introduction to computer networks Limit to >80% of the technologies used

today Technologies : TCP+UDP, IP, Ethernet Describe applications (file transfer, e-mail ,

Web access,…)

Introduction 1-3

Chapter 1 outline

1.1 What is the Internet?[1.2 Network edge][1.3 Network core][1.4 Network access and physical media]1.5 Internet structure and ISPs[1.6 Delay & loss in packet-switched

networks]1.7 Protocol layers, service models[1.8 History]

Introduction 1-4

Move towards all-IP

VoIP Skype Video over IP Belgacom TV Internet of Things Smart environments

Operators are transforming their network towards all IP

Introduction 1-5

BT's 21st Century Network : current network

IP

ATM

PSTN

DSL

KStream

PSTNDPCN

PDH

Fibre

Copper

DWSS

ASDH

EndUser

~5knodes

~2knodes

~400nodes

~100nodes

~15nodes

MSH -SDH

~1knodes

Mesh -SDH

Inter-node transmission provided by

SDH/PDH platforms

CWSS

Today: multiple services

on multiple platforms

Other Networks

Introduction 1-6

BT's 21st Century Network : Future

IP-MPLS-WDMDSL

Fibre &Copper

Copper

Agg Box

EndUser

~5knodes

~100nodes

Class 5 Call Server

GFP on SDH

Content

WWW

ISPPSTN services migrate to IP

Other Networks

access aggregation core

Introduction 1-7

ISP

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

router workstation

servermobile

ISP : Internet Service Provider

• How to address the terminals ?• How to find them ?• How to route the information ?• …

Introduction 1-11

The network edge

end systems (hosts): run application programs e.g. Web, email at “edge of network”

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. Gnutella, KaZaA

Introduction 1-12

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 1-13

Q: How to connect end systems to edge router?

residential access nets institutional access

networks (school, company)

mobile access networks

Keep in mind: bandwidth (bits per

second) of access network?

shared or dedicated?

Access networks and physical media

Introduction 1-14

Network taxonomy

Telecommunicationnetworks

FDM TDMNetworkswith VCs

DatagramNetworks

Circuit-switchednetworks

Packet-switchednetworks

Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps.

Introduction 1-15

Chapter 1 outline

1.1 What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched

networks1.7 Protocol layers, service models1.8 History

Introduction 1-16

roughly hierarchical at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity,

Sprint, AT&T), national/international coverage treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1 providers interconnect (peer) privately

NAP

Tier-1 providers also interconnect at public network access points (NAPs)

Internet structure: network of networks

Introduction 1-17

Tier-1 ISP: e.g., Sprint

Sprint US backbone network

Introduction 1-18

“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

NAP

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, interconnect at NAP


Introduction 1-19

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

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



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 1-20

a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP


Introduction 1-21

Routers in the Internet : Global

In 2005 the number of (pubic) routers is in the 100.000 - 200.000 range. The average number of hops a packet has to cross is in the order of 13.

Introduction 1-22

Routers in the Internet : Zoom-In

Introduction 1-23


www.cybergeography.org/atlas/geographic.html

NSFNET1992

Introduction 1-24


2001

Introduction 1-25


2000

Introduction 1-26

Chapter 1 outline

1.1 What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched

networks1.7 Protocol layers, service models1.8 History

Introduction 1-27

Protocol “Layers”

Networks are complex!

many “pieces”: hosts routers links of various

media applications protocols hardware,

software

Question: Is there any hope of

organizing the structure of a network?

Or at least in our discussion of networks?

Introduction 1-28

An example : postal services

writer friend“application” service : friend reads book

they agree and make a “connection”

they use the unreliablepostal services “network”

Introduction 1-29

client server

An example : web access

Internet Protocol

10 Mbit/s local area network

RFC 1011 : “Internet Protocols”

router

TCP-Connection

100 Gbit/s WDM transatlantic optical cable

2 Mbit/sISDN linklocal telephone

switch

56.6 kbit/smodem connection

140 Mbit/sPDH link

URL: www.ietf.org

IETF webpage

IP-datagram

find info about Internet on the Web !

Introduction 1-30

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, reception

Introduction 1-31

What’s a protocol ?

a human protocol and a computer network protocol:

Hi

Hi

Got thetime?

2:00

TCP connection req

TCP connectionresponse

Get http://www.awl.com/kurose-ross

<file>

time

Introduction 1-32

Why layering ?

Dealing with complex systems: explicit structure allows identification of functions,

relationship between complex system’s possible layered reference model

modularization eases maintenance and updating of system change of implementation of layer’s service is

transparent to rest of system e.g., change in postal service implementation

doesn’t affect rest of system (as long as interfaces are the same)

Introduction 1-33

Internet protocol stack

application: supporting network applications FTP, SMTP, HTTP

transport: host-host data transfer TCP, UDP

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

data link: data transfer between neighboring network elements PPP, Ethernet

physical: bits “on the wire”

5. Application Layer

4. Transport Layer

3. Network Layer

2. Data Link Layer

1. Physical Layer

Introduction 1-34

Each layer: distributed “entities”

implement layer functions in the node

entities perform actions, exchange messages with peers

applicationtransportnetworkdata linkphysical




networkdata link data linkphysical physical

Layering: logical communication

Introduction 1-35

E.g.: transport take data from

application layer add addressing,

reliability check, info to form “segment”

send segment to peer

wait for peer to ack receip






data

data

Layering: logical communication

Introduction 1-36






data

data

Layering: “physical” communication

Introduction 1-37

Application Layer : File Transfer Protocol

OPENconnection

TCP control connection

Login, password OK Request directory

TCP transfer connection

directory

TCP transfer connection

file transfer

CLOSEconnection

FTPserver

Request file transfer

Introduction 1-38

Login, passwordOK

read directorydirectory

Request file transferfile transfer

application layer : FTP

transport layer : TCP

client layerFTP-server

“peer to peer” communication

server layer

Remark : client - server

SAP SAP

SAP : Service Access point

Application/Transport Layer

Introduction 1-39

Transmission Control Protocol

TCP connection

connection oriented (virtual connection in software of terminals : state)

3-way handshake protocol point to point, full duplex exchange of segments (=unit of data)

(during a file transfer the file will be cut in pieces : segments) reliable transport (=acknowledgement, retransmission, timers, …) flow control (sender won’t overwhelm receiver) congestion control

(senders “slow down sending rate” when network congested) segments are sent over a network of routers in the IP layer typically used for http, ftp, smtp, pop, …

Introduction 1-40

<SYN_C>

<ACK of SYN_C,SYN_S>

<ACK of SYN_S>3-w

ay h

an

dsh

ake

If set-up segment is lost==> time-outs

Client side Server side

Setup TCP connection

pro

gre

ssin

g t

ime

SYN : SYNchronizationACK : ACKnowledgment

C : Client sideS : Server side

TCP connection setup

Introduction 1-41

TCP for file transfer

<SYN_S>

<ACK of SYN_S,SYN_C>

<ACK of SYN_C>

<bytes 1-1000>

<ACK bytes 1-1000 >

<bytes 1001-2000>

<ACK bytes 1001-2000 >

<bytes 2001-3000>

<ACK bytes 2001-3000 >

<bytes 2001-3000>

time-out

<ACK bytes 3001-4000 >

<bytes 3001-4000>

0001-1000

1001-2000

2001-3000

3001-4000

4001-5000

0001-1000

1001-2000

2001-3000

3001-4000

4001-5000

TCP connection for file transfer

Introduction 1-42

User Datagram Protocol

UDP audioserver

very simple “protocol” alternative to complex TCP unreliable and connectionless no flow control or congestion control unidirectional no extra delays due to acknowledgments typically used for real-time and control applications

Introduction 1-43

UDP real time audio

<bytes 1-1000>

<bytes 1001-2000>

<bytes 2001-3000>

<bytes 3001-4000>

<bytes 4001-5000>

• send as quick as possible• no extra delay due to acknowledgment• no retransmissions

0001-1000

1001-2000

2001-3000

3001-4000

4001-5000

0001-1000

1001-2000

2001-3000

3001-4000

4001-5000

UDP for real time audio transfer

Introduction 1-44

network layer : IP

Transport/Network Layer

server layer

transport layer : TCP

client layer

TCP connection

SERVICE : Transfer TCP segment from source to destination SOLUTION : Encapsulate TCP segment in IP datagram (destination indicated !).IP network layer will transfer IP datagram over links and routers to destination.

router

link

IP datagrams

Introduction 1-45

01101011101011010101

10101101010101110101

00110101011100010101

01101011100001010100

11111101010100000110

server

Data file

Encapsulation example: FT /TCP/IP

IP datagram

TCP segment

TCP, S-D

IPheader

IPpayload

TCPpayload

FTP

TCPheader

01101011101011010101FTP

IPN

ETW

OR

KLA

YER

TC

PTR

AN

SP

OR

TLA

YER

FTP

AP

PLIC

ATIO

NLA

YER

01101011101011010101

Introduction 1-46

A B

C

D

E

Y:to BZ:to D

Y:to CZ:to E

Y:to Y

Source:XDestination:YContent:TCP

Storeand

Forward

RoutingTable

Buffer

Router

Link

computerhost

terminal

W

X

Y

Z

Network Layer : Internet Protocol

Introduction 1-47

Unidirectional Datagram (“packet”) based store and forward Connectionless Flexibility is provided by network elements (routers) Best effort : no guarantee on delay, delivery, …

(no Quality of Service : QoS) IP layer is the server layer of the TCP layer

and the client layer of the Data Link Layer

Network Layer : Internet Protocol

Introduction 1-48Physical layer

data link layer

server layer

network layer : IP

client layer

point-to-point shared

twisted pairfiber

server layer

client layer

Network/Data Link/Physical Layer

Introduction 1-49

Data Link Layer

point-to-point example : PPP protocol (Point-to-Point Protocol) establish a connection between two routers or a router

and a terminal can use e.g. an SDH VC-4 150 Mbit/s connection

between 2 routers or a telephone ISDN connection of 64 kbit/s between a terminal at home and the access router of an ISP.

shared medium example : Ethernet MAC : CSMA/CD

Les 1-2

Introduction 1-50

transport

application

network

data link

physical

terminal

network

data link

physical

data link

physical

router

data link

physicalphysical

switch

transport

application

network

data link

physical

terminal

IP

FTP HTTP DNS ... SNMP

TCP UDP

PPP ...CSMA/CD

fiber ...coax

Summary

Introduction 1-51

FTP20,21

HTTP80

DNS53

... SNMP161,162

TCP6

UDP17

Identification : Application : port number

FTP port 20 (data), 21 (control)TCP or UDP : protocol number

TCP : 6 UDP : 17

Host : IP address (e.g. 157.193.122.1)

Note : some terminology : Application : messageTransport : segment Network : datagram (or packet)Data Link : frame

IP157.193.

122.1

Summary

Introduction 1-52

Table of contents

1.1 What is the Internet? 3 1.5 Internet structure and ISPs 15 1.7 Protocol layers, service models 26 Summary 50 Table of contents 52

Introduction1-1 Part of slides provided by J.F Kurose and K.W. Ross, All Rights Reserved Chapter 1...

Documents

Transcript of Introduction1-1 Part of slides provided by J.F Kurose and K.W. Ross, All Rights Reserved Chapter 1...