computer networks slides

8/12/2019 Computer Networks Slides

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Course book:Computer NetworkingTop Down approach 3rd edition

y m urose an e ross

Computer Networks 3rd edition

Introduction 1-1

y n rew . anen aum


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Cha ter 1Computer Networks

Computer Networking:A Top Down ApproachFeaturing the Internet,

.Jim Kurose, Keith Ross

Introduction 1-2


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:Our goal: Overview:

get feel andterminology

whats the Internet whats a protocol?

,laterin course

approach:

ne wor e ge

network core

use Internet as

example

,

Internet/ISP structure

rotocol la ers, service models

network modeling

Introduction 1-3


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C a ter 1: road a

1.2 Network edge.

1.4 Network access and physical media

.

1.6 Protocol layers, service models

.

Introduction 1-4


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Whats the Internet: nuts and bolts view millions of connected

com utin devices: hostsrouter workstation

= end systems running network apps local ISP

servermobile

communication links

fiber, copper, radio,satellite re ional I P transmission rate =

bandwidth

(chunks of data)

company

Introduction 1-5

network


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Whats the Internet: nuts and bolts viewprotocolscontrol sending, router workstation

e.g., TCP, IP, HTTP, FTP, PPP

Internet: network of local ISP

servermobile

networks

loosely hierarchical re ional I Pprivate intranet

Internet standards

RFC: Request for comments IETF: Internet Engineering

Task Force company

Introduction 1-6

network


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Whats the Internet: a service view communication

infrastructure enables

distributed applications: Web, email, games, e-

,

communication services

provided to apps: Connectionless unreliable

connection-orientedreliable

Introduction 1-7


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ats a rotocolhuman protocols:

network protocols:

w a s e me

I have a question

mac nes ra er anhumans

specific msgs sent

activity in Internet

governed by protocols specific actions taken

when msgs received,protocols define format,

order of msgs sent and

entities, and actionstaken on msg

Introduction 1-8

transmission, receipt


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ats a rotocola human protocol and a computer network protocol:

Hi TCP connection

Hi

req

TCP connectiontime?

2:00Get http://www.awl.com/kurose-ross

time

Introduction 1-9


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C a ter 1: road a

1.2 Network edge.


.


.

Introduction 1-10


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A closer look at network structure:

applications andhosts

network core: routers network of

networks

access ne wor s,physical media:

Introduction 1-11


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T e networ ed e: end systems (hosts):

e.g. Web, email at edge of network

c en server mo e client host requests, receives

service from always-on server e.g. We rowser server; emai

client/server

peer-peer model: minimal (or no) use of dedicated

servers

e.g. Gnutella, KaZaA,bit torrent

Introduction 1-12


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Network ed e: connectionless service

:

between end systems same as before!

HTTP (Web), FTP (filetransfer), Telnet

UDP - User DatagramProtocol [RFC 768]:

remote ogin , SMTP(email)

unreliable datatransfer

Apps using UDP:

no flow control no congestion control

,teleconferencing, DNS,Internet telephony

Introduction 1-14


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C a ter 1: road a

1.2 Network edge.


.


.

Introduction 1-15


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T e Networ Core mesh of interconnected

routers thefundamental

ques on: ow s a atransferred through net?

circuit switchin :dedicated circuit percall: telephone net

pac e -sw c ng: a asent thru net indiscrete chunks

Introduction 1-16


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Network Core: Circuit Switchin

-

reserved for call link bandwidth, switch

capacity

dedicated resources:

circuit-like( uaranteed)

performance call setup required

Introduction 1-17


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Network Core: Circuit Switchinnetwork resources dividing link bandwidth

e.g., an wdivided into pieces

into pieces

frequency division

resource piece idleif

not used b ownin call(no sharing)

Introduction 1-18


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Circuit witc in : and TFDM

Example:

time

TDM

frequency

Introduction 1-19time


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Nu erical exa le

640,000 bits from host A to host B over acircuit-switched network? All links are 1.536 Mbps

Each link uses TDM with 24 slots 500 msec to establish end-to-end circuit

or ou

Introduction 1-20


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Network Core: Packet Switchineach end-end data stream resource contention:

user A, B packets share

network resources

aggrega e resource

demand can exceedamount available

each packet uses full link

bandwidth

congestion: packets

queue, wait for link use resources use as nee e store an orwar :

packets move one hopat a time Node receives complete

packet before forwardingBandwidth division into pieces

Dedicated allocation

Introduction 1-21


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Packet switchin versus circuit switchinPacket switching allows more users to use network!

1 Mb/s link each user:

100 kb/s when active

active 10% of time

circuit-switching:

10 users

1 Mbps link

pac e sw c ng: with 35 users,

probability > 10 active

Introduction 1-23

less than .0004


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Packet switchin versus circuit switchinIs packet switching a slam dunk winner?

Great for bursty data resource sharing

simpler, no call setup

Excessive congestion: packet delay and lossro oco s nee e or re a e a a rans er,congestion control

: How to rovide circuit-like behavior?

bandwidth guarantees needed for audio/videoapps

Introduction 1-24

still an unsolved problem (chapter 6)


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Packet-switchin : store-and- orwardL

Takes L/R seconds to Example:

packet of L bits on to

link or R bps

= . s

R = 1.5 Mbps

= Entire packet must

arrive at router before

on next link: store andforward

Introduction 1-25

e ay =


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Packet-switched networks: forwardin Goal:move packets through routers from source to

well study several path selection (i.e. routing) algorithms(chapter 4)

datagram network: destination address in packet determines next hop

routes ma chan e durin session

analogy: driving, asking directions

virtual circuit network:

eac packet carries tag virtua circuit ID , tagdetermines next hop

fixed path determined at call setup time, remains fixed

Introduction 1-26

t ru ca

routers maintain per-call state


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Network Taxonomy

Telecommunicationnetworks

Circuit-switched Packet-switchednetworks networks

FDM TDM Networkswith VCs

DatagramNetworks

Datagram network is noteither connection-orientedor connectionless. -

Introduction 1-27

connectionless services (UDP) to apps.


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C a ter 1: road a

1.2 Network edge.


.


.

Introduction 1-28


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Access networks and h sical mediaQ: How to connect end

residential access nets

networks (school,

company) mo e access networ s

Keep in mind:

an w t ts persecond) of accessnetwork?

Introduction 1-29

shared or dedicated?


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Residential access: oint to oint access

Dialu via modem

up to 56Kbps direct access torouter (often less)

Cant surf and phone at sametime: cant be always on

ADSL: asymmetric digital subscriber line

up to 1 Mbps upstream (today typically < 256 kbps)

FDM: 50 kHz - 1 MHz for downstream

4 kHz - 50 kHz for u stream

Introduction 1-30

0 kHz - 4 kHz for ordinary telephone


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Residential access: cable modems

Introduction 1-32Diagram: http://www.cabledatacomnews.com/cmic/diagram.html


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Cable Network Architecture: Overview

Typically 500 to 5,000 homes

home

cable headend

Introduction 1-33

network (simplified)


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home

cable headend

Introduction 1-34

network (simplified)


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server(s)

home

cable headend

Introduction 1-35

network


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FDM:

VI

D

E

VI

D

E

VI

D

E

VI

D

E

VI

D

E

VI

D

E

D

A

T

D

A

T

C

O

NT

R

O

Channels

1 2 3 4 5 6 7 8 9

home

cable headend

Introduction 1-36

network


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Com an access: local area networks company/univ local area

end system to edge router Ethernet:

shared or dedicated link

connects end system

10 Mbs, 100Mbps,Gi abit Ethernet

LANs: chapter 5

Introduction 1-37


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Wireless access networks shared wirelessaccess

to router via base station aka access

router

po n

wireless LANs: 802.11b (WiFi): 11 Mb s

basestation

wider-area wireless access provided by telco operator

~ ps

Will it happen??

WAP/GPRS in Europe

mobilehosts

Introduction 1-38


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Home networks

Typical home network components:

router/firewall/NAT Ethernet

wireless access

pointwirelesslaptops

router/cableto/from

wirelessaccess

irewamo emheadend

Introduction 1-39

po n


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Ph sical Media Bit: ro a ates between

Twisted Pair (TP)

transmitter/rcvr pairs

physical link: what lies wires Category 3: traditionale ween ransm er

receiver

uided media:

p one w res, psEthernet

Category 5: signals propagate in solid

media: copper, fiber, coax

ps erne

signals propagate freely,

e.g., radio

Introduction 1-40


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Ph sical Media: coax fiberCoaxial cable: Fiber optic cable:

two concentric copper

conductors

pulses, each pulse a bit high-speed operation:

baseband:

single channel on cable

high-speed point-to-pointtransmission (e.g., 5 Gps)

: legacy Ethernet

broadband:

spaced far apart ; immuneto electromagnetic noise

HFC

Introduction 1-41


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Ph sical media: radio signal carried in Radio link types:

spectrum no h sical wire

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

bidirectional

propagation

2Mbps, 11Mbps

wide-area (e.g., cellular)env ronment e ects:

reflection

obstruction b ob ects

e.g. : un re s o ps

satellite u to 50Mb s channel or

interference multiple smaller channels) 270 msec end-end delay

Introduction 1-42

altitude


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C a ter 1: road a

1.2 Network edge.


.1.6 Protocol layers, service models

.

Introduction 1-43


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Internet structure: network of networks roughly hierarchical

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

Sprint, AT&T), national/international coverage

Tier-1 providers

also interconnectTier 1 ISPer-

providersinterconnect

eer

NAP

at public networkaccess points(NAPs)

Tier 1 ISP Tier 1 ISPprivately

Introduction 1-44


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Tier-1 I P: e rintSprint US backbone network

Introduction 1-45


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Internet structure: network of networks

Tier-2 ISPs: smaller (often regional) ISPs onnect to one or more tier- S s, possi y ot er tier- S s

Tier-2 ISPTier-2 ISPTier-2 ISP pays-

Tier-2 ISPsalso peer

privately withTier 1 ISP

NAP

connectivity torest of Internet tier-2 ISP is

each other,interconnectat NAP

Tier 1 ISP Tier 1 ISP

- -

Tier-2 ISP

cus omerotier-1 provider

Introduction 1-46


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Tier-3 ISPs and local ISPs ast op access networ c osest to en systems

local

Tier-2 ISPTier-2 ISP

ISPlocalISP

ocaISP

ISP

Local and tier-

3 ISPs areTier 1 ISP

NAPcustomersofhigher tierISPs


- -

Tier-2 ISP

local

them to restof Internet

Introduction 1-47

localISP

local

ISP

local

ISP

ISP


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a packet passes through many networks!

local

Tier-2 ISPTier-2 ISP

ISPlocalISP

ocaISP

ISP

Tier 1 ISPNAP


- -

Tier-2 ISP

local

Introduction 1-48

localISP

local

ISP

local

ISP

ISP


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C a ter 1: road a

1.2 Network edge.


. 1.6 Protocol layers, service models

.

Introduction 1-49


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Protocol a ersNetworks are complex!

many p eces :

hosts Question:

links of various

media

s ere any ope oorganizingstructure of

network? applications

protocols Or at least our discussion

hardware,software

o ne wor s

Introduction 1-50


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Or anization o air travelticket (purchase) ticket (complain)

baggage (check)

baggage (claim)

gates oa

runway takeoff

ga es un oa

runway landing

airplane routing airplane routing

airplane routing

a series o ste s

Introduction 1-51

Layering of airline functionality


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Layering of airline functionality

ticket (purchase)

baggage (check)gates (load)

ticket (complain)

baggage (claimgates (unload)

ticket

baggage

gate

runway (takeoff)

airplane routing

departure arrivalintermediate air-traffic

airplane routing airplane routing

runway (land)

airplane routing

takeoff/landing

airplane routing

airport airportcontrol centers

Layers: each layer implements a service

via its own internal-layer actions relying on services provided by layer below

Introduction 1-52


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la erinDealing with complex systems:

exp icit structure a ows i enti ication,

relationship of complex systems pieces

modularization eases maintenance, updating of

system change of implementation of layers service

transparent to rest of system

. .,rest of system

la erin considered harmful?

Introduction 1-53


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Internet rotocol stac application: supporting network

app ca ons

FTP, SMTP, STTP trans ort: host-host data transfer

application

TCP, UDP

network: routing of datagrams fromnetwork

source o es na on IP, routing protocols

in : data trans er between

link

neighboring network elements PPP, Ethernet

physical

Introduction 1-54

p ys ca : s on e w re

source Encapsulation


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messa e a licationMEncapsulation

segmentdatagram

frame

transportnetwork

linkHtHnHl MHtHn M

Ht M

physical

linkh sical

HtHnHl M HtHnHl M

switch

destination

a licationM

networklinkHtHnHl M

HtHn M

HtHnHl M

HtHn M

transportnetworklinkHtHnHl M

HtHn M

Ht M

physical

router

Introduction 1-55

physical


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C a ter 1: road a

1.2 Network edge.


. 1.6 Protocol layers, service models

.

Introduction 1-56

Internet History


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Internet History

1961-1972: Early packet-switching principles

-theory showseffectiveness of packet-

:

ARPAnet demonstratedpublicly

1964: Baran - packet-

switching in military nets

NCP Network ControProtocol) first host-host protocol

by Advanced ResearchProjects Agency

irst e-mai program

ARPAnet has 15 nodes

operational

Introduction 1-57

Internet History


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Internet History

:

1972-1980: Internetworking, new and proprietary nets

network in Hawaii

1973: Metcalfes PhD thesis

er an a n sinternetworking principles:

minimalism, autonomy -

1974: Cerf and Kahn -architecture for

no n erna c angesrequired tointerconnect networks

late70s: proprietary

architectures: DECnet, SNA,XNA

model

stateless routers

late 70s: switching fixed

length packets (ATMrecursor

ecentra ze contro

define todays Internetarchitecture

Introduction 1-58

1979: ARPAnet has 200 nodes

Internet History


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Internet History

1990, 2000s: commercialization, the Web, new apps

decommissioned

1991: NSF lifts restrictions on

a e s s:

more killer apps: instantmessaging, P2P file sharing

(decommissioned, 1995)

early 1990s: Web

network security toforefront

est. 50 million host, 100 ypertext us , e son1960s]

HTML, HTTP: Berners-Lee

million+ users

backbone links running atGbps

1994: Mosaic, later Netscape

late 1990s:commercialization of the Web

Introduction 1-59


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Introduction: u arCovered a ton of material! You now have: Internet overview whats a protocol?

context, overview,

feel of networking, ,

network

packet-switching versus

,follow!

circuit-switc ing Internet/ISP structure

,

layering and servicemodels

Introduction 1-60

s ory

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