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Stan Kurkovsky

Computer NetworksComputer Networks

Network Edge and Network Edge and Network CoreNetwork Core

Based on Computer Networking, 4th Edition by Kurose and Ross

Stan Kurkovsky

WhatWhat’’s the Internet: s the Internet: ““Nuts and BoltsNuts and Bolts”” ViewView

•• millions of connected millions of connected computing devices: computing devices: hosts hosts = end systems= end systems

•• running running network appsnetwork apps•• communication linkscommunication links

•• fiber, copper, radio, fiber, copper, radio, satellitesatellite

•• transmission rate = transmission rate = bandwidthbandwidth

•• routers:routers: forward packets forward packets (chunks of data)(chunks of data)

Home network

Institutional network

Mobile network

Global ISP

Regional ISP

router

PC

server

wirelesslaptopcellular handheld

wiredlinks

access points

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Stan Kurkovsky

““CoolCool”” Internet AppliancesInternet Appliances

Shaver with a LAN connectivity

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

Web-enabled toaster +weather forecaster

Internet phones

Stan Kurkovsky

WhatWhat’’s the Internet: s the Internet: ““Nuts and BoltsNuts and Bolts”” ViewView

•• protocolsprotocols control sending, control sending, receiving of messagesreceiving of messages•• e.g., TCP, IP, HTTP, FTP, PPP, e.g., TCP, IP, HTTP, FTP, PPP,

Skype, EthernetSkype, Ethernet

•• Internet: Internet: ““network of networksnetwork of networks””•• loosely hierarchicalloosely hierarchical•• public Internet versus private public Internet versus private

intranetintranet

•• Internet standardsInternet standards•• RFC: Request for commentsRFC: Request for comments•• IETF: Internet Engineering Task IETF: Internet Engineering Task

ForceForce

Home network

Institutional network

Mobile network

Global ISP

Regional ISP

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Stan Kurkovsky

WhatWhat’’s the Internet: a Service Views the Internet: a Service View

•• communication communication infrastructure infrastructure enables distributed applications:enables distributed applications:•• Web, email, voice over IP, Web, email, voice over IP,

games, egames, e--commerce, file sharingcommerce, file sharing

•• communication services provided communication services provided to apps:to apps:•• reliable data delivery from source reliable data delivery from source

to destinationto destination•• ““best effortbest effort”” (unreliable) data (unreliable) data

deliverydelivery

Stan Kurkovsky

WhatWhat’’s a Protocol?s a Protocol?

human protocols:human protocols:•• ““whatwhat’’s the time?s the time?””•• ““I have a questionI have a question””•• introductionsintroductions

…… specific specific msgsmsgs sentsent…… specific actions taken when specific actions taken when msgsmsgs

received, or other eventsreceived, or other events

network protocols:network protocols:•• machines rather than humansmachines rather than humans•• all communication activity in Internet all communication activity in Internet

governed by protocolsgoverned by protocols

protocols define format, order of protocols define format, order of msgsmsgs sent and received among sent and received among network entities, and actions taken network entities, and actions taken on on msgmsg transmission, receipttransmission, receipt

Hi

HiGot thetime?2:00

TCP connectionrequest

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

<file>time

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Stan Kurkovsky

A closer Look at Network StructureA closer Look at Network Structure

•• network edge:network edge:•• applications and hostsapplications and hosts

•• network core:network core:•• interconnected routersinterconnected routers•• network of networksnetwork of networks

•• access networks, physical access networks, physical media:media:•• wired and wireless wired and wireless

communication linkscommunication links

Stan Kurkovsky

The Network EdgeThe Network Edge

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

•• client/server model:client/server model:•• client host requests, receives client host requests, receives

service from alwaysservice from always--on serveron server•• e.g. Web browser/server; email e.g. Web browser/server; email

client/serverclient/server

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

serversservers•• e.g. Gnutella, e.g. Gnutella, KaZaAKaZaA, Skype, , Skype,

BitTorrentBitTorrent

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Stan Kurkovsky

Network Edge: Reliable Data Transfer ServiceNetwork Edge: Reliable Data Transfer Service

Goal:Goal: data transfer between end systemsdata transfer between end systems•• handshaking:handshaking: setup (prepare for) data transfer ahead of timesetup (prepare for) data transfer ahead of time

•• Hello, hello back human protocolHello, hello back human protocol•• set up set up ““statestate”” in two communicating hostsin two communicating hosts

•• TCP TCP -- Transmission Control Protocol Transmission Control Protocol •• InternetInternet’’s connections connection--oriented serviceoriented service

TCP serviceTCP service [RFC 793][RFC 793]•• reliable, inreliable, in--orderorder bytebyte--stream data transferstream data transfer

•• loss: acknowledgements and retransmissionsloss: acknowledgements and retransmissions

•• flow control:flow control:•• sender wonsender won’’t overwhelm receivert overwhelm receiver

•• congestion control:congestion control:•• senders senders ““slow down sending rateslow down sending rate”” when network congestedwhen network congested

Stan Kurkovsky

Network Edge: Best Effort (Unreliable) Data Transfer ServiceNetwork Edge: Best Effort (Unreliable) Data Transfer Service

Goal:Goal: data transfer between end systemsdata transfer between end systems•• same as before!same as before!

•• UDPUDP -- User Datagram Protocol [RFC 768]: User Datagram Protocol [RFC 768]: •• connectionless connectionless •• unreliable data transferunreliable data transfer•• no flow controlno flow control•• no congestion controlno congestion control

AppApp’’s using TCP:s using TCP:•• HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (emHTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email)ail)

AppApp’’s using UDP:s using UDP:•• streaming media, teleconferencing, DNS, Internet telephonystreaming media, teleconferencing, DNS, Internet telephony

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Stan Kurkovsky

Access Networks and Physical MediaAccess Networks and Physical Media

•• How to connect end systems to How to connect end systems to edge router?edge router?•• residential access netsresidential access nets•• institutional access networks institutional access networks

(school, company)(school, company)•• mobile access networksmobile access networks

•• Keep in mind:Keep in mind:•• bandwidth (bits per second) of bandwidth (bits per second) of

access network?access network?•• shared or dedicated?shared or dedicated?

Stan Kurkovsky

Residential Access: Point to Point AccessResidential Access: Point to Point Access

•• Dialup via modemDialup via modem•• up to 56Kbps direct access to router up to 56Kbps direct access to router

(often less)(often less)•• CanCan’’t surf and phone at same time: t surf and phone at same time:

cancan’’t be t be ““always onalways on””

•• DSL:DSL: digital subscriber linedigital subscriber line•• deployment: telephone company deployment: telephone company

(typically)(typically)•• up to 1 Mbps upstream (today up to 1 Mbps upstream (today

typically < 256 kbps)typically < 256 kbps)•• up to 8 Mbps downstream (today up to 8 Mbps downstream (today

typically < 1 Mbps)typically < 1 Mbps)•• dedicated physical line to telephone dedicated physical line to telephone

central officecentral office

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Stan Kurkovsky

Residential Access: Cable ModemsResidential Access: Cable Modems

•• HFC: hybrid fiber coaxHFC: hybrid fiber coax•• asymmetric: up to 30Mbps downstream, 2 Mbps upstreamasymmetric: up to 30Mbps downstream, 2 Mbps upstream

•• network of cable and fiber attaches homes to ISP routernetwork of cable and fiber attaches homes to ISP router•• homes share homes share

access to access to router router

•• deployment: deployment: available via available via cable TV cable TV companiescompanies

Diagram: http://Diagram: http://www.cabledatacomnews.com/cmic/diagram.htmlwww.cabledatacomnews.com/cmic/diagram.html

Stan Kurkovsky

Cable Network Architecture: OverviewCable Network Architecture: Overview

server(s) home

cable headend

cable distributionnetwork (simplified) Typically 500 to 5,000 homes

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

FDM

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Stan Kurkovsky

Company Access: Local Area NetworksCompany Access: Local Area Networks

•• company/university company/university local area local area networknetwork (LAN) connects end (LAN) connects end system to edge routersystem to edge router

•• Ethernet:Ethernet:•• 10 10 MbsMbs, 100Mbps, 1Gbps, , 100Mbps, 1Gbps,

10Gbps Ethernet10Gbps Ethernet•• modern configuration: end modern configuration: end

systems connect into systems connect into EthernetEthernet switchswitch

•• LANs: chapter 5LANs: chapter 5

Stan Kurkovsky

Wireless Access NetworksWireless Access Networks

•• shared shared wirelesswireless access network access network connects end system to routerconnects end system to router•• via base station aka via base station aka ““access access

pointpoint””

•• wireless LANs:wireless LANs:•• 802.11b/g (802.11b/g (WiFiWiFi): 11 or 54 Mbps): 11 or 54 Mbps

•• widerwider--area wireless accessarea wireless access•• provided by provided by telcotelco operatoroperator•• ~1Mbps over cellular system ~1Mbps over cellular system

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

over wide areaover wide area

basestation

mobilehosts

router

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Stan Kurkovsky

Home NetworksHome Networks

Typical home network components: Typical home network components: •• DSL or cable modemDSL or cable modem•• router/firewall/NATrouter/firewall/NAT•• EthernetEthernet•• wireless access pointwireless access point

wirelessaccess point

wirelesslaptops

router/firewall

cablemodem

to/fromcable

headend

Ethernet

Stan Kurkovsky

Physical MediaPhysical Media

•• Bit:Bit: propagates between propagates between transmitter/receiver pairstransmitter/receiver pairs

•• physical link:physical link: what lies between what lies between transmitter & receivertransmitter & receiver

•• guided media:guided media:•• signals propagate in solid media: signals propagate in solid media:

copper, fiber, coaxcopper, fiber, coax

•• unguided media:unguided media:•• signals propagate freely, e.g., signals propagate freely, e.g.,

radioradio

•• Twisted Pair (TP):Twisted Pair (TP): two insulated two insulated copper wirescopper wires•• Category 3: traditional phone Category 3: traditional phone

wires, 10 Mbps Ethernetwires, 10 Mbps Ethernet•• Category 5: Category 5:

100Mbps Ethernet100Mbps Ethernet

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Stan Kurkovsky

Physical MediaPhysical Media

•• Coaxial cable:Coaxial cable: two concentric two concentric copper conductorscopper conductors

•• bidirectionalbidirectional•• baseband:baseband:

•• single channel on cablesingle channel on cable•• legacy Ethernetlegacy Ethernet

•• broadband:broadband:•• multiple channels on cablemultiple channels on cable•• HFCHFC

•• Fiber optic cable:Fiber optic cable: glass fiber glass fiber carrying light pulses, each pulse a carrying light pulses, each pulse a bitbit

•• highhigh--speed operation:speed operation:•• highhigh--speed pointspeed point--toto--point point

transmission (e.g., 10transmission (e.g., 10’’ss--100100’’s s GpsGps))

•• low error rate: repeaters spaced low error rate: repeaters spaced far apart; far apart;

•• immune to electromagnetic noiseimmune to electromagnetic noise

Stan Kurkovsky

Physical MediaPhysical Media

•• Radio:Radio: signal carried in electromagnetic spectrumsignal carried in electromagnetic spectrum•• no physical no physical ““wirewire””•• bidirectionalbidirectional•• propagation environment effects:propagation environment effects:

•• reflection reflection •• obstruction by objectsobstruction by objects•• interferenceinterference

•• Radio link types:Radio link types:•• terrestrial microwaveterrestrial microwave

•• e.g. up to 45 Mbps channelse.g. up to 45 Mbps channels

•• LAN (e.g., LAN (e.g., WiFiWiFi))•• 2Mbps, 11Mbps, 54 Mbps2Mbps, 11Mbps, 54 Mbps

•• widewide--area (e.g., cellular)area (e.g., cellular)•• e.g. 3G: hundreds of kbpse.g. 3G: hundreds of kbps

•• satellitesatellite•• Kbps to 45Mbps channel (or multiple smaller channels)Kbps to 45Mbps channel (or multiple smaller channels)•• 270 270 msecmsec endend--end delayend delay•• geosynchronous versus low altitudegeosynchronous versus low altitude

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Stan Kurkovsky

The Network CoreThe Network Core

•• mesh of interconnected routersmesh of interconnected routers•• thethe fundamental question:fundamental question: how is how is

data transferred through net?data transferred through net?

•• circuit switching:circuit switching: dedicated circuit dedicated circuit per call: telephone netper call: telephone net

•• packetpacket--switching:switching: data sent thru data sent thru net in discrete net in discrete ““chunkschunks””

Stan Kurkovsky

Network Core: Circuit SwitchingNetwork Core: Circuit Switching

EndEnd--end resources reserved for end resources reserved for ““callcall””

•• link bandwidth, switch capacitylink bandwidth, switch capacity•• dedicated resources: no sharingdedicated resources: no sharing•• circuitcircuit--like (guaranteed) like (guaranteed)

performanceperformance•• call setup requiredcall setup required

•• network resources (e.g., network resources (e.g., bandwidth) bandwidth) divided into divided into ““piecespieces””•• pieces allocated to callspieces allocated to calls•• resource piece resource piece idleidle if not used by if not used by

owning call owning call (no sharing)(no sharing)•• dividing link bandwidth into dividing link bandwidth into

““piecespieces””•• frequency divisionfrequency division•• time divisiontime division

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Stan Kurkovsky

Circuit Switching: FDM and TDMCircuit Switching: FDM and TDM

FDM

frequency

timeTDM

frequency

time

4 usersExample:

Stan Kurkovsky

Numerical ExamplesNumerical Examples

•• How long does it take to send a file of 640,000 bits from host How long does it take to send a file of 640,000 bits from host A to host B over a circuitA to host B over a circuit--switched network?switched network?

•• All links are 1.536 MbpsAll links are 1.536 Mbps•• Each link uses FDM with 24 Each link uses FDM with 24

channels/frequencieschannels/frequencies•• 500 500 msecmsec to establish endto establish end--toto--end end

circuitcircuit

•• All links are 1.536 MbpsAll links are 1.536 Mbps•• Each link uses TDM with 24 Each link uses TDM with 24

slots/secslots/sec•• 500 500 msecmsec to establish endto establish end--toto--end end

circuitcircuit

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Stan Kurkovsky

Network Core: Packet SwitchingNetwork Core: Packet Switching

each endeach end--end data stream divided end data stream divided into into packetspackets

•• user A, B packets user A, B packets shareshare network network resourcesresources

•• each packet uses full link each packet uses full link bandwidth bandwidth

•• resources used resources used as neededas needed

resource contention:resource contention:•• aggregate resource demand can aggregate resource demand can

exceed amount availableexceed amount available•• congestion: packets queue, wait congestion: packets queue, wait

for link usefor link use•• store and forward: packets move store and forward: packets move

one hop at a timeone hop at a time•• Node receives complete packet Node receives complete packet

before forwardingbefore forwarding

Bandwidth division into Bandwidth division into ““piecespieces””Dedicated allocationDedicated allocationResource reservationResource reservation

Stan Kurkovsky

Packet Switching: Statistical MultiplexingPacket Switching: Statistical Multiplexing

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

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

A

B

C10 Mb/sEthernet

1.5 Mb/s

D E

statistical multiplexing

queue of packetswaiting for output

link

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Stan Kurkovsky

Packet Switching: StorePacket Switching: Store--andand--ForwardForward

•• Takes L/R seconds to transmit (push out) packet of L bits on to Takes L/R seconds to transmit (push out) packet of L bits on to link or R link or R bpsbps

•• Entire packet must arrive at router before it can be transmitteEntire packet must arrive at router before it can be transmitted on next d on next link: link: store and forwardstore and forward

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

•• Example:Example:•• L = 7.5 L = 7.5 MbitsMbits•• R = 1.5 MbpsR = 1.5 Mbps•• Transmission delay = 15 secTransmission delay = 15 sec

R R RL

Stan Kurkovsky

Packet Switching versus Circuit SwitchingPacket Switching versus Circuit Switching

•• Packet switching allows more users to use network!Packet switching allows more users to use network!

•• Great for Great for burstybursty datadata•• resource sharingresource sharing•• simpler, no call setupsimpler, no call setup

•• Excessive congestion:Excessive congestion: packet delay and losspacket delay and loss•• protocols needed for reliable data transfer, congestion controlprotocols needed for reliable data transfer, congestion control

•• Q: How to provide circuitQ: How to provide circuit--like behavior?like behavior?•• bandwidth guarantees needed for audio/video appsbandwidth guarantees needed for audio/video apps•• still an unsolved problemstill an unsolved problem

•• Q: What are human analogies?Q: What are human analogies?•• reserved resources (circuit switching) reserved resources (circuit switching) •• onon--demand allocation (packetdemand allocation (packet--switching)switching)

N users1 Mbps link

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Stan Kurkovsky

Internet Structure: Network of NetworksInternet Structure: Network of Networks

•• roughly hierarchicalroughly hierarchical•• at center: at center: ““tiertier--11”” ISPs ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), (e.g., Verizon, Sprint, AT&T, Cable and Wireless),

national/international coveragenational/international coverage•• treat each other as equalstreat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1 providers interconnect (peer) privately

Stan Kurkovsky

TierTier--1 ISP: e.g., Sprint1 ISP: e.g., Sprint

…

to/from customers

peering

to/from backbone

….

………

POP: point-of-presence

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Stan Kurkovsky

Internet Structure: Network of NetworksInternet Structure: Network of Networks

•• ““TierTier--22”” ISPs: smaller (often regional) ISPsISPs: smaller (often regional) ISPs•• Connect to one or more tierConnect to one or more tier--1 ISPs, possibly other tier1 ISPs, possibly other tier--2 ISPs2 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 InternetTier-2 ISP is customer oftier-1 provider

Tier-2 ISPs also peer privately with each other.

Stan Kurkovsky

Internet Structure: Network of NetworksInternet Structure: Network of Networks

•• ““TierTier--33”” ISPs and local ISPs ISPs and local ISPs •• last hop (last hop (““accessaccess””) network (closest to end systems)) 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

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Stan Kurkovsky

Internet Internet StructureStructure: : NetworkNetwork of of NetworksNetworks

•• a packet passes through many networksa 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