Introduction1-*Chapter 1 IntroductionComputer Networking: A Top Down Approach , 5th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009. A note on the use of these ppt slides:Were making these slides freely available to all (faculty, students, readers). Theyre in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, wed like people to use our book!) If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.

Thanks and enjoy! JFK/KWR

All material copyright 1996-2009J.F Kurose and K.W. Ross, All Rights Reserved

Introduction

Introduction1-*Chapter 1: IntroductionOur goal: get feel and terminologymore depth, detail later in courseapproach:use Internet as example

Overview:whats the Internet?whats a protocol?network edge; hosts, access net, physical medianetwork core: packet/circuit switching, Internet structureperformance: loss, delay, throughputsecurityprotocol layers, service modelshistory

Introduction

Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History

Introduction

Introduction1-*Whats the Internet: nuts and bolts viewmillions of connected computing devices: hosts = end systems running network appscommunication linksfiber, copper, radio, satellitetransmission rate = bandwidthrouters: forward packets (chunks of data)

Introduction

Introduction1-*Cool internet appliancesWorlds smallest web serverhttp://www-ccs.cs.umass.edu/~shri/iPic.htmlIP picture framehttp://www.ceiva.com/Web-enabled toaster +weather forecasterInternet phones

Introduction

Introduction1-*Whats the Internet: nuts and bolts viewprotocols control sending, receiving of msgse.g., TCP, IP, HTTP, Skype, EthernetInternet: network of networksloosely hierarchicalpublic Internet versus private intranetInternet standardsRFC: Request for commentsIETF: Internet Engineering Task Force

Introduction

Introduction1-*Whats the Internet: a service viewcommunication infrastructure enables distributed applications:Web, VoIP, email, games, e-commerce, file sharingcommunication services provided to apps:reliable data delivery from source to destinationbest effort (unreliable) data delivery

Introduction

Introduction1-*Whats a protocol?human protocols:whats the time?I have a questionintroductions

specific msgs sent specific actions taken when msgs received, or other eventsnetwork protocols:machines rather than humansall communication activity in Internet governed by protocolsprotocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

Introduction

Introduction1-*Whats a protocol?a human protocol and a computer network protocol:

Q: Other human protocols? HiHiTCP connection request

Introduction

Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History

Introduction

Introduction1-*A closer look at network structure:network edge: applications and hostsaccess networks, physical media: wired, wireless communication links network core: interconnected routersnetwork of networks

Introduction

Introduction1-*The network edge:end systems (hosts):run application programse.g. Web, emailat edge of networkclient/server modelclient host requests, receives service from always-on servere.g. Web browser/server; email client/serverpeer-peer model: minimal (or no) use of dedicated serverse.g. Skype, BitTorrent

Introduction

Introduction1-*Access networks and physical mediaQ: How to connect end systems to edge router?residential access netsinstitutional access networks (school, company)mobile access networksKeep in mind: bandwidth (bits per second) of access network?shared or dedicated?

Introduction

Uses existing telephony infrastructureHome is connected to central officeup to 56Kbps direct access to router (often less)Cant surf and phone at same time: not always onDial-up Modem

Introduction

Digital Subscriber Line (DSL)

Also uses existing telephone infrastrutureup to 1 Mbps upstream (today typically < 256 kbps)up to 8 Mbps downstream (today typically < 1 Mbps)dedicated physical line to telephone central office

Introduction

Introduction1-*Residential access: cable modemsDoes not use telephone infrastructureInstead uses cable TV infrastructureHFC: hybrid fiber coaxasymmetric: up to 30Mbps downstream, 2 Mbps upstreamnetwork of cable and fiber attaches homes to ISP routerhomes share access to router unlike DSL, which has dedicated access

Introduction

Introduction1-*Residential access: cable modemsDiagram: http://www.cabledatacomnews.com/cmic/diagram.html

Introduction

Introduction1-*Cable Network Architecture: Overviewhomecable headendcable distributionnetwork (simplified)Typically 500 to 5,000 homes

Introduction

Introduction1-*Cable Network Architecture: Overviewhomecable headendcable distributionnetwork

Introduction

Introduction1-*Cable Network Architecture: Overviewhomecable headendcable distributionnetwork (simplified)

Introduction

Introduction1-*Cable Network Architecture: Overviewhomecable headendcable distributionnetworkFDM (more shortly):

Introduction

Fiber to the HomeOptical links from central office to the homeTwo competing optical technologies: Passive Optical network (PON) Active Optical Network (AON)Much higher Internet rates; fiber also carries television and phone services

Introduction

Ethernet Internet accessTypically used in companies, universities, etc10 Mbs, 100Mbps, 1Gbps, 10Gbps EthernetToday, end systems typically connect into Ethernet switch

Introduction

Introduction1-*Wireless access networksshared wireless access network connects end system to routervia base station aka access pointwireless LANs:802.11b/g (WiFi): 11 or 54 Mbpswider-area wireless accessprovided by telco operator~1Mbps over cellular system (EVDO, HSDPA)next up (?): WiMAX (10s Mbps) over wide areabasestationmobilehostsrouter

Introduction

Introduction1-*Home networksTypical home network components: DSL or cable modemrouter/firewall/NATEthernetwireless access pointwirelessaccess pointwirelesslaptopsrouter/firewallcablemodemto/fromcableheadendEthernet

Introduction

Introduction1-*Physical MediaBit: propagates between transmitter/rcvr pairsphysical link: what lies between transmitter & receiverguided media: signals propagate in solid media: copper, fiber, coaxunguided media: signals propagate freely, e.g., radioa. Twisted Pair (TP)two insulated copper wiresCategory 3: traditional phone wires, 10 Mbps EthernetCategory 5: 100Mbps Ethernet

Introduction

Introduction1-*Physical Media: coax, fiberb. Coaxial cable:two concentric copper conductorsbidirectionalbaseband:single channel on cablelegacy Ethernetbroadband: multiple channels on cable HFCc. Fiber optic cable:glass fiber carrying light pulses, each pulse a bithigh-speed operation:high-speed point-to-point transmission (e.g., 10s-100s Gps)low error rate: repeaters spaced far apart ; immune to electromagnetic noise

Introduction

The internet undersea world Introduction1-*

Introduction

Introduction1-*Physical media: radiosignal carried in electromagnetic spectrumno physical wirebidirectionalpropagation environment effects:reflection obstruction by objectsinterferenceRadio link types:terrestrial microwavee.g. up to 45 Mbps channelsWLAN (e.g., Wifi)11Mbps, 54 Mbpswide-area (e.g., cellular)3G cellular: ~ 1 MbpssatelliteKbps to 45Mbps channel (or multiple smaller channels)270 msec end-end delaygeosynchronous versus low altitude

Introduction

Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History

Introduction

Introduction1-*The Network Coremesh of interconnected routersthe fundamental question: how is data transferred through net?circuit switching: dedicated circuit per call: telephone netpacket-switching: data sent thru net in discrete chunks

Introduction

Introduction1-*Network Core: Circuit SwitchingEnd-end resources reserved for calllink bandwidth, switch capacitydedicated resources: no sharingcircuit-like (guaranteed) performancecall setup required

Introduction

Introduction1-*Network Core: Circuit Switchingnetwork resources (e.g., bandwidth) divided into piecespieces allocated to callsresource piece idle if not used by owning call (no sharing)dividing link bandwidth into piecesfrequency divisiontime division

Introduction

Introduction1-*Circuit Switching: FDM and TDM

Introduction

Introduction1-*Numerical exampleHow 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 MbpsEach link uses TDM with 24 slots/sec500 msec to establish end-to-end circuit

Lets work it out!

Introduction

Introduction1-*Network Core: Packet Switchingeach end-end data stream divided into packetsuser A, B packets share network resources each packet uses full link bandwidth resources used as needed

resource contention: aggregate resource demand can exceed amount availablecongestion: packets queue, wait for link usestore and forward: packets move one hop at a timeNode receives complete packet before forwarding

Introduction

Introduction1-*Packet Switching: Statistical MultiplexingSequence 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.

ABC100 Mb/sEthernet1.5 Mb/sstatistical multiplexingqueue of packetswaiting for outputlink

Introduction

Introduction1-*Packet-switching: store-and-forwardtakes L/R seconds to transmit (push out) packet of L bits on to link at R bpsstore and forward: entire packet must arrive at router before it can be transmitted on next linkdelay = 3L/R (assuming zero propagation delay)Example:L = 7.5 MbitsR = 1.5 Mbpstransmission delay = 15 secRRRLmore on delay shortly

Introduction

Introduction1-*Packet switching versus circuit switching1 Mb/s linkeach user: 100 kb/s when activeactive 10% of time

circuit-switching: 10 userspacket switching: with 35 users, probability > 10 active at same time is less than .0004

Packet switching allows more users to use network!N users1 Mbps link

Introduction

Introduction1-*Packet switching versus circuit switchinggreat for bursty dataresource sharingsimpler, no call setupexcessive congestion: packet delay and lossprotocols needed for reliable data transfer, congestion controlQ: How to provide circuit-like behavior?bandwidth guarantees needed for audio/video appsstill 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

Introduction1-*Internet structure: network of networksroughly hierarchicalat center: tier-1 ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coveragetreat each other as equalsTier 1 ISPTier 1 ISPTier 1 ISP

Introduction

Introduction1-*Tier-1 ISP: e.g., Sprint

Introduction

Introduction1-*Internet structure: network of networksTier-2 ISPs: smaller (often regional) ISPsConnect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISPTier 1 ISPTier 1 ISP

Introduction

Introduction1-*Internet structure: network of networksTier-3 ISPs and local ISPs last hop (access) network (closest to end systems)

Tier 1 ISPTier 1 ISPTier 1 ISP

Introduction

Introduction1-*Internet structure: network of networksa packet passes through many networks!

Tier 1 ISPTier 1 ISPTier 1 ISP

Introduction

Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History

Introduction

Introduction1-*How do loss and delay occur?packets queue in router buffers packet arrival rate to link exceeds output link capacitypackets queue, wait for turnAB

Introduction

Introduction1-*Four sources of packet delay1. nodal processing: check bit errorsdetermine output link2. queueingtime waiting at output link for transmission depends on congestion level of router

Introduction

Introduction1-*Delay in packet-switched networks3. Transmission delay:R=link bandwidth (bps)L=packet length (bits)time to send bits into link = L/R4. Propagation delay:d = length of physical links = propagation speed in medium (~2x108 m/sec)propagation delay = d/sNote: s and R are very different quantities!

Introduction

Introduction1-*Caravan analogycars propagate at 100 km/hrtoll booth takes 12 sec to service car (transmission time)car~bit; caravan ~ packetQ: How long until caravan is lined up before 2nd toll booth?

Time to push entire caravan through toll booth onto highway = 12*10 = 120 secTime for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hrA: 62 minutes

Introduction

Introduction1-*Caravan analogy (more)Cars now propagate at 1000 km/hrToll booth now takes 1 min to service a carQ: Will cars arrive to 2nd booth before all cars serviced at 1st booth?

Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st booth.1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router!See Ethernet applet at AWL Web site

Introduction

Introduction1-*Nodal delaydproc = processing delaytypically a few microsecs or lessdqueue = queuing delaydepends on congestiondtrans = transmission delay= L/R, significant for low-speed linksdprop = propagation delaya few microsecs to hundreds of msecs

Introduction

Introduction1-*Queueing delay (revisited)R=link bandwidth (bps)L=packet length (bits)a=average packet arrival ratetraffic intensity = La/RLa/R ~ 0: average queueing delay smallLa/R -> 1: delays become largeLa/R > 1: more work arriving than can be serviced, average delay infinite!

Introduction

Introduction1-*Real Internet delays and routesWhat do real Internet delay & loss look like? Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i:sends three packets that will reach router i on path towards destinationrouter i will return packets to sendersender times interval between transmission and reply.

3 probes3 probes3 probes

Introduction

Introduction1-*Real Internet delays and routes1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 mstraceroute: gaia.cs.umass.edu to www.eurecom.frThree delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means no response (probe lost, router not replying)trans-oceaniclink

Introduction

Introduction1-*Packet lossqueue (aka buffer) preceding link in buffer has finite capacitypacket arriving to full queue dropped (aka lost)lost packet may be retransmitted by previous node, by source end system, or not at allABpacket being transmittedpacket arriving tofull buffer is lostbuffer (waiting area)

Introduction

Introduction1-*Throughputthroughput: rate (bits/time unit) at which bits transferred between sender/receiverinstantaneous: rate at given point in timeaverage: rate over longer period of timeserver, withfile of F bits to send to clientlink capacity Rs bits/seclink capacity Rc bits/secserver sends bits (fluid) into pipe

Introduction

Introduction1-*Throughput (more)Rs < Rc What is average end-end throughput? Rs bits/sec

Introduction

Introduction1-*Throughput: Internet scenario10 connections (fairly) share backbone bottleneck link R bits/secRsRsRsRcRcRcRper-connection end-end throughput: min(Rc,Rs,R/10)in practice: Rc or Rs is often bottleneck

Introduction

Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History

Introduction

Introduction1-*Protocol LayersNetworks are complex! many pieces:hostsrouterslinks of various mediaapplicationsprotocolshardware, softwareQuestion: Is there any hope of organizing structure of network?

Or at least our discussion of networks?

Introduction

Introduction1-*Organization of air travela series of steps

Introduction

Introduction1-*Layering of airline functionalityLayers: each layer implements a servicevia its own internal-layer actionsrelying on services provided by layer below

Introduction

Introduction1-*Why layering?Dealing with complex systems:explicit structure allows identification, relationship of complex systems pieceslayered reference model for discussionmodularization eases maintenance, updating of systemchange of implementation of layers service transparent to rest of systeme.g., change in gate procedure doesnt affect rest of systemlayering considered harmful?

Introduction

Introduction1-*Internet Protocol (TCP/IP) stackapplication: supporting network applicationsFTP, SMTP, HTTPtransport: process-to-process process data transferTCP, UDPNetwork/internet: routing of datagrams from source to destination (network-to-network)IP, routing proto colslink: data transfer between neighboring network elements (host-to-host)PPP, Ethernetphysical: bits on the wire

Introduction

Introduction1-*ISO/OSI reference modelpresentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventionssession: synchronization, checkpointing, recovery of data exchangeInternet stack missing these layers!these services, if needed, must be implemented in applicationneeded?

Introduction

Introduction1-*sourceapplicationtransportnetworklinkphysicalsegmentdatagramdestinationapplicationtransportnetworklinkphysicalrouterswitchEncapsulationmessageframe

Introduction

Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History

Introduction

Introduction1-*Network SecurityThe field of network security is about:how bad guys can attack computer networkshow we can defend networks against attackshow to design architectures that are immune to attacksInternet not originally designed with (much) security in mindoriginal vision: a group of mutually trusting users attached to a transparent network Internet protocol designers playing catch-upSecurity considerations in all layers!

Introduction

Introduction1-*Bad guys can put malware into hosts via InternetMalware can get in host from a virus, worm, or trojan horse. Spyware malware can record keystrokes, web sites visited, upload info to collection site. Infected host can be enrolled in a botnet, used for spam and DDoS attacks. Malware is often self-replicating: from an infected host, seeks entry into other hosts

Introduction

Introduction1-*Bad guys can put malware into hosts via InternetTrojan horseHidden part of some otherwise useful softwareToday often on a Web page (Active-X, plugin)Virusinfection by receiving object (e.g., e-mail attachment), actively executingself-replicating: propagate itself to other hosts, usersWorm:infection by passively receiving object that gets itself executedself- replicating: propagates to other hosts, usersSapphire Worm: aggregate scans/sec in first 5 minutes of outbreak (CAIDA, UWisc data)

Introduction

Introduction1-*Bad guys can attack servers and network infrastructureDenial of service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus trafficselect targetbreak into hosts around the network (see botnet)

send packets toward target from compromised hosts

Introduction

Introduction1-*The bad guys can sniff packetsPacket sniffing: broadcast media (shared Ethernet, wireless)promiscuous network interface reads/records all packets (e.g., including passwords!) passing byABCWireshark software used for end-of-chapter labs is a (free) packet-sniffer

Introduction

Introduction1-*The bad guys can use false source addressesIP spoofing: send packet with false source addressABC

Introduction

Introduction1-*The bad guys can record and playbackrecord-and-playback: sniff sensitive info (e.g., password), and use laterpassword holder is that user from system point of viewABCsrc:B dest:A user: B; password: foo

Introduction

Introduction1-*Network Securitymore throughout this coursechapter 8: focus on securitycrypographic techniques: obvious uses and not so obvious uses

Introduction

Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2 Network edge end systems, access networks, links1.3 Network core circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History

Introduction

Introduction1-*Internet History1961: Kleinrock - queueing theory shows effectiveness of packet-switching1964: Baran - packet-switching in military nets1967: ARPAnet conceived by Advanced Research Projects Agency1969: first ARPAnet node operational

1972: ARPAnet public demonstrationNCP (Network Control Protocol) first host-host protocol first e-mail programARPAnet has 15 nodes1961-1972: Early packet-switching principles

Introduction

Introduction1-*Internet History1970: ALOHAnet satellite network in Hawaii1974: Cerf and Kahn - architecture for interconnecting networks1976: Ethernet at Xerox PARCate70s: proprietary architectures: DECnet, SNA, XNAlate 70s: switching fixed length packets (ATM precursor)1979: ARPAnet has 200 nodesCerf and Kahns internetworking principles:minimalism, autonomy - no internal changes required to interconnect networksbest effort service modelstateless routersdecentralized controldefine todays Internet architecture1972-1980: Internetworking, new and proprietary nets

Introduction

Introduction1-*Internet History1983: deployment of TCP/IP1982: smtp e-mail protocol defined 1983: DNS defined for name-to-IP-address translation1985: ftp protocol defined1988: TCP congestion controlnew national networks: Csnet, BITnet, NSFnet, Minitel100,000 hosts connected to confederation of networks

1980-1990: new protocols, a proliferation of networks

Introduction

Introduction1-*Internet HistoryEarly 1990s: ARPAnet decommissioned1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)early 1990s: Webhypertext [Bush 1945, Nelson 1960s]HTML, HTTP: Berners-Lee1994: Mosaic, later Netscapelate 1990s: commercialization of the Web

Late 1990s 2000s:more killer apps: instant messaging, P2P file sharingnetwork security to forefrontest. 50 million host, 100 million+ usersbackbone links running at Gbps

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

Introduction

Introduction1-*Internet History2007:~500 million hostsVoice, Video over IPP2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video)more applications: YouTube, gamingwireless, mobility

Introduction

Introduction1-*Introduction: SummaryCovered a ton of material!Internet overviewwhats a protocol?network edge, core, access networkpacket-switching versus circuit-switchingInternet structureperformance: loss, delay, throughputlayering, service modelssecurityhistoryYou now have: context, overview, feel of networkingmore depth, detail to follow!

Introduction

*****************************Two simple multiple access control techniques.

Each mobiles share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling.

As we will see, used in AMPS, GSM, IS-54/136*The link is 1,536 Mbps, but is time divisioned multiplexed. One circuit uses one timeslot, which means it gets 1/24th of the link bandwidth. So, one circuit has a bandwidth of 64 Kbps (=1.536/24).So the actual transfer time to move 640.000 bits (=640 Kb) over that circuit is 10 seconds (=640/64).Add the connection setup time of 500 msec and you get a total of 10.500 msec or 10,5 seconds.

*************************************