Computer networking_Chapter1_5th_April2009

nullnull 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 关于艾滋病ppt课件精益管理ppt下载地图下载ppt可编辑假如ppt教学课件下载triz基础知识ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re 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, we’d 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 1996-2009 J.F Kurose and K.W. Ross, All Rights ReservedChapter 1: Introduction Introduction1-*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 performance: loss, delay, throughput security protocol layers, service models history Chapter 1: roadmap Introduction1-*Chapter 1: roadmap1.1 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 models 1.6 Networks under attack: security 1.7 History What’s the Internet: “nuts and bolts” view Introduction1-*What’s the Internet: “nuts and bolts” viewmillions of connected computing devices: hosts = end systems running network appscommunication links fiber, copper, radio, satellite transmission rate = bandwidthrouters: forward packets (chunks of data)“Cool” internet appliances Introduction1-*“Cool” internet appliancesWorld’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.htmlIP picture frame http://www.ceiva.com/Web-enabled toaster + weather forecasterInternet phonesWhat’s the Internet: “nuts and bolts” view Introduction1-*What’s the Internet: “nuts and bolts” viewprotocols 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 ForceWhat’s the Internet: a service view Introduction1-*What’s the Internet: a service viewcommunication 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 deliveryWhat’s a protocol? Introduction1-*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 eventsnetwork protocols: machines rather than humans all 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 What’s a protocol? Introduction1-*What’s a protocol?a human protocol and a computer network protocol: Q: Other human protocols? HiHiTCP connection requestChapter 1: roadmap Introduction1-*Chapter 1: roadmap1.1 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 models 1.6 Networks under attack: security 1.7 History A closer look at network structure: Introduction1-*A closer look at network structure:network edge: applications and hostsaccess networks, physical media: wired, wireless communication links network core: interconnected routers network of networks The network edge: Introduction1-*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/serverpeer-peer model: minimal (or no) use of dedicated servers e.g. Skype, BitTorrentAccess networks and physical media Introduction1-*Access networks and physical mediaQ: 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?Dial-up Modem Uses existing telephony infrastructure Home is connected to central office up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: not “always on”Dial-up ModemDigital Subscriber Line (DSL)Digital Subscriber Line (DSL) Also uses existing telephone infrastruture up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps) dedicated physical line to telephone central officeResidential access: cable modems Introduction1-*Residential access: cable modemsDoes not use telephone infrastructure Instead uses cable TV infrastructure HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream, 2 Mbps upstream network of cable and fiber attaches homes to ISP router homes share access to router unlike DSL, which has dedicated access Residential access: cable modems Introduction1-*Residential access: cable modemsDiagram: http://www.cabledatacomnews.com/cmic/diagram.htmlCable Network Architecture: Overview Introduction1-*Cable Network Architecture: Overviewhomecable headendcable distribution network (simplified)Typically 500 to 5,000 homesCable Network Architecture: Overview Introduction1-*Cable Network Architecture: Overviewhomecable headendcable distribution networkCable Network Architecture: Overview Introduction1-*Cable Network Architecture: Overviewhomecable headendcable distribution network (simplified)Cable Network Architecture: Overview Introduction1-*Cable Network Architecture: Overviewhomecable headendcable distribution networkFDM (more shortly):Fiber to the HomeFiber to the HomeOptical links from central office to the home Two competing optical technologies: Passive Optical network (PON) Active Optical Network (PAN) Much higher Internet rates; fiber also carries television and phone servicesEthernet Internet accessEthernet Internet accessTypically used in companies, universities, etc 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet Today, end systems typically connect into Ethernet switch Wireless access networks Introduction1-*Wireless access networksshared 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 areabase stationmobile hostsrouterHome networks Introduction1-*Home networksTypical home network components: DSL or cable modem router/firewall/NAT Ethernet wireless access pointwireless access pointwireless laptopsrouter/ firewallcable modemto/from cable headendEthernet Physical Media Introduction1-*Physical MediaBit: propagates between transmitter/rcvr pairs physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radioTwisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 Mbps Ethernet Category 5: 100Mbps EthernetPhysical Media: coax, fiber Introduction1-*Physical Media: coax, fiberCoaxial cable: two concentric copper conductors bidirectional baseband: single channel on cable legacy Ethernet broadband: multiple channels on cable HFCFiber optic cable: glass fiber carrying light pulses, each pulse a bit high-speed operation: high-speed point-to-point transmission (e.g., 10’s-100’s Gps) low error rate: repeaters spaced far apart ; immune to electromagnetic noisePhysical media: radio Introduction1-*Physical media: radiosignal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: reflection obstruction by objects interferenceRadio link types: terrestrial microwave e.g. up to 45 Mbps channels LAN (e.g., Wifi) 11Mbps, 54 Mbps wide-area (e.g., cellular) 3G cellular: ~ 1 Mbps satellite Kbps to 45Mbps channel (or multiple smaller channels) 270 msec end-end delay geosynchronous versus low altitudeChapter 1: roadmap Introduction1-*Chapter 1: roadmap1.1 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 models 1.6 Networks under attack: security 1.7 History HW #1HW #1Post one question written in English at the e-class Q&A bulletin board before the next Monday class From now on, one question and one answer will be given 0.5 and 1 point respectively Introduction1-*The Network Core Introduction1-*The Network CoreWhat is at the core of networks? mesh of interconnected routers the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net In the jargon of telephony, a connection is referred to a circuit packet-switching: data sent thru net in discrete “chunks”Network Core: Circuit Switching Introduction1-*Network Core: Circuit SwitchingEnd-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance: a constant rate such as 64kbps in telephone networks In the exchange of the constant speed, call setup required Network Core: Circuit Switching Introduction1-*Network Core: Circuit SwitchingHow to carry some number of connections over one physical link? 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” A link is considered to be a medium providing a range of frequencies over all times frequency division in frequency domain time division in time domainCircuit Switching: FDM and TDM Introduction1-*Circuit Switching: FDM and TDMNumerical example 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 Mbps Each link uses TDM with 24 slots/sec 500 msec to establish end-to-end circuit Let’s work it out!Network Core: Packet Switching Introduction1-*Network Core: Packet Switchingeach 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 No admission control: circuit switching only allows the number of connections it can afford congestion: packets queue, wait for link use store and forward: packets move one hop at a time Node receives complete packet before forwardingPacket Switching: Statistical Multiplexing Introduction1-*Packet Switching: Statistical MultiplexingSequence of A & B packets does not have fixed pattern, bandwidth shared on demand  statistical Time Division multiplexing vs synchronous TDM. TDM: each host gets same slot in revolving TDM frame. ABC100 Mb/s Ethernet1.5 Mb/sstatistical multiplexingqueue of packets waiting for output linkPacket-switching: store-and-forward Introduction1-*Packet-switching: store-and-forwardtakes 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 secRRRLmore on delay shortly …Packet switching versus circuit switching Introduction1-*Packet switching versus circuit switching1 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 users1 Mbps linkQ: how did we get value 0.0004?Packet switching versus circuit switching Introduction1-*Packet switching versus circuit switchinggreat for bursty data Greater efficiency in terms of 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)?Internet structure: network of networks Introduction1-*Internet structure: network of networksRoughly (loosely) hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage treat each other as equalsTier 1 ISPTier 1 ISPTier 1 ISPTier-1 ISP: e.g., Sprint Introduction1-*Tier-1 ISP: e.g., SprintInternet structure: network of networks Introduction1-*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 ISPTier 1 ISPTier 1 ISPInternet structure: network of networks Introduction1-*Internet structure: network of networks“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems) Tier 1 ISPTier 1 ISPTier 1 ISPInternet structure: network of networks Introduction1-*Internet structure: network of networksa packet passes through many networks! Tier 1 ISPTier 1 ISPTier 1 ISPChapter 1: roadmap Introduction1-*Chapter 1: roadmap1.1 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 How long does a packet take to pass through a router? 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History HW #2HW #2Read the booklet combining the essays about the English-conducted courses and write down one-page study plan in English about how you will survive this course You can download the pdf file of this booklet from e-class Introduction1-*White DayWhite DayWhite Day was first celebrated in 1978 in Japan. It was started by the National Confectionery Industry Association (全国飴菓子工業協同組合) as an "answer day" to Valentine's Day on the grounds that men should pay back the women who gave them chocolate and other gifts on Valentine's Day. In 1977, a Fukuoka-based confectionery company, Ishimura Manseido (石村萬盛堂), marketed marshmallows to men on March 14, calling it Marshmallow Day (マシュマロデー).[4] Soon thereafter, confectionery companies began marketing white chocolate. Now, men give both white and dark chocolate, as well as other edible and non-edible gifts, such as jewelry or objects of sentimental value, or white clothing like lingerie, to women from whom they received chocolate on Valentine's Day one month earlier. If the chocolate given to him was giri-choco, the man, likewise, may not be expressing actual romantic interest, but rather a social obligation. Male should give gift two or three times expensive that the one gotten at Valentine’s Day !! Introduction1-*How do loss and delay occur? Introduction1-*How do loss and delay occur?packets queue in router buffers packet arrival rate to link exceeds output link capacity packets queue, wait for turnABFour sources of packet delay Introduction1-*Four sources of packet delay1. nodal processing: check bit errors determine output link2. queueing time waiting at output link for transmission depends on congestion level of router happens mainly in statistical TDM, namely packet-switched networksDelay in packet-switched networks Introduction1-*Delay in packet-switched networks3. Transmission delay: R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R Time to covert data into signals4. Propagation delay: d = length of physical link s = propagation speed in medium (~2x108 m/sec) propagation delay = d/sNote: s and R are very different quantities!Caravan analogy Introduction1-*Caravan analogycars “propagate” at 100 km/hr toll booth takes 12 sec to service car (transmission time) car~bit; caravan ~ packet Q: How long until caravan is lined up before 2nd toll booth? Time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec Time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr A: 62 minutesCaravan analogy (more) Introduction1-*Caravan analogy (more)Cars now “propagate” at 1000 km/hr Toll booth now takes 1 min to service a car Q: 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 siteNodal delay Introduction1-*Nodal delaydproc = processing delay typically a few microsecs or less dqueue = queuing delay depends on congestion dtrans = transmission delay = L/R, significant for low-speed links dprop = propagation delay a few microsecs to hundreds of msecsQueueing delay (revisited) Introduction1-*Queueing delay (revisited)R=link bandwidth (bps) L=packet length (bits) a=average packet arrival ratetraffic intensity = La/R A ratio of the average arrival rate to the average departure rateLa/R ~ 0: average queueing delay small La/R -> 1: delays become large La/R > 1: more “work” arriving than can be serviced, average delay infinite! “Real” Internet delays and routes 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 destination router i will return packets to sender sender times interval between transmission and reply. 3 probes3 probes3 probes“Real” Internet delays and routes Introduction1-*“Real” Internet delays and routes1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 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 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 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-oceanic linkPacket loss Introduction1-*Packet lossqueue (aka buffer) preceding link in buffer has finite capacity