Chap1 Intro

Chap1 Intro - Today’s Agenda CS/ECE 4457 Ma....

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Unformatted text preview: 2/4/10 Today’s Agenda CS/ECE 4457 Ma. Ce.ei Olsson 226B mmc5y •  •  •  •  Textbook Grading and Schedule Assignments A.endance Many slides in this document adapted from materials for Kurose and Ross, Computer Networking, 5th edition. copyright 1996-2009 J.F Kurose and K.W. Ross, All Rights Reserved PC What’s the Internet: “nuts and bolts” view Mobile network •  millions of connected compuQng devices: hosts = end systems –  running network apps satellite transmission rate = bandwidth Global ISP 1 m Home network Regional ISP Networks Classified by Scale Host Distance Category Personal area network Local area network Metropolitan area network Wide area network The Internet server wireless laptop cellular handheld 10 ­1000 m 10 km 100 km – 1000 km wired links   communication links access points   fiber, copper, radio,   Institutional network 10000 km router   routers: forward packets (chunks of data) IntroducQon 1 ­3 Networks by ConnecQon Type •  Circuit ­switched –  Guaranteed bandwidth Circuit Switching: FDM and TDM Example: FDM 4 users •  Packet ­switched –  Efficient use of resources TDM frequency time frequency time IntroducQon 1 ­6 1 2/4/10 Protocol Stacks Controversy of the Week! •  Today’s controversy: Did Al Gore invent the Internet? What he said (1999): …I took the iniQaQve in creaQng the Internet. Vint Cerf and Bob Kahn defend Gore: “Al Gore was the first poliQcal leader to recognize the importance of the Internet and to promote and support its development.” The High Performance CompuQng Act of 1991, sponsored by Gore, led to the creaQon of Mosaic. Digital Subscriber Line (DSL) home phone ExisQng phone line: 0 ­4KHz phone; 4 ­50KHz upstream data; 50KHz ­1MHz downstream data ResidenQal access: cable modems Internet DSLAM DSL modem home PC         telephone network central office Also uses exisQng 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 office Diagram: IntroducQon 1 ­10 Cable Network Architecture: Overview Cable Network Architecture: Overview server(s) Typically 500 to 5,000 homes cable headend cable distribution network (simplified) home cable headend cable distribution network 1 ­11 home IntroducQon IntroducQon 1 ­12 2 2/4/10 Cable Network Architecture: Overview Cable Network Architecture: Overview V I D E O 1 V I D E O 2 V I D E O 3 V I D E O 4 V I D E O 5 V I D E O 6 D A T A 7 D A T A 8 C O N T R O L 9 Channels cable headend cable distribution network (simplified) home cable headend cable distribution network 1 ­13 home IntroducQon IntroducQon 1 ­14 Ethernet Internet access 100 Mbps Ethernet switch 100 Mbps InsQtuQonal router To InsQtuQon’s ISP Technology Dial-UP ISDN Speeds 56 kbps (kilobits/ sec) 128 kbps 256 kbps-24Mbps 3 min mp3 DL 7 minutes 3.5 minutes Shared? No No 1 Gbps 100 Mbps DSL Cable 1sec – 90 sec No 3 – 8 sec 16 seconds .16 seconds Yes Yes, usually No server •  Typically used in companies, universiQes, etc   10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet   Today, end systems typically connect into Ethernet 3-15 Mbps download Ethernet – T1 1.5 Mbps Optical-OC3 153 Mbps switch Packet ­switching: store ­and ­forward L R R R Packet switching versus circuit switching Packet switching allows more users to use network! •  1 Mb/s link •  each user: –  100 kb/s when “acQve” –  acQve 10% of Qme N users •  takes L/R seconds to transmit (push out) packet of L bits on to link at R bps •  store and forward: enQre packet must arrive at router before it can be transmi.ed on next link •  delay = 3L/R (assuming zero propagaQon delay) Example: •  L = 7.5 Mbits •  R = 1.5 Mbps •  transmission delay = 15 sec •  circuit ­switching: –  10 users 1 Mbps link •  packet switching: –  with 35 users, probability > 10 acQve at same Qme is less than .0004 1 ­17 Q: how did we get value 0.0004? IntroducQon IntroducQon 1 ­18 3 2/4/10 Tier ­1 ISP: e.g., Sprint POP: point-of-presence Internet structure: network of networks •  a packet passes through many networks! local ISP to/from backbone … peering …. Tier 3 ISP Tier-2 ISP local ISP local ISP Tier-2 ISP local ISP … to/from customers … … Tier 1 ISP Tier 1 ISP Tier-2 ISP local local ISP ISP Tier 1 ISP Tier-2 ISP local I IntroducQonSP Tier-2 ISP local ISP 1 ­20 IntroducQon 1 ­19 Four sources of packet delay •  1. nodal processing: –  check bit errors –  determine output link Delay in packet ­switched networks 3. Transmission delay: •  R=link bandwidth (bps) •  L=packet length (bits) •  Qme to send bits into link = L/R 4. PropagaQon delay: •  d = length of physical link •  s = propagaQon speed in medium (~2x108 m/sec) •  propagaQon delay = d/s Note: s and R are very different quantities! A transmission propagation B 1 ­21   2. queueing   Qme waiQng at output link for transmission   depends on congesQon level of router A transmission propagation B nodal processing queueing IntroducQon nodal processing queueing IntroducQon 1 ­22 Nodal delay •  dproc = processing delay –  typically a few microsecs or less Queueing delay (revisited) •  R=link bandwidth (bps) •  L=packet length (bits) •  a=average packet arrival rate traffic intensity = La/R •  dqueue = queuing delay –  depends on congesQon –  = L/R, significant for low ­speed links •  dtrans = transmission delay •  dprop = propagaQon delay –  a few microsecs to hundreds of msecs   La/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! IntroducQon 1 ­23 IntroducQon 1 ­24 4 2/4/10 Throughput: Internet scenario •  per ­connecQon end ­end throughput: min (Rc,Rs,R/10) •  in pracQce: Rc or Rs is oren bo.leneck Rs Rs R Rc Rc Rc Rs 10 connecQons (fairly) share backbone bo.leneck link R bits/sec IntroducQon 1 ­25 5 ...
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This note was uploaded on 03/21/2010 for the course CS 4457 taught by Professor Cetti during the Spring '10 term at UVA.

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