Chapter_1_V6.1.ppt

Chapter 1 Introduction A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They o...

Chapter 1 Introduction A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and 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) that you mention their source (after all, we’d like people to use our book!)  If you post any slides 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 Computer Networking: A Top Down Approach 6th edition Jim Kurose, Keith Ross Addison-Wesley March 2012 All material copyright 1996-2012 J.F Kurose and K.W. Ross, All Rights Reserved Public 1-1 Chapter 1: introduction our 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 Public 1-2 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge  end systems, access networks, links 1.3 network core  packet switching, circuit switching, network structure 1.4 1.5 1.6 1.7 delay, loss, throughput in networks protocol layers, service models networks under attack: security history Public 1-3 What’s the Internet: “nuts and bolts” view  millions PC of connected computing devices:  hosts = end systems  running network apps server wireless laptop mobile network global ISP smartphone home network  communication wireless links wired links links  fiber, copper, radio, satellite  transmission rate: bandwidth  Packet router switches: forward packets (chunks of data)  routers and switches regional ISP Public institutional network 1-4 “Fun” internet appliances Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ Tweet-a-watt: monitor energy use Slingbox: watch, control cable TV remotely Internet refrigerator Internet phones Public 1-5 What’s the Internet: “nuts and bolts” view  mobile network Internet: “network of networks” global ISP  Interconnected ISPs  protocols control sending, receiving of msgs  e.g., TCP, IP, HTTP, Skype, 802.11  home network regional ISP Internet standards  RFC: Request for comments  IETF: Internet Engineering Task Force institutional network Public 1-6 What’s the Internet: a service view  mobile network Infrastructure that provides services to applications: global ISP  Web, VoIP, email, games, ecommerce, social nets, …  provides programming interface to apps home network regional ISP  hooks that allow sending and receiving app programs to “connect” to Internet  provides service options, analogous to postal service institutional network Public 1-7 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 events network protocols:   machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt Public 1-8 What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection response Got the time? Get http://www.awl.com/kurose-ross 2:00 time Q: other human protocols? Public 1-9 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge  end systems, access networks, links 1.3 network core  packet switching, circuit switching, network structure 1.4 1.5 1.6 1.7 delay, loss, throughput in networks protocol layers, service models networks under attack: security history Public 1-10 A closer look at network structure:  network edge:     mobile network hosts: clients and servers servers often in data centers global ISP home network access networks, physical media: wired, wireless communication links regional ISP network core:  interconnected routers  network of networks institutional network Public 1-11 Access networks and physical media Q: 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? Public 1-12 Access net: digital subscriber line (DSL) central office DSL splitter modem voice, data transmitted at different frequencies over dedicated line to central office    telephone network DSLAM ISP DSL access multiplexer use existing telephone line to central office DSLAM  data over DSL phone line goes to Internet  voice over DSL phone line goes to telephone net < 2.5 Mbps upstream transmission rate (typically < 1 Mbps) < 24 Mbps downstreamPublic transmission rate (typically 1-13 Access net: cable network cable headend … cable splitter modem V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 Channels equency division multiplexing: different channels transmitte different frequency bands Public 1-14 Access net: cable network cable headend … cable splitter modem CMTS data, TV transmitted at different frequencies over shared cable distribution network   cable modem termination system ISP HFC: hybrid fiber coax  asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate network of cable, fiber attaches homes to ISP router  homes share access network to cable headend  unlike DSL, which has dedicated access to central office Public 1-15 Access net: home network wireless devices to/from headend or central office often combined in single box cable or DSL modem wireless access point (54 Mbps) router, firewall, NAT wired Ethernet (100 Mbps) Public 1-16 Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet switch    institutional mail, web servers typically used in companies, universities, etc 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates today, end systems typically connect into Ethernet switch Public 1-17 Wireless access networks  shared wireless access network connects end system to router  via base station aka “access point” wireless LANs:  within building (100 ft)  802.11b/g (WiFi): 11, 54 Mbps transmission rate wide-area wireless access  provided by telco (cellular) operator, 10’s km  between 1 and 10 Mbps  3G, 4G: LTE to Internet to Internet Public 1-18 Host: sends packets of data host sending function: takes application message breaks into smaller chunks, known as packets, of length L bits transmits packet into access network at transmission rate R  link transmission rate, aka link capacity, aka link bandwidth packet transmission delay = two packets, L bits each 2 1 R: link transmission rate host time needed to transmit L-bit packet into link Public = L (bits) R (bits/sec) 1-19 Physical media     bit: propagates between transmitter/receiver 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., radio Public twisted pair (TP)  two insulated copper wires   Category 5: 100 Mbps, 1 Gpbs Ethernet Category 6: 10Gbps 1-20 Physical media: coax, fiber coaxial cable:    fiber optic cable: two concentric copper conductors bidirectional broadband:   glass fiber carrying light pulses, each pulse a bit high-speed operation:  high-speed point-to-point transmission (e.g., 10’s-100’s Gpbs transmission rate)  multiple channels on cable  HFC  low error rate:  repeaters spaced far apart  immune to electromagnetic noise Public 1-21 Physical media: radio     radio link types: signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects:  reflection  obstruction by objects  interference  terrestrial microwave  e.g. up to 45 Mbps channels  LAN (e.g., WiFi)  11Mbps, 54 Mbps  wide-area (e.g., cellular)  3G cellular: ~ few Mbps  satellite  Kbps to 45Mbps channel (or multiple smaller channels)  270 msec end-end delay  geosynchronous versus low altitude Public 1-22 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge  end systems, access networks, links 1.3 network core  packet switching, circuit switching, network structure 1.4 1.5 1.6 1.7 delay, loss, throughput in networks protocol layers, service models networks under attack: security history Public 1-23 How do loss and delay occur? packets queue in router buffers   packet arrival rate to link (temporarily) exceeds output link capacity packets queue, wait for turn packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Public 1-24 Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dproc: nodal processing    check bit errors determine output link typically < msec dqueue: queueing delay   Public time waiting at output link for transmission depends on congestion level of router 1-25 Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dtrans: transmission delay:    L: packet length (bits) R: link bandwidth (bps) dtrans and dprop dtrans = L/R very different dprop: propagation delay:    d: length of physical link s: propagation speed in medium (~2x108 m/sec) dprop = d/s * Check out the Java applet for an interactive animation on trans vs. prop delay Public 1-26 Caravan analogy 100 km ten-car caravan     100 km toll booth toll booth cars “propagate” at 100 km/hr toll booth takes 12 sec to service car (bit transmission time) car~bit; caravan ~ packet Q: How long until caravan is lined up before 2nd toll booth? Public    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 minutes 1-27 Caravan analogy (more) 100 km ten-car caravan    toll booth 100 km toll booth suppose cars now “propagate” at 1000 km/hr and suppose toll booth now takes one min to service a car Q: Will cars arrive to 2nd booth before all cars serviced at first booth?  A: Yes! after 7 min, 1st car arrives at second booth; three cars still at 1st booth. Public 1-28       R: link bandwidth (bps) L: packet length (bits) a: average packet arrival rate average queueing delay Queueing delay (revisited) traffic intensity = La/R La/R ~ 0: avg. queueing delay small La/R -> 1: avg. queueing delay large La/R > 1: more “work” arriving than can be serviced, average delay infinite! * Check out the Java applet for an interactive animation on queuing and loss Public La/R ~ 0 La/R -> 1 1-29 “Real” Internet delays and routes what do “real” Internet delay & loss look like?  traceroute program: provides delay measurement from source to router along endend 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 probes 3 probes 3 probes Public 1-30 “Real” Internet delays, routes traceroute: gaia.cs.umass.edu to www.eurecom.fr 3 delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 1 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 trans-oceanic 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms link 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 * * * * means no response (probe lost, router not replying) 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms * Do some traceroutes from exotic countries at www.traceroute.org Public 1-31 Packet loss queue (aka buffer) preceding link in buffer has finite capacity  packet arriving to full queue dropped (aka lost)  lost packet may be retransmitted by previous node, by source end system, or not at all  buffer (waiting area) A packet being transmitted B packet arriving to full buffer is lost * Check out the Java applet for an interactive animation on queuing and loss Public 1-32 Throughput  throughput: rate (bits/time unit) at which bits transferred between sender/receiver  instantaneous: rate at given point in time  average: rate over longer period of time server, with server sends file ofbits F bits to(fluid) send into to client pipe link capacity capacity pipe that can carry link pipe that can carry fluid at rate fluid at rate Rs bits/sec Rc bits/sec Rs bits/sec) Rc bits/sec) Public 1-33 Throughput (more)  Rs < Rc What is average end-end throughput? Rs bits/sec  Rc bits/sec Rs > Rc What is average end-end throughput? Rs bits/sec Rc bits/sec bottleneck link onlink end-end path that constrains end-end throughput Public 1-34 Throughput: Internet scenario per-connection end-end throughput: min(Rc,Rs,R/10)  in practice: R or c Rs is often bottleneck  Rs Rs Rs R Rc Rc Rc 10 connections (fairly) share backbone bottleneck link R bits/sec Public 1-35