Chapter_1_V6.1 copy.pptx

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 Introduction 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 Introduction 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 Introduction 1-3 What’s the Internet: “nuts and bolts” view of connected server computing devices:  hosts = end wireless laptop systems smartphone  running network  communication apps links wireless links  fiber, copper, wired radio, satellite links  transmission rate: bandwidth PC  millions global ISP home network regional ISP  Packet router switches: forward packets (chunks of data)  routers and mobile network institutional network Introduction 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 Introduction 1-5 What’s the Internet: “nuts and bolts” view  Internet: “network of networks” mobile network 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 Introductio 1-6 n What’s the Internet: a service view  Infrastructure that provides services to applications:  Web, VoIP, email, games, e-commerce, social nets, …  mobile network global ISP home network regional ISP provides programming interface to apps  hooks that allow sending and receiving app programs to “connect” to Internet  provides service institutional network Introductio 1-7 n 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 Introduction 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? Introduction 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 Introduction 1-10 A closer look at network structure:  network edge:   hosts: clients and servers servers often in data centers access networks, physical media: wired, wireless communication links  network core:  mobile network global ISP home network regional ISP  interconnected routers  network of networks institutional network Introduction 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? Introduction 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 downstream transmission rate (typically Introduction 1-13 < 10 Mbps) 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 Introduction 1-14 Access net: cable network cable headend … cable splitter modem data, TV transmitted at different frequencies over shared cable distribution network   CMTS 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 Introduction 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) Introduction 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 Introduction 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 Introduction 1-18 Host: sends packets of data host sending function:  takes application message two packets, L bits each  breaks into smaller chunks, known as packets, of length L bits 2 1  transmits packet into R: link transmission rate access network at host transmission rate R  link transmission rate, aka link capacity, aka linktime needed to packet L (bits) bandwidth transmission = transmit L-bit = R (bits/sec) packet into link delay 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 twisted pair (TP)  two insulated copper wires   Category 5: 100 Mbps, 1 Gpbs Ethernet Category 6: 10Gbps Introduction 1-20 Physical media: coax, fiber coaxial cable:    two concentric copper conductors bidirectional broadband:  multiple channels on cable  HFC fiber optic cable:   glass fiber carrying light pulses, each pulse a bit high-speed operation:  high-speed point-to-point transmission (e.g., 10’s100’s Gpbs transmission rate)  low error rate:  repeaters spaced far apart  immune to electromagnetic noise Introduction 1-21 Physical media: radio     signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects:  reflection  obstruction by objects  interference radio 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: ~ few Mbps  satellite  Kbps to 45Mbps channel (or multiple smaller channels)  270 msec end-end delay  geosynchronous versus low altitude Introduction 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 Introduction 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 Introduction 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  time waiting at output link for transmission  depends on Introduction 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 Introduction 1-26 Caravan analogy 100 km ten-car caravan     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? 100 km 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 minutes Introduction 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. Introduction 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 La/R ~ 0 La/R -> 1 Introduction 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 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 probes 3 probes 3 probes Introduction 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 Introduction 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 Introduction 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) Introduction 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 Introduction 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 Introduction 1-35