Quiz1.pdf

Chapter 1 Introduction A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). Computer 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 n...

Chapter 1 Introduction A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). Computer 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. Networking: A Top They obviously represent a lot of work on our part. In return for use, we only ask the following: Down Approach  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!) 6th edition  If you post any slides on a www site, that you note that they are adapted Jim Kurose, Keith Ross from (or perhaps identical to) our slides, and note our copyright of this material. Addison-Wesley March 2012 Thanks and enjoy! JFK/KWR All material copyright 1996-2012 J.F Kurose and K.W. Ross, All Rights Reserved Introduction 1-1 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge  end systems, access networks, links 1.4 delay, loss, throughput in networks Introduction 1-2 What’s the Internet: “nuts and bolts” view  millions of connected PC mobile network server computing devices: wireless  hosts = end systems global ISP laptop smartphone  running network apps home  communication links network regional ISP wireless  fiber, copper, radio, links satellite wired links  transmission rate: bandwidth  Packetswitches: forward router packets (chunks of data) institutional network  routers and switches Introduction 1-3 What’s the Internet: “nuts and bolts” view mobile network  Internet: “network of networks”  Interconnected ISPs global ISP  protocols control sending, receiving of msgs  e.g., TCP, IP, HTTP, Skype, 802.11 home network  Internet standards regional ISP  RFC: Request for comments  IETF: Internet Engineering Task Force institutional network Introduction 1-4 What’s the Internet: a service view mobile network  Infrastructure that provides services to applications: global ISP  Web, VoIP, email, games, e- commerce, social nets, … home  provides programming network regional ISP interface to apps  hooks that allow sending and receiving app programs to “connect” to Internet  provides service options, analogous to postal service institutional network Introduction 1-5 What’s a protocol? human protocols: network protocols:  “what’s the time?”  machines rather than  “I have a question” humans  introductions  all communication activity in Internet governed by protocols … specific msgs sent … specific actions taken when msgs received, or protocols define format, order other events of msgs sent and received among network entities, and actions taken on msg transmission, receipt Introduction 1-6 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 1-7 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 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history Introduction 1-8 A closer look at network structure:  network edge: mobile network  hosts: clients and servers global ISP  servers often in data centers home  access networks, physical network regional ISP media: wired, wireless communication links  network core:  interconnected routers  network of networks institutional network Introduction 1-9 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 1-10 Access net: digital subscriber line (DSL) central office telephone network DSL splitter modem DSLAM ISP voice, data transmitted at different frequencies over DSL access dedicated line to central office 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 < 10 Mbps) Introduction 1-11 Access net: cable network cable headend … cable splitter modem C O V V V V V V N I I I I I I D D T D D D D D D A A R E E E E E E T T O O O O O O O A A L 1 2 3 4 5 6 7 8 9 Channels frequency division multiplexing: different channels transmitted in different frequency bands Introduction 1-12 Access net: cable network cable headend … cable splitter cable modem modem CMTS termination system data, TV transmitted at different frequencies over shared cable ISP distribution network  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 Introduction 1-13  Access net: home network wireless devices to/from headend or central office often combined in single box cable or DSL modem wireless access router, firewall, NAT point (54 Mbps) wired Ethernet (100 Mbps) Introduction 1-14 Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet institutional mail, switch web servers  typically used in companies, universities, etc  10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates  today, end systems typically connect into Ethernet switch Introduction 1-15 Wireless access networks  shared wireless access network connects end system to router  via base station aka “access point” wireless LANs: wide-area wireless access  within building (100 ft)  provided by telco (cellular)  802.11b/g (WiFi): 11, 54 Mbps operator, 10’s km transmission rate  between 1 and 10 Mbps  3G, 4G: LTE to Internet to Internet Introduction 1-16 Host: sends packets of data host sending function:  takes application message  breaks into smaller two packets, chunks, known as packets, L bits each of length L bits  transmits packet into access network at 2 1 transmission rate R R: link transmission rate  link transmission rate, host aka link capacity, aka link bandwidth packet time needed to L (bits) transmission = transmit L-bit = delay packet into link R (bits/sec) 1-17 Physical media  bit: propagates between transmitter/receiver pairs  physical link: what lies twisted pair (TP) between transmitter &  two insulated copper receiver wires  guided media:  Category 5: 100 Mbps, 1 Gpbs Ethernet  signals propagate in solid  Category 6: 10Gbps media: copper, fiber, coax  unguided media:  signals propagate freely, e.g., radio Introduction 1-18 Physical media: coax, fiber coaxial cable: fiber optic cable:  two concentric copper  glass fiber carrying light conductors pulses, each pulse a bit  bidirectional  high-speed operation:  broadband:  high-speed point-to-point  multiple channels on cable transmission (e.g., 10’s-100’s Gpbs transmission rate)  HFC  low error rate:  repeaters spaced far apart  immune to electromagnetic noise Introduction 1-19 Physical media: radio  signal carried in radio link types: electromagnetic spectrum  terrestrial microwave  no physical “wire”  e.g. up to 45 Mbps channels  bidirectional  LAN (e.g., WiFi)  propagation environment  11Mbps, 54 Mbps effects:  wide-area (e.g., cellular)  reflection  3G cellular: ~ few Mbps  obstruction by objects  satellite  interference  Kbps to 45Mbps channel (or multiple smaller channels)  270 msec end-end delay  geosynchronous versus low altitude Introduction 1-20 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 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history Introduction 1-21 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 1-22 Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dproc: nodal processing dqueue: queueing delay  check bit errors  time waiting at output link  determine output link for transmission  typically < msec  depends on congestion level of router Introduction 1-23 Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dtrans: transmission delay: dprop: propagation delay:  L: packet length (bits)  d: length of physical link  R: link bandwidth (bps)  s: propagation speed in medium  dtrans = L/R (~2x108 m/sec) dtrans and dprop  dprop = d/s very different * Check out the Java applet for an interactive animation on trans vs. prop delay Introduction 1-24 Caravan analogy 100 km 100 km ten-car toll toll caravan booth booth  cars “propagate” at  time to “push” entire 100 km/hr caravan through toll  toll booth takes 12 sec to booth onto highway = service car (bit transmission 12*10 = 120 sec time)  time for last car to  car~bit; caravan ~ packet propagate from 1st to  Q: How long until caravan is 2nd toll both: lined up before 2nd toll 100km/(100km/hr)= 1 booth? hr  A: 62 minutes Introduction 1-25 Caravan analogy (more) 100 km 100 km ten-car toll toll caravan booth 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 1-26 Queueing delay (revisited) average queueing  R: link bandwidth (bps) delay  L: packet length (bits)  a: average packet arrival rate traffic intensity = La/R  La/R ~ 0: avg. queueing delay small La/R ~ 0  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 -> 1 Introduction 1-27 “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 1-28 “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 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms link 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 * * * * means no response (probe lost, router not replying) 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 1-29 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) packet being transmitted A B packet arriving to full buffer is lost * Check out the Java applet for an interactive animation on queuing and loss Introduction 1-30 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, server withbits sends linkpipe capacity that can carry linkpipe capacity that can carry file of into (fluid) F bitspipe Rs bits/sec fluid at rate Rc bits/sec fluid at rate to send to client Rs bits/sec) Rc bits/sec) Introduction 1-31 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 link on end-end path that constrains end-end throughput Introduction 1-32 Throughput: Internet scenario  per-connection end- end throughput: Rs min(Rc,Rs,R/10) Rs Rs  in practice: Rc or Rs is often bottleneck R Rc Rc Rc 10 connections (fairly) share backbone bottleneck link R bits/sec Introduction 1-33