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Introduction to computer networks lecture

The document is an introduction to computer networking, focusing on the structure and function of the Internet, as presented in the book 'Computer Networking: A Top-Down Approach' by Kurose and Ross. It covers key concepts such as the Internet's architecture, different types of protocols (TCP, UDP), network edge and core components, access networks, and physical media. Additionally, it highlights the hierarchical nature of ISPs and the functioning of data transmission, including packet-switching and circuit-switching methods.

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Introduction 1-1 Chapter 1 Introduction Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004. 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 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 1996-2004 J.F Kurose and K.W. Ross, All Rights Reserved
Introduction 1-2 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  network core  access net, physical media  Internet/ISP structure  performance: loss, delay  protocol layers, service models  network modeling
Introduction 1-3 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
Introduction 1-4 What’s the Internet: “nuts and bolts” view  millions of connected computing devices: hosts = end systems  running network apps  communication links  fiber, copper, radio, satellite  transmission rate = bandwidth  routers: forward packets (chunks of data) local ISP company network regional ISP router workstation server mobile
Introduction 1-5 What’s the Internet: “nuts and bolts” view  protocols control sending, receiving of msgs  e.g., TCP, IP, HTTP, FTP, PPP  Internet: “network of networks”  loosely hierarchical  public Internet versus private intranet  Internet standards  RFC: Request for comments  IETF: Internet Engineering Task Force local ISP company network regional ISP router workstation server mobile
Introduction 1-6 What’s the Internet: a service view  communication infrastructure enables distributed applications:  Web, email, games, e- commerce, file sharing  communication services provided to apps:  Connectionless unreliable  connection-oriented reliable
Introduction 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
Introduction 1-8 What’s a protocol? a human protocol and a computer network protocol: Q: Other human protocols? Hi Hi Got the time? 2:00 TCP connection req TCP connection response Get http://www.awl.com/kurose-ross <file> time
Introduction 1-9 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
Introduction 1-10 A closer look at network structure:  network edge: applications and hosts  network core:  routers  network of networks  access networks, physical media: communication links
Introduction 1-11 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/server  peer-peer model:  minimal (or no) use of dedicated servers  e.g. Gnutella, KaZaA
Introduction 1-12 Network edge: connection-oriented service Goal: data transfer between end systems  handshaking: setup (prepare for) data transfer ahead of time  Hello, hello back human protocol  set up “state” in two communicating hosts  TCP - Transmission Control Protocol  Internet’s connection- oriented service TCP service [RFC 793]  reliable, in-order byte- stream data transfer  loss: acknowledgements and retransmissions  flow control:  sender won’t overwhelm receiver  congestion control:  senders “slow down sending rate” when network congested
Introduction 1-13 Network edge: connectionless service Goal: data transfer between end systems  same as before!  UDP - User Datagram Protocol [RFC 768]:  connectionless  unreliable data transfer  no flow control  no congestion control App’s using TCP:  HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP:  streaming media, teleconferencing, DNS, Internet telephony
Introduction 1-14 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
Introduction 1-15 The Network Core  mesh of interconnected routers  the fundamental question: how is data transferred through net?  circuit switching: dedicated circuit per call: telephone net  packet-switching: data sent thru net in discrete “chunks”
Introduction 1-16 Network Core: Circuit Switching End-end resources reserved for “call”  link bandwidth, switch capacity  dedicated resources: no sharing  circuit-like (guaranteed) performance  call setup required
Introduction 1-17 Network Core: Circuit Switching 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”  frequency division  time division
Introduction 1-18 Circuit Switching: FDM and TDM FDM frequency time TDM frequency time 4 users Example:
Introduction 1-19 Numerical example  How 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  500 msec to establish end-to-end circuit Work it out!
Introduction 1-20 Network Core: Packet Switching each 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  congestion: packets queue, wait for link use  store and forward: packets move one hop at a time  Node receives complete packet before forwarding Bandwidth division into “pieces” Dedicated allocation Resource reservation
Introduction 1-21 Packet Switching: Statistical Multiplexing Sequence of A & B packets does not have fixed pattern  statistical multiplexing. In TDM each host gets same slot in revolving TDM frame. A B C 10 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link
Introduction 1-22 Packet switching versus circuit switching  1 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 less than .0004 Packet switching allows more users to use network! N users 1 Mbps link
Introduction 1-23 Packet switching versus circuit switching  Great for bursty data  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 6) Is packet switching a “slam dunk winner?”
Introduction 1-24 Packet-switching: store-and-forward  Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps  Entire packet must arrive at router before it can be transmitted on next link: store and forward  delay = 3L/R Example:  L = 7.5 Mbits  R = 1.5 Mbps  delay = 15 sec R R R L
Introduction 1-25 Packet-switched networks: forwarding  Goal: move packets through routers from source to destination  we’ll study several path selection (i.e. routing) algorithms (chapter 4)  datagram network:  destination address in packet determines next hop  routes may change during session  analogy: driving, asking directions  virtual circuit network:  each packet carries tag (virtual circuit ID), tag determines next hop  fixed path determined at call setup time, remains fixed thru call  routers maintain per-call state
Introduction 1-26 Network Taxonomy Telecommunication networks Circuit-switched networks FDM TDM Packet-switched networks Networks with VCs Datagram Networks • Datagram network is not either connection-oriented or connectionless. • Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps.
Introduction 1-27 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
Introduction 1-28 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 1-29 Residential access: point to point access  Dialup via modem  up to 56Kbps direct access to router (often less)  Can’t surf and phone at same time: can’t be “always on”  ADSL: asymmetric digital subscriber line  up to 1 Mbps upstream (today typically < 256 kbps)  up to 8 Mbps downstream (today typically < 1 Mbps)  FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone
Introduction 1-30 Residential access: cable modems  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  deployment: available via cable TV companies
Introduction 1-31 Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
Introduction 1-32 Cable Network Architecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes
Introduction 1-33 Cable Network Architecture: Overview home cable headend cable distribution network (simplified)
Introduction 1-34 Cable Network Architecture: Overview home cable headend cable distribution network server(s)
Introduction 1-35 Cable Network Architecture: Overview home cable headend cable distribution network Channels 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 FDM:
Introduction 1-36 Company access: local area networks  company/univ local area network (LAN) connects end system to edge router  Ethernet:  shared or dedicated link connects end system and router  10 Mbs, 100Mbps, Gigabit Ethernet  LANs: chapter 5
Introduction 1-37 Wireless access networks  shared wireless access network connects end system to router  via base station aka “access point”  wireless LANs:  802.11b (WiFi): 11 Mbps  wider-area wireless access  provided by telco operator  3G ~ 384 kbps • Will it happen??  WAP/GPRS in Europe base station mobile hosts router
Introduction 1-38 Home networks Typical home network components:  ADSL or cable modem  router/firewall/NAT  Ethernet  wireless access point wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet
Introduction 1-39 Physical Media  Bit: 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., radio Twisted Pair (TP)  two insulated copper wires  Category 3: traditional phone wires, 10 Mbps Ethernet  Category 5: 100Mbps Ethernet
Introduction 1-40 Physical Media: coax, fiber Coaxial cable:  two concentric copper conductors  bidirectional  baseband:  single channel on cable  legacy Ethernet  broadband:  multiple channel 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., 5 Gps)  low error rate: repeaters spaced far apart ; immune to electromagnetic noise
Introduction 1-41 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)  2Mbps, 11Mbps  wide-area (e.g., cellular)  e.g. 3G: hundreds of kbps  satellite  up to 50Mbps channel (or multiple smaller channels)  270 msec end-end delay  geosynchronous versus low altitude
Introduction 1-42 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
Introduction 1-43 Internet structure: network of networks  roughly hierarchical  at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage  treat each other as equals Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-1 providers interconnect (peer) privately NAP Tier-1 providers also interconnect at public network access points (NAPs)
Introduction 1-44 Tier-1 ISP: e.g., Sprint Sprint US backbone network
Introduction 1-45 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 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet  tier-2 ISP is customer of tier-1 provider Tier-2 ISPs also peer privately with each other, interconnect at NAP
Introduction 1-46 Internet structure: network of networks  “Tier-3” ISPs and local ISPs  last hop (“access”) network (closest to end systems) Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet
Introduction 1-47 Internet structure: network of networks  a packet passes through many networks! Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP
Introduction 1-48 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
Introduction 1-49 How do loss and delay occur? packets queue in router buffers  packet arrival rate to link exceeds output link capacity  packets queue, wait for turn A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers
Introduction 1-50 Four sources of packet delay  1. nodal processing:  check bit errors  determine output link A B propagation transmission nodal processing queueing  2. queueing  time waiting at output link for transmission  depends on congestion level of router
Introduction 1-51 Delay in packet-switched networks 3. Transmission delay:  R=link bandwidth (bps)  L=packet length (bits)  time to send bits into link = L/R 4. Propagation delay:  d = length of physical link  s = propagation speed in medium (~2x108 m/sec)  propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantities!
Introduction 1-52 Caravan analogy  Cars “propagate” at 100 km/hr  Toll booth takes 12 sec to service a 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 minutes toll booth toll booth ten-car caravan 100 km 100 km
Introduction 1-53 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 site toll booth toll booth ten-car caravan 100 km 100 km
Introduction 1-54 Nodal delay  dproc = 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 msecs prop trans queue proc nodal d d d d d + + + =
Introduction 1-55 Queueing delay (revisited)  R=link bandwidth (bps)  L=packet length (bits)  a=average packet arrival rate traffic intensity = La/R  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!
Introduction 1-56 “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 1-57 “Real” Internet delays and routes 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 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 ms traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means no reponse (probe lost, router not replying) trans-oceanic link
Introduction 1-58 Packet loss  queue (aka buffer) preceding link in buffer has finite capacity  when packet arrives to full queue, packet is dropped (aka lost)  lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all
Introduction 1-59 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
Introduction 1-60 Protocol “Layers” Networks are complex!  many “pieces”:  hosts  routers  links of various media  applications  protocols  hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks?
Introduction 1-61 Organization of air travel  a series of steps ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing
Introduction 1-62 ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Layering of airline functionality Layers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer below
Introduction 1-63 Why layering? Dealing with complex systems:  explicit structure allows identification, relationship of complex system’s pieces  layered reference model for discussion  modularization eases maintenance, updating of system  change of implementation of layer’s service transparent to rest of system  e.g., change in gate procedure doesn’t affect rest of system  layering considered harmful?
Introduction 1-64 Internet protocol stack  application: supporting network applications  FTP, SMTP, STTP  transport: host-host data transfer  TCP, UDP  network: routing of datagrams from source to destination  IP, routing protocols  link: data transfer between neighboring network elements  PPP, Ethernet  physical: bits “on the wire” application transport network link physical
Introduction 1-65 message segment datagram frame source application transport network link physical Ht Hn Hl M Ht Hn M Ht M M destination application transport network link physical Ht Hn Hl M Ht Hn M Ht M M network link physical link physical Ht Hn Hl M Ht Hn M Ht Hn Hl M Ht Hn M Ht Hn Hl M Ht Hn Hl M router switch Encapsulation
Introduction 1-66 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
Introduction 1-67 Internet History  1961: Kleinrock - queueing theory shows effectiveness of packet- switching  1964: Baran - packet- switching in military nets  1967: ARPAnet conceived by Advanced Research Projects Agency  1969: first ARPAnet node operational  1972:  ARPAnet demonstrated publicly  NCP (Network Control Protocol) first host- host protocol  first e-mail program  ARPAnet has 15 nodes 1961-1972: Early packet-switching principles
Introduction 1-68 Internet History  1970: ALOHAnet satellite network in Hawaii  1973: Metcalfe’s PhD thesis proposes Ethernet  1974: Cerf and Kahn - architecture for interconnecting networks  late70’s: proprietary architectures: DECnet, SNA, XNA  late 70’s: switching fixed length packets (ATM precursor)  1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles:  minimalism, autonomy - no internal changes required to interconnect networks  best effort service model  stateless routers  decentralized control define today’s Internet architecture 1972-1980: Internetworking, new and proprietary nets
Introduction 1-69 Internet History  Early 1990’s: ARPAnet decommissioned  1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)  early 1990s: Web  hypertext [Bush 1945, Nelson 1960’s]  HTML, HTTP: Berners-Lee  1994: Mosaic, later Netscape  late 1990’s: commercialization of the Web Late 1990’s – 2000’s:  more killer apps: instant messaging, P2P file sharing  network security to forefront  est. 50 million host, 100 million+ users  backbone links running at Gbps 1990, 2000’s: commercialization, the Web, new apps
Introduction 1-70 Introduction: Summary Covered a “ton” of material!  Internet overview  what’s a protocol?  network edge, core, access network  packet-switching versus circuit-switching  Internet/ISP structure  performance: loss, delay  layering and service models  history You now have:  context, overview, “feel” of networking  more depth, detail to follow!

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Introduction to computer networks lecture

  • 1.
    Introduction 1-1 Chapter 1 Introduction ComputerNetworking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004. 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 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 1996-2004 J.F Kurose and K.W. Ross, All Rights Reserved
  • 2.
    Introduction 1-2 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  network core  access net, physical media  Internet/ISP structure  performance: loss, delay  protocol layers, service models  network modeling
  • 3.
    Introduction 1-3 Chapter 1:roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
  • 4.
    Introduction 1-4 What’s theInternet: “nuts and bolts” view  millions of connected computing devices: hosts = end systems  running network apps  communication links  fiber, copper, radio, satellite  transmission rate = bandwidth  routers: forward packets (chunks of data) local ISP company network regional ISP router workstation server mobile
  • 5.
    Introduction 1-5 What’s theInternet: “nuts and bolts” view  protocols control sending, receiving of msgs  e.g., TCP, IP, HTTP, FTP, PPP  Internet: “network of networks”  loosely hierarchical  public Internet versus private intranet  Internet standards  RFC: Request for comments  IETF: Internet Engineering Task Force local ISP company network regional ISP router workstation server mobile
  • 6.
    Introduction 1-6 What’s theInternet: a service view  communication infrastructure enables distributed applications:  Web, email, games, e- commerce, file sharing  communication services provided to apps:  Connectionless unreliable  connection-oriented reliable
  • 7.
    Introduction 1-7 What’s aprotocol? 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
  • 8.
    Introduction 1-8 What’s aprotocol? a human protocol and a computer network protocol: Q: Other human protocols? Hi Hi Got the time? 2:00 TCP connection req TCP connection response Get http://www.awl.com/kurose-ross <file> time
  • 9.
    Introduction 1-9 Chapter 1:roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
  • 10.
    Introduction 1-10 A closerlook at network structure:  network edge: applications and hosts  network core:  routers  network of networks  access networks, physical media: communication links
  • 11.
    Introduction 1-11 The networkedge:  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/server  peer-peer model:  minimal (or no) use of dedicated servers  e.g. Gnutella, KaZaA
  • 12.
    Introduction 1-12 Network edge:connection-oriented service Goal: data transfer between end systems  handshaking: setup (prepare for) data transfer ahead of time  Hello, hello back human protocol  set up “state” in two communicating hosts  TCP - Transmission Control Protocol  Internet’s connection- oriented service TCP service [RFC 793]  reliable, in-order byte- stream data transfer  loss: acknowledgements and retransmissions  flow control:  sender won’t overwhelm receiver  congestion control:  senders “slow down sending rate” when network congested
  • 13.
    Introduction 1-13 Network edge:connectionless service Goal: data transfer between end systems  same as before!  UDP - User Datagram Protocol [RFC 768]:  connectionless  unreliable data transfer  no flow control  no congestion control App’s using TCP:  HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP:  streaming media, teleconferencing, DNS, Internet telephony
  • 14.
    Introduction 1-14 Chapter 1:roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
  • 15.
    Introduction 1-15 The NetworkCore  mesh of interconnected routers  the fundamental question: how is data transferred through net?  circuit switching: dedicated circuit per call: telephone net  packet-switching: data sent thru net in discrete “chunks”
  • 16.
    Introduction 1-16 Network Core:Circuit Switching End-end resources reserved for “call”  link bandwidth, switch capacity  dedicated resources: no sharing  circuit-like (guaranteed) performance  call setup required
  • 17.
    Introduction 1-17 Network Core:Circuit Switching 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”  frequency division  time division
  • 18.
    Introduction 1-18 Circuit Switching:FDM and TDM FDM frequency time TDM frequency time 4 users Example:
  • 19.
    Introduction 1-19 Numerical example How 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  500 msec to establish end-to-end circuit Work it out!
  • 20.
    Introduction 1-20 Network Core:Packet Switching each 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  congestion: packets queue, wait for link use  store and forward: packets move one hop at a time  Node receives complete packet before forwarding Bandwidth division into “pieces” Dedicated allocation Resource reservation
  • 21.
    Introduction 1-21 Packet Switching:Statistical Multiplexing Sequence of A & B packets does not have fixed pattern  statistical multiplexing. In TDM each host gets same slot in revolving TDM frame. A B C 10 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link
  • 22.
    Introduction 1-22 Packet switchingversus circuit switching  1 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 less than .0004 Packet switching allows more users to use network! N users 1 Mbps link
  • 23.
    Introduction 1-23 Packet switchingversus circuit switching  Great for bursty data  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 6) Is packet switching a “slam dunk winner?”
  • 24.
    Introduction 1-24 Packet-switching: store-and-forward Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps  Entire packet must arrive at router before it can be transmitted on next link: store and forward  delay = 3L/R Example:  L = 7.5 Mbits  R = 1.5 Mbps  delay = 15 sec R R R L
  • 25.
    Introduction 1-25 Packet-switched networks:forwarding  Goal: move packets through routers from source to destination  we’ll study several path selection (i.e. routing) algorithms (chapter 4)  datagram network:  destination address in packet determines next hop  routes may change during session  analogy: driving, asking directions  virtual circuit network:  each packet carries tag (virtual circuit ID), tag determines next hop  fixed path determined at call setup time, remains fixed thru call  routers maintain per-call state
  • 26.
    Introduction 1-26 Network Taxonomy Telecommunication networks Circuit-switched networks FDMTDM Packet-switched networks Networks with VCs Datagram Networks • Datagram network is not either connection-oriented or connectionless. • Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps.
  • 27.
    Introduction 1-27 Chapter 1:roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
  • 28.
    Introduction 1-28 Access networksand 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?
  • 29.
    Introduction 1-29 Residential access:point to point access  Dialup via modem  up to 56Kbps direct access to router (often less)  Can’t surf and phone at same time: can’t be “always on”  ADSL: asymmetric digital subscriber line  up to 1 Mbps upstream (today typically < 256 kbps)  up to 8 Mbps downstream (today typically < 1 Mbps)  FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone
  • 30.
    Introduction 1-30 Residential access:cable modems  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  deployment: available via cable TV companies
  • 31.
    Introduction 1-31 Residential access:cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
  • 32.
    Introduction 1-32 Cable NetworkArchitecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes
  • 33.
    Introduction 1-33 Cable NetworkArchitecture: Overview home cable headend cable distribution network (simplified)
  • 34.
    Introduction 1-34 Cable NetworkArchitecture: Overview home cable headend cable distribution network server(s)
  • 35.
    Introduction 1-35 Cable NetworkArchitecture: Overview home cable headend cable distribution network Channels 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 FDM:
  • 36.
    Introduction 1-36 Company access:local area networks  company/univ local area network (LAN) connects end system to edge router  Ethernet:  shared or dedicated link connects end system and router  10 Mbs, 100Mbps, Gigabit Ethernet  LANs: chapter 5
  • 37.
    Introduction 1-37 Wireless accessnetworks  shared wireless access network connects end system to router  via base station aka “access point”  wireless LANs:  802.11b (WiFi): 11 Mbps  wider-area wireless access  provided by telco operator  3G ~ 384 kbps • Will it happen??  WAP/GPRS in Europe base station mobile hosts router
  • 38.
    Introduction 1-38 Home networks Typicalhome network components:  ADSL or cable modem  router/firewall/NAT  Ethernet  wireless access point wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet
  • 39.
    Introduction 1-39 Physical Media Bit: 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., radio Twisted Pair (TP)  two insulated copper wires  Category 3: traditional phone wires, 10 Mbps Ethernet  Category 5: 100Mbps Ethernet
  • 40.
    Introduction 1-40 Physical Media:coax, fiber Coaxial cable:  two concentric copper conductors  bidirectional  baseband:  single channel on cable  legacy Ethernet  broadband:  multiple channel 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., 5 Gps)  low error rate: repeaters spaced far apart ; immune to electromagnetic noise
  • 41.
    Introduction 1-41 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)  2Mbps, 11Mbps  wide-area (e.g., cellular)  e.g. 3G: hundreds of kbps  satellite  up to 50Mbps channel (or multiple smaller channels)  270 msec end-end delay  geosynchronous versus low altitude
  • 42.
    Introduction 1-42 Chapter 1:roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
  • 43.
    Introduction 1-43 Internet structure:network of networks  roughly hierarchical  at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage  treat each other as equals Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-1 providers interconnect (peer) privately NAP Tier-1 providers also interconnect at public network access points (NAPs)
  • 44.
    Introduction 1-44 Tier-1 ISP:e.g., Sprint Sprint US backbone network
  • 45.
    Introduction 1-45 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 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet  tier-2 ISP is customer of tier-1 provider Tier-2 ISPs also peer privately with each other, interconnect at NAP
  • 46.
    Introduction 1-46 Internet structure:network of networks  “Tier-3” ISPs and local ISPs  last hop (“access”) network (closest to end systems) Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet
  • 47.
    Introduction 1-47 Internet structure:network of networks  a packet passes through many networks! Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP
  • 48.
    Introduction 1-48 Chapter 1:roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
  • 49.
    Introduction 1-49 How doloss and delay occur? packets queue in router buffers  packet arrival rate to link exceeds output link capacity  packets queue, wait for turn A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers
  • 50.
    Introduction 1-50 Four sourcesof packet delay  1. nodal processing:  check bit errors  determine output link A B propagation transmission nodal processing queueing  2. queueing  time waiting at output link for transmission  depends on congestion level of router
  • 51.
    Introduction 1-51 Delay inpacket-switched networks 3. Transmission delay:  R=link bandwidth (bps)  L=packet length (bits)  time to send bits into link = L/R 4. Propagation delay:  d = length of physical link  s = propagation speed in medium (~2x108 m/sec)  propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantities!
  • 52.
    Introduction 1-52 Caravan analogy Cars “propagate” at 100 km/hr  Toll booth takes 12 sec to service a 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 minutes toll booth toll booth ten-car caravan 100 km 100 km
  • 53.
    Introduction 1-53 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 site toll booth toll booth ten-car caravan 100 km 100 km
  • 54.
    Introduction 1-54 Nodal delay dproc = 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 msecs prop trans queue proc nodal d d d d d + + + =
  • 55.
    Introduction 1-55 Queueing delay(revisited)  R=link bandwidth (bps)  L=packet length (bits)  a=average packet arrival rate traffic intensity = La/R  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!
  • 56.
    Introduction 1-56 “Real” Internetdelays 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
  • 57.
    Introduction 1-57 “Real” Internetdelays and routes 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 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 ms traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means no reponse (probe lost, router not replying) trans-oceanic link
  • 58.
    Introduction 1-58 Packet loss queue (aka buffer) preceding link in buffer has finite capacity  when packet arrives to full queue, packet is dropped (aka lost)  lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all
  • 59.
    Introduction 1-59 Chapter 1:roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
  • 60.
    Introduction 1-60 Protocol “Layers” Networksare complex!  many “pieces”:  hosts  routers  links of various media  applications  protocols  hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks?
  • 61.
    Introduction 1-61 Organization ofair travel  a series of steps ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing
  • 62.
    Introduction 1-62 ticket (purchase) baggage(check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Layering of airline functionality Layers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer below
  • 63.
    Introduction 1-63 Why layering? Dealingwith complex systems:  explicit structure allows identification, relationship of complex system’s pieces  layered reference model for discussion  modularization eases maintenance, updating of system  change of implementation of layer’s service transparent to rest of system  e.g., change in gate procedure doesn’t affect rest of system  layering considered harmful?
  • 64.
    Introduction 1-64 Internet protocolstack  application: supporting network applications  FTP, SMTP, STTP  transport: host-host data transfer  TCP, UDP  network: routing of datagrams from source to destination  IP, routing protocols  link: data transfer between neighboring network elements  PPP, Ethernet  physical: bits “on the wire” application transport network link physical
  • 65.
    Introduction 1-65 message segment datagram frame source application transport network link physical Ht Hn Hl M Ht HnM Ht M M destination application transport network link physical Ht Hn Hl M Ht Hn M Ht M M network link physical link physical Ht Hn Hl M Ht Hn M Ht Hn Hl M Ht Hn M Ht Hn Hl M Ht Hn Hl M router switch Encapsulation
  • 66.
    Introduction 1-66 Chapter 1:roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History
  • 67.
    Introduction 1-67 Internet History 1961: Kleinrock - queueing theory shows effectiveness of packet- switching  1964: Baran - packet- switching in military nets  1967: ARPAnet conceived by Advanced Research Projects Agency  1969: first ARPAnet node operational  1972:  ARPAnet demonstrated publicly  NCP (Network Control Protocol) first host- host protocol  first e-mail program  ARPAnet has 15 nodes 1961-1972: Early packet-switching principles
  • 68.
    Introduction 1-68 Internet History 1970: ALOHAnet satellite network in Hawaii  1973: Metcalfe’s PhD thesis proposes Ethernet  1974: Cerf and Kahn - architecture for interconnecting networks  late70’s: proprietary architectures: DECnet, SNA, XNA  late 70’s: switching fixed length packets (ATM precursor)  1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles:  minimalism, autonomy - no internal changes required to interconnect networks  best effort service model  stateless routers  decentralized control define today’s Internet architecture 1972-1980: Internetworking, new and proprietary nets
  • 69.
    Introduction 1-69 Internet History Early 1990’s: ARPAnet decommissioned  1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)  early 1990s: Web  hypertext [Bush 1945, Nelson 1960’s]  HTML, HTTP: Berners-Lee  1994: Mosaic, later Netscape  late 1990’s: commercialization of the Web Late 1990’s – 2000’s:  more killer apps: instant messaging, P2P file sharing  network security to forefront  est. 50 million host, 100 million+ users  backbone links running at Gbps 1990, 2000’s: commercialization, the Web, new apps
  • 70.
    Introduction 1-70 Introduction: Summary Covereda “ton” of material!  Internet overview  what’s a protocol?  network edge, core, access network  packet-switching versus circuit-switching  Internet/ISP structure  performance: loss, delay  layering and service models  history You now have:  context, overview, “feel” of networking  more depth, detail to follow!

Editor's Notes

  • #18 Two simple multiple access control techniques. Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling. As we will see, used in AMPS, GSM, IS-54/136