1. Introduction1-1 Chapter 1: Introduction Our goal:  get context, overview, “feel” of networking  more depth, detail later in course  approach: m descriptive m 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

2. Introduction1-2 What’s the Internet: “nuts and bolts” view  millions of connected computing devices: hosts, end-systems m PCs workstations, servers m PDAs phones, toasters running network apps  communication links m fiber, copper, radio, satellite m transmission rate = bandwidth  routers: forward packets (chunks of data) local ISP company network regional ISP router workstation server mobile

3. Introduction1-3 “Cool” internet appliances IP picture frame http://www.ceiva.com/ Web-enabled toaster+weather forecaster Surfing

4. Introduction1-4 “Cool” internet appliances an Internet-ready washing machine built-in 15-inch LCD (liquid crystal display) screen for watching TV, surfing the Internet or looking at digital pictures

5. Introduction1-5 What’s the Internet: “nuts and bolts” view  protocols control sending, receiving of msgs m e.g., TCP, IP, HTTP, FTP, PPP  Internet: “network of networks” m loosely hierarchical m public Internet versus private intranet  Internet standards m RFC: Request for comments m IETF: Internet Engineering Task Force local ISP company network regional ISP router workstation server mobile

6. Introduction1-6 What’s the Internet: a service view  communication infrastructure enables distributed applications: m Web, email, games, e- commerce, database., voting, file (MP3) sharing  communication services provided to apps: m connectionless m connection-oriented

7. Introduction1-7 What’s a protocol? a human protocol and a computer network protocol: Q: Other human protocols? Hi Got the time? 2:00 TCP connection req TCP connection response Get http://www.awl.com/kurose-ross time

8. Introduction1-8 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, other events

9. Introduction1-9 A closer look at network structure:  network edge: applications and hosts  network core: m routers m network of networks  access networks, physical media: communication links

10. Introduction1-10 The network edge:  end systems (hosts): m run application programs m e.g. Web, email m at “edge of network”  client/server model m client host requests, receives service from always-on server m e.g. Web browser/server; email client/server

11. Introduction1-11 The network edge:  peer-peer model: m minimal (or no) use of dedicated servers m e.g. Gnutella, KaZaA

12. Introduction1-12 Network edge: connection-oriented service Goal: data transfer between end systems  handshaking: setup (prepare for) data transfer ahead of time m Hello, hello back human protocol m set up “state” in two communicating hosts  TCP - Transmission Control Protocol m Internet’s connection- oriented service TCP service [RFC 793]  reliable, in-order byte- stream data transfer m loss: acknowledgements and retransmissions  flow control: m sender won’t overwhelm receiver  congestion control: m senders “slow down sending rate” when network congested

13. Introduction1-13 Network edge: connectionless service Goal: data transfer between end systems m same as before!  UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service m unreliable data transfer m no flow control m no congestion control App’s using TCP:  HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP:  RTP, streaming media, teleconferencing, DNS, Internet telephony

14. Introduction1-14 The Network Core  mesh of interconnected routers  the fundamental question: how is data transferred through net? m circuit switching: dedicated circuit per call: telephone net m packet-switching: data sent thru net in discrete “chunks”

15. Introduction1-15 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

16. Introduction1-16 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” m frequency division m time division

17. Introduction1-17 Circuit Switching: FDMA and TDMA FDMA frequency time TDMA frequency time 4 users Example:

18. Introduction1-18 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 available capacity  congestion: packets queue, wait for link use  store and forward: packets move one hop at a time m transmit over link m wait turn at next link Bandwidth division into “pieces” Dedicated allocation Resource reservation

19. Introduction1-19 Packet Switching: Statistical Multiplexing Sequence of A & B packets does not have fixed pattern  statistical multiplexing. A B C 10 Mbs Ethernet 1.5 Mbs D E statistical multiplexing queue of packets waiting for output link

20. Introduction1-20 Packet switching versus circuit switching  1 Mbit link  each user: m 100 kbps when “active” m active 10% of time  circuit-switching: m 10 users  packet switching: m with 35 users, probability > 10 active less than.0004 Packet switching allows more users to use network! N users 1 Mbps link

21. Introduction1-21 Packet switching versus circuit switching  Great for bursty data m resource sharing m simpler, no call setup  Excessive congestion: packet delay and loss m protocols needed for reliable data transfer, congestion control  Q: How to provide circuit-like behavior? m bandwidth guarantees needed for audio/video apps m still an unsolved problem (chapter 7) Is packet switching a “slam dunk winner?”

22. Introduction1-22 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 Example:  L = 7.5 Mbits  R = 1.5 Mbps  delay = 15 sec R R R L

23. Introduction1-23 Packet Switching: Message Fragmentation Now break up message L into 1500 bits packets  Total of 5000 packets  1 msec to transmit packet on one link  pipelining: each link works in parallel  Delay reduced from 15 sec to 5.002 sec

24. Introduction1-24 Packet-switched networks: forwarding  Goal: move packets through routers from source to destination m we’ll study several path selection (i.e. routing)algorithms (chapter 4)  datagram network: m destination address in packet determines next hop m routes may change during session m analogy: post office, driving, asking directions  virtual circuit network: m each packet carries tag (virtual circuit ID), tag determines next hop m fixed path determined at call setup time, remains fixed thru call m routers maintain per-call state

25. Introduction1-25 Access Networks 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?

26. Introduction1-26 Residential access: point to point access  Dialup via modem m up to 56Kbps direct access to router (often less)  ISDN: integrated services digital network m 128kbps + regular phone line  ADSL: asymmetric digital subscriber line m up to 1 Mbps upstream (today typically < 256 kbps) m up to 8 Mbps downstream (today typically < 1 Mbps)

27. Introduction1-27 Residential access: cable modems  HFC: hybrid fiber coax m asymmetric: up to 10Mbps downstream, 1 Mbps upstream  network of cable and fiber attaches homes to ISP router m shared access to router among home m issues: congestion, dimensioning  deployment: available via cable companies, e.g., MediaOne, ATT, Comcast

28. Introduction1-28 Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

29. Introduction1-29 Cable Network Architecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes

30. Introduction1-30 Cable Network Architecture: Overview home cable headend cable distribution network server(s)

31. Introduction1-31 Cable Network Architecture: Overview home cable headend cable distribution network Channels VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO DATADATA DATADATA CONTROLCONTROL 1234 56789 FDM:

32. Introduction1-32 Company access: local area networks  company/univ local area network (LAN) connects end system to edge router  Ethernet: m shared or dedicated link connects end system and router m 10 Mbs, 100Mbps, Gigabit Ethernet  deployment: institutions, home LANs happening now  LANs: chapter 5 To/From ISP

33. Introduction1-33 Wireless access networks  shared wireless access network connects end system to router m via base station aka “access point”  wireless LANs: m 802.11b (WiFi): 11 Mbps  wider-area wireless access m provided by telcom operator m 3G ~ 384 kbps Will it happen?? m WAP/GPRS in Europe base station mobile hosts router

34. Introduction1-34 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 (switched)

35. Introduction1-35 Physical Media  Bit: propagates between transmitter/rcvr pairs  physical link: what lies between transmitter & receiver  guided media: m signals propagate in solid media: copper, fiber, coax  unguided media: m signals propagate freely, e.g., radio Twisted Pair (TP)  two insulated copper wires m Category 3: traditional phone wires, 10 Mbps Ethernet m Category 5 TP: 100Mbps Ethernet

36. Introduction1-36 Physical Media: coax, fiber Coaxial cable:  two concentric copper conductors  bidirectional  baseband: m single channel on cable m legacy Ethernet  broadband: m multiple channel on cable m HFC Fiber optic cable:  glass fiber carrying light pulses, each pulse a bit  high-speed operation: m high-speed point-to-point transmission (e.g., 5 Gps)  low error rate: repeaters spaced far apart ; immune to electromagnetic noise

37. Introduction1-37 Physical media: radio  signal carried in electromagnetic spectrum  no physical “wire”  bidirectional  propagation environment effects: m reflection m obstruction by objects m interference Radio link types:  terrestrial microwave m e.g. up to 45 Mbps channels  LAN (e.g., WaveLAN) m 2Mbps, 11Mbps  wide-area (e.g., cellular) m e.g. 3G: hundreds of kbps  satellite m up to 50Mbps channel (or multiple smaller channels) m 270 msec end-end delay m geosynchronous versus LEOS