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

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

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 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 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:

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

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