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Networking

Based on the powerpoint presentation of Computer Networking: A Top Down Approach Featuring the Internet , Third Edition, J.F. Kurose and K.W. Ross, Addison-Wesley, ISBN: 0-321-22735-2. Networking. millions of connected computing devices called hosts and end-systems PCs workstations, servers

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Networking

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  1. Based on the powerpoint presentation ofComputer Networking: A Top Down Approach Featuring the Internet, Third Edition, J.F. Kurose and K.W. Ross, Addison-Wesley, ISBN: 0-321-22735-2. Networking

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

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

  4. protocolscontrol 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 What’s the Internet: “nuts and bolts” view router workstation server mobile local ISP regional ISP company network

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

  6. 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 actionstaken on msg transmission, receipt, other events What’s a protocol?

  7. network edge: applications and hosts network core: routers network of networks network structure:

  8. 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 The network edge:

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

  10. Goal: data transfer between end systems handshaking 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 flow control sender won’t overwhelm receiver congestion control senders “slow down sending rate” when network congested Network edge: connection-oriented service

  11. Goal: data transfer between end systems UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service 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 Network edge: connectionless service

  12. mesh of interconnected routers the fundamental question: how is data transferred through net? packet-switching: data sent thru net in discrete “chunks” The Network Core

  13. each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth Network Core: Packet Switching resource contention: • demand can exceed available capacity • congestion: packets queue, wait for link use • store and forward: packets move one hop at a time • transmit over link • wait turn at next link

  14. D E Packet Switching: C A 1.5 Mbs B queue of packets waiting for output link

  15. Takes 4 seconds to transmit (push out) packet of 5000 bits on to link or 1250 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 Packet-switching: store-and-forward L R R R

  16. Now break up message into 1500 bits packets Packet Switching: Message Fragmentation • Total of 5000 packets • 1 msec to transmit packet on one link • pipelining: each link works in parallel

  17. 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? Access Networks

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

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

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

  21. server(s) Cable Network Architecture: Overview cable headend home cable distribution network

  22. 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 Company access: local area networks To/From ISP

  23. shared wireless access network connects end system to router via base station aka “access point” wireless LANs: 802.11b (WiFi): 11 Mbps router base station mobile hosts Wireless access networks

  24. Typical home network components: ADSL or cable modem router/firewall/NAT Ethernet wireless access point Home networks wireless laptops to/from cable headend cable modem router/ firewall wireless access point Ethernet (switched)

  25. Twisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 Mbps Ethernet Category 5 TP: 100Mbps Ethernet Physical Media

  26. Coaxial cable: two concentric copper conductors Physical Media: coax, fiber 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

  27. no physical “wire” bidirectional propagation environment effects: reflection obstruction by objects interference Physical media: radio Radio link types: • terrestrial microwave • e.g. up to 45 Mbps channels • LAN (e.g., WaveLAN) • 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 LEOS

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