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Networks and Protocols

Networks and Protocols. networks and protocols definitions motivation history protocol hierarchy reasons for layering quick tour through the layers main example: the Internet. Networks. A network is a set of machines connected by communication links. Machines can be

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Networks and Protocols

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  1. Networks and Protocols • networks and protocols • definitions • motivation • history • protocol hierarchy • reasons for layering • quick tour through the layers • main example: the Internet

  2. Networks • A network is a set of machines connected by communication links. • Machines can be • general-purpose computers • other devices (phones, Coke machines) • specialized network components • routers • switches

  3. Motivation • Why connect to a network? • share resources • help people communicate • Sharing resources • from printers to supercomputer centers • Helping people communicate • email, Web, active documents

  4. point-to-point network multiple access network Direct connectivity • point-to-point or multiple access

  5. Media • links can use many physical media • copper wire • optical fiber • radio • infrared • line-of-sight laser • layer on another network • example: modem connection uses phone network

  6. Copper Wires vs. Optical Fibers • advantages of fiber • higher bandwidth • smaller and lighter • less prone to interference • less prone to eavesdropping • advantages of copper • simple • cheap to interface to

  7. Topologies ring bus star mesh

  8. Network elements • Intranet: many elements in one administrative domain • Internet: collection of interconnected networks, across administrative domains • host: a computer on the net • router: host that routes packets from one link to another • often dedicated, with no applications

  9. Circuit Switching • example: telephony • resources reserved during call setup • resources dedicated for duration of call • conservative • guarantee quality of service to all calls • resources dedicated even if call doesn’t always need them • good for constant-bit-rate traffic

  10. Circuit Switching

  11. Packet Switching • alternative to circuit switching • example: Internet • entering data divided into packets • packets in network share resources • no performance guarantees • queue packets if link contention • statistical multiplexing of resources

  12. Packet Switching

  13. Packet Switching in the Internet local net local net local net local net

  14. Virtual Circuit • cross between circuit switching and packet switching • set up path before data flows • resources along path are shared • example: asynchronous transfer mode (ATM) • cheaper than circuit switching, better guarantees than packet switching • but: complicated

  15. History of Networking • 1870’s • circuit-switched phone network • 1960’s • packet-switched data networks • 4-node ARPAnet in 1969 • 1970’s • multiple-access nets (Aloha, Ethernet) • commercial nets (DECnet, IBM SNA) • 100-node ARPAnet in 1979

  16. History of Networking • 1980’s • proliferation of LANs, WANs • 100k-node Internet in 1989 • 1990’s • 4M-node Internet in 1995 • commercialization • ISPs • wireless LANs

  17. Layering in Networks • simplify complex engineering • layer N relies on services of layer N-1 • layer N provides services to layer N+1 • interfaces between layers define services • hide complexity • separate implementation from interface

  18. layer N+1 layer N+1 Layered Protocols abstract view of layer N layer N layer N

  19. Protocol • a protocol specifies: • a set of rules for how network elements interact • the format of the messages exchanged • actions to take on receipt of messages • specifications must be exact • interoperability: ability of different implementations to work together

  20. Protocol Hierarchy • “official” seven-layer model • usually taught and memorized • seldom used except as terminology • in practice, Internet uses four-layer model • focus on this model in this course • top to bottom: application layer, transport layer, network layer, data link layer

  21. Application Layer • process-to-process communication • supports application functionality • examples • file transfer protocol (FTP) • simple mail transfer protocol (SMTP) • hypertext transfer protocol (HTTP) • network news transfer protocol (NNTP) • you can add your own

  22. Transport Layer • transmission control protocol (TCP) • provides reliable byte stream service • flow control • congestion control • user datagram protocol (UDP) • provides unreliable unordered datagram service

  23. Network Layer • Internet protocol (IP) • the key to the architecture • can use many different data links layers • treats each network in the Internet as a link • no quality of service guarantee • can lose and misorder packets • “best effort” service

  24. Data Link/Physical Layer • comes from underlying network • Ethernet • ATM • phone/modem • you can (in theory) build your own

  25. Internet Hierarchy application layer FTP HTTP SMTP DNS Finger transport layer TCP UDP network layer IP data link layer Ethernet ATM modem SHRIMP

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