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Internetworking

Internetworking. An internetwork is typically comprised of many physical networks over which data travels There are many different types of physical networks: Ethernet FDDI ATM Goals of internetworking: Make all the diverse network technologies function as a coordinated whole

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Internetworking

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  1. Internetworking • An internetwork is typically comprised of many physical networks over which data travels • There are many different types of physical networks: • Ethernet • FDDI • ATM • Goals of internetworking: • Make all the diverse network technologies function as a coordinated whole • Hide the details of the underlying network hardware • Provide universal communication services

  2. Review: Ethernet • A popular packet-switched LAN technology invented at Xerox PARC in the 1970’s

  3. Properties of an Ethernet • 10 – 100 Mbps • Broadcast bus • Best-effort delivery • Distributed access control (CSMA/CD)

  4. Distributed Access Control • Carrier Sense Multiple Access (CSMA) • If two transceivers both sense that the network is idle and begin transmission simultaneously a collision occurs • Collision Detection (CD) • Recovery

  5. Ethernet Addressing • Each machine connected to the network has a unique 48-bit number (it’s address) • To send a packet a computer puts the destination address in the destination field • That address can be: • A unicast address • A broadcast address • A multicast address

  6. Ethernet Frame Format • Variable length (no shorter than 64 octets and no larger than 1518 octets) • Fields: • Preamble • Destination address • Source address • Frame type • Data • Cyclic Redundancy Check (CRC)

  7. An Ethernet Frame

  8. Extending an Ethernet • Repeaters - hardware devices used to relay electrical signals from one cable to another • Advantages • Disadvantages

  9. Extending an Ethernet (cont) • Bridges - receives valid frames and retransmits it on another another cable • Advantages • Disadvantages

  10. Access Control Alternatives • Ethernet - distributed • Advantages • Disadvantages • Can you think of other alternatives?

  11. Fiber Distributed Data Interconnect (FDDI) • Popular LAN technology • Higher bandwidth (100 Mbps) than Ethernet • Uses optical fiber • Implements a token ring

  12. FDDI (cont)

  13. FDDI’s Self-Healing Capability • Two rings • Counter rotating • Uses the backup ring to bypass a failed computer or link

  14. FDDI Self-Healing (cont)

  15. Asynchronous Transfer Mode (ATM) • A high-speed connection-oriented network technology • Operates from 100 Mbps to >1 Gbps • Expensive

  16. Recall: How Internetworking Works

  17. Goals of Internetworking • Make all the diverse network technologies function as a coordinated whole • Hide the details of the underlying network hardware • Provide universal communication services

  18. Application-Level Interconnection • One application-level program per machine cooperating/interoperating with other programs • Example? • Advantages • Disadvantages

  19. Network-Level Interconnection • Have a set of communication conventions • The O.S. for each computer provides communication services for all application programs • Example? • Advantages • Disadvantages

  20. Internetworking • Takes the network-level interconnection approach • Functions as a virtual packet-switched network • Attempts to build a unified, cooperative interconnection of networks that supports a universal communication service

  21. Properties of the Internet • Hides underlying internet architecture from the user • Does not mandate a network interconnection topology • Establishes network independence in the user interface

  22. Network Interconnection • Internet router • A small computer that physically attaches to two networks • Passes packets from one network to the other • As the Internet’s topology becomes more complex, routers need to know about that topology • More on routers later…

  23. Routing Decisions • Can be complex • Want to keep routing hardware simple and cheap • So routers only use the destination network (not the destination machine) to make routing decisions • Routing table is proportional to the # of networks in the internet (not the # of hosts)

  24. All Networks Are Equal • Any communication system capable of transferring packets counts as a single network independent of: • its delay • throughput characteristics • packet size • scale

  25. Big Advantages of Internetworking • Users perceive a single, virtual network through which all machines can be reached • Users do not need to know the underlying details of the network • Application-level programs do not need to know the underlying details of the network

  26. Big Responsibilities of Internetworking • Cooperation • Communication conventions • Each participating network agrees to handle traffic to/from other hosts in return for their handling of its traffic

  27. Unanswered Questions • What is the addressing scheme in an internet? • What do packets look like? • How is routing done? • What happens when routers/hosts malfunction? • What happens when routers/hosts get overloaded?

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