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ATM: A view from the trenches

This presentation provides an in-depth look at Asynchronous Transfer Mode (ATM) technology, detailing its integration within the Cisco environment at Northwestern University. It discusses the rationale behind adopting ATM in the mid-1990s, the decision processes, and the technology's backbone architecture for voice, data, and video services. Alongside foundational ATM theory, the session outlines practical solutions for traditional networking challenges, specifically in relation to LAN emulation and broadcast issues, as well as future directions for network technology at NU.

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ATM: A view from the trenches

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  1. ATM: A view from the trenches .

  2. Introduction • Laura Grill: l-grill@nwu.edu • *my* experience with ATM • cisco environment at Northwestern University

  3. Agenda • Why ATM? • Review of basic ATM theory and LANE • A look at NU’s network topology

  4. Why ATM? • 1996 ATM was the next big thing • connection oriented benefits of circuit switched using virtual circuits • efficient use of bandwidth as in packet switched • Decision was made at executive level for: • combine voice and data worlds • ATM to the desktop • 1997 built ATM backbone and bought OC-12 to Ameritech NAP • to handle voice data and video to and from the university

  5. New technologies:New strategy • The enabling technologies that make it feasible to integrate services w/o ATM • voice over IP • QOS for connectionless networks • gigabit ethernet • Today, ATM as a backbone and wan technology w/ no plans to grow it • Moving gigabit into the backbone (keeping existing ATM) • Frame versus cell: I'd rather have frames

  6. Basic ATM theory • Connection oriented vs. connectionless • 53 byte cells • Uses virtual circuits, identified with VPI/VCI

  7. Broadcast based "legacy" protocols • IP, IPX, AppleTalk (use broadcast discovery) • Why is this a problem? • Catch 22 - can’t talk on the network until a circuit is established and can’t establish a circuit without an address • Can’t broadcast on the phone network (no mechanism for this)

  8. Ways to solve the broadcast problem • RFC 1483 [native IP over ATM] • RFC 1577 [classical IP] • LANE (LAN Emulation) • MPOA

  9. LANE system • 3 servers: LECS, LES, BUS • 1 client: LEC

  10. Servers • LECS - LAN Emulation Configuration Server • hold information about the LES for each emulated LAN and gives that info to the LEC when it comes on-line • LES - client register their MAC and ATM address with the LES • BUS- maintains a VC that connects all the clients together emulated a broadcast

  11. Client • LEC - LAN Emulation Client (can be a host or router or switch)

  12. Procedure for a LEC to become part of the emulated LAN • LEC comes up and creates VC to LECS (using well known address or ILMI or statically configured) • LECS tells it what to emulate and who the LES is and what it's ATM address is • The client then registers it's MAC and ATM address with the LES • LES assigns a BUS • At this point many VC’s have been built to mesh all the LEC’s together

  13. ATM Topology at NU • See diagrams • ATM as a backbone technology to connect buildings to the core • use ATM for our WAN - OC-3c to NAP and OC-3c to Chicago campus • Some FDDI still remains • Will add gigabit this year

  14. The end • Questions?

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