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Lecture 14

Lecture 14. ATM and Switches Homework 3.21-38 Next Class: Selected Homework Solutions. Cell Switching (ATM). Fixed Size Cells-53 bytes 48 bytes of data 5 bytes of header Address formats-Network Service Access Point (NSAP) or E.164 formats-Not the same as ethernet MAC addresses.

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Lecture 14

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  1. Lecture 14 ATM and Switches Homework 3.21-38 Next Class: Selected Homework Solutions

  2. Cell Switching (ATM) • Fixed Size Cells-53 bytes • 48 bytes of data • 5 bytes of header • Address formats-Network Service Access Point (NSAP) or E.164 formats-Not the same as ethernet MAC addresses.

  3. ATM and Telephone Traffic • 8 bit sampling at 8KHz • 125msec/ 1 Byte sample • Time to accumulate a N byte cell is N*125 msec • 48 byte cell takes 6 msec

  4. ATM Header • Generic Flow Control • Virtual Circuit Identifier • VPI –Virtual Path Identifier • VCI-Virtual Channel Identifier

  5. VPI-Hierarchy in ATM 24 bits virtual circuit identifier for UNI Interface (28 for NNI) Virtual Path Identifier=8 Most Significant Bits (MSBs) Virtual Circuit Identifier=16 bits Purpose: To minimize switching tables in the public network

  6. ATM LAN Emulation (LANE) • Purpose to make the ATM network operate like ethernet • Broadcast • Multicast • High bandwidth—e.g. 622 Mbps • QOS

  7. An ATM LAN backbone

  8. LANE Protocol Stack

  9. LANE Servers • LECS-LANE Configuration Server • LES=LAN Emulation Server • BUS=Broadcast and Unknown Server

  10. LANE Servers • LEConfigurationS- • LANE clients set up VC to LECS • Client provides ATM address to LES • LECS • identifies type of LAN being emulated • Identifies maximum packet size • ATM address of LES

  11. Lane Servers • LES • Client sets up VC to LES • Registers MAC and ATM addresses • LES provides ATM address of BUS

  12. LANE SERVERS • BUS • LANE Clients (LECs) set up a point-to-point VC to the Bus • Bus maintains a single point-to-multipoint VC to all registered clients-

  13. LANE Schematic

  14. The LEC Viewpoint • Initially, • VC’s to BUS and LES • Does not know MAC or ATM address of other LECs • Sends first packet to BUS for broadcast • Sends “address resolution” request to LES which returns ATM address for specified MAC address

  15. The LEC Viewpoint • Sets up VC to destination for all subsequent frames • Closes unused VCs

  16. Switch Design Goals • Throughput • Scalability • Cost • Metrics: e.g. • per unit cost • Cost/port with a given throughput

  17. Throughput • Concerns • Bits/second • Packets/second • Throughput depends on traffic pattern • Contention

  18. Scalability • Cost • Physical Limits

  19. Switch Terminology

  20. Port Functions in a VC network • Input port • Determine output port for a given VCI • Output port • Remaps VCI for the outbound link • Buffering

  21. Input Buffering: Head-of-line blocking

  22. Cross-bar Switch Every input connected to every output Complexity grows as n2 We don’t need this flexibility most of the time

  23. 8 X 4 Knockout Concentrator “Section”

  24. Output buffering for a knock-out switch

  25. Shared Media Switches • Better buffer utilization • Buses must run n-times faster than line speed-wide buffers • Control electronics must really be fast

  26. Self-routing fabricsEight input banyan network

  27. Packet Routing through a banyan network

  28. 8 X 8 Batcher Network

  29. Routing Packets through a Batcher Network

  30. Sunshine Network

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