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Chapter Objectives

Learn the basic concepts of ATM, reasons for implementing an ATM service, and the general format and structure of ATM. Understand how ATM handles different traffic types and its impact on bandwidth usage. Explore the integration of multimedia, ATM technology, protocols, and features.

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Chapter Objectives

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  1. Chapter Objectives • After completing this chapter you will be able to: • Understand the basic concepts of ATM • List some reasons for implementing an ATM service • Describe the general format of the ATM structure • Understand the basic concept of virtual circuits • Describe ATM’s handling of traffic types

  2. Never Underestimate • Famous quotes “I think there’s a world market for maybe 5 computers” - Thomas Watson, IBM chairman, 1943 “Computers in the future will weigh no more than 1.5 tons” - Prediction in Popular Mechanics, 1949 “Clever, but, what is a microchip good for?” - Engineer at IBM, 1952 “There is no reason why anyone would want to have a computer in their home” - Ken Olson, DEC chairman, 1977 “640K (RAM) ought to be enough for anybody” - Bill Gates Microsoft chairman, 1981 "There is one big problem -- telecommunications bandwidth” - Andy Grove, Intel, 1997

  3. Modern Requirements • Traditional voice, data, fax etc. • Plus • High-quality audio • High-quality video • Voice over the Internet • HTML • Multimedia etc. • Only networking standards supported • Scalability from office through corporate to operator • Same standards from operator down to the desktop • Guaranteed quality of service where appropriate

  4. Single Point of Access Multimedia • What is multimedia?

  5. Video/sound in Gigabytes Graphics in Megabytes Text in kilobytes Multimedia Storage • Impact on file size

  6. Demand for Bandwidth • Multiple users accessing multimedia - Creates a bandwidth bottleneck

  7. Frame Relay 33 MIN. 2.048 Mbps 0.5 Gbyte 155 Mbps 26 SEC. ATM . Bandwidth Use • Large files use a lot of bandwidth • Or response times become unacceptably long

  8. Connection- oriented Bandwidth requirement Delay variance Constant bit rate Variable bit rate Connectionless Delay Telephone Sensitive Low Sensitive   Internet Medium   Insensitive Insensitive Video Conference Sensitive Sensitive    High Integration • Different media types have different requirements

  9. ATM & ISDN • Narrowband ISDN (N-ISDN) • Broadband ISDN (B-ISDN) 2 x B(earer) 64 kbit/s 1 x D(ata) 16 kbit/s Basic rate 30 x B(earer) 64 kbit/s 1 x D(ata) 64 kbit/s Primary rate ATM 224 x B(earer) variable In-band signalling

  10. ATM Technology • Traditional Communications: • Circuit switching • Inefficient for bursty data • Packet switching • Unpredictable delays • ATM blends the best features of each system • Establishes end-to-end connections • Traffic is sent in packets and multiplexed on connections • Standards-based handling allows predictable delays

  11. 5-Byte Header 48-Byte Payload The ATM Cell • Fixed packet size

  12. Transport • Bearer channel based on fixed-length cells • 5-byte header -- 48-byte payload • Offers low latency at switches • Delays are more predictable

  13. signalling ATM Connections • Connections are virtual channels • Permanent (PVC) • Switched (SVC)

  14. A A1 A A2 B7 A4 B6 B5 A3 B B4 B3 B B1 B2 Circuits • Channels are connection-oriented • Cells arrive in sequence • No re-ordering required • Simplifies processing

  15. ATM Switching Inputs Outputs 104 Payload Payload 56 Payload 77 Payload 754 Cell Queues The ATM switch simply performs a hardware lookup of the connection identifier, and switches the cell accordingly. A new connection identifier is allocated at the output.

  16. ATM Multiplexing Constant bit rate (low) Constant bit rate (high) Packetised (bursty data) Variable bit rate Supported services AAL SAR Cells at required rate Multiplexing ATM cell stream

  17. Workgroup Corporate network Public network Corporate network ATM Protocol Suite • Not all ATM standards are yet in place • Promises to be the complete suite of protocols • From desktop to desktop • Over LAN and WAN • Seamless operation without conversion or encapsulation

  18. Analogue ATM Basics • The core network must be fast and reliable • ATM networks do not perform error correction • ATM does not work on Plain Old Telephone System (POTS) network

  19. Summary of Features • Connection-oriented • No out-of-sequence data • AAL to support connectionless data • Attempts to provide advantages of: • Circuit switching • low or no call set-up time • low predictable delays • bandwidth always available • Packet switching • efficient use of bandwidth • route switching

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