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EE 400 Asynchronous Transfer Mode (ATM)

EE 400 Asynchronous Transfer Mode (ATM). Abdullah AL-Harthi. Objective. Understand ATM technology, concepts and cell structure. Outline:. Introduction. ATM Layer . ATM Cell. ATM Service Categories. ATM Adaptation Layer (AAL). Conclusion. Introduction.

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EE 400 Asynchronous Transfer Mode (ATM)

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  1. EE 400 Asynchronous Transfer Mode (ATM) AbdullahAL-Harthi

  2. Objective • Understand ATM technology, concepts and cell structure.

  3. Outline: • Introduction. • ATM Layer . • ATM Cell. • ATM Service Categories. • ATM Adaptation Layer (AAL). • Conclusion .

  4. Introduction • ATM :Multi-speed network environment that provides a variety of complex network services. • Can carry voice, data, video separately or simultaneously. • Fixed-lenth packets (cells). • Can be used in LANs, or WANs. • Minimal error and flow control capabilities. • Connection-oriented virtual channel. • Allows multiple logical connections to be multiplexed.

  5. Protocol Architecture

  6. ATM Layer • Connection-oriented without acknowledgements. • Two possible interfaces: - UNI : User-Network Interface: Boundary between an ATM network and host. - NNI : Network-Network Interface: Between two ATM switches.

  7. UNI/NNI Interface

  8. ATM Cells • Fixed size – 53 bytes. • 5 octet header. • 48 octet information field. • Small cells reduce queuing delay for high priority cells. • Small cells can be switched more efficiently. • Easier to implement switching of small cells in hardware.

  9. Header Format • Generic flow control • Only at user to network interface • Controls flow only at this point • Virtual path identifier - a routing field for the network - 8 bits at user-network interface - 12 bits at the network-network interface • Virtual channel identifier - user for routing between end users • Payload type - indicates the type of information in the information field • e.g. user info or network management

  10. Header Format • Cell loss priority - used to provide guidance to the network in the event of congestion. value 0: cell of high priority, should not be discarded unless no other alternative is available value 1: cell is subject to discard within the network • Header error control -used for both error control and synchronization

  11. ATM Cell Format

  12. Virtual Connections • Virtual Channel Connection (VCC) Full duplex virtual circuit with logical connection between source and destination – can be PVC or SVC • Virtual Path Connection (VPC) Semi-permanent (or customer controlled or network controlled) connection that provides a logical collection of virtual channels that have the same endpoint

  13. ATM Service Categories • Real time • Constant bit rate (CBR) • Real time variable bit rate (rt-VBR) • Non-real time • Non-real time variable bit rate (nrt-VBR) • Available bit rate (ABR) • Unspecified bit rate (UBR) • Guaranteed frame rate (GFR)

  14. Real Time Services • If want to avoid or decrease variation of delay (jitter), use CBR or rt-VBR • CBR Fixed data rate continuously available • Commonly used for uncompressed audio and video • Video conferencing • Interactive audio • rt-VBR Best for time sensitive applications • Tightly constrained delay and delay variation • rt-VBR applications transmit at a rate that varies with time • e.g. compressed video • Produces varying sized image frames • Original (uncompressed) frame rate constant (isochronous) • So compressed data rate varies

  15. Non-Real Time • Intended for applications with bursty traffic and limited constraints on delay and delay variation. • Greater flexibility, greater use of statistical multiplexing.

  16. nrt-VBR • May be able to characterize expected traffic flow • Improve QoS in loss and delay

  17. UBR • Unused capacity of CBR and VBR traffic made available to UBR • For application that can tolerate some cell loss or variable delays • e.g. TCP based traffic

  18. ABR • Application specifies peak cell rate (PCR) it will use and minimum cell rate (MCR) it requires • Resources allocated to give at least MCR • Spare capacity shared among ABR and UBR sources • e.g. LAN interconnection

  19. ATM Adaptation Layer (AAL) • Maps higher-layer information into ATM cells to be transported over an ATM network • Collects information from ATM cells for delivery to higher layers • AAL-1: for CBR traffic • AAL-2: for VBR type traffic • AAL-3: connection-oriented VBR • AAL-4: connection-less service • AAL-5: most popular for data. Also called seal(simple and efficient adaptation layer)

  20. Conclusion • Minimal error and flow control • Fixed size simplified processing at each ATM node. • Small cells reduce queuing delay • Minimal addressing info on each cell • Efficient traffic management

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