ASYNCHORONOUS TRANSFER MODES

Points to be discussed are: Definition ATM standard ATM network ATM interfaces ATM cell ATM Adaptation layer(AAL) to be contd...

ATM Application ATM Services Categories ATM advatages ATM advantages ATM challenges References

ATM-Definition Asynchronous Transfer Mode (ATM) is a technology that has the potential of revolutionizing data communications and telecommunications. ATM is a packet switching.

What is it really? Low-level network layer Single transport mechanism Streamlined protocol

ATM Standard ITU-T I.361 Defines the ATM Layer functions. ITU-T I.363 Defines the ATM Adaptation Layer- protocols. ITU-T I.610 Defines the ATM Operation and Maintenance (OAM) functions

The ATM network 1) User-to-Network Interface (UNI) 2) Network-to-Network Interface (NNI) 3) Inter-Carrier Interface (ICI)

ATM Interfaces 1. User-to-Network Interface (UNI) Exists between a single end user and a public ATM network. 2. Network-to-Network Interface (NNI) Exists between switches in a single public ATM network. 3. Inter-Carrier Interface (ICI) It is located between two public ATM networks

Important parameters Virtual channel: A channel that provides transportation of ATM cells between two or more endpoints for information transfer. Virtual paths: It is a group of Virtual Channels that are carried on the same physical facility and share the same Virtual Path Identifier (VPI) value.

ATM cells Small size, may reduce queuing delay of high priority cells Fixed size, more efficient switching Diagram of the UNI ATM Cell Diagram of the NNI ATM Cell

ATM cell content 1) 5 bytes header: (I) General flow control defined across the UNI flow across the UNI intended to control the traffic 4 bits must be set to 0's. (II) Virtual path control routing field for network an 8-bit field for the UNI and a 12-bit field for the NNI, is used to identify virtual paths.

Continue…. Virtual Channel Identifier (VCI) 16-bit field is used to identify a virtual channel For idle cells, the VCI is set to all 0's. Payload Type Identifier (PTI) three bits of the PTI

Cell Loss Priority (CLP) The 1-bit CLP field used for explicit indication of the priority of the cell Header Error Control (HEC) 8-bit fieldIt capable of detecting all single-bit errors and some multiple-bit errors.

ATM Applications

ATM Service Categories Real-time services Constant bit rate – uncompressed audio/video info Videoconferencing, TV, pay-per-view, VOD, etc. Non-real-time services Available bit rate – bursty apps requiring reliable end- to-end connection e.g. LAN, router-to-router reliability

ATM Advantages Universality Mixed traffic types, real-time and non-real- time Scalability LANs, WANs, WLANs Efficient use of network resources Bandwidth on demand concept Simplified network infrastructure

ATM challenges In-network mux/buffering can lead to cell delay or loss Many types of traffic Large geographic distribution

References http://www.iec.org Amos E. Joel, Jr., Asynchronous Transfer Mode (IEEE Press, 1993) "Broadband ISDN and ATM". http://world-class-programme.com

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