ASYNCHORONOUS TRANSFER MODES

ASYNCHORONOUS TRANSFER MODES

Points to be discussed are: DefinitionATM standardATM networkATM interfacesATM cellATM Adaptation layer(AAL) to be contd...ATM ApplicationATM Services CategoriesATM advatagesATM advantagesATM challengesReferences 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 layerSingle transport mechanismStreamlined protocol

ATM StandardITU-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 parametersVirtual 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 cellsSmall size, may reduce queuing delay of high priority cellsFixed size, more efficient switching

Diagram of the UNI ATM Cell

Diagram of the NNI ATM Cell

ATM cell content1) 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. 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 PTIContinue.Cell Loss Priority (CLP)The 1-bit CLP field used for explicit indication of the priority of the cellHeader 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 servicesConstant bit rate uncompressed audio/video infoVideoconferencing, TV, pay-per-view, VOD, etc.

Non-real-time servicesAvailable bit rate bursty apps requiring reliable end-to-end connectione.g. LAN, router-to-router reliability

ATM Advantages

Universality Mixed traffic types, real-time and non-real- timeScalability LANs, WANs, WLANsEfficient use of network resources Bandwidth on demand conceptSimplified network infrastructure

ATM challenges

In-network mux/buffering can lead to cell delay or lossMany types of trafficLarge geographic distribution

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

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