The Many Faces of Asynchronous Transfer Mode

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  • Topic: Asynchronous Transfer Mode, OSI model, X.25
  • Pages : 10 (2904 words )
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  • Published : May 9, 2006
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Running head: ATM

The Many Faces of Asynchronous Transfer Mode

Table of Contents

ATM Objectives3
Basic Concepts in ATM4
ATM Standards7
ATM Switching11
Switching Networks12
Performance Issues12
ATM Applications14
Consumer Applications14
Commercial Applications16

The Many Faces of Asynchronous Transfer Mode

Asynchronous Transfer Mode (ATM) has been accepted universally as the transfer mode of choice for Broadband Integrated Services Digital Networks (BISDN). It can handle any kind of information such as voice, data, image, text and video in an integrated manner. ATM provides a good bandwidth flexibility and can be used efficiently from desktop computers to local area, metropolitan are network and wide area networks (LAN, MAN and WAN). It is a connection- oriented packet switching technique in which all packets are of fixed length. Although ATM is a technology, most users experience ATM through the use of both ATM equipment and services. This paper will attempt to explain a few of the basic principles and concept of Asynchronous Transfer Mode through objectives, basic concepts, standards, switching and application.

ATM Objectives
One must note that ATM meets the following objectives for BISDN networks. They support all existing services as well as emerging services in the future, utilize network resources very efficiently, minimizes the switching complexity, minimizes the processing time at the intermediate nodes and supports very high transmission speeds, minimizes the number of buffers required at the intermediate nodes to bound the delay and the complexity of buffer management, and guarantees performance requirements of existing and emerging applications.

Basic Concepts in ATM
Before continuing we must first review some basic concepts in ATM design. These terms were copied in their entirely to maintain definition integrity from McGraw-Hill, ATM Theory and Application, 1999.

Information Transfer - ATM is a fast packet oriented transfer mode based on asynchronous time division multiplexing and it uses fixed length (53 bytes) cells. Each ATM cell consists of 48 bytes for information field and 5 bytes for header. The header is used to identify cells belonging to the same virtual channel and thus used in appropriate routing. Cell sequence integrity is preserved per virtual channel. ATM Adaptation layers (AAL) are used to support various services and provide service specific functions. This AAL specific information is contained in the information field of the ATM cell. Basic ATM cell structure can be shown as follows.

Routing -ATM is a connection oriented mode. The header values such as VCI and VPI are assigned during the connection set up phase and translated when switched from one section to other. Signaling information is carried on a separate virtual channel than the user information. In routing, there are two types of connections i.e. Virtual channel connection (VCC) and Virtual path connection (VPC). A VPC is an aggregate of VCCs. Switching on cells is first done on the VPC and then on the VCC.

ATM Resources - ATM is connection-oriented and the establishment of the connections includes the allocation of a VCI i.e. virtual channel identifier and/or VPI i.e. virtual path identifier and also includes the allocation of the required resources on the user access and inside the network. These resources, expressed in terms of throughput and quality of service, can be negotiated between user and network either before the call-set up or during the call.

ATM Cell Identifiers - ATM cell identifiers, i.e. Virtual Path Identifier, Virtual Channel Identifier and Payload Type Identifier (PTI) are used to recognize an ATM cell on a physical transmission medium. VPI and VCI are same for cells belonging to the same virtual connection on a shared transmission medium.

Throughput - Peak Cell Rate (PCR) can be defined as a...
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