Chapter 12

ASYNCHRONOUS TRANSFER MODE

    Asynchronous Transfer Mode (ATM) is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that use variable sized packets or frames. ATM provides data link layer services that run over a wide range of OSI physical Layer links. ATM has functional similarity with both circuit switched networking and small packet switched networking. It was designed for a network that must handle both traditional high-throughput data traffic (e.g., file transfers), and real-time, low-latency content such as voice and video. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the actual data exchange begins. ATM is a core protocol used over the SONET/SDH backbone of the public switched telephone network (PSTN) and Integrated Services Digital Network (ISDN), but its use is declining in favour of all IP.

       Asynchronous Transfer Mode, a network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line.

      ATM (asynchronous transfer mode) is a dedicated-connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology. Individually, a cell is processed asynchronously relative to other related cells and is queued before being multiplexed over the transmission path.

            ATM creates a fixed channel, or route, between two points whenever data transfer begins. This differs from TCP/IP, in which messages are divided into packets and each packet can take a different route from source to destination. This difference makes it easier to track and bill data usage across an ATM network, but it makes it less adaptable to sudden surges in network traffic.

       Asynchronous Transfer Mode (ATM) represents a relatively recently developed communications technology designed to overcome the constraints associated with traditional, and for the most part separate, voice and data networks. ATM has its roots in the work of a CCITT (now known as ITU-T) study group formed to develop broadband ISDN standards during the mid-1980s. In 1988, a cell switching technology was chosen as the foundation for broadband ISDN, and in 1991, the ATM Forum was founded.

         The ATM Forum represents an international consortium of public and private equipment vendors, data communications and telecommunications service providers, consultants, and end users established to promote the implementation of ATM. To accomplish this goal, the ATM Forum develops standards with the ITU and other standards organizations.

       The first ATM Forum standard was released in 1992. Various ATM Forum working groups are busy defining additional standards required to enable ATM to provide a communications capability for the wide range of LAN and WAN transmission schemes it is designed to support. This standardization effort will probably remain in effect for a considerable period due to the comprehensive design goal of the technology, which was developed to support voice, data, and video on both local and wide area networks.

Benefits of ATM

      ATM provides a flexible and scalable solution to the increasing need for quality of service in networks where multiple information types (such as data, voice, and real-time video and audio) are supported. With ATM, each of these information types can pass through a single network connection.        

ATM can provide the following:

1.    High-speed communication

2.    Connection-oriented service, similar to traditional telephony

3.    Fast, hardware-based switching

4.    A single, universal, interoperable network transport

5.    A single network connection that can reliably mix voice, vedio, and data

6.    Flexible and efficient allocation of network bandwidth  

http://technet.microsoft.com/en-us/library/cc740081(WS.10).aspx

http://www.techfest.com/networking/atm/atm.htm

http://technet.microsoft.com/en-us/library/bb726929.aspx

http://www.webopedia.com/TERM/A/ATM.html

http://en.wikipedia.org/wiki/Asynchronous_Transfer_Mode