Standards Bodies and the ATM Forum
The standards bodies that have the greatest influence over how ATM is accepted and implemented throughout the world and that ensure multivendor interoperability are as follows:
The Development of ATM and B-ISDN 302
• ITU-T (well over 100 specifications)
• American National Standards Institute (ANSI) T1S1 Committee (more than 20 specifications)
• Internet Engineering Task Force (IETF) (more than 40 specifications)
Even the FRF has about four IAs that treat ATM, especially its interworking with Frame Relay. The largest body of work seems to have come from the AF and its almost 200 IAs, which govern the private use of ATM technology. Much of the latest public-network recommendations that make their way into international specifications owe their existence to the AF. Just to give you an appreciation for the sheer magnitude of ITU-T coverage, both in breadth and volume, for ATM and B-ISDN, specifications appear in the following series:
• E-series—Overall network operation, telephone service, service operation and human factors
• F-series—Non-telephone telecommunication services
• G-series—Transmission systems and media, digital systems and networks
• H-series—Audiovisual and multimedia systems
• I-series—Integrated services digital network
• J-Series—Transmission of television, sound programme and other multimedia signals
• M-series—Maintenance: transmission systems, telephone circuits, telegraphy, facsimile, leased circuits
• Q-series—Switching and signalling
• Y-series—Global information infrastructure and internet protocol aspects
NOTE The preceding series definitions are exactly as they appear at www.itu.int/rec/
recommendation.asp.
Specific recommendations and implementation agreements are cited throughout this chapter, as the topics to which they pertain are presented.
To reiterate, the ITU-T originally developed ATM to answer a need for a technology that would handle the public high-speed transfer of voice, video, and data on behalf of B-ISDN. What wound up happening was that the ITU-T and the market saw other directions for this technology that had the same basic goals in mind but that could also be used for LAN applications and private implementations. The market, in 1991, was comprised of four intrigued vendors that formed a consortium, now known as the ATM Forum. The four corporations were Cisco Systems, Sprint Corporation, Northern Telecom (Nortel Networks), and NET/ADAPTIVE.
Today, however, similar to the FRF, the AF is comprised of many hundreds of corporations. End users are even allowed to join. ATM, similar to Frame Relay, is not an access circuit itself, but rather a protocol that describes the relaying of fixed-size frames, called cells, across physical access links. Besides other recommendations, the AF, in its User-Network Interface (UNI) IAs, specifies the physical links for which ATM is standardized. Some of the more common links follow:
Continue reading here: ATM Functionality
Was this article helpful?