Over the last two decades telecommunications technology has evolved dramatically from analog to the new digital systems. Where once only voice transmission possible, new services such as video telephony, video-conferencing, video-on-demand, home education and TV distribution with totally different characteristics, are being planned or being already provided. The fact that every new service has its unique characteristics has led to a new digital telecommunications technique. It is called Asynchronous Transfer Mode (ATM), the next generation of networking. ATM is flexible enough to provide all existing and future services regardless of their types and their yet unknown requirements in the same way. Therefore it is also future-safe and able to adapt itself to changing or new demands.

ATM is currently one of the most attractive technologies in the digital data communications field. In ATM, information is transmitted in short fixed-length blocks that are called cells (Figure 1). An ATM cell consists of a header and a data field that carries the actual information-either video, voice or data. The cell header contains a label denoting the routing address.

Not only was ATM created to overcome the difficulties in existing transfer methods but also to allow the creation of a Broadband Integrated Service Digital Network (B-ISDN).

Transmission speeds up to the physical limits (e.g., 622.05 Mbps signaling rate nowadays) are achievable with ATM. By contrast, there are limitations to the upgrading possible, with the most popular traditional Local Area Network (LAN) topologies (e.g., Ethernet and Token Ring), to higher bandwidth, which means incapacity to support current and of course future real-time applications.

Although the connection-oriented ATM was initially designed for Wide Area Networks (WANs), its unique features including flexibility, scalability, high transfer capacity and support for multimedia applications, also fired the imagination of the LAN vendors in the early 1990s. Since ATM is suitable for both LANs and WANs, historical separation of traditional LANs that are connectionless and WANs that are connection-oriented will eventually disappear. This will form a universal platform for data communications as well as replace the conventional LAN topologies. With full deployment of ATM in design, manufacturing and maintenance of the future networks, the overall costs will be relatively smaller.

The traditional LANs use a shared media-access (e.g. bus) method. That means all stations of the network have to share one transmission medium and have to contend for access. The limitations of shared media-access method are overcome by the ATM’s new approach of switching systems based on central media-access management (Figure 2). Since each user has a dedicated connection to one of the ATM switch ports, users no longer need to contend for access as opposed to the legacy LANs. Moreover ATM LAN users are provided WAN services through another port on the LAN switch. On the other side, the traditional LANs have no direct wide-area capabilities-they must depend on a separate piece of equipment to convert the LAN rates and protocols into WAN-compatible format.

Problems that arise in transmission through the current networks of voice, video and data simultaneously (or in real-time) could well be prevented by using ATM.

With its low-cost networking and technology ATM will soon provide scientist and engineers greater global freedom to exchange data, images (e.g., medical imaging applications) and models in real-time. Beyond the physical boundaries of classrooms, students (especially disabled) will be able to be part of a class and interact with others just as though they were there using high-speed and reliable ATM networks.


B-ISDN: A high-speed (above 1.544 Mbps signaling rate) network standard that grew from traditional narrowband ISDN.

Connection-oriented: A network (e.g., WANs) that establishes, either permanently or on a call-by-call basis, a specific circuit path for transmission.

Connectionless: A network (e.g., legacy LANs) in which no particular path is established for the transfer of information.

Ethernet: A LAN using 10 Mbps signaling rate.

LAN: High-speed network connecting personal computers, printers, and other data equipment within an office or campus.

Mbps: Mega bit per second

Token Ring: A LAN using 4 or 16 Mbps signaling rate.

WAN: High-speed network connecting communications equipment nationally and internationally.


PARULKAR G. M.: ‘Local ATM Networks’, IEEE Network March 1993, p.S-9.


‘Efficient Use of Protocol Stacks for LAN/MAN-ATM Interworking’, IEEE Journal

on Selected Areas in Communications October 1993, 11(8) p.1160-1170,.

KIM B.G. & WANG P.: ‘ATM Network: Goals and Challenges’, Communications

of the ACM February 199538 (2), pp. 39-44.

The ATM Forum: http:/ /www.atmforum.com/

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