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ATM promises gigabit speeds, plunging prices.

How realistic are the claims for ATM, or Asynchronous Transfer Mode, the much ballyhoeed, "next-generation" networking technology?

Is it the much-needed salvation for anxious users rapidly running out of network capacity? Or is it the 1990s' version of ISDN, the highly touted integrated services digital network that never caught on with users?

Ironically, ATM was developed for ISDN, under the auspices of the CCITT, the world's communications authority. With this heritage, it was viewed initially as an attractive vehicle for wide area networks (WANs). More recently, however, users have begun to zero in on ATM's benefits for local area networks (LANs)--a marked departure from ISDN, which never anticipated the need for PC networks or client/server computing.

ATM's strength, and its ultimate claim to fame, though, may lie in its ability to integrate seamlessly an organization's LAN and WAN environments, using the same addressing schemes, switching mechanisms and network management.

Virtual channel

ATM combines gigabit-per-second capacity with packet-switching's efficient use of bandwidth and the minimal delays associated with circuit switching. Using hardware switches, it sets up a virtual channel between sender and receiver before transmitting the information in fixed-sized packets, called cells, each 53 bytes long.

It's the fixed-length cells that open the way to hardware switching, which is key to ATM's price/performance benefits. Also, the fixed-length cells allow simultaneous delivery of data and delay-sensitive information such as voice and video used in multimedia applications.

With its connection-oriented service and fixed cell lengths, ATM differs from conventional LANs, such as those based on Ethernet, token ring and FDDI. The most marked difference, though, lies in the way the LAN bandwidth is allocated. Instead of sharing the bandwidth, ATM gives users a dedicated channel, which means there is no service degradation with increasing numbers of users.

Apparently sold on ATM's benefits, AT&T and several other carriers are planning service rollouts later this year or in early 1994. Two dozen vendors are also readying ATM switches, so 1994 is shaping up as a banner year for the new networking technology.

ATM switches will come in all sizes, from large central-office models for carriers to premises hub switches for users. This feature of "scalability" is an important attribute of ATM that also applies to network bandwidth and geographical reach. ATM can be implemented incrementally, and the speed can be adjusted to meet current and future needs. Vendors are looking at a variety of speeds from 25 to 622 Mb/s, reaching ultimately to the gigabit-per-second range.


Despite the differences with other LAN architectures, migrating to ATM can be reasonably straightforward with proper planning. Any LAN using star wiring has the central point of wiring concentration needed for the ATM switch, and adapter cards can replace or supplement old Ethernet, token ring or FDDI cards.

Prices for ATM switches have also started to fall into the FDDI range, prompting users to hold off implementing FDDI in favor of ATM. Fore Systems of Pittsburgh, Pa., recently cut the cost of its 16-port ForeRunner ASX-100 ATM switch by 40% to $2,995 per port. By the end of 1994, the price will be under $2,000 per port, according to Mark Juliano, director of marketing.

Fore Systems also plans to be one of the first vendors to offer ATM adapters for personal computers. Juliano reports that development of an IBM Micro Channel Architecture ATM adapter is underway, and work will begin soon on an adapter for Apple Macintoshes. Meanwhile, the firm is about to unveil an adapter for Extended Industry Standard Architecture-based machines.

Another ATM leader, SynOptics Communications of Santa Clara, Calif., has teamed up with Sun Microsystems to develop a low-cost, 155-Mb/s card for Sun SPARC/Solaris workstations and servers, allowing them to be connected directly to an ATM LAN via a SynOptics switch.

At the Interop show last March, SynOptics unveiled a complete ATM-based networking solution, centered around its 16-port LattisCell ATM switch, adapter cards for workstations, and software for connection and network management. LattisCell is noteworthy for its per-port price of $1,495. Each port offers a dedicated 155-Mb/s bandwidth, which is made possible by an internal switching architecture with an aggregate capacity of 5 Gb/s.

AT&T has said that its ATM service will begin at the T3 speed of 45 Mb/s when it becomes available early next year. However, users who make up its Customer Advisory Council say they would like to see ATM services at fractional T3 and at the T1 speed of 1.544 Mb/s. While acknowledging the feasibility of lower-speed ATM access, AT&T claims it has not yet decided whether to offer it.
COPYRIGHT 1993 Nelson Publishing
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Title Annotation:asynchronous transfer mode
Author:Edwards, Morris
Publication:Communications News
Date:Aug 1, 1993
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