The battle lines are being drawn on which physical layer specification should be used as the basis for a 25Mbps Asynchronous Transfer Mode standard. This is despite the fact that the ATM Forum has already decided that a 25Mbps Asynchronous Mode standard is not needed. There are two proposals for a physical layer specification – one from PMC-Sierra Inc (CI No 2,516); the other from the Desktop ATM25 Alliance formed last September (CI No 2,506). Both camps hope that the Forum will reconsider its decision and will submit their specifications to its Physical Working Group at its meeting this month in Kyoto, Japan. Indeed, Vancouver, British Columbia-based PMC-Sierra last week made its specification public, as promised. Sierra’s UNI-PHY25, is based on the ATM Forum’s fractional Synchronous Optical Network, SONET, framing technology at 25.92Mbps. It would, says the company, enable the same switch ports and Network Interface Cards to be used for 25Mbps transmission over Category-3 twisted pair wiring and 155Mbps over Category-5 wiring. The Desktop ATM25 Alliance’s proposal is based primarily on Token Ring technology and while the Alliance admits this means that different Network Interface Cards and switch ports would be needed for 25Mbps and 155Mbps Asynchronous Mode implementations, it says its approach is inherently simpler, resulting in cheaper products. While PMC-Sierra is going it alone, membership of the Desktop ATM25 Alliance now numbers 30, with the news that five more companies have joined. The new members are Connectware Inc, LanOptics Ltd, ON Systems Inc, SGS-Thompson Microelectronics BV and Talus Technology Inc. The rivals last debated the respective merits of their proposals at a Saturn SONET/Synchronous Digital Hierarchy-Asynchronous Mode User Network Development Group meeting last month. According to Sierra’s manager of local area network products, Vernon Little, most Saturn delegates agreed that 25Mbps is a transitional technology and that low speed ATM is best served with Ethernet-to-ATM bridges today. However, he added that those that expressed an interest in Category-3 cabling could see the advantage of re-using most of their software and hardware designs implemented for 155Mbps, scaled down to 25Mbps, and of using a field-proven transmission convergence format. Little also said that UNI-PHY-25 would enable telecommunications companies to use SONET-based Asynchronous Transfer Mode at 25Mbps in neighbourhood ‘pedestals’ to offer video-on-demand to the home. IBM apparently reiterated its position that cost was the paramount consideration, but Sierra predicted that, with UNI-PHY25, Network Interface Cards would eventually be cheaper, because it would be possible for manufacturers to build on their existing high-volume 155Mbps designs. Copies of the UNI-PHY specifications can be requested by fax at 604 668 7301, or by electronic mailing a request to: info(AT)pmc-sierra.bc.ca
