CDDI Breathes Life into FDDI Standard

By Bruce Schneier
Network World
September 7, 1992

Why should anyone care about Fiber Distributed Data Interface (FDDI) anymore?

Wiring an office with fiber is expensive, as is purchasing fiberoptic switching and relay equipment. And with Asynchronous Transfer Mode (ATM) on the horizon, which promises flexible data rates of 150M to 600M bit/sec, FDDI's 100M bit/sec data rate hardly seems worth it.

But the recent emergence of FDDI over copper wiring under the evolving Copper Distributed Data Interface (CDDI) standard changes all that. CDDI has breathed life into the protocol and given network managers a new option for wiring high-performance data networks.

"FDDI over copper has promise," said Bob Olsen, vice-president of marketing at MultiMedia Networks, Inc., an ATM start-up in Lexington, Mass. "ATM will go to the desktop eventually, but CDDI is good in the short term."

Olsen said the increased number of users on today's networks and the increase in workstation computing power, combined with the rise in groupware applications and graphics-intensive applications, are all contributing to network congestion.

Users in data-intensive environments have tried to solve performance problems by segmenting their networks into smaller work groups. But even with a full 10M bit/sec of bandwidth, many high-performance users experience bottlenecks.

"With FDDI over copper, you can put a bunch of power users together and provide a high-performance, compute-intensive environment at a reasonable cost," Olsen said.

Users agreed. "FDDI over copper is a good low-cost solution for our networking applications," said Jim Ray, principal engineer at Harris Semiconductor Corp. in Palm Beach, Fla. "We have a large installed base of twisted-pair cable, and we can install FDDI quickly without having to spend money pulling fiber."

That's not to say that FDDI users will experience full 100M bit/sec bandwidth, whether over fiber or copper.

"Anyone who thinks they're going to get 100M bit/sec sustained is looking at the wrong technology," Ray said. "The CPUs are not fast enough to drive it yet. Still, it's the only way to get data transfer at anything close to disk transfer speeds and still have bandwidth left over.

On the downside, a standard for CDDI has yet to be established. Thus, vendors are building products to conflicting CDDI schemes, which may slow user acceptance of the technology.

For example, Crescendo Communications, Inc., the first company to ship CDDI products, bases its wares on a scheme that is designed for unshielded twisted-pair media.

Another CDDI faction, a consortium of 11 companies including Advanced Micro Devices, Inc., IBM, Motorola, Inc., National Semiconductor Corp. and SynOptics Communications, Inc., recently announced its own specification for supporting the technology over shielded twisted-pair wiring.

"If someone wants to implement a reliable FDDI link over shielded twisted pair, there are multiple vendors with products that interoperate using this specification," said Nick Schommer, product marketing manager at SynOptics and cochairman of the FDDI Solutions Showcase at the upcoming INTEROP 92 Fall show.

For example, IBM recently announced a set of FDDI and CDDI products based on this specification.

But eventually, a CDDI standard will be set, which should spur use of the technology. In June, the ANSI X3T9.5 subcommittee chose a coding scheme for CDDI, called MLT-3, which marks the first step in building a standard for FDDI over copper. The subcommittee plans to have the first draft of the standard ready for its October meeting.

earlier essay: Doing it Randomly: Probabilistic Algorithms in Programming
later essay: Dylan: A New Language Is Blowin' in the Wind
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