Gigabit Ethernet standards tweaked

Sept. 1, 1997

Gigabit Ethernet standards tweaked


Companies that have introduced Gigabit Ethernet products before the complete establishment of a standard are breathing easier after a recent meeting of the ieee 802.3z Gigabit Ethernet task force performed only minor tweaking to draft 3.1 of the specification. At the same time, a group of vendors agreed to form a consortium to promote and facilitate interoperability among their Gigabit Ethernet offerings.

Gigabit Ethernet promises speeds of what one source called "1250 Mbaud" over singlemode and multimode fiber as well as copper twinaxial cable and Category 5 wiring (see Lightwave, May 1997, page 10). Subsets of the standard address each of these media, with 1000Base-SX cover-ing short-wavelength (850-nm) optical transmission over multimode fiber and 1000Base-LX treating long-wavelength (1300-nm) operation over both multimode and singlemode fiber (see "A glossary of Gigabit Ethernet specifications," page 25).

The ieee task force closed the specification to the addition of new features in January. However, at its recent meeting in Maui, HI, the task force reviewed the results of what a source termed "a major survey" as well as recent tests and determined that the existing features treating 62.5-micron fiber needed adjustment. The group lowered the maximum distances on such fiber to 260 m (from 300 m) for 1000Base-SX and to 440 m (from 550 m) for 1000Base-LX.

The distance reductions should do little to dampen the enthusiasm of the Gigabit Ethernet Alliance, a vendor group established to promote the technology and facilitate development of the standards. In fact, several alliance members have already introduced Gigabit Ethernet products, even though balloting on the standard didn`t begin until this summer and final approval is not expected until March 1998. More than 30 vendors brought products to a Gigabit Ethernet interoperability demonstration at the Networld + Interop show in Las Vegas, NV, last June. Building on this demonstration, vendors used the recent task force meeting as a platform to create the Gigabit Ethernet Consortium, which will focus on interoperability issues.

Working together

The consortium set itself seven charter goals, according to 3Com, one of the founding members. Chief among these is the establishment of a long-term, independent interoperability test facility and the establishment of interoperability tests.

The consortium didn`t need to look far to settle on a test facility. The Inter-Operability Laboratory at the University of New Hampshire (unh), Durham, NH, already performs similar work in such technologies as Fiber Distributed Data Interface, Fast Ethernet, Fibre Channel, and Asynchronous Transfer Mode. Meanwhile, the consortium is meeting on a biweekly basis to define the tests the lab will perform, say Bob Gohn, program manager for Gigabit Ethernet at 3Com, and Mark Sankey, a network design engineer and the company`s representative in the consortium.

"This is a formalization of the kind of interoperability tests that we`re already doing as vendors," explains Gohn, who adds that the result of the testing will "give users some assurance that these products actually are interoperable with the emerging standard."

Once the consortium has developed the tests, they will be forwarded to unh, which will develop implementation schemes, adjusting the tests where necessary. "We have a lot of experience in doing this," says Sankey, echoing the general sense of confidence in the standard and its implementation. "We did the same thing when Fast Ethernet came on the scene with unh."

The consortium hopes to complete the test definition process by early September, in time for another interoperability demonstration at the Networld + Interop show in Atlanta, GA, in October. The equipment from this demonstration will be relocated to unh after the show for implementation in the Gigabit Ethernet test bed. Manufacturers could then use the facility to confirm or expand their internal test processes.

"The Gigabit Ethernet Consortium wants to be seen as an extension of the [manufacturer`s] R&D lab, so that you can provide your equipment to them when you think it`s ready and they`ll give you feedback on how it works against other [folks` products] and against the standard," explains Sankey.

As an extension of research and development activities, neither the lab nor the consortium will endorse the performance of individual products. "There`s not going to be a certified seal of approval or anything like that that`s going to come from the consortium," says Gohn. "Although users will be able to ask the vendors, `Have you passed the series of tests at unh and from the Gigabit Ethernet Consortium?` "

The 3Com sources predicted most vendors will likely be able to answer such questions in the affirmative. "I think that the risk of not having interoperability is actually relatively small. I think there`s not going to be a whole lot of `gotchas,` " predicts Gohn. "This is not necessarily as complex as other technologies. It is proven technology in terms of being Ethernet; we`ve already turned the crank up once before with Fast Ethernet and got through that pretty well....We`re already on track to do at least as well as, if not faster than, Fast Ethernet in the standards process. And I think the same will be true for interoperability."

Besides 3Com, other vendors who have pledged $10,000 to join the consortium include Bay Networks, Cabletron, Cisco Systems, Extreme Networks, Foundry Networks, Jato Technologies, Madge Networks, Matsushita Electric Works, Netcom Systems, Packet Engines, Prominet, Sun Microsystems, Texas Instruments, XaQti, and xlnt. q

A glossary of Gigabit Ethernet


1000Base-X is the ieee 802.3z specification that defines the 8b/10b coding scheme. The ieee 802.3z task force is responsible for all the Gigabit Ethernet specifications except that for Category 5 unshielded twisted-pair copper cable.

1000Base-SX covers 850-nm laser transceivers operating on multimode fiber. The task force recently reduced this specification?s maximum distance over 62.5-micron fiber to 260 m. The maximum distance specification for operation over 50-micron multimode fiber remains at 550 m.

1000Base-LX specifies parameters for 1300-nm laser transceivers operating on either multimode or singlemode fiber. Again, the task force shortened the maximum specified distance for 62.5-micron multimode fiber to 440 m. Operation over singlemode fiber increases the maximum distance to 3000 m.

1000Base-CX treats short-haul, low-cost copper jumpers operating on high-quality, shielded twisted-pair or coaxial cable up to 25 m.

1000Base-T, the specification for Category 5 copper cabling, is the responsibility of the ieee 802.3ab task force. Sources indicate that significant technical issues must be resolved before this standard is in place. It is not expected to be released at the same time as the other Gigabit Ethernet standards.

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