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Optical/IP

IEEE Eyeballs Compensation

The standards body for 10-Gbit/s Ethernet could give a boost to dispersion compensation technology.

The Institute of Electrical and Electronics Engineers Inc. (IEEE) 802.3ae Task Force is looking to add another interface to its list: a serial transceiver that uses electronic dispersion compensation (EDC) to make 10-Gbit/s signals readable on old multimode fiber.

The IEEE, which handles the standard for 10-Gbit/s Ethernet, heard the idea informally in July and could approve a standardization effort as early as November.

A similar effort for Fibre Channel is underway already, but it may prove less serious than the Ethernet effort. "I think the initial pull to look at this comes from the Ethernet side, but it's kind of hard to get things going in the IEEE," says Bob Zona, senior product marketing manager for Intel Corp. (Nasdaq: INTC).

The goal is to run 10-Gbit/s Ethernet down 300 meters of old multimode fiber, the kind that's already installed in many corporate networks. The LX4 interface for 10-Gbit/s Ethernet accomplishes that by splitting the signal into four lanes of 3.125 Gbit/s apiece. The slower transmissions can make it cleanly down the fiber, but the arrangement requires a four-laser transceiver.

The alternative to LX4, often called EDC in lieu of a formal name, would use electronic dispersion compensation to clean up the signal. This would allow the use of one 10-Gbit/s laser in the transceiver, presumably saving space and power.

The idea came up in the early days of 802.3ae but died early because it couldn't fit in the standard's power budget. "At that time, the technology wasn't ripe enough," Zona says.

Dispersion compensation has progressed since then. Big Bear Networks, for example, has shipped unspecified products with 10-Gbit/s dispersion compensation for more than a year, says John Jaeger, vice president of marketing. And startups are continuing to emerge in this area. This week, Scintera Networks Inc. announced production volumes of its dispersion compensation chip, which targets low-power operation (see Scintera Networks Launches).

There would still be work to do to get EDC to replace LX4. The EDC chips would still have to meet the 802.3ae power budget, and they would have to be optimized to handle multimode fiber, which is trickier than singlemode. "You can't take any old EDC and say you have a solution," Jaeger says.

Big Bear, Cisco Systems Inc. (Nasdaq: CSCO), Intel, and Network Elements Inc. presented the EDC idea at the last 802.3ae meetings in July. A more formal "call for interest" session is expected to be held at the November meeting, in Albuquerque. If 802.3ae committee members approve, the EDC effort could be blessed as a study group, the first step on the road to IEEE standardization.

One encouraging sign is that the Fibre Channel camp has launched its own 10-Gbit/s EDC effort. The project was blessed recently by the T11 I/O Interfaces Committee within the InterNational Committee for Information Technology Standards (INCITS).

But the wait for standards could be a while. "People believe [an 802.3ae EDC standard] is 18 months to two years away, and it may be even longer than that," says Pat Edsell, CEO of Gigabit Optics Corp. "A lot of people do believe ultimately it will be successful, but it's not here today."

In the meantime, LX4 continues to enjoy renewed attention as equipment makers eye the prospect of offering 10-Gbit/s Ethernet on old enterprise fibers. Cisco in particular is hoping to ship LX4 interfaces on some of its boxes by next year.

"They've been very vocal," Zona says. "But we've heard interest from other customers as well who haven't stepped in and publicly announced it."

Supply is a problem, however. Of the vendors to announce LX4 support early on, only Molex Inc. (Nasdaq: MOLX/MOLXA) appears to still be shipping transceivers.

That's spawning some activity among components makers, who are announcing the pieces needed to build LX4 transceivers. BitBlitz Communications Inc. touted the LX4 friendliness of its retimer chip recently, and yesterday, Gigabit Optics announced a mux/demux component aimed at LX4 transceivers (see BitBlitz Launches 10GigE Retimer and Gigabit Optics Does LX4).

— Craig Matsumoto, Senior Editor, Light Reading

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