The debate is over how to get 10-Gbit/s Ethernet signals to travel down 300 meters of multimode fiber, the kind that was installed years ago and is still in place as enterprises graduate to the 10-Gbit/s class. The 10GBase-LX4 specification within the IEEE 802.3ae standard uses coarse wavelength-division multiplexing (CWDM) to split the signal into four 3.125-Gbit/s feeds. Being slower, these are less prone to chromatic dispersion and can make it safely to the other side.
Last year, chip makers started stirring up interest in another method, one that keeps a serial 10-Gbit/s signal, using electronic dispersion compensation (EDC) to correct for signal distortion (see IEEE Eyeballs Compensation). The IEEE study group pursuing this idea got a preliminary OK in a January IEEE vote, and this week the group is expected to be granted Task Force status, meaning it will receive its own cool IEEE moniker of the form 802.3xx.
(The group's formal -- and extremely winning -- name is the 10Gb/s on FDDI-grade MM fiber Study Group.)
EDC is being met with a swelling of support from chip vendors and has gotten some pre-standard use with large OEMs such as Sumitomo Electric Industries Ltd., says Steven Kubes, vice president of marketing for EDC chip vendor Scintera Networks Inc.: "That didn't happen with LX4."
The IEEE works at a deliberate pace, however, so it's likely to take more than a year to fully ratify the standard. So, LX4 still has a headstart, even if a slow one.
Recent LX4 interest began when Cisco Systems Inc. (Nasdaq: CSCO) was readying its 10-Gbit/s Ethernet push. Many of these customers had older fiber, triggering the need for LX4. But most transceiver vendors had put their bets elsewhere, leading Cisco officials to start publicizing the need for the interface (see LX4 Gets Another Chance).
Only two module makers were doing LX4 at the time and both have since dropped their product lines. Molex Inc. (Nasdaq: MOLX/MOLXA) sold its transceiver business to Emcore Corp. (Nasdaq: EMKR); and Blaze Network Products Inc. -- which had been silent for months -- got its technology acquired by something called Aduro Inc. (see Molex Out, Emcore In, Emcore Intros Lx4 Transceiver, and Aduro Acquires Blaze).
Overall, though, it appears LX4 is making a comeback. Module vendors pledging LX4 support in recent months include E2O Communications Inc., MergeOptics GmbH, and Opnext Inc. (see E2O Stretches VCSEL Range, MergeOptics Launches Xenpak Module, and Opnext Intros 10-GigE Module).
As well, a few companies have announced components to go inside LX4 modules:
- Cube Optics Touts Tiny Mux
- Quake Tackles LX4, CX4
- Gigabit Optics Does LX4
- BitBlitz Launches 10GigE Retimer
In the long run, yes, says Bill Woodruff, vice president of marketing at BitBlitz Communications Inc. Eventually, all 10-Gbit/s Ethernet connections will be serial, making LX4 obsolete. But for now, most 10-Gbit/s links connect to the XAUI interface, which splits electrical signals into four lanes of 3.125 Gbit/s. XAUI is a necessity because most chips can't take 10-Gbit/s signals, and as long as XAUI rules, LX4 will have a place, Woodruff says.
"LX4 will be a year into products, and the IT manager will already own the transceivers. Why would he buy an EDC module? It has nothing LX4 doesn't do," Woodruff says.
EDC supporters are hoping they can counter with lower prices. EDC could cut the cost of an interface in half, to $300 versus $600 to $800 for an LX4 option, according to Tony Conoscenti, marketing director of transport products at Vitesse Semiconductor Corp. (Nasdaq: VTSS).
"When we talk to our customers, they are more interested in multimode EDC in the long term because they feel it will be cheaper," says Neal Neslusan, director of product marketing for Applied Micro Circuits Corp. (AMCC) (Nasdaq: AMCC). "LX4 is going to be the bigger marketplace in the short run," he adds -- no big deal for AMCC and other chip makers that sell to both sides of this debate.
— Craig Matsumoto, Senior Editor, Light Reading