It appears Cisco Systems Inc. (Nasdaq: CSCO) is gravitating toward the X2 multisource agreement (MSA) for 10-Gbit/s transceivers, a move that would be a setback for the rival XPAK MSA.

Cisco representatives weren't available for comment, but several sources in the component and module businesses say that key design groups within Cisco are leaning toward X2.

Though there doesn't appear to be a corporate-level decision in the works, if several Cisco design teams are choosing X2, it could spell trouble for XPAK. "If I were Cisco, I wouldn't be splitting my supply down the middle," says Carolyn Raab, vice president of marketing for chip vendor Quake Technologies Inc. "They'll probably go with one of the two."

To recap: X2 and XPAK are competing to be the successor to the Xenpak MSA for 10-Gbit/s transceivers. They perform the same function as Xenpak -- translating a 10-Gbit/s feed into four 3.125-Gbit/s channels and vice versa -- but they're smaller (see Is Xenpak Past It? and The X-Wars: Agilent Strikes First).

XPAK emerged first, proposed by Intel Corp. (Nasdaq: INTC) as a smaller alternative to Xenpak. Afterwards, the X2 camp, led by Agilent Technologies Inc. (NYSE: A), revealed what they'd been working on (see Can Intel Make Transceiver Peace?).

So far, they've battled on equal ground. Taking the storage industry as an example, Raab notes there's no consistent leaning towards XPAK or X2. Raab doesn't know for sure whether Cisco prefers X2 -- but if it's true, she says, it would shift momentum in X2's direction.

Other vendors think that's already begun. "The reason we're not doing XPAK is the interest in the market -- there's very little," says Leland Day, product manager for JDS Uniphase Corp. (Nasdaq: JDSU; Toronto: JDU).

Why would Cisco favor X2? Some sources say it's because X2 is a more "direct" derivative of Xenpak; then again, many observers have noted that X2 and XPAK have only minor differences between them. Others say Cisco likes the fact that X2 has a larger number of optical component firms backing it, including Agilent, Opnext Inc., and Mitsubishi Electric Corp.

Intel officials couldn't immediately be reached for comment, but it seems unlikely that the company would drop its XPAK efforts. As Raab notes, the XPAK MSA has customers -- including Intel itself, which uses XPAK modules in its server adapters.

In the long run, all this could turn out to be moot. Most industry sources agree that XPAK and X2 will eventually be supplanted by XFP, a serial 10-Gbit/s MSA -- it's mainly a question of how soon semiconductors can comfortably handle 10-Gbit/s signals. Some vendors, such as Finisar Corp. (Nasdaq: FNSR), are betting that day will come soon enough to make XPAK and X2 irrelevant (see Aelis Boosts Optical Reach, Speed).

— Craig Matsumoto, Senior Editor, Light Reading