Cisco's proprietary 100Gbit/s module format, called CPAK, debuted last week and triggered one major question: Why bother?

Cisco does have answers, but they're not likely to stop analysts and competitors from casting doubt on the proprietary modules, especially considering the standard CFP2 modules will be arriving on the market at about the same time.

Common knowledge around the industry since last fall, CPAK continues the development undertaken by startup Lightwire, which was acquired by Cisco in 2012.

As Cisco announced at OFC/NFOEC, CPAK will first appear on the ONS 15454 as the client-side interface (the one that connects to other equipment, such as routers). For the line side (which faces the wider network), Cisco is using its own 100Gbit/s technology acquired with CoreOptics.

What makes the CPAK questionable is its similarity to the CFP2, the newest 100Gbit/s interface and the subject of several vendors' demos at OFC/NFOEC. There were enough of them that they organized a treasure hunt -- a raffle that attendees entered by writing down the number of operating CFP2s found at six booths, including the stands representing four CFP2 vendors -- Avago Technologies Pte., Finisar Corp., Fujitsu Optical Components Ltd. and Oclaro Inc.

(The other two booths belonged to The Ethernet Alliance and the Optical Internetworking Forum (OIF). Among other module vendors, JDS Uniphase Corp. was showing CFP2s but didn't participate in the treasure hunt.)

Before this week, Cisco's rationale for launching CPAK was to speed up the process of shrinking pluggable 100Gbit/s modules from the big CFP size. (That's what Cisco people had been telling Light Reading.) A CFP measures about 5 by 7 inches. A CPAK is about half that -- but it's only slightly smaller than a CFP2, as Gazettabyte noted in a comparison in October.Moreover, the power consumption of CPAK and CFP2 is similar. Module vendors at OFC/NFOEC were saying CFP2 is specified for 7.5 W and that modules are using 5.5 W to 6 W in typical cases. Similiar figures are quoted in Cisco's marketing materials.

It makes some people wonder why Cisco is getting so much attention for having introduced CPAK. "They've got everyone transfixed. I don't understand," says Andrew Schmitt, an analyst with Infonetics Research Inc.

Cisco is sticking by its decision to make CPAK modules, though. Bill Gartner, vice president of the High End Routing and Optical group, ran down the reasons with Light Reading.

1. CFP2 still isn't ready enough.
Speaking at the OSA Executive Forum on Monday, Gartner happened to be holding a CFP module (he'd brought it to compare to the size of a CPAK) and made the comment, "This is what we felt we were designing against." It's possible CFP2 and CFP4 will be coming out faster than Cisco was expecting, making the need for CPAK less urgent.

But there's more to it than that, Gartner tells Light Reading. CFP2s are being shown at OFC/NFOEC -- module vendors even held a contest around that -- but that doesn't mean they're ready to ship. "I'm pretty certain it'll be some time before I see qualified parts," he says.

By that reasoning, CPAK would still be a faster route to a smaller module, Cisco thinks.

Gartner stresses that he'll use other vendors' modules if they're suitable. But the company has its heart set on giving CPAK a try.

2. One port can serve many purposes.
Cisco wants one module for 40Gbit/s and 100Gbit/s, but CFP and its successors are built with just 100Gbit/s in mind. Cisco also likes the ability to make CPAK support whatever reaches it thinks are important. Three types of CPAKs were issued this week, conforming to different IEEE standards: SR10 (100 meter reach), LR4 (10km) and ER4 (40km).

3. It helps Cisco's margins.
But maybe not in the way you're thinking. Gartner acknowledges that Cisco sells optical modules at a markup, the rationale being that Cisco has already tested and qualified those devices. Some hardware resellers have begun offering off-the-shelf modules that could do the trick as well, theoretically cutting into Cisco's module sales. CPAK, being proprietary, wouldn't be subjected to that competition.

Cisco's bigger margin concern, though, is that "there's a lot of margin stacking" between component, subsystems and systems vendors, Gartner says. "You either have to find ways to collapse some of that or find ways for people to gain margin."

Running the numbers
Whether CPAK will have much impact on module vendors is debatable. Finisar would seem to have the most to lose, as it gets about 5 percent of its revenues from Cisco specifically for CFP and, possibly now, CFP 2 modules, according to analyst Michael Genovese of MKM Partners.

But the analysts differ on how much those revenues are endangered. James Kisner of Jefferies & Co. Inc. has been saying for months that the ramifications are huge. "The threat to Finisar’s Datacom business is now tangible," he wrote in January.

Genovese isn't as convinced: "The eventual timing and scope of impact is difficult to forecast, but appears to be limited," he wrote in a research note from OFC/NFOEC.

For more

Review all our OFC/NFOEC coverage at http://www.lightreading.com/ofc-nfoec.

— Craig Matsumoto, Managing Editor, Light Reading