Ericsson AB (Nasdaq: ERIC) is trying out a 100Gbit/s technology that doesn't fit the Optical Internetworking Forum (OIF) framework but might have a place as a low-cost alternative.

Not yet ready in product form, Ericsson's 100Gbit/s technology uses 16-QAM modulation (meaning it encodes four bits at a time) that's been derived from the company's microwave and Long Term Evolution (LTE) work. Ericsson has put it through an 800km (497-mile) trial run in Sweden, as announced last week. (See Ericsson Assists in 100G Trial and Ericsson Completes 100G Trial.)

The point of the OIF framework -- a semi-formal standard for 100Gbit/s optical transmission based on coherent detection -- is to keep costs down by pointing vendors in the same direction. And Ericsson is working on an OIF-compliant 100Gbit/s technology, likely to be ready mid-2011, officials say. (See 100G Standards Aim for Lower Costs.)

So, why deviate from the pack with 16-QAM? For one thing, Ericsson sees potential in applying Ericsson's techniques to 400Gbit/s or faster speeds, a level at which the industry is still open to answers. (See The Terabit Ethernet Chase Begins and 100G Watch: Google Complains Again.)

More immediately, though, the technology might be just plain cheaper.

"It uses polarization multiplexing and coherent detection and DSPs [digital signal processors]. However, we have combined a simplified optical stage with a more advanced RF stage," says Tore Smedman, Ericsson's head of evolved transport platforms.

That last part means Ericsson can use cheaper chips in the optical stage. Specifically, the DSP gets its data at a slower bit rate and therefore doesn't have to be as sophisticated as the DSP in the OIF framework. (Whether that bit rate is low enough to use an off-the-shelf DSP, Smedman isn't saying.)

More of the processing does get pushed into the RF stage -- but that area has a ready supply of commoditized components, Smedman says. Again, that results in making things less expensive.

Ericsson isn't saying when (or even whether) 16-QAM 100Gbit/s will be put into a product.

— Craig Matsumoto, West Coast Editor, Light Reading