OIF Moves 100G Forward with DP-QPSK

Standardized Modulation Technique Should Help Drive Down Costs, Expedite Product Availability

The Optical Internetworking Forum (OIF) has locked in on DP-QPSK for 100G long-distance DWDM. The creation of a standardized modulation scheme should speed to market the delivery of more affordable and integrated optical components for this application, according to the group.

“The reason that OIF started that project is we’ve seen the great demand from carriers, in particular carriers in the United States, that want to be able to introduce 100G technology in their long-distance networks, as soon as possible,” said Joe Berthold of Ciena, who is the 100G project editor and a former president at OIF. (Berthold declined to proffer a view on when 100G gear will become available, but optical vendors interviewed by xchange at the NXTcomm event in June indicated early trials and deployments should begin in the 2009-2010 time frame.)

Berthold added that some of the push for a modulation standard may have been driven by “a fear” in the industry that 100G would end up like 40G, which has seen limited deployment. Providing optical component suppliers ─ which have to spend money to develop small and inexpensive solutions ─ with standards will help them move forward with those investments and, thus, move this market forward, he said.

“... if they’re faced with a variety of possible options, not knowing which will take off in the marketplace, they’ll just sit back,” Berthold said of the component companies, explaining that turnkey equipment suppliers ─ such as WDM transmission system, router and Ethernet switch vendors ─ emphasized to OIF the need for a robust supply chain around 100G. Creating standards around 100G, he added, will bring more cost-effective products to market sooner.

Of course, the OIF’s selection of DP-QPSK is just one standard effort around 100G long-distance DWDM, said Berthold. The IEEE is working to define the signal, he said, adding, this work presumes there is a whole fiber. The ITU, meanwhile, will be working on how to map signals and assign those signals overhead to allow for network management within transport networks, he said.

The ITU also was expected eventually to standardize modulation schemes, interfaces and wavelengths for 100G long-distance DWDM, Berthold added, but work on those issues wasn’t expected for a while, so the OIF got to work on the modulation issue. The OIF’s Physical & Link Layer Working Group put DP-QPSK on the table at its meeting in May, he said. When no other option was presented to the group, it locked in on DP-QPSK last month. OIF tomorrow will put out a formal news announcement on its selection of DP-QPSK for 100G.

The DP in DP-QPSK stands for dual polarization. That means there are two 50G optical signals, one field going up and down and the other moving side to side, within the same window. This method helps avoid signal interference and doubles spectrum efficiency, explained Berthold. The QPSK part stands for quadrature phase-shift keying; that means that rather than seeing 1s and 0s by turning a light on and off, the system shifts the phase of an optical carrier. There are four phase states resolved in this receiver technique. “That again takes your data rate down,” said Berthold, "So you’re down around two 25gigabaud signals."

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