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Optical/IP

OIF Sets Short-Range Sonet Standard

Today, the Optical Internetworking Forum adopted two standards for very short range (VSR) Sonet interfaces (see OIF Announces VSR Specs). These specify two almost opposing ways of accomplishing the same thing – transmitting OC192 (10 Gbit/s) signals over distances up to 300 meters inside a central office or equipment room.

At present, carriers are using pricey, long-distance interfaces to do the job. "Carriers and network service providers can save thousands of dollars per interface by using OIF VSR interfaces to link colocated equipment," says Russ Tuck, chairman of the OIF's Physical and Link Layer Working Group, who is from Pluris Inc.

Of course, the main point of having a standard is to ensure interoperability with other vendors' equipment, which helps open up the market. "[VSR Sonet] gives our customers a choice of two more transponders. Since routers connect to a lot of other equipment, we think it's going to be pretty attractive," says Tuck, wearing his Pluris hat.

The first standard, OIF-VSR-01.0, is a parallel implementation of 12 channels, each at a wavelength of 850 nanometers and delivering 1.25 Gbit/s per channel over multimode fiber. Ten channels carry data, one is used for error correction, and one is a back up in case one of the lasers in the array should fail. For more details see http://www.oiforum.com/public/documents/oif2001-009.pdf.

The second standard, OIF-VSR-02.0, is a serial link using a single 1310nm laser to transmit 10 Gbit/s over singlemode fiber. The laser is an uncooled Fabry Perot laser, to keep costs down. For more details see http://www.oiforum.com/public/documents/oif2000-147.pdf.

Individuals involved in the OIF agree that the 12-channel implementation got passed because it was further along in the process -– it's been under consideration for a couple of years. Another important factor is that the components are relatively available, which improves its time-to-market. Agilent Technologies Inc. (NYSE: A) and Infineon Technologies AG (NYSE/Frankfurt: IFX) are among the companies that already sell 12-channel parallel links.

The serial 1310nm version of the standard was pushed through more quickly because it's the only one that supports singlemode fiber, according to Mike Peppler at Agere Systems (formerly Lucent Technologies Microelectronics Group), who is editor and "champion" of the 1310nm standard. Carriers deploy singlemode fiber almost exclusively and want to have something that is compatible with the existing wiring in their offices.

Originally, there were five proposals for VSR interfaces. Are the remainder defunct? "No," says Peppler. "None of the proposals get ditched; they are simply not as far along in the approval process."

However, some members of the OIF question the need for additional standards. Having too many standards would be as bad as having no standards at all.

Just to keep things complicated, a sixth proposal emerged last August. WorldCom Inc. (Nasdaq: WCOM) requested an interface that could support optical crossconnects (OXCs). That means the transceiver needs to be able to cope with additional losses in the link, when a signal from an input fiber is bounced off a mirror and back into another fiber. Cielo Communications Inc. and Picolight Inc. rose to the challenge. They proposed a 1310nm link based on vertical cavity surface emitting lasers (VCSELs) (see Laser Blazers).

Bob Mayer, VP of marketing at Cielo, figures the OXC-compatible solution may turn out to be the cheapest of the lot, since VCSELs should be cheaper than uncooled Fabry Perot lasers. Unfortunately, it's not that simple. "Everyone's trying to balance the time-to-market with the price and performance points," he notes.

— Pauline Rigby, senior editor, Light Reading, http://www.lightreading.com

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