Comms chips

Velio 'Eliminates Framers'

Chip maker Velio Communications Inc. claims that its new family of Sonet-optimized backplane transceivers could help systems vendors save money by eliminating costly framers from their line-card designs (see Velio Adds to SerDes Line).

"It's not a universal replacement for framers; that would be an overstatement," says Velio's VP of marketing Bill Woodruff. "But you see framers in a lot of places in a line card where the full framer functionality is not required. You just need some artifacts that happen to be in framers." The most useful "artifacts" have been built into Velio's new chip family, he says.

Velio hopes that these extra features will give it a competitive edge over the two incumbents in Sonet backplane transceivers, namely Applied Micro Circuits Corp. (AMCC) (Nasdaq: AMCC) and Vitesse Semiconductor Corp. (Nasdaq: VTSS).

There are two chips in Velio's new product family. The VC1022 is targeted at protection switching applications, while the VC1021 has been designed with very-short-reach (VSR) optics in mind.

Like all backplane transceivers (also called SerDes for serializer/deserializers), the new chips are designed to send and receive signals over high-speed electronic backplanes, the connections between cards or racks inside telecom equipment.

To make the chips OC192 (10 Gbit/s) Sonet specific, they implement an SFI-4 (SerDes Framer Interface - Level 4) interface on the low-speed side, which is a 16-pin, 622MHz standard from the Optical Internetworking Forum (OIF). Most framers on the market today have SFI-4, so this allows a "glueless" connection between the framer and the backplane transceiver, says Woodruff. On the high-speed side, the interface runs at 2.488 Gbit/s or 2.67 Gbit/s -- one speed for OC192 (10 Gbit/s) Sonet, the other for traffic encoded in digital wrappers.

As noted, the VC1022 chip is designed with protection switching in mind, and to that end it has double the number of channels on the high-speed side (eight rather than four), which enables a single chip to talk to both the working and protection switch fabrics.

According to Woodruff, the most important feature of the VC1022 is that it is "hitless," meaning that no data is lost during the changeover from working to protection fabrics. This is achieved by monitoring the position of the so-called a1a2 boundary, which marks the beginning of each Sonet frame. That way the switch can only be made between frames of data, instead of in the midst of a frame transmission.

"In a packet world you can make the switch at any old packet boundary," explains Woodruff. "In Sonet, you have to wait for the start of a new frame. If you don't, it will take about a millisecond until the downstream framer recovers."

Hitless switching isn't unique. The competing product from Vitesse, the VSC9180, also claims to do hitless switching. However, Vitesse's is only a 2.5-Gbit/s device, and doesn't double up on outputs, so it would require eight chips from Vitesse to do the work of one chip from Velio. Vitesse could not be reached for comment.

Another feature -- which Woodruff claims is unique -- is that the new chip monitors the bit error rate on both its active and inactive channels, so that a system can't switch over to a channel that has worse signal quality. Previously, Woodruff says, two framers were required to do bit error rate monitoring, one for the active channel and one for the inactive channel.

Velio's VC1021 is similar to the VC1022, but only has one set of high-speed serial outputs. Rather than sending signals over a backplane, it targets the Sonet VSR 4.3 standard for optical modules, which delivers 2.5 Gbit/s over each of four parallel wavelengths.

"There are three [approved] standards for VSR, but only two of them are in moderate use," Woodruff notes. "The third [Sonet VSR 4.3] is not used because so far there hasn't been a good IC to address it."

The VC1021 is the answer, he says. It includes a feature that allows the chip to recognize where the most significant bit (MSB) of the incoming data is. Without this feature, customers might need to use a framer to align the data correctly, and that adds to the cost significantly. AMCC, for example, sells a package that includes the AfterBurner optical module from Blaze Network Products Inc. along with its Sonet backplane transceiver, the S2509 Verrazano, and a framer, the S19203 Hudson.

Velio is expected to back up its product introduction with three announcements today, detailing interoperability testing of its Sonet backplane transceiver with FPGAs from Altera Corp. (Nasdaq: ALTR) and Xilinx Inc. (Nasdaq: XLNX), as well as with optical modules from Alvesta Inc. These are aimed at providing hard evidence that the chip works in real systems.

Velio has already proved the basic ability of its backplane transceivers to deliver clear signals over long backplane traces. It introduced its first backplane products a year ago and appears to have gained a good reputation in this respect (see Velio Cleans Up and Velio Introduces Transceiver Suite).

The VC1022 costs $275 apiece in quantities of 1000, while the VC1021 costs $175 apiece in the same quantities. Both parts are sampling now.

— Pauline Rigby, Senior Editor, Light Reading

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