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Mindspeed Claims SerDes Superiority

Chip maker says it has the best chip for 10-gig Ethernet, but Broadcom and Marvell disagree

November 7, 2001

5 Min Read
Mindspeed Claims SerDes Superiority

Competition -- and bickering -- among manufacturers of SerDes (serializer/deserializer) transceiver chips for 10-gigabit Ethernet equipment is hotting up following a further product announcement in this field from Mindspeed Technologies on Monday (see Mindspeed Unveils Transceiver).

Like all SerDes transceivers, MindSpeed’s new chip, called the SkyRail M27205, is designed for use in high-speed connections between bays of optical networking equipment or in backplanes that link together cards in a single chassis. The chip prepares signals by converting them from a parallel, low-speed data interface to a high-speed, serial interface, and vice versa.

In the case of this particular chip, the conversion is between an XGMII interface on the low-speed side and a four-lane XAUI interface on the high-speed side. The SkyRail M27205 implements the latest version of the evolving 10-gig Ethernet standard, according to Eli Massabki, director of product marketing.

It's the latest addition to the industry's widest portfolio of transceivers in this field, he claims. Mindspeed now has single, quad, and octal chips (see Conexant SkyRail Transceiver, Mindspeed Intros Transceiver, and Mindspeed Unveils Octal SkyRail).

Offering such a wide choice of chips is a big deal, according to Massabki, who says a customer might need an eight-channel device on a switch card and a single or four-channel device on a line card. "Customers will want to get all these [chips] from a single vendor," he contends.

Another important feature of all of Mindspeed’s SerDes chips is that they support variable speeds, thanks to their "Flexiclock architecture." This makes it possible for Mindspeed to claim that its chips will support a range of protocols, based on the fact that it can tinker with the bit rate if it becomes necessary.

As a result, the company says the M27205 can be used in 10-gig Fibre Channel equipment, an emerging standard that's very closely based on 10-gigabit Ethernet. "At this point it's identical; the only change is the bit rate," says Massabki, although he acknowledges that the standard is immature and could change significantly in the future.

As well as supporting different protocols, this feature also allows Mindspeed's part to be backwards compatible with old backplanes and backplanes that operate at non-standard data rates.

Most other SerDes chips operate at fixed line rates. The equivalent transceiver from Broadcom Corp. (Nasdaq: BRCM) offers a 3.125 Gbit/s data rate only. The one from Marvell Technology Group Ltd. (Nasdaq: MRVL) operates at 1.0, 1.25, 2.0, 2.5, or 3.125 Gbit/s.

Another point in Mindspeed's favor is that its four-channel SerDes chip takes advantage of clock-forwarding, a technique that allows the full bandwidth of the signal to carry data. It does this by eliminating the need for data encoding, thus reclaiming a 20 percent overhead. "This is equivalent to 4.25 Gbit/s with 8b/10b encoding," Massabki notes.

But while Broadcom and Marvell's chips might not be as flexible or cover as many applications, both companies insist that their chips perform better in the functions they can do.

Broadcom, for instance, claims to have the only SerDes chips that employ receive-end equalization -- a technique that automatically corrects for tranmission distortion after the signal has travelled across the backplane. Other SerDes vendors, including Mindspeed, use pre-emphasis, which involves manually tuning each channel at the transmit end. (Gennum Corp. is planning to offer chips that use receive-end equalization, but its chips will not have full SerDes functionality -- see Gennum Gets Dense.)

Marvell, for its part, throws cold water over Mindspeed's claim to have industry-leading jitter performance. In Monday's press release Mindspeed claims the M27205 is the industry's "most robust" SerDes transceiver, with a jitter performance exceeding that required by the 10-gig Ethernet standard.

Marvell begs to differ. Both companies exhibited their wares in their booths at the Communications Design Conference tradeshow in early October. "The eye diagram in the Mindspeed demo indicated poor jitter performance compared to the Marvell demo," Gary Smerdon, VP of marketing for Marvell's communications business group, writes in an email to Light Reading. "Also Marvell's demo showed performance over 40 inches of backplane with six connectors, whereas Mindspeed's was measured directly off the device." In other words, in Smerdon's view, Marvell's device was demonstrated under real-world conditions, whereas Mindspeed's was not.

Mindspeed notes that the chip in its demo was not the M27205, but the M27211, an octal SerDes transceiver that was unveiled at the beginning of October. However, given that the M27205 is based on the technology developed for the M27211, according to Massabki, this doesn't appear to let Mindspeed off the hook completely.

Mindspeed’s Massabki also manages to raise the hackles of Broadcom and Marvell by claiming that the SkyRail M27205 is the only SerDes chip that's "strictly compliant" with the latest version of the 10-gig Ethernet standard. Although the standard has yet to be finalized, the important parts of it haven’t changed in the last three revisions, he says. "Mindspeed has been working with version 3.3... 3.x is fairly stable. Anything below that is significantly different and is not interoperable."

Marvell unveiled its 10-gig Ethernet product, the Alaska X, in September 2001 and says it's compliant with version 3.1 –- a claim that Massabki disputes, saying it’s compliant with an older, 2.x version of the evolving standard.

Broadcom was first to market with a 10-gig Ethernet transceiver chip, its BCM8011, in May 2001, at which time it was based on version 1.2 of the standard (see Broadcom Offers 10-Gig Ether Bits). "Since then, we have updated/revved the design so that we are consistent with draft version 2.3, and we are unaware of any interoperability issues between draft 2.3 and 3.2," emails Dave Sorenson, Broadcom's product line manager for SerDes.

In any case, Broadcom will most likely upgrade its chip again, after version 3.3 is finalized, which is supposed to take place at next week's meeting of the IEEE 802.3ae working group, Sorenson adds.

Other vendors, such as PMC-Sierra Inc. (Nasdaq: PMCS), Texas Instruments Inc. (NYSE: TXN), and Velio Communications Inc., also make SerDes transceivers, but their devices are compatible with, as opposed to "strictly compliant" with 10 gigabit Ethernet (see Velio Cleans Up).

— Pauline Rigby, Senior Editor, Light Reading

Want to know more? This very topic is the subject of a session at Lightspeed Europe,Light Reading’s annual conference, on December 4-6, 2001, in London. Details: Optical Ethernet

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