Comms chips

Copper Battles Optics in Backplanes

A couple of vendors have announced chips that could extend the life of copper in telecom backplanes -- the connections between shelves and racks of equipment inside optical networking gear.

Today Accelerant Networks Inc. announces its second product, AN5500, which can transmit a total of 31.25 Gbit/s of data over the copper traces that make up printed circuit boards (see Accelerant Intros Transceiver). Not only does it deliver more total bandwidth than existing solutions, the chip also increases the amount of data per individual copper trace. Accelerant has designed the chip to send 6.25 Gbit/s of data per channel, twice as much as existing products.

And speeds are going higher. Yesterday (April 22) Broadcom Corp. (Nasdaq: BRCM) announced a chip called BCM8102, which delivers a single serial 10-Gbit/s signal over a copper trace (see Broadcom Sends 10-Gig Over Copper). This chip was used to send and receive signals over 30 inches of FR-4 (a standard PCB material) in a private demonstration at the Optical Fiber Communication Conference and Exhibit (OFC) in Anaheim, Calif., last month, the company says.

Right now, many systems vendors are using -- or considering using -- parallel optical modules to connect their high-speed backplanes, because optics can travel farther at high speeds (see Parallel Optics Boosts Bandwidth). Will the new products from Accelerant and Broadcom make copper look more attractive again?

The verdict seems to be that for companies like Juniper Networks Inc. (Nasdaq: JNPR) and Pluris Inc., which are building massively-scaleable "terabit" routers, parallel optics may still be the best option (see Juniper Goes Terabit With the T640). But for smaller switches and routers, these new chips may allow vendors to stick with copper, which is cheaper, rather than force an upgrade to optics, says Jim Tavacoli, Accelerant's VP of marketing.

The drawback is that both products are unique, so systems vendors must use the same chip on both ends of the link. "This has been an issue with customers," says Tavacoli. But, he contends, when they realize what performance improvement they are getting, they are prepared to make the tradeoff.

"I firmly belive that as higher speeds are reached, interoperability will be impossible until standards are agreed to," he adds. There is no standard at present, but a group of twelve companies is aiming to form an industry consortium to promote the development of 6.25-Gbit/s links, he says. The consortium won't be announced for a few months yet.

— Pauline Rigby, Senior Editor, Light Reading
reoptic 12/4/2012 | 10:32:31 PM
re: Copper Battles Optics in Backplanes Like any battle between a mature (copper) and emerging technology (VCSEL), the mature products tend to last a lot longer than people think. Why? First copper is much cheaper than optical connections by a factor of 10. Second, copper connections burn less power as there are no lasers. Third, over a short range they can carry plenty of bandwidth. Lastly, because they are mature they are a lot more reliable than optical links. So while a lot of folks are touting optical for the future, copper is where the volume is today and for some time.
CMOS 12/4/2012 | 10:32:29 PM
re: Copper Battles Optics in Backplanes BRCM is pitching 10G CDR. Accelerant is pitching multi-level signalling scheme. Both are not real backplane solution. The world is really looking for strict NRZ CML SerDes that can drive FR-4.

When are they going to get a clue?
Xile 12/4/2012 | 10:32:24 PM
re: Copper Battles Optics in Backplanes I was under the impression that BRCM's approach was NRZ CML. Did I miss something?

Also, the battle lines between NRZ and MLS somewhat market segment driven. MLS is attempting to boot strap bandwidth legacy backplanes in the field. Higher speed NRZ is targeted toward new backplanes in development.
There is, of course, overlapping areas for both depending on the requirements of the backplane (from a signal integrity perspective) and the bandwidth demands.

The interesting new dynamic in all this is optical backplanes - specifically "without fiber". Cu regardless of coding will run out of gas somewhere between 12 and 25Gbps (IMHO). Optical backplanes will likely have to fill this need however, the limitations of fiber will be an inhibitor.

If I were Sanmina or others building backplanes now, I'd be investigating PCB waveguide development.
spookydoodle 12/4/2012 | 10:32:24 PM
re: Copper Battles Optics in Backplanes Well said Reoptic - but copper lines would also increase interference without proper shielding. Transmission on copper is also dependant on the shape of electrical pulses ......
taro 12/4/2012 | 10:31:19 PM
re: Copper Battles Optics in Backplanes Marvell demonstrated 10 Gigabit Ethernet Operation
over 15 meters of standard copper cable: This
invades the territory of fiber backplane interconnect vendors like www.coronasystems.com


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