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Engineers push beyond 10Gbit Ethernet limit

Posted: 10 Feb 2010 ?? ?Print Version ?Bookmark and Share

Keywords:Ethernet? 10Gbit data link? networtk? Serdes?

Pushing 25Gbits/s
Despite the hurdles, companies are inking 25Gbit/s Serdes into their road maps. One chip maker aims to deliver a component with 25G Serdes in 2011 using 28nm technology; another hopes to meet a similar target with a 40nm process. Neither is willing to talk about its plans because they consider the Serdes capability so strategic.

Members of the OIF have spent five years working toward their current draft spec for 25G Serdes and channels presented at an open workshop.

"We have been going back and forth discussing channels and signaling, and it's gotten to the point that it starting to become feasible," said David Stauffer, a senior member of technology staff at IBM who chairs the OIF's physical and link layer working group writing the 25G standard.

A proof-of-concept demo from the group used a tried-and-true non-return to zero signaling technique. However it did require both continuous time equalization and decision feedback equalization at the receiver, Stauffer said.

The combination of old and new techniques will not be easy to master for the uninitiated. Engineers say it would require a relatively exotic process technology such as silicon germanium to deliver 25G Serdes today.

The OIF demo did not use any working chips. Instead engineers created a simulated 25G Serdes stream and ran it over a prototype backplane board. Even then, the board company whose backplane was used insisted it remain anonymous so competitors would not know about its capabilities yet.

Despite the challenges, tomorrow's 25G components need to consume no more than 1.5x the power of today's 10G parts. "If we use more no one will buy them," Stauffer said.

The Ethernet community appears to be solidly behind the OIF draft specs. D'Ambrosia showed a slate of six new IEEE 100G Ethernet specs that could save cost and power if they migrated to new 4 x 25G configurations, though he stopped short of announcing a call for interest in such standards.

"The next electrical interfaces will clearly leverage 25G signaling," D'Ambrosia said at the OIF meeting.

A Broadcom senior engineer suggested today's 10x10 links are seriously constraining the number of 100G Ethernet ports that can be put on a telecom line card. A move to 25G links could enable smaller form factor 100GE modules, said a representative from Cisco Systems at the meeting.

Other communities including Fibre Channel and Infiniband are increasingly taking a close look at the OIF work.

A representative from Brocade told OIF members the Fibre Channel sector could move to 16 Gbit/s links as soon as 2011, although most backplanes are still running at 3- to 6Gbit/s. A 16G Fibre Channel standard could be complete by June and work on a 32G standard has started.

A representative from Xilinx told OIF members 25G signaling will be needed for chips, modules, backplanes and even passive copper cables in Ethernet, Fibre Channel and Infiniband interconnects. The group also needs to modify a draft 28G standard aimed at ASICs and modules, he added.

- Rick Merritt
EE Times


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