LONDON — Bell Labs and FCI have demonstrated 25 Gbit/s data transmission over an electrical backplane using a signaling architecture developed by Lucent Technologies' R&D arm and the connector maker's AirMax VS system. This doubles existing rates and could lead to 100 Gbits/s Ethernet being sent over electrical backplanes.
The application of duobinary signaling — a technique that uses three electrical signal levels to represent binary code in a communications transmission to high-speed electrical backplanes — was first documented by researchers Jeffrey Sinsky, Andrew Adamiecki and Marcus Duelk, of Bell Labs Photonic Networks Research group at the IEEE International Microwave Symposium in June 2004.
"The group has demonstrated performance at 10 Gbit/s over several different legacy backplanes, and is supporting a movement to use this technique as part of the IEEE 802.3ap standard for 10G PHY (physical layer) Ethernet over backplanes," said Mary Mandich, a technical manager in Lucent's Network Hardware Integration Research Department.
Jeffrey Sinsky, lead researcher on the duobinary effort at Bell Labs said the group needed a connector with carefully controlled impedance characteristics, which prevents signals from bouncing back and forth, plus low crosstalk — as well as the novel signaling architecture — to achieve 25 Gbit/s rates.
FCI's AirMax VS shows extremely low loss at frequencies up to 15 GHz by using air as a dielectric. The connector's design does not require metal shields, yet exhibits lower crosstalk than existing shielded high-speed connectors.
"While the flexibility and cost of AirMax VS has made it a winner at 2, 3 and 6 Gbit/s, it is the connector's superior electrical performance that makes it the most attractive choice " and sometimes the only choice " at 10 Gbit/s and above," said John Burkett, FCI product manager.
The duobinary signaling architecture for electrical backplanes takes advantage of the "natural rolloff" tendency of a backplane instead of fighting
it like traditional approaches, and uses it to help shape the data bits and provide a clean signal at the receiver.
"With a small amount of additional pre-emphasis and equalization to correct the frequency response — technologies that already are commonly used with today's communications transmitter and receivers — the output signal at the backplane requires only half the required bandwidth of traditional systems. And, we can convert the signal from duobinary format back to a traditional format using high-speed integrated circuit technology," said Andrew Adamiecki, a researcher with Bell Labs.
The team achieved error-free performance at 25 Gbit/s over electrical traces as long as 24 inches using a backplane made with FR4 laminate.
