Electronic Design

10-Gbit Ethernet Over Copper: It Had To Happen

We should have seen it coming. Once we got 1-Gbit Ethernet over copper, it was obvious someone would want to do 10 Gbits/s over copper also, even though we have a perfectly good 10-Gbit Ethernet (10GE) fiber standard with many suppliers. But while prices for fiber systems have been going down for years, they are still typically two to 10 times more expensive than almost any copper solution, depending on the application. Copper just makes sense economically.

Brad Booth, an architect in Intel's Communications CTO Office, says there was unanimous agreement at a recent IEEE 802.3 Working Group meeting to form two Study Groups to pursue two different approaches to 10GE over copper. One group will work toward a solution for 10GE over CAT5 unshielded twisted pair (UTP) for a distance up to 100 m. The other will address a shorter-range (10 to 15 m) version using the InfiniBand cabling scheme with dual coax cables (TwinAx).

TwinAx is easier, as it is based on available technology. Given a head start, this group could produce a final standard in a year or so. The UTP approach, which might be called 10GBaseT or 10000BaseT, is the real challenge. Can it be done? Probably.

How does one transmit 10 Gbits/s over a long twisted pair? It will no doubt be some mulitcable, multilevel coding and/or multilevel modulation scheme that most likely incorporates some kind of adaptive equalization. Doing 10 Gbits/s on CAT 5 won't be easy, and the IEEE standards process isn't fast. It could be three years before we see the final standard. By the time a 10GE copper solution emerges, further optical cost reductions may make it a real competitor.

We'll probably get 10GE copper to the desktop. Also, expect to see these systems used in storage-area networks (SANs) and to interconnect servers. Supercomputer builders will rejoice as they work toward linking thousands of processors at very high serial data rates. TwinAx ought to work well in those shorter-range applications. By then, a 40GE fiber local-area network (LAN) standard—the OC-768 Sonet wide-area network/metropolitan-area network is just about here—could be the backbone to link all these desktops to the LAN. And who's working on the 40-Gbit/s (or is it a 100-Gbit/s?) Ethernet standard? If no one is, this 10GE over copper effort will get the ball rolling.

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