Electronic Design

"10 Gbits/s Over UTP? Gimme A Break!"

That's basically what I said to Ron Cates, vice president of marketing at SolarFlare Communications, when he announced that his company had successfully demonstrated 10 Gbits/s over CAT5e UTP (unshielded twisted pair) cable.

With all that inductance and capacitance, crosstalk, and noise, I still believe that even the older 100-Mbit/s and 1-Gbit/s Ethernet performance over CAT5 is a bloody miracle. But 10 Gbits/s? Doesn't that defy some laws of physics or come close to perpetual motion? I guess it doesn't, given the SolarFlare demo.

Doing 10 Gbits/s over copper isn't actually new. It's routinely done over long pc-board runs on backplanes (up to about 70 inches or so) and on Twinax cable up to about 15 meters. But it's unusual when going over UTP at a distance of 50 to 100 meters.

Thanks to advanced CMOS processes and some proprietary designs and signal processing algorithms, it's possible to transmit at such an advanced data rate over copper. The design of SolarFlare's new Ethernet transceiver chip uses a scheme where the 10-Gbit/s serial signal is coded with 3 bits/baud/twisted pair using PAM-10 modulation.

All four twisted pairs are used, with the baud rate at 833 Mbaud/s. Error correction accounts for two of the pulse-amplitude modulation (PAM) levels. The method works with CAT5e or the newer CAT6. A four-dimensional trellis-coded Viterbi algorithm is used for symbol detection. With this arrangement, a bit-error rate of 10−12 is possible.

The key to making this work is a proprietary DSP that allows the signal to be extracted from all of the noise produced by near-end crosstalk (NEXT) and far-end crosstalk (FEXT), as well as all of the other stuff picked up by the UTP. A super-fast 9-bit analog-to-digital converter converts the signal to digital for the DSP that handles the echo cancellation, noise filtering, and adaptive line equalization. The expected result is 10 Gbits/s at a range up to 100 meters of UTP.

While optical 10-Gbit/s Ethernet is available now, it's still pretty expensive. Only those who need this super speed can justify the expense. And after all, most local-area networks are just now adopting 1-Gbit/s Ethernet (1GE) in backbones and the aggregation of the still dominant 100-Mbit/s Ethernet.

But with 1GE now built into the motherboards of most new PCs and laptops, 1GE to the desktop is gaining popularity. Soon, the need for the switching and aggregation of 1GE streams will be common. A 10GE system using the same UTP as 1GE would save tons of money as well as greatly speed up adoption. With over 800 million Ethernet ports installed and most using UTP, it makes a lot of sense economically to eventually put 10GE on the same wiring.

SolarFlare hopes that the IEEE's 802.3an Task Group will adopt and eventually approve its method as a physical-layer standard. The group is responsible for developing a standard for 10 Gbits/s over copper.

No timetable was given for the availability of the real 10GE transceiver. With the demo clearly successful, it can't be that far away. Look for competition from Intel, Broadcom, startup KeyEye Communications, and others.

SolarFlare Communications Inc.
www.solarflare.com

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