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Speeding Right Along

10 Gb/s Ethernet over UTP Cabling is creating a flurry of excitement in the cabling industry.


March 1, 2003  


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For this month’s column I’d like to discuss efforts underway in the IEEE 802.3 LAN/MAN Working Group that is studying the feasibility of 10 Gb/s data transmission speeds over UTP cabling.

It is creating quite a flurry of excitement in the cabling industry, as the technical wizards probe new horizons for copper, like a fast moving train travelling at 500 m.p.h. on train tracks where 100 m.p.h. seemed like quite an accomplishment just a few years ago.

It raises the eyebrows, can this be done, how, and does it make sense compared to other means of transportation?

I have used the analogy of the fast speed train to give a mental picture of the scope of the work required. We are looking at a technology that is two to three years into the future. Let’s take this analogy one step further and understand how this can be done.

TECHNICAL FEASIBILITY

One advantage of balanced twisted pair cabling is that the transportation medium is in fact four sets of tracks in parallel, corresponding to four twisted pairs of copper. Therefore, the information capacity is quadrupled. That means that to achieve a combined capacity of 10 Gb/s, the transmission speed is 2.5 Gb/s per track.

Let’s look at another advantage that comes from optimizing the design of the transportation vehicle or boxcar. One way to do this is through increasing the efficiency of the line encoding, which determines the number of bits in each boxcar. The current technology for Gigabit Ethernet (PAM-5) accommodates two bits per boxcar. A proposed line coding design for 10G Ethernet (PAM-9 or PAM-10) is looking to increase the efficiency up to 4 bits per boxcar.

In the jargon of Ethernet, a boxcar corresponds to a Symbol. Therefore, to achieve the same bit rate, the speed of the moving train is now reduced to (2.5 Gb/s / 4) = 0.625 Giga Symbols per second or 625 Mega Symbols per second. So we can imagine if we are standing on the side of the tracks, and counting the number of boxcars that pass by, we are counting 625 million boxcars per second.

It would seem like quite a blur to me, yet in the world of bits, bytes and symbols, things move at a blinding speed, indeed.

How does this compare with Gigabit Ethernet? The comparative speed for 1G Ethernet is 125 Mega Symbols/ second, which is a little more manageable. Not quite slow motion, but a little less stressful on the train tracks.

This gets me to the next point. To support five times the speed for each moving train (equivalent to bandwidth in the world of cabling) we need to do something drastic to improve the design of the locomotive and boxcar. But also, the train tracks need to be relatively straight, without any sharp bends and obstructions and relatively smooth and sturdy.

The corresponding parameter that determines the speed and the performance for cabling is the Signal-to-Noise Ratio. The technical wizards can design a vehicle suspension system to compensate for some of the bumps and grinds along the way and a sophisticated control system to tilt the vehicle to counteract centrifugal forces, yet the condition of the train tracks is critical in the overall performance.

The other interesting aspect about the world of cabling is that the trains can be considered as ghost trains. Each train track can support two directions of transmission simultaneouslyWe can visualize two high-speed trains running through each other as if the oncoming train was in another dimension. It’s like looking through a mirror in Alice in Wonderland. A better analogy in the physical world is two waves crossing each other on the surface of a lake.

Getting back to the real world, the IEEE study group is now examining the technical feasibility to support 10G transmission rates over Category 5, 5e or better cabling. Category 6 is well positioned to support these data rates because of a significantly higher Signal-to-Noise ratio and bandwidth. Yet at the time of writing, only about 15 per cent of the installed base cabling is Category 6.

In summary, 10GbE is an exciting new development for copper which offers great potential for the future. Time and speed are closely inter-related. What it means is that faster than I can say, here is the data, I can send you 500 MB of data in less than one second. Having timed this using my current network connection at 100 Mb/s it would take anywhere from two to five minutes. Happy computing!CS

Paul Kish is Director, IBDN Systems & Standards at NORDX/CDT. He is also vice chair of the TR-42 engineering committee.

Disclaimer: The information presented is the author’s view and is not official TIA correspondence.


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