The idea of using copper cabling for high-speed networking got a boost this spring when the Institute of Electrical and Electronics Engineers (IEEE) approved publication of the 10GBase-T standard.Meanwhile, the finishing touches are still being placed on another standard: Category 6 Augmented, or TIA/EIA-568 Addendum K. Cat 6A, as it’s usually called, is the standard for copper cable designed to carry 10 Gbps traffic as far as 100 meters.
The completion of the 10GBase-T standard brought an upsurge of interest in high-speed copper cabling, according to John Schmidt, senior product manager for structured cabling at ADC Telecommunications Inc. of Minneapolis, one of the pioneering manufacturers of twisted-pair cable capable of 10-Gbps speeds. However, there are few Category 6a installations today, and even fewer that are actually driving 10-Gbps traffic over those cables. To a large extent, Canadian organizations that are installing Cat 6a and even basic Category 6 copper cable are doing so mainly to prepare for a future they believe will eventually require higher network speeds.
That future could still be quite distant. Infonetics Research tracks shipments of 10-Gbps Ethernet ports, and “it’s a very small percentage of the market,” says Matthias Machowinski, directing analyst for enterprise voice and data at the Campbell, Calif., research firm. Of all the Ethernet ports shipping this year, about three quarters of one per cent will be 10 Gbps ports, Machowinski says.
However, some organizations are installing cabling today that can support 10 Gbps speeds. The reason is simple: future-proofing. Schmidt says cabling usually lasts through at least three generations of active network equipment such as switches – often for as long as an organization occupies its office space – so network planners usually install what they think they may need in a decade.
The Regional Municipality of Durham, east of Toronto, opened a new headquarters building in May 2005. Optical fibre links all its wiring closets, and pre-standard Category 6a cable runs to every desktop. High-speed copper is also used along with fibre in the data centre.
The municipality’s PCs have 100/1,000 Mbps network interface cards and the fibre backbone handles one Gbps per second, says Ron Blakey, manager of administration and strategic planning.
Despite an existing voice over IP application and plans to stream video over the network, Blakey doesn’t see an immediate need to increase bandwidth. But, he says, “the key there is the life of the building. Because it’s a public building, it’ll probably be here after I’m dead. It’ll probably have the same cabling in it, too.”
data centre main market for high-speed cabling
10GBase-T is not the only way of driving 10-Gbps traffic over copper cabling. It has been done for some time using InfiniBand Architecture – a standard for interconnecting servers and storage at speeds as high as 30 Gbps. While InfiniBand can use fibre, Thad Omura, director of product marketing at Santa Clara, Calif.-based Mellanox Technologies Inc., which makes InfiniBand products – says upwards of 95 per cent of InfiniBand traffic travels over copper.
InfiniBand does not use twisted pair, though. It relies on a special twin-axial InfiniBand cable, using at least four pairs. The standard four-pair InfiniBand cable carries 2.5 Gbps per pair for total bandwidth of 10 Gbps, Omura says, and 12-pair cable can handle 30 Gbps. Copper InfiniBand cable is only intended for distances up to 20 meters, because it is used primarily within data centres, where distances are relatively short. Omura says Mellanox has done installations that push 20 Gbps over the four-pair cable, but over distances of 10 meters or less.
Another IEEE standard, 10GBase-CX4, allows 10-Gbps Ethernet to run over four-pair InfiniBand cable. Like InfiniBand, 10GBase-CX4 is built for speed, not for distance – it is limited to 15 meters – and aimed mainly at data centres.
In fact, the data centre appears to account for most of the short-term market for high-speed copper cabling. Brad Booth, president of the Ethernet Alliance, says CX4 already has significant penetration in data centres, and there is considerable interest in 10GBase-T for extending the reach of high-speed copper. But even 10GBase-T is limited to 100 meters, and most network backbones require more than that, Booth says.
10 Gigabit over copper can’t travel very far
There is some potential for 10GBase-T in connecting desktop workstations with very high bandwidth requirements, such as those used for medical imaging or for computer graphics in the movie industry, Booth says. But for the most part, high-speed copper belongs in the data centre for the foreseeable future.
In fact, some argue the new 10GBase-T specification has limited value because copper’s role at 10 Gbps will be limited to very short distances. Dennis Almeida, director of sales at Vativ Technologies Inc. in San Diego, Calif., says his company was involved in the 10GBase-T proceedings but has opted not to produce products based on the standard, preferring to focus on proprietary physical-layer hardware for connections between backplanes less than 10 meters apart.
“We would love to do it if there was really a market for it,” Almeida says of 10GBase-T, but he argues that as 10GBase-T will require new, higher-speed copper cable, anyone looking for 10-Gbps speeds might as well install fibre.
One possible reason to choose copper would be a significant cost advantage over fibre, but the cost comparison remains unclear. While optical hardware has cost more than that for copper cabling in the past, Booth says it’s hard to assess total costs because 10GBase-T physical-layer devices aren’t in the market yet. When they appear, economies of scale will take time to develop. Their optical counterparts, on the other hand, have been in the market for a half-dozen years. “They’ve had a good six- to seven-year lead on copper,” Booth observes.
Another issue is the higher power requirements of the 10GBase-T standard. Lower power requirements have been a plus for copper in the past, says Booth, but “with 10-Gbps that’s not happening because it’s going to be much slower to bring that power curve down.”
Despite these uncertainties, copper could have a significant role. While most 10-Gbps installations to date have used fibre, Machowinski says, Infonetics expects copper to account for much of the growth in high-speed network cabling in the next few years.
With each increase in network speed and each new generation of cable, installation and testing become a little more complicated and unforgiving. The latest generation is no exception, experts say.
Crosstalk within cables – the tendency for the signal on one pair within a cable to interfere with the signal on other pairs – is a familiar concern with twisted pair. But with Category 6a cable, which operates at 500-megahertz frequency, alien crosstalk becomes a concern too. This is the problem of the signal on one cable interfering with the signal on adjacent cables.
wider conduits may be needed
The several manufacturers already making twisted-pair cable to carry data at 10 Gbps have taken steps to minimize the problem by making the cable thicker, thus forcing wires in adjacent cables to be farther apart, which cuts down on crosstalk.
This creates an additional installation gotcha, notes Schmidt at ADC. Since the cables are thicker, fewer fit in the same space. “What people need to think about when they’re building new facilities,” he warns, “is they need to make sure the conduit sizes are much larger than in the past.”
The way cable is installed also affects crosstalk. Ironically, Booth says, neatness counts against cable installers at high speed. Many installers like to bundle cables tightly and even “comb” them into neat bundles. That’s a bad idea at higher speeds, because the closer the cables are to parallel, the greater the crosstalk. Unbundling the cables for the first few meters helps, because the worst alien crosstalk problems occur near termination points, where strong signals originating at that network node interfere most with weak, attenuated signals nearing their destination.
To test for alien crosstalk problems, you need to put a signal through adjacent cables to see whether it affects the cable being tested, explains Brad Masterson, product manager for Canada at Fluke Electronics Canada, a Mississauga, Ont.-based subsidiary of network equipment provider Fluke Corp. Part of a testing kit Fluke introduced this year for 10GBase-T is the ability to simulate a signal on adjacent cables to allow accurate testing for alien crosstalk, he says.
Testing 10GBase-T installations will not be simple, Masterson warns, and cable installers will probably need to work at getting up to speed on the new technology. Industry organizations like Building Industry Consulting Service International Inc. (BICSI) will offer training and education to help. Work is also under way on testing guidelines that Masterson says will be codified as formal standards.
How widespread the need for 10-Gbps speeds will be remains to be seen, but if history is any indication, network traffic will expand to fill the bandwidth available.
“We’re certainly clever about how we can use the bandwidth that’s available,” Machowinski observes. So as volume drives down the cost of 10-Gbps installations and experience irons out the wrinkles in running such high-speed traffic over copper wire, no doubt a new and faster category will bring fresh challenges.
