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If 10Gigabit Ethernet has a problem, it's multiple personalities. 10G over fibre is well established as a network backbone technology, but in past generations it's been Ethernet over copper - and especially telephone-style twisted pair cabling - that has brought the big upsurge in usage and sales. 

While it's true that 10G over twisted pair is getting cheaper and less power-hungry, will it ever be cheap enough? And even if it is, how long it will take before it makes sense for server manufacturers to build it in?

"Most [10G] shipments to date have been optical fibre," says Jag Bolaria, senior analyst at the Linley Group. "We think in 2007 the market was about 700,000 switch ports, and this year will be something in the order of 1.2 to 1.3 million. To put that in perspective though, Gigabit is over 100 million ports and Fast Ethernet is over 200 million."

The problem is that fibre is too pricey to replace Gigabit to the server or desk. 10G over copper could fill the latter role, but is still maturing - with the exception of CX4, which is a short range (up to 15m) technology using relatively bulky cables.

The great hope among networking suppliers has been 10GBase-T, the standard for 10G over shielded or unshielded twisted-pair (STP/UTP) copper. It allows 10G to run up to 100 metres - or further, in some cases - over Cat6 cabling. 

Initial versions of 10GBase-T were costly and power-hungry, with server NICs costing over $500 and only just fitting within the 25W per slot specification for PCI Express (PCIe) expansion cards. 

Fresh chips

However, new chips on the way will make a big difference by halving its cost and power consumption, argues Kamal Dalmia, VP of marketing at Teranetics. His company recently began sampling a dual-port 10GBase-T PHY (or transceiver chip) that it claims needs just 6W per port. 

Other developers have also announced lower-power PHYs for delivery later this year or next, including Aquantia, Broadcom and Solarflare. All will be backwards-compatible with slower versions of Ethernet, so 10G switches and NICs can be used within existing networks. 

"The rule of thumb is the next Ethernet speed becomes attractive when it reaches three-times the cost, and Gigabit today is $100 a port. I expect 10G ports to be $250 to $300, where the first generation was $500," says Dalmia.

Switches will benefit most from the new PHYs now on the way, he says, adding: "The key factor is the ability to build 48-port 1U switches, because there's two main factors to switch density - power, and the physical size of the chip."

He explains that you can fit a maximum of 48 RJ45s in a 19-inch width, but when you put the PHYs on a circuit board behind that, they have to go in multiple rows. This PHY will allow 48 ports in just two rows - with more than two rows, the distance to the front panel becomes too long to meet the IEEE specs on the waveforms and the signal gets distorted. 

In addition, the lower power consumption means that a 24-port 10G switch might need 500W all told, Dalmia argues. That sounds like a lot, but it would offer the same switching bandwidth as ten 24-port Gigabit Ethernet switches, needing perhaps 150W each - a two-thirds saving, he claims.

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