To hear some people talk, you'd think copper cabling at the WAN level was passé, being replaced by fibre-optics. To them, fibre is where it's at - even outside the office, where they're boosting FTTH, or fibre-to-the-home.

Yet where are the teams of workers digging up the streets to lay all that fibre? They're not there, and neither is the fibre. The truth is that most commercial and residential sites are still connected by copper - or if you're the unlucky inheritor of certain past cost-cutting measures, aluminium.

That's why at the recent NetEvents forum, quite a few of the high-level discussions involved new ways of using that copper plant. In particular, that's ways to run long-range Ethernet connections over copper - such as a project called Carrier Ethernet, which has been co-ordinated by the Metro Ethernet Forum (MEF).

"Ethernet services are becoming mainstream," says Chip Redden, VP of marketing and product management at Overture Networks. "Everyone's focused on fibre and talks about copper being legacy, but there's a heck of a lot of copper out there and it ain't going away any time soon, so it's got to be used.

"For example, only eight percent of European office buildings with more than eight people have fibre, and in the US it's only 14 percent. All those remote offices too - most will be on copper. So you have to have a solution for copper - plus, a lot of service technicians know how to provision and test a T1."

Emulating TDM

So Overture has developed technology to bond several E1/T1 links together, run Ethernet over them. Like several other developers, it then uses circuit emulation to create a legacy TDM link for voice telephony over the packet network.

This is another area where the MEF has been active, says Olle Gustafsson. He is standardisation director at Ericsson Broadband Systems, but he also works with the MEF, and says it has developed "a test suite to prove that the IP circuit and equipment can do [TDM] circuit emulation."

He adds that there is still a clear need for TDM services, but as a network technology it's going to lose out to Ethernet and IP.

"This issue is E1/T1 scalability - Ethernet is more scalable. But the operators wanted to be sure Ethernet was as reliable as E1/T1," he says. "It's the same decision that enterprises took in deciding that Ethernet was ready and mature enough for mission-critical applications."

It would probably have been possible to update TDM beyond the limits of E1 and T1 - that's 2Mbit/s and 1.5Mbit/s respectively. Gustafsson argues though that it is easier to simply move over to Ethernet - not least because Ethernet is a much bigger market, so it offers economies of scale that an uprated TDM would not have.