Over the past few years, Ethernet speeds have gradually caught up with Sonet. Now there's a possibility that 40-Gbit/s transmission technology might get deployed in Ethernet environments ahead of Sonet ones.

The reason is a simple one: cost. History has shown that telecom operators only start upgrading transmission networks when there’s a strong economic argument to do so. And there's reason to believe that 40-gig Ethernet gear will prove to be 35 to 40 percent less expensive than 40-gig Sonet gear, according to Menachem Abraham, president and CEO of Mintera Corp., a startup developing 40-gig subsystems.

The potential savings could be even larger, because telecom operators will be able to avoid using expensive Sonet interfaces in other equipment such as routers, Abraham adds.

The best way to understand this argument is to consider a typical arrangement with a router connected to a 40-gig transmission system, via a 10-gig connection. If this is 10-gig Ethernet, the transponders at either end of the connection (which convert optical signals into electrical ones and vice versa) are likely to cost 80 percent less than those of 10-gig Sonet connection, according to Abraham.

Moreover, the use of Ethernet avoids a lot of complicated synchronization and multiplexing of signals inside the 40-gig gear, says Abraham, who points out that this eliminates the need for a couple of expensive Sonet chips. All that’s needed instead is a relatively low-cost asynchronous multiplexer that combines flows from different routers without carrying them in separate channels.

To understand this more fully, take a look at Light Reading's latest report, 40-Gig Forecast, published today. A diagram on page 4 identifies the key elements in a thoroughbred 40-gig Sonet system. In an Ethernet environment, a much lower-cost receiver could be used, and the Sonet processing block and Sonet mux could be replaced with a single, simple G.709 async mux, as already noted.

Abraham says he can already see the day when routers will have 40-gig Ethernet interfaces that will connect directly with the 40-gig forward error correction chip in this diagram. “I believe that 40-gig Ethernet may get enough momentum that people in the IEEE [Institute of Electrical and Electronics Engineers Inc.] will want to ratify it as a standard,” he says. “The cost savings are tremendous.”— Peter Heywood, International Editor, Light Reading http://www.lightreading.com