Last year, high-order virtual concatenation (Vcat) took center stage at shows like Supercomm. Why not? High-order allows carriers to provision services at the STS-1 level and make their Sonet rings a lot more Ethernet-friendly.

It's funny how things change in a year. With interest in Vcat settling down, there is a renewed push in the sector to move Vcat technology from its high-order road to a low-order path, where traffic can be provisioned at a VT1.5 level in the United States.

The motivation lies in efficiency. The people who once hailed the praises of high-order Vcat now say it might not efficiently meet the requirements of end users, who probably don't need 50-Mbit pipes to carry their Ethernet traffic over Sonet networks. By using low-order Vcat, you can provision traffic in 1.5-Mbit chunks and make Ethernet traffic delivery even more efficient.

On the surface, the argument makes sense. Bandwidth is clearly not free, as carriers and the stock market learned over the past few years. So the trick is packing as much as possible into a single pipe, an approach that fits well with low-order Vcat.

Almost all Vcat framer/mapper companies are developing low-order Vcat solutions. But when you ask OEMs whether they plan to implement the technology, the reaction is lukewarm at best. Most think that the move to low-order Vcat is unnecessary and that high-order STS-1 provisioning is the way to go for now.

The OEMs may have a point. While I agree with chip vendors that OEMs know how to provision T1s and that low-order Vcat is an extension of that provisioning, you have to wonder whether carriers will really want to deal with the processing overhead and management that low-order Vcat requires. At the STS-1 level, carriers are dealing with 48 channels in an OC-48 pipe. That number jumps by a factor of 28, to 1,344, when implementing low-order Vcat. That's a heck of a lot of channels to process, provision and manage, even for the most T1-savvy carrier.

Chip companies insist that there's a big market for low-order Vcat. But, with OEMs wavering on the topic, it's fair to ask whether taking the high road may still be the better option.

Robert Keenan (rkeenan@cmp.com) is the editor in Chief of Commsdesign.com, an EE Times network web site. He is substituting for Jeremey Donovan, who is taking a break.