DOCSIS is the international standard for providing data over cable, allowing Internet services to be provisioned alongside television channels. Cable operators have begun to make announcements as they migrate to DOCSIS 3.0 which put them ahead of the ADSL2+ phone-line operators. Some, like the UK's VirginMedia are making bold claims - "The UK's fastest broadband is over fibre", referring to their hybrid fibre and coax (HFC) network.  But will the fastest broadband be over cable for very long?

This latest European DOCSIS version supports about 55 Mbps per channel, and with channel bonding can be made to deliver 444 Mbps but this would eat 8 analogue TV channels along the way - DOCSIS is just a TV channel to the coax network. In today’s standard definition TV world this might not be a major headache as one analogue channel may carry 10 digital channels in a single multiplex but as the move to HD channels accelerates, a multiplex might only carry two or three channels of high-quality video; channel real-estate is about to become more of a premium again. Each channel allocated to internet access erodes the cable operators ability to deliver other media, and offering the full 444 Mbps today may reduce the channel count by 80 - robbing peter to pay paul.

As with a PON network, this bandwidth is shared between the users on a fibre-port – and cable companies typically group large numbers of coax subscribers on a single fibre port - in fact there could be several hundred subscribers per optical port! The latest version of DOCSIS may be able to offer over 400 Mbps but it may be contended at 400:1 before traffic even gets to the Internet.

So can DOCSIS 3 really be called a Next Gen technology? It doesn't feel like it. A polemicist might even say it’s more of a final throw of the dice for the old generation; without a major overhaul of the DOCSIS standard ebabling it to deliver more than just some channel bonding or inrementally better compression it’s hard to see how it will be able to keep up with the conflicting demands of HD content, increased video on demand, and ever higher bandwidths. The first generation of fibre technologies, PON and home-run Ethernet, sets the bar higher and is already able to race ahead.

The move by the cable companies should be welcomed - it proving there is demand for higher bandwidth services and it is helping this market sector regain come confidence. But we shouldn't begin to think of DOCSIS over a hybrid-fibre network as Next Generation.