Top BT man proposes web congestion charge

A couple of protocol tweaks could lead to lightning-fast browsing and end download caps – but they would need to be allied to a form of congestion charging, according to BT's chief internet architect.

Actually Bob Briscoe vehemently opposes the term congestion charge because he believes it has been tainted by its imposition of central London traffic. But as people would be charged for the congestion they cause, it is hard to see how he can avoid it.

Briscoe, who heads a BT team trying to steer the future of the internet, says much of the congestion on the internet today is caused by limitations in the hallowed TCP/IP protocols.

He points in particular to the Transport Control Protocol, which incorporates the principle of a fair share of capacity for each data stream.

This was good enough for the bursty traffic of the early internet but it becomes distinctly unfair in the age of applications such as peer-to-peer file sharing that stay online more or less continuously and can grab scores of data streams to speed up transfers.

Briscoe has no objection to heavy use of internet links. His proposals, which he is trying to get approved by the governing Internet Engineering Task Force (IETF), shift focus from data volume to what he calls congestion volume, as measured by the proportion of data packets dropped by congested routers.

He points out that lots of cars going down clear roads are no problem; it's when they go through crowded roads that the trouble starts.

The similarity with road traffic is close. Some of the mathematical analysis behind Briscoe's proposals was done by Professor Frank Kelly, who was chief adviser to the Department of Transport when the London congestion charge was introduced.

Briscoe proposes a measure called 'weighted TCP' that he says will speed up browsing while hardly affecting heavy traffic, and the use of a single bit left spare by the Internet Protocol that would facilitate the monitoring of congestion.

It would mean a congestion limit rather than a download cap. The limit would be paid for as part of a user's flat-rate broadband charge; a user who exceeds it could still use the internet but only along uncongested routes. But users pay more for a higher congestion limit, or to extend their existing one.

See Money for jams for an interview with Briscoe and a fuller explanation of how this would work.