The real reason Skype isn't as good as it was

"Filesharing means the narrowband upstream is being consumed by peer to peer; other people on the fibre node are being compromised, said a Sandvine official today. "The traditional way for ISPs to cope, was to add extra CMTS or cable ports, or pulling more fibre or reduce the contention - the sharing of nodes; so, if they had 1000 homes per node, they'd change that to 500 or even 250 homes per node."

Sandvine can take that expensive option, and make it cheap for the ISP. "We can make this a $2 per household cost by building our product just north of the access network," said a company spokesman.

It's done by inspecting the packets as they are transmitted through the network. Voice calls can be detected by their "signature" and when too many people are doing Skype or Vonage or Free World dialup calls, the ISP can set limits.

After (say) 100 sessions are started, "we can disconnect, or block new ones, or even slow down the rate they are transmitted," said Sandvine. "With customers who use this technology, we've got the traffic from 70 per cent to 20 per cent," he boasted.

One reason ISPs like doing this, is to encourage their customers to use the company's own VoIP system, rather than a rival's. If the packet is void, and is detected as from the cable company's own product, it is optimised - sent through faster than normal. Other packets are allowed to take their place in what's left of the queue.

He said: "A year ago, 90 per cent of VoIP was Skype; today is more like 50 per cent as the service provider favours their own service. So they prioritise their own branded VoIP services when the network is congested. "They don't manage Skype or Vonage down. They just do 'best efforts' for them, but generate superior quality for their own."

That's clearly one way of looking at it. When you actually block sessions from starting on peer to peer networks, it would be quite easy to persuade some users that you're managing it down.

This isn't a secret. Sandvine's ability to manage VoIP packets has been published before. What wasn't realised was just how big an impact this sort of traffic management was having on users. ®