Theodore Peckler lives in Monrovia, California, and is one of the 1.5 million people in the US who uses Voice over Internet Protocol (VoIP) systems to make cheap phone calls via his cable modem connection. But last year, after five months using the VoIP service from the US provider Vonage without problems, he noticed an abrupt deterioration. "The line was choppy, very choppy and you could not understand any words spoken," he recalls. Puzzled, Peckler ran pingplotter - a program to detect problems such as packet loss and latency (delays in sending over the separate "packets" of internet traffic). It revealed major latency between his cable modem and local internet service provider (ISP).

"I contacted the ISP and was told it did not support third party VoIP," explains Peckler. "Vonage ran a test. It seems the ISP was blocking the cable modem when the Vonage adapter went into use. I ran a test of my own. I ran pingplotter for 10 minutes: no blockage, then I picked up my Vonage phone and placed a call: immediately there was a 100% blockage on the cable modem. This was a continuous loss as long as the phone was used."

Peckler is not alone. Users on VoIP online forums in the US and other countries, including Qatar and Mexico, have been noting similar problems since last year. For while VoIP (often pronounced "voype") might seem like a great deal for the average person, entrenched interests in the telecoms industry see it differently - and are taking action against it.

Consultation

Mindful of what has happened in other countries, the UK telecoms regulator Ofcom took the unusual step in February of announcing that it will look at the growing VoIP market, and report next month on whether new laws are needed to protect it. The consultation document says: "VoIP service providers have expressed concern that their ability to provide a reliable service may be impacted by internet access providers (ISPs) selectively degrading or blocking their VoIP traffic."

Ofcom says it has no evidence this is happening in the UK; only about 500,000 customers use it. But the forecast is for that to rise by 3m in the next six months.

And VoIP blocking happens in other countries, often those where there is still only a single telecoms company. In Saudi Arabia, for instance, national carrier Saudi Telecom is using software from US supplier Narus to block all VoIP calls.

Telcos in the US and other countries are reluctant to have their bandwidth encroached on by traffic from which they earn no revenue, and have been challenged over similar alleged incidents of VoIP blocking. Blocking VoIP traffic is technically difficult, but not illegal, and blocking specific types of internet traffic is on the increase.

Luxembourg-based VoIP provider Skype, now owned by eBay, has been particularly controversial. Skype is used by 75m people. But not everyone wants Skype on their network.

Skype is considered by many to pose a potential security threat because it opens an encrypted tunnel out of the network and forms supernodes that sit on a network and set up VoIP calls. There is considerable debate about how much bandwidth such supernodes eat up. US blogger Paul Kedrosky (http://tinyurl.com/mjelx) noted a major impact on his main office PC, and links to warnings that in supernode mode, Skype may even saturate a 100 Mbps line.

"Skype calls can be very scary for the owners of the networks over which they run," says Steve Bannerman, vice president of marketing at Narus.

Bandwidth

Skype says its software does not put undue pressure on bandwidth. "Users who have become 'supernodes' will not be able to notice any performance decreases on their computers," says Kurt Sauer, head of Skype's security operations. "A supernode will use approximately a tenth of the bandwidth of a user listening to radio on the internet. There are companies blocking or attempting to block Skype, but we believe they are making a mistake."

There's a lot of divided feeling about Skype, says Louise Cooke, managing director of Blue Coat Systems, whose ProxySG software can block Skype. "Some IT managers detest it," she says. "They don't want their network becoming a super-hub for Skype. But others see it as something that may have business benefits. We use it all the time."

VoIP blocking is often a function added to network or security management software, such as Narus's IP Platform, Verso Technologies' NetSpective 2.0 and SonicWall's enterprise appliances. Other providers with software capable of blocking VoIP include Bitek International, Packeteer, iPoque and Blue Coat Systems, and the list is growing.

One UK organisation that has blocked Skype is Brunel University. "We had a number of concerns about uncontrolled traffic," says Simon Furber, Brunel's network manager. "Skype is unpredictable because of its uncanny ability to become a supernode, so ... we shut the front door."

This is still Brunel's official policy. "But this is a balancing act: a lot of people use Skype and asked us why we were blocking it," explains Furber. "And Skype just finds another way out of the network."

So Brunel has now partitioned off its Skype traffic, using Packeteer's Packetshaper software. "We have corralled it so we can keep an eye on it and see what impact it is having," says Furber.

How blocking works

Blocking specific types of traffic over an IP network is usually done by blocking "ports" - equivalent to boarding up doors (if you imagine a network as a house with 65,536 doors) or denying access to specific IP addresses (equivalent to turning away particular people).

But Skype traffic is hard to identify, because Skype uses proprietary protocols, is encrypted and spreads from peer to peer, using a random combination of IP addresses and ports that defeats traditional port-blocking filters.

That means it can be blocked only by investigating the headers of every internet packet crossing the network to find the "Skype" ones. The challenge is to do this quickly enough so that other services aren't degraded. Narus claims its software can do this, and a major European customer confirms this.

A proxy appliance, widely used to apply controls to web traffic, can also be used to block specified unwanted traffic, including voice calls, if necessary.

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