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VoIP call quality on the decline

Advances in technology have made VoIP more common, but that hasn't stopped VoIP call quality from dropping steadily over the last 18 months, according to a recent study by Brix Networks.

Voice over Internet Protocol (VoIP) call quality is going down the tubes, or so says a recent study by Brix Networks, which found that one out of every five VoIP calls is of unacceptable quality.

"It was a real head snap," said John Burnham, Brix Networks' marketing vice president. "It really did surprise us."

Chelmsford, Mass.-based Brix has been asking VoIP users -- residential, business and consumers -- to test their call quality free of charge at the voice quality testing portal.

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 Since March 2004, more than 1 million VoIP users tested their systems' call quality through the portal. Of those 1 million calls, about 20% were considered low quality and therefore unacceptable. Around the same time last year, only about 15% of VoIP calls were considered to be of unacceptable quality, according to Kaynam Hedayat, Brix Networks' CTO.

Brix tested VoIP call quality by calculating a Mean Opinion Score (MOS) that rates calls on a scale of one to five, with five being bad and one being excellent. Calls with a MOS of 3.6 or better are typically regarded as having satisfactory quality. Overall, only about 81% of calls tested achieved a MOS of 3.6 or better, which Brix dubbed Acceptable Call Quality (ACQ).

In 2005, roughly 82% of calls tested had acceptable quality; that slipped to 80% in the first half of 2006.

One theory for the slide in overall call quality is the complexity of applications being run over the Internet and IP networks, Hedayat said. Adding in video and a host of other downloadable applications slows down voice packets, resulting in call degradation.

Hedayat said that VoIP service providers now must focus more closely on why quality is slipping.

"For long-term sustainability, providers of [VoIP] will need to concentrate on the root causes of call quality degradation, including late packet discards, lost packets and round-trip voice latency," he said.

Brix's testing site,, uses both hardware and software to test and monitor IP service and application quality. To use the testing, users download a small applet that initiates a test phone call using the SIP call-signaling protocol. Then, appliance-based Brix Verifiers -- in Boston, Helsinki, London, Montreal, San Jose, Sydney and Vienna -- answer the test calls to measure the call quality.

Along with maintaining the testing sites, Brix Networks makes VoIP monitoring products for enterprises and service providers.

Zeus Kerravala, a vice president at Boston-based The Yankee Group, said most enterprise users need not worry about call quality degradation because many companies run VoIP over their own networks. Call quality could plummet, however, for companies using hosted services or services where the hosting company doesn't own the network.

"I think there's a lot of truth to that," Kerravala said of the overall slide in call quality. Most users run some sort of instant messaging service, file sharing software and video, while also using voice. That can destroy call quality and introduce latency and jitter.

"People are using the network for more things," he said, later adding that "this is going to become a bigger issue" as more services are piled onto the network.

Kerravala said that while adding bandwidth is one solution, carriers may also want to start charging more to prioritize voice traffic in order to ensure quality.

"The reason it's a problem now is because nothing's prioritized," he said. "But no one's really trying to address that yet."

This article originally appeared on

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