The quality of Internet telephony continues to decline, even as the service goes mainstream, according to service assurance provider Brix Networks.

Based on consumer-generated calls to their company's free voice quality testing portal, www.TestYourVoIP.com, Brix officials said nearly 20% of voice-over-IP (VoIP) calls have unacceptable voice quality.

"We think the cause is the volume of data and the new applications being used on the Internet," said Kaynam Hedayat, vice president, engineering, and chief technology officer at Brix, which sells service assurance software. "Broadband is a disruptive technology, as it is introduced, there are things that follow. There is more and more video, more file transfers and bulkier e-mails."

The test results generated by Test YourVoIP.com have steadily declined since 2004 when the testing began. Overall voice quality is measured via a Mean Opinion Score (MOS), which is also used in the wireless industry, that rates calls on a scale from one (bad) to five (excellent), with MOST scores of 3.6 or above considered of satisfactory quality. Only 81% of VoIP calls achieved this level.

Since best-effort Internet-based services are differentiated, latency-sensitive services such as VoIP will suffer, he said.

"It is our view that it will continue to decline, until there is some kind of differentiated service," Hedayat said.

While some service providers, including cable companies and managed service providers, are promising to do better than "best effort," even their services will be degraded when they move off-net, he added.

"What happens when a cable VoIP calls goes to a Vonage customer--the quality can degrade," Hedayat said. "Customers are concerned with their call, not the provider. They aren't going to call Vonage, they are going to call their service provider."

For VoIP to be a true business tool, there needs to be differentiated services with service level agreements that can be validated, he said.

"My personal belief is that VoIP is not about the replacement of telephony, it is about a better service, with better voice quality and the services that come with convergence--video, data and voice," Hedayat said. "Where people are getting the idea that it is not just replacement of old telephony, they will care more and more about quality. Right now VoIP is free because people are okay with the quality they are getting but as you move toward better quality voice and better services, then the customer will care more and more about quality on and off the network. Within the next 2-3 years, we will see a huge convergence of voice peering and you will even have more issues around quality."

Brix is already seeing a large uptick in interest in service assurance as more business customers are using VoIP and expecting business-class SLAs, he said.