Best-effort voice over IP succeeds in delivering cellular-level voice quality only 60% of the time, according to research done by InterNAP, the Seattle-based company that sells Fortune 1000 companies the technology and services to make the Internet more reliable, such as network optimization. Eight percent of the time best-effort VoIP is unable to complete a call.

“That percentage surprises me, because I use a best-effort VoIP service at home,” said Kevin Mitchell, Infonetics Research analyst. “But it points to the difference between the best-effort VoIP services and the VoIP services being offered by carriers with their own networks, who do traffic engineering and never touch the public Internet.”

InterNAP conducted a two-month study involving the IP backbones of the top nine U.S. carriers, including AT&T, MCI, Qwest Communications, Level 3 Communications, Sprint, Verio, Wiltel and XO Communications, and simulated 1.5 million VoIP calls from 15 different locations, said Eric Klinker, senior vice president of engineering for InterNAP.

“If we took the default performance from the carriers to any given destination, voice quality on calls was acceptable roughly 60% of the time without any extra work to optimize the connection,” he said. “It's really low. That is accessing some rather remote destinations and looking at that over a two-month period, which is when carrier quality begins to degrade. We are working on our first ‘nine’ relative to the PSTN and its five nines.” Call acceptability was based on the mean opinion score (MOS) rating, a subjective score; the threshold of acceptability was set at 3.6, the MOS score typical of cell phone calls, Klinker said.

InterNAP offers services that optimize VoIP quality by seeking the best route available at any given moment from various IP backbones. According to its survey, 33% of the VoIP calls were of acceptable quality given network optimization.

Of course, one of the goals of InterNAP's research is to prove to its commercial customers that they need the company's technology and services, which help them pick the best available backbone and maximize VoIP call quality for corporate customers. InterNAP just introduced a voice control module to its Flow Control Platform (FCP).

“The FCP is a piece of network equipment that incorporates our technology for selecting the best route,” Klinker said. The company can sell the FCP as part of its service, or “put it in the hands of the [VoIP] service provider themselves to use.” InterNAP currently has more than 30 VoIP service providers on its client list, he added.

Experience has shown that no single IP backbone serves every site with its highest quality of service, Klinker said. “If you want to trust your default carrier, you should expect relatively low reliability.”

Other companies are expected to capitalize on the need to make VoIP more reliable. For example, Acterna is introducing support for VoIP as part of its NetComplete platform, which includes both passive monitoring and active probing of network quality, said Roger Lingle, vice president of marketing for Acterna's Service Assurance Solutions Division.

Because voice is latency sensitive, the quality of a VoIP offering may degrade as it passes through the network without any awareness on the part of the service provider, he said.

“When you look down into the network and the separate elements, everything looks fine, all the lights are green,” he said. “But there is a additive problem that can affect the end-user when one device adds a little bit of delay and another adds a little bit more.”

Acterna's approach is to correlate passive monitoring data and active probing in a way that identifies the service degradation and helps the service provider quickly determine the root cause of the problem.