Keynotes third VOIP Competitive Intelligence Study, conducted in August, found that service quality of VOIP (voice over IP) among the providers measured has improved across the board since its last study in December 2005.
In some cases VOIP even bested traditional phone service from PSTN (Public Switched Telephone Network) carriers in overall audio quality. But those VOIP providers still come up short when it comes to audio delay.
Keynote tested the service quality of 12 providers, including AT&T, Comcast, Lingo, Packet8 (8x8), Skype, SunRocket, TimeWarner Cable, TrueVoice (EarthLink), Verizon, Vonage, Vonics Digital and Microsofts Windows Live Messenger. The study looked at the performance of both local and long distance calls made between New York and San Francisco. Officials would not provide ranking details on individual providers.
The study sought to compare the performance of four types of services: softphone services (Skype, MSN Messenger Live, Vonage); broadband VOIP services (Vonage, Verizon, VoiceWing, Packet8, AT&T); and digital cable services (Time Warner and Comcast).
"In some cases the cable providers were performing at par or better than PSTN providers," said Arun Bhardwaj, senior product manager for VOIP and streaming media for Keynote, in San Mateo, Calif.
The study looked at multiple measures of performance, including reliability, audio clarity, audio delay, and latency and jitter.
The broadband VOIP cable providers ranked highest in reliability, which takes into account service availability, average number of dial attempts and dropped calls. They also ranked first in audio clarity, according to their MOS (Mean Opinion Scores), and in audio delay.
The other types of service providers, however, have improvements to make. The study found that 10 of the 12 VOIP service providers achieved an MOS score under 4.0, which is considered toll quality for regular PSTN phone service.
Keynote also looked at the performance of VOIP calls made during peak hours—specifically audio delay and MOS scores. Surprisingly, MOS scores were not affected by traffic increases during peak hours. Still, some cable modem subscribers experienced more instances of audio delay during peak hours. Conversely, Digital Subscriber Line connections were more consistent regarding peak versus non-peak audio delay, but saw lower MOS scores during peak hours.
The study was based on the results of 125,000 calls placed at 30 minute intervals during August, and compared VOIP calls to traditional PSTN calls.
The study is unique in its inclusion of last mile connections, according to Bhardwaj. "The ATA box and the phone that youre using to make calls [are] part of the monitored path. We are sending a human voice sample that goes to the ATA box that Vonage gave to you and it goes through this last mile," he said.
The full study is available from Keynote.