Hunting for a QOS consensus

Telcos face a new set of challenges as they seek to deliver IPTV services, and although many of the hurdles have to do with how to package and market video content, the ability to effectively measure quality of service for IPTV also is vitally important. Yet, video testing does not exactly come as second nature to telcos. They have made a science out of testing for voice quality and maintaining nearly perfect records for voice reliability, becoming so good at maintaining quality, in fact, that voice quality ceased to be an issue long ago.

However, with video, there are many new methods for measuring quality, new kinds of quality scores, a boatload of industry groups contributing to still-evolving standards and essentially a whole new language for carriers to learn.

“The state of things is that there are a lot of algorithms, but no official standard,” said Jeff Schmitz, vice president of product management for Spirent Communications.

Those algorithms include mean opinion score (MOS), a value imported from the old world of voice and audio quality. To determine a MOS score for video, a focus group of users watches a video sample and grades aspects of quality on a scale from 1 to 5. Another algorithm — which unlike MOS is based on scientific measurement of network occurrences such as delay, jitter and frame loss — is the media delivery index (MDI). Other algorithms in use include proprietary approaches from vendors such as QoSMetrics and SwissQual, which is owned by test system vendor Spirent.

“There are over 10 contenders for a standard,” said Joe Haver, wireline program manager for Agilent Technologies' network test systems operations group. Haver said that although the International Telecommunications Union and the Alliance for Telecommunications Industry Solutions both have dedicated large task groups pursuing IPTV standards, there are just as many contributing forces as there are potential quality standards. He said the Video Quality Experts Group, which draws membership from a diversity of industry companies, has been instrumental in the standards effort.

Schmitz said much of the ongoing work of various groups is being funneled into the ITU effort, and the ITU's IPTV Focus Group likely will make several quality standard recommendations based on these contributions. “There probably will continue to be more than one standard,” he said. “Some of the algorithms are lightweight protocols, and some are based on harder and more complex measurements.”

Aside from test and measurement, there are also methods, including forward error correction, for improving the quality of video while it is being transmitted. Forward error correction uses a small amount of IPTV bandwidth to create a redundant transmission that reconstructs frames that have been lost, according to Bill Brown, CEO and chief technology officer of Metric Systems. “You can improve the recovery of packets. It is capable of handling a video dropout of several seconds,” he said. “It's a great performance enhancer.”

Industry observers agree that delivering a high-quality, highly reliable service is critical to the IPTV aspirations of telcos and that there is no room for failure or early glitches as they contend as newcomers against entrenched cable TV providers. “The revenue promise of video is so important,” Schmitz said. “It's something they have to get right the first time.”

However, although a multitude of quality measurements and potential standards remain in play, Schmitz said that the lack of a single consensus quality metric “isn't stopping anyone from launching IPTV services. Still, before these services scale into the millions of subscribers, this is something that will need to be addressed.”

Ultimately, for service providers and the vendors helping them launch IPTV services in the short term, the key to QOS will be a combination of passive analysis of video streams along with new measurements based on subscriber perception and experience with video.

“The new paradigm is quality of experience,” said Luis Hernandez, marketing manager for Agilent. “How the application is perceived by the end user is the most important thing.”