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March 17, 2010
Demand Grows for Digital Testing
By any number of indicators, interest in digital video (and audio) test and monitoring tools is growing.
Companies focused entirely on providing such solutions are touting strong growth that flies in the face of the economic downturn. Some traditional test and measurement companies have expanded to embrace MPEG testing technologies.
And at industry events, such as the NCTC Winter Educational Conference (WEC) and the SCTE Canadian Summit, operators are speaking directly about the need for these tools. (For more from WEC, click here).
“If you’re not using a monitoring probe presently, go out and get one,” said Stephen Shaw, senior digital cable engineer at Cogeco Cable at the Canadian Summit. “You need to monitor. You need to have the tools.”
On that panel were engineers from Rogers, Videotron and the Comcast Media Center (CMC).
More tools, please
With competition and expectations both on the rise, ensuring that consumer QoE is high has become increasingly important, even as it has become more difficult to achieve.
CMC Vice President of Quality Assurance, Dave Higgins identified eight touch points where video quality should be measured:
- content source
- master control facility
- MPEG encoders and multiplexers
- point of entry into CMC facilities where MPEG is encapsulated onto IP
- interface with the IP delivery system
- QAM device
- set-top box
- consumer video display
While there are a lot of testing tools available today, one thing the CMC is looking for is a device that would give it a real-time assessment of the impairments, by way of what Higgins termed a video mean opinion score (MOS). (For related coverage, click here).
Higgins isn’t alone in requesting enhanced tools.
“I still haven’t got a piece of test equipment that analyzes a digital signal and tells me we have a problem with audio phase,” said Michel Lapointe, senior analyst, digital video technologies development, Videotron.
At the same time, Lapointe warned against “MPEG-2 voodoo diagnostics,” underscoring the current limits of technology. “I need experienced people to interpret test equipment warnings and results,” he said.
Even with trained experts and the right tools, there are always customers, whose eyes matter most. “I welcome those calls,” Lapointe said. “If someone calls and says he saw or heard something wrong, well chances are, he saw or heard something wrong.”
The CMC’s Higgins agreed: “If you use the lens of your customers to measure your service quality, you can’t go wrong.”
As it happens, both Mixed Signals and Volicon have announced enhancements to their respective platforms this month. Mixed Signals is enabling more insight into complex and recurring QoE issues, and Volicon unveiled five modules, one of which promises more visibility into the customer experience.
Detective work
Getting to the root cause of audio or video impairments sometimes requires detective work, and a bit of humility. In an example recounted in the paper presented at the Canadian Summit, Cogeco’s Shaw pointed to an audio dropout on some HD services.
Their first answer to the puzzle indicated a presentation time stamp (PTS) error recorded at the source. Yet even after the source provider admitted an issue and had moved to resolve it, the dropout persisted.
Cogeco then found that levels hitting their receivers were at 1 dB over specification. That led them to update the firmware on those receivers.
“What we learned from this case was that what appeared to be a provider-related issue was actually on our side,” he wrote.
Other real-world lessons from Cogeco include the discovery that a critical switch to the SONET backbone should have been fiber instead of copper CAT6 jumper and the insufficiency of a PC-based media player to display actual errors.
That is not to diminish the high value of captured video, both for trouble-shooting and training.
“Create a bank of defective MPEG-2 content,” Lapointe recommended. “So first I can show people, ‘This is a field reversal problem. This is a bad channel.’”
It’s also useful for “challenging test equipment people,” he added.
-Jonathan Tombes
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CABLEFAX MAGAZINE 
