Achieving high availability for video programming
Aug 1, 2009 12:00 PM, By Jim Metzler
Designing and deploying high-availability systems begins with selecting components that have been tested and offer proven reliability.
Figure 1. A digital TV network with a routed IP core
Select figure to enlarge.
Service providers who have deployed next-generation video services on massive IP networks are striving for 99.999 percent reliability to enhance quality, be competitive and increase profitability. They are investing billions of dollars in delivery infrastructure by purchasing complex, advanced equipment such as routers, QAM modulators, ad insertion servers and splicers, multiplexers, passive optical network (PON) gear, and STBs. (See Figure 1.)While this equipment is expected to handle the demanding and unique nature of video content, the unfortunate reality is that manufacturers often don't test it for the stress of a video-centric network.
The performance of these devices is cumulative, i.e., one device's impairments add to the impairments from other devices in the long winding path to the subscriber. (See Figure 2.)With the explosion of digital video, the need for video performance testing has reached a critical stage, and the network equipment manufacturers (NEMs) who provide these devices will need to play a key role.
Service providers have already recognized the need to monitor program availability performance after deployment to ensure their systems are operating as expected. Service providers will also need NEMs to provide per video program availability performance reports on all components and systems before deployment to ensure proper component selection and configuration.
This concept, supported by several industry experts, will improve video quality by verifying video component device quality before deployment and lead to increased revenues for all. Without such verification, the current ad-hoc approach to video testing will continue to produce transient operational issues with no accountability and systematic method for improvement.
Recognizing these needs, the SCTE standards organization in the hybrid management sublayer (HMS) subcommittee has been developing specifications and practices for video system monitoring and equipment testing with direction from both service providers and equipment manufacturers based on experience from current deployments.
Measuring the performance of video devices
While there are many metrics that are already gathered during network device testing, video payload availability is often ignored. Some video service providers now use measurements of per-program availability in evaluating the operation of their deployed equipment. They expect their systems will have 99.999 percent availability, which requires that programs be available for all but five minutes in a year. If any single device delivers only 99.000 percent availability, the provider's five-nines goal will be unattainable.
What's needed is a standardized program availability methodology that would give video service providers a way to measure the expected performance of their delivery networks and NEMs a way to measure the reliability of their devices on these networks. This approach would also provide a common language at a crucial point where the two industries meet with a measurement that shows the impact to subscriber experience.
Is program availability an appropriate measurement?
A group of industry experts were asked to comment on this approach. There is widespread agreement that delivering high-quality video services is challenging.
Figure 2. Availability of series and parallel subsystem configurations
Select figure to enlarge.
“Video services are critical to Comcast and becoming even more so as additional high definition channels become available,” said Charlotte Field, senior vice president, NETO infrastructure and operations, Comcast. Field said that poor video quality tends to frustrate customers, and that frustration is increased if the customer stays home for a half day for a service call that does not resolve the problem.
Stuart Elby, vice president of advanced technology networks, Verizon, pointed out that customers often call to complain about a problem that occurred sometime during the previous few days and that because the problem is not currently occurring, identifying the cause of the problem is “very, very difficult.”
Hung Nguyen, the HMS subcommittee chairman at SCTE, highlighted a fundamental challenge associated with delivering high-quality video services. He said that the industry has done a good job of delivering relatively high-quality analog video signals. However, he added that delivering a digital video signal is relatively new and is much more complex because it requires so many components, any of which could either fail or could introduce some form of degradation.
Another fundamental challenge in delivering high-quality video services is that the networking equipment deployed to support these services lacks the same, embedded management capabilities and product resiliency that customers are used to having in the traditional telecommunications environment.
“There is nothing built into routers that will give us meaningful management data about the quality of video services,” said Jerry Murphy, senior design specialist, TV assurance, Telus Communications.“Troubleshooting video quality based just on use of the command line interface (CLI) of a router is pretty much impossible.”
Achieving high availability is a two-part process
First, service providers must enable 24/7 monitoring of each program at multiple locations. Without continuous precision monitoring, they will not be able to measure program availability to five-nines granularity, much less guarantee it. Second, NEMs must test and certify their devices for five-nines availability before they are deployed in these video networks. The devices need to be tested under real-world conditions, over extended periods of time, using real video. Many of the network devices currently used across large deployments were never even tested with real video but are expected to keep pace with years of growth in video loads and evolving SD/HD/MPTS traffic mixes. Consider that even a simple link up and link down (link flap) can drop the program availability of all carried programs to four-nines. The prevailing ad-hoc approach to testing and measurement does not scale to service the needs of the video industry.
Recognizing these needs, the SCTE HMS subcommittee is currently developing specifications for video system monitoring and equipment testing with contributions from both service providers and equipment manufacturers based on experience from current deployments.
| Want to use this article? Click here for options! |  |
