June 21, 2007

Planning Is Key to Switched Digital

By Justin J. Junkus

The underlying message of the switched digital technical sessions is that if a relatively few strategic parameters are carefully planned, implementation can be a short and easy process. BigBand's Bob Wolfe pointed out some key variables in the "Installation and Monitoring" technical session.

Wolfe noted that switched digital is a statistical gain process, and to avoid service degradation from blocking, knowledge of traffic characteristics is essential. He also noted that there is a need for IP network and device configuration, with literally hundreds of edge devices that need IP address assignment.

Digital set-top control systems also need to be planned and modified, especially interactive guides, which must be configured for switched digital. One key difference between switched digital and broadcast is that the fixed relationship between channel and frequency no longer exists. To minimize delays during channel changes while set-tops find programs, data mini-carousels have been created at nodes, so set-tops do not have to use the reverse path all the way to the headend to find this data.

Time Warner's Glen Hardin expanded on the need for monitoring and pointed out that monitoring must be done both at the control plane for traffic and at the video plane for proper content-to-channel correlation. He summarized the use of digital watermarks that can be viewed as far down the distribution path as possible to ensure that content has in fact been properly correlated to channel choice.

In the "Lessons Learned" session, Time Warner's Todd Bowen pretty much summed up early Time Warner experiences by noting that an operator will not be able to anticipate and fix all network problems before they occur, but should be able to get in front of the major ones before they become issues, largely because of experience gained from VOD. He also noted that experience showed them that the choice of programs that are candidates for SDV may not be as simple as picking low use programs, and that more than the number of simultaneous viewers needs to be considered.

Event pay-per-view, for example, may appear to be a good choice, but when major events, such as a boxing match, occur, not only take rates, but also new subscriber counts increase substantially. Each new sub needs to install a set-top, and many do not follow required procedures, resulting in a barrage of calls to a support center. Children's channels are another possible problem area because viewer take may be small, but use as a virtual "babysitter" creates constant use.

As switched service grows, continuous traffic monitoring is essential to maintaining quality. Service group splits are a valuable traffic management option, but switched digital works differently than VOD. Traffic needs to be closely monitored to determine which groups can be split off. Unlike VOD, in a split, the new groups may not have equal traffic. Monitoring may in fact be one of the bigger challenges because of the lack of off-the-shelf tools. Time Warner, for example, needed to create its own database and tracking from server logging data.

The bottom line for switched digital is, of course, vastly improved bandwidth utilization. As Time Warner found, it opens up a once bandwidth-sparse environment to required new services, such as high definition programming, without loss of existing services to the subscriber.