What matters most to TV viewers is the ability to watch their choice of shows or movies without a hitch. Monitoring is a critical element of broadcast operations that helps ensure that, apart from the character and quality of programming itself, the viewing experience is a good one.
Most viewers don't care about standards and formats such as MPEG, 8-VSB, IP, RTP and QAM, but these standards are everyday concerns for the broadcaster. The ability to monitor the entire content distribution system is crucial in assuring the integrity and quality of an end-to-end broadcast service. With all the information now incorporated into the DTV stream, monitoring can be a complicated task and one threatened by alarm overload. By establishing tactical and strategic monitoring appropriate to existing service and business models, the broadcaster can maximize uptime and the viewability of their channel lineup, in turn reducing complaints and viewer churn.
Issues that commonly plague DTV services include dropped packets, metadata errors and inconsistencies, PCR jitter, AV buffer under/overflow and underprovisioning, all of which can affect the viewing experience by causing such visible errors as video tiling and lip-sync problems, as well as practical problems, such as the loss of channel-related information or the inability to tune a channel. Because every device across the broadcast chain that touches the MPEG stream has the potential to introduce a problem, isolating and troubleshooting these issues can be very difficult. By implementing proactive monitoring of the MPEG transport layer, the broadcaster can catch issues and reduce or eliminate any negative effect on the viewer experience.
Troubleshooting vs. monitoring
The difference between troubleshooting and monitoring is that the former is a reactive approach, and the latter is a proactive approach. Troubleshooting generally is triggered only after a problem is discovered — often by a subscriber rather than an engineer. After the on-air issue is discovered, the broadcaster performs analysis to uncover and mitigate the root cause. If troubleshooting is the only way in which transport stream errors are addressed, both uptime and the reputation of the broadcaster can suffer.
Proactive monitoring is a preferable approach, and it is essential if the broadcaster is to minimize the time and resources that must be dedicated to resolving transport stream issues. Through 24/7 monitoring of the MPEG transport layer, the broadcaster can continuously test and compare transport streams against preset rules. When a stream violates these rules, the monitoring system can apply a standards-based filter and determine the severity of the problem and its likelihood of affecting the on-screen product. With urgent issues automatically brought to the attention of engineers, the facility is equipped to solve problems before they lead to a visibly compromised signal.
Tactical and strategic monitoring points
Simple cost constraints make it impossible to monitor every point in the broadcast chain, but a combination of strategic and tactical monitoring can help the broadcaster keep an eye on the most critical areas in the most effective manner.
Typical strategic monitoring points include the satellite down/uplink and the transmitter. Monitors fixed at these more remote locations ensure the integrity of incoming and outgoing signals, effectively addressing the two ends of the chain. As a rule, any signal being delivered from an external source should be monitored, and the studio output is also often included among the continuously monitored points. Across the station, tactical monitoring supports a more focused approach to stream monitoring and analysis.
By bringing these two monitoring models together, starting with strategic monitoring and enhancing it with tactical monitoring points, the broadcaster can cost-effectively realize an end-to-end services view as well as get more complete reporting. In addition, the targeted deployment of monitoring and analysis systems enables engineering staff to narrow the focus of their troubleshooting efforts and use portable systems to test the stream at specific points in the chain. By positioning monitors tactically, broadcasters can isolate actionable impairments quickly and limit subsequent troubleshooting to a reasonable subset of systems.
Monitoring in centralized architectures
Larger networks and station groups have centralized operations at one or more hubs to reduce their operational and capital expenditures. This model tends to put expertise at the central hub, maintaining fewer resources at the edges. Just as day-to-day broadcast operations benefit from consolidation of resources, so too can the monitoring workflow.
Figure 1 illustrates a monitoring model for large, centralized architectures incorporating a number of regional hubs. Some large groups have centralized all their monitoring, with some transmitter sites being monitored from one office. Others, however, have taken a multistep approach, each with a regional site boasting a resident expert and a connection into the central hub in what's effectively a multihop chain. Depending on how the network has developed, regarding taking on or launching new stations as well as its approach to adopting new technologies, either architecture works equally well.
Real-world monitoring success
The strategic and tactical monitoring model has shown in real-world implementations to provide both broadcasters and cable operators with a valuable tool when resolving stream issues that threaten the quality of the on-air broadcast. In one case, the subscribers of a cable service were seeing glitches in their pictures every seven minutes, whereas those viewers watching the over-the-air broadcast saw nothing irregular. Working together using a combination of strategic and tactical monitoring, the broadcaster and cable operator were able to track down a buffer problem in a conversion device that took seven minutes to overflow, affecting video, audio and, sometimes, nothing at all. These types of issues are commonplace, and with a thoughtful approach to monitoring, their effect on the viewer can be minimized quickly with little waste of time or resources.
Ralph Bachofen is vice president of sales and head of marketing at Triveni Digital.
