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Video Quality is a 24/7 Endeavor

Wed, 09/30/2009 - 8:45pm
Richard Chernock, CTO at Triveni Digital

Strategic monitoring and analysis simplifies proactive stream maintenance

Businesses involved in delivering digital television understand that the quality and continuity of the viewer experience is essential to the bottom line. Whether delivered over the air from the broadcast station, via the cable plant or over an IP network, the signal that reaches the viewer’s television set simply must work, and this occurs only when the transport bit stream adheres to the strict series of characteristics outlined by industry standards.

Noncompliance of the stream to standards such as ATSC, SCTE and MPEG-2 can take a channel off-air or cause issues. Lip sync errors and picture break-up or blocking too frequently lead the viewer to switch to another channel. When viewers are the first to discover such issues, their satisfaction with the service quickly erodes. Missing or incomplete ads resulting from stream errors also negatively impact the bottom-line revenue. Service providers’ reputations and diverse new revenue opportunities depend on the integrity and reliability of their transport streams. Thus, it is critical that operators be proactive in their maintenance of stream compliance and, in turn, video/audio quality and metadata integrity.

The complexity of operators’ transmission chains, with their numerous contributing components, presents multiple opportunities for the introduction of error within the transport stream. Finding the source of these errors can be difficult, as the wide variety of receiving devices respond differently to the violations of transport stream standards. Furthermore, visual symptoms do not correlate directly to single and easily identifiable problems. For example, one particular tuning issue could be the result of dropped packets or due to metadata errors in MPEG and/or PSIP tables. Picture break-up might be the result of issues such as PCR jitter, video buffer over/underflow or under-provisioning introduced by any of the MPEG-altering devices in the broadcast chain.

Digital TV Monitoring Architecture

Given the complexity of pinning down errors in the transport bit stream, the only reliable means of assuring a quality viewing experience is to institute standards-based monitoring and analysis. In doing so, operators must have tools that offer a depth of monitoring that supports rapid localization and troubleshooting of the problem, as well as the means to test and verify that the issue has been resolved.

Across cable, broadcast and telco environments, effective monitoring of the transport bit stream and localization of stream errors requires extensive examination of the MPEG layer in real time. In order to understand which device is causing the problem, it is often necessary for operators to examine the MPEG layer comprehensively. Targeted deployment of monitoring and analysis systems allows the operator to narrow the focus of troubleshooting efforts and test the stream in a specific area of the workflow. Positioned strategically, robust DTV stream monitoring and analysis systems allow the operator to identify the transport stream source, test the composition of the programs within the stream against specific standards, and narrow errors to their root causes.

The ability to perform this type of drill-down analysis is key to effective troubleshooting, testing and resolution. Through close comparison of actual stream properties with those stream properties defined by DTV standards, the operator can pinpoint a stream error. As the virtual channels (services), elementary streams and PIDs within the transport stream are tested against the selected standard, as well as against user-defined specifications and business rules, engineers acquire the details they need to address and resolve the problem.

As the stream is tested, data collected for each program might include PIDs of video and audio (including secondary audio) streams, SCTE 35 cue tone PIDs, bit rates for each stream, warnings of buffer over/underflow, and an indication of PCR jitter or offset. This stream data often is complemented by thumbnail views of the actual programming being delivered within the stream. The comparison of data within the stream’s PSIP and MPEG tables also allows the operator to ensure the metadata consistency needed to guarantee proper program tuning and EPG information for the viewer.

During day-to-day operations, the monitoring system can be used not only to identify stream errors, but also to categorize those errors according to urgency. Because numerous compliance errors naturally occur in preparation of the transport stream, and because a good number of these have no noticeable impact from the viewer’s perspective, operators benefit significantly from the ability to sift out and address the problems that threaten the viability or viewability of their programming.

The development of the ATSC A/78 recommended practice and the SCTE 142 standard has provided a foundation that enables the monitoring system to prioritize error severity and deliver meaningful alarms to engineering staff. As a result, alerts for serious errors such as missing PAT/PMT or missing video elementary streams can be routed directly to operations personnel, and less-intrusive actions for QoS or slight table timing errors can be logged for later attention during routine maintenance.

Strategic placement of interconnected monitoring systems across a plant, station group or geographically distributed network can provide the operator with a complete picture of stream health across the full broadcast chain. In an ideal world, the operator’s strategy might involve placing monitors at all points that manipulate the digital signal. Facing the real-world pressures of a tight budget, the operator might instead position permanent monitoring equipment at strategic points and use portable equipment to uncover stream impairments at tactical points.

In a cable headend, for example, the operator might establish monitoring between the incoming satellite feed and receiver, between the multiplexer and QAM modulator, and on the output of the QAM modulator. Comprehensive in-router monitoring offers additional advantages, including tight integration with the network management/operations support system, the capacity to unobtrusively monitor the flows through the core networks at the deep transport level, and the ability to perform impairment-driven automated switchover. The goal in this and any DTV environment is to position monitors in such a way that actionable impairments can be isolated quickly and subsequent troubleshooting efforts can be limited to a reasonable subset of systems.

For larger operations, a network of centralized and remote (often unattended) monitoring systems can be created to enable troubleshooting across the enterprise. This approach allows a small number of technical and engineering staff, regardless of their location, to analyze and resolve issues and to identify more easily any recurring or systemic problems enterprise- wide. As a result, the operator can achieve more sophisticated and proactive stream monitoring, as well as a higher standard for customer service, while reducing associated operational costs.

As operators strive to maintain an edge in an increasingly competitive environment, they have no choice but to institute systems for proactive maintenance of service quality. Offering operators a straightforward means of addressing issues in complex DTV streams, strategic, real-time stream monitoring and analysis systems serve as a valuable asset in any broadcast model.

E-mail: rchernock@trivenidigital.com

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