As they move from analogue to digital television transmission, broadcasters are seeing the complexity of the TV signal rise significantly, presenting a variety of potential pitfalls in delivering clear and consistent audio and video to viewers. Monitoring the analogue signals that broadcasters dealt with for so many years simply involved the wiggling of voltages at the right times, with a moving dot getting brighter or dimmer on the TV screen.
Ensuring the integrity of the digital signal is not so straightforward. Without a tool for analysing and monitoring this stream, broadcasters find it virtually impossible to discover the causes of issues within the stream. This inability can lead to recurring problems not only with audio and video, but also with the data required within the stream.
Unlike analogue signals, the digital signal essentially uses database-generated information for tuning and to ensure the precise timing of different elements of the broadcast stream. Arrays of numbers are used to calculate the pictures. A DTV "channel" carries multiple television programmes, and a great deal of interlinked information connects these different elements to decode the correct video and audio streams to create a watchable TV programme. Rigid timing and buffer models have been established to make certain that regardless of the encoding or decoding equipment used within a particular TV set, the set will be able to interpret and correctly display the signal.
A number of standards specify all the necessary guidelines for a viable stream, and if the broadcaster provides a stream that's in compliance with the standards, then the broadcast signal is displayed as intended. If not, viewers may experience issues with the on-screen picture.
One example of how a compromised digital stream can affect the end result is the problem of "tiling," also called pixelisation or macroblocking, as a result of the display's inability to decode video properly. This problem can be difficult to address because it can be caused by several different error types including interruption of the transmission due to lost packets, PCR (programme clock reference) issues affecting the timeline relationship between the encoder and decoder, or buffer issues when data is being sent to quickly or slowly. With the possibility of multiple problem types being responsible for a faulty image, use of an extensive DTV monitoring solution is critical.
Early monitoring systems for digital television streams looked for strict adherence to the standards that specified the allowed bounds for information in DTV streams. DVB, ATSC, MPEG and SCTE standards specify what must be present in a stream and what the limits are for a number of parameters that can affect tuning and viewability. Due to the complexity of these standards, broadcast engineers' monitoring systems were illuminated by a large number of red lights showing things that weren't quite right. With the overwhelming prospect of trying to deal with all of these alarms, many engineers simply wound up ignoring those warnings.
The first step forward in addressing this problem originated from DVB with the creation of ETSI ETR 101 290, which categorised classes of errors into priority levels. While monitoring was still a black-and-white issue, maintaining strict adherence to standards, this shift allowed operators to focus on the more important alarms and issues.
The development of the ATSC A/78 recommended practice standard, titled Transport Stream Verification, took this trend one step farther by adding the notion of error severity. Error conditions that violate standards but have no visible effect to the viewer are not as important to fix as those that impair visual quality - or make a particular channel unwatchable. With the "grey" scales that A/78 establishes, it is possible to set up a monitoring system that informs the operator only of impairments that matter, leaving the others to be logged and fixed later. The A/78 monitoring standard classifies error conditions into five different severity classes, ranging from critical (no viewer reception) to trivial (not in compliance with technical standards, but not having any impact on the viewer experience). The five classes, or severity levels, within this scheme include transport stream off-air (TOA), programme off-air (POA), component missing (CM), quality of service (QOS), and technically non-conformant (TNC).
The classification of alerts into specific categories gives broadcast engineers and technicians the information they need to maintain the digital signal efficiently and ensure the greatest channel uptime and image quality. In order to take advantage of the new A/78 standard, however, they need a monitoring system that supports that standard. Triveni Digital is a pioneer of the A/78 standard and has incorporated support for the standard, along with support for MPEG-2, ATSC, DVB/SI and SCTE, into its StreamScope suite of monitoring systems.
To ensure the digital stream is both compliant to standards and in line with the broadcasters' business strategy, a "business intent assurance" feature can help verify that channels are continuously distributed to air and keep the electronic programme guide properly updated through complete PSIP data. By bringing an awareness of these factors into the realm of monitoring and analysis, business intent assurance can alert broadcasters to lapses or problems that threaten the smooth delivery of the DTV service.
Other capabilities critical to monitoring digital streams include the capacity to analyse and monitor a number of different types of signals simultaneously, as well as the ability to provide aggregate viewing and monitoring of the entire distribution network from a centralized location or from multiple remote locations. For broadcast groups with more than one station, network wide monitoring from a single location can reduce the technical and administrative burden of monitoring at the local level. With access to critical stream-related information, an engineer working remotely can evaluate and troubleshoot issues from afar. Thus, only one engineer need be available at any given time to help solve problems with the digital stream.
The depth to which the monitoring solution can examine the stream determines just how comprehensive a view the broadcaster can get of the full MPEG structure and its adherence - or lack thereof - to appropriate standards and recommended practices. If this functionality is paired with a user interface requiring little user training and intervention, the broadcaster can ensure the quality of the DTV stream without investing in a deep knowledge of the intricacies of the MPEG standard.
With systems that can automatically monitor stream compliance and perform real-time analysis in extensive detail, broadcasters gain valuable insight into the complex elements that make up digital television streams. Thanks to products that support advanced monitoring standards, broadcasters can take advantage of highly efficient categorization and alerting of stream-related errors to improve the quality and consistency of their on-air product.
The StreamScope product family from Triveni Digital is a set of tools for remotely monitoring, evaluating and troubleshooting transport video streams. It measures, records and analyses DTV signals to ensure compliance with standards, integrity and reliability.
Built on the A/78 (ATSC Transport Stream Verification Recommended Practice) specification for transport-stream verification, StreamScope allows users to detect and correct service impairments quickly, and classifies errors in the stream by severity so that operators can first focus on issues that threaten viewing quality, and then on other problems that may affect or compromise regulatory compliance.
Innovative elements of the new StreamScope architecture also include a Business Intent Assurance feature, and network-wide monitoring capability.
The device provides end-to-end MPEG-2 and MPEG-4 monitoring for broadcast, cable, satellite, IPTV or mobile networks. It is available in rack-mounted or portable configurations and can support ASI, SMPTE 310, QAM, 8-VSB, QPSK and other signals.
The StreamScope can be monitored from any SNMP agent in the network and provides alarms that can be distributed via e-mail, SMS or SNMP traps. The unit also supports stream profiling, comparison and template learning.