Because many broadcasters today promote multicasting as an added value to their IP services, it is important for them to have efficient solutions to prevent the pitfalls associated with increased network demand. Viewers expect 24/7 service 365 days a year.
If a triple-play service already contains voice, video and data, what else is there? In addition to ensuring the quality of the video, a provider must also guarantee that the Internet Group Management Protocol (IGMP) — the signaling protocol used to deliver multicast services — is performing optimally. A variety of issues must be addressed, including IGMP and channel change request latency. It is important for customer satisfaction that minimal delay is experienced when viewers change the channel. Typically, providers must be at or close to the customer's premise to accurately measure these parameters.
Traditional IP transport test equipment often cannot effectively shed light on the health of the underlying video transport layer. Those parameters include error conditions such as loss of audio, lip-sync errors, absence of an entire program or its components (audio or video), or the loss of a subscriber's EPG. For these reasons, an effective test platform must be able to dig deeper into the video transport to identify problems.
New solution
To address this need, JDSU's Test and Measurement group recently added multicast IP video services analysis to its IP and digital video test platform, DTS. This functionality is comprehensive, accurate and easy-to-use for IP video deployment and multicast testing platforms. It identifies trouble spots for any IPTV platform. Operators can proactively check for problems and issues without waiting for the customer to call in with a complaint. The goal of DTS is to improve operational efficiency and maintain a high quality of service within the network.
Here is a typical test example: A video service delivered over an IP network is experiencing problems in the quality of the video presentation. Throughout of the presentation, parts of the audio and video are out of sync, the audio is completely absent or blocks of the picture are missing.
A test of the IP transport platform confirms that the IP transport performance, including IP packet jitter, packet loss and other key parameters, is within acceptable values. Yet, the problems still persist.
By testing the IP transport first, the operator has obtained a first level of confidence monitoring. Now, it's time to analyze the MPEG-2 transport stream.
Measuring MPEG
There are several types of problems that could cause errors. (See Photo 1.) The causes include:
- inaccuracy in the program clock's reference-time values;
- jitter in the MPEG-2 PCR arrivals;
- discontinuity of the MPEG program elements;
- inaccuracy of the various packer identifier information for the program elements at the MPEG level;
- loss of frames or MPEG packets resulting in continuity counter errors.
Such problems, even those that exist when the IP transport is performing at acceptable levels, can be caused by IP errors.
Using the DTS-330 test platform or DTS-200 for in the field testing, the operator can perform a real-time investigation of a wide selection of important MPEG parameters. (See Figure 1.) This includes presence of all audio and video content, PCR accuracy and jitter, continuity counter measurements and packet loss. The test system can also view the accompanying MPEG metadata that is needed by the set-top box.
In addition, the multicast analysis feature allows an engineer to perform the complete suite of in-depth protocol tests at or close to the customer premise by remote control, if needed. This simulates the viewer's experience, as the test has to order each channel individually as done via an set-top box's channel change request.
An engineer can leverage the DTS to quickly and easily join and leave multicast service groups, just like a set-top box does. This provides an effective method to troubleshoot video service issues.
With DTS, service providers can perform in-service, non-disruptive tests by sharing the same quality-of-experience as the viewer, providing the same perspective as if the engineer were located in the customer's home.
These new functions and capabilities, along with the DTS' existing remote troubleshooting versatility, allow the network operator to perform in-depth troubleshooting and service assurance checks of a subscriber's quality of experience without ever leaving the central office. (See Figure 2.) The DTS-330 and DTS-200 can be remotely located from the central office, yet still permit technicians to perform the full array of in-depth video transport analysis.
Sudeep Bose is product marketing manager for the cable networks business unit of JDSU's Test and Measurement DTS product line.
