At present, many equipment manufacturers have provided IPTV system platforms and equipment. The industry recognized that IPTV services include two basic services: VOD on demand and TV live broadcasting. The development of domestic IPTV is in full swing, and the testing of the IPTV system also needs to be standardized. This article intends to briefly discuss the performance testing of these two basic services of the IPTV system. This article only considers the end-to-end performance test. The observation point of the test is on the user side and does not consider the server-level hierarchical cache performance.
Due to the difference in network structure between the VOD on-demand network and the TV live broadcast network, VOD distribution needs to rely on the CDN network, while TV distribution needs to rely on the multicast network, and does not require the CDN network to cache. The focus is also different.
1. Introduction to VOD Business Performance Testing
VOD programs are usually transmitted on demand. On-demand users can freely control the progress of the program and terminate the program, but each on-demand user needs to occupy a certain amount of network bandwidth, so the number of concurrent users is limited by network bandwidth and server performance. The test indicators of VOD service performance mainly include the maximum number of concurrent streams, bandwidth fluctuation, average bandwidth used, packet loss rate and average response time.
Maximum number of concurrent streams: The maximum number of online users that the streaming media system can support at the same time, and requires that each user can watch the complete video program normally. Before the number of users gradually increases to the maximum, the system will not cause users who are already online to be unable to obtain services because of the newly added users. Some video systems can provide a huge number of concurrent streams, but there are many failures. Since most users use TCP, the number of concurrent streams does not decrease after retransmission. However, for a single stream that has failed, the user has already Can't continue to get video service. Therefore, the maximum number of concurrent streams should be an effective maximum number of users that can be supported by the video system and can watch normal programs online at the same time. Bandwidth fluctuation: During the playback of video files, the bandwidth of the media stream will change due to changes in the picture. For example, for classroom teaching programs, the continuous picture changes little before and after, so the program code rate is relatively constant, and the bandwidth fluctuation is relatively small; for sports programs, the continuous picture changes before and after the big picture, so the program code rate The change is correspondingly larger, and the bandwidth fluctuation is also larger. The size of the program code rate fluctuation is a severe test for the throughput of the video server. If too many users order programs with higher code rates, it is likely that the number of users that the server can support decreases, or the video server will Reduce the output bandwidth of the program stream. The average bandwidth used: the average value of the bandwidth used by all users during the user watching the program. The larger the value, the stronger the bandwidth capability that the streaming media video system can provide.
Packet loss rate: When users receive video-on-demand services, they need to obtain video files from the server, and whether packet loss occurs during the transmission of video files. The value of the packet loss rate is generally small, but the impact on users is very important, especially the compression ratios currently used are relatively high. Even the loss of very few video packets will affect the user's viewing and even the phenomenon of disconnection. The upper limit of the end-to-end packet loss rate of VOD should not exceed 0.1%.
Average response time: The overall distribution of the time from when a user issues an on-demand request to when they get a video service. Of course, the shorter the average response time, the better. Generally speaking, the average end-to-end delay of VOD should not exceed 2s (tentative).
2. Introduction to TV Service Performance Testing
TV programs are usually transmitted using multicast. Multicast is a network technology that allows one or more senders (multicast sources) to send a single data packet to multiple receivers at once. The multicast source sends the data packet to a specific multicast group, and only the addresses belonging to the multicast group can receive the data packet. In IPTV, there is often only one multicast source. Even if the number of users increases exponentially, the backbone bandwidth does not need to increase, because no matter how many destination addresses there are, only a single video is transmitted on any backbone link of the entire network Streaming, so-called "send once, broadcast within group". Multicasting improves data transmission efficiency and reduces the possibility of congestion in the backbone network. For the TV system, the number of users it can support is only limited by the ability to access the network, and has nothing to do with the push capability of the front-end push system.
Therefore, the main test indicators for TV service performance are the maximum number of channels pushed, the average channel bandwidth, the average channel switching time, the average channel leaving delay, the average channel joining delay, the channel overlap time, and the channel interval time.
Maximum number of channels pushed: the maximum number of channels that the streaming media system can provide, and users can traverse all channels in a short time.
Channel average bandwidth: the bandwidth occupied by each channel program. Standard-definition programs (SDTV) and high-definition programs (HDTV) occupy different bandwidths. The bandwidth occupied by HDTV programs is much higher than that of SDTV programs.
Average channel switching time: the time from sending the IGMPleave message to receiving the first multicast packet of the requested channel. Because the channel switching of TV programs on the IP network can only be achieved through IGMP, in contrast, the channel switching of traditional TVs is much faster. Therefore, according to personal subjective feelings, usually the IPTV channel switching time should not exceed 2s (tentative), otherwise the user cannot bear the waiting time for channel switching. At present, the IPTV channel switching time is too slow is also a problem to be solved urgently.
Average channel leaving delay: the time from sending an IGMPleave message to receiving the last multicast packet of the channel. Generally, the shorter the channel leaving delay, the better.
Average channel join delay: The time from sending an IGMP join message to receiving the first multicast packet for that channel. Generally, the shorter the channel joining delay, the better. Channel overlap time: If the system channel switching adopts the method of stopping the multicast packet of the original channel after receiving the multicast packet of the requested channel, the channel overlap time refers to the first multicast packet and the reception of the requested channel. The time interval to the last multicast packet of the original channel.
Channel interval time: If the system channel switching adopts the method of stopping the multicast packets of the original channel first and then receiving the multicast packets of the requested channel, the channel interval time refers to the last multicast packet received from the original channel and the request received The time interval between the first multicast packets of the channel.
3. Other considerations
In addition to the performance test indicators discussed above, there are some practical factors that need to be considered and tested.
The stability of the system. Since most tasks of the IPTV video system are to provide entertainment programs, users pay more attention to the integrity and continuity of the programs when watching entertainment programs. Therefore, stability is a key point for the video system. When watching a favorite video program, the user has a strong emotional color, and any interruption will greatly affect the user's appreciation effect, such as a black screen when the user watches a TV series. The stability of the IPTV video system includes: the stable maximum number of concurrent streams / programs, the stable program bandwidth, and the stability of long-term work.
Network damage factors. Various damages in the network have a great impact on the quality of the video program. The occasional damage in the network directly affects the user's psychological acceptance of the video program. The most direct impact is the user's subjective evaluation of the video image quality, such as When the bit error rate of the network line reaches 10E-6, the VOD program may show obvious mosaic, picture discoloration, and picture lag. In this case, the user is likely to terminate the video on demand. Therefore, we should carefully study the damage caused by various impairments in the network (including delay, jitter, packet loss, out-of-order, and line error) to the quality of the video program. When formulating IPTV service-related technical indicators, the impact of network damage on service quality QoS should be fully considered.
4. Conclusion
In recent years, with the rapid development of broadband construction, video streaming services have become one of the most important applications of the Internet. The IPTV system is a major entry point for providing video services. At present, major operators have begun to gradually provide users with To provide IPTV services, the IPTV trial network has been in trial operation in many cities in China. Testing the service performance of the IPTV system is a key step that operators need to perform before launching the IPTV service.
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