Brief introduction of VOD and TV service performan

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Introduction to VOD and TV service performance test of IPTV system

the future development of IPTV is becoming a hot topic in the industry. According to the statistics of market research company MRG, the global IPTV users will increase from 2million in 2004 to 20million in 2010. It is estimated that the compound growth rate of the global IPTV market from 2005 to 2010 will be 102%. In China, the IPTV industry is still in the experimental stage, and China Telecom, China Unicom and China Railcom are actively carrying out IPTV experiments

at present, many equipment manufacturers have provided IPTV system platforms and equipment. It is recognized in the industry that IPTV business includes two basic businesses: VOD on demand and TV live broadcast. The development of IPTV in China is in full swing, and the testing of IPTV system also needs to be standardized. This paper intends to briefly discuss the performance testing of these two basic services of IPTV system. This paper only considers the end-to-end performance test. The observation point of the test is the user side, and does not consider the hierarchical cache performance of the server side

due to the difference in network structure between VOD on demand network and TV live network, VOD distribution needs to rely on CDN network, while TV distribution needs to rely on multicast network, and CDN network is not required for caching. Based on this, the focus of these two service performance tests is also different

I. Introduction to VOD service performance test

VOD programs are usually transmitted on demand. On demand users can freely control the progress of the program and terminate the play of the program, but each on-demand user needs to occupy a certain network bandwidth, so the number of concurrent users is limited by the network bandwidth and server performance

vod service performance test indicators 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 users that the streaming media system can support at the same time, and each user is required to watch the complete video program normally. Before the number of users gradually increases to the maximum, the system will not make existing users unable to obtain services because of new users. Although some video systems can provide a huge number of concurrent streams, there are a lot of failures. Because most users use TCP, the number of concurrent streams does not decrease after retransmission, but for the original failed single stream, the user can no longer get video services. Therefore, the maximum number of concurrent streams should be the maximum number of effective users who can watch programs at the same time

bandwidth fluctuation: during the playback of video files, the bandwidth of media streams will change due to the change of pictures. 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 greatly before and after, so the program code rate changes correspondingly, and the bandwidth fluctuation is also large. The fluctuation of program code rate is a severe test for the throughput of frequency servers with aluminum magnesium alloy new materials and new technologies for aerospace, weapon equipment and national key engineering models. If too many users demand programs with higher code rate, it is likely that the number of users supported by the server will be reduced, or the output bandwidth of the program stream will be reduced by the video server

the average bandwidth used for harmonic amplification: the average value of the bandwidth used by all users in the process of watching the program. The larger the value, the stronger the bandwidth capacity that the streaming media video system can provide

packet loss rate: when users receive video on demand service, they need to obtain video files from the server. Whether packet loss occurs in the process of video file transmission. The value of packet loss rate is generally small, but the impact on users is very important, especially the currently used compression ratio is relatively high. Even if a few video packets are lost, it will affect users' viewing and even disconnect. The upper limit of end-to-end packet loss rate of video on demand should not exceed 0.1%

average response time: the overall distribution of time from the time users send an on-demand request to the time they receive video services. Of course, the shorter the average response time, the better. Generally speaking, the average end-to-end delay of video on demand should not exceed 2S (tentative)

II. Introduction to TV service performance test

tv programs are usually transmitted by multicast. Multicast is a network technology that allows one or more senders (multicast sources) to send a single packet to multiple recipients at the same time. The multicast source sends the data packet to a specific multicast group, and only the address 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 with it, because no matter how many target addresses there are, only a single video stream is transmitted on any backbone link of the whole network, that is, the so-called "once sent, intra group broadcast". Multicast improves the efficiency of data transmission and reduces the possibility of trunk congestion with deficits of $17billion, $16.6 billion and $17.7 billion respectively. For the TV system, the number of users it can support is only limited by the access network capacity, and has nothing to do with the push capacity of the front-end push system

therefore, the main test indicators of TV service performance include the maximum number of channels pushed, the average channel bandwidth, the average channel switching time, the average channel departure delay, the average channel join 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. Users can traverse all channels in a very short time

channel average bandwidth: the bandwidth occupied by each channel program. The bandwidth occupied by standard definition programs (SDTV) and high-definition programs (HDTV) is different, and the bandwidth occupied by HDTV programs is much higher than that of SDTV programs

average channel switching time: the time from sending igmclear message to receiving the first multicast packet of the requested channel. Because the channel switching of TV programs on IP network can only be realized through IGMP, compared with the channel switching of traditional TV is much faster. Therefore, according to personal subjective feelings, usually the IPTV channel switching time should not exceed 2S (tentative), otherwise users can't stand the waiting time of channel switching. At present, the slow switching time of IPTV channel is also an urgent problem to be solved

average channel departure delay: the time from sending igmleave message to receiving the last multicast packet of the channel. Usually, the shorter the channel departure delay is, the better

average channel join delay: the time between sending igmpjoin message and receiving the first multicast packet of the channel. Usually, the shorter the channel join delay is, 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 time interval between receiving the first multicast packet of the requested channel and receiving the last multicast packet of the original channel

channel interval: if the system adopts the method of stopping the multicast packet of the original channel before receiving the multicast packet of the requested channel for channel switching, the channel interval refers to the time interval between receiving the last multicast packet of the original channel and receiving the first multicast packet of the requested channel

III. other considerations

in addition to the performance test indicators discussed above, there are also some practical factors that need to be considered and tested

stability of the system. Since most of the tasks of IPTV video system are to provide entertainment programs, users pay more attention to the integrity and continuity of programs in the process of watching entertainment programs. Therefore, stability is a key point for video system. Users have strong feelings when watching their favorite video programs, and any disconnection will greatly affect the user's appreciation effect, such as the black screen when users watch TV dramas. The stability of IPTV video system includes: stable maximum number of concurrent streams/programs, stable program bandwidth, and long-time stability

collateral injury factors. Various damages in the network have a great impact on the quality of video programs. The occasional damage in the network directly affects the psychological acceptance of users to the video program. The most direct impact is the reduction of users' subjective evaluation of video image quality. For example, when the bit error rate of the network line reaches 10e-6, VOD programs may appear obvious mosaic, picture discoloration, and picture hysteresis. In this case, Users are likely to terminate this VOD. Therefore, we should carefully study the damage caused by various damages in the network (including delay, jitter, packet loss, out of sequence, line error code) to the quality of video programs. When formulating IPTV service related technical indicators, we should fully consider the impact of network damage on service quality and QoS

IV. conclusion

in recent years, with the rapid development of broadband construction, video streaming media service has become one of the most important applications of interconnection. IPTV system is the most important entry point for providing video services. At present, major operators have begun to gradually provide IPTV services to users, and IPTV experiments have been put into trial operation in many cities in China. Testing the service performance of IPTV system is a key step for operators to carry out IPTV services. At present, IPTV technology is in the initial stage of development. Due to the large amount of content involved in IPTV, relevant technologies and businesses are still in the process of research. However, with the continuous development of technology, the testing technology of IPTV business will continue to mature and improve, which will inevitably promote the development of domestic IPTV business. The direction of tearing and cutting should be consistent with the direction of calendering. (end)

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