At present, many equipment manufacturers have provided IPTV system platform and equipment, and the industry recognized that IPTV business includes two basic services: VOD and TV live broadcast. The development of IPTV in China is in full swing, and the test of IPTV system is in urgent need of standardization. This paper intends to conduct a simple discussion on the performance test of these two basic services of IPTV system. This article only considers end-to-end performance testing, which looks at the user side and does not consider the server-side hierarchical cache performance.
Due to the difference in network structure between VOD network and TV live broadcast network, VOD distribution needs to rely on CDN network, while TV distribution needs to rely on multicast network and does not need CDN network to cache, based on this, the two kinds of service performance test focus is also different.
1. A brief introduction to VOD service performance testing
VOD programs are usually delivered on demand. VOD users can freely control the progress of the program and terminate the broadcast of the program, but each VOD user needs to occupy a certain amount of network bandwidth, so the number of concurrent users is limited by the network bandwidth and server performance. The main test indexes of VOD service performance 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 a streaming system can support at the same time, with the requirement that each user can normally watch the full video program. Before the number of users has gradually increased to a maximum, the system will not make the already online users unable to access the service because of the addition of new users. Some video systems can provide a large number of concurrent streams, but the number of failures is large. Since most users use TCP, the number of concurrent streams does not decrease after retransmission. However, for the original failed single stream, the user cannot continue to get the video service. Therefore, the maximum number of concurrent streams should be the maximum number of users that the video system can support to effectively watch programs online at the same time.
Bandwidth fluctuation: During the playing of video files, the bandwidth of media stream will change due to the change of 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, continuous pictures change greatly before and after the show, so the program code rate changes correspondently, and the bandwidth fluctuates accordingly.
The fluctuation of program code rate is a severe test to the throughput of the video server. If too many users demand programs with higher code rate, the number of users that the server can support is likely to decrease, or the video server will reduce the output bandwidth of the program stream.
Average bandwidth used: the average of the bandwidth used by all users during the process of watching a program. The greater the value, the stronger the bandwidth capacity provided by the streaming video system.
Packet loss rate: When users accept VOD service, they need to obtain video files from the server, and whether packet loss occurs in the process of video file transmission. The value of packet loss rate is generally relatively small, but it has a very important impact on users. Especially, the compression ratio used at present is relatively high. Even the loss of a few video packets will affect users' viewing and even break the connection phenomenon. The maximum end-to-end packet loss rate for VOD should not exceed 0.1%.
Average response time: the overall distribution of the time between a user making a VOD request and receiving a video service.
Of course, the shorter the average response time, the better. In general, the average end-to-end VOD delay should not exceed 2s (tentative).
2. Brief 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 simultaneously send a single packet to multiple receivers at once. A multicast source sends a packet to a specific multicast group, and only addresses belonging to that multicast group can receive the packet. In IPTV, there is often only one multicast source, and even if the number of users grows exponentially, the backbone bandwidth does not need to increase, because no matter how many target addresses there are, only a single video stream is transmitted over any backbone link of the entire network, which is called "send once, broadcast within a group". Multicast improves the efficiency of data transmission and reduces the possibility of congestion in the backbone. For the TV system, the number of users it can support is only limited by the ability to access the network, which 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, average channel bandwidth, average channel switching time, average channel departure delay, average channel joining delay, channel overlap time and channel interval time.
Maximum number of channels pushed: The maximum number of channels that a streaming system can provide, allowing users to traversal all channels in a short period of time.
Average channel bandwidth: The amount of bandwidth used by a program on each channel.
Standard definition (SDTV) and high-definition (HDTV) programs occupy different bandwidth, HDTV programs occupy much more bandwidth than SDTV programs.
Average channel switching time: The time between sending the IGMPLEAVE message and receiving the first multicast packet for the requested channel. Because the channel switching of TV programs on IP network can only be realized through IGMP, compared with the traditional TV channel switching is much faster. Therefore, according to personal subjective feeling, usually IPTV channel switching time should not exceed 2S (tentative), otherwise the user can hardly bear 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 between sending an IGMPLEAVE message and receiving the last multicast packet for that channel. In general, the shorter the channel departure delay, the better.
Average channel join delay: The time between the IGMPJOIN message being sent and the first multicast packet for the channel being received. In general, the shorter the channel add delay, the better.
Channel overlap time: if the system channel switch takes the mode of receiving the requested channel's multicast packet before the original channel's multicast packet is stopped, 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 time: if the system channel switch takes the way of stopping the original channel's multicast packet before receiving the requested channel's multicast packet, the channel interval time 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.
3. other considerations
In addition to the performance test metrics discussed above, there are 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 consistency of the programs when watching entertainment programs. Therefore, stability is a very key point for the video system. Users will have a strong emotional color when watching their favorite video programs, and any interruption of the stream will greatly affect the appreciation effect of users. For example, when users watch TV dramas, the screen will be black. The stability of IPTV video system includes: stable maximum number of concurrent streams/programs, stable program bandwidth and long time working stability.
Network damage factors. Various kinds of damage in the network have a great impact on the quality of video programs. The occasional damage in the network directly affects users' psychological acceptance of the video programs. The most direct impact is the reduction of users' subjective evaluation on the quality of video images. VOD programs may show significant Mosaic, discoloration, and lag, in which case the user is likely to terminate the VOD program. Therefore, we should carefully study the damage caused by various kinds of network damage (including delay, jitter, packet loss, out of order, line error code) to the quality of video programs. The impact of network damage on QoS of IPTV service should be taken into full consideration when the relevant technical indicators of IPTV service are formulated.
4. Conclusion
In recent years, with the high-speed development of the broadband, video streaming service has become one of the major applications of the Internet, IPTV system is to provide video service of one of the major, at present, operators have begun to gradually provide IPTV business, IPTV trials network has been in trial operation of the domestic cities. It is a key step for operators to test IPTV system service performance before launching IPTV service.
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How far(long) the transmitter cover?
The transmission range depends on many factors. The true distance is based on the antenna installing height , antenna gain, using environment like building and other obstructions , sensitivity of the receiver, antenna of the receiver . Installing antenna more high and using in the countryside , the distance will much more far.
EXAMPLE 5W FM Transmitter use in the city and hometown:
I have a USA customer use 5W fm transmitter with GP antenna in his hometown ,and he test it with a car, it cover 10km(6.21mile).
I test the 5W fm transmitter with GP antenna in my hometown ,it cover about 2km(1.24mile).
I test the 5W fm transmitter with GP antenna in Guangzhou city ,it cover about only 300meter(984ft).
Below are the approximate range of different power FM Transmitters. ( The range is diameter )
0.1W ~ 5W FM Transmitter ：100M ~1KM
5W ~15W FM Ttransmitter : 1KM ~ 3KM
15W ~ 80W FM Transmitter : 3KM ~10KM
80W ~500W FM Transmitter : 10KM ~30KM
500W ~1000W FM Transmitter : 30KM ~ 50KM
1KW ~ 2KW FM Transmitter : 50KM ~100KM
2KW ~5KW FM Transmitter : 100KM ~150KM
5KW ~10KW FM Transmitter : 150KM ~200KM
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