JP2004266599A - Transmitting side terminal and receiving side terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain highly accurate synchronism between a transmitting side and a receiving side even on a variable delay transmission line where transmission delay fluctuation is great. <P>SOLUTION: A synchronizing signal generating source 4 generates a digitized synchronizing signal 71. The digitized synchronizing signal 71 is inputted to a transmitting side terminal 1 and a receiving side terminal 2 by fixed delay transmission lines 51, 52 different from a variable delay transmission line. Besides, the transmitting side terminal 1 transmits the digitized synchronizing signal 71 that is received from the synchronizing signal generating source 4, to the receiving side terminal 2 via the variable delay transmission line 3. The receiving side terminal 2 receives the digitized synchronizing signal 71. With the digitized synchronizing signal 71 received from the fixed delay transmission line 52 as a reference timing, the receiving side terminal 2 performs processing of data 6 on the basis of comparison between count values of the digitized synchronizing signal 71 received from the variable delay transmission line 3 and that of the reference timing. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a communication system for transmitting video, audio, and other real-time data via a variable delay transmission path.
[0002]
[Prior art]
2. Description of the Related Art In an IP network such as the Internet or an ATM (Asynchronous Transfer Mode) network, the transmission delay between transmission and reception fluctuates because the degree of congestion in the network changes with time. That is, the variable delay transmission line has a large delay fluctuation. On the other hand, in transmission of real-time data such as video and audio that requires real-time performance, synchronization between the transmitting terminal and the receiving terminal is required. When transmitting real-time data via the variable delay transmission line, if information data for synchronization is also transmitted via the variable delay transmission line, it becomes difficult to maintain synchronization between transmission and reception due to delay fluctuation. Become.
[0003]
As a conventional example for this problem, there is, for example, Japanese Patent Application Laid-Open No. 11-88305. This is a method in which signal information for synchronization is supplied to a transmitting / receiving terminal via a fixed delay transmission line different from a variable delay transmission line.
[0004]
FIG. 8 shows a conventional real-time data communication system disclosed in Japanese Patent Application Laid-Open No. 11-88305. In this system, a transmitting terminal 1 and a receiving terminal 2 are connected via a variable delay transmission line 3 and transmit and receive real-time data 6 such as video.
[0005]
The synchronization signal 7 output from the synchronization signal generation source 4 is input to the transmitting terminal 1 and the receiving terminal 2 via fixed delay transmission lines 51 and 52 different from the variable delay transmission line 3.
[0006]
In the prior art described in Japanese Patent Application Laid-Open No. 11-88305, a BS broadcast satellite is used as a synchronizing signal source 4, its broadcast waves are used as fixed delay transmission lines 51 and 52, and a vertical synchronizing signal 7 is used as a synchronizing signal 7. It is assumed that the signal is video data stored in the recording device as real-time data 6.
[0007]
Next, the operation will be described with reference to a time chart shown in FIG. FIG. 9 is a diagram showing the timing at which the synchronization signal and the data are transferred. The horizontal direction indicates the passage of time, the synchronization signal is indicated by a white rectangle, and the portion at which the data is transferred is indicated by hatching.
[0008]
The synchronization signal generation source 4 generates the synchronization signal 7 at a constant cycle (FIG. 9A). The synchronization signal 7 is transmitted via the fixed delay transmission lines 51 and 52 and is received by the transmitting terminal 1 and the receiving terminal 2 (FIGS. 9B and 9D). Since the transmission delay at this time is fixed in each of the fixed delay transmission lines 51 and 52, the time interval of the synchronization signal 7 received by the transmission terminal 1 and the reception terminal 2 is the time interval of the synchronization signal generation source 4. Will be maintained.
[0009]
The transmitting terminal 1 reads out one frame of video data stored in the recording device at a constant cycle based on the received synchronization signal 7 and transmits it as data 6 via the variable delay transmission path 3 (FIG. 9C). ). The receiving terminal 2 receives the data 6 and outputs a video on a monitor screen at a constant cycle based on the received synchronization signal 7 (FIG. 9E).
[0010]
The transmitting terminal 1 outputs data at a fixed period t1. However, the receiving terminal 2 receives the data t2 and t3 with respect to the output timing of the transmitting terminal 1 due to the delay fluctuation of the variable delay transmission line 3. The data is input with a variable delay such as. Therefore, the time intervals of the data received by the receiving terminal 2 become uneven. However, by waiting for the video output of the received data until the timing of the reception synchronization signal 7, the video output at equal intervals in time is restored.
[0011]
Note that the video data is usually 1/30 second and one frame, and t1 in the above assumed example is also 1/30 second.
[0012]
In FIG. 8, the synchronization signal generation source 4 is separated from the transmission terminal 1 and the reception terminal 2, but the synchronization signal generation source 4 may be provided inside the transmission terminal 1 or the reception terminal 2. .
[0013]
[Patent Document 1]
JP-A-11-88305
[0014]
[Problems to be solved by the invention]
By the way, the above conventional technique has a problem that the real-time property cannot be maintained when the transmission delay fluctuation is larger than the synchronization cycle. This problem will be described with reference to a time chart shown in FIG. As in FIG. 9, the horizontal direction indicates the passage of time, the synchronization signal is indicated by a white rectangle, and the portion to which data is transferred is indicated by oblique lines.
[0015]
In FIG. 10, the delay until the data 6 transmitted by the transmitting terminal 1 is received by the receiving terminal 2 fluctuates more greatly than in FIG. Phenomena such as reception of video data for minutes or failure to receive video frames within the synchronization period occur. For this reason, loss of a video frame or drop of a frame occurs, and as a result, continuity and isochronism of data are impaired. That is, the real-time property cannot be maintained.
[0016]
Conversely, since the synchronization cycle must be longer than the magnitude of the delay fluctuation, a highly accurate synchronization cycle cannot be applied to a variable delay transmission line having a large delay fluctuation.
[0017]
Further, although not particularly mentioned in the above-mentioned conventional technology, a radio wave such as a BS satellite broadcast includes a plurality of channels, and television images are broadcast on these channels. When the transmitting terminal 1 and the receiving terminal 2 receive synchronizing signals from television images of different channels, the frequencies of the synchronizing signals are not completely the same, so that the synchronizing between the transmitting and receiving terminals will eventually be lost. Thus, the identity of the synchronization signal referred to by the transmitting / receiving terminal is not guaranteed, and there is a possibility that real-time data communication cannot be established.
[0018]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a transmission terminal and a reception terminal capable of maintaining high-precision synchronization between transmission and reception even on a variable delay transmission line having large transmission delay fluctuation. The purpose is to provide.
[0019]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention, the transmitting terminal and the receiving terminal, via a variable delay transmission line, in the transmitting terminal in a real-time data communication system that transmits and receives real-time data that requires a synchronization signal, Basically, the synchronization signal is transmitted through both a variable delay transmission line and another fixed delay transmission line. Also, in a receiving terminal in a real-time data communication system in which a transmitting terminal and a receiving terminal transmit and receive real-time data requiring a synchronization signal via a variable delay transmission path, the variable delay transmission path is different from the variable delay transmission path. Basically, the synchronous signal is received and the real-time data is reproduced on both of the fixed delay transmission path.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
FIG. 1 is a system configuration diagram showing Embodiment 1 of the present invention.
In FIG. 1, a transmitting terminal 1 and a receiving terminal 2 are connected via a variable delay transmission line 3 and transmit and receive real-time data 6 such as video.
[0021]
The synchronization signal generation source 4 generates a counting synchronization signal 71. The numerical synchronization signal 71 is input to the transmitting terminal 1 and the receiving terminal 2 via fixed delay transmission lines 51 and 52 different from the variable delay transmission line 3.
[0022]
In addition, the transmitting terminal 1 transmits the numerical synchronization signal 71 received from the synchronization signal generating source 4 to the receiving terminal 2 via the variable delay transmission path 3. The receiving terminal 2 receives the count synchronization signal 71.
[0023]
Next, the operation will be described with reference to the time chart shown in FIG.
FIG. 2 is a diagram showing the timing at which the synchronization signal and the data are transferred. The horizontal direction indicates the passage of time, the numerical synchronization signal 71 is indicated by a white rectangle, and the portion at which the data is transferred is indicated by hatching. ing. The count value is added to the numerical synchronization signal 71.
[0024]
The synchronization signal generation source 4 generates a count synchronization signal 71 at a constant cycle (FIG. 2A). The numerical synchronization signal 71 is transmitted via the fixed delay transmission lines 51 and 52 and received by the transmitting terminal 1 and the receiving terminal 2 (FIGS. 2B and 2D). Since the transmission delay at this time is fixed in each of the fixed delay transmission lines 51 and 52, the time interval of the count synchronization signal 71 received by the transmitting terminal 1 and the receiving terminal 2 is The time interval is maintained. However, the distance between the transmitting terminal 1 and the receiving terminal 2 from the synchronization signal generating source 4, that is, the time when data passes through the fixed delay transmission lines 51 and 52 is usually different, so that the transmitting terminal 1 and the receiving terminal 2 The reception timing of the received numerical synchronizing signal 71 is shifted at fixed time intervals.
[0025]
The transmission side terminal 1 is stored in a recording device (not shown) inside and outside the transmission side terminal 1 at a fixed period based on the counted synchronization synchronization signal 71 received from the synchronization signal generation source 4 via the fixed delay transmission line 51. One frame of the video data is read out and transmitted as data 6 to the receiving terminal 2 via the variable delay transmission line 3 together with the numerical synchronization signal 71 (FIG. 2 (c)).
[0026]
The receiving side terminal 2 receives the count synchronous synchronization signal 71 from the synchronization signal generating source 4 via the fixed delay transmission line 51 and counts the data 6 from the transmission side terminal 1 via the variable delay transmission line 3. And the dynamic synchronization signal 71.
At this time, the receiving terminal 2 sets the count value of the reference timing and the count synchronization signal 71 received from the variable delay transmission path 3 as a reference timing using the count synchronization signal 71 received from the fixed delay transmission path 52 as a reference timing. The data 6 is processed based on the comparison. Specifically, taking into account the maximum delay of the variable delay transmission line 3, the delay time of the fixed delay transmission line 51, and the delay time of the fixed delay transmission line 52, for example, Video output is performed after waiting until a reference timing obtained by adding an offset of +20 to the count value of the synchronization signal 71 (FIG. 2E).
[0027]
In FIG. 2, similarly to FIG. 10, the delay until the data 6 transmitted by the transmitting terminal 1 is received by the receiving terminal 2 fluctuates significantly more than the synchronization cycle. Phenomena such as reception of video data for a plurality of frames within a cycle and failure to receive video frames within a synchronization cycle have occurred. However, by comparing the numerical synchronization signal 71 received from the variable delay transmission path 3 and the fixed delay transmission path 52, the time interval of the data 6 transmitted by the transmitting terminal 1 is correctly restored, so that the real-time property is improved. Can be maintained accurately.
[0028]
That is, in the above example, the count value of the numerical synchronization signal 71 received from the variable delay transmission line 3 is set to +20, but the offset value is (maximum delay of the variable delay transmission line 3) + ( A value corresponding to a time larger than (delay time of fixed delay transmission line 51)-(delay time of fixed delay transmission line 52) is desirable. If this value is known, the value may be applied. Otherwise, the receiving terminal 2 may dynamically determine the value by comparing and monitoring the count value of the count synchronization signal 71 received from the variable delay transmission line 3 and the fixed delay transmission line 52. . Note that this (maximum delay of the variable delay transmission path 3) + (delay time of the fixed delay transmission path 51) is obtained by dividing the numerical synchronization signal 71 transmitted from the synchronization signal generation source 4 to the transmitting terminal 1 by the fixed delay transmission Since the signal arrives at the receiving terminal 2 via the path 51 and the variable delay transmission path 3, the delay time can be obtained by obtaining the delay time.
[0029]
In the above example, the synchronizing signal generation source 4 has been described as generating the counting synchronizing signal 71 at a fixed cycle, but it is not always necessary to generate the synchronizing signal 71 at regular intervals. This is because if the transmitting terminal 1 and the receiving terminal 2 are provided with a frequency reproducing mechanism using a PLL (Phase Locked Loop) or the like, the reference timing can be reproduced from the non-equidistant numerical synchronization signal 71. For example, the timing corresponding to the count value 40 is 4/3 times the time from the count value 0 to the count value 30 even if the count synchronization signal 71 of the count value 40 is omitted in FIG. Further, the determination can be made based on the numerical synchronization signal 71 up to that time.
[0030]
Further, in FIG. 2, the synchronization signal generation source 4 is separated from the transmission side terminal 1 and the reception side terminal 2, but the synchronization signal generation source 4 is provided inside the transmission side terminal 1 or the reception side terminal 2. What is good is the same as the above-mentioned conventional example. However, when the synchronization signal generation source 4 is provided in the transmitting terminal 1, the fixed delay transmission line 51 is not provided, and thus the offset value is (maximum delay of the variable delay transmission line 3) − (fixed delay transmission line 3). A time longer than the delay time of the path 52) is desirable. Further, when the synchronization signal generation source 4 is provided in the receiving terminal 2, the fixed delay transmission line 52 is not provided, and thus the offset value is (maximum delay of the variable delay transmission line 3) + (fixed delay transmission line 3). It is desirable that the time is larger than (delay time of line 51) (maximum delay of variable delay transmission line 3)-(delay time of fixed delay transmission line 52).
[0031]
As described above, according to the first embodiment, the count synchronization signal 71 is transmitted not only via the fixed delay transmission line 51 between the synchronization signal generation source 4 and the reception terminal 2 but also between the transmission terminal 1 and the reception terminal. Since transmission is performed through both the variable delay transmission lines 3 between the terminals 2, even if the transmission delay fluctuations of the variable delay transmission lines 3 are large, the reception side terminal 2 causes the delay due to the transmission delay fluctuations in the variable delay transmission lines 3. Considering the time, the reproduction timing of the synchronization signal required for reproducing the real-time data can be determined. As a result, even when the transmission delay fluctuation of the variable delay transmission line 3 is large, a highly accurate synchronization between transmission and reception can be maintained, and a real-time data communication system capable of maintaining real-time properties can be obtained.
[0032]
Embodiment 2 FIG.
In the above first embodiment, the case where the transmitting terminal 1 transmits the video data stored in the recording device has been described. However, in the case of a live video, the synchronization signal cycle from the synchronization signal generation source 4 is used. And the phase of the video frame cycle do not match. Next, an embodiment in such a case will be described.
[0033]
FIG. 3 is a system configuration diagram showing Embodiment 2 of the present invention.
The difference from FIG. 1 is that the synchronization signal transferred from the transmission terminal 1 to the reception terminal 2 via the variable delay transmission line 3 is a numerical relative synchronization signal 72. In FIG. 3, the transmitting terminal 1 and the receiving terminal 2 each include a frequency reproducing unit 8.
[0034]
Next, the operation will be described with reference to the time chart shown in FIG.
FIG. 4 is a diagram showing timings at which the synchronization signal and the data are transferred. The horizontal direction indicates the passage of time, and the count synchronization signal 71 and the count relative synchronization signal 72 are outlined rectangles. Are indicated by oblique lines. The count value is added to the count synchronization signal 71 and the count relative synchronization signal 72.
[0035]
The synchronization signal generation source 4 generates a count synchronization signal 71 at a constant period (FIG. 4A). This numerical synchronization signal 71 is transmitted via the fixed delay transmission lines 51 and 52, and received by the transmitting terminal 1 and the receiving terminal 2 while maintaining a time interval (FIG. 4B, (D)). As described above, the transmission side terminal 1 and the reception side terminal 2 usually have different distances from the synchronization signal generation source 4, that is, the time during which data passes through the fixed delay transmission lines 51 and 52. The reception timing of the numerical synchronization signal 71 received by the receiving terminal 2 is shifted at regular time intervals.
[0036]
The transmitting terminal 1 and the receiving terminal 2 use the frequency reproducing means 8 to reproduce the increment frequency of the count value in the synchronous signal generating source 4 from the received numerical synchronizing signal 71. Therefore, even during the period between the receptions of the numerical synchronization signal 71, the count value corresponding to that time can be identified at any time. For example, the time corresponding to the count value 13 is a time point at which three advance cycles have elapsed from the time point at which the count synchronization signal 71 of the count value 10 is received. The count value corresponding to each time point is hereinafter referred to as a reproduction count value.
[0037]
When a video frame is generated from a video data generation source (for example, a video camera) (not shown), the transmitting terminal 1 transmits it as data 6 via the variable delay transmission path 3. At this time, the reproduction count value at the time when the video frame is generated is transmitted as a numerical relative synchronization signal 72 along with the data 6 (FIG. 4C).
[0038]
The receiving terminal 2 receives the data 6 and the numerical relative synchronization signal 72. The receiving side terminal 2 uses the reproduction count value reproduced by the frequency reproduction means 8 from the count synchronization signal 71 received by the fixed delay transmission line 52 as a reference timing, and uses the count relative synchronization signal received from the variable delay transmission line 3 as a reference timing. The processing of the data 6 is performed based on the comparison between the count value 72 and the reference timing. In FIG. 4, video output is performed after waiting for a reference timing obtained by adding an offset of, for example, +17 to the count value of the numerical relative synchronization signal 72 received from the variable delay transmission line 3 (FIG. 4 (e)). .
[0039]
In FIG. 4 as well, the delay until the data 6 transmitted by the transmitting terminal 1 is received by the receiving terminal 2 fluctuates significantly more than the synchronization period, but occurs at the transmitting terminal 1 as in FIG. The time interval of the video frame thus restored is correctly restored, and the real-time property can be accurately maintained.
[0040]
Note that the discussion on the offset value and the discussion on the signal generation interval of the synchronization signal generation source 4 in the second embodiment are the same as those in the first embodiment.
[0041]
Also, the synchronization signal generation source 4 may be provided inside the transmission side terminal 1 or the reception side terminal 2 in the same manner as in the first embodiment. The reproducing means 8 can be omitted.
[0042]
Further, if the synchronization signal generation source 4 generates the count synchronization signal 71 each time the count value increases, the frequency reproducing means 8 of the transmitting terminal 1 and the receiving terminal 2 can be omitted. is there.
[0043]
Further, in the above example, video data that is generated periodically at a fixed period is assumed. However, even data that is generated at irregular intervals may be accompanied by the reproduction count value at the time of occurrence, so that it does not matter.
[0044]
Furthermore, in the above example, the transmitting terminal has been described as transmitting data at the same time as the generation of video data. However, if the reproduction count value at the time of data generation is appended, transmission may be appropriately delayed.
[0045]
As described above, according to the second embodiment, the count synchronization signal 71 from the synchronization signal generation source 4 is simply transmitted to the transmitting terminal 1 and the receiving terminal 2 via the fixed delay transmission lines 51 and 52, respectively. Instead, the relative count value at the time of data generation with respect to the count value of the quantitative synchronization signal 71 is transmitted from the transmitting terminal 1 to the receiving terminal 2 via the variable delay transmission line 3 together with the data 6 as the quantitative relative synchronization signal 72. Since transmission is performed, high-precision synchronization can be maintained between transmission and reception for real-time data that is out of phase with the synchronization signal cycle, even if the transmission delay fluctuation of the variable delay transmission path is large, real-time performance is improved. A communication system that can be maintained can be obtained.
[0046]
Embodiment 3 FIG.
By the way, there is an MPEG System (international standard ISO13818-1) as a digital video / audio transmission system, which is mainly used for transmission via a fixed delay transmission line such as satellite broadcasting and cable television broadcasting.
[0047]
The MPEG System is a standard for multiplexing MPEG individual streams obtained by compressing and encoding data of individual media such as video and audio into one MPEG multiplexed stream. The transmitting side terminal and the receiving side terminal of the MPEG System each have a count value called STC (System Time Clock). The transmitting terminal inserts its own STC value into the MPEG multiplexed stream as a synchronization signal called SCR (System Clock Reference) or PCR (Program Clock Reference). The receiving terminal that receives the MPEG multiplexed stream inputs the SCR / PCR to a frequency reproducing mechanism using a PLL or the like and reproduces the STC stepping frequency of the transmitting terminal, thereby obtaining the STC value of the transmitting terminal. To play.
[0048]
A synchronization signal called PTS (Presentation Time Stamp) or DTS (Decode Time Stamp) is added to the MPEG individual stream for each decoded data unit such as a video / audio frame. These synchronization signals indicate the STC value of the timing at which decoding and reproduction of the corresponding decoding data unit should be performed.
[0049]
As Embodiment 3, an embodiment in which the present invention is applied to the transmission of an MPEG multiplexed stream will be described.
[0050]
FIG. 5 is a system configuration diagram showing the third embodiment of the present invention.
In FIG. 5, a transmitting terminal 1 and a receiving terminal 2 are connected via a variable delay transmission line 3, and transmit and receive an MPEG multiplexed stream 61.
[0051]
The synchronization signal generation source 4 includes an STC generator 41, and generates an SCR / PCR 711 as the STC value. The SCR / PCR 711 is input to the transmitting terminal 1 and the receiving terminal 2 via fixed delay transmission lines 51 and 52, respectively.
[0052]
The transmitting terminal 1 includes an MPEG multiplexer 101. The MPEG multiplexer 101 inserts the SCR / PCR 711 received from the synchronization signal generation source 4 into the MPEG multiplexed stream 61 and transmits it to the variable delay transmission path 3.
[0053]
The receiving terminal 2 includes a buffer 201 for temporarily storing the MPEG multiplexed stream 61 received from the variable delay transmission path 3, a read control unit 202 for reading the MPEG multiplexed stream 61 from the buffer 201, and an MPEG multiplexed stream 61. An MPEG separator 203 for separating the individual MPEG stream 62 and an MPEG decoder 204 for decoding and reproducing the individual MPEG stream 62 are provided.
[0054]
In the receiving terminal 2, the SCR / PCR 711 received via the fixed delay transmission line 52 is input to the read control unit 202. The read control unit 202 executes reading from the buffer 201 using the SCR / PCR 711 as a reference timing. That is, the reading speed is set so that the reference timing when reading the SCR / PCR 711 inserted into the MPEG multiplexed stream 61 in the buffer 201 becomes a value obtained by adding a fixed offset to the inserted SCR / PCR 711. To adjust.
[0055]
When the third embodiment is compared with the first embodiment, the MPEG multiplexed stream 61 corresponds to the data 6, and the SCR / PCR 711 corresponds to the numerical synchronization signal 71.
[0056]
As described above, according to the third embodiment, by comparing the SCR / PCR 711 received from the variable delay transmission line 3 and the fixed delay transmission line 52, the output of the read control unit 202 of the reception side terminal 2 is obtained. Then, the MPEG multiplexed stream transmitted by the transmitting terminal 1 is temporally correctly restored.
[0057]
The discussion on the offset value, the discussion on the frequency reproduction mechanism, and the discussion on the separation and integration of the synchronization signal source 4 are the same as those in the first embodiment. The frequency reproduction mechanism in the present embodiment corresponds to the above-mentioned STC reproduction means.
[0058]
In the above example, the transmission format of the SCR / PCR 711 on the fixed delay transmission lines 51 and 52 is not limited. However, the transmission format may be an MPEG multiplexed stream or another format.
[0059]
Further, in the above example, the description has been made assuming that the SCR / PCR 711 is inserted into the MPEG multiplexed stream 61. However, if the MPEG multiplexed stream 61 can be associated with the SCR / PCR 711, other methods may be used. May be. For example, when the variable delay transmission line 3 is an IP network, the SCR / PCR711 or a value obtained by converting the SCR / PCR711 according to a certain rule may be inserted into the header area of the TCP / IP protocol stack. Similar effects can be obtained. As an example, insertion into a header area of RTP (Realtime Transport Protocol) or insertion into the header area by providing a dedicated protocol is also conceivable.
[0060]
As described above, according to the third embodiment, the SCR / PCR 711 is transmitted through both the fixed delay transmission lines 51 and 52 and the variable delay transmission line 3, so that the transmission through the variable delay transmission line 3 is performed. It is possible to obtain an MPEG multiplexed stream communication system capable of maintaining real-time properties even when delay fluctuation is large.
[0061]
Embodiment 4 FIG.
Another embodiment when the present invention is applied to the transmission of an MPEG multiplexed stream will be described.
[0062]
FIG. 6 is a system configuration diagram showing the fourth embodiment of the present invention.
In FIG. 6, a transmitting terminal 1 and a receiving terminal 2 are connected via a variable delay transmission line 3, and transmit and receive an MPEG multiplexed stream 61.
[0063]
The synchronization signal generation source 4 includes an STC generator 41, and generates an SCR / PCR 711 as the STC value. The SCR / PCR 711 is input to the transmitting terminal 1 and the receiving terminal 2 via the fixed delay transmission lines 51 and 52.
[0064]
The transmitting terminal 1 includes an MPEG multiplexer 101, an MPEG encoder 102, and an STC reproducing unit 81. The SCR / PCR 711 received from the synchronization signal source 4 via the fixed delay transmission path 51 is input to the STC reproducing means 81. The STC reproducing means 81 reproduces the reproduction STC 712 as described above. The MPEG encoder 102 adds the PTS / DTS 713 to the MPEG individual stream 62 with reference to the reproduction STC 712. The MPEG multiplexer 101 multiplexes the MPEG individual stream 62 from the MPEG encoder 102 to form an MPEG multiplexed stream 61 and transmits it to the variable delay transmission path 3.
[0065]
The receiving side terminal 2 comprises: an MPEG separator 203 for separating the MPEG multiplexed stream 61 received from the variable delay transmission path 3 into an individual MPEG stream 62; a buffer 201 for temporarily storing the MPEG individual stream 62; A read control unit 202 for reading the individual stream 62 and an MPEG decoder 204 for decoding and reproducing the MPEG individual stream 62 are provided. In addition, an STC reproducing unit 81 is provided.
[0066]
In the receiving terminal 2, the SCR / PCR 711 received from the synchronization signal generation source 4 via the fixed delay transmission line 52 is input to the STC reproducing means 81. The STC reproducing means 81 reproduces the reproduction STC 712 as described above. The reproduction STC 712 is input to the read control unit 202. The read control unit 202 executes reading from the buffer 201 using the reproduction STC 712 as a reference timing. That is, the decoding data unit included in the MPEG individual stream 62 in the buffer 201 is read when the value obtained by adding a fixed offset to the added PTS / DTS 713 and the value of the reproduction STC 712 match, and the MPEG decoder 204.
[0067]
When the fourth embodiment is compared with the second embodiment, the MPEG multiplexed stream 61 is used as the data 6, the SCR / PCR 711 is used as the count synchronization signal 71, the PTS / DTS 713 is used as the count relative synchronization signal 72, and the STC reproducing means. 81 corresponds to the frequency reproducing means 8.
[0068]
As described above, according to the fourth embodiment, the SCR / PCR 711 received from the fixed delay transmission line 52 is received from the variable delay transmission line 3 with the reproduction STC 712 reproduced by the STC reproduction unit 81 as the reference timing. Since the decoding / reproduction processing is performed in units of decoded data based on the comparison between the PTS / DTS 713 and the reproduction STC 712, the time interval of video / audio or the like generated in the transmission side terminal 1 is correctly restored in the reception side terminal 2. .
[0069]
The discussion on the offset value, the discussion on the frequency reproduction mechanism, and the discussion on the separation and integration of the synchronization signal source 4 are the same as those in the second embodiment. The discussion of the SCR / PCR transmission format on the fixed delay transmission path is the same as in the third embodiment.
[0070]
As described above, according to the fourth embodiment, the SCR / PCR 711 is transmitted through the fixed delay transmission lines 51 and 52, and the PTS / DTS 713 is transmitted through the variable delay transmission line 3. According to the fourth embodiment, an MPEG multiplexed stream communication system capable of maintaining real-time performance even when the transmission delay fluctuation of the variable delay transmission line 3 is large can be obtained.
[0071]
Embodiment 5 FIG.
FIG. 7 is a system configuration diagram showing Embodiment 5 of the present invention.
In the fifth embodiment, the transmitting terminal 1 and the receiving terminal 2 include the synchronization signal selecting means 91. The transmitting terminal 1 further includes a synchronization signal determination unit 92, and the synchronization signal determination unit 92 notifies the synchronization signal selection unit 91 of the synchronization signal selection information 93. The synchronization signal determination unit 92 further notifies the synchronization signal selection unit 91 of the receiving terminal 2 of the synchronization signal selection information 93 via the variable delay transmission line 3. Except for this, the configuration is the same as that of the conventional system shown in FIG.
[0072]
The synchronization signal determining means 92 determines a synchronization signal to be commonly referred to by the transmitting terminal 1 and the receiving terminal 2 for a certain real-time data communication, and sets information that can identify the synchronization signal as synchronization signal selection information 93 as synchronization signal selection information 93 The selection means 91 is notified.
[0073]
As the synchronization signal selection information 93, for example, a set such as a broadcasting type such as BS satellite broadcasting, CS satellite broadcasting, terrestrial broadcasting, and cable broadcasting; It is conceivable that the synchronization signal is specified by the information of (1).
[0074]
The synchronization signal selection means 91 selectively receives the synchronization signal 7 according to the synchronization signal selection information 93. This selection is, for example, selection of a broadcast receiving antenna or tuning to a specific frequency by a tuner.
[0075]
The transmitting terminal 1 and the receiving terminal 2 execute respective real-time data communication processes based on the synchronization signal 7 selectively received by the synchronization signal selecting means 91.
[0076]
In FIG. 7, the synchronization signal determination means 92 is arranged inside the transmission side terminal 1. However, if it is a place where a specific real-time communication can be associated with the synchronization signal selection information, it is arranged at another place in the system. May be. For example, in the case of a real-time communication session started from the receiving terminal 2, the synchronization signal determining means 92 may be arranged inside the receiving terminal 2.
[0077]
As described above, according to the fifth embodiment, since the same synchronization signal selection information 93 is notified to both the transmitting terminal 1 and the receiving terminal 2, the synchronization signal to be referred to is A real-time data communication system in which the identity is guaranteed can be obtained.
[0078]
It is also possible to configure a system in which the fifth embodiment is combined with the first to fourth embodiments. In this case, the synchronization signal selection information 93 is information that can specify the numerical synchronization signal 71 or the SCR / PCR 711. In particular, when the SCR / PCR711 transmission format on the fixed delay transmission path is an MPEG multiplexed stream, a broadcast type (BS satellite broadcast, CS satellite broadcast, terrestrial broadcast, cable broadcast) for specifying the MPEG multiplexed stream is used. ), A broadcast channel (service) number, an MPEG multiplexed stream identification number (Transport Stream Identifier), and a PID (Program Identifier) -specific identifier.
[0079]
【The invention's effect】
As described above, according to the present invention, a transmitting side terminal and a receiving side terminal transmit and receive a real time data requiring a synchronization signal via a variable delay transmission line. The basic concept is to transmit the synchronization signal on both a variable delay transmission line and a fixed delay transmission line different from the variable delay transmission line. On the receiving side, the variable delay transmission line and another fixed delay transmission line The basic principle is to receive the synchronization signal and reproduce the real-time data on both sides of the transmission path, so that the receiving terminal considers the delay time due to the transmission delay fluctuation in the variable delay transmission path, and , It is possible to determine the reproduction timing of the synchronization signal required for the reproduction of As a result, even when the transmission delay fluctuation of the variable delay transmission line is large, a highly accurate synchronization between transmission and reception can be maintained, and a real-time data communication system capable of maintaining real-time performance can be obtained. Thus, the same effect can be obtained for real-time data that is out of phase with the synchronization signal cycle. Also, for example, the same effect can be obtained for transmission of a multiplexed stream such as MPEG.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram showing a first embodiment of the present invention.
FIG. 2 is a time chart showing the operation of the first embodiment of the present invention.
FIG. 3 is a system configuration diagram showing a second embodiment of the present invention.
FIG. 4 is a time chart showing the operation of the second embodiment of the present invention.
FIG. 5 is a system configuration diagram showing a third embodiment of the present invention.
FIG. 6 is a system configuration diagram showing a fourth embodiment of the present invention.
FIG. 7 is a system configuration diagram showing a fifth embodiment of the present invention.
FIG. 8 is a system configuration diagram showing a configuration of a conventional communication system.
FIG. 9 is a time chart showing the operation of a conventional communication system.
FIG. 10 is a time chart showing a problem of a conventional communication system.
[Explanation of symbols]
1 sender terminal
2 Receiving terminal
3 Variable delay transmission line
4 Synchronous signal source
51, 52 Fixed delay transmission line
7 Sync signal
71 Counting synchronization signal
72 count relative synchronization signal
61 MPEG multiplexed stream
711 SCR / PCR
713 PTS / DTS
92 Synchronization signal determination means
93 Sync signal selection information

Claims (8)

In a transmitting terminal in a real-time data communication system in which a transmitting terminal and a receiving terminal transmit and receive real-time data requiring a synchronization signal via a variable delay transmission line, the variable delay transmission line and another fixed A transmission-side terminal that transmits the synchronization signal through both a delay transmission path. The transmitting terminal according to claim 1, wherein the synchronization signal is a count synchronization signal. 3. The transmitting terminal according to claim 2, wherein, among the synchronization signals, a synchronization signal transmitted through the variable delay transmission path is a numerical relative synchronization signal. 3. The transmitting terminal according to claim 2, wherein the real-time data is an MPEG multiplexed stream, and the count synchronization signal is SCR / PCR. 4. The transmitting terminal according to claim 3, wherein the real-time data is an MPEG multiplexed stream, the counted synchronization signal is SCR / PCR, and the counted relative synchronization signal is PTS / DTS. Real-time data in which a transmitting terminal and a receiving terminal transmit and receive real-time data requiring a synchronization signal via a variable delay transmission path, and transmit the synchronization signal via the variable delay transmission path and another fixed delay transmission path. A transmitting terminal in a communication system, comprising: a synchronizing signal determining unit, wherein the synchronizing signal determining unit notifies both the transmitting terminal and the receiving terminal of synchronization signal selection information. The synchronization signal determination unit according to claim 1, further comprising: a synchronization signal determination unit that notifies both the transmission side terminal and the reception side terminal of synchronization signal selection information. Sending terminal. In a receiving terminal in a real-time data communication system in which a transmitting terminal and a receiving terminal transmit and receive real-time data requiring a synchronization signal via a variable delay transmission line, the variable delay transmission line and another fixed terminal are used. A receiving terminal that receives the synchronization signal and reproduces the real-time data in both of the delay transmission path.

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