JP3566585B2 - Track switching device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line switching device, and in particular, realizes stable video distribution by transmitting a video signal on a plurality of paths and transmitting a video signal on the other path even if a failure occurs on one of the paths. The present invention relates to a line switching device that does not affect a receiver.
[0002]
[Prior art]
Conventionally, a system has been used in which the same image is divided into two paths and transmitted, and a normal path is selected on the output side to ensure high reliability of image transmission. 7 is shown.
[0003]
In the figure, an encoding section 51, a transmission path (for example, an ATM network), and a decoding section 52 constitute a first path, and an encoding section 53, a transmission path (for example, an ATM network), and a decoding section 54 constitute a first path. 2 are configured. The failure detecting unit 55 detects a failure when a synchronization signal is lost from a transmitted image signal, or when a transmission error rate exceeds a predetermined value.
[0004]
When the failure detecting section 55 detects a failure in the working path, the switching control section 56 performs synchronization in units of video frames, and switches the switcher 57 to the protection path.
As described above, the line switching is achieved so that the path failure does not affect the receiver.
[0005]
[Problems to be solved by the invention]
However, in the above-described conventional technology, synchronization is performed in video frame units, so that line switching always incurs a delay of one frame time (that is, 33 ms), and the amount of delay is reduced. There was a problem of being big. Further, in the prior art, the line switching is performed after the received video signal is decoded once, so that the number of decoding devices is required as many as the number of paths, and there is a problem that the price of the device becomes high.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide a line switching device capable of eliminating the above-mentioned problems of the prior art and switching between lines without using a decoding device. Another object of the present invention is to provide a line switching device capable of switching lines in a short time when a path failure occurs.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a first buffer individually provided for each transmission path, a failure detection unit for detecting that a failure has occurred in the transmission path, and a first buffer A data converter for converting the first data format on the transmission path into a second data format for output, a second buffer receiving the data converted by the data converter, and A synchronization means for synchronizing data by using data in the data format of 2, wherein when a failure occurs in the transmission path, the synchronization means synchronizes the data and passes through another path. The feature is that the data is switched to the arrived data.
[0008]
According to this feature, since the data is synchronized using the output data in the second data format converted by the data conversion unit, the data can be synchronized without using the decoding device. Data can be switched in synchronization.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention. In the following, an operation in the case where an ATM network is used as a network and MPEG-2 is used for video compression will be described, but the present invention is not limited to this.
[0010]
ATM cells of a plurality of streams (for example, two streams) of the same video signal input via an ATM network (not shown) are stored in network buffers 1a and 1b, respectively, to absorb data propagation time differences between transmission paths. . Next, the ATM cells stored in the network buffers 1a and 1b are converted by the data converters 2a and 2b into TS packets in the form of compressed data in MPEG-2 as shown in FIG. You. The TS packets converted by the data converters 2a and 2b are input to the switching buffers 3a and 3b.
[0011]
The monitoring unit 4 monitors the occurrence of a path failure. The arrival intervals of the ATM cells arriving at the network buffers 1a and 1b fluctuate depending on the state of the ATM network. Therefore, the data conversion units 2a and 2b read the ATM cells from the network buffers 1a and 1b and convert them into TS packets when the ATM cells have been accumulated in the middle of the network buffers 1a and 1b. At this time, if a failure occurs on the path, the input of the ATM cells to the network buffers 1a and 1b is interrupted, while the ATM cells in the network buffers 1a and 1b are read out by the data converters 2a and 2b. Approaching zero. The monitoring unit 4 monitors the behavior of the network buffers 1a and 1b, and determines that a path failure has occurred when the amount of stored ATM in the network buffers 1a and 1b falls below a predetermined threshold. I do. That is, the monitoring unit 4 functions as a failure detection unit that detects occurrence of a path failure.
[0012]
Next, upon receiving a notification from the monitoring unit 4 that a path failure has occurred, the data analysis unit 5 determines which TS packet in the switching buffers 3a and 3b is the same. Here, the configuration of the TS packet will be described with reference to FIG. The TS packet includes a header (header) and a payload (payload), and has 188 bytes. As shown, the header includes a continuity-counter and an adaptation field. The continuity-counter is a 4-bit counter, and is counted up for each TS packet.
[0013]
A 42-bit PCR (Program Clock Reference) area is set in the optional field of the adaptation field. In this PCR area, time management information is recorded, and the time management information is expressed in units of a 27 MHz clock. The original role of the PCR is to transmit the time information at the time of encoding to the decoder, and the decoder adjusts the internal clock of the decoder based on the PCR value, and obtains the time management information at the time of encoding. This is to ensure consistency with the decoding time management information.
[0014]
In addition, as shown in FIG. 4, the MPEG standard requires that an insertion interval of an MPEG-TS packet holding a PCR value be less than 100 ms. The data analysis unit 5 constantly monitors the data in the switching buffers 3a and 3b, monitors the continuity-counter value from 0 to 15, and also resets the value to 0 due to overflow (..., n). , N + 1,..., N + m,. Further, the number of TS packets per 33 msec corresponding to one frame of an image depends on the bit rate at the time of encoding, but is usually about 130 (= N).
[0015]
Next, the operation of the main part of the present embodiment will be described with reference to the flowcharts of FIGS. Upon receiving a notification from the monitoring unit 4 that a path failure has occurred (step S1), the data analysis unit 5 sets the TS packet in the active switching buffer 3a in which the PCR value has been written about every 100 ms. And reads out the PCR value from the standby switching buffer 3b (step S3). Then, the read address of the read address control unit 6 is controlled so that the same TS packet as the TS packet at the time of the occurrence of the failure in the active system is read from the switching buffer 3a or 3b of the standby system (step S4). Further, the switching control unit 7 switches the switcher 8 seamlessly from the active system to the standby system (step S5). The output of the switcher 8 is input to an MPEG-2 decoder (not shown), and video is reproduced without interruption by the switching. The data analysis unit 5 and the read address control unit 6 function as synchronization means for synchronizing data.
[0016]
According to this embodiment, it is possible to switch from the active system to the standby system in the state of the TS packet, and there is no need to switch after decoding once, as in the related art. As a result, a decoder becomes unnecessary, which contributes to simplification of the device and cost reduction.
[0017]
Next, a second embodiment of the present invention will be described with reference to the flowcharts of FIGS. In this embodiment, the data analysis unit 5 analyzes the continuity-counter value to determine whether a TS packet is different. Upon receiving a notification from the monitoring unit 4 that a path failure has occurred (step S11), the data analysis unit 5 reads a continuity-counter value from the TS packet in the active switching buffer 3a (step S12). Next, it is determined whether or not a standby TS packet having the same number of resets and the same continuity-counter value as the active TS packet is found (step S13). In this case, it is preferable to perform synchronization by collating the PCR-value as a base in the order of the number of continuity-counter resets and the value of the continuity-counter itself. If this determination is affirmative, the read address control unit 6 controls the read address so that the same TS packet as the TS packet at the time of the occurrence of the failure in the active system is read from the switching buffer 3a or 3b of the standby system (step S14). ). Further, the switching control unit 7 switches the switcher 8 from the active system to the standby system (step S15).
[0018]
Therefore, according to this embodiment, the switching of the route can be performed in TS packet units, and the switching can be performed in a minimum of (33 / N) m seconds. For example, when N = 130, it is possible to switch from the active system to the standby system in 0.25 ms, which can be greatly reduced as compared with the conventional 33 ms.
[0019]
In the above-described embodiment, the MPEG-2 transmission over the ATM network has been described as an example. However, the present invention is not limited to this, and can be applied to, for example, MPEG-1 transmission over an IP (internet protocol) network. can do. In this case, synchronization can be achieved using the SCR value of the MPEG-1 system packet.
[0020]
【The invention's effect】
As is clear from the above description, according to the present invention, the data is synchronized by using the data in the second data format for output, which is converted by the data converter. Data can be switched by synchronizing data without using a device. Therefore, the configuration of the device can be simplified and the price can be reduced.
[0021]
In addition, since it is possible to switch the path in units of TS packets, it is possible to shorten the data synchronization time and to shorten the time required to switch to the standby path when a failure occurs in the active path. Will be able to
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention.
FIG. 2 is a conceptual diagram of data conversion from an ATM cell to a TS packet.
FIG. 3 is an explanatory diagram of a configuration of a TS packet.
FIG. 4 is a timing chart showing a temporal relationship between an image frame and a TS packet.
FIG. 5 is a flowchart showing the operation of the first embodiment of the present invention.
FIG. 6 is a flowchart showing an operation of the second embodiment of the present invention.
FIG. 7 is a block diagram showing an example of a conventional device.
[Explanation of symbols]
1a, 1b network buffer, 2a, 2b data conversion unit, 3a, 3b switching buffer, 4 monitoring unit, 5 data analysis unit, 6 read address control unit, 7 switching control unit, 8 switcher.

Claims (3)

A first buffer individually provided for each transmission path;
A failure detection unit that detects that a failure has occurred in the transmission path;
A data converter connected to the first buffer and configured to convert a first data format on a transmission path into a second data format for output;
A second buffer that receives the data converted by the data conversion unit,
A synchronizing means for synchronizing data by using the data of the second data format;
When a failure occurs in the transmission path, the synchronization means synchronizes data and switches to data arriving through another path. The line switching device according to claim 1,
The data format converted by the data conversion unit is an MPEG-2 TS packet,
The line switching device, wherein the synchronization means synchronizes the TS packets by using at least one of a PCR value and a continuity-counter value included in the TS packet. 3. The line switching device according to claim 1, wherein the failure detection unit is configured to determine that a failure has occurred in a transmission path based on a decrease in the amount of data in the first buffer. 4. Characteristic line switching device.

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