JPH07123084A - Communications system - Google Patents

Abstract

PURPOSE:To provide a communications system which can flexibly deal with a synchronization system and also can improve the quality of communication in a system where the communication is carried out in a prescribed format through a communication channel. CONSTITUTION:At a transmission terminal 1, the video data received from a TV camera 11 are written in a buffer memory via a video coding device 12 and the video data written on another surface are read out through a channel 2. When the reading speed is higher than the writing speed, the stand-by data are read on the channel 2 and sent to a video signal frame together with a flag showing the presence of the stand-by data. At a reception terminal 3, the video data are written in the buffer memory from the channel 2 based on the header detection timing of a reception frame. Then the video data written on another surface are read out by a video decoding device 31 based on the flag retrieving result and projected on a TV monitor 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a communication system applied to a communication system in which terminals connected via a digital network communicate in a predetermined format.

[0002]

2. Description of the Related Art For example, in the case of a communication system which uses a digital network (hereinafter referred to simply as "communication path") to perform communication in a predetermined format, usually, each of a transmission source, a reception source and a communication path of communication information is The operating clock source must be common. This request is, in part,
If the connection is made asynchronously, an interface circuit that can operate asynchronously for input and output is needed, and this is caused from the viewpoint of avoiding complication of the configuration.

In this type of communication system, the transmission source,
A system configuration example for making the operation clock sources of the reception source and the communication path common will be briefly described with reference to FIGS. That is, a PLL synchronization method, a stuff synchronization method, and a buffer memory synchronization method are known as typical synchronization methods for commonizing a transmission source, a reception source, and a clock source of a communication path of communication information.

The PLL synchronization system is a system in which the operation clocks f1 and f3 of the transmission source 1a and the reception source 3a and the operation clock f2 of the communication path are synchronized by a PLL circuit, as shown in the system configuration of FIG. In this PLL synchronization method, the frequency division ratio of each of the PLL circuits 101 and 301 on the transmitting side and the receiving side must be f1 / N = f2 / M (N,
M is an integer). If there are no integers N and M that satisfy the above equation, n · f1 / N = m · f2 / M (similarly,
(n, m, N, M are integers). Next, the stuff synchronization method is realized by the system configuration as shown in FIG. In this stuff synchronization method, for example, f2 (communication path 2
Operating clock) / N so that it has a slightly higher frequency
When the phases of f1 and f2 / N are shifted by one clock or more, the stuff circuit 111 extracts one clock of f2 / N.

The process of extracting the clock is called stuffing, and information indicating that the stuffing has been performed (stuffing information) is multiplexed in the encoded video signal and transmitted on the communication path 2. On the receiving side, the destuff circuit 311 operates to remove the stuff pulse each time the stuff information is received. Then, the decoding operation clock frequency f3 is synchronized with f1 by phase comparison with the clock thinned out from f2 / N according to the destuffing by the PLL circuit 312.

Further, the buffer memory synchronization system is used when variable length coding is performed, and a smoothing buffer memory is used to transmit at a fixed rate, and an example of the system configuration is as shown in FIG. . In this buffer memory synchronization method, the operation clock f1 of the transmission source 1c is controlled so that the buffer memory occupation amount of the transmission side buffer memory 121 becomes a prescribed value (for example, 1/2 of the memory capacity) on a long-term average. The reception side detects the buffer memory occupation amount of the buffer memory 321 and controls the operation clock f3 of the reception source 3c so that the occupation amount is synchronized with the transmission side.

With each of the above synchronization methods, the transmitting side,
The operation clock source of the receiving side and the communication path can be made common, and there are merits such as the need for an interface circuit that can operate asynchronously for input and output when trying to connect asynchronously, but regarding these system configurations However, there are still technical problems to be solved as described below. For example, in the case of the PLL synchronization method (see FIG. 3), n · f1 / N
= M · f2 / M (n, m, N, and M are integers), but generally f1 and f2 are not simple integer ratios, and N and M are considerably large integers. The advantage of this method is that the transmission source and the reception source maintain synchronization with the clock of the communication path 2 as a reference, so that synchronization can be achieved without requiring particularly complicated control. However, unless f1 and f2 have a simple frequency division ratio as described above, it becomes difficult to subordinately synchronize the transmission source and the reception source with the clock of the communication path. Therefore, the synchronization system is not flexible and the clock frequency cannot be easily changed.

On the other hand, in the case of the stuff synchronization method (see FIG. 4) and the buffer memory synchronization method (see FIG. 5),
Both the transmission source and the reception source can operate independently of the clock of the communication path, and the synchronization system is highly flexible. In particular, the buffer memory synchronization method has an advantage that the synchronization between the transmission source and the reception source can be established without considering the communication path.

However, in these synchronization systems, control is liable to become unstable due to a transmission path error of the communication path 2 and the communication quality is often seriously affected. As an example, in the buffer memory synchronization method, when the buffer occupancy of the buffer memory 321 on the reception side is offset due to the transmission path error or the like, synchronization with the transmission side cannot be established, and the operation clock f3 of the reception source 3c has a low frequency. There is a possibility that the communication quality will be impaired due to the occurrence of jitter, etc.

[0010]

As described above, in the conventional communication system for performing communication in a predetermined format by using a communication path, an interface circuit capable of operating input / output asynchronously when trying to connect in an asynchronous state is provided. The system is configured by using the PLL synchronization method, the stuff synchronization method, the buffer memory synchronization method, etc. in order to share the operation clock source of each of the transmission source, the reception source, and the communication path in order to obtain the merits such as unnecessary. It was common to do.

Among these conventional systems, for example, PL
In the L-synchronization method, since synchronization is maintained at the end of transmission / reception with reference to the clock of the communication path, there is a case where the division ratio of each clock does not become a simple integer ratio although it does not require complicated control. In many cases, it is difficult to subordinately synchronize the transmission source and the reception source with the clock of the communication path, and there is a problem in that the synchronization method lacks flexibility and the clock frequency cannot be easily changed. It was

On the other hand, in the stuff synchronization method and the buffer memory synchronization method, both the transmission source and the reception source can operate independently of the clock of the communication path, and it is easy to establish the synchronization between the transmission source and the reception source. There is a problem that the establishment of synchronization becomes unstable due to an error in the transmission path of the path, and the effect of this easily causes deterioration of communication quality.

The present invention eliminates these problems, can flexibly cope with the establishment of synchronization between the transmission source and the reception source without being aware of the communication path, and operates stably even with errors in the transmission path to achieve high communication. An object is to provide a communication method that can maintain quality.

[0014]

According to the present invention, there is provided a transmission terminal having at least means for transmitting communication information in a predetermined format, and a reception terminal having at least means for decoding reception information in a predetermined format and outputting it. In a communication system in which terminals are connected via a communication network and the communication information is transmitted in a predetermined format, a transmitting terminal has a fixed length for absorbing a speed difference between the terminal and the communication network or the receiving terminal. The spare data and a flag indicating the presence or absence of the spare data are inserted in the format and transmitted, and the receiving terminal determines the number of the spare data inserted from the content of the flag in the received format, and the determination is made. It is characterized in that the communication information in the format is decrypted based on the result.

[0015]

According to the present invention, when transmitting the communication information in a certain communication format, n (n) fixed length spare data for absorbing the speed difference between the terminals or between the terminal and the communication path are included in the communication format. ≧ 0) is inserted, and a flag indicating the presence or absence of the preliminary data is added.
Then, the receiving side recognizes the amount of preliminary data based on the flag in the received frame, and performs demodulation processing to remove unnecessary preliminary data so as to absorb the speed difference between the transmitting / receiving terminal and the communication path. ing.

According to this communication system, the transmission source, the reception source and the communication path of the communication information can be operated by independent clock sources, the synchronization system can be flexibly supported, and the clock frequency can be easily changed. Like

Further, according to the present invention, the flag indicating the existence thereof is added together with the spare data, so that the receiving side can determine the transfer frame length on the communication path based on the flag, and the frame synchronization protection is applied. Will be available.
If a plurality of the above flags are distributed and described in the transfer frame, even if some of the flags are destroyed due to a transmission error in the communication path, the transfer frame length is determined using the normal flag. This makes it possible to construct a system that operates stably even with transmission line errors.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of a communication system to which the communication system of the present invention is applied.

This communication system is a system that handles video information as communication information, and includes a transmitter terminal 1 equipped with a television camera 11 and a video encoder 12, a video decoder 31, and a receiver 32 equipped with a television monitor 32. The side terminal 3 is connected via a communication path (digital network) 2.

In this video communication system, the video coding device 12, the video decoding device 31, and the clock sources f1, f3, f2 of the communication path 2 are assumed to be independent. The video encoding device 12 and the video decoding device 31 are provided with buffer memories for two planes each having an interface function for asynchronous input / output.

In the transmitting side terminal 1, the video encoding device 1
2 CCIT the NTSC signal from the TV camera 11
It is quantized and encoded into the CIF video format specified by the T recommendation. On the other hand, in the receiving side terminal 2, the video decoding device 31 decodes the NTSC signal from the CIF video format received through the communication path 2. In the video encoding device 12 and the video decoding device 31, 13.
Encode and decode NTSC signals with a 5 MHz clock.

Here, the format of the video signal frame for performing video information communication between the terminals has a structure as shown in FIG. 2, for example.

As can be seen from FIG. 3A, this video signal frame is (1) a frame header (FH) pattern indicating a frame delimiter of the video signal, and (2) an analog video signal is quantized and encoded. Video data (3) Fixed-length spare data added according to the speed difference between the video decoding device 12 and the digital network (4) Eight flags indicating whether or not the spare data is added (5) Between the terminals The frame structure has a variable length, which includes at least control information (remaining area) used in the above, and whose length changes depending on the presence or absence of the above-mentioned spare data.

More specifically, the spare data is divided into two areas (spare data 1 and spare data 2) as shown in FIG. 3B, and one or two areas are included in the frame. It is possible to select three ways when it is not included.

The transfer rate of the communication path 2 is 37.44M.
It is bps and has a frame structure of every 29.97 Hz. In the present invention, the color signal and volatility signal level not used in CIF, binary 8-digit 00000000 pattern 4
Bytes are used in the frame header. Further, the data length of the spare data is set to 80 bytes. By adding or deleting the spare data (spare data 1 and spare data 2), the video transfer frame length becomes 156116 or 1
56196 bytes, which is about ± 256 pp
The speed difference of m can be absorbed.

The video data is divided into 8 blocks, and a flag indicating the presence or absence of preliminary data is provided for each block. As an example, when there is preliminary data, a binary 8-digit 01110011 pattern is used, and when there is no preliminary data, a binary 8-digit 1 is used.
The 0000111 pattern is used to describe the flags at all locations. Furthermore, the surplus area can be used for the purpose of passing control information and the like used by the transmission side terminal 1 and the reception side terminal 2 and the like.

Next, a specific communication control operation in this video communication system will be described. First, in the video signal transmission side terminal 1, the video encoding device 12 writes the video data from the television camera 11 to one side of a buffer memory (not shown) provided on two sides, and from the communication path 2 side. The video data already written on the other side of the buffer memory is read.

At this time, switching between the reading surface and the writing surface is performed in synchronization with the vertical synchronizing signal of the video signal detected by the video encoding device 12. When the reading speed on the communication path 2 side is faster than the writing speed on the video encoding device 12 side and the underflow state occurs, the spare data irrelevant to the video data is read on the communication path 2 side. That is, in this communication system, the video signal frame is added with an amount of spare data according to the speed difference between the terminal and the communication path 2 and transmitted. Also, if you add preliminary data at the sending terminal,
In the sending video coding device 12, it is described that a spare data exists in the video communication frame by using a flag.

On the contrary, when the reading speed on the communication path 2 side is slower than the writing speed on the video encoding device 12 side and an overflow occurs, the video communication frame is transmitted without adding the preliminary data. At this time, it is noted that the flag in the frame does not have spare data.

On the other hand, when receiving a frame from the communication path 2, the receiving side terminal 3 first detects the frame header pattern of the frame, and then searches for the flag. Here, the receiving side terminal 3 can determine the video transfer frame length by judging the presence or absence of the spare data by the above flag, and thereby can predict the next frame break.
As a result, synchronization protection of the video transfer frame can be applied.

As described above, the receiving side terminal 3 sequentially detects the frame header pattern of the received frame and smoothes the detection timing to generate the switching timing between the reading and writing of the buffer memory for two planes. . And according to this switching timing,
While writing the video data from the communication path 2 side to the one side having the buffer memory, the video decoding device 31 reads the already written video data from the other side and displays it on the television monitor 32.

When reading the video data from the buffer memory, when the video decoding device 31 receives, for example, a transfer frame to which the spare data is added, the spare data indicated by the flag in the frame is read from the frame. Control is performed so that only the legitimate video signal sent from the transmission side is decoded while being removed.

The spare data for the above frame can be added to a certain position all together, but as in the above embodiment, the video data is divided into 8 blocks, and the spare data is added to each block. If a format for providing a flag indicating presence / absence of data is provided, and if a pattern other than the above-described presence / absence pattern of spare data appears in some of the above eight flags due to a transmission path error or the like, another flag is set. The communication quality can be kept stable by counting the total of the presence / absence of the pattern while referencing and determining the presence / absence of the preliminary data with a large number of patterns.

This processing is carried out by dividing the information into fixed-length cells on the communication path and transmitting the cells by C in an ATM (asynchronous transfer mode) network.
This is especially effective when the BR mode (fixed bit rate mode) is used. In the ATM network, a phenomenon of cell loss may occur. In this case, information corresponding to the cell length (53 bytes) is lost and complemented with a certain specific pattern. Even if the video transfer frame is lost due to the cell loss, the presence or absence of the preliminary data can be determined because the flags are dispersed.

Video encoder 12 and video decoder 3
When the clock can be supplied to the communication channel 1 from the communication path 2, all the clock sources are common, so that the transfer frame can have a fixed length. In that case, as shown in FIG.
The spare data may be divided into two areas (spare data 1 and 2), and only the spare data 1 may be added to the frame. In this case, the flag is 1000 in binary 8 digits.
It is conceivable to describe by 1111 patterns.

[0036]

As described above, according to the present invention,
In the transfer frame from the transmitting side, the spare data corresponding to the speed difference with the communication path and a flag indicating the presence or absence of the spare data are added and transferred, and the receiving side removes unnecessary spare data according to the flag in the transfer frame. Since the demodulation process is performed to absorb the speed difference between the transmission / reception terminal and the communication path, the transmission source, the reception source and the communication path can be operated by independent clock sources, and the flexibility regarding the synchronization method is increased, and It also becomes easy to change the clock frequency. Further, in terms of countermeasures against communication failures, since a flag indicating the presence or absence of the spare data is added together with the spare data, the transfer frame length on the communication path can be determined based on the flag, and frame synchronization protection can be applied. Here, a plurality of the above flags in the transfer frame,
By adding them in a distributed manner, even if some flags are destroyed due to transmission error in the communication path, the transfer frame length can be determined using other normal flags, and stable operation is possible even with transmission path errors. It has an excellent advantage that high communication quality can be maintained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a video communication system using the communication system of the present invention.

FIG. 2 is a diagram showing an example of a configuration of a video transfer frame and spare data in the frame according to the communication system of the present invention.

FIG. 3 is a block diagram showing a general configuration of a communication system to which a PLL synchronization system is applied.

FIG. 4 is a block diagram showing a general configuration of a communication system to which the stuff synchronization method is applied.

FIG. 5 is a block diagram showing a general configuration of a communication system to which a buffer memory synchronization method is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmission side terminal 11 Television camera 12 Video encoding apparatus 2 Communication channel 3 Reception side terminal 31 Video decoding apparatus 32 Television monitor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Wakahara 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Kazuo Unemoto 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo No. Japan Telegraph and Telephone Corporation

Claims (6)

[Claims] 1. A transmission terminal having at least means for transmitting communication information in a predetermined format and a reception terminal having at least means for decoding reception information in a predetermined format and outputting the connection information are connected via a communication network. In the communication system that transmits the communication information in a predetermined format, the transmitting terminal has a fixed length of spare data for absorbing a speed difference between the terminal and the communication network or the receiving terminal, and the existence of the spare data. The flag indicating the presence or absence of the flag is inserted in the format and transmitted, and the receiving terminal determines the number of spare data inserted from the content of the flag in the received format, and the communication in the format is performed based on the determination result. A communication method characterized by performing information decoding processing. 2. The communication system according to claim 1, wherein the flags are distributed and arranged in the format. 3. The communication system according to claim 1, wherein the flags are collectively arranged in a predetermined area in the format. 4. The communication system according to claim 1, wherein the format length is fixed during communication. 5. The communication system according to claim 1, wherein the format is divided into a plurality of fixed length cells and transmitted. 6. The communication system according to claim 1, wherein the communication information is video information.