JPH0322736A - Priority packet multiplexing circuit and video packet transmission system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a system that decomposes a video signal into packets (hereinafter referred to as cells) and transmits a plurality of videos by cell multiplexing.

Conventional technology Railway ●In monitoring expressways, etc., monitoring points are scattered along a straight line. A conventional example of a bus-type video transmission system in which many cameras are arranged in a straight line (National Convention of the Institute of Electronics, Information and Communication Engineers, 70th Anniversary, 1823; Tanabe,
etc.) are shown in Figure 4.

In the uplink video transmission system, the video signal of the selected camera 420 is DPCM encoded by a high-efficiency encoder 419, and the signal 418 from the adjacent terminal is converted to CHI by a multiple input circuit 417.
3 into any free time slot. Such a digital video signal is converted into an optical signal at 413 and transmitted. At the center 40, the received signal is converted into an electrical signal at 412, separated into three signals by TDMA DMUX 405, converted into video signals by DPCM decoders 406 to 408, and then sent to TVI to TV3 (409 to 411).
will be displayed on the screen.

Transmission of a terminal selection signal will be explained. keyboard 4
02 or a terminal number with the joystick 404, the CPU 403 outputs a selection control signal, and the driver 401 drives the twisted pair wire. The signal received at 414 is used by the SCC (Single Chip Computer) 416 of each terminal to determine whether or not its own terminal is selected. If your own terminal is selected, the signals from the cameras are multiplexed using TDMA417 as described above.

Further, the control signal is relayed to the adjacent terminal by the driver 415.

In the conventional example described above, the video signal is encoded at a fixed rate of 32 Mbps. The speed of the transmission line is 128
Three channels of DPCM video signals are multiplexed at Mbps. (Three bits of the video signal and one bit of signals such as frame synchronization are time-division multiplexed.) With this method, three channels can be selected from N terminals along the railway, but using a high-speed transmission line of 128 Mbps, However, the disadvantage is that the number of video signal channels that can be transmitted is small. The reason why the number of channels is small is because the video signal is encoded at a fixed rate, and since encoding at a low rate deteriorates the image quality, it is encoded at 32 Mbps. ATM transmission technology and its associated variable rate coding are technologies that have the potential to solve this problem.

Here, ATM (Asynchronous T
transfer mode) will be explained. Figure 4 shows the concept of ATM transmission. (Nikkei Electronics 1988.1.11 No.438ppl22) A
TM transmits fixed-length cells on time slots that repeat at a constant period. By increasing or decreasing the number of cells to be transferred, the effective communication speed can be changed.

Figure 5 shows STM (Synchronous Tr).
This figure shows the difference between the multiplex transmission method (Ansfer Mode) and ATM. ATM attempts to realize high-speed communication by boldly eliminating the parts that hinder high speeds in conventional packet switching methods and by incorporating technology developed in circuit switching.

X. Packet communication conforming to 25 is originally suitable for transmitting burst signals and is highly flexible. Just send as much information as you need, when you want to send it. However, the protocol is complex and there are limits to transmitting high-speed signals.

In ATM, information to be sent is divided into short blocks (cells) and multiplexed. A header indicating the destination etc. is attached to the cell.

A block with a header is called a cell. Inside the network, the contents of the header are referenced, the cells are exchanged in units of cells, and the data is delivered to the other party.

Continuous signals such as audio and video are also broken down into cells, which are then converted back into continuous signals at the receiving end. Conventional cell signals are also divided into short cells and sent out. On the other hand, STM is an antonym for ATM. This is conventional time division multiplexing.

Research and development in the field of high-efficiency encoding of video signals is also part of ATMs.
It suddenly became lively with the appearance of ATM will soon solve the problems that have hitherto limited high-efficiency encoding technology. The main premise of conventional high-efficiency encoding is to keep the transmission speed constant. However, with an ATM, you only need to send the necessary information when you need it. Transmission speed can be changed dynamically. This enables high-efficiency encoding with constant image quality.

Even the current standard television signal requires a transmission capacity of about 100 Mb/s if it is digitally converted and sent as is. Reducing the amount of transmitted information by eliminating redundant parts is the basis of high-efficiency encoding. For example, in the case of still images where the subject does not move, it is wasteful to send the same signal over and over again. be.

Assuming ATM is used, moving images may be sent at a rate of about 100 Mb/S, and still images may be sent at a transmission rate of zero. However, in the past, it was necessary to reduce the transmission speed even when moving pictures, so the image quality of the pictures had to be sacrificed. If a video signal is encoded at a variable rate using ATM transmission, a video signal of constant quality can be transmitted with high efficiency. However, a problem arises here. In transmission systems arranged in a straight line, such as in a monitoring system, terminals far from the center can perform variable rate encoding based on the characteristics of the image, but terminals close to the center can encode video signals sent from previous terminals. When the transmission capacity of a cell becomes full, the available transmission capacity decreases, or in extreme cases, there is no remaining transmission capacity. In such a case, video cells generated at terminals after the node (coupling section) that has run out of transmission capacity cannot be transmitted. In this way, generally speaking, the farther a terminal is from the center, the higher the transmission rate can be achieved, while the terminal closer to the center is unable to obtain a large transmission capacity.

Problems to be Solved by the Invention As explained above, the conventional video signal bus type transmission system has the drawback that the number of multiplexed video signals cannot be increased. On the other hand, in the method of transmitting video signals in packets (cells), terminals far from the center can secure a sufficient transmission rate, but terminals close to the center may not be able to secure transmission capacity in some cases.

In view of this, the present invention can lower the average transmission rate, and when the encoding rate of each terminal increases and the transmission capacity becomes insufficient, even terminals close to the center can receive information on the same level as other terminals. The purpose is to send out.

Means for solving the problem: Separate the video signal from information that causes significant deterioration to image quality to information that does not cause significant deterioration to image quality, and prioritize information in descending order of priority from information that has the greatest significance to image quality. If information is attached and the transmission path becomes congested as it approaches the center, causing congestion, cells with lower priority that have been transmitted from before the congested node are discarded.

Effect of the Invention According to the present invention, when a cell is discarded on a transmission line or the like, cells with lower priority are discarded first. Therefore, the image quality of the video information that reaches the center is made uniform among each terminal. Furthermore, by encoding the video signal at a variable rate, the number of transmission channels is increased.

Embodiment In FIG. 1, two ATM cell input terminals 101,
A timing circuit 103 determines the phase of the cell (the timing of cell division) for the cell input from 102 . One input cell is input to the buffer memory 104 and delayed so that the cell header portions of the input cells 101 and 102 do not overlap.

Cell header extraction sections 105 and 106 extract only the headers, and header identification circuits 107 to 109 identify the priority order. On the other hand, cell information is stored in the address counter 110.
The data is recorded in the buffer memories 111 and 112 according to the following. The recording address 110 at this time is recorded in queues 113 to 115 according to the priority order. For example, the user information of the cell with the highest priority when the address counter value is (212) is 111 (buffer number (1)) or l12 (
buffer number 72) and address (212). ! :
Puffer memory number ((1) or (2) where the cell was recorded
)) is recorded in the PIFO 113. If the priority is the lowest, it is recorded in the PIFO 115. From the number of queues in the queue groups 113 to 115 and the capacity of the transmission path,
A transmission cell determining circuit 116 determines the next cell to be transmitted. Based on the determination result, outputs (buffer memory numbers and addresses) are read out from the FIFOs 113 to 115 in accordance with the control signal of the readout circuit 117. According to this output, the user information of the cell is read from the buffer memory 111 or 112. The read cells are multiplexed by 118 and output.

Next, another embodiment will be described with reference to FIG. The transmitted cell 209 is recorded in the buffer 201 for the time required to analyze the header. The header portion is analyzed at 202 to detect priority information in the cell header. On the other hand, the video signal 210 is converted into a digital signal by the high-efficiency encoder 204, and then subjected to high-efficiency encoding. Among the high-efficiency encoded signals, high-priority information is stored in 205 and low-priority information is stored in 206. The sending cell determining circuit 203 determines the cell to be sent next based on the amount of information accumulated in this buffer (queue length) and the number of cells by priority (transmission path free capacity) from the priority identifying circuit 202. . According to this decision, the cell is sent out from switch 208. That is, when the free capacity of the transmission path is small, cells with low priority among the cells input from the terminal 209 are discarded.

Next, an embodiment of the video monitoring system will be described with reference to FIG. The video cell sending device 302 receives an input video signal 30
3 is converted into a PCM signal by the encoding unit 304, and then 16
Blocks are made up of pixels and are divided into moving image parts and still image parts. Video signals of still image blocks are not transmitted. Next, a cell disassembly circuit 305 configures a cell with the lowest two bits of priority, a cell with the highest six bits with intermediate priority, and an identification information cell for still images and moving images with the highest priority.

Output cells are sent to node 307 and sent to center device 308
will be sent to. The center device assembles the sent video cells, converts them to the original video signals, and monitors the video signals from each terminal. The terminal 301 and the node 308 are 302
, 307, each performs the same operation. node 307
, the video cells from the terminal 302 and the video cells from before the node 306 are input. Cell multiplexing is performed at this node according to the cell multiplexing algorithm explained in FIGS. 1 and 2.

In this video signal bus type transmission system, even if the terminal is close to the center, cells with higher priority can be used by overriding cells with lower priority, so the video signal of the same quality as that of terminals located far away can be transmitted. I can do something. On the other hand, the terminal selection signal 309 is transmitted to each node, and cells of unselected terminals are not transmitted. Further, the number of terminals to be selected is determined by the formula: transmission capacity x usage rate = number of terminals x average amount of transmitted information. The usage rate is usually around 80%.

Note that in this embodiment, PCM is the cell with the highest priority.
The upper 4 bits of the signal, PCM as a cell with intermediate priority
The middle 2 bits of the signal, P as the lowest priority cell
The lower two pits of the CM signal were used. However, it is clear that, for example, as a method of prioritizing video signals, it is also possible to separate low-order components and high-order components of DCT coefficients. As described above, the priority cell decomposition method for video signals is based on the invention filed separately by the present inventors.According to the present invention, video signals are encoded at a variable rate according to the amount of information, and cells are , so the average transmission rate can be lowered.

In addition, in a transmission system in which video cell transmitters are arranged in a straight line, even if the encoding rate of each terminal increases and the transmission capacity becomes insufficient, non-priority cells from each terminal are discarded first, so the center Even nearby terminals can send information in the same way as other terminals.

[Brief explanation of drawings]

Fig. 1 is a block diagram of one embodiment of the present invention, Fig. 2 is a block diagram of another embodiment of the present invention, Fig. 3 is a block diagram of another embodiment of the present invention, and Fig. 4 is a conventional block diagram. Configuration diagram of the embodiment, Fig. 5, Fig. 6
The figure is an explanatory diagram of ATM transmission.

Claims (2)

[Claims] (1) At least one input terminal for packets, a buffer for adjusting the timing of packets from the input terminal, a circuit for identifying the priority of the header part, and a memory for recording packet information according to the priority. a circuit that compares the queue length of the memory circuit and the free capacity of the transmission line to determine a packet to be sent, and a circuit that outputs a packet based on the result of the sending packet determination circuit. Features a priority packet multiplexing circuit. (2) A plurality of video packet transmitting devices having a function of decomposing video signal packets into video signal packets that cause relatively little deterioration in image quality even if they are lost and video signal packets that cause a large deterioration in image quality if they are lost; It is composed of a center device for restoring a signal to an original video signal, and a plurality of node devices for arranging the plurality of packet sending devices and the center device in a straight line, and the node device is connected to its own node. 1. A video packet transmission system comprising a priority packet multiplexing circuit as claimed in claim 1, which multiplexes video packets from a terminal and video packets sent from before the own node.