Priority packet multiplexing circuit and video packet transmission system

[Detailed Description of the Invention]

Field of the Invention The present invention decomposes a picture signal into packets (a cell is called hereafter), and relates to the system which transmits a plurality of images by a cell multiplex. PRIOR ART Under the surveillance of a railroad - highway etc., the straight line-like area along the railroad line is dotted with the surveillance part. The conventional example (70th anniversary synthesis national conference 1823 of the Institute of Electronics, Information and Communication Engineers foundation; Tanabe, others) of the bus type image transmission systems which arrange many cameras located in a line such in the shape of a straight line is shown in Drawing 4. By an uphill image transmission system, DPCM coding is carried out with high-efficiency-coding device 419, and the picture signal of selected camera 420 is inserted in the arbitrary empty Times lots of CHI~3 in signal 418 from a next door terminal in multiplex closet circuit 417. Such a digital picture signal is changed and transmitted to a lightwave signal by 413. In the center 40, a received signal is changed into an electric signal by 412, and it is TDMA. DMUX It separates into three signals by 405, is changed into a video signal by DPCM decoder 406~408, and projects on TVI~TV3 (409~411). Transmission of the selection signal of a terminal is explained. It is CPU when a terminal number is chosen with keyboard 402 or joy stick 404. A selection control signal is taken out with 403 and a twisted pair wire is driven with driver 401. The signal received by 414 is SCC of each terminal. (sink * Ru Chihufu * and Combi * Utah) 4 1 It is judged whether its own terminal is chosen by 6. It is TDMA4 as it explained previously, when its own terminal was chosen. 1 It carries out multiplex [ of the signal from a camera ] by 7. A control signal is relayed to the next terminal by driver 415. At the conventional example explained above, a picture signal is 3. It is coded by the fixed rate of 2Mbps. The speed of the transmission way is carrying out three-channel multiplex [ of the DPCM picture signal ] by 128Mbps. (Time Division Multiplexing of 3 bits of picture signals and 1 bit of the signals, such as a frame synchronization, is carried out.) Although three channels can be chosen from N terminal along the railroad line by this gentleman formula, in spite of using 128Mbps and a high-speed transmission way, there is a fault with few channels of the picture signal which can be transmitted. It is because picture quality will worsen if it codes at a low rate since the thing with few channels has coded the picture signal at the fixed rate, so it has coded to 32Mbps. As art which may solve this, there are ATM transmission art and variable rate coding accompanying it. Here, A T M (Asynchronous Transfer Mode) is explained. The concept of ATM transmission is shown in Drawing 4. (Nikkei electronics 1988.1.11 No.438ppl22) On the time slot repeated with a constant period, A T M puts and transmits a fixed-length cell. By making the number of the cells to transmit fluctuate, effectual transmission speed is changeable. The difference of a multiplex transmission method between S T M (Synchronous Transfer Mode) and ATM is shown in Drawing 5. ATM tends to remove decisively the portion which obstructed improvement in the speed with the conventional packet exchange system, and tends to realize high-speed communication by taking in the art cultivated by the line switching. X. Packet communication based on 25 is fit for transmission of a burst signal from the first. It is rich in flexibility. What is necessary is to send only required information to send. However, there is a limit in a protocol transmitting a complicated and high-speed signal. In ATM, the information to send is divided into a short block (cell), and it carries out multiplex. The header which shows an address etc. is attached to a cell. The block to which the header was attached is called a cell. Within the net, with reference to the contents of the header, it exchanges per cell, and sends to the partner point. It decomposes into cells and also returns continuation signals, such as a sound and video, to the form of a continuation signal again by the receptacle side. The conventional cell signal is also divided and sent out to the cell of short length. On the other hand, STM is an irony to ATM. It is the conventional Time Division Multiplexing. Research and development of the field which carries out high efficiency coding of the video signal have also been suddenly revitalized by the appearance of ATM. ATM solves to Itsuki the problem which has so far bound high-efficiency-coding art. It was a major premise that the conventional high efficiency coding makes access speed regularity. However, in ATM, when required, required information may be sent. Access speed is changed dynamically. High efficiency coding of image quality regularity becomes possible now. If digital conversion is carried out and it sends as it is also with the present standard TV signal, the data-transmission capacity of about 100 Mb/s is required. When it is the still picture that it is the foundations of high efficiency coding to exclude the redundant portion in this and to reduce the transmission amount of information and that a photographic subject does not move, for example, it is useless to repeat the same signal repeatedly and to send it. As long as it is premised on ATM, at the time of an animation, it may send by about 100 Mb/S, and may make access speed into zero at the time of a still picture. However, since access speed needed to be conventionally stopped also at the time of an animation, a sacrifice fake colander was not obtained for the image quality of the animation. If the variable rate coding of the picture signal is carried out using ATM transmission, a picture signal with constant quality can be transmitted highly efficiently. However, a problem arises here. Although the variable rate coding based on the character of the picture with the terminal which separated distantly from a center in transmission like the surveillance system located in a line in the shape of a straight line is possible, At the terminal near a center, when data-transmission capacity becomes full in the picture signal cell which has transmitted from the terminal before it, the capacity which can be transmitted decreases, or when extreme, the remaining data-transmission capacity is lost. It becomes impossible in such a case, to transmit the image cell which occurred at the terminal after the node (bonding link) whose data-transmission capacity was lost. Thus, a transmission rate is made highly as the terminal which is generally distant from a center, and, as for the terminal near a center, the fault that large data-transmission capacity cannot be taken arises. Object of the Invention As explained above, in the conventional picture signal bus type transmission systems, there was a fault which cannot take the large multiplex number of a picture signal. On the other hand, although the terminal which is distant from a center can secure sufficient transmission rate by the method which packet(cell )-turns and transmits a picture signal, the fault that data-transmission capacity is not securable depending on the case produces the terminal near a center. The present invention can make an average transmission rate low in view of this point, and the coding rate of each terminal increases, and when data-transmission capacity becomes insufficient, it aims at sending out information on a par [ the terminal near a center ] with other terminals. Means for solving problem It separates into the information which does not give big degradation to image quality from the information which gives big degradation to image quality for a picture signal one by one, The high priority information on a priority is given in an order from the information which has a big meaning in image quality, and when a transmission way is congested and I will obey as a center is approached, but it produces, a low-priority cell is discarded in the cell transmitted from before the node which will obey. OPERATION When the present invention changes into the state where cell abandonment takes place on a transmission way etc., a low-priority cell is discarded previously. Therefore, drawing quality of the video information which reaches a center is made uniform between each terminal. The number of transmission channels is increased by coding a picture signal at a variable rate. EXAMPLE In Drawing 1, the cell inputted from input terminal 101,102 of two ATM cells judges the phase (timing of the pause eye of a cell) of a cell in timing circuit 103. One input cell is inputted into buffer memory 104, and it is delayed so that the cell header portion of input cells 101 and 102 may not overlap. Cell header sampling part 105 Only a header is taken out by 106 and a priority is identified in header discernment circuit 107~109. On the other hand, the information on a cell is recorded on buffer memory 111,112 according to address counter 110. Record address 110 at this time is recorded on cue 113~115 according to a priority. For example, as for the user information on the cell whose priority was the highest, the value of an address counter is recorded on 111 (buffer (1) watch) or l12 (A buff No. 72) by (212), Address (212) .! : it is PIFO about the puffer memory number ((1) or (2)) which recorded the cell. It records on 113. It is PIFO when the lowest-priority. It is recorded on 115. From the number of Queue of cue group 113~115, and the capacity of a transmission way, the cell sent out to the next in sending-out cell determination circuit 116 is determined. The control signal of readout circuitry 117 is followed from a determination result, and it is FIF0. An output (the number and address of a buffer memory) is read from 1l.3~115. According to this output, the user information on a cell is read from buffer memory 111 or 112. 1l., by 8, multiplex [ of the read cell ] is carried out and it is outputted. Next, another example is described with Drawing 2. Only time for transmitted cell 209 to analyze a header is recorded on buffer 201. A header portion is analyzed by 202 and the priority information on a cell header is detected. On the other hand, after being changed into a digital signal with high-efficiency-coding machine 204, high efficiency coding of the picture signal 210 is carried out. The information that a priority is high among the signals by which high efficiency coding was carried out is accumulated in 205, and the information that a priority is low is accumulated in 206. The cell which sends out the amount of information (Queue length) accumulated in this buffer and the number of cells according to priority from priority discernment circuit 202 (availability of a transmission way) to the next in sending-out cell determination circuit 203 is determined. According to this determination, a cell is sent out from switch 208. That is, when there are few availabilities of a transmission way, the cell with a priority low among the cells inputted from terminal 209 is discarded. Next, the example of an image supervising system is described with Drawing 3. Image cell sending device 302 constitutes a block from 16 pixels, after input picture signal 303 is changed into a PCM signal in coding part 304, and it is identified by an animation portion and the still picture portion. The picture signal of a still picture block does not transmit. Next, top 2 bits low-priority cell, top 6-bit cell of a middle priority, and the discernment information cell of the highest still picture of a priority and an animation consist of cell decomposition circuits 305. An output cell is sent to node 307 and sent out to center device 308. In a center device, the image cell made by being sent is assembled, and it changes into the original picture signal, and supervises by the picture signal of each terminal. Terminal 301 and node 308 set respectively same operation to 302 and 307. The image cell from terminal 302 and the image cell from node 306 or before are inputted into node 307. According to the cell multiplex algorithm explained in Drawing 1 and Drawing 2, a cell multiplex is performed by this node. Since the cell with a high priority can crush and use a cell with a low priority even if it is a terminal near [ in these picture signal bus type transmission systems ] a center, it can do [ sending out the picture signal of the terminal which exists in the distance, and the quality, or ]. On the other hand, channel select signal 309 of a terminal is transmitted to each node, and the cell of the terminal which is not chosen is not sent out. The number of terminals to choose is determined by the formula of the number of data-transmission capacity x usage rate = terminals x average sending-out amount of information. A usage rate is usually only 80%. In this example, low rank 2 pit of the PCM signal was used as a cell of middle [ priority / top 4 bits of a PCM signal, and ] as highest cell of a priority as 2 bits in the middle of a PCM signal, and lowest cell of a priority. However, it is clear that the low order ingredient and high order ingredient of a DCT coefficient can be separated as how to attach the priority of a picture signal, for example. the priority cell decomposition method of a picture signal -- carrying out -- the effect of the invention which is performing another application by these artificers As mentioned above, according to the present invention, since a picture signal is coded and cell-ized at a variable rate according to the amount of information, an average transmission rate can be made low. In the transmission systems which arranged the image cell sending device in the shape of a straight line, since it is discarded from the cell from each terminal not giving priority when the coding rate of each terminal increases and data-transmission capacity becomes insufficient or, the terminal near a center is also made [ sending out information on a par with other terminals, or ].

[Brief Description of the Drawings]

The lineblock diagram of the example of the former [ Drawing / 1 / Drawing / the lineblock diagram of one example of the present invention, the lineblock diagram of the example of everything / Drawing / 2 / but the present invention, the lineblock diagram of example in which the present invention of Drawing 3 is another, and / 4 ], Drawing 5, and Drawing 6 are explanatory views of ATM transmission.