JP3880022B2 - Packet communication system - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a packet communication system in which a transmission device and a reception device perform packet communication via a communication line.
[0002]
[Prior art]
Conventionally, there is known a security system in which an image transmission device installed on the terminal side to be guarded and an image center device installed on the center side are connected by a telephone line. Such a security system is well known, but its general configuration and operation will be described with reference to FIG. 2, FIG. 3, and FIG. In FIG. 2, 1 is an image transmission device, 2 is a control device, 3 is a line control unit, 4 is a line control unit, 5 is a center device, 6 is the nearest exchange, and L is a telephone line.
[0003]
The image transmission apparatus 1 is installed at a predetermined location on the terminal side that is the subject of security. The image transmission device 1 performs bidirectional communication with the image center device 5 through the processing unit and its peripheral circuit via the telephone line L by the full-duplex communication method, and exchanges data. A line control unit 3 is provided. The line control unit 3 is composed of a modem or the like.
[0004]
The control device 2 is connected to a security sensor and a monitoring camera for detecting an abnormality such as a heat ray sensor. The surveillance camera and the security sensor are associated with each other, and when a certain security sensor reports, an image from the surveillance camera associated with the security sensor is stored and transmitted to the image center device 5. It is made so that. In general, a plurality of security sensors and surveillance cameras are provided. However, in order to avoid complication of the figure, the figure simply shows that the security sensor and the surveillance camera are connected to the control device 2. Yes. Also, the security sensor alert means that the security sensor detects a predetermined state. Therefore, in the case of a heat ray sensor, a notification is issued when the movement of a person is detected.
[0005]
A setting device is also connected to the control device 2. This setting device is for setting a warning state / release state for each warning area set for the area to be guarded, and is generally called a remote controller or the like. . Although a plurality of setting devices are generally provided, in order to avoid complication of the drawing, the drawing simply shows that the setting device is connected to the control device 2.
[0006]
On the other hand, an image center device 5 and a line control unit 4 are provided on the center side. The image center device 5 performs processing such as management of image data sent from the image transmission device 1 and other data relating to the security state, setting of various data to be transmitted to the image transmission device 1, and the like. If a personal computer is used. Although only one image transmission apparatus 1 is shown in FIG. 2, the image center apparatus 5 is usually configured to exchange data with a plurality of image transmission apparatuses.
[0007]
Then, the control device 2 of the image transmission device 1 notifies the image center device 5 when the warning of a certain warning area is canceled by the setting device, or when a warning state is set for the certain warning area by the setting device. I do. Further, when a security sensor in the warning area set in the warning state issues a report, the image from the monitoring camera corresponding to the security sensor that has issued the report is transmitted to the image center device 5. Furthermore, the control device 2 may be configured to make a regular notification every certain time.
[0008]
By the way, when any notification is made from the image transmission apparatus 1 or when an image is transmitted, packet communication is usually performed. FIG. 3 is a chart showing an example of a sequence in that case. FIG. 3 shows a case where only one packet is transmitted.
[0009]
When performing notification or image transmission, the control device 2 of the image transmission device 1 creates a packet based on the data to be transmitted, and passes the packet and the telephone number of the image center device 5 to the line control unit 3 for transmission. Instruct.
[0010]
In response to this, the line control unit 3 dials the telephone number of the image center device 5 (step S1). When the image center apparatus receives the call, it issues a packet transmission request and requests packet transmission (step S2). Upon receiving this transmission request, the line control unit 3 of the image transmission apparatus 1 performs predetermined modulation on the packet passed from the control apparatus 2 and sends it to the telephone line L (step S3).
[0011]
When the line control unit 4 of the image center apparatus 5 completes reception of the packet, it returns an affirmative response (step S4) and releases the station line. On the other hand, the line control unit 3 of the image transmission apparatus 1 releases the office line when receiving the acknowledgment.
[0012]
The above is a case where the image center apparatus 5 has successfully received the packet, but when the packet has not been received normally, a sequence as shown in FIG. 4 is performed. In this case, it is assumed that only one packet is transmitted.
[0013]
As described above, when the packet and the telephone number of the image center device 5 are passed from the control device 2, the line control unit 3 dials the telephone number of the image center device 5 (step S11). When the image center apparatus receives a call, the image center apparatus requests transmission of a packet (step S12). Upon receiving this transmission request, the line control unit 3 of the image transmission apparatus 1 performs predetermined modulation on the packet passed from the control apparatus 2 and sends it to the telephone line L (step S13). If the packet cannot be normally received at this time, the line control unit 4 of the image center device 5 returns a negative response (step S14).
[0014]
On the other hand, when the line control unit 3 of the image transmission apparatus 1 receives a negative response, it again transmits the same packet as the packet transmitted in step S13. That is, the packet is retransmitted (step S15). The line control unit 4 of the image center apparatus 5 returns an affirmative response when the packet retransmitted at step S15 is normally received, but returns a negative response again when the packet cannot be normally received.
[0015]
If the line control unit 3 does not return an affirmative response from the image center device 5 even after retransmitting the packet a predetermined number of times, the line control unit 3 once releases the office line, and then again the image center device 5. Will be called.
[0016]
[Problems to be solved by the invention]
By the way, as an affirmative response to be returned from the image center apparatus 5 side to the image transmission apparatus 1 side, it is a code defined as an ACK code in ASCII code, specifically 06 _h (h is a hexadecimal number. The same is true of 1-byte codes). The same applies to the negative response, and a 1-byte code defined as an NAK code in the ASCII code is used.
[0017]
However, since the above-described security system uses a telephone line, depending on the state of the telephone line, there may be cases where a large amount of noise is mixed into the transmitted data and the other party cannot receive normally. This is remarkable when the data to be transmitted has a short data length such as a positive response or negative response.
[0018]
Therefore, for example, in step S4 of FIG. 3, when a positive response is returned from the line control unit 4, a lot of noise is mixed, and the line control unit 3 of the image transmission apparatus 1 cannot normally receive this positive response. In the case where it is determined, the control device 2 determines that the transmitted packet is not normally received, and retransmits the packet transmitted in step S3.
[0019]
Thus, in the past, since both the acknowledgment and negative acknowledgment are codes with a short data length of 1 byte, even if a packet is normally received on the receiving side and an acknowledgment is returned, There was a case where the acknowledgment could not be received normally and retransmitted. This is wasteful in terms of time, and the receiving side receives the same packet twice or more, which is also wasteful in this respect.
[0020]
Accordingly, an object of the present invention is to provide a packet communication system capable of more reliably receiving an acknowledgment or a negative response returned from the receiving side on the transmitting side.
[0021]
[Means for Solving the Problems]
In order to achieve the above object, the packet communication system according to claim 1 is a packet communication system in which a transmission apparatus and a reception apparatus perform packet communication via a communication line, and the reception apparatus acknowledges a received packet. Alternatively, when a negative response is returned to the transmitter , the data having a structure in which a plurality of acknowledgment codes are continuous and the data having a structure in which a plurality of negative response codes are used are used as an acknowledgment and a negative response, respectively. To do.
[0022]
The packet communication system according to claim 2, wherein in the packet communication system in which the transmission device and the reception device perform packet communication via a communication line, the reception device returns an acknowledgment or a negative response to the received packet to the transmission device. , acknowledgment, as a negative acknowledgment, respectively, data of a plurality of acknowledgment code is continuous structure, a plurality of negative acknowledgment code with the data of the continuous structure, the transmitting device, the two acknowledgment codes in succession Is received, it is determined that an affirmative response has been received, and when two negative response codes are received in succession, it is determined that a negative response has been received .
[0023]
The packet communication system according to claim 3 is the packet communication system according to claim 1 or 2 , wherein each of the plurality of consecutive acknowledgment codes and each of the plurality of consecutive acknowledgment codes is two dummy codes. It is characterized by being sandwiched between .
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments will be described with reference to the drawings. Here, a case where the present invention is applied to a security system in which an image transmission apparatus and an image center apparatus are connected via a telephone line will be described.
[0025]
The configuration of the security system is the same as that shown in FIG. 2, but the acknowledgment and negative response codes returned to the image transmission apparatus 1 when the line control unit 4 of the image center apparatus 5 receives the packet are different from the conventional ones. ing. An example of a positive response code is shown in FIG. 1A, and an example of a negative response code is shown in FIG.
[0026]
The acknowledgment code has a structure in which three ACK codes are sandwiched between two dummy codes. Each dummy code is 1 byte. Each ACK code is also 1 byte. In other words, this acknowledgment code is 5 bytes. As the ACK code here, for example, a code defined as an ACK code in the ASCII code may be used. The dummy code may be an appropriate 1-byte code, for example, FF _h .
[0027]
Similarly, the negative response code has a structure in which three NAK codes are sandwiched between two dummy codes. Each dummy code is 1 byte. Each NAK code is also 1 byte. That is, the negative response code is 5 bytes. As the NAK code here, for example, a code defined as a NAK code in the ASCII code may be used. The dummy code may be an appropriate 1-byte code, for example, FF _h .
[0028]
Accordingly, when the line control unit 4 of the image center apparatus 5 returns an affirmative response in step S4 of FIG. 3, it returns a 5-byte acknowledgment code having the structure shown in FIG. On the other hand, the line control unit 3 of the image transmission apparatus 1 determines that an acknowledgment has been received when two consecutive ACK codes included in the acknowledgment code have been received. This is because if it is determined that an affirmative response has been received when the ACK code is received continuously for 2 bytes, it is possible to make it more resistant to errors.
[0029]
Similarly, when the line control unit 4 of the image center apparatus 5 returns an affirmative response in step S14 of FIG. 4, it returns a 5-byte negative response code having the structure shown in FIG. On the other hand, the line control unit 3 of the image transmission apparatus 1 determines that a negative response has been received when two consecutive bytes of the NAK code included in the negative response code are received.
[0030]
As described above, according to this packet communication system, the acknowledgment code and the negative response code are composed of a plurality of bytes. Receiving can be performed with higher accuracy than in the past, so that reliability can be improved and unnecessary retransmission of unnecessary packets as in the past can be prevented.
[0031]
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, although the case of the security system has been described in the above embodiment, the present invention is not limited to the security system and can be applied to a system that performs packet communication.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of the structure of an acknowledgment code and a negative response code used in a packet communication system according to the present invention.
FIG. 2 is a diagram illustrating a configuration example of a security system in which an image transmission device and an image center device are connected via a telephone line.
FIG. 3 is a sequence chart showing a communication mode when a packet transmitted from the image transmission apparatus 1 is normally received by the image center apparatus 5;
4 is a sequence chart showing a communication mode when a packet transmitted from the image transmission apparatus 1 is not normally received by the image center apparatus 5. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image transmission apparatus, 2 ... Control apparatus, 3 ... Line control part, 4 ... Line control part, 5 ... Center apparatus, 6 ... Nearest exchange, L ... Telephone line.

Claims (3)

In a packet communication system in which a transmission device and a reception device perform packet communication via a communication line,
When the receiving device returns an acknowledgment or a negative response to the received packet to the transmitting device, data having a structure in which a plurality of acknowledgment codes are consecutive and a plurality of negative acknowledgment codes are consecutive as an acknowledgment and a negative response, respectively. A packet communication system characterized by using data having the above structure . In a packet communication system in which a transmission device and a reception device perform packet communication via a communication line,
When the receiving device returns an acknowledgment or a negative response to the received packet to the transmitting device, data having a structure in which a plurality of acknowledgment codes are consecutive and a plurality of negative acknowledgment codes are consecutive as an acknowledgment and a negative response, respectively. Using the data of the structure
The transmitting device determines that an acknowledgment has been received when two acknowledgment codes are received in succession, and determines that a negative response has been received when two negative acknowledgment codes are received in succession. A packet communication system. Each of the plurality of consecutive acknowledgment codes and the plurality of consecutive negative acknowledgment codes are sandwiched between two dummy codes.
The packet communication system according to claim 1 or 2.

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