JPH01115240A - Data communication equipment - Google Patents

Abstract

PURPOSE:To prevent a communication procedure from endlessly repeating due to an equipment trouble by setting a counter means to count the number of control commands sent from an opposite communicating equipment. CONSTITUTION:An equipment sends a calling, and it is connected to a session level. At such a time point, the value of a continuous receiving counter in a memory 4-4 is at 0. Next, a session alteration command CSCC from the equipment on the calling side is received, the counter is increased by 1. Next, the counter value is compared with the continuous receiving prescribed value of the CSCC, when it is smaller than the prescribed value, a processor 4-3 returns a session alteration control positive response RSCCP, and when data to be transferred exist, the data are transferred. In such a case, when the counter value is larger than the prescribed value, the processor 4-3 clears the counter as the equipment trouble, cuts off a transport layer or below, and the communication is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a data communication device such as a teletex or a group 4 facsimile for transmitting and receiving character code data and image data.

<Conventional technology> CCITT (International Telegraph and Telephone Consultative Committee)T.

Recommendation No. 62 defines control procedures for teletex and Group 4 facsimile. Among them, for example, C5
CC (Session Change Control Command) is a command that changes the source/sink relationship between the calling device and the called device in the session layer. FIG. 1 is a diagram showing a normal communication sequence. Upon receiving the above C5CC command (1-3), the called device first uses RSCCP.
(Session change control affirmative response) Return 1-4)
If the called side has data to send to the calling side, the called side then moves to the document layer and transfers the data (1-5 to 1-io). When the transfer is completed, the called party sends cscc again (1-11),
Expects the called party to terminate the session.

Also, if the called device does not have data to send (
2-9), receives cscc from calling device (2-3), RSCCP (2-4)
2-5) Expect the calling side to disconnect the session. (Figure 2) However, if the calling side is a defective device, the called side or C5CC
Even after returning cscc (3-5), there is a possibility that cscc will be sent back (3-3). Even if the C5CC is exchanged multiple times, it is not a violation of the communication procedure, so in the case of the called side or the conventional device, the CSCC exchange would be repeated an infinite number of times. (Fig. 3) Purpose> The present invention provides a data communication device that eliminates the drawbacks of the conventional example described above and can prevent endless repetition of communication procedures.

<Example> Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 4 is a block diagram showing one embodiment of the present invention. 4
4-2 is an interface control unit that connects the communication control unit with the main unit of the device 4-1; 3 is a microprocessor which is the core of the communication control unit surrounded by a solid line, 4-4 is a memory in the communication control unit, and 4-5 is a transmitting/receiving unit that receives data from the line or transmits data to the line. . 4-6 is a line for exchanging data with the other party's terminal.

FIG. 5 is a flowchart showing the operation of this embodiment. The device in this embodiment is a called device, and when a call is made from a certain device, the call reaches the session level (s-
i). At this point, the continuous reception counter is 0. Next, when the CSCC is received from the calling device (5-2), the continuous reception counter is incremented by 1 (5-3).Next, this counter specifies in advance how many times continuous transmission of CSCC can be disabled. Compare it with the specified value (5-4), and if it is smaller than the specified value, return RSCCP (5-5), determine whether there is data to be transferred, and if there is, transfer the data. Returns C3CC 5-10) and receives RSCCP (5-11). If I receive C5CC again (5-12)
, 5-3, and if not, the continuous reception counter (actually 5-13), the session is disconnected by the calling side, and the lower layer of the session, ie, transport and lower layers, is disconnected and the communication is terminated.

If the counter exceeds the specified value in 5-4, send C5A (session interruption command) as shown in Figure 6.
35P (session interruption response), the called side forcibly interrupts the session to avoid falling into an infinite cscc loop.

Note that the present invention is not limited to the above-mentioned C5CC, and can be used for other commands as well.

<Effects> As described above, according to the present invention, communication efficiency can be improved by preventing IL from exchanging control commands an infinite number of times.

[Brief explanation of the drawing]

Figure 1 is a normal communication sequence diagram in which the cscc command in the session layer is used and the called side transfers data. Figure 2 is a communication sequence diagram in which the called side does not perform data communication. Figure 3 is an incoming call. Fig. 4 is a block diagram showing an example of this embodiment. 5-1 and 5-2 are flowcharts showing the operation of this embodiment, and FIG. 6 is a communication sequence diagram of this embodiment. 4-1 is a communication device main unit, 4-2 is an interface control unit, 4-3 is a microprocessor, 4-4 is a memory, 4-2 is an interface control unit, 4-3 is a microprocessor, 4-4 is a memory;
-5 is a transmitting/receiving unit, and 4-6 is a line.

Claims (1)

[Scope of Claims] A data communication device that exchanges control commands and sends and receives data with a partner communication device, comprising: a counting means for counting the number of control commands sent from the partner communication device; A data communication device comprising: means for interrupting the return of a response to the control command when the count value in the counting means exceeds a predetermined value.