JPS63115437A - Data communication system - Google Patents

Abstract

PURPOSE:To hold a communication circuit even though the preparation is not finished yet for data communication by repeating negotiation to set a communication mode with a device set at the remote side with a communication circuit is set. CONSTITUTION:A host computer 10 processes the picture data and the character code data. A communication controller 20 processes communication with the remote side to set up a communication circuit. When the calling side transmits a CDCL (document function list command), the called side transmits an RDCLP (document function list acknowledge command) in reply for each reception of the CDLC. If those data to be transferred are not ready yet or preparation is not finished yet for communication of data in another type of process mode, these actions are repeated. When preparation is finished for communication of data at a time T1, the calling side sends a document start command CDS to the called side to start communication of data.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a data communication system for communicating data such as images and character codes.

[Prior art]

Conventionally, in such data communication, when a communication circuit is set, negotiation for setting a communication mode is performed, and then data communication is executed.

However, if preparations for data communication are not completed when negotiation is completed, an error will occur and the communication line will be released.

Therefore, even if there is data to be communicated urgently, the communication line must be established again, and if the other party is busy when the call is made again, the data communication will be delayed.

[Purpose of the invention]

In view of the above-mentioned problems, the present invention aims to provide a data communication system that can maintain a communication line even if preparation for data communication is not completed.

(Embodiment) An embodiment of the present invention will be described in detail below with reference to the drawings.This embodiment is based on the control procedure of teletex and G4 facsimile recommended by CCITT and T62.

FIG. 1 is a protocol flow showing one embodiment of the method of the present invention. 1, a session connection request is sent from the calling side. At this point, the call must be disconnected up to layer 4.

2 is an acknowledgment from the called party to 1; This 1,
By the operation 2, it becomes possible to enter the document sublayer of layer 5. In the CCITT (DT62 recommendation), Layer 5 is divided into a lower session sublayer and an upper document sublayer.When entering the document layer, first the CDCL (document Function list command) and RDCLP (document function list acknowledgment response) are exchanged.
'EL is 4. In the case of normal communication, a document start command CDS is sent, and the process moves on to sending data. However, if the data to be communicated is not available or preparations for data communication are not completed due to other processing, it is possible to repeat the exchange operation in 3.4 as shown in 5.6. becomes. In a normal communication control device, when receiving a CDCL, if it is in the correct format, it will send an RDCLP, so even if an infinite number of CDCLs are received, it is not counted each time. Since there is no RDCLP, RDCLP will be sent. Therefore, when the calling party sends the CDCL, the called party receives the CDCL.
Every time a CL is received, an RDCLP is sent as a response. When preparations for data communication are completed at time T, the calling side sends a document start command CDS to the called side to start data communication.

FIG. 2 shows a block diagram of a communication device that performs the above processing.

In FIG. 2, a host computer 10 processes image data and character code data. A communication control device 20 performs communication processing with the other party. 30 establishes a communication line.

FIG. 3 shows a flowchart of processing operations of the communication control device. The flowchart in FIG. 3 will be explained.

In step S1, a communication line with the other device is established, and the CCI
Connections are made up to layer 4 of the 7-layer structure defined in TT Recommendation X200. Then, in S2, the session sublayer of layer 5 is connected. This is the session start command C
This is an exchange in which 3S is transmitted and R35P, which is an acknowledgment signal, is received. Then, CDCL is transmitted in S3, and RDCLP is received in S4. At this point, it is checked at 35 whether preparations for data communication have been completed. S31 until preparation is complete. When a signal indicating that preparation is completed is received from the host computer 10 by repeating the reaching steps of S4 and S5, the process proceeds to S6, transmits the CDS, and moves to data communication in S7.

With the above configuration, it is possible to hold the line until the preparation for data communication is completed, and data communication can be performed as soon as the preparation is completed.

In this embodiment, the control procedures for teletex according to CCITT T62 recommendation and facsimile according to G4 are explained as examples, but it is of course possible to apply the present invention to other telematics terminals.

(Effects) As described above, according to the present invention, even if the preparation for data communication is not completed, the line can be maintained until the preparation is completed, and data communication can be performed as soon as the preparation is completed.

FIG. 2 is a block diagram of the communication device, and FIG. 3 is a flowchart showing the flow of control of the communication control device on the calling side.

Claims (1)

[Claims] A data communication method that, when a communication line is set up, repeats negotiation to set the communication mode with the other device in order to hold the line until data communication is ready.