JPS63290034A - Data transmission method - Google Patents

Abstract

PURPOSE:To improve a transmission efficiency at the time when a transmission line with long delay time is used by setting the number of frames to be a transmission unit, according to the measured result of line delay time. CONSTITUTION:When a calling terminal is connected to a called terminal by a digital line, the calling terminal sends a mode set command in order to connect a link level, and at the same time, starts an internal timer and starts to measure the delay time of the digital line. The mode set command is received by the called terminal after the delay time of the digital line, and after the called terminal sets an operation mode, the called terminal sends a response. When the response is received, the calling terminal stops the timer at this point of time, and sets the modulo value and the outstanding number of the order number of a transmission frame, according to the counted result of the timer. Thus, because the number of the frames to be the transmission unit is set according to the measured result of the line delay time, the transmission efficiency at the time of using the transmission line of the long delay time can be improved.

Description

[Detailed description of the invention] [Technical field] The present invention relates to a data transmission system.

[Prior Art] Transmission data exchanged between data terminal devices via a transmission path is subject to various disturbances on the transmission path. Therefore, the data sent from the transmitting device may be received by the receiving device with incorrect contents.

In order to recover from such data transmission errors, various data transmission procedures are in use, one of which is HDLC (
High Level Data Link Cont
orl) There is a procedure.

In this) IDLC procedure, transmission data is divided into consecutive frame data of a predetermined number of bits, each frame data is formatted into a frame in a predetermined format with an error detection code added, and data is transmitted in that frame format. do.

Then, transmission error detection processing is performed with reference to the error detection code, and for frames determined to have caused a transmission error, the device that transmitted the frame is requested to retransmit the same frame.

Furthermore, by setting the number of data frames (outstanding number) that can be unilaterally transmitted without an acknowledgment from the partner device, efficient data transmission can be performed.

For example, using a modulo 8 serial number as the frame number,
When the outstanding number is set to 7, Figure 4 (
As shown in a), the transmitting device TX successively transmits seven frames 5o-56 of an outstanding number FS.

Upon receiving each frame SO-86, the receiving device RX immediately responds with a corresponding response signal AO-A6.

Therefore, before the transmitting device TX finishes transmitting frames 5o-36, it is possible to obtain acknowledgments for the frames SO to S6, so that the transmitting device TX can transmit subsequent frames S7... Can be sent.

By the way, like, for example, satellite communication systems.

Conventionally, when such a data transmission system is applied to a point-to-point transmission line with a very large line delay time, the following problems have occurred.

That is, as shown in FIG. 4(b), after the transmitter TX transmits the first frame SO and until the transmitter TX receives the response signal AO from the receiver RX, at least: The delay time Td is twice the delay time in one direction of the line.

For this purpose, the transmitter [TX has an outstanding number F
If there is free time between the end of the continuous transmission of frames 5o-36 of S and the reception of the first response signal AO, frames 87-8 of the next outstanding number FS are transmitted.
5 cannot be transmitted consecutively to the immediately preceding frame, resulting in an inconvenience that the transmission time increases. This effect is particularly large when the amount of transmitted data is large.

[Purpose] The present invention has been made in order to eliminate the disadvantages of the prior art, and aims to provide a data transmission method that can improve transmission efficiency when using a transmission line with a large delay time. .

[Configuration] In order to achieve this object, the present invention sets the number of frames forming a transmission unit based on the measurement result of line delay time.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a group 4 facsimile device (hereinafter referred to as facsimile device) according to an embodiment of the present invention. Furthermore, in this case, the facsimile machine uses a digital line that connects terminals point-to-point as a transmission line.

In the figure, a system control unit l performs various internal processes of this facsimile machine and controls each element, a scanner 2 is for reading an original image at a predetermined resolution, and a plotter 3 is for recording and outputting a recorded image at a predetermined resolution.

The image memory 4 is for storing encoded and compressed image information, and the operation display section 5 is for storing encoded and compressed image information.

It consists of various operation keys and a display for operating this facsimile machine.

The encoding/decoding unit 6 encodes and compresses both signals and decodes the encoded and compressed image information into the original signals, and the clock circuit 7 outputs various time information. It is for.

The communication control unit 8 is for performing predetermined transmission control procedures and exchanging various data, and the line interface 9 is for connecting this facsimile device to a digital line.

In addition, these system control section 1, scanner 2, plotter 31, image memory 4, operation display section 5, encoding/decoding section 6
, the clock circuit 7, the communication control unit 8, and the line interface 9 exchange necessary data via the system bus 10.

With the above configuration, data transmission between the facsimile machines is performed as follows. Note that the following transmission procedure is mainly performed by the function of the communication control section 8.

That is, as shown in Figure 2, when the calling terminal connects to the called terminal via a digital line (physical level connection), it issues a mode setting command S to connect the link level.
At the same time as sending out the ABM, an internal timer (not shown?) is started to begin measuring the delay time of the digital line.

The mode setting command SABM is received by the called terminal after the delay time of the digital line, and the called terminal sends the response UA after setting the operating mode.

This response UA is received by the calling terminal after the delay time of the digital line.

When the response UA is received, the timer is stopped at that point. The measurement result of this timer is the mode setting command S.
This is the time required from sending the ABM to receiving the response UA, and in other words, this is the round-trip line delay time of the digital line being used.

Further, the calling terminal that has received the response UA sends a transport connection request command TCR to connect the transport level. In response to this transport connection request command TCR, the called terminal sends a transport connection acceptance response TCA.

The calling terminal sets the modulo value of the sequence number and the outstanding number of the transmission frame based on the timing result of the above-described timer.

That is, in this case, the time required to transmit seven consecutive frames is compared with the time measurement result of the timer, and if the former is greater than the latter, the modulo value of the sequence number of the transmitted frame is set to 8, and The outstanding number is set to 7, and if the latter is greater than 1), the modulo of the transmission frame sequence number is set to 128, and the outstanding number is set to 127.

Note that in standard facsimile transmission, the sequence number of the transmission frame is modulo 8 and the outstanding number is 7, so hereinafter this transmission mode will be referred to as the standard mode, and the sequence number is modulo 128 and the outstanding number is 127. The transmission mode is called the extended mode.

Here, if it is determined that the time measurement result of the timer is longer than the time required to transmit seven consecutive frames and it is determined to use the extended mode, the calling terminal transmits the session user data. A session start command C8S is used to instruct the start of a session with data set indicating that the extended mode should be set.
Send out.

The called terminal sends a session start affirmative response R35P in response to the session start command C8S.

At this time, if the extended mode can be set, data indicating that the extended mode can be set is set in the session user data.

When the calling terminal learns that the called terminal can set the extended mode, it sends the extended mode setting command SA8ME to perform a link reset to use the extended mode.

Upon receiving the extended mode setting command SABME, the called terminal sets the operation mode and then sends a response UA.

From this point on, higher-level function settings are performed in sequence (
negotiation). That is, the transport levels of the calling terminal and the called terminal are connected through the exchange of the transport connection request command TCR and the transport connection acceptance response TCA, and the session start command C3 is executed.
The session levels of the calling terminal and the called terminal are connected through the exchange of S and the session start acknowledgment response R35P.

After the terminal device functions are negotiated by exchanging the document function list command CDCL and the document function list affirmative response RDCLP, the calling terminal issues a document start command CDS.
is sent to notify the start of the document, and image information is transmitted using the document user information command CDUI.

At this time, since the extended mode is set as described above, even when the line delay time Td is very large, the transmitting device (calling terminal) While continuously transmitting 127 frames SO to 8126, the receiving device (called terminal) R
A response signal AO corresponding to the first frame SO sent by X can be received.

That is, before the transmitter TX finishes transmitting frames SO~5126, it is possible to obtain an acknowledgment for frames SO~8126, so the transmitter TX can subsequently transmit the subsequent frames 5127... Can be sent.

This allows efficient data transmission.

In addition, it is determined that the time required to transmit seven consecutive frames is longer than the timer measurement result,
If it is determined that the standard mode is to be used, do not set the extended mode setting data in the session user data [1! A session start command C8S is sent, and subsequent transmission procedures are executed.

In this way, in this embodiment, the sequence number and the outstanding number are set according to the delay time of the digital line used, so that efficient data transmission can be performed.

In the above-described embodiment, the sequence number and the outstanding number are set in two cases, but the outstanding number can be set to an appropriate value depending on the delay time of one line. In that case, the outstanding number may be set so that a response signal for the first frame can be received from the receiving device while continuously transmitting the outstanding number of frames.

8...Communication control unit.

Further, in the above-described embodiment, the case where the present invention is applied to a group 4 facsimile device has been described, but the present invention can be applied to other data terminal devices.

[Effects] As explained above, according to the present invention, the number of frames constituting a transmission unit is set based on the measurement result of line delay time, so transmission when using a transmission line with a large delay time is Benefit from improved efficiency.

[Brief explanation of drawings]

FIG. 1 is a block diagram illustrating a Group 4 facsimile device according to an embodiment of the present invention, FIG. 2 is a timing chart illustrating an example of a data transmission procedure, and FIG. 3 is an example of data transmission when line delay time is large. Figure 4 (a) is a time chart showing an example of data transmission when the line delay time is small, and Figure 4 (b) is a time chart to explain the inconvenience that conventionally occurs when the line delay time is large It is a chart. Agent Patent Attorney Crest 1) Makoto Figure 1 Figure 2 + Tadashi ＾x4 ＾×x −－に5 Ω=壬

Claims (1)

[Claims] A data transmission system that transmits data while performing transmission error recovery control in units of a predetermined number of frames, comprising a measuring means for measuring line delay time, and setting the number of frames forming a transmission unit based on the measurement result of the measuring means. A data transmission method characterized by: