JPS607264A - Automatic retransmission system - Google Patents

Abstract

PURPOSE:To attain the shift control in following to the state of a transmission line by controlling the shift of a transmission speed based on the data transmission speed and an external condition such as terminal state and state of retransmission request from an opposite station. CONSTITUTION:An MODEM controller 4 controls the transmission speed of an MODEM3 based on a transmission speed data CT1 applied from a signal processing section (DSP)10. a response signal DR representing the reception state (normal reception ACK or abnormal reception NACK) or a data transmitted from an opposite station is applied to a buffer 2a and a shift condition check section 2c via the MODEM3, and the section 2c discriminates whether or not the condition reaches a shift-down and shift-up condition. A reception section RX discriminates whether the reception is abnormal reception or not by means of a serial/parallel converter frame error check section 6a of the automatic retransmission control section 6.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an automatic retransmission method, which is one of data transmission methods.

BACKGROUND ART As is well known in the art, in a data transmission device such as a facsimile machine, modem training is performed by selecting the transmission speed of the modem in the transmission procedure (transmission phase) before sending out the menoseno data, and if successful, the modem training is performed. Data is transmitted at the transmission speed. However, successful modem training does not necessarily mean that data transmission will be successful; if the line condition deteriorates, data may be lost during transmission, which may prevent normal data reception. There is also.

Therefore, in order to avoid such inconveniences, an automatic retransmission (ARQ) method is applied to data transmission.

This divides data into blocks of a predetermined number of bits, and adds start flags, stop flags, commands (including programs) to this block data.

data (number) and CRC (cyclic redundancy check) code are added to frame the data, and the data is transmitted in units of blocks. The receiving side requests the transmitting side to retransmit the block data if the CRC check of the received block data is abnormal, if the block data is different from what the receiving side expects, or if the flag is destroyed.

According to this method, each time a reception abnormality occurs during transmission, the data is retransmitted. As a result, the receiving side can always receive normal data, and therefore, for example, in a facsimile machine, a received image faithful to the original can be obtained.

However, if the condition of the transmission line is so poor that the receiving side repeatedly requests retransmission, the transmitting side will have to continuously retransmit the same block of data. Therefore, the time required to finish transmitting all data becomes longer, resulting in a substantial reduction in data transmission speed, which may lead to adverse effects such as deterioration of transmission efficiency and line utilization rate.

In order to deal with such a situation, if a predetermined condition (shift-down condition), such as the number of playback requests that occur within a unit time, satisfies a predetermined condition (shift-down condition), the data transmission speed is gradually reduced. It was performing so-called downshift control (of data transmission speed).

However, in this conventional downshift control, the downshift conditions are fixed and the transmission speed is simply lowered one step at a time, making it impossible to accurately follow changes in line conditions. Therefore 1. This has sometimes caused the inconvenience of not being able to perform optimal data transmission.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an automatic regeneration method that can overcome the drawbacks of the prior art, accurately follow changes in line conditions, and improve data transmission efficiency.

Configuration The configuration of the present invention will be described below based on one embodiment.

FIG. 1 shows a part of a transmitter TX of a data transmission apparatus according to an embodiment of the present invention, and FIG. 2 shows a part of a receiver RX of the same.

In the transmitter TX, the transmission data DT sent from the data terminal 11 is encoded in a predetermined manner via a code compression/decompression device (DCR>1). After that, it is divided into 7 parts and applied to the rooming parallel-to-serial converter 2b, and sent out to the transmission line via the modem 3 as serial data SDT that has been subjected to a predetermined 7-raming process. It is preferable that the automatic retransmission control section 2 is constituted by a digital processor.

The modem controller 4 includes a signal processing unit (DSP) lO
The transmission rate of the modem 3 is controlled based on the transmission rate R-CTI added.

Reception status of data returned from the partner station (normal reception AC
response signal D representing abnormal reception (NACK or abnormal reception NACK)
R is applied to the buffer 2a and the shift condition check section 2c via the modem 3, and the latter determines whether or not the shift down and shift up conditions have been reached.

If the response signal DR is abnormally received, the buffer 2a
outputs the same block of data again.

The transmission speed shift condition referred to by the shift condition check section 2c is transferred from the DSP 10 and set in the shift condition control section 2d according to the initial condition CC and the like. When the response signal DR reaches the transmission speed shift condition, the shift condition check section 2c outputs a shift command signal C8 to the DSPIO.

Accordingly, the DSP 10 changes the transmission speed data CTI to change the transmission speed of the modem 3 and transmits to the other station that the transmission speed will be downshifted.

In the receiving section RX, the transmission data received by the modem 5 is judged by the serial-to-parallel converter/frame error checking section 6a of the automatic retransmission control section 6 to determine whether or not it has been received abnormally. The result is sent back to the transmitting station as a response signal DR.

In this way, only normally received data is converted into parallel data, temporarily stored in the buffer 6b, further transferred to the DCR 7, decoded, and output to the data terminal 13. This automatic retransmission control section 6 may also be constructed from a digital processor.

Also, if there is a shift down 4W notification in the received data,
The transmission speed of the modem 5 is controlled by transmission speed data CT2 applied to the DSP 12 and the modem controller 8.

The shift condition control unit 2d changes the shift conditions and controls the order of shifting transmission speeds in the following manner.

First, the initial value of the transmission rate set in modem training before transmission is given from the DSPIO as the initial condition CC, and the downshift condition is set accordingly. Furthermore, the shift conditions may be changed not only according to the initially set transmission speed but also according to the current transmission speed. Generally, if the line conditions are the same, for example, the initial value of the transmission speed is 96.
00 bps (bits per second), 4800 bps
Reception errors are more likely to occur than in the case of Also, there are many retransmission requests, so even if you shift down from 9600 bps to 7200 bps, the transmission time will only increase by 1.3 times, but
Shifting down from 800 bps to 2400 bps doubles the transmission time. Therefore, in the case of 4800 bps, it may be advantageous to downshift. Therefore, when the initial value is 9,600 bps, the shift 1 down conditions (judgment criteria such as frequency of retransmission requests) may be made stricter than when the initial value is 4,800 bps. In addition, when the data terminal 11 is a facsimile machine, the shift down conditions may be changed depending on the terminal state such as the paper size. For example, if the remaining portion of the transmitted image is small, the transmission may be completed at the same transmission speed without downshifting even if there are many retransmission requests.

The shift condition checking section 2c monitors the reception frequency of normal reception (ACK) and/or abnormal reception (NACK). The shift condition control unit 2d prepares a plurality of types of downshift modes, and receives this ACK.

These modes may be selected depending on the frequency of NACK reception. For example, if the line deteriorates rapidly, such as when retransmission is requested from the other station continuously after several frames have been successfully received, the transmission speed will be changed to two steps lower instead of shifting down to the one step lower transmission speed. For example, two types of downshift modes are set so that the shift I/down is performed.

As a result, if the line condition continues to be poor, it is possible to avoid wasteful downshifts, such as two consecutive downshifts, when downshifting for each step.

Furthermore, the shift condition control unit 2d sets a condition for shifting the transmission speed when there is no retransmission request for a certain period of time or more, and shifts the transmission speed up, for example, by one step when the line condition is restored. It's okay.

By combining such upshift control and downshift control of the transmission speed, for example, 9600 bp
s −+ 4800 bps −) 7200 bps
→ 4800 bps → 7200 bps-+'-. It is possible to realize highly flexible transmission speed control according to line conditions.

Effects As explained above, according to the present invention, data transmission speed,
Since the transmission speed shift is controlled based on external conditions such as the terminal status and the status of retransmission requests from the other station, shift control that follows the status of the transmission line is OJ.
This has the advantage that substantial data transmission time can be saved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a part of a transmitting section of a data transmission apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a part of a receiving section thereof. Explanation of symbols of main parts 2.6... Automatic retransmission control section, 2C... Shift condition checking section, 2d... Shift condition control section. Patent applicant Ricoh Co., Ltd.

Claims (1)

[Claims] If the transmitted block data is not received normally on the receiving side and a request is made to retransmit the block data,
In an automatic retransmission method that retransmits the block data and shifts the data transmission rate when the frequency of this retransmission request satisfies the first condition, the shift mode of the data transmission rate and the first condition are as follows:
An automatic retransmission method characterized in that the automatic retransmission method is changed based on a second condition including a data transmission rate, a terminal state, and a retransmission request frequency state.