JPH0496534A - Selection retransmission system for hold - Google Patents

Abstract

PURPOSE:To attain retransmission of all information frames relating to identification information included in a retransmission request frame through the reception of the retransmission request frame by incorporating error frame information with respect to plural information frames into the retransmission request frame. CONSTITUTION:A data C1 representing a new retransmission request frame MREJ and a number C2 representing a last frame in consecutive frames having no transmission error in received information frames are included in a control field D of a retransmission request frame MREJ. Moreover, an error frame bit pattern EF is inserted in an information field of the retransmission request frame MREJ. Each bit of an error frame bit pattern EF represents the reception state of the information frame after the last frame without an error. When a bit pattern EF of error frame information of a received NREJ frame differs from the bit pattern EF of an error frame information buffer 206 and an information frame on retransmission request is in existence in a transmission frame buffer 202, the information frame on retransmission request is informed to a retransmission request section 207.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to an HDLC selective retransmission method for selectively retransmitting information frames (■ frames) in high-level data link control (HDLC) procedures. [Prior Art] In conventional HDLC, a retransmission method using select rejection (SREJ) frames and rejection (REJ) frames is defined. The retransmission method using SR and EJ frames has better performance than the retransmission method using REJ frames because it can selectively instruct retransmission frames.

FIG. 2 shows an example of retransmission using 5REJ frames, and the conventional retransmission method will be explained using FIG.

Station A sends numbered information frames ■(1), I (
2>, I (3L I (4) and I (5) are continuously transmitted to station B. Here, the information frame I (1
), I (4) and ■(5) are received by station B without error, and a transmission error occurs in information frames ■(2) and ■(3).

Since the B station has received the first information frame T(1) without error, it transmits a response frame RR(2) having the number of the next information frame to the A station. When station A receives response frame RR(2), it sends information frame ■(
1) is recognized as being correctly received by station B. As mentioned above, if a transmission error occurs in information frames ■(2) and ■(3) due to a line error, station B transmits information frame ■(2) and ■(3) when receiving the subsequent information frame ■<4).
It is recognized that a transmission error has occurred in (2) and f(3).

Therefore, when the B station receives the information frame (4), it transmits a retransmission request frame 5REJ (2>) to the A station requesting the A station to retransmit the information frame (2). , The 5ERJ frame, which is a retransmission request frame according to this conventional example, can request retransmission only for one information frame.Therefore, if multiple frames are erroneous, the 5ERJ frame can be sent individually by the number of erroneous frames. 5
It is necessary to send a REJ frame. As mentioned above, even if a transmission error occurs in information frames (2) and (3), the retransmission of information frame I (2) is first requested.

When station A receives the retransmission request frame 5REJ (2>, it retransmits the information frame ■(2) accordingly. However, before retransmitting the information frame ■(2), it transmits the information frame ■(5). Therefore, information frame ■(5>) was received first by station B, and information frame 1, which requested retransmission, is
(2) has not been received, the B station again requests retransmission of the information frame (2) using the retransmission request frame 5REJ (2>).

Station A sends the second retransmission request frame 5REJ with the same content.
Even when (2) is not received, information frame (2) is retransmitted.

When the B station receives the first retransmitted information frame (2), it transmits a retransmission request frame 5REJ (3) indicating a retransmission request for the information frame (3). However, after transmitting this retransmission request frame 5REJ (3), station B receives the information frame (2) again. At this time, since the information frame E(3) has not yet been received, the retransmission request frame 5REJ(3) with the same content is transmitted again.

On the other hand, since station A receives the retransmission request frame 5REJ (3) twice, it will retransmit the information frame (3) twice.

Note that station B, which received the first retransmitted information frame E (3), indicates that it has received information frames up to (5) without error, and that it is capable of receiving information frame (6). A response frame RR(6) representing the above is transmitted to the A station.

As described above, since the 5REJ frame requests retransmission for one information frame, the same frame may be transmitted many times even though there is no error in the conventional retransmission method.

[Problems to be Solved by the Invention] As described above, even with the retransmission method using 5REJ frames, which is more efficient than the retransmission method using REJ frames, the same information frame is sent multiple times even though no transmission error has occurred. It may be sent again in succession.

When the amount of data contained in an information frame is small, the deterioration in transmission efficiency due to multiple transmission of the same frame is not so large, but the turnaround time is affected. Furthermore, when a large amount of data is included in an information frame, the transmission efficiency deteriorates significantly due to multiplex transmission and the like. especially,
On a line with a high line error rate, retransmission requests occur frequently, so the deterioration in transmission efficiency due to multiplex transmission caused by the fact that only one frame of 5REJ frames can be requested for retransmission is significant.

The above are problems when the transmission line is full-duplex, but the following problems also occur when the transmission line is half-duplex. In addition,
In the case of half-duplex, a frame for which retransmission is requested will not be transmitted multiple times. As mentioned above, since the 5REJ frame can only request retransmission of one frame, the 5REJ frame
It is necessary to transmit as many REJ frames as the number of information frames for which retransmission is requested, and if there are many information frames for which retransmission is requested, the number of 5 REJ frames also increases. Therefore, when there is an information frame to be transmitted to the local station, the greater the number of 5REJ frames, the more the transmission of the information frame will be delayed.

The present invention has been made in consideration of the above points, and it is possible to minimize the number of times an information frame for which retransmission is requested is transmitted, and also to efficiently transmit a retransmission request frame, thereby improving transmission efficiency. The present invention attempts to provide a selective retransmission method in HDLC that can improve transmission time.

[Means for Solving the Problem] In order to solve the problem, in the present invention, when the received information frame is incorrect, a retransmission request frame is sent from the information frame receiving system to the transmitting system to send the information. In the selective retransmission method in HDLC that retransmits frames, error frame information that can identify all information frames that the receiving system recognizes as erroneous is included in a retransmission request frame and transmitted, and the transmitting system transmits this retransmission request frame. All erroneous information frames are retransmitted based on the erroneous frame information inserted into the erroneous frames.

Preferably, such a selective retransmission method consists of the following parts.

That is, a transmission frame buffer in which transmission data is stored in the form of a frame, an error frame inspection unit that searches for one or more information frames containing errors from retransmission request frames received from the other station, and a retransmission request frame. An information frame transmission system is provided with an error frame information buffer section for temporarily storing error frame information of the information frame, and a retransmission request section for selecting all the frames for which retransmission is requested from the transmission frame buffer and retransmitting them. , a reception buffer inspection unit that searches for an information frame to be retransmitted from the other station based on the received information frame; and one or more recognized error frames can be identified from the error frame information output from the reception buffer inspection unit. An error information creation unit that creates a retransmission request frame with information inserted, and a retransmission request that determines whether or not to transmit the retransmission request frame based on the retransmission request frame output from the error information creation unit and the received information frame. It is preferable that the information frame receiving system includes a frame determination section.

[Operation] The present invention is characterized by the format itself of the retransmission request frame. In other words, error frame information for identifying an erroneous information frame can be included in a retransmission request frame, not only for one information frame but also for a plurality of information frames.

Therefore, if there are a plurality of information frames that the information frame receiving system recognizes as errors, the identification information of the recognized plurality of information frames is included in one retransmission request frame and transmitted. The information frame transmission system that receives this is
Upon reception of one retransmission request frame, all information frames related to the identification information included therein are retransmitted.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Here, FIG. 1 is a format diagram of a retransmission request frame in this embodiment, FIG. 3 is a block diagram of a communication control device that executes the HDLC procedure, and FIG. 4 is a diagram of the transmission side of an information frame in the above embodiment. FIG. 5 is a functional block diagram of the information frame receiving side of the above embodiment.

First, the hardware configuration of the communication control device that executes the HD LC procedure will be explained. In FIG. 3, this communication control device 10 includes a microprocessor (C
PU) 100, a read-only memory (ROM) 103 as a program memory, a random access memory (RAM>104 as a working memory), and a frame buffer 107 for storing transmitted or received frames. The terminal interface 1 executes the HD Lc procedure in order to receive data to be transmitted from an external terminal device (not shown) and to provide received data to the external terminal device.
It is equipped with 02. Furthermore, there is a serial interface that performs an interface function for exchanging data with a modem (not shown).
A parallel converter (SIO) 105 and a modem control circuit 106 are provided for controlling the operation of the modem, such as placing the modem in an off-hook state or on-hook state.

exchanged between communication control devices having such a configuration,
Retransmission request frame MREJ (hereinafter referred to as
The format of an MREJ frame (sometimes referred to as an MREJ frame) is shown in FIG.

This retransmission request frame MREJ also naturally includes a leading flag sequence F, an address field A, a control field C5, an information field 1, and a frame check sequence F.
C8 and end flag sequence F.

The control field C of this retransmission request frame MREJ contains data C]- indicating that the frame is a new retransmission request frame MREJ according to this embodiment, and a series of received information frames without a transmission error. The number C2 indicating the last frame among the frames included is included. Here, the last frame among consecutive frames without transmission errors indicates that this frame and all previous frames have been correctly received.

Furthermore, an error frame bit pattern EF is inserted into the information field (2) of the retransmission request frame VIREJ. This wrong frame pops! - Pattern EF has bits equal to the number of outstanding frames. Here, the number of outstand frames is the number of information frames that the transmitting station of the information frame can continuously transmit at one time without receiving a response from the receiving station. Determined in advance. Each bit of the error frame bit pattern EF indicates the reception status of information frames subsequent to the last error-free frame.

Erroneous information frames and information frames that have not yet been received are assigned the binary number 11111, and error-free information frames are assigned the binary number ``0''.

Example of error frame bit pattern EF shown in Figure 1
11011111" means that the number of outstanding frames is 8, the information frame next to the last information frame without a transmission error and the next information frame is an erroneous frame, and the last information without a transmission error. This indicates that the third information frame counting from the frame is a correctly received frame, and the fourth and subsequent information frames counting from the last information frame without a transmission error are frames that have not yet been received. There is.

In this way, in this retransmission request frame MREJ, error frame information is formed by the last frame number C2 without an error and the error frame bit pattern EF.

Next, the functional configuration of an information frame transmitting side that may receive a retransmission request frame MREJ according to such a format will be explained using FIG. 4.

In FIG. 4, a frame division section 200 divides data from a terminal device etc. into frames, and is connected to a transmission frame buffer 202. The transmission frame buffer 202 has buffers for a predetermined number of outstanding frames, and one or more new frame data is inserted into the transmission frame buffer 202 each time there is an acknowledgment from the partner station. Therefore, when there is a large amount of transmission data, the transmission frame buffer 20
2, frames equal to the number of outstanding frames are always prepared. Transmission frame buffer 20
From No. 2 onwards, frame data is output to the HDLC encoding unit 203 in descending order of number, and the HDLC encoder 203 adds flags, addresses, controls, and frame check sequences necessary for HDLC to this data, and sends it to a line interface such as a modem. Sent.

On the other hand, data received from a modem etc. is sent to the HDLC decoder 2.
04 and decoded and obtained by HDLC decoding section 204 , the frame is input to error frame checking section 205 .

The error frame checking unit 205 contains error frame information C2 and EF of the retransmission request frame MREJ received one before.
An error frame information buffer 206 for buffering (see FIG. 1) and a retransmission request unit 207 for instructing the transmission frame buffer 202 which information frame to retransmit are connected.

The error frame inspection unit 205 detects the retransmission request frame MRE.
If J is received, error frame information C2 and EF
Inspect. That is, the error frame information C2 of the previously received retransmission request frame MREJ stored in the error frame 1.6-frame information buffer 206
and EF, and the error frame information C2 and EF of the retransmission request frame MREJ received this time.

When the following requirements (■ to ■) are satisfied, the error frame checking unit 205 sends the error frame information C to the retransmission request unit 207.
2 and EF do not give the number of the frame for which retransmission is requested. (2) The bit pattern EF of the error frame information of the MREJ frame received this time is the same as the bit pattern EF of the error frame information buffer 206. (2) The last frame number C2 received without error inserted in the control field C is the same as the previous last frame number C2. ■When the retransmission of the information frame for which retransmission was requested has been completed or is in the middle of retransmission.

This is to avoid redundantly retransmitting the same information frame when MREJ frames with the same content are received two or more times in a row.

Therefore, for example, the bit pattern EF of the error frame information of the received MREJ frame is different from the bit pattern EF of the error frame information buffer 206 and the information frame for which retransmission is requested is stored in the transmission frame buffer 206.
2, the retransmission request unit 207 is notified of the information frame for which retransmission is requested. Also, for example,
Even if the bit pattern EF of the error frame information of the received MREJ frame is the same as the bit pattern EF of the error frame information buffer 206, the last frame number C2 inserted in the control field C and received without error.
However, the information frame that is different from the previous last frame number C2 and is requested to be retransmitted is sent to the transmission frame buffer 2.
02, the retransmission request unit 207 is notified of the information frame for which retransmission is requested.

Upon receiving the notification, the retransmission requesting unit 207 stops the normal transmission operation, immediately searches for the requested information frame from the transmission frame buffer 202, and causes it to be retransmitted. In this case, if more than one information frame is requested,
Retransmission is executed for the plurality of frames.

Next, the functional configuration of the information frame receiving side that may transmit the retransmission request frame MREJ shown in FIG. 1 will be explained using FIG. 5.

In Figure 5, the signal received from the modem etc. is HDLC.
After the received frame is decoded by the decoding unit decoding unit 00 and inspected by the frame check sequence (Fe2), the correct frame is sent to the receive frame buffer 301.
to the appropriate buffer. The frame disassembly unit 302 receives the received frame buffer 301. The received frame 301 is searched in ascending order of number, and if it is correctly received, the data in the received frame buffer 301 is transmitted to a terminal device or the like.

On the other hand, a reception buffer inspection unit 303 provided in relation to the reception frame buffer 301 is a frame disassembly unit 3
This function checks the receive frame buffer 301 in the same way as the function 02, and searches for information frames that could not be received by mistake. Then, the last frame number of successive information frames that have been correctly received and the information frame to be retransmitted are sent to the error information creation section 304. The error information creation unit 304 creates error frame information C2 and EF of the MREJ frame shown in FIG. 1 based on these information, and sends it to the retransmission request frame transmission determination unit 305. This retransmission request frame transmission determination section 305 examines the error information C2 and EF sequentially sent from the error information creation section 304, and 1. When a pattern different from the previously received error information C2 and EF is received, it is immediately output in the format of the retransmission request frame MREJ shown in FIG. 1, and this is encoded by the HDLC encoding section 306 and transmitted. .

Note that even if the information frame requested for retransmission is received correctly and the error information is changed, the retransmission request frame MREJ
will not be sent.

Although not shown, the retransmission request frame transmission determination unit 305 also monitors the number of the received information frame, and when a frame indicating a response request is received from the other station (information frame transmitting station), , the error frame information sent from the error information creation unit 304 is immediately formatted into a retransmission request frame MREJ and transmitted. The fact that the received information frame is abnormal can be recognized not only by the fact that subsequent frames have been correctly received, but also by the fact that it can be recognized when a frame indicating a response request is received from the transmitting station. The latter allows recognition even if the latter information frames are incorrect up to the last frame.

FIG. 6 is an explanatory diagram showing an example of retransmission according to this embodiment. The retransmission system according to the embodiment will be explained below using FIG. 6.

Note that in FIG. 6, station A is an information frame transmitting station;
Station B is the receiving station for information frames, and from station A, four numbered information frames ■ (1,), I (2) are received.
, I (3) and I (4) are successively transmitted. Also, during normal transmission, an information frame ■ (2
) and ■(3) are incorrect.

When the B station receives the information frame ■(1>), it transmits the normal reception response frame RR (2>) to the A station.When the B station receives the information frame I (4), the B station sends the information frame I
It is recognized that (2> and I(3)) are incorrect. At this time, the reception buffer inspection unit 303 and error information creation unit 304 in FIG. The requested error information C2 and EF are created. Here, the bit pattern EF of the error information is '.

11,011.1.11", and the number C2 of the last information frame before the correctly received error frame is "1".
becomes. This information is sent to the retransmission request frame determining unit 305.
is the retransmission request frame MREJ (2, 3
) format and send it to station A.

Station A, which has not received the retransmission request frame MREJ (2, 3>), transmits the contents of control field C and error frame information EF.
It checks that information frames ■(2) and 1(3) are requested to be retransmitted, and sends the retransmission request frame MREJ.
Immediately after receiving (2, 3), information frames (2) and (3) are retransmitted to station B.

Upon correctly receiving the retransmitted information frames E (2) and (3), the station sends a response frame RR (6) to that effect to A.
transmit to the station.

In addition, in this embodiment, the information frame ■ (2
) is correctly received, neither the response frame RR nor the retransmission request frame MREJ indicating correct reception is transmitted.

However, these may be transmitted as described later.

Therefore, according to the above embodiment, even if there are multiple frames to be retransmitted, the multiple frames can be indicated by one retransmission request frame, so the number of exchanges of retransmission request frames is reduced. In this way, transmission efficiency and transmission time can be improved, and meaningless multiple transmission of the same information frame can be minimized.

Furthermore, even when the transmission line is half-duplex, transmission efficiency and transmission time can be improved.

In particular, by buffering the error frame information of the previous retransmission request frame, it is possible to further prevent multiple transmission of retransmission frames.

In the above embodiment, the last frame number of successive correctly transmitted information frames is inserted into the control field C of the retransmission request frame MREJ, but it may also be included in the information field ■. good.

Furthermore, in the above embodiment, in the error frame bit pattern E)P, for unreceived frames,
The one in which bits 11111 are assigned like an error frame is shown, but the bit '°0 like a no-error frame is assigned.
“ may be assigned.

Furthermore, the configurations of the transmitting side and the receiving side are not limited to those described above, and may be other configurations. For example, the receiving system may be configured to always transmit an R, R frame or an MREJ frame when an information frame is correctly received. Even in this case, wasteful transmission can be prevented by the transmission system buffering the error frame information of the previous MREJ frame.

In addition, regarding the transmission system, instead of using a complete match between the buffered bit pattern and the bit pattern that has not been received as a condition for not accepting a retransmission request, it is possible to Matching and mismatching may be set as a condition for not accepting a retransmission request.

In short, any configuration is sufficient as long as it can effectively utilize the MREJ frame shown in FIG. 1, which can selectively indicate that a plurality of frames are erroneous.

[Effects of the Invention] As described above, according to the present invention, even when there are multiple information frames to be retransmitted, retransmission can be instructed using a single retransmission request frame. It is possible to minimize the number of retransmissions of the data, and improve transmission efficiency and transmission time.

[Brief explanation of the drawing]

FIG. 1 is a format diagram of a retransmission request frame in an embodiment of the selective reversible method in HDLC according to the present invention;
Figure 2 is an explanatory diagram of an example of retransmission using the conventional method, and Figure 3 is an illustration of an example of retransmission using the conventional method.
FIG. 4 is a functional block diagram of the information frame transmitting side of the above embodiment, and FIG. 5 is a functional block diagram of the information frame receiving side of the above embodiment. FIG. 6 is an explanatory diagram of an example of retransmission in the above embodiment. MRE J...Retransmission request frame, C2...Last frame number of successive correctly transmitted information frames, EF...Error frame bit pattern, 202...
- Transmission frame buffer, 205...Error frame inspection unit, 206...Error frame information buffer unit, 20
7...Retransmission request unit, 301...Reception frame buffer, 303...Reception buffer inspection unit, 304...Error information creation unit, 305...Retransmission request frame determination unit.

Claims (4)

[Claims] (1) In the selective retransmission method in HDLC, in which when the received information frame is incorrect, a retransmission request frame is sent from the information frame receiving system to the transmitting system to retransmit the information frame. Error frame information that can identify all recognized information frames is included in the retransmission request frame and transmitted, and the transmission system identifies all erroneous information frames based on the error frame information inserted in the retransmission request frame. A selective retransmission method in HDLC characterized by retransmitting information frames. (2) The transmission system has a buffer section for error frame information of the retransmission request frame, and prevents the retransmission operation from starting when the error frame information received last time and the error frame information received this time are the same. Claim 1
Selective retransmission method in HDLC described in . (3) Claim 1 characterized in that the receiving system does not start the transmission operation when the retransmission request frame transmitted last time and the retransmission request frame to be transmitted this time are the same.
Selective retransmission method in HDLC described in . (4) a transmission frame buffer in which transmission data is stored in the form of a frame; an error frame check unit that searches for one or more erroneous information frames from retransmission request frames received from the other station; and the retransmission request described above. an error frame information buffer section that temporarily stores error frame information of frames; a retransmission request section that selects and retransmits all frames for which retransmission is requested from the transmission frame buffer; A reception buffer inspection unit that searches for information frames to be retransmitted from the other station; and information that can identify one or more recognized error information frames is inserted based on the information on the error frames output from this reception buffer inspection unit. an error information creation unit that creates a retransmission request frame; and a retransmission request frame determination unit that determines whether or not to transmit the retransmission request frame based on the retransmission request frame output from the error information creation unit and the received information frame. A selective retransmission method in HDLC, characterized by comprising: