JPS6351623B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a reception processing method when an abort frame occurs in a high-level data link (HDLC) procedure, and in particular, it is discarded when an abort is detected due to an error. This is an attempt to eliminate waste by minimizing the number of normal data frames.

Prior Art and Problems In normal HDLC procedures, an abort frame means abandonment of the frame, and the transmission of an abort frame by a secondary station also means abandonment of transmission rights. Therefore, if a frame transmitted by a secondary station becomes an abort frame due to a bit error on the line, etc., there is a problem that the subsequent frame will be discarded.

FIG. 1 is an explanatory diagram of transmission and abort processing according to the HDLC protocol. When the primary station passes the transmission right to the secondary station by polling, the secondary station that obtained the transmission right sends data (1) to (n) to the primary station, and finally sends an abort to regain the transmission right. It can be returned to the primary station (usually with a final display in the frame).
HDLC abort is indicated by 7 to 15 consecutive bits of "1" in the data.

By the way, with the abort processing described above, even if a bit error occurs due to poor line quality and an abort signal is accidentally generated, the secondary station assumes that it has given up the right to transmit, and the data it receives thereafter is discarded. There is. FIG. 2 is an explanatory diagram of this, and shows how an abort occurs due to unintended poor line quality at the secondary station while transmitting data (3).
A normal abort, which means relinquishing the right to transmit, is issued after the final data (7), but when this is detected in data (3), the primary station determines that the secondary station has relinquished the right to transmit. , since reception monitoring will be stopped.
All subsequent data (3) to (7) will be discarded.
Of course, the received data is up to the second one, and this is known on the receiving side, that is, the primary station, so it is possible to have the missing data retransmitted by displaying the data number to send in the next polling frame. It is. However, it is necessary to discard data 3 to 7 and wait until the next polling timing to perform the same transmission request procedure again, which inevitably reduces transmission efficiency.

Purpose of the Invention The present invention continues to monitor reception for a certain period of time even when an abort frame is received, and if the next data is received within that certain period of time, it is determined that the abort is not intended by the secondary station. Then, a retransmission request is immediately made, thereby reducing the rate at which received data is wasted and improving transmission efficiency.

Structure of the Invention According to the present invention, when an abort frame is received while receiving a data frame in an HDLC procedure, a timer is started, but reception monitoring continues, and if the next data frame is received within a certain period of time before the timer times out. request the other station to retransmit the data of the frame in which the abort was detected, and if the data frame is not received within the certain period of time, it is assumed that the other station has abandoned the transmission right and reception monitoring is stopped. This will be described in detail below with reference to embodiments not shown.

Embodiment of the Invention FIG. 3 is an explanatory diagram showing an embodiment of the present invention, and similarly to FIG. 2, it shows an example in which an abort due to an error occurs during transmission of data (3). In the present invention, even if an abort frame is detected, it is not immediately regarded as an abandonment of the transmission right by the secondary station, so reception monitoring continues and a timer is started. As a result, the next data is transmitted within a certain period of time (this corresponds to the transmission data interval and is determined by the transmission speed of the communication line, etc.).
If (4) is detected, the abort in data (3) that was the source of the timer start is not regarded as the final indication, and is determined to be due to poor line quality, etc., and the data (3) (this (can be determined to have caused a bit error) and requests retransmission. This is the meaning of retransmission request (3). In terms of timing, by the time this retransmission request (3) is received by the secondary station, the secondary station has transmitted up to data (5), so data 3 to 5
will be retransmitted. However, there is no need to poll again as shown in Figure 2, and data (6) and (7)
Since there is no need to retransmit up to the point, transmission efficiency increases accordingly. The example in Figure 3 ends with data (7), but when this is generalized to data (n), the data that is always wasted in the present invention is only three frames including the frame in which the abort occurs, so The larger the number of frames n is, the more remarkable the effect is.

FIG. 4 shows the HDLC frame structure, where F is a flag, A is an address, C is a control, and FCS is a frame check sequence. Control field C indicates whether the subsequent field is data, polling information, data link setting/release performed at the start/end of transmission, etc. The above-mentioned retransmission start data number at the time of retransmission or polling is also included in this control field.
HDLC prohibits 5 or more consecutive 1's in normal data, and if there are 5 or more consecutive 1's, insert 0's in between to keep it within 5 bits, and the inserted 0's are discarded on the receiving side. It's become a rule. Flag F is represented by 01111110, and is made up of six consecutive 1s with 0s placed on both sides. And 1 is 7~
Consecutive 1's between 15 bits indicate an abort, and 16 or more consecutive 1's indicate an idle state of the line. An abort may be inserted at any position in a frame (FIG. 4 also shows an example of inserting this abort), and a frame in which an abort is present is considered an abort frame. Also, a frame starts and ends with a flag, but the next frame may have its start flag in common with the end flag of the previous frame, or it may be different, or it may have several flags in succession, then A, C, etc. You can continue with data...

FIG. 5 is a block diagram of an apparatus implementing the present invention, in which 13 is a character processing section connected to a line, and 10 is a received frame check section. The character processing unit 13 decomposes the received frame into elements F, A, C, . . . , terminates characters in data, stores them in a character buffer, detects aborts, and so on. The checking section 10 checks whether the frame structure of the received data conforms to FIG.
(Actually, the address of the character buffer of the character processing unit 13 is notified.) Further, when an abort is detected, the timer processing unit 12 is activated. The character processing unit 13 determines whether the received text is a flag or a general character.
Part 1 that determines whether to abort, etc. and checks the result.
Notify 0. The timer processing unit 12 is started upon reception of an abort, and when a certain period of time has elapsed and a timeout occurs, the reception monitoring in the character processing unit 13 is stopped. In other words, the operation of the character processing unit, that is, reception monitoring, is continued until the timeout occurs. At the same time, it is determined that the other party no longer has the transmission right, and the transmission scheduler 14 starts polling processing. That is, a timer that determines the polling cycle is started, and polling at a constant cycle is started.
However, when the next data is received within a certain period of time, the data processing unit 11 requests the timer processing unit 12 to stop timing, prohibits the activation of the transmission scheduler 14, and checks the sequence number to determine if retransmission is necessary. A retransmission request based on the data number is sent to the secondary station.

Conventionally, there was no timer processing section 12, and the check section 1
0 started the transmission scheduler 14 immediately upon receiving the abort, but in the present invention, the timer processing unit 1
2 to allow time to determine whether it is a true abort. This will immediately request retransmission if there is an error.
Therefore, the transmitting side can immediately stop transmitting subsequent data and retransmit data starting from the data in which the error occurred.

Effects of the Invention As described above, according to the present invention, even if an abort occurs due to an error during data transmission in the communication system of the HDLC procedure, it is not considered to be an abandonment of the transmission right, so the amount of data to be retransmitted can be reduced, and the transmission This has the advantage of improved efficiency.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of normal abort processing according to the HDLC protocol, FIG. 2 is an explanatory diagram of conventional abort processing during data transmission, FIG. 3 is an explanatory diagram showing an embodiment of the present invention, and FIG. FIG. 5, a frame configuration diagram of HDLC, is a block diagram showing an example of an apparatus implementing the present invention. In the figure, 10 is a received frame check section, 11 is a data processing section, 12 is a timer processing section, 13 is a character processing section, and 14 is a transmission scheduler.

Claims (1)

[Claims] 1 If an abort frame is received while receiving a data frame in the HDLC procedure, a timer is started, but reception monitoring continues, and if the next data frame is received within a certain period of time before the timer times out, the abort is detected. The HDLC is characterized in that the other station is requested to retransmit the data of the received frame, and if the data frame is not received within the certain period of time, the other station is deemed to have abandoned the transmission right and reception monitoring is stopped. Various methods for receiving abort frames in procedures.