JP3709462B2 - HDLC signal transmission / reception method, HDLC signal device, program thereof, and recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a signal transmission / reception method and signal apparatus for transmitting and receiving a message signal using an HDLC frame via a transmission line, and more specifically, a transmission signal length total waiting for delivery confirmation in a data link does not exceed a threshold. The present invention relates to an HDLC protocol signal transmission / reception method and signal apparatus for controlling the program, a program, and a recording medium for storing the program.
[0002]
[Prior art]
HDLC is known as a highly efficient and reliable transmission control procedure (data link layer procedure). According to this transmission control procedure, continuous transfer is possible, it is possible to postpone without a response within a certain range, a CRC is employed, and a data error detection rate is high.
FIG. 4 is a diagram illustrating a configuration example of a conventional general HDLC signal device.
As shown in FIG. 4, the conventional HDLC signal apparatus is for transmitting a message of a higher layer than the data link to the line transmission interface and receiving a message of a higher layer than the data link from the line reception interface. . In the HDLC signal device 1, a message processing unit 4, a data link signal processing unit 2, and a line interface processing unit 3 are provided. In the data link processing unit 3, a message signal transmission queue 5, a data link signal transmission processing unit 6, a data link signal reception processing unit 7, and a transmission confirmation waiting signal number counter 8 are arranged. In the line interface processing unit 3, a transmission signal FIFO 9, a line transmission unit 10, a line reception unit 11, and a reception signal FIFO 12 are arranged.
[0003]
When the message processing unit 4 generates a message, the message processing unit 4 queues the generated message in the message transmission queue 5.
When the value indicated by the transmission confirmation wait signal number counter 8 is smaller than a preset threshold value (maximum outstanding number), the data link signal transmission processing unit 6 performs transmission in the message signal transmission queue 5 according to the protocol operation. The message is mapped to the data link signal, transmitted to the transmission signal FIFO 9, and the value of the transmission confirmation wait signal number counter 8 is incremented by one.
When there is a signal in the transmission signal FIFO 9, the line transmission unit 10 assigns a flag pattern “01111110” to the head of the signal, converts it to “111110” when detecting a “11111” pattern in the bit pattern of the signal, The patterns other than the 11111 ′ pattern are transmitted to the line transmission interface transparently.
[0004]
The line receiving unit 11 removes the flag from the bit pattern received by the line interface, and when the '111110' pattern is detected in the received signal, converts it into the '11111' signal, extracts the data link signal, and outputs it to the received signal FIFO 12 Send.
The data link signal reception processing unit 7 reads the data link signal from the reception signal FIFO 12, extracts a message from the read data link signal, transmits the message to the message processing unit 4, and the data link signal sends a delivery confirmation notification or a retransmission request. If included, the number of messages confirmed for delivery or the number of lost messages is subtracted from the delivery confirmation waiting signal number counter 8.
Regarding transmission / reception processing of the HDLC protocol, descriptions such as ISO-3309 (HDLC), TTC standard X25 (LAPB), Q921 (LAPD), and Q703 (MTP level 2) can be referred to.
[0005]
[Problems to be solved by the invention]
The problem in the configuration example of FIG. 4 is that (a) when burst transmission from the message processing unit 4 occurs, the delay in the transmission signal FIFO 9 increases. In addition, (b) in general, a data link protocol has a problem that if the transfer delay time is remarkably increased, a malfunction occurs in the protocol operation.
For example, in the case of a data link conforming to TTC standard Q703, there is a level 1 link speed = 4.8 kbit / s, but since the maximum outstanding number = 40 and the maximum signal length = 272 bytes, transmission is performed in the worst condition. The maximum delay in the signal FIFO 9 is about 18 seconds. In MTP2, a T7 timer (response delay timer: 3 seconds for a 4.8 kbit / s link) is started when an MSU (data frame) is transmitted, and the link is released if the T7 timer expires before delivery confirmation returns. .
[0006]
For this reason, if a message is transmitted from the other station to the own station at intervals longer than the T7 timer while the link is being used with a load close to 1 in the transmission direction from the own station to the other station, Since the delivery confirmation sent back to the other station is significantly delayed by the transmission signal FIFO 9, there is a possibility that the T7 timer will expire at the other station and the link will be released.
In addition, in the data link protocol, since delivery confirmation is generally monitored by a timer, there is a concern that unnecessary link release may occur depending on the relationship between the link speed, the number of standings, the signal length, and the timer.
However, if the size of the transmission signal FIFO 9 is made smaller than the maximum number of outstanding signals in order to reduce the delay in the transmission signal FIFO 9, in the case of the configuration of FIG. 4, signal discard due to signal overflow occurs in the transmission signal FIFO 9. Link performance is degraded.
Alternatively, when the transmission signal FIFO 9 overflows, a configuration in which the operation of the data link signal transmission processing unit 6 is stopped to prevent signal discard in the transmission signal FIFO 9 is also conceivable. In this case, the transmission signal FIFO 9 to the data link signal processing unit 2 requires a new signal line.
[0007]
As another countermeasure, a data link that is transmitted per unit time by the data link transmission processing unit 2 by applying the method of “ATM signal transmission method and ATM signal device” described in the specification and drawings of Japanese Patent Application No. 11-210271 A method of controlling the total signal length so that it does not exceed the line speed is also conceivable. In the technique described in the above publication, since the signal length at the ATM interface can be obtained from the signal length of the message by simple calculation on the premise of application to the ATM interface, the speed at the data link signal transmission processing unit 6 Adjustment was realized sufficiently effectively. By the way, unlike the above-described ATM interface, the HDLC protocol as in the present invention has a characteristic that a pattern (11111) having five consecutive “1” s in a data link signal is replaced with “111110” for transmission. are doing. For this reason, the data link signal transmission processing unit 6 cannot strictly calculate the signal length at the line interface. Therefore, when the technique of the above publication is applied to the HDLC protocol, when a large number of data having a large ratio of “1” is transmitted, the bit rate of the transmission signal exceeds the line speed by about 20% at the worst. Stagnation occurs. Therefore, a sufficient effect is not achieved.
[0008]
Therefore, an object of the present invention is to solve these conventional problems, prevent signal overflow in the transmission signal FIFO, and at the same time, reduce the maximum delay time in the transmission signal FIFO so that link release does not occur. An object is to provide a transmission / reception method, an HDLC signal device, a program thereof, and a recording medium.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the HDLC signal transmission / reception method of the present invention is an HDLC protocol data link layer having a characteristic of converting to '111110' when transmitting a signal when detecting a '11111' pattern, and transmitting a signal for waiting for delivery confirmation. The transmission of the HDLC protocol data link signal is controlled so that the total of the message length and the data link header length does not exceed a threshold value.
[0010]
Specifically, it has the following means.
That is, the HDLC signal transmission / reception method of the present invention includes a delivery confirmation waiting signal length table that holds a signal length obtained by adding up the data length of each delivery confirmation waiting signal and the data link header length in the processing means of the data link protocol, and a delivery confirmation. It has a delivery confirmation waiting total signal length counter that indicates the total signal length of the waiting signal data length and the data link header length for all delivery confirmation waiting signals,
If the value of the total signal length counter waiting for delivery confirmation is larger than a preset threshold, transmission of the message signal is blocked ,
When the value of the counter is less than or equal to a preset threshold value, the data link signal is transmitted to the line transmission interface, and the signal length obtained by adding the data length of the message and the data link header length to the transmission confirmation wait signal length table And adding the signal length to the counter,
When a data link delivery confirmation or retransmission request is received from the other station, the delivery confirmation waiting signal length table is referred to, the signal length of the message confirmed for delivery and the lost message is read, and the signal length is subtracted from the counter. It is characterized by that.
[0011]
Since the data link header length of a normal HDLC protocol is a fixed length, the above calculation can be easily realized. For example, in the case of the MTP level 2 protocol, the data link layer header length of the MSU (significant signal unit) used for message transfer is 5 bytes (fixed) if the flag at the head of the signal is included except for LI (signal length display). is there.
Further, the present invention can be embodied as an HDLC signal device to which the above method is applied.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a configuration diagram of an HDLC signal device showing an embodiment of the present invention.
The HDLC signal apparatus of FIG. 1 is for transmitting a message in a layer higher than the data link layer to the line transmission interface and receiving a message in a layer higher than the data link layer from the line reception interface.
1 shows the case where the present invention is applied to the HDLC protocol. However, the HDLC protocol having the characteristic of converting to '111110' when detecting the '11111' pattern at the time of signal transmission and transmitting it. For example, it can be easily applied to ISO-3309 (HDLC), TTC standard X25 (LAPB), Q921 (LAPD), Q703 (MTP level 2), or the like.
[0013]
In the HDLC signal apparatus 100, a message processing unit 400, a data link signal processing unit 200, and a line interface processing unit 300 are provided.
In the data link signal processing unit 200, there are a message signal transmission queue 201, a data link signal transmission processing unit 202, a data link signal reception processing unit 203, a delivery confirmation waiting signal length table 205, and a delivery confirmation waiting total signal length. A counter 204 is arranged.
In the line interface processing unit 300, a transmission signal FIFO 201, a line transmission processing unit 302, a line reception processing unit 303, and a reception signal FIFO 304 are arranged.
The delivery confirmation wait signal length table 205 stores 128 signal length holding registers 206-1 to 206-128 (hereinafter, represented by 206) corresponding to the sequence number modulo of the data link signal.
[0014]
FIG. 2 is an operation flowchart of the data link signal transmission processing unit in FIG.
When the message processing unit 400 generates a message, the message processing unit 400 queues the generated message in the message transmission queue 201.
The data link signal transmission processing unit 202 determines whether the message can be transmitted by the protocol operation (step 101), and if possible, determines whether there is a message in the message signal transmission queue next ( Step 102) If there is a message, next, referring to the transmission confirmation waiting total signal length counter 204, it is determined whether or not it is equal to or less than a preset threshold value (Step 103). If the threshold is less than or equal to the threshold value, the message in the message transmission queue 201 is mapped to the data link signal according to the protocol operation, transmitted to the transmission signal FIFO 301, and the message length and data link of the message are stored in the transmission confirmation waiting signal number counter 204. The total header length of the layer is added, and the total of the message length of the message and the data link layer header length is written in the signal length holding register 206 corresponding to the sequence number of the data link layer assigned to the message (step 104). ).
[0015]
On the other hand, if the value of the transmission confirmation waiting total signal length counter 204 is larger than a preset threshold value (step 103), message transmission is suppressed until the value of the delivery confirmation waiting total signal length counter 204 becomes equal to or less than the threshold value. .
When there is a signal in the transmission signal FIFO 301, the line transmission unit 302 adds a flag pattern “01111110” to the head of the signal, and converts this to “111110” when a “11111” pattern is detected in the bit pattern of the signal. However, the patterns other than the “11111” pattern are transmitted transparently to the line transmission interface.
[0016]
FIG. 3 is an operation flowchart of the data link signal reception processing unit in FIG.
The data link signal reception processing unit 203 determines whether or not there is a reception signal in the reception signal FIFO 301 (step 201). If there is a reception signal, the data link signal reception processing unit 203 performs processing based on the protocol specification on the reception signal (step 201). 202). That is, the data link signal is read from the reception signal FIFO 301, a message is extracted from the data link signal, and is transmitted to the message processing unit 400. At the same time, it is determined whether or not the data link signal includes a delivery confirmation notification or a retransmission request (step 203). If either of them is included, the sequence number of the confirmed delivery message and the lost message is added. The value of the corresponding signal length holding register 206 is subtracted from the delivery confirmation waiting total signal length counter 204 (step 204).
[0017]
(Threshold setting example)
Hereinafter, an example of setting the threshold will be described. The number of signal bytes that can stay in the transmission signal FIFO 301 depends on the value of S and the frequency of occurrence of the '11111' pattern in the transmitted data, where the threshold is S bytes. Assuming that the bit pattern of the data to be transmitted is random, the probability that any 5 bits are “11111” is 1/32, so the number of signal bytes that can stay in the transmission signal FIFO 301 is S * 33 / 32.
When the bit patterns of the data to be transmitted are all “11111”, the number of signal bytes that can stay in the transmission signal FIFO 301 is S * 6/5.
[0018]
Assuming MTP level 2 as the HDLC protocol, the threshold = S needs to satisfy the following formula (1). However, care should be taken because if a very small value is set as the threshold with respect to the upper limit of S determined by Equation (1), the link performance may be lowered.
RTD + T1 + T2 + S * 6/5 / V <T7 timer (1)
Here, RTD = round-trip propagation delay time T1 = processing delay time in the data link signal processing unit of the local station T2 = processing delay time in the data link signal processing unit of the partner station T7 timer = delivery confirmation monitoring timer in the partner station S = threshold value V = line speed.
[0019]
(Program and its recording medium)
If the operation flow of the data link signal transmission processing unit and the operation flow of the data link signal reception processing unit described in FIGS. 2 and 3 are converted into a program and stored in a recording medium such as a CD-ROM, the HDLC signal The present invention can be easily realized by mounting the recording medium on the processor of the apparatus, loading the program, and executing the program. In addition, the present invention can be easily realized in other programs by downloading the program from the processor to another processor via a network.
[0020]
【The invention's effect】
As described above, according to the present invention, when the '11111' pattern is detected during signal transmission, in the data link layer of the HDLC protocol that converts this to '111110' and transmits, Since the transmission of the HDLC protocol data link signal is controlled so that the total overhead of the data link header length does not exceed the threshold value, as a result, the overflow of the signal in the transmission signal FIFO is prevented and the maximum in the transmission signal FIFO is prevented. There is an effect that the delay time can be reduced to prevent the link release.
[Brief description of the drawings]
FIG. 1 is a block diagram of an HDLC signal device showing an embodiment of the present invention.
FIG. 2 is an operation flowchart of a data link signal transmission processing unit according to an embodiment of the present invention.
FIG. 3 is an operation flowchart of a data link signal reception processing unit according to an embodiment of the present invention.
FIG. 4 is a block diagram showing an example of a conventional HDLC signal device.
[Explanation of symbols]
100: HDLC signal device, 200: Data link signal processing unit,
300 ... line interface processing unit, 400 ... message processing unit,
201 ... Message signal transmission queue, 202 ... Data link signal transmission processing unit,
205 ... Delivery confirmation waiting signal length table,
206-1 to 206-128 ... signal length holding register,
204 ... Total signal length counter waiting for delivery confirmation,
203 ... Data link signal reception processing unit, 301 ... Transmission signal FIFO,
302: Line transmission unit, 303: Line reception unit, 304: Reception signal.

Claims (4)

In a signal transmission / reception method for transmitting and receiving a message signal by an HDLC frame via a transmission line,
The processing means of the data link protocol includes a delivery confirmation wait signal length table holding a signal length obtained by adding up the data length of each delivery confirmation wait signal and the data link header length, and the data length and data link header length of the delivery confirmation wait signal. When the value of the total signal length counter waiting for delivery confirmation is larger than a preset threshold value by providing a total signal length counter waiting for delivery confirmation indicating the total signal length of all the signals waiting for delivery confirmation Prevents sending message signals,
When the value of the counter is less than or equal to a preset threshold value, the data link signal is transmitted to the line transmission interface, and the signal length obtained by adding the data length of the message and the data link header length to the transmission confirmation wait signal length table And adding the signal length to the counter,
When a data link delivery confirmation or retransmission request is received from the other station, the delivery confirmation waiting signal length table is referred to, the signal length of the message confirmed for delivery and the lost message is read, and the signal length is subtracted from the counter. An HDLC signal transmitting / receiving method characterized by the above. In an HDLC signal device that transmits and receives a message signal by an HDLC frame via a transmission line,
Message processing means for generating and terminating message signals;
A data link signal processing means for mapping the message generated by the message processing means to a data link signal, reproducing the message from the data link signal received from the counterpart station, and transmitting the message to the message processing means;
The data link signal generated by the data link signal processing means is transmitted to the partner station via the line transmission interface, and the data link signal is reproduced from the signal received from the partner station to the line reception interface, and the data link signal processing means Line interface processing means for transmitting,
The data link signal processing means includes message signal holding means for holding a message received from the message processing means,
Means for reading a message signal from the message signal holding means, mapping it to a data link frame, and transmitting it to the line interface processing means;
When transmitting the message to the line interface processing means, a signal length holding means for holding a total value of the data length of the message signal and the data link header length, and a cumulative length of the data length of the delivery confirmation waiting signal and the data link header length. A delivery confirmation waiting total signal length holding means for holding an arithmetic value;
When the data link signal received from the line interface processing means includes a delivery confirmation or a retransmission request, a value obtained by adding the data length and the data link header length of the message for which the delivery has been confirmed and the lost message is obtained. A means for reading from the length holding means and subtracting from the delivery confirmation waiting total signal length holding means, and transmitting a message if the value held by the delivery confirmation waiting total signal length holding means exceeds a preset threshold value An HDLC signal device characterized in that An HDLC signal transmission / reception program for executing the HDLC signal transmission / reception method according to claim 1 . A computer-readable recording medium storing the HDLC signal transmission / reception program according to claim 3 .

Images