JP3425839B2 - Communications system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system, and more particularly to a communication system that performs communication protocol control for selectively retransmitting an abnormal information frame.

[0002]

2. Description of the Related Art There is known a communication system in which an information frame to which a transmission sequence number is added is received and a missing information frame is selectively retransmitted by referring to the information frame.

Conventionally, this communication system uses the ITU-T Recommendation Q.3 in order to avoid a so-called deadlock state in which the selective retransmission information frame cannot be received because the reception buffer is completely used up by the selective retransmission waiting information frame. Two
The reception buffer for the window size was prepared as recommended in 110.

Since the total number of the selective retransmission waiting information frames and the selective retransmission waiting information frames is the maximum window size, if a receiving buffer for the window size is prepared, even if there are selective retransmission waiting information frames, the selected retransmission waiting information frames are selected. Since the receiving buffer for the retransmission information frame is always secured, the deadlock state does not occur.

On the other hand, in Japanese Patent Laid-Open No. 1-22937, a buffer having an appropriate memory size is prepared for normal demand, a priority is given to a buffer use request, and a buffer use request with a lower priority is given. Discloses a multiprocessing method in which a device is added to allow only when the number of empty buffers is a certain value or more.

[0006]

However, the conventional communication system has a drawback in that the capacity of the receiving buffer increases. This is because it is necessary to secure a receive buffer for the window size for each link, and especially for link multiplexing, it is necessary to secure a receive buffer for the window size for the multiplex.

In order to improve the transmission efficiency, it is necessary to increase the window size, and in order to improve the usage efficiency of the device, it is necessary to increase the multiplicity. Therefore, the higher the efficiency, the larger the capacity of the reception buffer.

Secondly, there is a drawback that the memory usage efficiency is low. This is because the receiving buffer corresponding to the maximum load is always secured.

Data communication generally has a characteristic of frequent sporadic burst transfer. This means that frames are rarely received up to the window size limit and most of the time the receive buffer is empty. Further, in the case of multiplexing, it is rare to receive a frame up to the window size limit on all links at the same time, and most of the links usually have no receive frame and the receive buffer is empty.

Further, the invention disclosed in Japanese Patent Laid-Open No. 1-22937 has a drawback in that processing of information having low priority is delayed.

Therefore, an object of the present invention is to avoid deadlock with a reception buffer having a relatively small capacity.
Another object of the present invention is to provide a communication system that does not need to prioritize buffer use requests.

[0012]

In order to solve the above problems, the present invention receives an information frame to which a transmission sequence number is added and refers to the information frame to selectively retransmit a missing information frame. A communication system configured to receive the information frame,
Storage means for storing the information frame received by the receiving means; first comparing means for comparing the transmission sequence number of the information frame received by the receiving means with an expected transmission sequence number; and the storing means. A second comparing means for comparing the number of information frames already stored in the storage device with a constant value, and whether to send the information frame stored in the storing means to the host device based on the comparison result in the first comparing means. Control means for determining whether or not to discard whether or not the information frames that have become inconsistent in the first comparing means are discarded based on the comparison result in the second comparing means, When the number of information frames already stored in the storage means exceeds a certain value as a result of comparison by the second comparison means,
The feature is that all the mismatched information frames received after that are discarded.

[0013]

According to the present invention, when the number of mismatched information frames stored in the storage means exceeds a certain value, all mismatched information frames received thereafter are discarded.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a configuration diagram of an embodiment of a communication system according to the present invention.

The communication system comprises a communication procedure processing unit 1, an empty reception buffer chain 2, a reception buffer 4, a reception line control unit 5, and a selective retransmission waiting reception buffer group 7.

Further, the communication procedure processing unit 1 includes a sequence number judging unit 9, a receiving state variable 10, a selective retransmission waiting reception buffer managing unit 11, a selective retransmission waiting receiving buffer plane number counter 12, and an avoidance process start reception. Number of buffer side 13
, Comparison unit 14, sequence number determination unit 9 to comparison unit 1
4 and the control unit 15 for controlling 4.

The empty reception buffer chain 2 is a pool (store) portion of unused empty reception buffers 3a to 3c. In the figure, the head of the chain is empty reception buffer 3
a, the next is the empty reception buffer 3b, and the last is the empty reception buffer 3d.

The reception buffer 4 is a reception buffer acquired by the communication procedure processing unit 1 from the empty reception buffer chain 2 in order to store the information frame received from the partner station.

The reception line control section 5 is a section for transferring the information frame received from the partner station to the reception buffer 4.

The sequence number judging section 9 is a section for judging the normality of the transmission sequence number of the information frame transferred to the receiving buffer 4.

The reception state variable 10 is the transmission sequence number of the information frame expected to be received next, and is incremented by +1 every time the information frame having the expected transmission sequence number is received.
To be done.

The selective retransmission waiting reception buffer group 7 is a collection of reception buffers storing information frames having a transmission sequence number different from the reception state variable 10. The figure shows an example in which the selective retransmission waiting reception buffers 8a, 8b, 8c are held.

The selective retransmission waiting reception buffer management unit 11 is
This is a part for managing the selective retransmission waiting reception buffer group.

Selective retransmission waiting reception buffer side counter 1
Reference numeral 2 is a part for counting the number of faces of the reception buffer waiting for selective retransmission.

The avoidance processing start reception buffer plane number 13 is a portion in which the start trigger of the process for avoiding the deadlock is indicated by the number of selective retransmission waiting reception buffer planes.

The comparison unit 14 includes a selective retransmission waiting reception buffer plane number counter 12 and an avoidance processing start reception buffer plane number 13
This is the part to compare with.

The upper layer 6 is a part for performing a layer process higher than the device of the present invention. A reception buffer storing an information frame having a transmission sequence number that matches the reception state variable 10 is transferred to the upper layer 6. The upper layer 6 returns the reception buffer to the empty reception buffer chain 2 when the processing is completed.

Next, the operation of the communication system will be described with reference to the flowchart. FIG. 2 is a flowchart showing the operation of this communication system. It should be noted that this flowchart shows a process of processing one received frame. The control of the sequence number determination unit 9 to the comparison unit 14 of the communication procedure processing unit 1 is performed by the control unit 15.

First, when the control unit 15 receives the information frame reception notification from the reception line control unit 5, it acquires the reception buffer 4 from the empty reception buffer chain 2 (S2).
1). The reception line control unit 5 writes the data of the received information frame in the reception buffer 4 (S22).

Next, when the reception of the information frame is completed,
The sequence number determination unit 9 determines whether the transmission sequence number of the information frame received and the reception state variable 10 match (S23).

If the determinations match, the transmission sequence number of the received frame is normal, so the sequence number determination unit 9 notifies the upper layer 6 of the reception (S24),
The reception state variable 10 is incremented by 1 (S25).

Next, the selective retransmission waiting reception buffer management unit 1
1 checks whether or not the selected retransmission waiting reception buffer group 7 has a reception buffer storing an information frame having the same transmission sequence number as the reception state variable 10 (S26).

Then, when there is a reception buffer storing information frames having the same transmission sequence number, the selective retransmission waiting reception buffer management section 11 causes the reception state variable 1
The upper layer 6 is notified of the reception buffer storing the information frame having the same transmission sequence number as 0 (S2
7).

Since one reception buffer waiting for selective retransmission has been transferred to the upper layer 6, the selective retransmission waiting reception buffer number counter 12 is decremented by 1 (S28). Further, since the upper layer 6 is notified of the information frame having the same transmission sequence number as the reception state variable 10, the reception state variable 10 is incremented by 1 (S29).

After that, as long as there is a reception buffer storing an information frame having the same transmission sequence as the reception state variable 10 in the selective retransmission waiting reception buffer group 7, the processing from S26 to S29 is repeated.

On the other hand, in S23, when the transmission sequence number of the received frame and the reception state variable 10 do not match, the comparison unit 14 determines that the selection retransmission waiting reception buffer surface number counter 12 and the avoidance processing start reception buffer surface number 13 are Are compared (S30). As a result of the comparison, when the selected retransmission waiting reception buffer number counter 12 is smaller than the avoidance processing start receiving buffer number 13, the reception buffer number has a margin. (S31). Then, the selective retransmission waiting reception buffer surface number counter 12 is incremented by 1 (S32), and the process is terminated.

Further, in S30, when the selection retransmission waiting reception buffer plane number counter 12 is equal to or more than the avoidance processing start reception buffer plane number 13, there is no margin in the reception buffer plane number, and the reception buffer 4 is newly selected. Since it cannot be placed in the retransmission waiting reception buffer group 7, the information frame is discarded and the reception buffer 4 is returned to the empty reception buffer chain 2 (S33).

Next, the operation when the information frames are continuously received will be described. FIG. 3 is a schematic explanatory view showing an operation when information frames are continuously received.

In this example, the empty reception buffer has three faces (3
a to 3c), the reception state variable is initially set to “0”, there is no selective retransmission waiting reception buffer, and the avoidance processing start reception buffer number 13 is set to “2”. Of course, the number of these surfaces is not limited to this numerical value, and is arbitrary. However, the condition is that the avoidance processing start reception buffer number 13 is smaller than the total number of empty reception buffers.

First, it is assumed that an information frame having a transmission sequence number "0" has been sent from the partner station, but could not be received for some reason (S41). afterwards,
When an information frame having the transmission sequence number "1" arrives from the partner station (S42), the empty buffer chain 2
The reception buffer 3a is hunted (captured) and the received information frame is stored in the reception buffer 3a (S4).
3).

Next, when the transmission sequence number "1" of the received information frame is compared with the reception state variable "0", they do not match. Therefore, the reception buffer 3a storing the received information frame is selected as the retransmission waiting buffer. 8a (S44), and the selected retransmission waiting reception buffer plane number counter 12 is incremented by 1 (S45).

At this time, the selective resend request frame is sent to the other party so as to resend the information frame having the transmission sequence number "0".

Next, when the information frame having the transmission sequence number "2" arrives from the partner station (S46),
First, the information frame is transferred to the empty reception buffer chain 2
It is stored in the reception buffer 3b hunted from (S4
7). Then, as a result of comparing the transmission sequence number “2” of this information frame with the reception state variable 10 “0”, it is found that the information frame is in the state of waiting for selective retransmission because it does not match. Since the counter 12 is "1" and is smaller than the number "2" of the avoidance process start reception buffer number 13 (S48), it can be seen that the selective retransmission waiting may be performed. Therefore, the reception buffer storing the information frame of the transmission sequence number “2” is put into the reception buffer 8b of the reception buffer group 7 for selection retransmission waiting (S49), and the reception buffer number counter 1 for selection retransmission waiting 1
2 is incremented by 1 to be "2" (S50).

Further, when the information frame having the transmission sequence number "3" arrives from the partner station (S51),
First, the information frame is stored in the reception buffer 3c hunted from the empty reception buffer chain 2 (S52).
Then, this information frame is also the transmission sequence number "3"
And the reception state variable 10 "0" do not match, it can be seen that the information frame is waiting for selective retransmission. However, the selective retransmission waiting reception buffer number counter 12 is "2" and the avoidance processing start reception buffer number Since the number of frames is equal to "2" of 13 (S53), it is found that the selective retransmit waiting should not be performed, and the reception buffer 3c is returned to the empty reception buffer chain 2 (S54). That is, the transmission sequence number "3"
The information frame of is discarded.

At this time, if the receiving buffer is put into the selective retransmission waiting receiving buffer, the empty receiving buffer is exhausted, and the information frame of the selective retransmitted transmission sequence number "0" cannot be received, and the dead frame is dead. It will be locked.

After that, when the information frame having the transmission sequence number "0" is selectively retransmitted (S55), the information frame is first stored in the reception buffer 3c hunted from the empty reception buffer chain 2 (S56). .
Then, the transmission sequence number "0" of this information frame
And the reception state variable 10 “0” are compared and they match, so the upper layer 6 is notified of reception of the information frame (S5
7) The reception state variable 10 is incremented by 1 to "1" (not shown).

Then, since there is an information frame having a transmission sequence number "1" equal to the variable "1" of the reception state variable 10 in the selective retransmission waiting reception buffer group 7, this is notified to the upper layer 6 and selected. The retransmission waiting reception buffer number counter 12 is decremented by 1 to "1", and the reception state variable 10
Is incremented by 1 to “2” (not shown).

Then, since there is an information frame having a transmission sequence number "2" equal to the variable "2" of the reception state variable 10 in the selective retransmission waiting reception buffer group 7, this is notified to the upper layer 6 and selected. The retransmission waiting reception buffer surface number counter 12 is decremented to "0" by the reception state variable 10
Is incremented by 1 to "3" (S58).

Then, since there is no information frame having the transmission sequence number "3" equal to the variable "3" of the reception state variable 10 in the selective retransmission waiting reception buffer group 7, the processing is ended.

When the upper layer 6 finishes processing, the receiving buffers 3a to 3c are returned and are connected to the free buffer chain 2 (S59).

Regarding the information frames after the discarded transmission sequence number "3" information frame,
Reception can be performed by repeating the same operation as described above. In this case, the reception state variable 10 is set to "3".
Needless to say, set it on.

[0052]

According to the present invention, the mismatching information frames are stored in the storing means, and when the number of mismatching information frames exceeds a certain value, all the mismatching information frames received thereafter are discarded. With this configuration, it is possible to avoid deadlock with a storage unit having a relatively small capacity, and because it is not necessary to prioritize the information frames, the processing of information depends on the priority. Nor.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a communication system according to the present invention.

FIG. 2 is a flowchart showing an operation of the communication system.

FIG. 3 is a schematic explanatory diagram showing an operation when information frames are continuously received.

[Explanation of symbols]

1 Communication procedure processing unit 2 Free receive buffer chain 3a to 3c Free reception buffer 4 Receive buffer 5 Reception line control unit 7 Selective retransmit waiting reception buffer group 8a to 8c Selective retransmission waiting reception buffer 9 Sequence number judgment unit 10 Receive state variable 11 Selective Retransmission Waiting Reception Buffer Management Unit 12 Selective retransmission waiting reception buffer number counter 13 Avoidance processing start Number of receive buffers 14 Comparison section 15 Control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michiharu Mito 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nihon Telegraph and Telephone Corporation (56) Reference JP-A-7-250082 (JP, A) ( 58) Fields investigated (Int.Cl. ⁷ , DB name) H04L 29/08 H04L 12/58 H04L 1/16

Claims (4)

(57) [Claims] 1. A communication system for receiving an information frame to which a transmission sequence number is added and selectively retransmitting a missing information frame by referring to the information frame, wherein the information frame is received. Receiving means, storing means for storing the information frame received by the receiving means, and first comparing means for comparing the transmission sequence number of the information frame received by the receiving means with an expected transmission sequence number ,
Second comparison means for comparing the number of information frames already stored in the storage means with a constant value, and the information frame stored in the storage means to a host device based on the comparison result in the first comparison means. determining whether to deliver, and saw including a controller for determining whether to discard the information frames not matched by the second said first comparing means based on the comparison result of the comparing means , The control means is the result of the comparison by the second comparison means,
The number of information frames already stored in the storage means is below a certain value.
If it is above, the information frame of the mismatch received after that
A communication system characterized by discarding all games.
A communication system characterized by the above. 2. The communication system according to claim 1, wherein the control unit sends the information frame to a higher-level device when the comparison result of the first comparison unit is a match. Wherein said control means after transmitting the information frame to the higher-level device, a communication system according to claim 1, wherein clearing the contents of said storing means. 4. A communication system according to any one of claims 1-3, characterized in that said predetermined value is a numerical value obtained by subtracting 1 from the number of information frames may be stored in at least said storage means.