JPH0644759B2 - Congestion control method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a congestion control method in a packet switching network.

(Prior art) In the packet switching method, individual communication is only set logically, and physical resources for transmission and switching are not secured for each communication channel, and information to be communicated is set. There is always the problem of congestion, where the amount temporarily exceeds the capacity of physical resources.

On the other hand, conventionally, flow control is performed by a protocol to prevent congestion. However, this method is difficult to apply to high-speed communication because the throughput is reduced because of the complicated control. Therefore, in high-speed packet communication, which is a new communication method that incorporates high speed and high quality due to recent advances in digital transmission technology and optical communication technology, the protocol in the network is simplified as much as possible, and in principle the edge of the network is
There is a trend toward high-speed protocol processing at to edge.
Receiving / not receiving in the network for the above congestion problem
(RR / RNR ... ・ Receive Ready / Receive Not Ready) is limited to simple control, and memory elements and transmission paths with large capacity are used to reduce congestion probabilistically.

(Problems to be Solved by the Invention) In the above-mentioned conventional technique, when the buffer memory for transmission waiting and exchange waiting becomes full and further reception becomes impossible, the buffer memory in the previous stage cannot receive. (RNR)
A signal is transmitted and the transmission of a new packet to the buffer memory is stopped. Then, this time, the buffer in the previous stage becomes full, and the state in which the reception disable signal is transmitted to the memory in the previous stage is likely to occur. Generally, for one buffer memory (or switching node), a plurality of buffer memories are connected via a bus type, a matrix type switch, etc., and when the above congestion occurs somewhere in the network, This means that it spreads over a wide area of the network in a chained manner, affecting communication that is irrelevant to the buffer memory where congestion first occurred. In high-speed packet switching, the policy is to reduce the probability of congestion significantly by designing the buffer memory capacity etc. with a considerable margin, and it is considered that the congestion resistance against normal traffic will be considerably high. If a failure occurs in a part of the network and the communication of traffic in that part is stopped, the above congestion state may sufficiently occur.

(Means for Solving Problems) The present invention is a congestion control method in a packet switching network, wherein when congestion occurs in a certain switching node in the network or a certain buffer memory in the switching node, the switching node Alternatively, the buffer memory expresses the unreceivable signal and the congestion stage number n (initial value = 1) in the preceding exchange node or buffer memory by using the control signal transfer means installed between the exchange node control devices or between the buffer memory control circuits. A signal is transmitted to temporarily stop the transmission from the switching node or the buffer memory in the preceding stage, and the switching node or the buffer memory in the preceding stage is If there is congestion, there is a switching node in the preceding stage or a switching node in the preceding stage of the buffer memory. Solves the above-mentioned problem by transmitting an unreceivable signal and the number of congestion stages n + 1 to the buffer memory using the control signal transfer means, and repeating the above operation until the number of congestion stages reaches a predetermined number N. It is a congestion control method.

(Function) In the present invention, the information indicating the number of congestion stages is added to the unreceivable signal and the buffer memory that is congested (or the exchange node, hereinafter simply referred to as buffer memory for simplicity) is sent to the buffer memory in the previous stage, and congestion occurs. When the number of stages reaches a predetermined constant value, even if the buffer memory is congested, the transmission of the unreceivable signal to the preceding stage is stopped to prevent the congestion state from propagating to a wide area.

(Examples) The present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the present invention. The present invention can be applied to the level of the buffer memories connected in multiple stages in the exchange as well as the level of the switching nodes connected in multiple stages in the network, but FIG. 1 shows the former case. An example of

In FIG. 1, switch matrices 12, 22, 32, 42 are connected in multiple stages by buffer memories 10, 11, 20, 21, ..., 40, 41. In this configuration, it is assumed that, for example, the traffic to a specific outgoing line of the switch matrix 12 temporarily increases, and as a result, the buffer memory 10 becomes full and falls into a congestion state. Control circuit of buffer memory 10 (first
(Not shown in the figure) transmits a reception disable signal to which the information of the number of congestion stages n = 1 is added to the buffer memories 20 and 21 coupled to the buffer memory 10 via the switch matrix 22. In reality, from the control circuit of the buffer memories 20 and 21 to the control circuit of the buffer memories 20 and 21, although not shown in the figure, reception is not possible via a dedicated control signal transfer line or control signal transfer switch. The signal is transmitted. As a result, the buffer memories 20 and 21 stop transmitting packets to the buffer memory 10. Then,
This time, the buffer memories 20 and 21 are easily congested. For example, if the buffer memory 20 is congested as shown in FIG. 1, the control circuit of the buffer memory 20 sends the reception disable signal to the buffer memories 30 and 31 in the previous stage, as in the case of the congestion of the buffer memory 10. . This transmission is also transmitted via the control signal transfer line or the control signal transfer switch similar to the above. However, the congestion stage number information n is increased by 1 to 2. Now, if the upper limit of the number of congestion stages: N = 2 is set, as a result of the above reception-not-ready signal reception, the buffer memory
Even if 31 falls into the congestion state, the reception not possible signal is not sent to the previous stage, and as a result, the buffer memory 40, 4
Packets sent from 1 to the buffer memory 31 will be discarded. After that, this state continues until the congestion state of each buffer memory is resolved.

(Effect of the Invention) As described above, according to the present invention, it is possible to prevent the congestion of a part of the network from propagating in a wide range. On the other hand, compared to the method of discarding incoming packets without sending unrecoverable packets when congestion occurs, it is possible to absorb peak traffic to a specific outgoing line by using several buffer memories connected in multiple stages, and normal traffic can be absorbed. The proof stress can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing an embodiment of the present invention. In FIG. 1, 12, 22, 32 and 42 are switch matrices, and 1
0,11,20,21,30,31,40,41 are buffer memories.

Claims (1)

[Claims] 1. A congestion control system in a packet switching network, wherein when congestion occurs in a certain switching node in the network or a certain buffer memory in the switching node, the switching node or the buffer memory is a switching node control device. Between the buffer nodes and the buffer memory control circuit, a reception signal and a signal indicating the congestion stage number n (initial value = 1) are transmitted to the switching node in the preceding stage or the buffer memory by using the control signal transfer means provided in the preceding switching node. Alternatively, the transmission from the buffer memory is temporarily stopped, and the switching node or the buffer memory at the preceding stage is the switching node at the preceding stage when the node itself or the buffer memory is congested while the transmission is stopped by the reception disable signal from the succeeding stage. Or for the exchange node or buffer memory in the previous stage of the buffer memory, Congestion Control serial control signal transfer means transmits the unreceivable signal congestion number n + 1 by using, characterized in that repeated until the number N that is determined in advance operation congestion stages above.