JPH0779253A - Packet switchboard - Google Patents

Abstract

PURPOSE:To improve the effective through-put of an entire packet switching network by operating the priority control of a packet corresponding to a transmission origin based on a packet reaching ratio and transmission delay. CONSTITUTION:The packet reaching an input link 181-i of a switchboard is inputted through an arrival ration and transmission delay measuring means 15, packet control means 16, and input buffer 12 to a switch 11, and switching- outputted to an output buffer 13. The means 15 measures the packet arrival ratio per unit time for each transmission origin, measures the packet transmission delay between the transmission origin and the switchboard by using a prescribed protocol, and transmits it to the means 16. A congestion detecting means 14 detects a congested state, and transmits a congestion detection signal to the means 16 and a congestion informing means 17. The means 16 decides a priority at the time of the occurrence of the congestion for each transmission origin. The means 17 receives the congestion detection signal, generates a control packet for congestion information, and transmits it to the transmission origin of passing packet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packet switch for controlling a packet from a transmission source at the time of congestion.

[0002]

2. Description of the Related Art Generally, a packet switch has a buffer for accumulating packets, and even if the number of packets temporarily exceeds the transmission capacity of the output line of the switch,
Can be absorbed in the buffer. However, when the number of packets that exceeds the transmission capacity of the output line of the exchange arrives continuously, the buffer cannot absorb the packets. This is called a congestion state.

Therefore, when the packet switch is in a congestion state, the packet is discarded, or the source of the packet is notified of the congestion, and the source which receives the congestion notification suppresses the packet transmission. It is necessary to eliminate the congestion state promptly by performing control such as.

Conventionally, when a packet is discarded in order to eliminate the congestion state of the exchange, the arriving packet is discarded for a certain period, or in order to maintain fairness, it is transmitted from a source having a large arrival rate. The control method is to preferentially discard the received packets.

Further, between the packet transmission source and the packet transmission destination, window flow control based on the number of packet delivery confirmations and rate flow control based on the packet transmission interval,
The amount of packet transmission at the time of congestion is suppressed by combining it with the congestion notification transmitted from the exchange.

Here, the connection area extends over a wide area, and
In a packet switching network that provides a very high communication speed, the packet propagation delay time between the switching devices is relatively large with respect to the packet processing time in the packet switching device. For this reason, the packet transmission delay time, which is the time required for a packet to reach the exchange after leaving the transmission source, also becomes relatively large.

When conventional congestion control is performed in such a situation, if a packet from a source having a large transmission delay and a large packet arrival rate is discarded, the packet is already transmitted by the time the source recognizes the congestion. The number of packets that have been made increases, and as a result, throughput may decrease due to an increase in the number of retransmitted packets, and the time required to recover from congestion may increase. In fact, it is known in the literature International Conference on Communications91 that packets with large transmission delays are processed preferentially in a switch.
(ICC '91), pp. 1666-1670.

However, the number of retransmitted packets for a packet generated by a transmission source having a low arrival rate even if the transmission delay is large does not increase so much even if it is discarded. On the other hand, when the transmission delays are the same, if the packets generated by the transmission source with a high arrival rate are discarded, the number of retransmitted packets is increased as compared with the case where the packets with a transmission source with a low arrival rate are discarded, and the throughput is lowered. As described above, there is a problem that the priority control based only on the transmission delay is insufficient.

[0009]

As described above, in the conventional packet switch, the priority control of the packet is performed only on the basis of the packet arrival rate in order to solve the congestion state. There is a drawback that the number increases and the throughput decreases.

An object of the present invention is to provide a packet switch that improves throughput by performing priority control of packets based on the packet arrival rate and the transmission delay in response to the source in order to solve the congestion state. .

[0011]

The present invention provides an input / output buffer for accumulating transmitted packets, measuring means for measuring a packet arrival rate and a transmission delay from a packet source, and the input / output buffer. Congestion detection means for detecting the congestion state of the, determining the priority to the source correspondence using the packet arrival rate and transmission delay measured by the measuring means when the congestion state is detected by this congestion detection means, A packet restriction means for restricting input of packets according to the priority, and a congestion notification means for notifying the sender of the congestion when a congestion state is detected by the congestion detection means. Is.

[0012]

As a result, according to the present invention, when congestion occurs in the exchange, it becomes possible to preferentially process packets from a transmission source having a large transmission delay and a large packet arrival rate. Since it is possible to avoid the decrease in throughput due to the increase in the number of retransmitted packets due to the discarding of packets from the source and reduce the time required to recover from congestion, it is possible to improve the effective throughput of the entire packet switching network. Can be expected.

Further, a packet from a source having a large packet arrival rate and a small transmission delay, or conversely, a packet from a source having a large transmission delay and a small packet arrival rate, is discarded by the transmission source. Since the number of already transmitted packets does not increase from the time of recognition until the packet is retransmitted, non-priority processing of such a packet does not increase the number of retransmitted packets. The overall effective throughput can be improved.

Further, since it is expected that the recovery from the congestion state will be faster than that of the conventional control method, by using this control method, the influence on the communication quality of the non-priority processed transmission source is small. Can be suppressed.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic structure of an m-input n-output packet switch using the present invention. In FIG. 1, 11
Is a switch, 12 is an input buffer, 13 is an output buffer, 14 is a congestion detecting means, 15 is an arrival rate / transmission delay measuring means, 16 is a packet regulating means, 17 is a congestion notifying means,
, 181-m are input links of the exchange, 182-1, 182-2, ..., 182-n are output links of the exchange, and 191 is between the input buffer 12 and the congestion detection means 14. A control line, 192 is a control line between the output buffer 13 and the congestion detecting means 14, and 193 is the congestion detecting means 1.
4 is a control line between the packet regulation means 16 and 194 is a control line between the congestion detection means 14 and the congestion notification means 17 and 195 is a control line between the arrival rate / transmission delay measurement means 15 and the packet regulation means 16.

Here, the packet is the input link 1 of the exchange.
81-1, 181-2, ..., 181-m arrive at the exchange. Switch input link 181-i (1 < i < m)
Packets arriving at the arrival rate / transmission delay measuring means 15,
It is input to the switch 11 through the packet restriction means 16 and the input buffer 12, and is switched and output to the output buffer 13 by the switch 11.

Further, the packets exchange-outputted to the output buffer 13 pass through the congestion notifying means 17 and are output from the exchange through the output link 182-j of the exchange. The arrival rate / transmission delay measuring means 15 measures the packet arrival rate per unit time for each transmission source of passing packets. Also, the packet transmission delay between the transmission source and the exchange is measured using a predetermined protocol. Further, the measured packet arrival rate and packet transmission delay value for each transmission source are output to the packet regulation unit 6 using the control line 195.

Input buffer 12 and output buffer 1
3 temporarily stores packets in order to absorb the difference between the arrival rate of packets to the exchange and the output rate from the exchange, and uses control lines 191 and 192, respectively.
The number of buffers currently used for each input or output link of the exchange is output to the congestion detecting means 14.

The congestion detecting means 14 uses control lines 191, 192.
The number of buffers input from the control line 19 is monitored, and when the number of buffer use of the input or output link in the congestion state exceeds a certain value, it is considered that the congestion state has been entered, and the control line 19
3, 194 is used to output a congestion detection signal to the packet restricting means 16 and the congestion notifying means 17, respectively. Also, when the number of buffers input from the control lines 191 and 192 falls below a certain value, it is considered that the input or output link in the congestion state has entered the non-congestion state, and the control line 193 is used to perform packet restriction. The non-congestion detection signal is output to the means 16.

The packet regulation means 16 determines the priority at the time of congestion occurrence for each transmission source using the packet arrival rate and the packet transmission delay value for each transmission source input from the arrival rate / transmission delay measurement means 15. To do. Furthermore, the congestion detection means 1
When the congestion detection signal is received from 4, the arrival packet from the transmission source with a low priority is preferentially discarded based on the determined priority. When a non-congestion detection signal is received from the congestion detection means 14, the priority process that was performed in the congestion state is stopped and the normal process is performed.

When the congestion notifying means 17 receives the congestion detection signal from the congestion detecting means 14, the congestion notifying means 17 generates a congestion notifying control packet and transmits it to the source of the passing packet. Next, FIG. 2 shows an example of a packet switching network according to the present invention. In FIG. 2, reference numerals 21, 22, 23 denote terminals, 24,
25 and 26 are packet switches according to the present invention, 27 is a bidirectional physical link, and 28 is a packet transmitted in the network. The terminals 21, 22, 23 share the output link of the exchange 26. It is assumed that the terminal 21 has a low packet arrival rate and a large packet transmission delay up to the exchange 26. Terminal 22
It is assumed that the packet arrival rate and the packet transmission delay up to the exchange 26 are large. The terminal 23 has a high packet arrival rate and a small packet transmission delay to the exchange 26. If the exchange 26 becomes congested in this situation, the exchange 26 assigns a priority among the terminals 21, 22, and 23 based on the measured packet arrival rate and packet propagation delay values, and based on the priority. Congestion is notified to the terminals 21, 22, and 23 at the same time that the packet input is regulated.

FIG. 3 shows an example of the priority determination method. Figure 3
(A) is basically transmission delay priority, and when the transmission delay is the same, the one with the higher arrival rate is preferentially inserted.
3B shows the case where the transmission delay is completely prioritized regardless of the arrival rate, and FIG. 3C shows the arrival rate is basically prioritized. When the arrival rates are the same, the larger transmission delay is preferentially inserted. FIG. 3D is a priority determination table when the arrival rate is completely prioritized regardless of the transmission delay. The highest priority is 1,
It is set to 2, 3, and 4.

Next, FIG. 4 shows a sequence diagram as an embodiment of the means for measuring the transmission delay when the transmission side terminal issues a request. In FIG. 4, 41 is a transmission delay measurement request packet, 42 is a transmission delay measurement response packet, 43,
44 and 45 are transmission delay measurement end packets, 46 is a transmission delay measurement packet response time from the sender terminal to the exchange 1, 47 is a transmission delay measurement packet response time from the sender terminal to the exchange 2, and 48 is a sender terminal. Indicates the packet delay time of the transmission delay measurement packet to the receiving side terminal. The values of the transmission delay measurement packet response times 46, 47, and 48 are included in the transmission delay measurement end packets 43, 44, and 45, respectively.

Next, FIG. 5 shows a sequence diagram as an embodiment of means for measuring the transmission delay when the exchange issues a request. In FIG. 5, 51 is a transmission delay measurement request packet, 52 is a transmission delay measurement response packet, and 53 is a transmission delay measurement packet response time from the exchange to the transmission side terminal. The value of 53 is the transmission delay time from the exchange to the terminal on the transmitting side.

Next, the arrival rate / transmission delay measuring means 1 is shown in FIG.
5 shows a configuration diagram of No. 5. In FIG. 6, 181-1 and 181
-2, ..., 181-m is an input link, 183-1, 18
3-2, ..., 183-m are arrival rate / transmission delay measuring means 1
5 and the packet restriction means 16 links 61-1, 61
-2, ..., 61-m is port-specific measuring means, 62 is packet latching means, 63 is packet selecting means, 64 is arrival rate measuring means, 65 is transmission delay measuring means, 66 is transmission delay measuring response creating means, 67 Is packet insertion means, 68, 6
Reference numerals 9, 610 and 611 represent internal data lines.

The packet latch means 62 takes out a copy of the packet arriving from the input link and takes out the internal data line 6
8 to send to the packet selection means 63. If the packet received from the packet latch means 62 is the transmission delay measurement request packet, the packet selecting means 63 uses this packet to transmit the transmission delay measurement response creating means 6 using the internal data line 611.
6, the packet is a transmission delay measurement completion packet addressed to the next node, the packet is sent to the transmission delay measuring means 65 using the internal data line 610, and the packets other than the control packet arrive using the internal data line 69. Rate measuring means 6
Send to 4.

The arrival rate measuring means 64 counts the number of arriving packets per fixed time from the packet received from the packet selecting means 63 for each source address, and sets 195 as a set of the value of the source address and the number of arriving packets. It is used to output to the packet restriction means.

The transmission delay measuring means 65 uses 195 as a set of the transmission source address of the transmission delay measurement completion packet received from the packet selecting means 63 and the value of the transmission delay written in the data part of the packet. Output to.

Upon receiving the transmission delay measurement request packet received from the packet selection means 63, the transmission delay measurement response means 66 indicates that the destination address is the transmission source address of the transmission delay measurement request packet and the transmission source address is the address of the next node. A certain transmission delay measurement response packet is generated and sent to the packet inserting means 67 using the internal data line 612.

Upon receiving the transmission delay measurement response packet from the transmission delay measurement response creating means 66, the packet inserting means 67 preferentially receives the transmission delay measurement response packet from the links 183-1 and 183-.
2, ..., 183-m.

Finally, FIG. 7 shows a schematic configuration of an m-input n-output packet switch having means for notifying congestion release according to the present invention. In FIG. 7, 71 is a congestion notification / congestion release notification means, 72 is a congestion detection means, and 73 is a control line between the congestion detection means 72 and the congestion notification / congestion release notification means 71.

The congestion detecting means 72 uses the control lines 191, 192.
The number of used buffers is monitored, and when the number of used buffers on the input or output links in a congested state falls below a certain value, it is considered that a non-congested state has been entered, and control line 1
A non-congestion detection signal is output to each of the packet restriction unit 16 and the congestion notification / congestion release notification unit 71 by using the control line 93 and the control line 73.

When receiving the non-congestion detection signal from the congestion detecting means 72, the congestion notifying / congestion releasing notifying means 71 generates a congestion releasing notifying control packet and transmits it to the transmission source of the passing packet.

[0034]

According to the present invention, when the packet switch is congested, the buffer control is performed in consideration of the packet arrival rate and the transmission delay, so that the decrease in the network throughput can be minimized. In addition, by combining with flow control, it becomes possible to reduce the time required for recovery from congestion to be small.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an m × n packet switch which is an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a packet switching network using an embodiment of the present invention.

FIG. 3 is a diagram showing a plurality of examples of a priority determination method based on a packet arrival rate and a packet transmission delay in the present invention.

FIG. 4 is a diagram showing a procedure for measuring a transmission delay caused by a request generated by a transmitting terminal according to the present invention.

FIG. 5 is a diagram showing a procedure for measuring a transmission delay caused by a request generated by the exchange according to the present invention.

FIG. 6 is a schematic diagram showing an embodiment of arrival rate / transmission delay measuring means in the present invention.

FIG. 7 is a diagram showing a schematic configuration of an m × n packet switch having means for notifying congestion release, which is one of the embodiments of the present invention.

[Explanation of symbols]

11 ... Switch 12 ... Input buffer 13 ... Output buffer 14 ... Congestion detecting means 15 ... Arrival rate / transmission delay measuring means 16 ... Packet restricting means 17 ... Congestion notifying means 181-1, 181-2, 181-m ... Switch input Link 182-1, 182-2, 182-n ... Output link of exchange 191, 192, 193, 194, 195 ... Control line

Claims (4)

[Claims] 1. An input / output buffer for accumulating transmitted packets, measuring means for measuring a packet arrival rate and a transmission delay from a packet source, and congestion detection for detecting a congestion state of the input / output buffer. And a packet input regulation according to the priority by means for determining the priority corresponding to the sender by using the packet arrival rate and the transmission delay measured by the measuring means when the congestion state is detected by the congestion detecting means. A packet switching device comprising: a packet restriction unit that performs the above; and a congestion notification unit that notifies the transmission source of congestion when a congestion state is detected by the congestion detection unit. 2. The packet restriction means increases the priority of a packet from a transmission source having a packet arrival rate of a first predetermined value or more and a transmission delay of a second predetermined value or more. The packet switch according to claim 1. 3. The transmission source transmits a transmission delay measurement request packet to the packet switch and stores the transmission time, and when the packet exchange receives the transmission delay measurement request packet, the transmission delay measurement response packet is sent to the transmission source. When the transmission source receives the transmission delay measurement response packet, the transmission source calculates the transmission delay value from the reception time and the transmission time, puts it in the transmission delay measurement end packet, and transmits the packet to the packet switch. 2. The packet switch according to claim 1, wherein the value of the transmitted transmission delay is held in association with the source address. 4. The packet switch transmits a transmission delay measurement request packet to the transmission source and stores the transmission time, and when the transmission source receives the transmission delay measurement request packet, the transmission delay measurement response packet is sent to the packet switch. 2. When the packet switch receives the transmission delay measurement response packet, the measuring means calculates and holds the transmission delay from the reception time and the transmission time.
Packet switch described.