JP3394478B2 - Congestion avoidance apparatus and method using RED - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a congestion avoidance apparatus and method by RED, and more particularly, in a network based on the IP over ATM method to which AAL5 is applied.
The present invention relates to a congestion avoidance apparatus and method by RED in which the processing amount is reduced by improving a method for realizing congestion avoidance by RED.

[0002]

2. Description of the Related Art At present, the transmission of information by computer communication is the mainstream regardless of individual level or company level.

However, in computer communication, the traffic from each terminal has a strong burst property, and
There is a problem that it is difficult to estimate this traffic pattern in advance.

Therefore, congestion occurs in each relay switching node on the network, and the communication speed of the entire network is delayed.

Therefore, in order to efficiently avoid the above-mentioned harmful effects in the ATM network, the conventional CBR service,
Best effort to efficiently transmit information by controlling according to the congestion degree in the network by a method that does not pre-allocate a band such as UBR service and ABR service instead of a method that pre-allocates a band like VBR service The agenda regarding services is being discussed at ATM forums and the like.

Among these, particularly in the UBR service, the ATM layer does not perform any quality assurance in communication, and the congestion avoidance is performed by the function of an upper layer, for example, the window flow control in the case of TCP as an alternative means. Therefore, there is an advantage that computer communication can be performed at a low charge, and future development is greatly desired.

However, in the above UBR service,
Compared with the case where the packet switch having the same buffer size is used, there arises a problem that the packet throughput is deteriorated as compared with other services.

[0008] The main reason for this is that in ATM communication, discarding occurs not on a packet basis but on a cell basis in order to eliminate a congestion state. That is,
Since the receiving side controls the discarding after the packet containing the discarded cells (hereinafter referred to as incomplete packet) arrives, the transmitting side needs retransmission control, so the cells forming the incomplete packet are transmitted. This is because the capacity of the road is wasted.

In addition, in the ATM system, when cell discard is generally performed, since discarded cells are distributed in different packets, there is a problem that a large number of incomplete packets are generated.

As a method for solving the above problems,
In a relay switching node of an internet protocol (hereinafter referred to as IP), a packet is randomly selected from a passing packet at the time when a symptom of congestion starts to appear and discarded, or a congestion notification in a packet header is sent. There is congestion avoidance by the Random Early Detection (RED) method, which is a method of notifying the application or transport protocol of some hosts of the occurrence of congestion by setting a bit and inducing a reduction in the amount of transmission from that host. .

Congestion avoidance by this RED is described in "Random by Sally Floyd, Van Jacobson" in the prior art document 1.
Early Detection Gateways for Congestion Avoidanc
e ”, (IEEE / ACM Transaction on Networking, Vol.1 No.
4 August, 1993.).

Further, in the above-mentioned prior art document 1, as a method for determining a packet to be discarded, a method for identifying a packet to be discarded by randomly determining an interval between a packet to be discarded and a packet to be subsequently discarded. Is further disclosed.

Congestion avoidance by RED disclosed in the above-mentioned prior art document 1 will be explained here. First, in AAL5, since the packet is recognized at the cell level, the last cell constituting the packet, that is, End Of Packet (EOP). EOP is distinguished from other cells by setting the AUU parameter of the cell (which is the same as the last cell) to 1 and the AUU parameters of the other cells to 0.

Therefore, in AAL5, one ATM virtual circuit (hereinafter, V
Paying attention to (C), the cells from the cell next to the received EOP cell to the EOP cell first received next can be regarded as cells forming the same packet.

However, the congestion avoidance by RED based on the technique of recognizing a packet at the cell level by using the EOP cell as described above is performed by the EOP of the packet.
When a cell is discarded, even if all cells forming the next packet reach the receiving side, it is impossible to distinguish from the immediately preceding packet, and therefore error detection by CRC code or the like occurs, There arises a problem that all the received packets (complete packets) are discarded.

In addition to the above-mentioned Prior Art 1, the packet discarding method by the IP over ATM method using AAL5 is described in Prior Art 2 by Masayoshi Nabeshima, "End Of Pac".
Study on selective cell discarding method for preventing ket cell discard "(SSE98-88, IN96-72, CS96-96).

As the packet discarding method disclosed in this prior art document 2, there are an Early Packet Discard (EPD) method, a method used in Partial Packet Discard (PPD), and an improved EPD method.

In the IP over ATM system on AAL5, one IP packet is divided into a plurality of ATM data cells and transferred. Therefore, in AAL5, A
A bit indicating the end (hereinafter referred to as the last bit) is defined in the TM cell header part.

Therefore, the congestion avoidance by the EPD method is a method for eliminating the congestion state by discarding the packets that cannot be processed when the congestion occurs in the relay switching node.

In the method used in PPD, when the leading cell arrives at the relay switching node, the relay switching node is in a congestion state, that is, the queue length stored in the buffer of the relay switching node is set in advance. If the set threshold is exceeded, the head cell and the cells that form the same packet from the cell are forcibly discarded, and
If it is not in a congestion state, it receives from the first cell to the last cell forming the same packet and inputs it to its own buffer. Furthermore, in the process of entering cells in the buffer,
When there is no free space in the buffer, the congestion state is alleviated by forcibly discarding cells other than the last cell that compose the same packet that arrived from that point.

In other words, in the method used in PPD, regardless of whether the head cell of the divided packet is limited or not, the cells from the time when it is determined that they need to be discarded to the cell immediately before the last cell are forcibly discarded. Was being processed.

Further, in this improved EPD method, when discarding a packet, attention is paid to one VC, and the discarding of a cell from the cell next to the cell in which the last bit is ON (hereinafter referred to as the head cell) is started. The cells up to the next last bit (hereinafter referred to as the last cell) are discarded.

Further, in this improved EPD method, two types of improved methods are proposed in which the final cell is identified and the final cell is not discarded.

First, in the first improved method of EPD, if the immediately preceding cell is not the last cell when the leading cell forming the packet arrives at the relay switching node, regardless of whether it is in a congestion state, Forcibly discards all cells up to the next last cell. Also, when the immediately preceding cell is the final cell when the leading cell forming the packet arrives at the relay switching node and is in a congestion state, all cells up to the immediately preceding cell of the next final cell are forcibly discarded. If the immediately preceding cell is the final cell when the head cell forming the packet arrives at the relay switching node and is not in a congested state, all the cells up to the next final cell are input to its own buffer. Furthermore, in the process of inputting cells to the buffer, when there is no free space in the buffer, cells other than the final cell are forcibly discarded among cells constituting the same packet that arrived from that point.

Further, in the second improved method of EPD, by providing two kinds of thresholds for detecting the congestion state, a high threshold and a low threshold, the free capacity of the buffer is insufficient in the process of inputting cells to the buffer. The method of preventing the discarding of the cell by is taken.

[0026]

[Problems to be Solved by the Invention] However, RED
If the above is realized by using the packet discarding function according to the EPD method or the PPD method described above, the following problems occur.

The first problem is the EPD method or PP.
In the D method, one packet that is disassembled and transferred is AT
Since a method of discarding the entire packet by discarding in units of M cells (hereinafter referred to as a packet level discard method) is adopted, all the ATM cells created by disassembling one packet by monitoring a specific VC It becomes necessary to identify and dispose of them, increasing the amount of processing.

The reason is that in order to realize the packet level discarding method, the last cell is detected, and all the cells constituting one packet up to the next final cell are discarded. This is because it is necessary to execute different processing of.

Further, although the first and second EPD improvements have been improved so as not to discard the final cell,
The process of discarding packets in VC units remains, which causes a problem that the processing amount increases.

The reason for this is that RED targets the entire aggregate of multiple connections.
Is applied to IP over ATM, processing for the VC of the entire flow that determines the packet to be discarded next and packet-level discard processing for the specific VC to which the packet to be discarded is sent are processed. This is because it is necessary to combine them.

Further, the congestion avoidance by the EPD and PPD methods is means for accelerating the recovery of the congestion state when the congestion is detected at the relay switching node. On the other hand, in the congestion avoidance by RED, by utilizing the characteristics of TCP, packets are always discarded with a small probability, and the TCP transmission amount (transmission rate)
Is not to grow.

Therefore, the above EPD and PPD methods and R
Since ED has a different purpose, configuration, and means, RED has an EP
When applied to the D and PPD methods, there arises a problem that the processing amount increases.

Therefore, the present invention has been made in view of the above problems, and by randomly discarding cells other than the last cell, it is possible to discard packets with a small amount of processing, thereby suppressing / controlling congestion. It is an object of the present invention to provide a congestion avoidance device and a method thereof by RED.

[0034]

In order to achieve the above object, the invention according to claim 1 uses AAL5 as a protocol.
RED (Random Early in a network using
A congestion avoidance apparatus according Detection), a cell other than the last cell is specified based on cell interval calculated by a predetermined probability, have cell discarding means for discarding the cell specified, the predetermined probability, Average of one packet split
Dropped packets depending on the number of cells and congestion level
The cell spacing is calculated based on the
Find the value of 1 divided by the power of 2
Based on the value, the value is equal to 0 to twice the power of 2
Create a pseudo-random number for the rate, identify based on the pseudo-random number, and
The final cell is the cell specified by the cell spacing.
If not, it is characterized by discarding the identified cells
It

The invention according to claim 2 is a RED in a network to which AAL5 is applied as a protocol.
A congestion avoidance device according to the above, wherein buffering means for temporarily holding cells received from the line, queue length monitoring means for calculating the queue length of cells held by the buffering means, and queue calculated by the queue length monitoring means Based on the length, congestion state determination means to determine the occurrence of congestion state, and if the occurrence of congestion state is determined by the congestion state determination means, the final cell determination to determine whether the arrived cell is the final cell If the arriving cell is determined not to be the final cell by the means and the final cell determining means, the cell is identified based on the cell interval calculated with a predetermined probability, and the cell is identified .
The cell has a cell discarding means for discarding the cell, and the predetermined probability is
Average number of cells into which one packet is divided and congestion state
It is calculated based on the packet discard rate corresponding to the level of
The cell spacing can be approximated by a certain probability 2
The power of 1 is calculated, and the power of 2 is used to calculate the value from 0.
Generate pseudo-random numbers with equal probability in the range up to twice the power of 2.
Generated and specified based on pseudo-random numbers.
If the cell identified by the interval is not the last cell, then
It is characterized in that the discarded cells are discarded.

According to the invention described in claim 3, in the congestion avoidance apparatus by RED according to claim 2, the queue length monitoring means detects the queue length in the buffering means at every predetermined time interval, The queue length of the cell held by the buffering means is calculated by calculating the average queue length including the latest queue length based on the detected queue length.

Further, according to the invention described in claim 4, in the congestion avoidance apparatus by RED according to claim 2 or 3, a cell has a header portion forming a cell and a cell among the cells forming the same packet. , A final cell indicating whether or not the cell is the final cell, and the final cell determining means determines whether or not the cell is the final cell based on the final bit included in the header portion of the cell. And

Further, according to the invention of claim 5, the congestion avoidance apparatus by RED according to any one of claims 2 to 4 further comprises queue length storage means for storing a predetermined queue length as a threshold value. The congestion state determination means is characterized by determining the occurrence of congestion by comparing the queue length calculated by the queue length monitoring means with a predetermined queue length stored in the queue length storage means.

According to the invention described in claim 6, in the congestion avoidance apparatus by RED according to any one of claims 2 to 4, a plurality of predetermined queue lengths as threshold values are stored with different values, and a plurality of queue lengths are stored. The queue length congestion level storage means further stores the level of the congestion state corresponding to a predetermined queue length, the congestion determination means, the queue length calculated by the queue length monitoring means, and the queue length congestion level storage means Each of the plurality of stored predetermined queue lengths is compared, and as a result of the comparison, the predetermined queue length, which is the largest value among the predetermined queue lengths exceeding the queue length calculated by the queue length monitoring means, is corresponded to. It is characterized in that the congestion level to be specified is specified and the occurrence of congestion is judged in stages.

Further, according to the invention of claim 7, wherein
In the congestion avoidance apparatus by RED described in any one of Items 1 to 6 , the network to which AAL5 is applied as a protocol is a network adopting an IP over ATM method.

According to the invention described in claim 8 , there is provided a congestion avoidance method by RED in a network to which AAL5 is applied as a protocol, in which cells other than the last cell are calculated based on a cell interval calculated by a predetermined probability. identified, has a cell discard process of discarding the cell specified, where
The constant probability is the average number of cells into which one packet is divided.
And the packet drop rate corresponding to the congestion level.
Calculated based on the above, the cell spacing should be similar to the specified probability.
The value of the power of 2 is calculated based on the value of the power of 2
In the range of 0 to twice the power of 2
Create similar random numbers, specify based on pseudo-random numbers, and discard cells
Is the cell specified by the cell spacing if it is not the final cell.
In this case, the specified cell is discarded.

Further, according to the invention described in claim 9 , there is provided a method for avoiding congestion by RED in a network to which AAL5 is applied as a protocol, which comprises a buffering step for temporarily holding cells received from a line and a buffering step. Queue length monitoring step to calculate the queue length of the held cell, based on the queue length calculated in the queue length monitoring step, congestion state determination step to determine the occurrence of congestion state, congestion state determination step congestion state If it is determined that the arriving cell is the final cell, the final cell determining step of determining whether or not the arriving cell is the final cell, and if the arriving cell is determined not to be the final cell in the final cell determining step, a predetermined probability identified on the basis of the calculated cell intervals by, and a cell discard process of discarding the cell specified, the predetermined probability, The average of the One packet is divided
Dropped packets depending on the number of cells and congestion level
The cell spacing is calculated based on the
Find the value of 1 divided by the power of 2
Based on the value, the value is equal to 0 to twice the power of 2
Create a pseudo-random number for the rate, identify based on the pseudo-random number, and
In the discarding process, the cell specified by the cell interval is the final cell.
If not, it is characterized by discarding the identified cells
It

According to the invention of claim 10 , the contract
In the congestion avoidance method by RED according to claim 9 , the queue length monitoring step includes buffering at predetermined time intervals.
Detects the queue length in the process, based on the queue length is detected, by calculating the queue length average including the latest queue length, and calculating a queue length of a cell buffering process holds .

According to the invention of claim 11 , the contract
In the congestion avoidance method by RED described in claim 9 or 10 , the cell has a final bit in a header part that constitutes the cell, which indicates whether or not the cell is the last cell among the cells constituting the same packet. The final cell determination step is characterized by determining whether or not the cell is the final cell based on the final bit included in the header portion of the cell.

According to the invention of claim 12 , the contract
In the congestion avoidance method by RED according to any one of claim 9 to 11 , further comprising a queue length storage step of storing a predetermined queue length as a threshold, the congestion state determination step,
It is characterized in that the occurrence of congestion is determined by comparing the queue length calculated in the queue length monitoring step with a predetermined queue length stored in the queue length storage step.

According to the invention of claim 13 , the contract
In the congestion avoidance method by RED described in any one of claim 9 to 11 , the congestion determination step is stored such that the queue length calculated in the queue length monitoring step and a plurality of congestion state levels correspond to each other. A plurality of queue lengths are compared with each other, and as a result of the comparison, the predetermined queue length, which is the largest value among the predetermined queue lengths exceeded by the queue length calculated by the queue length monitoring step , is determined. The feature is that the corresponding congestion level is specified and the occurrence of congestion is determined stepwise.

According to the invention of claim 14 , the contract
In the congestion avoidance method by RED described in any one of claims 8 to 13 , a network to which AAL5 is applied as a protocol is a network adopting an IP over ATM method.

[0048]

BEST MODE FOR CARRYING OUT THE INVENTION A RED congestion control apparatus and method according to the present invention will be described in detail below with reference to the drawings.

(Overview of RED) Here, the RED in the embodiment of the present invention uses the IP over ATM method and uses TCP as its upper protocol.
Is assumed.

Since this TCP performs end-to-end flow control, the transmission window size is controlled to gradually increase until it reaches the reception window size (upper limit value) on the reception side. Therefore, when TCP reduces the transmission window size to reduce the transmission amount, it is limited to when the packet discard is detected.

Therefore, the relay switching node monitors the time average value of the queue length, and when the time average value becomes large to some extent, the packet is discarded with a small probability. This is based on the EPD method and PPD described in the above-mentioned related art.
The method is fundamentally different in purpose, structure, and means.

Further, in TCP, the transmission window size is increased to the detection of packet discard, so packet discard is a prerequisite. Therefore, using the packet discard by TCP for the purpose of avoiding congestion in the network does not cause any trouble.

In RED, packets to be discarded are randomly selected in order to equalize the used bandwidth. Therefore, in each TCP connection, the number of discarded packets increases in proportion to the used bandwidth.

Further, in RED, packets are randomly discarded, and as a result, the intervals of packets to be discarded are randomly selected.

(Outline of IP over ATM) Further, in the congestion control apparatus and method by RED according to the present invention, the communication mode is the IP over ATM method. The IP over ATM system has AAL5 as a protocol that is intended for computer communication. The purpose of this is to easily realize ATM communication by omitting advanced additional functions such as ATM cell loss compensation and delay fluctuation compensation as much as possible.

Here, the feature of AAL5 is that packets are assembled on the transmission side / reception side (end / end) in communication, and therefore, at the end node, among a plurality of cells forming one packet, That is, the final cell and cells other than the final cell can be easily determined.

Further, in the relay exchange node (relay ATM node) in ATM communication, the ATM flowing through one VC is
By continuously monitoring the cells, it is possible to distinguish in detail a plurality of cells that form a packet decomposed by a certain ATM cell as a head cell, a last cell, and an intermediate cell (cells that are neither the head cell nor the last cell).

Here, in the packet discarding by the IP over ATM system, there are the EPD system and the PPD system, and both of them, when discarding cells that cannot be processed at the time of congestion occurrence, of all ATM cells that compose one packet. It is intended for disposal. Therefore, when cells that form a packet are selectively discarded, by discarding cells at random, many packets are discarded, and a large number of retransmission packets from the upper layer (TCP) occur. This is for avoiding the deterioration of the state of congestion caused by it.

Therefore, RED is simply over IP over ATM.
However, if the packet is randomly discarded by applying the above method, the processing amount will increase. this is,
This is because it is considered that the RED always operates because it operates even when the usage rate is low. Therefore, if the processing amount is large, the overhead increases. This is an ATM switch that accommodates ultra-high speed lines.
This is a problem that appears more prominently.

The reason why the processing amount increases as described above is that two different levels of processing are performed as follows.

First, as the first processing, the relay ATM
This is a process of observing all the cells passing through the node and determining the next discard packet, and the second process is
This is a VC-based process of discarding a packet. The second process is a process of discarding all the ATM cells that form the packet next to the VC determined in the first process, and this process occupies a large proportion as a cause of increasing the processing amount.

(Characteristics of the Present Invention) Therefore, according to the present invention, the discarding of the entire packet is delegated to the end AAL5, so that the relay ATM node (A
It is to reduce the processing amount of the TM switch).

That is, the ATM switch is not the final AT.
When discarding one M cell, the discard of the packet including this ATM cell is delegated to the end AAL5. Also, AT
The probability of discarding M cells is calculated from (average number of cells / packet) and the packet discard rate. Furthermore, cells other than the final cell are discarded at random cell intervals according to this discard probability.

As a result, in the congestion avoidance apparatus and method by RED according to the present invention, the RED does not operate when congestion occurs, but the packets are discarded at a low discard rate when the average resource usage rate becomes high to some extent. Therefore, compared to the conventional method of discarding all cells constituting one packet, unnecessary cells may flow on the line, but the effect of this is small, and congestion is efficiently prevented. It is possible.

Accordingly, the RED congestion avoidance apparatus and method according to the present invention does not discard all the ATM cells that make up one packet, but rather disassembles one packet at random cell intervals. Of
The feature is that ATM cells that are not the final cells (hereinafter abbreviated as intermediate cells) are discarded.

For this reason, at the start of the process, first, the interval (cell interval) between the cell to be discarded and the cell to be subsequently discarded is obtained, and then the intermediate which arrives first after separating the obtained cell interval. Discard the cell.

The cell interval between the cell to be discarded and the cell to be discarded next is calculated from the minimum value 0, the average number of cells required to transfer one packet, and the packet discard rate according to the congestion level. It is determined by randomly selecting from the cell interval with the maximum value. The method of calculating the cell spacing will be described in detail below.

By discarding the intermediate cell, the AT (packet receiving side) receives the AT input to the buffer.
In the process of assembling a packet from M cells, this 1
The control by AAL5 is utilized, which detects whether or not the number of cells forming a packet is insufficient, and when the number of cells is insufficient, the packet is discarded.

Therefore, it is possible to obtain the same congestion avoidance effect as discarding one packet by discarding the intermediate cell.

Regarding the case of discarding the last cell which has been a problem in the prior art, in the prior art, the receiving side has a portion excluding the last cell of the first packet and a cell obtained by decomposing the second packet. As a result, an excessive number of cells forming one packet is detected, and the completely received second packet is discarded in addition to the first packet to be discarded. However, in contrast to this, the congestion avoidance apparatus and method by RED according to the present invention selectively discards the intermediate cell instead of the final cell, and thus solves such a problem. Is possible.

Further, in the congestion avoidance apparatus and method by RED according to the present invention, packet discarding (or congestion indicator setting) is started at the time when a symptom of congestion is discovered, and therefore ATM cells other than intermediate cells are discarded. Instead, by performing normal control, it is possible to avoid the retransmission of a completely received packet. Therefore, it is possible to prevent the congestion of the network from being further deteriorated.

(First Embodiment) A first embodiment of a congestion avoidance apparatus and method by RED according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing the structure of an ATM switch (relay switching node). In FIG. 1,
The ATM switch has a line interface 3.
1 to line interface 3. It is composed of N line-corresponding sections up to N and a switch section 2.

In FIG. 1, the ATM cell received from the line is sent to the line corresponding part corresponding to the line sent via the switch part 2.

FIG. 2 is a block diagram showing the structure of the line interface 3 shown in FIG. In FIG. 2, the line interface 3 has a line controller 21 and a receiver 2 as its main components.
2 and a transmitter 23.

In FIG. 2, the ATM cell received from the line is sent to the switch unit 2 via the line control unit 21 and the receiving unit 22. In addition, A received from the switch unit 2
The TM cell is sent to the switch unit via the transmission unit 23 and the line control unit 21.

Here, the present invention is an invention relating to the function of the transmitting unit 23 in the line interface 3 shown in FIGS. 1 and 2.

Referring to FIG. 3, FIG. 3 is a block diagram showing the configuration of the transmission unit 23 shown in FIG. 2, and has the functions and data necessary for the description of the (first embodiment) of the present invention. Is configured. In FIG. 3, only the configuration necessary for explaining the first embodiment of the present invention is shown.

In FIG. 3, the ATM cell received from the switch unit 2 is discarded by the cell discard determining unit 43, and it is determined whether the ATM cell is connected to the transmission waiting queue 31. Here, the transmission waiting queue 31 is a waiting queue until a cell can be sent out via the line control unit 21.

Further, the average queue length monitoring unit 4 in FIG.
1 has a function of monitoring the average queue length in the transmission waiting queue 31 for each reference time.

Further, the congestion state determination unit 42, based on the output of the average queue length monitoring unit 41, its own ATM switch 1
Has a function of determining whether or not congestion has occurred, or whether or not the congestion state has been resolved.

As a method for determining the congestion state at this time, a threshold is set for the length of the queue length detected by the average queue length monitoring unit 41, and it is determined whether the detected average queue length exceeds this threshold. Determines the occurrence of congestion.

Further, the congestion state judging unit 42 can judge the level of the congestion state stepwise by having a plurality of thresholds as described above.

The data types shown in FIG. 3 are data types used by the cell discard determining unit 43 to determine whether or not to discard the received cell.

The pseudo random number table 51 is a table composed of 2 K powers of data, and 2 K powers of values from 0 to (2 K powers) −1 are randomly stored. ing.

Further, the pseudo random number table index 5
2 is data that stores an index for indexing the pseudo-random number table 51, and is 1 every time this value is referenced.
Is a cyclic counter that adds.

The shift bit number data 53 is data set when the congestion state judging unit 42 judges that the ATM switch 1 is in the congestion state. Also, after discarding one ATM cell, the maximum number of non-discarded cells until the next discarded ATM cell is {(2 to the power of L)-
1} is set, the congestion determination unit 42 sets (L-
The value of K) is set.

Therefore, the obtained pseudo random number value is right-shifted by the value of the shift bit number data 53 (divided by the power of 2) to obtain the cell interval to the next discarded cell.

More specifically, the process for determining the cell interval will be described. First, the packet discard rate corresponding to the congestion level determined by the congestion state determination unit and the average number of cells into which one packet is divided. The cell loss rate is calculated by the following equation, and the closest approximation to this cell loss rate is 1 / (2 n
Power) is specified. Pseudo-random numbers with equal probability are created in the range of 0 to (2 (n + 1) th power) based on the specified n-th power of 2. Therefore, the interval to the cell to be discarded next is specified by referring to this pseudo random number table.

The discarded cell interval obtained as described above is temporarily stored in the discarded cell counter 54. Therefore,
The cell discard determination unit 43 refers to the value of the discard cell counter 54 every time it receives an ATM cell, and
Determine whether to discard the TM cell.

The congestion state data 55 is data for setting a value corresponding to the numerical representation of the congestion state when the congestion state determination unit 42 detects the start and end of the congestion. This numerical expression expresses the degree of congestion by setting the level of congestion for each queue length waiting for transmission.

Therefore, by varying the probability of discarding cells according to this level, it becomes possible to avoid congestion according to the congestion state. Further, similarly, it becomes possible to notify each transmitting node of the congestion state according to the congestion state.

The configuration of the first embodiment has been described in detail above. The average queue length monitoring unit 41 shown in FIG.
Since the congestion state determination unit 42 and the congestion state determination unit 42 are not directly related to the present invention, detailed processing thereof will be omitted.

Next, the operation of the cell discard determining unit 43 in the congestion state will be described in detail with reference to FIG.

As shown in FIG.
When the M cell arrives, the cell reception is determined in step S61. If the cell is received, step S
At 62, the process of determining the value of the discarded cell counter 54 is executed.

If the value of the discarded cell counter 54 is not 0, the value of the discarded cell counter 54 is decremented by 1 in step S66, and then the received AT is received in step S67.
Execute the process of registering the M cell in the transmission waiting queue 31,
Then, it returns to step S61.

If the value of the discarded cell counter 54 is 0, the value of the ATM header of the received cell is referred to in step S63 to determine whether the value of the last bit defined by AAL5 is 0, that is, OFF. Whether or not the received cell is the final cell is determined depending on whether or not the received cell is the final cell.

If the value of the ATM header of the received cell is not OFF, the received ATM is received in step S67.
The process of registering the cell in the transmission queue is executed, and then the process returns to step S61.

Further, when the value of the ATM header of the received cell is OFF, the received ATM cell is discarded in step S64, the discarded cell counter updating process is executed in step S65, and the process returns to step S61.

Next, the discard cell counter updating process shown in step S65 of FIG. 4 will be described in detail with reference to FIG.

First, in step S71, the value of the pseudo random number table index 52 is added with 1 and stored.

Next, in step S72, the value of the pseudo random number is obtained by indexing the pseudo random number table 51 with the value of the pseudo random number table index 52. Further, the value obtained by right-shifting the value of the pseudo random number by the value of the shift bit number data 53 is stored in the discard cell counter 54, and the processing is ended.

As described above, in the first embodiment, since the cell received by the relay switching node is the intermediate cell, it is determined whether or not the cell can be discarded. The amount of processing is extremely small.

Furthermore, in the first embodiment, 1
Since all the received cells flowing on one line are collectively determined as discard cells, in order to discard the entire packet as in the packet discard processing by the EPD method, attention is paid to all VCs and ATM cell headers are separately provided. No need to monitor.

Therefore, it is possible to avoid performing the processing for each VC and the processing for the entire aggregated VC together.

In the first embodiment, all the connections are handled as the IP over ATM method. However, by adding the service class determination processing for each VC, the IP over A method is used.
Since it is possible to use UBR in the TM system and to use other than UBR in other ATM communication,
It is also possible to apply to a mode in which communication by IP over ATM and communication of other types are mixed and used.

(Other Embodiments) In addition, in the first embodiment described above, one embodiment in which an ATM switch is applied is shown. However, other AAL5 IP over ATM traffic such as a host ATM network interface card is shown. In the part that processes
It is possible to apply the RED congestion avoidance apparatus and method according to the present invention.

[0108]

As described above, the RE according to the present invention is used.
According to the congestion avoidance apparatus and the method therefor according to D, the following effects unique to the present invention can be achieved.

First, as a first effect, since only one intermediate cell is selected and discarded, it is possible to notify the application of packet discard with less processing than the packet discard method by the EPD method. Becomes

The reason is that it is possible to reduce a lot of processing required for discarding all cells forming one packet in the discard processing by the EPD method.

The second effect is that since only one intermediate cell is discarded from the aggregated flows, RED requires less processing than the method using the packet discard method based on the EPD method. It is also possible to realize.

The reason is that it is possible to reduce the processing for discarding all cells forming one packet for each VC in the packet discarding method by the EPD method.

Further, the congestion avoidance by RED does not operate when congestion occurs, but the packets are discarded at a low discard rate when the average resource usage rate becomes high to some extent. Therefore, all cells constituting one packet are discarded. Compared with the conventional method, unnecessary cells flow on the line, but the effect of this is small, and it is possible to efficiently avoid the occurrence of congestion.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an ATM switch (relay switching node).

FIG. 2 is a block diagram showing a configuration of a line interface unit 3 shown in FIG.

FIG. 3 is a block diagram showing a configuration of a transmission unit 23 shown in FIG. 2, which is configured to have functions and data necessary for explaining the first embodiment of the present invention.

FIG. 4 is a flowchart showing an operation of a cell discard determination unit 43 in a congestion state.

5 is a flowchart showing a discard cell counter updating process shown in step S65 of FIG.

[Explanation of symbols]

1 ATM switch 2 switch part 3.1 to 3.n line support 21 Line control unit 22 Receiver 23 Transmitter 31 Send queue 41 Average queue length monitor 42 Congestion judgment unit 43 Cell discard determination unit 51 Pseudo-random number table 52 Pseudo random number table index 53 Shift bit number data 54 Discarded cell counter 55 Congestion status data

Claims (14)

(57) [Claims] 1. A congestion avoidance apparatus according RED (Random Early Detection) in a network according to the AAL5 as a protocol, a cell other than the last cell is specified based on cell interval calculated by a predetermined probability, is identified Cell discard means for discarding a cell, and the predetermined probability is the average of the division of one packet.
Dropped packets depending on the number of cells and congestion level
And the cell spacing can be approximated by the predetermined probability.
Value of 1 to the power of 2, and based on the value of the power of 2
In the range from 0 to twice the power of 2 above, the pseudo probability of equal probability is
A similar random number is created and specified based on the pseudo random number, and the cell discarding means determines the cell specified by the cell interval.
Discard the specified cell if it is not the last cell
A congestion avoidance apparatus based on RED characterized by the following. 2. A congestion avoidance apparatus by RED in a network to which AAL5 is applied as a protocol, wherein buffering means for temporarily holding cells received from a line and queue length of cells held by the buffering means are calculated. Based on the queue length monitoring means and the queue length calculated by the queue length monitoring means,
Congestion state determination means for determining the occurrence of a congestion state, if the congestion state determination means determines the occurrence of a congestion state, the final cell determination means for determining whether the arrived cell is the final cell, When the final cell determination unit determines that the arrived cell is not the final cell, the final cell determination unit specifies a cell interval calculated based on a predetermined probability, and discards the specified cell. , The predetermined probability is the average of one packet divided
Dropped packets depending on the number of cells and congestion level
And the cell spacing can be approximated by the predetermined probability.
Value of 1 to the power of 2, and based on the value of the power of 2
In the range from 0 to twice the power of 2 above, the pseudo probability of equal probability is
A similar random number is created and specified based on the pseudo random number, and the cell discarding means determines the cell specified by the cell interval.
Discard the specified cell if it is not the last cell
A congestion avoidance apparatus based on RED characterized by the following. 3. The queue length monitoring means detects the queue length in the buffering means at predetermined time intervals, and based on the detected queue length, an average queue length including the latest queue length. 3. The congestion avoidance apparatus by RED according to claim 2, wherein the queue length of the cell held by the buffering unit is calculated by the calculation. 4. The cell has a final bit indicating whether or not the cell is a final cell among cells forming the same packet in a header part of the cell, and the final cell determining means. Is based on the last bit included in the header part of the cell,
The RED congestion congestion avoiding apparatus according to claim 2 or 3, wherein it is determined whether the cell is a final cell. 5. A queue length storage means for storing a predetermined queue length as a threshold value is further provided, and the congestion state determination means stores the queue length calculated by the queue length monitoring means in the queue length storage means. The RE according to any one of claims 2 to 4, wherein the occurrence of congestion is determined by comparing the stored predetermined queue length.
Congestion avoidance device by D. 6. A queue length congestion level storage means for storing a plurality of predetermined queue lengths as threshold values with different values, and further storing a congestion state level corresponding to the plurality of predetermined queue lengths, The congestion determination means, the queue length calculated by the queue length monitoring means, and a plurality of the predetermined queue length stored in the queue length congestion level storage means, respectively, as a result of the comparison, Among the predetermined queue lengths exceeding the queue length calculated by the queue length monitoring means, the congestion level corresponding to the predetermined queue length that is the largest value is specified, and the occurrence of congestion is determined stepwise. The congestion avoidance apparatus by RED according to any one of claims 2 to 4, wherein 7. A network according to the AAL5 as the protocol, congestion avoidance device according RED according to any of claims 1, characterized in that a network employing the IP over ATM scheme 6. 8. A congestion avoidance method by RED in a network to which AAL5 is applied as a protocol, wherein cells other than the final cell are identified based on a cell interval calculated by a predetermined probability, and the identified cells are discarded. A cell discard step, and the predetermined probability is the average of one packet being divided.
Dropped packets depending on the number of cells and congestion level
And the cell spacing can be approximated by the predetermined probability.
Value of 1 to the power of 2, and based on the value of the power of 2
In the range from 0 to twice the power of 2 above, the pseudo probability of equal probability is
A similar random number is created and specified based on the pseudo random number. The cell discarding step is performed by the cell specified by the cell interval.
Discard the specified cell if it is not the last cell
A method for avoiding congestion by RED, which is characterized in that 9. A method for avoiding congestion by RED in a network to which AAL5 is applied as a protocol, wherein a buffering step of temporarily holding cells received from a line and a queue length of the cells held in the buffering step are calculated. A queue length monitoring step to perform, a congestion state determination step of determining the occurrence of a congestion state based on the queue length calculated in the queue length monitoring step, and the occurrence of a congestion state is determined in the congestion state determination step A final cell determination step of determining whether the arrived cell is the final cell, and a cell calculated with a predetermined probability when the arrived cell is determined not to be the final cell in the final cell determination step identified on the basis of distance, and a cell discard process of discarding the cell specified, the predetermined probability, one packet Division is the average of the
Dropped packets depending on the number of cells and congestion level
And the cell spacing can be approximated by the predetermined probability.
Value of 1 to the power of 2, and based on the value of the power of 2
In the range from 0 to twice the power of 2 above, the pseudo probability of equal probability is
A similar random number is created and specified based on the pseudo random number. The cell discarding step is performed by the cell specified by the cell interval.
Discard the specified cell if it is not the last cell
A method for avoiding congestion by RED, which is characterized in that Wherein said queue length monitoring step, a predetermined time interval, and detects the queue length in said buffering step, based on the queue length and the detected queue length average including the latest queue length 10. The congestion avoidance method by RED according to claim 9 , wherein the queue length of the cell held in the buffering step is calculated by calculating. 11. The final cell determining step, wherein the cell has a final bit indicating whether or not the cell is a final cell among cells constituting the same packet in a header part of the cell, Is based on the last bit included in the header part of the cell,
The congestion avoidance method by RED according to claim 9 or 10, wherein it is determined whether or not the cell is a final cell. 12. A queue length storage step of storing a predetermined queue length as a threshold value, wherein the congestion state determination step includes the queue length calculated in the queue length monitoring step and the queue length storage step. 12. The congestion avoidance method by RED according to claim 9 , wherein the occurrence of congestion is determined by comparing the stored predetermined queue length. 13. The congestion determining step compares the queue length calculated in the queue length monitoring step with a plurality of queue lengths stored so that a plurality of congestion state levels respectively correspond to each other, As a result of the comparison, the congestion level corresponding to the predetermined queue length which is the largest value among the predetermined queue lengths exceeded by the queue length calculated by the queue length monitoring step is specified, and stepwise The congestion avoidance method by RED according to claim 9 , wherein the occurrence of congestion is determined. 14. A network according to the AAL5 as the protocol, the claim 8, characterized in that a network employing the IP over ATM system 13
The congestion avoidance method by RED described in any one of 1.