JP3637879B2 - Packet discard method and ATM switch device in ATM communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a packet discarding method and an ATM switch device in an ATM (Asynchoronous Transfer Mode) communication method, and more specifically, abnormal packets among packets input to the ATM switch device are discarded at an early point. The present invention relates to a packet discarding method and an ATM switch device in the ATM communication system.
[0002]
[Prior art]
In communication systems, ATMs that can transmit information more efficiently than the conventionally known STM (Synchoronous Transfer Mode) have become widespread. In the ATM communication system, as shown in FIG. 7, all information is divided into cells 51 of a certain length and sent to a transmission path (network) in the form of a packet to which destination information is added. An ATM switch device (hereinafter also simply referred to as a switch device) 52 is connected to the transmission path, and the input cells are sorted by the switch device 52 based on the destination information and then multiplexed to the corresponding terminals. Is transmitted to.
[0003]
In this case, in the transfer mode using synchronous multiplexing such as STM, if no information is sent, an idle time occurs in the transmission path. However, in the case of the transfer mode using cell multiplexing such as ATM, the idle time is used. Since other information cells can be transmitted, efficient transmission can be performed. Here, when a plurality of cells are input to the switch device 52 at the same time, one of the cells is stored (written) in the cell buffer provided in the switch device 52, and when the transmission path is free, The cell is configured to be output (read) under control.
[0004]
However, when a communication request exceeding the processing capacity is made on the transmission path, the number of cells exceeding the preset threshold value is input to the switch device 52, so that the capacity of the cell buffer is exceeded. Therefore, a so-called congestion state occurs. As a result, the loss of the cell occurs and important information disappears, and the reliability of communication decreases. Therefore, in the ATM communication system, transmission path congestion control is performed in order to return the congestion state to the normal state.
[0005]
Conventionally, as such a congestion control method, packets called EPD (Early Packet Discard) and PPD (Partial Packet Discard) intended for packets of AAL Type 5 (ATM Adaption Layer Type 5: hereinafter referred to as AAL5). Disposal methods have been proposed.
[0006]
Here, the EPD monitors the occupancy of the cell buffer of the ATM switch device existing in the transmission path, and when the cell exceeds the threshold that is the upper limit for storing the cell and the head of the AAL5 packet arrives, The cells constituting the packet are discarded without being stored in the cell buffer, and when the head of the AAL5 packet arrives below the threshold, all the cells constituting the same packet that arrive thereafter are stored in the cell buffer. Is the method.
On the other hand, even if a part of the AAL5 packet is already stored in the cell buffer, the PPD is discarded if the cell of the corresponding packet arrives after the threshold is exceeded, but the subsequent packet is configured. This is a method of discarding all cells to be performed.
[0007]
That is, in EPD and PPD, packets including cells that cause cell buffer overflow are actively discarded to avoid cell buffer overflow, and other packets are avoided from being discarded as much as possible. It is intended to improve throughput by suppressing waste at the packet level.
[0008]
[Problems to be solved by the invention]
By the way, in the conventional packet discarding method, there is a problem that a decrease in throughput cannot be avoided in both EPD and PPD.
In other words, in the conventional packet discarding method, cells are discarded by the ATM switch device up to the previous stage in the transmission path, and when an abnormal cell is input as a packet, either EPD or PPD is used. However, an abnormal packet cannot be discarded unless a threshold value is exceeded and a cell arrives. Examples of such an abnormal packet include a packet in which an intermediate cell constituting the packet is lost and a packet in which two or more packets are connected. Accordingly, even in the ATM switch device in the subsequent stage, such abnormal packets continue to use bandwidth resources unnecessarily, and thus a reduction in throughput is unavoidable.
[0009]
The present invention has been made in view of the above circumstances, and an ATM communication system which can improve throughput by discarding abnormal packets at an early point even when the cell buffer threshold is not exceeded. An object of the present invention is to provide a packet discarding method and an ATM switch device.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problem, the invention according to claim 1 is directed to a case where, when a packet input from a transmission line to an ATM switch device including a cell buffer is abnormal, the number of cells constituting the packet is equal to the cell buffer. Even when the threshold is not exceeded, according to the packet discarding method in the ATM communication system in which the abnormal packet is discarded, the actual number of cells constituting the packet is counted from the first cell input for each connection, After calculating the converted cell number from the packet PDU length stored in the payload of the last cell of the packet, the actual cell number is compared with the converted cell number, and the actual cell number is calculated as the converted cell number. If exceeded, and if the actual number of cells has not reached the number of converted cells, packets composed of the corresponding cells are packetized. Is characterized by discarding is determined that the length abnormality.
[0011]
The invention according to claim 2 relates to the packet discarding method in the ATM communication system according to claim 1, and when it is determined that the packet length is abnormal, the packet of the same connection inputted next to the cell buffer is transmitted to the cell By overwriting with a buffer, the cells constituting the abnormal packet are discarded.
[0012]
According to a third aspect of the present invention, when a packet input from a transmission path to a cell buffer is abnormal, the abnormal packet is discarded even if the number of cells constituting the packet does not exceed the threshold of the cell buffer. According to the ATM switch apparatus used for the packet discarding method in the ATM communication system as described above, a cell buffer unit for storing cells constituting a packet input from the transmission path, and a packet from a head cell input for each connection A cell count unit that counts the actual number of cells to be configured; a cell number extraction unit that calculates the number of converted cells from the packet PDU length stored in the payload of the last cell of the packet; and the actual cell number and the converted cell When the packet length is determined to be abnormal, the cell count value is output to the cell buffer unit. It is characterized in that it is composed of a Tsu preparative length abnormality detecting unit.
[0013]
According to a fourth aspect of the present invention, there is provided the ATM switch device according to the third aspect, wherein the VPI and VCI of the input cell are extracted, cell data is generated together with a connection number, and the cell data is output to the cell determination unit. A connection extracting unit that generates a cell pulse every time and outputs the cell pulse together with the connection number to the cell counting unit, and whether the cell is the first cell indicating the beginning of the packet or the last cell indicating the end Each cell is determined, and the first cell is output to the cell count unit, and the cell determination unit that outputs the last cell to the cell number extraction unit is added.
[0014]
The invention according to claim 5 relates to the ATM switch device according to claim 3, wherein the cell buffer unit holds a plurality of buffer units for writing the cells, and a write pointer value of the cells to the buffer units, A write control unit that performs write control of the cell to the buffer unit; a read control unit that holds a read pointer value of the cell from the buffer unit and performs read control of the cell from the buffer unit; and Based on the cell write pointer value obtained from the write control unit, the cell read pointer value obtained from the read control unit, and the cell count value input from the packet length abnormality detection unit, Write to overwrite the next received packet to the buffer unit To generate address value is characterized by being composed of the address determination unit and output to the write control unit.
[0015]
A sixth aspect of the present invention relates to the ATM switch apparatus according to the third aspect, wherein the packet length abnormality detection unit compares the actual cell number with the converted cell number, and the actual cell number is When the number of converted cells is exceeded and when the actual number of cells does not reach the number of converted cells, it is determined that the packet length is abnormal.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. The description will be made specifically with reference to examples.
FIG. 1 is a block diagram showing a configuration of an ATM switch device used in a packet discarding method in an ATM communication system according to an embodiment of the present invention. FIG. 2 is a diagram showing in detail the configuration of the main part of FIG. FIG. 4 is a diagram for explaining an operation for determining an abnormal packet length in the packet discarding method, and FIGS. 5 and 6 are diagrams for explaining a packet discarding operation in the packet discarding method.
As shown in FIG. 1, an ATM switch device 10 used in the packet discarding method in the ATM communication system of this example includes a cell buffer unit 1 for storing cells constituting a packet inputted from a transmission path, and an inputted cell. VPI (Virtual Path Identify) and VCI (Virtual Channel Identify) are extracted, cell data is generated together with the connection number, is output to the cell determination unit 3, and a cell pulse is generated for each input cell, together with the connection number. The connection extraction unit 2 that outputs to the cell count unit 4, and the input cell is the first cell (BOM (Beginnig Of Message) cell) indicating the beginning of the packet, or the last cell (EOM (End Of Message) indicating the end ) Cell) for each connection, the BOM cell is output to the cell count unit 4, and the EOM cell and The cell determination unit 3 that outputs the input cell to the cell number extraction unit 5, the cell count unit 4 that counts the actual number of cells constituting the packet from the BOM cell input for each connection, and the payload of the EOM cell of the packet When the cell number extraction unit 5 that converts the number of cells in the AAL5 packet from the stored packet PDU (Protocol Data Unit) length is compared with the actual cell number and the converted cell number, and when the packet length abnormality is determined The packet length abnormality detecting unit 6 outputs a cell count value to the cell buffer unit 1.
[0017]
Here, as shown in FIG. 2, the cell buffer unit 1 which is the main part of the ATM switch device 10 is configured separately for each connection, and includes a plurality of buffer units 11 for writing cells, and cell buffers to the buffer unit 11. A write control unit 12 that holds a write pointer value and controls writing of a cell to the buffer unit 11, and a read that holds a cell read pointer value from the buffer unit 11 and controls the reading of a cell from the buffer unit 11 Based on the cell write pointer value obtained from the control unit 14 and the write control unit 12, the cell read pointer value obtained from the read control unit 14, and the cell count value input from the packet length abnormality detection unit 6, the buffer unit 11 Judge the state of the written packet and overwrite the next AAL5 packet to be received into the buffer unit 11 It generates a write address value to, and an address determination unit 13 for outputting to the write control unit 12.
[0018]
Next, the operation of the ATM switch device 10 will be described with reference to FIGS.
The cells constituting the packet are input from the transmission path to the cell buffer unit 1 and input to the connection extraction unit 2. The cell buffer unit 1 writes the cells into the corresponding buffer unit 11 under the control of the write control unit 12 for each connection in the order in which the cells are input, and reads the cells until reading is performed under the control of the read control unit 14. Let it stay. The connection extraction unit 2 extracts the VPI and VCI of the input cell, generates cell data together with the connection number, and outputs the cell data to the cell determination unit 3. Further, the connection extraction unit 2 generates a cell pulse used for cell counting for each input cell and outputs the cell pulse together with the connection number to the cell count unit 4.
[0019]
The cell determination unit 3 determines for each connection whether the cell input through the connection extraction unit 2 is a BOM cell indicating the beginning of a packet or an EOM cell indicating the end of the packet, and determines the BOM cell as a cell count unit 4. And the EOM cell and the input cell are output to the cell number extraction unit 5. Here, PT (Payload Type) in the cell header of the input connection is monitored, and when a cell with PT = 001 is detected, it is determined that the cell is an EOM cell of an AAL5 packet. On the other hand, the cell that arrives next to the EOM cell in the connection is determined to be the BOM cell of the AAL5 packet.
[0020]
The cell count unit 4 counts the actual number of cells constituting a packet from the BOM cells input for each connection. The count is incremented by 1 for each connection based on the cell pulse input from the connection extraction unit 2, and when the cell determination unit 3 determines that the cell is a BOM, the count of the corresponding connection is returned to 1. Then, the counted number of cells is output to the packet length abnormality detection unit 6.
[0021]
The cell number extraction unit 5 detects the SAR (Segmentation And Reassembly) -PDU length stored in the trailer portion of the AAL5 packet from the payload of the cell determined as the EOM cell by the cell determination unit 3, and this PDU length To the number of AAL5 packet cells. Then, the converted number of cells (converted number of cells) is output to the packet length abnormality detection unit 6.
[0022]
The packet length abnormality detection unit 6 compares the actual cell number input from the cell count unit 4 with the converted cell number input from the cell number extraction unit 5, and the actual cell number exceeds the converted cell number. If the actual number of cells does not reach the number of converted cells (small), it is determined that the packet length is abnormal. Then, the packet length abnormality detection unit 6 notifies the packet length abnormality information, its connection number, and cell count value by simultaneously outputting them to the cell buffer unit 1.
[0023]
Next, an example in which the packet discarding method in the ATM communication system of this example is implemented using the ATM switch device 10 of FIGS. 1 and 2 will be described. First, an example in which it is determined that the packet length is abnormal that requires packet discard will be described.
(1) Example in which a packet configured with missing intermediate cells is determined to have an abnormal packet length As shown in FIG. 3, an example in which a packet configured with three intermediate cells missing is input. The actual cell of the AAL5 packet 21 counted by the cell count unit 4 is more than the number of constituent cells of the AAL5 packet 20 (AAL5 cell number = 8) detected from the SAR-PDU trailer of AAL5 which is the cell number extraction unit 5 The number (cell count = 5) decreases.
Therefore, as described above, the actual cell number (5) counted by the cell count unit 4 is smaller than the converted cell number (8) converted by the cell number extraction unit 5, so the packet length abnormality detection unit 6 Thus, it is determined that the packet length is abnormal.
[0024]
(2) Example in which a packet in which two or more packets are connected is determined to have an abnormal packet length As shown in FIG. 4, an AAL5 packet 22 from which a BOM cell is missing and an AAL5 packet 23 from which an EOM cell is missing are consecutive. In this example, since the break between the packets 22 and 23 cannot be determined, it is treated as one long packet. Therefore, the actual number of cells of the AAL5 packet 24 counted by the cell counting unit 4 (cell count = cell count = rather than the number of constituent cells of the AAL5 packet 20 detected from the SAR-PDU trailer of AAL5 (number of AAL5 cells = 3). 5) will increase.
Therefore, as described above, the actual cell number (5) counted by the cell count unit 4 exceeds the converted cell number (3) converted by the cell number extraction unit 5, so the packet length abnormality detection unit 6 Thus, it is determined that the packet length is abnormal.
[0025]
Next, a method for discarding a packet determined to have an abnormal packet length as described above will be described.
In the ATM switch device 10 shown in FIGS. 1 and 2, when the packet length abnormality is detected by the notification from the packet length abnormality detection unit 6, the cell buffer unit 1 writes the write pointer value for the connection having the packet length abnormality. To change.
The read control unit 14 holds the read address value of the cell output from the buffer unit 11 and outputs the read address to the address determination unit 13 in order to perform read control of the cell of the corresponding connection. Note that the address determination unit 13 operates based on the connection number input from the packet length abnormality detection unit 6 if the block is a corresponding connection.
[0026]
The address determination unit 13 determines the next packet to be input from the packet length abnormality information and the cell count value input from the packet length abnormality detection unit 6 simultaneously with the connection number and the read address value input from the read control unit 14. The write head address is calculated, and the changed address value is output to the write control unit 12. The write control unit 12 changes the write address value to the changed address value input from the address determination unit 13 when the packet length is abnormal. The change of the write pointer value is determined by comparing the write pointer value and the read pointer value of the BOM cell of the corresponding connection.
[0027]
FIG. 5 illustrates the operation when the entire AAL5 packet to be discarded stays in the buffer unit 11. In the figure, when the read pointer value Rp is compared with the write pointer value Wp of the BOM cell, the BOM write pointer value Wp is later than the read pointer value Rp, so that the buffer unit 11 stores the entire AAL5 packet to be discarded. It can be judged that is staying. As described above, when the entire AAL5 packet stays in the buffer unit 11, the BOM write pointer value is set as the write pointer value of the corresponding connection.
[0028]
FIG. 6 illustrates an operation when a part of the AAL5 packet to be discarded stays in the buffer unit 11. In the figure, if the write pointer value Wp of the BOM cell is ahead of the read pointer value Rp, it can be determined that the BOM cell of the packet of the relevant connection has already been read. Therefore, all the cells staying in the buffer unit 11 of the connection are determined to be part of the packet to be discarded, and the pointer value of the cell to be read next is set as the write pointer value of the connection.
[0029]
When the write pointer value of the buffer unit 11 of the corresponding connection is updated, the cell of the corresponding connection (BOM cell of the next packet) to be input next is an abnormal packet in the buffer unit 11 due to the changed write pointer value. Will be overwritten from the BOM cell.
[0030]
As described above, according to the packet discarding method in the ATM communication system of this example, even when the cells constituting the packet do not exceed the cell buffer threshold, the actual number of input cells exceeds the number of converted cells. If the actual number of cells does not reach the number of converted cells, it is determined that the packet length is abnormal, and these packets are discarded. Abnormal packets such as packets connected can be discarded at an early point. Therefore, unnecessary data communication on the transmission path can be suppressed, and throughput between terminals can be improved. In this way, even if an abnormal packet is transmitted to the end, it is discarded at the end destination. Therefore, discarding at an early point in time, as in this example, is not limited to the own device but the subsequent devices and transmission paths. Therefore, it is possible to effectively use the band resources.
[0031]
Thus, according to the packet discarding method in the ATM communication system of this example, the actual number of cells counted from the BOM cell input for each connection by the counting unit 4 and the EOM cell of the packet by the cell number extracting unit 5 Compared with the number of converted cells in the AAL5 packet converted from the packet PDU length stored in the payload, when the actual number of cells exceeds the number of converted cells, and the actual number of cells reaches the number of converted cells. If not, the packet length abnormality detection unit 6 determines that the packet constituted by the corresponding cell is abnormal and discards the packet, so that the abnormal packet can be discarded at an early point.
In addition, according to the ATM switch device 10 of this example, the cell buffer unit 1 for storing the cells constituting the packet input from the transmission line, the VPI and VCI of the input cell are extracted, and the cell data together with the connection number is extracted. Is generated and output to the cell determination unit 3, and further, a connection extraction unit 2 that generates a cell pulse for each input cell and outputs it to the cell count unit 4 together with the connection number, and the input cell indicates the head of the packet It is determined for each connection whether it is the first cell or the last cell indicating the end, and the first cell is output to the cell count unit 4 and the final cell and the input cell are output to the cell number extraction unit 5 Unit 3 and cell count unit 4 for counting the actual number of cells constituting a packet from the first cell input for each connection, The cell number extraction unit 5 that converts the number of cells of the AAL5 packet from the packet PDU length stored in the payload of the last cell of the packet is compared with the actual cell number and the converted cell number to determine the packet length abnormality. In this case, the packet length abnormality detection unit 6 that outputs the cell count value to the cell buffer unit 1 can be reliably discarded.
Therefore, even if the cell buffer threshold is not exceeded, it is possible to improve throughput by discarding abnormal packets.
[0032]
The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and the present invention can be changed even if there is a design change without departing from the gist of the present invention. include. For example, the buffer unit of the ATM switch device has been described as an example in which it is configured to be physically prepared for each connection for convenience, but is not limited thereto, and is configured to be logically prepared for each connection. May be. Moreover, the example of arrangement | positioning of the cell which comprises an abnormal packet shows an example, and it can cope with the abnormal packet which consists of an arrangement example of not only this example but various cells.
[0033]
【The invention's effect】
As described above, according to the packet discarding method in the ATM communication system of the present invention, the actual number of cells counted by the counting unit is compared with the converted number of cells converted by the cell number extracting unit. When the number of cells exceeds the number of converted cells, and the actual number of cells does not reach the number of converted cells, the packet length abnormality detection unit determines that the packet composed of the corresponding cells is abnormal in packet length. Since it is discarded, an abnormal packet can be discarded at an early point.
Further, according to the ATM switch device of this example, the cell buffer unit for storing the cells constituting the packet, the VPI and VCI of the input cell are extracted, the cell data is generated and output together with the connection number, and further inputted. A connection extraction unit that generates a cell pulse for each cell and outputs the cell pulse together with the connection number; determines whether the input cell is the first cell or the last cell of the packet for each connection, and outputs the first cell In addition, a cell determination unit that outputs the final cell and the input cell, a cell count unit that counts the actual number of cells from the first cell input for each connection, and a packet PDU length stored in the payload of the final cell of the packet Compare the cell number extractor that converts the number of cells with the actual cell number and the converted cell number. Because if it is determined the door length abnormality is composed of a packet length abnormality detecting unit for outputting a cell count value can be discarded reliably abnormal packet.
Therefore, even if the cell buffer threshold is not exceeded, the throughput can be improved by discarding abnormal packets.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an ATM switch device used in a packet discarding method in an ATM communication system according to an embodiment of the present invention.
FIG. 2 is a diagram showing in detail the configuration of the main part of FIG.
FIG. 3 is a diagram for explaining an operation for determining an abnormal packet length in the packet discarding method.
FIG. 4 is a diagram for explaining an operation for determining an abnormal packet length in the packet discard method.
FIG. 5 is a diagram for explaining a packet discarding operation;
FIG. 6 is a diagram for explaining a packet discarding operation;
FIG. 7 is a diagram schematically showing an ATM communication system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cell buffer part 2 Connection extraction part 3 Cell determination part 4 Cell count part 5 Cell number extraction part 6 Packet length abnormality detection part 10 ATM switch apparatus 11 Buffer part 12 Write control part 13 Address determination part 14 Read control part 20-24 AAL5 packet

Claims (6)

When a packet input from the transmission path to an ATM switch device having a cell buffer is abnormal, the abnormal packet is discarded even if the number of cells constituting the packet does not exceed the threshold of the cell buffer. A packet discarding method in the ATM communication system,
While counting the actual number of cells that make up a packet from the first cell entered for each connection,
After calculating the number of converted cells from the packet PDU length stored in the payload of the last cell of the packet,
Compare the actual cell number with the converted cell number, if the actual cell number exceeds the converted cell number, and if the actual cell number does not reach the converted cell number, A packet discard method in the ATM communication system, wherein a packet constituted by a cell to be determined is determined to be an abnormal packet length and discarded.   When it is determined that the packet length is abnormal, a cell constituting the abnormal packet is discarded by overwriting the packet of the same connection next input to the cell buffer by the cell buffer. A packet discarding method in the ATM communication system according to 1. Packets in the ATM communication system in which, when a packet input from a transmission path to a cell buffer is abnormal, the abnormal packet is discarded even if the number of cells constituting the packet does not exceed the threshold of the cell buffer An ATM switch device used in a disposal method,
A cell buffer unit for storing cells constituting a packet input from the transmission path;
A cell count unit that counts the actual number of cells constituting a packet from the first cell input for each connection;
A cell number extraction unit that calculates the number of converted cells from the packet PDU length stored in the payload of the last cell of the packet;
Comparing the actual cell number with the converted cell number, when it is determined that the packet length is abnormal, the packet length abnormality detecting unit outputs a cell count value to the cell buffer unit. ATM switch device. A connection that extracts the VPI and VCI of the input cell, generates cell data together with a connection number, outputs the cell data to a cell determination unit, generates a cell pulse for each cell, and outputs the cell pulse together with the connection number to the cell count unit An extractor;
It is determined for each connection whether the cell is the first cell indicating the beginning of a packet or the last cell indicating the end, and the first cell is output to the cell count unit, and the last cell is 4. The ATM switch device according to claim 3, further comprising a cell determination unit for outputting to the cell number extraction unit .   The cell buffer unit includes a plurality of buffer units for writing the cells, a write control unit that holds a write pointer value of the cells to the buffer unit, and controls the writing of the cells to the buffer unit, and the buffer A read control unit that holds a read pointer value of the cell from the buffer unit, and performs read control of the cell from the buffer unit; a write pointer value of the cell obtained from the write control unit; and the read control unit that obtains from the read control unit Based on the cell read pointer value and the cell count value input from the packet length abnormality detection unit, the state of the packet written in the buffer unit is determined, and the packet received next to the buffer unit is determined. Address determination to generate a write address value for overwriting and output to the write control unit It is composed of an ATM switch according to claim 3, wherein. The packet length abnormality detection unit compares the actual cell number with the converted cell number, and when the actual cell number exceeds the converted cell number, and the actual cell number is the converted cell number. 4. The ATM switch device according to claim 3 , wherein the packet switching length is determined to be abnormal when the packet length has not been reached.

Images