JP2000013390A - Atm switch device and packet abort method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve utilizing efficiency of a network by aborting a packet only in the case of minimum necessity. SOLUTION: A VCI/VPI extract circuit 101 receiving a cell provides an output of a cell pulse 2 to a cell counter 103 and a selection VCI/VPI cell 11 to an ATM adoptation layer AAL 5 final cell extract circuit 102. The cell counter 103 supplies a count result to a packet length comparator circuit 104 as a packet length signal 4. The packet length comparator circuit 104 compares the packet length signal 4 with a packet length threshold signal 5 and gives the result to an early packet discard EPD decision circuit 105. A packet head position signal 3 outputted from the AAL 5 final cell extract circuit 102 is given to the EPD decision circuit 105. A cell buffer 106 outputs a buffer occupancy amount signal 8 to the EPD decision circuit 105 and outputs a cell output 10 from an output terminal. The EPD decision circuit 105 generates a cell abort signal 9 from a packet abort threshold signal 7, a long packet selection signal 6 and a buffer occupancy signal 8 and gives the signal 9 to the cell buffer 106.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for discarding cells stored in a buffer memory, and more particularly to an ATM (As
ynchronous Transfer Mode:
Asynchronous Transfer Mode) A used in the network
The present invention relates to a cell discarding method for a cell buffer in a TM switch.

[0002]

2. Description of the Related Art As a congestion control method for an ATM network, an AAL (ATM Adaptation) has conventionally been used.
Layer) EP for Type 5 packets
A method called D (Early Packet Discard) is known.

[0003] EPD means that a threshold value, which is an upper limit for permitting cell storage in a buffer of a switching node, is determined in advance, and when the number of cells stored in the buffer exceeds this threshold value, the next arrival time is reached. It is assumed that the buffer is overflowed by the packet to be dropped and that the cell is discarded. Then, when the cell located at the head of the packet arrives, all the cells constituting the packet are discarded without being taken into the buffer. That is, with this method, only if the number of cells in the buffer of the switching node is below the threshold,
All cells arriving after that are fetched into the buffer.

[0004] By performing such EPD, by actively discarding packets including cells that cause the buffer to overflow, it is possible to prevent other cells from discarding all cells.

[0005]

In the conventional cell discarding system described above, when there is only one ATM switch, there is no need to use useless bandwidth resources, and the network can be used efficiently.

However, when ATM switches are connected in multiple stages, if a packet is discarded for the first time in an intermediate stage, the bandwidth resources up to the immediately preceding stage are wasted. When one discarded packet is a long packet composed of many cells, the waste is particularly large, and the influence on the network is large.

An object of the present invention is to provide a cell discarding method which solves the above-mentioned problem, prevents long packets from being discarded as much as possible, and enables efficient use of bandwidth in the entire network.

[0008]

In order to achieve the above object, an ATM switch device according to the present invention stores input cells and outputs the number of stored cells as a buffer occupancy signal. A cell buffer for erasing cells stored according to a cell discard signal input from
Count the number of cells constituting the packet, compare the result with a predetermined packet length threshold, and as a result, the packet length signal is smaller than the packet length threshold, and the buffer occupancy A cell discard signal generating circuit for outputting the cell discard signal for erasing the cells constituting the packet from the cell buffer when the signal is larger than a predetermined packet discard threshold signal.

Further, the ATM switch device of the present invention stores input cells, outputs the number of stored cells as a buffer occupancy signal, and stores the cells in accordance with an externally input cell discard signal. A cell buffer for erasing cells, counting the number of cells constituting the packet, a cell counter for outputting the counting result as a packet length signal, and comparing the packet length signal with a predetermined packet length threshold, A packet length comparison circuit that outputs the result as a long packet selection signal, a final cell extraction circuit that outputs a packet head position signal indicating a head position of the packet, the buffer occupancy signal, the long packet selection signal, A packet head position signal and a predetermined packet discard threshold signal are input, and the long packet signal is When the packet length signal is smaller than the packet length threshold value and the buffer occupancy signal is larger than the packet discard threshold signal, the cell constituting the packet is deleted from the cell buffer. And an EPD determination circuit that outputs the cell discard signal of the above.

[0010] The EPD determination circuit constituting the ATM switch device may further include the cell discard signal even when the buffer occupancy signal indicates that the remaining capacity of the cell buffer is zero. You may comprise so that it may output.

Further, the EPD determination circuit constituting the ATM switch device may be configured to perform the cell discarding even when the buffer occupancy signal is larger than the packet discard threshold signal at the time when the head cell arrives. It may be configured to output a signal.

Further, the ATM switch device of the present invention comprises:
In addition to the above configuration, the cell is input, a selected cell having a predetermined attribute among the cells is output and supplied to the final cell extraction circuit, and a cell pulse is output each time the selected cell arrives And a VCI / VPI extraction circuit for supplying the VCI / VPI to the cell counter.

[0013] Further, the selected cell having the predetermined attribute may be a selected VCI / VPI cell having a predetermined VCI / VPI.

Further, in the cell discarding method according to the present invention, there is provided a counting step for counting the number of cells included in an input packet, wherein the cell number is smaller than a predetermined packet length and the occupancy of the cell buffer is smaller than the predetermined packet length. A discarding step of discarding the packet when the packet is larger than a packet discarding threshold determined by the capacity of the cell buffer.

Further, in the packet discarding method, the discarding step may discard the packet even when the remaining capacity of the cell buffer becomes zero.

[0016] Further, the discarding step of the packet discarding method may be configured such that, when the cell located at the head of the packet arrives, the occupancy of the cell buffer is larger than the packet discard threshold. , The packet may be discarded.

Further, the counting step and the discarding step may be performed on the cells constituting the packet and having a predetermined attribute, and the predetermined attribute may be: VCI /
It may be a VPI.

Further, the counting step and the discarding step include the steps of:
It may be performed for each I.

As described above, in the present invention, the length of the packet being stored is monitored. Then, when discarding the cells stored in the cell buffer,
Even if the cell buffer occupancy threshold is exceeded, if the cell buffer does not overflow and the remaining number of unstored cells of the packet is found to be small, Are all stored. By adopting such a configuration, it is possible to prevent a packet that can be stored just barely from the capacity of the cell buffer from being discarded, and it is possible to use the bandwidth efficiently.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The cell discarding method of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a configuration diagram of an ATM switch according to one embodiment of the present invention. In the present embodiment, although only one cell buffer is physically indicated by 106, logically, a cell buffer exists individually for each VCI / VPI, and different VCI / VPIs Is not written to It is also assumed that the packet discard service is performed for each predetermined VCI / VPI.

The ATM switch according to this embodiment has a VCI
/ VPI extraction circuit 101, cell buffer 106, AAL
(5) A final cell extracting circuit 102, a cell counter 103, a packet length comparing circuit 104, and an EPD determining circuit 105.

Cell counter 10 for counting cell pulse 2
3 outputs a packet length signal 4 and inputs it to the packet length comparison circuit 104. The packet length threshold signal 5 is input to the packet length comparison circuit 104, and the packet length signal 4
Is compared to The packet length comparison circuit 104 outputs a long packet selection signal 6 as a comparison result, which is input to the EPD determination circuit 105. AAL5 last cell extraction circuit 1
From 02, the packet head position 8 is output and input to the EPD determination circuit 105. The buffer occupancy 8 and the cell output 10 are output from the cell buffer 6. The buffer occupancy 8 is input to the EPD determination circuit 105, and the cell output 10 is output from the output terminal B. The packet discard threshold signal 7 is input to the EPD determination circuit 105. EPD decision circuit 1
05, a cell discard signal 9 is output and the cell buffer 1
06.

Hereinafter, the operation of this embodiment will be described. FIG. 3 is a timing chart showing the operation of the present embodiment. In the present embodiment, the capacity of the cell buffer 106 is 256 cells, and the packet length threshold is 250. Also, in FIG. 3, VCI / VPI = 1/1 and VCI / V
Operations for two cases of PI = 2/1 will be described. Among them, when VCI / VPI = 1/1, the cell discarding according to the present invention is performed, and when VCI / VPI = 2/1, the conventional EPD is performed. The VCI / VPI value and the cell number in the packet are, for example, "1/1" in each cell in FIG.
-1 ". In this example, VCI / VPI = 1
/ 1, indicating that it is the first cell in the packet. Also, in FIG. 3, the number 7 with a circle, such as “1 / 1-”, indicates that it is the last cell of the packet for the VCI / VPI = 1/1.

In FIG. 1, a cell input signal 1 input from an input terminal A is input to a VCI / VPI extraction circuit 101 and a cell buffer 106.

Among them, the VCI / VPI extraction circuit 101
From the cell pulse 2 and the selected VCI / VPI cell 11
Is output, the selected VCI / VPI cell 11 is input to the AAL5 final cell extraction circuit 102, and the cell pulse 2 is input to the cell counter 103. The selected VCI / VPI cell 11 is a predetermined VCI / VPI cell.

In the AAL5 last cell extracting circuit 102, AAL T is inputted from the input selected VCI / VPI cell 11.
The last cell of the packet of type 5 is extracted, the next cell of the last cell of the packet is determined as the packet head cell of AAL Type 5, and a signal indicating this position is output as the packet head position signal 3. The AAL Type 5 packet has a configuration in which a special cell serving as a trailer is arranged only at the end. Whether it is a trailer can be determined by the polarity of the CLP bit of the cell. Therefore, by monitoring the CLP bit of the cell, the last cell of the packet can be extracted. The next cell following the last cell is the first cell of the packet.

In the cell counter 103, AAL Type
The length of the packet is detected by counting the cell pulse 2 of e5, and is output to the packet length comparison circuit 104 as the packet length signal 4. Note that the cell counter 103
It is reset at the falling part of the packet head position signal 3.

The packet length comparing circuit 104 compares the input packet length signal 4 with the packet length threshold signal 5, and determines that the input packet is a long packet when the packet length signal 4 is equal to or larger than the packet length threshold. Then, a long packet selection signal 6 is output. For example, IP packet is AAL
When the packet is converted into Type 5 packets, the maximum packet length as AAL Type 5 is 32 cells. Therefore, 30 cells that are two less than 32 cells are set as the packet length threshold value 5.
A packet having a packet length of 30 cells or more is determined to be a long packet, and a long packet selection signal 6 is output.

The cell buffer 106 writes the input cell input signal into its own storage area, and outputs the VCI / VP
I or according to a band assigned to a plurality of VCI / VPI groups. Here, if the allocated band is smaller than the band of the input cell, the cell stays in the cell buffer 106. At this time, if the staying amount exceeds the capacity of the cell buffer, the buffer overflows and the cell is discarded. In the present embodiment, EPD is used to cope with the stagnation of the buffer. In such a case, the EPD is one of the methods of discarding the packets collectively instead of discarding the cells constituting the packets. The EPD monitors the buffer occupancy 8 of the cell buffer 106 and, when the buffer occupancy 8 becomes equal to or larger than the packet discard threshold, the last AA written in the cell buffer.
The packet of L Type 5 is discarded from the head (the position specified by the packet head position signal 3), and the AAL Type input after the packet exceeds the packet discard threshold value
The writing of the cell of the packet of e5 to the cell buffer is realized by stopping until the packet head position signal 3 indicating the position of the head cell of the next packet is input.

In the case of VCI / VPI = 1/1 in this embodiment, the long packet selection signal 6 is further used to determine whether or not to perform EPD. When the buffer occupancy signal 8 becomes equal to or greater than the packet discard threshold indicated by the packet discard threshold signal 7, the long packet selection signal 6 is used to determine how much of the discarded packet has been written. Conventionally, EPD was immediately performed when the buffer occupancy signal 8 reached the packet discard threshold. In this embodiment, however, when the packet length is equal to or greater than the packet length threshold signal 5, It is determined that the remainder of the packet (the number of cells up to the last cell) is already small, and EPD is not performed on the packet.

For example, when the buffer occupancy signal 8 reaches the packet discard threshold (250), the number of cells from the beginning of the packet is 31 cells, the IP packet is converted into AAL Type 5 packets, the AAL Ty
The maximum packet length as pe5 is 32 cells. For this reason, abnormal or non-IP packets are sent to AAL Ty
Except for the packetization of pe5, it is determined that this packet has only one cell remaining. At this time, E
Although it is about to implement PD, it can be seen from the buffer occupancy signal 8 and the packet length signal 4 that the buffer capacity is still large enough to accommodate the remaining cells of the packet, so that the discard is not performed. . Further, the cells subsequent to the cell are also written into the cell buffer 106, and the portion of the packet remaining in the cell buffer 106 from the head cell is not discarded. If a true buffer overflow occurs, EPD or cell discard is performed. The above control is performed by the EPD determination circuit 105.
FIG. 2 is a configuration diagram of the cell buffer 106, showing the arrangement of the buffer overflow and the packet discarding threshold 7.

With the above operation, occurrence of EPD of a long packet which has been written in the cell buffer 106 is suppressed.

[0034]

As described above, in the cell discarding method of the present invention, the length of the packet being stored is monitored, and the number of unstored cells of the packet determined as a result is also used as a material for judging cell discard. Used as When discarding the cells stored in the cell buffer, even if the threshold of the occupancy of the cell buffer used as a judgment material in the prior art is exceeded, the cell buffer does not overflow, In addition, when it is determined that the packet is relatively long and the number of remaining unstored cells is small, all the unstored cells are stored. By adopting such a configuration, it is possible to prevent a packet that can be stored as much as possible in view of the capacity of the cell buffer and that has a large number of cells from being discarded. Along with this, it is possible to efficiently use the bandwidth of the network especially when switches are connected in multiple stages.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a cell buffer according to an embodiment of the present invention.

FIG. 3 is a timing chart showing the operation of the embodiment of the present invention.

[Explanation of symbols]

 1 Cell input 2 Cell pulse 3 Packet head position signal 4 Packet length signal 5 Packet length threshold signal 6 Long packet selection signal 7 Packet discard threshold signal 8 Buffer occupancy signal 9 Cell discard signal 10 Cell output 11 Selected VCI / VPI cell 101 VCI / VPI extraction circuit 102 AAL5 last cell extraction circuit 103 cell counter 104 packet length comparison circuit 105 EPD determination circuit 106 cell buffer

Claims (12)

[Claims] 1. An ATM switch device for switching cells input in packet units, wherein said ATM switch device stores said cells and outputs the number of stored cells as a buffer occupancy signal. A cell buffer for erasing cells stored according to a cell discard signal input from the outside, counting the number of cells constituting the packet, comparing the result with a predetermined packet length threshold, and When the packet length signal is smaller than the packet length threshold and the buffer occupancy signal is larger than a predetermined packet discard threshold signal, the cells constituting the packet are deleted from the cell buffer. And a cell discard signal generating circuit for outputting the cell discard signal. Switch. 2. An ATM switch device for switching cells input in packet units, wherein said ATM switch device stores said cells, and outputs the number of stored cells as a buffer occupancy signal. A cell buffer for erasing cells stored according to a cell discard signal input from the outside; a cell counter for counting the number of the cells constituting the packet, and outputting a counting result as a packet length signal; A packet length comparison circuit that compares the signal with a predetermined packet length threshold, and outputs the result as a long packet selection signal; a final cell extraction circuit that outputs a packet head position signal indicating the head position of the packet; The long packet signal indicates that the packet length signal is smaller than the packet length threshold, and When the buffer occupancy signal is larger than a predetermined packet discard threshold signal, an EPD determination circuit that outputs the cell discard signal for erasing the cells constituting the packet from the cell buffer. An ATM switch device comprising: 3. The ATM switch device according to claim 2, wherein said EPD determination circuit is configured to output the buffer occupancy signal indicating that the remaining capacity of said cell buffer is zero. An ATM switch device for outputting the cell discard signal. 4. The ATM switch device according to claim 2, wherein said EPD determination circuit is configured to control said buffer when said first cell arrives. The ATM switch device outputs the cell discard signal even when the occupancy signal is larger than the packet discard threshold signal. 5. The ATM switch device according to claim 2, wherein said ATM switch device comprises:
The M switch device further receives the cell, outputs a selected cell having a predetermined attribute among the cells, supplies the selected cell to the final cell extraction circuit, and further generates a cell pulse every time the selected cell arrives. A virtual channel identifier / virtual path identifier (hereinafter, referred to as VCI / VPI) which is output and supplied to the cell counter.
An ATM switch device comprising an extraction circuit. 6. The ATM switch device according to claim 5, wherein the selected cell having the predetermined attribute is a selected VCI / VP having a predetermined VCI / VPI.
An ATM switch device comprising an I cell. 7. A packet discarding method for controlling discarding of a packet stored in a cell buffer, comprising: a counting step of counting the number of cells included in an input packet; and wherein the number of cells is smaller than a predetermined packet length. And discarding the packet when the occupancy of the cell buffer is greater than a packet discard threshold determined by the capacity of the cell buffer. 8. The packet discarding method according to claim 7, wherein in the discarding step, the packet is discarded even when the remaining capacity of the cell buffer becomes zero. Method. 9. The packet discarding method according to claim 7, wherein the discarding step is performed when the cell located at the head of the packet arrives. A packet discarding method, wherein the packet is discarded even when the cell buffer occupancy is larger than the packet discard threshold. 10. The packet discarding method according to claim 7, wherein said counting step and said discarding step are performed in said cells constituting said packet, and are performed in advance. A packet discarding method for a packet having a given attribute. 11. The packet discarding method according to claim 10, wherein the predetermined attribute is a VCI / VPI assigned to the cell. 12. The packet discarding method according to claim 7, wherein the counting step and the discarding step are performed by using a VCI / CCI assigned to each cell constituting the packet. A packet discarding method which is performed for each VPI.