JP2994217B2 - Buffer management system for ATM node equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a buffer management system in an ATM node device including a buffer memory for temporarily storing an ATM cell in order to select an output line based on a destination described in a cell header for a TM cell. The present invention relates to a buffer management system capable of improving an effective throughput at an upper layer packet level by adding a hardware amount.

[0002]

2. Description of the Related Art In an ATM node device such as an ATM exchange, a buffer memory for collision avoidance is provided in order to prevent collision of ATM cells going to the same output line. The capacity of this buffer memory is finite, and if there is an input exceeding the allowable amount, the overflow occurs and the ATM cells corresponding to the overflow are discarded. Since the upper layer packet lacking even one cell cannot be used by the upper protocol layer, even if it arrives at the destination terminal, it is immediately discarded and retransmitted.

[0003] It is difficult to uselessly store such a useless packet including a cell loss in a cell buffer in an ATM exchange and transfer it to a network after knowing that the packet is unusable from the viewpoint of effective use of network resources. This is undesirable and causes congestion.

[0004]

Heretofore, no special processing has been performed even if a buffer overflow occurs in the ATM exchange. For this reason, a large amount of useless ATM cells already passed through the ATM switch to the network before the cell discard occurs waste network bandwidth, and the cell buffer stored in the cell buffer at the time of the cell discard occurs. There is a problem that the ATM cell group of the VC continuously occupies the buffer area unnecessarily, and furthermore, the ATM cell group flows to the network, so that the band is wasted.

[0005] ATM which constitutes these useless packets
The effect of cell transfer does not remain locally, causing network congestion in a wide range, and as a result, lowering the effective throughput at the upper layer packet level.

An object of the present invention is to provide a buffer management system capable of improving the suppression of the effective throughput which has been a problem in such a conventional method by adding as little hardware as possible.

[0007]

In order to solve the above-mentioned problems, in the present invention, a buffer occupancy counting means for counting an occupancy of a buffer memory and a buffer occupancy measured by the counting means are provided. Logical channel (V
C) a cell discarding management table for each VC which sets whether reception is possible or not is provided. If the setting of the management table is "reception possible", the ATM cell of the logical channel (VC) is received,
If "reception is impossible", the logical channel (VC) is discarded.

[0008]

Before the ATM cells are stored in the buffer, the processing of the ATM cells is determined by referring to the management table. Therefore, unnecessary ATM cells are discarded in advance, stored in the buffer, and then transmitted to the network. No more.

[0009]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a buffer management system according to the present invention, in which the present invention is applied to an ATM exchange. With respect to the configuration of the ATM exchange, a common buffer type is adopted from several switch architectures, but the present invention is also applicable to an individual buffer type in which a cell buffer is individually provided for each input / output line.

In FIG. 1, a portion 20 surrounded by a broken line is a buffer management device according to the present invention.

The input line 13 is connected to a multiplexer 11 via a buffer management unit 20, and the multiplexer 11 is connected to a common cell buffer memory 10, a separator 12, and an output line 14 in this order. Reference numeral 15 in the figure is a switch control circuit.

The buffer management device 20 includes a management control circuit 2
1, a status storage unit 22 storing a VC discarding management table (hereinafter abbreviated as a “management table”), a buffer occupancy counting unit 23 for monitoring the buffer occupancy of the buffer 10, And a corresponding unit 24.

The line handling unit 24 checks the cell header of the arriving ATM cell to detect a VCI (VC identifier), or detects whether the ATM cell is AAL (ATM Ada).
It identifies whether the cell is an EOP (End of Packet) cell indicating the end of the packet. Further, the line corresponding unit 24 includes the management control circuit 2
The ATM cell is discarded in accordance with the discard command from 1.

The management control circuit 21 receives the cell information from the line correspondence unit 24 and updates the management table in the status storage unit 22 with reference to the buffer occupancy detected by the buffer occupancy counting unit 23.

FIG. 2 shows V stored in the status storage unit 22.
3 shows a configuration example of a C-specific cell discard management table 30. The VC-specific cell discarding management table 30 is provided with a column for registering a VCI and a column (1 bit) indicating an attribute corresponding to the column. The ATM column of the VC is receivable (bit “0”) in the attribute column. It indicates whether or not there is no reception (bit “1”).

The management table 30 has about several hundred entries. This is defined as 12 in the ATM transmission system.
It is based on the consideration that at most about several hundred VCIs (4096 bits) are used at the same time.

In the initial state, nothing is registered in the management table 30. When an ATM cell arrives from a new VC having no entry in the management table 30, the ATM cell arrives.
The cell is determined to be the first cell of the upper layer packet (AAL packet), and if the occupancy of the cell buffer at that time is below the threshold, the VCI and the attribute “0” (receivable) are set. If the occupancy of the cell buffer exceeds the threshold, the VCI and the attribute “1” (reception disabled) are displayed in the management table 30.

When a cell is discarded due to a buffer overflow, the attribute of the VC column corresponding to the discarded cell in the table is set to "1" (reception disabled).

With respect to all ATM cells arriving at the ATM exchange, the cell discard management table for each VC is referred to based on the VCI, and if the attribute is "0" (receivable), it is stored in the cell buffer 10 as it is. If the attribute is “1” (cannot be received), the line corresponding unit 24
Based on the discard instruction of the management control circuit 21,
Discard the M cell.

When an EOP cell indicating the end of the AAL packet arrives, the entry of the VC in the management table 30 is deleted, and the free area of the management table 30 is increased for another new VC registration. If an ATM cell from a new VC arrives when there is no free area in the management table 30, all ATM cells from that VC must be unconditionally stored in the cell buffer. As soon as the table 30 becomes empty, it is determined that there is no entry for the arriving cell immediately after the table 30 is empty. In addition, the number of possible entries in the management table 30 is optimized so that the frequency of occurrence of such a situation can be minimized. In the configuration according to this embodiment, the number of entries in the management table 30 is about several hundred, as described above, but this can be implemented by adding a small-capacity hard memory.

Although the management table 30 of the embodiment is configured to register only the VC currently being received, the number of entries is suppressed to about several hundreds. However, it is needless to say that the number of entries is increased and all VCs are registered in advance. You may put it.

Next, the operation of the embodiment will be described with reference to the flowchart of FIG. First, when an ATM cell is input to the line corresponding unit 24 (F1), the VC is referred to the VC-specific cell discarding management table 30 (F2), and it is checked whether the VC has been entered in the management table 30 (F3). If the entry has been made, the attribute is examined next (F4). If the attribute is "0" (receivable), the occupancy of the buffer is measured (F5). If the buffer is not full (F6), the buffer is left as it is. A reception process is performed (F7), and the data is stored in the cell buffer 10 (F8). Finally, the arriving cell is the EOP cell (A
(Indicating the end of the AL packet).
9) If the cell is an EOP cell, the corresponding VC entry is deleted from the management table 30 (F10).

On the other hand, if the attribute is "1" (reception is not possible) in step F4, the ATM cell is discarded by the line corresponding unit 24. In step F6,
Even when the buffer is full, the attribute is changed to "1" (reception disabled) (F12), and the cell is discarded (F1).
3). As a result, the table 30 can be used for new VC registration.
Increase the free space of At this time, if there is an ATM cell already stored in the buffer memory 10, it is discarded because it becomes invalid.

In step F3, the management table 30
If the ATM cell is a new VC ATM cell having no entry, the ATM cell may be regarded as the head cell of the upper layer packet. Therefore, it is next checked whether or not there is a free space in the management table (F14). If there is a free space, the occupancy of the cell buffer 10 at that time is measured (F15). If the buffer occupancy is equal to or less than the threshold (F16), it is determined that all ATM cells for the packet can be accommodated, and the VC
I and the attribute “0” (receivable) are registered in the table 30 (F17). If the occupancy of the cell buffer 10 is equal to or larger than the threshold value (F16), it is determined that cell discard will occur due to buffer overflow soon, and the VC is determined.
I and the attribute “1” (reception disabled) are registered in the management table 30 (F18).

In step F14, the management table 3
If there is no free area of 0, all ATM cells from that VC must be subjected to reception processing unconditionally (F7) and accumulated in the cell buffer (F8). It is determined that there is no entry for the arriving cell, and it is registered in the management table 30, albeit halfway, and its influence can be minimized.

As described above, according to the above-described embodiment, the cell discarding management table 3 for each VC that sets whether or not reception is possible for each logical channel (VC) based on the buffer occupancy.
For a VC whose attribute is “1” in the management table 30 by setting 0, the line corresponding unit 24 discards the cell before inputting to the buffer. As a result, ATM cells constituting useless packets including cell loss do not waste network bandwidth, and of course, cell discarding is concentrated on packets of a specific VC and cell discarding extends to a large number of packets. Thus, the finite cell buffer in the ATM exchange can be effectively used, and the effective throughput of the upper layer packet level can be improved.

An upper layer packet (AAL packet)
If the buffer occupancy at the time of arrival of the first ATM cell constituting the packet exceeds the threshold value, the line handling unit 24 discards all ATM cells constituting the packet until the EOP cell arrives. To This means that this packet will be
This means that the corresponding packet is discarded beforehand in anticipation that the M cell will be lost. However, a useless packet that may include the cell loss does not occupy the buffer for one cell. Thus, it is possible to improve the buffer use efficiency and increase the effective throughput at the upper layer packet level.

Next, specific cases are shown in FIGS.

First, FIG. 4 and FIG.
ATM cell having a VC with an entry in line 2
4 shows an example of the operation when the vehicle arrives at No. 4. FIG. 4A shows the VC
This shows a state when an ATM cell of VC1 having an entry of “0” (receivable) in the separate cell discard management table 30 arrives. Since the attribute is receivable, the upper layer packet transmitted by VC1 has no cell loss yet and its AT
The M cell is determined to be valid, and is subjected to reception processing by the line corresponding unit 24 and then stored in the cell buffer 10 (FIG. 4).
(B)).

FIG. 5A shows “1” in the management table 30.
FIG. 8 is a state diagram when an ATM cell of VC2 having an entry of (reception unacceptable) arrives at a line corresponding unit 24; The reason that the attribute is unreceivable is considered that cell loss has already occurred in the upper layer packet sent by VC2, or that the buffer occupancy when the first cell arrived was equal to or larger than the threshold value. Anyway, this VC2 AT
Since the M cell is completely invalid, it is discarded by the line handling unit 24 (FIG. 5 (b)).

FIGS. 6 and 7 show an operation example when an ATM cell having a VC having no entry in the cell discard management table 30 for each VC arrives at the line corresponding unit 24. FIG. First, FIG. 6 will be described. FIG. 6A shows a state in which an ATM cell of VC3 having no entry in the management table 30 arrives at the line corresponding unit 24 when the occupancy of the cell buffer 10 is equal to or less than the threshold value. Is shown. Since there is no corresponding VC entry in the management table 30, this cell is determined to be the first cell of the upper layer packet, and since the cell buffer 10 has a sufficient free space, all ATM cells for the packet are accommodated. I guess I can do that, and the next state (Fig. 6 (b))
Then, the VCI is stored in the cell discard management table 30 for each VC.
(VC3) and the attribute “0” (receivable) are registered, and the first cell is stored in the cell buffer 10. Unless a cell loss due to a buffer overflow occurs, all ATM cells of the VC 3 arriving thereafter are accumulated in the cell buffer 10 and subjected to exchange processing.

FIG. 7A shows a state in which an ATM cell of VC3 having no entry in the management table 30 arrives at the line corresponding unit 24 when the occupation amount of the cell buffer 10 is equal to or larger than the threshold value. Since there is no corresponding VC entry in the management table 30 as in FIG. 6, the ATM cell is determined to be the head cell of the upper layer packet. However, since the occupation amount of the cell buffer 10 is equal to or larger than the threshold value, it is determined that the upper layer packet constituted by the head cell will include a cell loss due to buffer overflow, and the VCI (VC
4) and the attribute “1” (reception not possible) are registered, and the first cell is discarded by the line corresponding unit 24 (FIG. 7B). All ATM cells of the VC4 arriving thereafter are discarded by the line handling unit 24.

FIG. 8A shows a state in which an ATM cell of VC5 having an entry of "0" in the management table 30 arrives at the line corresponding unit 24 when the cell buffer 10 is full. Since the VC5 can be received, the ATM cell is to be stored in the cell buffer 10.
Since the cell buffer 10 is full, the cell buffer 10 is discarded without abuse. Since this single cell loss completely invalidates the upper layer packet of the VC5, the ATM cells of the VC5 already stored in the cell buffer 10 are discarded, and the bit of the VC5 column of the management table 30 is set to "1". "(Cannot be received)"
All the ATM cells of No. 5 are discarded by the line handling unit 24 (FIG. 8B).

FIG. 9A shows a state in which an EOP cell of the VC 6 having an entry of “1” which cannot be received in the management table 30 has arrived at the line corresponding unit 24. Since the attribute is unreceivable, it is understood that all ATM cells of this VC have been discarded by the line handling unit 24 so far. The arrival of the EOP cell means that all the cells for the packet have arrived for this VC, and that the next ATM cell of VC6 is the first cell of another upper layer packet. Therefore, as shown in FIG. 9B, the entry of the VC6 is deleted from the management table 30 in order to increase the free space of the management table 30, and the VC6 is executed for the next ATM cell (head cell) of the VC6. To prepare for cell discard control based on the buffer occupancy.

FIG. 10A shows a VC 7 having no entry in the management table 30 when there is no free space in the management table 30.
2 shows a state in which the ATM cell of FIG. In this case, the reception processing is unconditionally performed by the line corresponding unit 24 and then stored in the cell buffer 10 (FIG. 10).
(B)).

Although the present invention has been described with reference to an ATM switch, the present invention is not limited to the ATM switch but can be applied to other ATM node devices. For example, ATM
The AAL layer, which is located between the ATM layer, which is the lowest layer of the communication protocol layer in the communication network, and the network layer, and plays a role of data format conversion processing and address conversion processing for connecting the two layers. In an ATM network interface module that executes actual processing, it can also be used as a management system for a cell buffer memory that stores ATM cells for reassembly into upper layer packets.

[0038]

As described above, according to the present invention,
By adding a small amount of hardware, a finite cell buffer can be used efficiently, and this has the effect of improving the effective throughput at the upper layer packet level.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a buffer management system according to the present invention.

FIG. 2 is a diagram illustrating a VC provided in a status storage unit in the embodiment of FIG. 1;
It is a block diagram of another cell discard management table.

FIG. 3 is a flowchart showing a processing procedure for an ATM cell in the embodiment of FIG. 1;

FIG. 4 is a state diagram illustrating a processing procedure when a VC ATM cell having an entry of “0” in the management table in the management table arrives at the ATM exchange in the embodiment of FIG. 1;

FIG. 5 is a state diagram illustrating a processing procedure when a VC ATM cell having an entry of “1” in the management table that cannot be received in the management table arrives at the ATM exchange;

FIG. 6 is a state diagram illustrating a processing procedure when an ATM cell of a VC having no entry in the management table arrives at the ATM exchange when the occupancy of the cell buffer is equal to or less than the threshold value in the embodiment of FIG. .

FIG. 7 is a state diagram illustrating a processing procedure when an ATM cell of a VC having no entry in the management table arrives at the ATM exchange when the occupancy of the cell buffer is equal to or larger than the threshold value in the embodiment of FIG. .

FIG. 8 is a diagram showing an example in which when the cell buffer is full in the embodiment of FIG.
It is a state diagram explaining the processing procedure when the ATM cell of C arrives at the ATM exchange.

FIG. 9 is a state diagram illustrating a processing procedure when an EOP cell arrives in the embodiment of FIG. 1;

10 is a state diagram illustrating a processing procedure when an ATM cell of a VC having no entry in the management table arrives at the ATM exchange when there is no free space in the management table in the embodiment of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Common cell buffer memory 11 Multiplexer 12 Separator 13 Input line 14 Output line 15 Switch control circuit 20 Buffer management device 21 Management control circuit 22 Status storage unit 23 Buffer occupancy calculation unit 24 Line correspondence unit 30 VC cell discard management table

Claims (3)

(57) [Claims] 1. For an ATM cell arriving at an input line,
A buffer management system in an ATM node device including a buffer memory for temporarily storing an ATM cell for selecting an output line based on a destination described in a cell header, wherein the ATM cell occupies the buffer memory. Buffer occupancy counting means for counting the amount; VC-specific cell discarding management table for setting whether or not reception is possible for each logical channel (VC) based on the buffer occupancy measured by the buffer occupancy counting means; If the setting in the table is "receivable", the ATM cell of the logical channel (VC) is received, and "reception is not possible".
The discarding-line means the logical channel (VC) is provided if, without registering the propriety of the reception to the management table in the initial state, not registered in the management table new logical channels ( VC), when the ATM cell arrives, it is determined that the ATM cell is the first cell, and if the buffer occupancy at the time of arrival exceeds a predetermined value, "Receivable"; buffer management system with ", the management control means for setting the management table for the new logical channel (VC). 2. The buffer management according to claim 1, wherein when cell discard due to buffer overflow occurs, “unreceivable” is set for a logical channel (VC) corresponding to the discarded cell in the management table. system. 3. An entry for a corresponding logical channel (VC) is deleted from said management table when an EOP cell indicating the end of an AAL packet is detected by said line corresponding means . 3. The buffer management system according to item 2.