JPH09214520A - ATM cell relay device - Google Patents

Abstract

(57) Abstract: To effectively use an ATM cell buffer and reduce frame discard in an ATM network. In an ATM cell relay device having a buffer for accumulating ATM cells on an ATM network and an ATM line of at least two ports, ATM cell receiving means for receiving ATM cells from the ATM line,
A reception cell buffer that stores the received ATM cell, and an ATM cell that is received after the threshold of the reception cell buffer is exceeded are discarded, and a final cell of a dummy frame that causes a CRC32 error at the transmission destination is generated. It comprises a relay management means to be inserted into the reception cell buffer and an ATM cell transmission means to sequentially transmit the ATM cells stored in the reception cell buffer based on the header information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a higher-order frame such as an IP frame for ATM (Asynchronous
Transfer Mode) An AT that makes a cell and communicates
More specifically, the present invention relates to an ATM cell relay device for an M network.
AAL5 (ATM Adaptation La), which is one of the ATM adaptation layers, is provided between the TM terminating devices.
VC (Virtual Channel) by yer 5)
The present invention relates to a technique effective when applied to an ATM cell relay device when performing communication using e.

[0002]

2. Description of Related Art AAL5's Best Effort, which is one of the traffic control technologies in ATM networks.
In the t-class, the AT with the maximum bandwidth in the ATM cell relay device
Since an attempt is made to transfer M cells, ATM cell discard may occur for burst traffic.

As a method of UPC of AAL5's Best Effort class, Partial Packet is used.
Discard (PPD) and Early Packe
There is tDiscard (EPD).

In the former PPD, as shown in FIG. 8, when cell discard occurs due to ATM cell buffer overflow of the ATM cell relay device, a group of cells forming the same frame arriving after that is sent to the ATM cell relay device. Discard on arrival.

The AAL5 frame is stored in the payload portion of each cell every 48 bytes and is transmitted to the destination ATM termination device through the ATM network.

In the AAL5 layer on the receiving side, the payload parts of the cells are spread in the frame assembly buffer in the cell arrival order, and the cell in which the PT (payload type) frame final cell display is detected is recognized as the last cell of the frame. . At this time, the frame confirms by CRC32 whether the content of the frame is correct.

In this AAL5 system, only the discrimination as to whether or not the next cell exists is not possible, and the cell at the head of the frame cannot be detected.

Therefore, the cell that first arrives at the VC is recognized as the frame head cell.

[0009] Therefore, the ATM cell relay device receives the beginning portion of the frame discarded from the middle and the last cell of the frame by the ATM cell relay device which is receiving and discarding the PP.
The normally arrived frame that has been relayed when D is released is regarded as the same frame as the first half of the frame whose latter half was discarded by the ATM cell repeater.

As a result, in the ATM terminating device, the head portion of the first-arrival frame and the last-arrival normal frame are subject to CRC32 computation, and a mismatch occurs with the result of computation of the normal CRC32 included in the trailer of the later-arrival normal frame.
Two errors are discarded up to the normal frame that arrives later.

In the latter EPD, as shown in FIG. 9, a threshold value is set for the ATM cell buffer capacity of the ATM cell repeater, and a new frame is set when the buffer usage exceeds the threshold value. The frame in which the first cell that constitutes the frame arrives is a method in which all the cells that constitute the frame are discarded.

However, in AAL5, the ATM terminal device does not know the frame length until the last cell of the frame is received. Therefore, it is difficult for the ATM cell relay device to predict and secure a buffer for the call in advance.

Therefore, when the head cell arrives at the ATM cell relay device, even if the ATM cell buffer usage amount is less than the threshold value and the ATM cell is relayed, the cell of the frame passing through the VC already passed by the head cell. , The ATM cell buffer of the ATM cell relay device overflows, and the ATM cell relay device may discard the newly received ATM cell.

In this case, the ATM cells may be indiscriminately discarded with respect to other VCs using the same ATM cell buffer received by the ATM cell relay device.

When the threshold value is lowered so that this phenomenon does not occur, cell discard is started even though there is still a buffer, so that the ATM cell buffer is used less efficiently and is discarded as a whole. The number of frames also increases.

[0016]

SUMMARY OF THE INVENTION As a result of studying the above prior art, the present inventor has found the following problems.

In the case of the conventional PPD described above, A
When one cell is discarded by the TM cell relay device, one or two frames are discarded by the ATM terminating device, and in the case of EPD, the threshold value is set assuming the number of cells arriving at the ATM cell relay device. When more cells than the remaining ATM cell buffer amount of the ATM cell relay device arrive, the ATM cells that are not subject to this control and need not be discarded are also discarded.

An object of the present invention is to provide a technique capable of effectively utilizing the ATM cell buffer and reducing the discard of frames in the ATM network.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0020]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

In an ATM cell repeater having a buffer for accumulating ATM cells on an ATM network and at least a two-port ATM line, an ATM cell receiving means for receiving an ATM cell from the ATM line and its A receive cell buffer for storing received ATM cells,
Relay management means for discarding an ATM cell received after exceeding the threshold value of the reception cell buffer, generating a final cell of a dummy frame having a CRC32 error at the transmission destination, and inserting the cell in the reception cell buffer, and reception thereof. ATM cell transmitting means for sequentially transmitting the ATM cells stored in the cell buffer based on the header information thereof.

[0022]

1 is a block diagram of an AT according to an embodiment of the present invention.
It is a figure for demonstrating M network structure.

In the ATM network of this embodiment shown in FIG. 1, one VC is provided for each of the lines 5 to 7 and the lines 6 to 7 of the ATM cell relay device 1.

The lines 5 to 7 are optical fiber communication lines of 155 Mbps, and the lines 5 to 5 of the ATM cell relay device 1 are used.
ATM terminators 2 to 4 are connected to the terminals 7, respectively.

FIG. 2 is a diagram for explaining the configuration of the ATM cell relay device 1 described above.

The ATM cell relay device 1 of this embodiment is shown in FIG.
As shown in, the ATM receiving unit 11 for receiving ATM cells
And a received cell buffer 1 for storing the received ATM cell
2 and the ATM cell transmission unit 13 that sequentially transmits the reception cells stored in the reception cell buffer 12, and the VPI / VCI of the ATM cell that cannot be stored because it exceeds the threshold of the reception cell buffer and is registered. Reception discard table 14
Upon receiving the threshold overflow notification of the receiving cell buffer 12, the ATM cell is discarded based on the value reception discarding table 14, and immediately after that, the final cell of the dummy frame that causes the CRC32 error is generated and received. The relay management unit 15 is inserted into the cell buffer.

FIG. 3 shows the ATM cell user / network interface (UNI) and network / node interface (NN).
It is a figure for demonstrating the cell structure of I).

UNI and NNI are G headers as cell headers.
FC (general flow control) and VPI (virtual path identifier)
And VCI (virtual channel identifier), CLP (cell loss priority indication), HEC (header error control), and PT (payload type).

Here, when PT is "001", it indicates the user cell / frame last cell, and when it is "011", it indicates the user cell / congested / frame last cell.

FIG. 4 is a diagram showing a frame format of AAL5 applied in this embodiment.

The AAL5 frame includes a high-order protocol frame, PAD (padding), Reg. (Extended area), LEN (length), and CRC32 (cyclic code). Here, the case where the ATM terminating device 2 and the ATM terminating device 3 shown in FIG. 1 transmit to the ATM terminating device 4 will be described. When the total amount of data generated by the ATM terminating device 2 and the ATM terminating device 3 connected to the line 5 and the line 6 of the cell relay device exceeds 155 Mbps, the line 7 passing through the ATM cell relay device has a maximum speed of 155 Mbps. Since only cells can be transmitted, cells are accumulated in a buffer in the ATM cell relay device, and
If the ATM cell buffer of the ATM cell relay device overflows when a cell is received, the cells received from the line 5 cannot be stored in the buffer and are discarded.

In the ATM cell relay device 1, when cell discard occurs in an established call, VP of the discarded cell
The I / VCI is registered in the reception discard table, and the VPI / VCI frame cell registered thereafter is discarded.

At this time, the AAL class of the corresponding VC is AA.
If L5, CR including cell for relayed frame
The last cell of the frame that causes a C32 error is generated and transmitted in the forward direction.

Next, the above-mentioned cell discard and generation of the frame last cell will be specifically described with reference to FIG.

FIG. 5 shows an ATM cell relay device 1 of this embodiment.
4 is a diagram for explaining cell discard and generation of a frame last cell in FIG.

In the case of the common buffer type ATM relay device, as shown in FIG. 1, when a buffer overflow occurs due to the reception of ATM cells, the cells are randomly discarded, resulting in a maximum number of discarded cells. Minute frames are discarded due to CRC32 error at the ATM termination point,
By discarding cells that compose the same frame that arrive after that at the time of arrival at the device, cells to be discarded by the switch are cells C14 (2) that compose the same frame.
1) and cell C15 (22).

At this time, if the ATM cell relay device 1 has already relayed the cell of the same VC to the ATM terminating device B, the ATM cell relay device forwards the VC of the cell forming the discarded frame. Device 1 is ATM termination device B
By generating a frame final cell E27 which causes a CRC32 error of AAL5 at, a CRC32 error is generated (cell group 25) for the cell group 28 (C11 to C13) forming the frame in which the cell discard has occurred, After releasing the VC frame reception buffer, the cell group 24 (C21 to C23) forming the next frame, that is,
The cell group 26 is normally received.

Here, as a method of generating the frame final cell E27 which causes a CRC32 error of AAL5, all relay cells are CRC3 of 32 bits for each VPI / VCI.
The same VP at the time when the ATM cell discard occurs after performing two calculations
A value different from the CRC32 calculation result of I / VCI is used.

Same VPI at the time when ATM cell discard occurs
The value different from the CRC32 calculation result of / VCI is, for example, as shown in FIG. 6, a value obtained by adding 1 to the 32-bit CRC32 calculation result, or a value different from the specified initial value.

Next, the control of the ATM cell relay device 1 of this embodiment will be described with reference to the transition diagram of FIG.

The ATM cell relay device 1 of this embodiment is AA
In the L5 communication, as shown in FIG. 7, for each established call, an “idle” state 45, a “frame relay” state 46, a “dummy cell transmission waiting frame relay” state 47,
It has either a "dummy cell transmission waiting idle" state 48 or a "cell discard" state 49.

When the ATM cell relay device 1 of this embodiment receives one cell, if the cell is the last cell 33 of the frame of AAL5, the state is set to the "idle" state 45, and if the cell 32 is in the middle of the frame, "frame" is set. Transition to the "relay" state 46.

When the frame final cells 30 and 40 of AAL5 are received in the "idle" state 45, no transition is made regardless of relay or discard.

When a cell is discarded by the ATM cell relay device 1 in the "frame relay" state 46, the "dummy cell transmission waiting frame relay" state 47 and the "dummy cell transmission waiting" state are set by the intermediate cell 34 and the frame final cell 44, respectively. Transition to the “idle” state 48.

When the mid-frame cell 31 is discarded in the "idle" state 45, the state transits to the "dummy cell transmission waiting frame relay" state 47.

In the "dummy cell transmission waiting frame relay" state 47 and the "dummy cell transmission waiting idle" state 48,
Until the CRC32 error dummy cells 43 and 42 can be transmitted, the discarding 35 to 38 are repeated, and if the cells 35 and 37 in the middle of the reception frame are discarded, the state transits to the "dummy cell transmission waiting frame relay" state 47 and the last cell 3 of the reception frame.
If 6 and 38 are discarded, "dummy cell transmission waiting idle"
Transition to state 48.

"Dummy cell transmission waiting idle" state 48
When the CRC32 error dummy cell 42 is transmitted during the transmission, the state transits to the "idle" state 45, and when the CRC32 error dummy cell 43 is transmitted during the "dummy cell transmission waiting frame relay" state 47, the remaining frame constituent cells are discarded. Therefore, the state changes to “cell discard” state 49.

In the "cell discard", the receiving cell 39 is continuously discarded, and when the last cell 41 of the frame is discarded, the state transits to the "idle" state 45.

As a result of the above control, the AAL5 frame is discarded at the entrance of the line of the ATM relay device 1 in frame units, so that the number of cells registered in the ATM cell buffer in the ATM relay device decreases, The passing rate of normal frames is improved.

The ATM cell relay device 1 calculates the payload for each VC of all the frame cells to be judged by the PT shown in FIG.
When the TM cell discard occurs, the result of the operation up to that time and the newly generated dummy cell are operated in the same manner as the relayed cell, and the result is the final 4 bytes of the CRC32 check sequence storage area of the dummy cell shown in FIG. Store in and send forward.

In this process, the initial value is initialized every time the last cell of the frame is passed, but the initial value is originally 0.
On the other hand, in this control, it is set to 1 in order to always cause a CRC32 error.

Although a CRC32 error can be generated with certainty by this method described above, it may happen that they coincide with each other or it is difficult to realize them.
By substituting the fixed value 0 into the 32 storage areas, the same effect can be obtained in practice.

Therefore, as described above, the ATM
When the frame transmitted from the terminating device is discarded by the ATM cell relay device, another ATM cell terminating device generates a frame final cell that causes a CRC32 error during frame assembly according to the AAL5 procedure, and sends it to the same VC. By doing so, the preceding pass frame releases the receive buffer of the same VC due to the CRC32 error and the next frame can be received normally. Therefore, the ATM cell buffer is effectively used and the frame is discarded in the ATM network. Can be reduced.

Further, the loss of ATM cells due to congestion causes frame discarding in the ATM terminating device, and it is possible to reduce the frequency of heavy congestion or reduction in throughput caused by the retransmission of the discarded frames.

The present invention is also applied to the case of discarding an ATM cell due to an ATM cell speed violation in the policing of the ATM cell relay device.

As described above, the invention made by the present inventor is:
Although the present invention has been described in detail with reference to the embodiment, the present invention is not limited to the embodiment, and it is needless to say that various changes can be made without departing from the scope of the invention.

[0057]

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.

Effective use of ATM cell buffer
It is possible to reduce the discard of frames in the network.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an ATM network configuration that is an embodiment of the present invention.

FIG. 2 is a diagram for explaining the configuration of an ATM cell relay device 1 of this embodiment.

FIG. 3 ATM cell user-network interface (UN
FIG. 3 is a diagram for explaining a cell configuration of I) and a network / node interface (NNI).

FIG. 4 is a diagram showing a frame format of AAL5 applied in this embodiment.

FIG. 5 is a diagram for explaining cell discard and generation of a frame last cell in the ATM cell relay device 1 of the present embodiment.

FIG. 6 is a diagram showing a calculation formula of CRC32 of AAL5 of the present embodiment.

FIG. 7 is a transition diagram for explaining control of the ATM cell relay device 1 according to the present embodiment.

FIG. 8 is a diagram for explaining cell discard in an ATM cell relay device according to a conventional PPD method.

FIG. 9 is a diagram for explaining cell discard in a conventional ATM cell relay device according to the EPD method.

[Explanation of symbols]

1 ... ATM cell relay device, 2-4 ... ATM termination device, 5
7 ... Line, 11 ... ATM receiving unit, 12 ... Reception cell buffer, 13 ... ATM cell transmitting unit, 14 ... Reception discard table, 15 ... Relay management unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Eiji Takahashi Eiji Takahashi 1 Horiyamashita, Hadano-shi, Kanagawa Hitachi Computer Engineering Co., Ltd. (72) Inventor Kenji Ishida 810 Shimoimaizumi, Ebina, Kanagawa Prefecture Hitachi Factory Office Systems Division

Claims (1)

[Claims] 1. An ATM cell repeater having a buffer for accumulating ATM cells on an ATM network and an ATM line of at least two ports, comprising: ATM cell receiving means for receiving an ATM cell from the ATM line. , A received cell buffer that stores the received ATM cell, and an ATM cell that is received after the threshold value of the received cell buffer is exceeded, and a final cell of a dummy frame that causes a CRC32 error at the destination is generated. An ATM cell relay device comprising: relay management means for inserting the received cell buffer; and ATM cell transmission means for sequentially transmitting the ATM cells stored in the received cell buffer based on the header information.