JP2000341274A - Method for controlling cell discarding in atm switching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the frequency of AAL5 retransmission of a frame by making it possible to store cells up to the discarding threshold of discarded nonpreferential cells in a buffer queue even when the cell discarding priority(CDP) of the final cell of the frame has discarding priority specification. SOLUTION: When a cell inputted from a line interface part 50 exceeds a discharging threshold for CLP, a cell discarding control part 61 discards the cell. At this time, when the inputted cell has CLP=1, the cell is not discarded by a frame final cell management flag 63, but stored in a buffer even if the threshold of the buffer is exceeded on condition that the frame final cell with PT(Payload type)=1 the final cell management flag are inactive. Then when a cell taken out of the buffer is the frame final cell with PT=1, the final cell management flag is set active at the time of transmission and when not, the flag is set inactive, so that the cell is outputted to a line interface part 51.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for reducing the number of AAL5 frame retransmissions by effectively utilizing a buffer queue in an ATM switching apparatus.

[0002]

2. Description of the Related Art In an ATM switching apparatus, when a cell buffer width congestion occurs in the ATM switching apparatus or a UPC (Usage Paramete) is used as a traffic control method.
erControl), there is a priority discard function that preferentially discards a cell when an infringing cell is detected and guarantees an important cell as much as possible. The priority disposal function is
Cell discard priority in ATM cell header (CL
Cell drop priority designation by P) field (CLP = 1)
And a cell discard non-priority designation (CLP = 0).

Here, the prior art will be described by taking as an example the cell buffer width congestion in an ATM switching apparatus. In the conventional priority discard function, as shown in FIG.
Thresholds for limiting the amount of cells stored for each cell discard priority (threshold 2 for CLP = 0, CLP
This is realized by setting a threshold value 3) for = 1 and restricting the accumulation of cells in the buffer queue exceeding the discard threshold value. When recognizing a frame in AAL5, the payload type (PT) in the cell header
In the display between the ATM layer and the user embedded in the field, it is recognized as the top and continuation cell of the frame (PT = 0) or the last cell of the frame (PT = 1). However, when cells are accumulated in excess of the discard threshold 3 of the discard priority designation, even if the cell is the last cell in the frame, the cell whose cell discard priority is the discard priority designation (CLP = 1) is accumulated in the buffer queue. Discarded without being. For this reason, in the AAL5 frame recognition in the end terminal, the abnormal frame in which the last cell is missing and the next received frame are erroneously recognized as one frame. Therefore, CRC-3 for verifying the normality check of the frame is performed.
2, an error is detected, and as a result, retransmission of two frames, that is, retransmission of the abnormal frame and retransmission of the next normal frame received, becomes necessary.

[0004]

In the above prior art, A
In the frame transfer of the TM switching technology, for example, the frame transfer using AAL5, the delimiter of the frame is recognized by the last cell of the frame indicated by the payload type in the received cell header. However, even if the cell is the last cell of the frame, if the cell discard priority is the discard priority, if the cells are already accumulated up to the discard threshold of the discard priority specified cell and the buffer queue is exhausted, the end of the frame Cells are discarded without being stored in the buffer queue. For this reason, in the frame recognition in the end terminal, the abnormal frame lacking the last cell and the next received frame are erroneously recognized as one frame. As a result, it is necessary to retransmit to a normal frame due to the influence of the abnormal frame. Problem arises.

[0005] An object of the present invention is to solve such problems and to make effective use of the buffer queue to achieve AAL5.
And a method for reducing the number of retransmissions of frames in the above.

[0006]

In order to solve the above problems, in the present invention, in the frame transfer using the ATM switching technique, for example, the frame transfer using AAL5, the cell discard priority of the last cell of the frame is a discard priority designation. This also allows cells to be stored up to the discard threshold of the discarded non-priority cells in the buffer queue. As a result, the last cell of the frame is protected, and the erroneous recognition of the frame does not affect the frame received next to the abnormal frame. Further, when all the last cells of the frame specified to be discarded are stored in the buffer queue, the buffer queue may be depleted, which may affect discarded non-priority specified cells. For this reason, a flag for managing the last cell of the frame is provided, and when the second last cell is received while the first last cell is received in the buffer queue, the flag is stored in the buffer queue of the second last cell received later. Is not stored. Then, by discarding the second last cell received later, it is possible to effectively use the buffer queue and reduce the number of retransmissions of the frame.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described with reference to the drawings.

FIG. 1 is a diagram showing a cell discarding threshold with respect to a buffer queue and a cell discarding priority of an ATM switching apparatus according to the present invention. In the buffer queue 1 in the ATM exchange, the cell discarding threshold of CLP = 1 is conventionally set as 3, but in the present invention, the cell containing the header of CLP = 1 and PT = 1 and the CLP
By similarly setting the discarding threshold value of the cell including the header of = 0 as 2, the last cell of the frame in AAL5 can be protected.

FIG. 2 is a diagram showing AAL5 frame reception, frame recognition and retransmission frames according to the present invention. 10 to 11 are cells including a header of CLP = 1 and PT = 0, 12 is a cell including a header of CLP = 1 and PT = 1, 20 is a cell including a header of CLP = 0 and PT = 0, and Reference numeral 21 denotes a cell including a header of CLP = 0 and PT = 1. Conventional frame recognition in AAL5 when cells are received in the order of 10, 11, 12, 20, 21 is performed as follows. When cells can be sufficiently stored in the buffer queue of the ATM switching apparatus, the end terminal sets cell 10 with PT = 0 to the beginning of the frame, cell 11 with PT = 0 to the continuation of the frame, and cell 12 with PT = 1 to the frame. Of the frame 100 as the end of the
The cell 20 of = 0 and the cell 21 of PT = 1 are recognized as one frame 200. The problem with the prior art is that, for example, when cells 10 and 11 are stored in the buffer queue of the ATM switching device, cells are stored up to the discard threshold 3 at CLP = 1, and subsequently received CLP = 1 and PT = 1. Occurs when the last cell 12 of a frame is discarded, and the subsequent cells 20 and 21 are stored in the buffer queue since CLP = 0, so that the cells 10, 11, 20, and 21 are stored at the end terminal. That is, one frame 300 is recognized. Therefore, the frames that need to be retransmitted due to misrecognition of frame 100 are frames 100 and 200. In the present invention, even when cells are accumulated up to the discard threshold 3 in CLP = 1, CLP = 1,
By allowing cells with PT = 1 to be stored up to the discard threshold 2, no frame retransmission is performed in this example. In addition, when the cell 10 is stored, the cell is stored up to the discard threshold 3 in CLP = 1, and then the received cell 11 is stored.
Is discarded, the cell 12 can be stored with PT = 1,
Only the frame 100 related to the abnormal frame needs to be retransmitted. As described above, according to the present invention, the number of retransmissions of a frame can be reduced. But C
If the last cell with LP = 1 and PT = 1 is continuously received, there is a possibility that cell accumulation with CLP = 0 may be prevented.
The invention for avoiding this will be described with reference to FIGS.

FIG. 3 shows CLP = 1 and PT in AAL5.
= 1 is an example of continuous reception of the last cell, where 30 to 31 and 40 are cells with CLP = 1 and PT = 1, and 30 to 31
Is set to VC = 10, and 40 is set to VC = 20. FIG. 4 shows CLP = 1 and PT = 1 in AAL5.
Indicates the state of the last cell management flag when the last cell is received in the order of 30, 31, and 40. In the present invention, a management flag of the last cell is provided in the ATM switching device, for example, for each VC, and a CL
In the state where the last cell including P = 1 and PT = 1 is set to be active at the time of transmission, and the other cells are set to be inactive at the time of transmission, and the same VC is received while the cell of CLP = 1 and PT = 1 is received,
When a cell with CLP = 1 and PT = 1 is received, if the last cell management flag is active, the cell is discarded to prevent the buffer queue from being exhausted. The initial state of the last cell management flag is set to all inactive as shown in FIG.
At the time of transmission of the cell 30, the cell is the last cell of CLP = 1 and PT = 1, so the last cell management flag of VC = 10 is set to active, and the state of the last cell management flag at that time is shown in FIG.
It becomes like (2). Subsequently, the received cell 31 is cell 3
Since it is the same VC as 0 and the last cell management flag is active, it is discarded without being stored in the buffer queue, and the state of the last cell management flag is as shown in FIG. The following cell 40 is V
Since C = 20 and the last cell management flag is inactive, the last cell management flag is accumulated in the buffer queue, and the state of the last cell management flag when the cell 40 is transmitted is as shown in FIG. By managing the last cell in this way, the buffer queue is effectively used.
In this example, the cell management flag is provided for each VC.
The same effect can be obtained by providing one cell management flag for two or more VCs.

FIG. 5 is a diagram showing a cell switching process of the ATM switching device according to the present invention. Line interface unit 5
A process in which cells input from 0 to the ATM switching device 60 are output to the line interface unit 51 will be described.
The cell input from the line interface 50 is checked by the buffer management unit 62 for the discard threshold for the CLP. If the cell exceeds the threshold, the cell input by the cell discard control unit 61 is discarded. At this time, if the input cell is a cell with CLP = 1, the frame last cell with PT = 1 and the last cell management flag are inactive by the frame last cell management flag 63 that manages cells for each VC. This is checked, and if so, even if the threshold value of the buffer is exceeded, the cell is stored in the buffer without being discarded. If the cell taken out from the buffer is the last cell of the frame of PT = 1, the last cell management flag is set to active at the time of transmission, and if it is any other cell, the last cell management flag is set to inactive and sent to the line interface unit 51. Is output. By such processing, it becomes possible to effectively use the buffer queue in the ATM switching device,
The number of frame retransmissions in AAL5 can be reduced.

[0012]

According to the present invention, even if the cell discard priority of the last cell of the frame is the discard priority designation in AAL5 in the ATM switching technology, the cells are accumulated in the buffer queue up to the discard threshold of the discard non-priority designated cell. To prevent the frame received after the abnormal frame due to misrecognition of the frame, and when the last cell of the frame specified with discard priority is accumulated in the buffer queue, the buffer queue is exhausted and discarded. Since there is a possibility of affecting non-priority designated cells, it is possible to reduce the number of frame retransmissions by managing the last cell of the frame and making effective use of the buffer queue.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cell discarding threshold with respect to a buffer queue and a cell discarding priority in an ATM switching device according to an embodiment of the present invention.

FIG. 2 is a diagram showing AAL5 frame reception, frame recognition, and retransmission frames according to one embodiment of the present invention.

FIG. 3 is a diagram showing continuous reception of the last cell in AAL5 according to one embodiment of the present invention.

FIG. 4 is a diagram showing a state of a last cell management flag according to an embodiment of the present invention.

FIG. 5 is a diagram showing a cell switching process in an ATM switching device according to one embodiment of the present invention.

[Explanation of symbols]

1 ... Buffer queue of ATM switching device 2 ... Discard threshold of cell including header of CLP = 0 and CLP = 1, PT = 1 3 ... Discard threshold of cell including header of CLP = 1 10 , 11 ... CLP = 1, cell containing a PT = 0 header, 12 ... CLP = 1, cell containing a PT = 1 header, 20 ... CLP = 0, cell containing a PT = 0 header, 21 ... CLP = 0, a cell including a header of PT = 1, 30, 31... A cell including a header of CLP = 1, PT = 1, VC = 10, 40... A cell including a header of CLP = 1, PT = 1, VC = 20 50, 51: Line interface unit, 60: ATM switching device, 61: Cell discard control unit, 62: Buffer management unit, 63: Frame last cell management flag, 100: Frame composed of 10 to 12; Frame constituted by 0 to 21, a frame constituted by 300 ... 10,11,20,21.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shingo Morikawa 6-26-3 Minamioi, Shinagawa-ku, Tokyo Inside the Hitachi Information Network Co., Ltd. (72) Inventor Takehiko Milk 6-26 Minamioi, Shinagawa-ku, Tokyo No. Within the Hitachi Information Network Co., Ltd. (72) Motohide Nomi, Inventor 1-Horiyamashita, Hadano-shi, Kanagawa F-term in the Enterprise Server Division, Hitachi, Ltd. 5K030 GA06 GA08 HA10 HB17 HB29 KX11 LA03 LC18 LE05

Claims (3)

[Claims] An ATM switching device judges information on the last cell of a frame provided in an ATM cell header, and if the cell is the last cell, designates cell discard priority of cell discard priority information as cell discard priority. A cell discarding control method characterized by determining priority designation. 2. The cell discard control method according to claim 1, wherein the received second final cell is determined to be discarding priority while the first final cell is determined to be discarding non-priority. Cell discard control method. 3. The cell discard control method according to claim 2, wherein when the second final cell is a single frame, the second final cell is determined to be non-prioritized. Cell discard control method.