JP2001144764A - Cell scheduling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell scheduling device capable of holding a cell interval at a prescribed value and suppressing the fluctuations of the cell interval in a prescribed range in the case of controlling the contention of cells belonging to the same connection. SOLUTION: This device is provided with a transmission time deciding means, a buffer memory, a cell transmitting means, a connection linkage means which preliminarily defines the number of transmissible maximum cells at each transmission time, stores a pointer instructing the address of the buffer memory where the cells are stored and connects the cells of the same connection according to the pointer, and a cell moving means which moves cells that can not be transmitted when cells surpassing the number of transmissible maximum cells are stored and cells connected to a connection link to which the cells belong to another entry. The device can also be provided with a movement postponing means which postpones moving cells to the other entry when the cells can not be transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cell scheduler for shaping fixed-length packets such as ATM cells (hereinafter simply referred to as "cells").

[0002]

2. Description of the Related Art Cell shaping is a function of transmitting input cells at intervals of at least a predetermined cell interval in connection units. A functional element of the cell scheduler includes: a transmission time determining unit that determines a cell transmission time for each connection based on a transmission cell rate;
A buffer memory for storing a cell in an entry corresponding to the cell transmission time; and a cell transmission means for transmitting a cell stored in the buffer memory in accordance with the cell transmission time.

In such a cell scheduler, cells input for each connection are assigned a cell transmission time for each connection by transmission time determination means based on a transmission cell rate, and are stored in a buffer memory. Is sent out to the communication network when. In this case, the means for allocating the cell transmission time is known as GCRA, and there is also known an example in which the buffer memory performs control in the case of contention in which the transmission times of the cells of two or more connections are the same.

[0004] An example of a conventional means for controlling competition in which cell transmission times are the same is the ring calendar method (E. Wallmeier, T. Worster, "The Spacing Policser, An.
Algorithm for Efficient Peak Bit Rate Control in A
TM Networks ", International Switching Symposium 199
2, Vol. 2, No. A5.5, pp. 22-26, Oct. 1992). FIG. 1 shows an example of a conventional cell scheduler using the ring calendar system.

In the figure, 101 is a calendar, 102 and 108 are calendar entry heads, 103 and 109 are calendar entry tails, 104, 106 and 110 are cell data, 105 is a pointer to the next data 106, and 107 is here. data
Contains NULL indicating the end of the list starting with 104. The list is a linear list. A combination of a calendar entry head and a calendar entry tail is defined as an entry. One entry corresponds to one cell cycle.
The calendar entry head holds a pointer to the head of the list held in the entry, and the calendar entry tail holds a pointer to the tail of the list held in the entry.

Reference numeral 111 denotes a pointer for marking an entry to be transmitted. The pointer 111 indicates the entry 102/103 according to a predetermined time width, and then the entry 108/103.
Mark cyclically as in 109. 112 is an output list head, 113 is an output list tail, and 114 is an output list. Output list head 112 is output list 114
The output list tail 113 holds a pointer to the tail of the list held in the output list 114.

In this device, T is the current time, D is the delay time calculated by the cell transmission time determining means, N is
If ca is the number of entries, when a certain cell is entered,
Cell transmission time X = INT ((T +
D) Determine mod Nca). INT () represents the integer part. The cell is linked to a list of entries corresponding to the cell transmission time X. Pointer 111 marks a calendar entry every one cell cycle time. Here, it is assumed that the entry 102/103 is marked. Cell data 104 and 106 of marked calendar entries are output list
Connected to 114 tails. The cells in the output list are transmitted in the cell cycle of the transmission line.

As described above, the cell scheduler based on the ring calendar system controls competition of cells at the same time in each connection. For this reason, in the conventional cell scheduler based on the ring calendar system, a cell that has arrived at the cell transmission time and has been moved to the output list in a state where cells to be transmitted exist in the output list belongs to the same connection as the cell to be transmitted. In this case, there is a first problem that the cell interval is shortened. The degree of shortening of the interval between cells belonging to the same connection is CDVT (ce
ll delay variance tolerance: Cell delay variation tolerance
Is allowed, but if it exceeds, it is determined to be a violation cell.

[0009] In the conventional cell scheduler based on the ring calendar system, all cells of the marked entry whose transmission time has arrived are moved to the output list.
There is a second problem that cell control in consideration of CDVT cannot be performed since the cells are sequentially transmitted to the communication network.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cell scheduling apparatus in which the intervals between cells belonging to the same connection are not shortened, and to further take into account cell delay fluctuations. It is to provide a cell schedule device which can perform the above.

[0011]

In order to achieve the above object, a cell scheduler according to the present invention has a transmission time determining means for determining a cell transmission time for each connection based on a transmission cell rate, and sets a cell as a cell transmission time. In a cell scheduler having a buffer memory for storing a corresponding entry and a cell transmitting means for transmitting a cell stored in the buffer memory corresponding to the cell transmission time, the entry may be transmitted at each cell transmission time. The maximum possible number of cells is predetermined, a pointer indicating the address of the buffer memory in which the cell is stored is stored in a pair with the cell, and the pointer paired with the cell stored in the buffer memory is the pointer of the cell. Indicate the address of the buffer memory where the next cell in the connection belongs Connection link means for linking cells of the same connection, and a cell which cannot be transmitted at the cell transmission time when the cell which has reached the cell transmission time has stored more than the maximum number of cells that can be transmitted. And a cell moving means for moving the cell connected to the connection link to which the cell belongs to each other entry.

According to another aspect of the present invention, there is provided a cell scheduling apparatus for storing cells exceeding the maximum number of cells that can be transmitted by an entry reaching a cell transmission time in order to achieve the second object. In the cell transmission time, the maximum number of movement grace times for arranging to move a cell that cannot be transmitted at the cell transmission time and a cell connected to the connection link to which the cell belongs to another entry is predetermined for each connection, When the cells are moved to another entry, the number of movements counting means that counts the number of movements for each connection to which the cell belongs, and when those cells are moved to another entry, the number of movements counted by the movement number counting means. Is compared with the number of grace periods,
If the number of times of movement does not reach the number of times allowed to move, the cell that cannot be transmitted at the cell transmission time stored in the entry that has reached the cell transmission time is moved to another entry and connected to the connection link to which the cell belongs. Each cell is moved to a different entry by means of movement grace means. If the number of movements is equal to or greater than the number of movement grace times, the cell cannot be transmitted at the transmission time and the connection link to which the cell belongs is connected. Cell moving means for moving a cell to each other entry, and reset means for resetting the number of times of movement in a connection to which the cell belongs when the cell is transmitted.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a block diagram showing a configuration example of the cell schedule device of the present invention. The configuration example of FIG. 2A includes a transmission time determining means 201 for determining a cell transmission time for each connection based on a transmission cell rate, and a buffer memory for storing cells in an entry corresponding to the cell transmission time.
202, a cell sending means 203 for sending a cell stored in the buffer memory in accordance with the cell sending time, and a pointer paired with the cell stored in the buffer memory storing the next cell in the connection to which the cell belongs. Connection link means 204 for linking cells of the same connection by designating the address of the buffer memory that stores the data, and stores cells exceeding the maximum number of cells that can be transmitted by the entry that has reached the cell transmission time. In this case, the cell moving means 205 for moving the cell that cannot be transmitted at the cell transmission time and the cell connected to the connection link to which the cell belongs to another entry.
Equipped.

FIG. 2B shows a configuration example of the transmission time determining means 211, the buffer memory 212, the cell transmitting means 213,
The connection link means 214 counts the number of times of movement for each connection to which a cell stored exceeding the maximum number of cells that can be transmitted by an entry reaching the cell transmission time is moved to another entry. When the cells are moved to another entry, if the number of movements does not reach the number of times allowed to move, the number of movements counting means 216 may be a cell that cannot be transmitted at the cell transmission time stored in the entry that has reached the cell transmission time. Is moved to another entry, and the cells connected to the connection link to which the cell belongs move grace means 217 for grace of moving to the other entry. A cell that cannot be transmitted to a cell and a cell connected to the connection link to which the cell belongs Cell moving means 215 for moving the tree, and comprising a reset means 218 which is the cell when the cell is sent to reset the number of movements in connection belongs.

[Embodiment 1] FIGS. 3 and 4 are diagrams for explaining the operation of the example of the configuration of the cell scheduler shown in FIG. 2 (a) which can store the cell interval according to the present invention. FIG. 3 shows the initial state. 301 is the calendar, 302 is the calendar entry head, and 303 is the calendar entry tail. The combination of a calendar entry head and a calendar entry tail is defined as an entry. The calendar entry head holds a pointer to the head of the list held in the entry, and the calendar entry tail holds a pointer to the tail of the list held in the entry.

Reference numeral 304 denotes cell data, 305 denotes cell data 304
Next cell data 312 in connection 1 to which
The pointer 306 holds a pointer indicating the next cell data 307 in the entry 302/303. 307 is cell data, 308 is cell data 30
Next cell data 32 in connection 2 to which 7 belongs
Holds a pointer to 0. 309 is entry 302 /
A pointer indicating the next cell data in 303 is held. Here, since there is no next cell data, NULL is entered to indicate the end of the list.

310 is a calendar entry head, 311
Are calendar entry tails, each of which points to cell data 312. 313 is a pointer to the next cell data of the connection to which the cell data 312 belongs, 314
Holds NULL respectively. 315 is a calendar entry head, 316 is a calendar entry tail, and the head cell 317 and the tail cell 320 of the list, respectively.
Pointing to. 317 holds cell data, 318 holds NULL, and 319 holds a pointer indicating the next cell data 320 in the entry 302/303. NULL for 321 and 322
Enters.

Reference numeral 323 denotes a list of connection 1 to which the cell data 304, 312, and 317 belong (connection link).
Is a pointer indicating the head of the list, and 324 is a pointer indicating the tail of the list. 325 is a pointer indicating the head of the list of the connection 2 to which the cell data 307 and 320 belong, 32
6 is a pointer to the tail of this list. 327 is a calendar entry head, and 328 is a calendar entry tail. Since there is no connection, NULL is entered to indicate the end. 329 is a pointer for marking the entry to be sent. The pointer 329 is set to 302/303, according to a predetermined time width (cell cycle time).
Mark cyclically in the order of 310/311, 315/316, 327/328. That is, the calendar 301 as a set of entries can be regarded as a time axis.

FIG. 4 shows a state after a time (entry cycle time) corresponding to the number of cells that can be transmitted by one entry has elapsed from the state shown in FIG. Reference numeral 401 denotes a state in which the cell data 307 has moved to the entry at the next transmission time, and 402 corresponds to the cell data 312. Reference numeral 403 indicates a state in which the cell data 320 has moved to the entry at the next transmission time. Reference numeral 404 indicates a state where the pointer 329 has marked the entry at the next transmission time. Hereinafter, an operation example of the cell scheduler capable of maintaining the cell interval in this method will be described.

First, the cell 320 is set in the cell scheduler.
The process performed when arrives will be described with reference to FIG. Cell 320
Arrives, the entry to be stored is determined based on the transmission time assigned to the cell by the cell transmission time determination means 201 for each connection based on the cell rate to be transmitted. Here, the entry is 315/316.
The cell is then stored at the end of the list of entries. If the cell stored in the entry 315/316 is only 317, the arriving cell 320 is connected to the tail of the cell 317. Thus, the arriving cell is in the state of cell 320 in FIG. At this time, if the cell 320 has the same connection as the cell 307, the cell 320 is connected to the tail of the connection list. To connect a cell to the list, the pointer 308 indicating the next cell data in the connection points to the cell data 320, and further, the connection entry
326 of 325/326 are cell 32 as end of connection
Indicates 0.

Next, a process for transmitting a cell 304 from the cell scheduler by the cell transmitting means 203 will be described with reference to FIGS. Here, it is assumed that the entry cycle time is one cell time. When one cell time elapses from the state of FIG. 3, the pointer 329 moves to the entry 302/303.
Point to. At this time, since the number of cells that can be transmitted by one entry is one, only the cell 304 is transmitted. Cell 307 that could not be transmitted at this transmission time is the next entry
Moved to head of 310/311 list. With this process,
The sending time assigned to the entry is stored. For entry movement, pointer 310 points 307, pointer 30
9 by pointing to cell 312. The state where the cell 307 has been moved is 401, and the cell 312 is 402. At this time, the cells belonging to the same connection and already scheduled are also moved to the next entry. That is, the cell 320 indicated by the pointer 308 is also moved to the next entry 327/328. The state where the cell 320 has moved to the next entry 327/328 is 403. By this processing, the cell interval of connection 2 is saved.

[Embodiment 2] FIGS. 5, 6 and 7 are diagrams for explaining the operation of the configuration example of the cell scheduler shown in FIG. FIG. 5 shows the initial state. 501 is the calendar entry head,
502 is a calendar entry tail, 503 and 504 are cell data, 505 is a calendar entry head, 506 is a calendar entry tail, 507 is a cell data, 508 is a calendar entry head, 509 is a calendar entry tail, 510 and 511 are cell data, 512 Is a calendar entry head, 513 is a calendar entry tail, and 514 is a pointer that marks the entry to be sent.

Reference numeral 515 denotes the number of movements of the connection 1 (when moving a cell that cannot be transmitted at the transmission time to another entry because the entry reaching the transmission time stores a cell exceeding the maximum number of cells that can be transmitted, The number of times of movement is counted by the number-of-movements counting means 216 for counting the number of times of movement for each connection to which it belongs.
6 is the number of times to move the connection 1 (when the cell that cannot be transmitted at the transmission time is moved to another entry because the entry that has reached the transmission time stores a cell that exceeds the maximum number of cells that can be transmitted) (The maximum number of times that a cell connected to the connection link to which it belongs is allowed to move to another entry).
Cell data 503, 507, and 510 belong to connection 1.

Reference numeral 517 holds the number of times the connection 2 has been moved, and 518 holds the number of times the connection 2 has been allowed to move. Cell data 504 and 511 belong to the connection 2. 519 is the connection 2 to which the cell data 504 belongs
Holds the pointer indicating the next cell data 511 in the. 520 is a pointer pointing to the head of the connection 1 list (connection link), 521 is a pointer to the tail of the list, 522 is a pointer to the head of the connection 2 list, and 523 is the tail of the list. It is a pointer.

FIG. 6 shows that, from the state shown in FIG. 5, a time (entry cycle time) corresponding to the number of cells that can be transmitted by one entry has elapsed when the number of movements of the connection 2 is less than the number of times of movement grace. Indicates the status. 601 indicates a state in which the cell data 504 has moved to the entry at the next transmission time, 602 corresponds to the cell data 507, and 603 corresponds to the cell data 511. Reference numeral 604 holds the number of movements of the connection 2, and 605 holds the number of allowed movements of the connection 2. Reference numeral 606 indicates a state in which the pointer 514 has marked the entry at the next transmission time.

FIG. 7 shows that, from the state shown in FIG. 5, a time (entry cycle time) corresponding to the number of cells that can be transmitted by one entry has elapsed when the number of movements of the connection 2 is equal to or greater than the number of movements. Indicates the status. 701 indicates a state where the cell data 504 has moved to the entry at the next transmission time, 702 corresponds to the cell data 507, and 703 indicates a state where the cell data 511 has moved to the entry at the next transmission time. 704 holds the number of movements of connection 2 and 705
Holds the number of times the connection 2 is allowed to move. Reference numeral 706 indicates a state in which the pointer 514 has marked the entry at the next transmission time. Hereinafter, an operation example of the cell scheduler that allows the cell interval to be shortened up to the CDVT in this method will be described.

First, a cell 511 is added to the cell scheduler.
The processing when arrives will be described with reference to FIG. Cell 511
Arrives, the entry to be stored is determined based on the transmission time assigned to the cell by the cell transmission time determination means 211 for each connection based on the transmitted cell rate. Here, the entry is 508/509.
The cell is then stored at the end of the list of entries. If the cell stored in the entry 508/509 is only 510, the arriving cell 510 is connected to the tail of the cell 317. Therefore, the arriving cell is in the state of cell 511 in FIG. At this time, assuming that the cell 511 has the same connection 2 as the cell 504, the cell 511 is connected to the tail of the connection list. To connect a cell to the list, a pointer 519 indicating the next cell data in the connection
Indicates the cell data 511, and 523 of the connection entries 522/523 have a cell as the end of the connection.
Indicates 511.

Next, a cell 503 is sent from the cell scheduler.
Will be described with reference to FIGS. 5, 6, and 7. FIG. Here, it is assumed that the entry cycle time is one cell time. After one cell time has passed from the state of FIG. 5,
Pointer 514 points to entry 501/502. At this time,
Since the number of cells that can be transmitted by one entry is one, only the cell 503 is transmitted. Therefore, it is necessary to move a cell (excess cell) 504 other than a cell that can be transmitted to the next entry. Therefore, the number of movements in the connection 2 to which the cell 504 belongs is incremented, and the number of movements X (517) is increased. Compare with the grace count Y (518). Movement grace count is INT (CDTV / entry cycle time)
Is a value calculated in advance by Here, the entry cycle time = the number of cells that can be transmitted by one entry × 1
Cell time, where INT () represents the integer part.

When the number of times of movement is less than the number of times of movement grace, only cells that are stored in the entry and cannot be transmitted at the transmission time are moved. At this time, a cell connected to the connection link to which the cell belongs (belonging to the same connection and already scheduled) does not move. This example will be described with reference to FIGS.

The number of movements X (517) in the connection 2 to which the cell 504 which cannot be transmitted at the transmission time belongs (in this example, it is set to 1 and the state is shown in 604) is the number of times of movement grace (Y (518)) (in this example, 2 and its state is 605
If the cell 504 is not transmitted at the transmission time, the cell 504 that cannot be transmitted is moved to the head of the list of the next entry 505/506, but the cell 511 does not move to the next entry 512/513. 601 indicates a state in which the cell 504 has moved, and cell 60
2 corresponds to cell 507, and cell 603 corresponds to cell 511.

The number of movements X in the connection 2 to which the cell 504 that cannot be transmitted at the transmission time belongs belongs to the number of movement grace Y
In this case, as in the first embodiment, the cell stored in the entry and not transmitted at the transmission time and the cell connected to the connection link to which the cell belongs are both moved to the next entry. I do. This example is shown in FIG.
This will be described with reference to FIGS.

The number of movements X (517) of the cell 504 that cannot be transmitted at the transmission time in connection 2 (here, it is assumed to be 2, for example, and the state is indicated by 704) is the number of times of movement allowance Y (51).
8) If it is more than 2 (here, 2 as an example, the status is indicated by 705), the cell 504 that could not be transmitted at the transmission time is moved to the head of the list of the next entry 505/506, and the cell 511 is also transmitted. Move to the next entry 512/513.
701 indicates the state where the cell 504 has moved, and cell 702 indicates the cell
Corresponding to 507, cell 703 indicates a state in which cell 511 has moved. The number of movements in the connection to which the transmitted cell belongs is reset by the reset unit 218 at the time when the cell is transmitted. For example, the number of movements X (517) is
Reset when 504 is sent. This allows
The cell interval between the cell and the next cell can be reduced to the cell interval allowed by the CDVT.

[0033]

As described above, according to the cell scheduler of the present invention, when contention is controlled, the cell interval is maintained at a predetermined value, and the fluctuation of the cell interval is suppressed to a predetermined range. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a conventional cell schedule device.

FIG. 2 is a block diagram illustrating a configuration example of a cell schedule device of the present invention.

FIG. 3 is a diagram illustrating an operation example of a cell scheduler of the present invention that can save a cell interval.

FIG. 4 is a diagram for explaining an operation example of the cell scheduler of the present invention that can store cell intervals.

FIG. 5 is a diagram illustrating an operation example of the cell scheduler of the present invention that allows a cell interval up to CDVT.

FIG. 6 is a diagram illustrating an operation example of the cell scheduler of the present invention that allows a cell interval up to CDVT.

FIG. 7 is a diagram illustrating an operation example of the cell scheduler of the present invention that allows a cell interval up to CDVT.

[Explanation of symbols]

101 Calendar 102, 108 Calendar entry head 103, 109 Calendar entry tail 104, 106, 110 Cell data 105, 107 Pointer 106 Cell data 111 Pointer 112 Output list head 113 Output list tail 114 Output list 201, 211 Transmission time determination means 202 , 212 buffer memory 203, 213 cell sending means 204, 214 connection link means 205, 215 cell moving means 216 movement count means 217 movement grace means 218 resetting means 301 calendar 302, 310, 315, 327 calendar entry head 303, 311, 316, 328 Calendar entry tail 304, 307, 312, 317, 320 Cell data 305, 306, 308, 309, 313, 314, 318, 319, 32
1, 322, 323, 324, 325, 326, 329 pointer 401, 402, 403 Cell data 404 pointer 501, 505, 508, 512 Calendar entry head 502, 506, 509, 513 Calendar entry tail 503, 504, 507, 510 , 511 cell data 514, 519, 520, 521, 522, 523 pointers 515, 517 Number of movements 516, 518 Number of movements 601, 602, 603 cell data 604 number of movements 605 Number of movements 606 pointer 701, 702, 703 cell data 704 Number of moves 705 Number of grace moves 706 Pointer

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Claims (2)

[Claims] 1. A transmission time determining means for determining a cell transmission time for each connection based on a transmission cell rate, a buffer memory for storing a cell in an entry corresponding to the cell transmission time, and a buffer corresponding to the cell transmission time. In a cell scheduler comprising cell transmission means for transmitting cells stored in a memory, the maximum number of cells that the entry can transmit at each cell transmission time is predetermined, and the cell is stored. A pointer indicating the address of the buffer memory is stored in a pair with the cell, and a pointer paired with the cell stored in the buffer memory indicates the address of the buffer memory where the next cell in the connection to which the cell belongs is stored. By doing so, the connection link that connects cells of the same connection If the cell that has exceeded the maximum number of cells that can be transmitted by the entry that has reached the cell transmission time and that has reached the cell transmission time, the cell that cannot be transmitted at the cell transmission time and the connection link to which the cell belongs are connected. A cell moving unit for moving each of the existing cells to another entry. 2. When an entry that has reached the cell transmission time stores cells that exceed the maximum number of cells that can be transmitted, the cell that cannot be transmitted at the cell transmission time is connected to the connection link to which the cell belongs. The maximum number of times that a cell that has been moved to another entry is deferred is determined in advance for each connection, and when those cells are moved to another entry, the number of times that each cell belongs is moved. When the cells are moved to another entry, the number of movements counted by the number-of-movements counting means is compared with the number of times of movement, and if the number of times of movement does not reach the number of times of movement The cell that cannot be transmitted at the cell transmission time stored in the entry that has reached the cell transmission time Cell, and the cells connected to the connection link to which the cell belongs move grace means for delaying the movement to another entry. If the number of movements is equal to or greater than the movement grace number, the cell is transmitted at the transmission time. Cell moving means for moving the cell which cannot be connected and the cell connected to the connection link to which the cell belongs to another entry, and resets the number of movements in the connection to which the cell belongs when the cell is transmitted. The cell scheduling apparatus according to claim 1, further comprising a reset unit that performs resetting.