JP2014060664A - Cell multiplexing device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell multiplexing device and method for multiplexing high priority cells and low priority cells while reducing variation in delay of the low priority cells.SOLUTION: A cell multiplexing device includes: scheduling means for reading out high priority cells of the first predetermined number to be transmitted from first storage means at each predetermined scheduling period, performing scheduling processing of storing the cells in time slots corresponding to a transmission time point of a block composed of a string of time slots corresponding to the predetermined scheduling period, and outputting the block; reading means for reading out low priority cells of the second predetermined number to be transmitted from second storage means; and low priority cell allocation means for allocating the read low priority cells to idle time slots including no high priority cells in the output block to make multiplexed output. The low priority cell allocation means divides the block output from the scheduling means into subblocks of the second predetermined number in the units of time slots, and allocates the low priority cells one by one to idle time slots in each subblock.

Description

  The present invention relates to a multiplexing apparatus and method for multiplexing cells having different priorities in a communication network.

  In a communication network using an asynchronous transfer mode (hereinafter referred to as ATM), data transfer is performed in units of fixed-length cells. In ATM communication networks, there are ATM cells classified into various classes such as voice, video, and IP data. In ATM devices such as node devices constituting an ATM network, such ATM cells are used. Is multiplexed according to the class of each service and transmitted.

  In such an ATM cell multiplexing apparatus, a class queue that is a buffer for each priority class defined in the cell is prepared, and a cell stored in a class queue having a high priority is read preferentially by a scheduling process. When there are no more cells stored in the class queue having a high priority, a method of reading and transmitting the cells stored in the class queue having a low priority is used (see Patent Document 1). Further, in this conventional multiplexing apparatus, shaping is performed so that the number of cells transmitted within the time limit range is equal to or less than the number of cells corresponding to the band in order to limit the band for each class queue in the scheduling process. ing.

JP 2000-165386 A

  However, in the conventional ATM cell multiplexing apparatus, cells of a high priority class (high priority cells) are read from the class queue and transmitted preferentially. (Low priority cell) cannot be taken out from the class queue within a predetermined limit range and sent out, so cell delay fluctuations that cause a reduction in the reproduction quality of information carried by the cell are low-priority cells. There was a disadvantage that it occurred.

  For example, as shown in FIG. 1A, a high priority cell is located in a time slot in each limited range (16 time slots) as shown in FIG. Is located in the time slot. In such a state, the low-priority cell is transmitted at the timing of a time slot (“empty” in FIG. 1A) in which no high-priority cell actually exists. As shown in FIG. 1 (c), a low priority cell that does not compete with a high priority cell in time is transmitted at an appropriate timing, but a low priority cell that competes in time with a high priority cell is transmitted as a high priority cell. Therefore, the low priority cell cannot be transmitted within the control range to which the low priority cell belongs.

  In addition, if low priority cells are sent without shaping and at the timing of a time slot in which no high priority cells exist, low priority cells are sent continuously in a limited range where many low priority cells are stored in the class queue. Similarly, there is a drawback that cell delay fluctuation occurs.

  For example, a high priority cell is located in a time slot in each restricted range as shown in FIG. 2 (a), whereas a low priority cell is continuously located in a time slot as shown in FIG. 2 (b). In this case, as shown in FIG. 2 (c), the low priority cells are continuously transmitted at the timing of time slots that do not compete with the high priority cells in time.

  Accordingly, an object of the present invention is to provide a cell multiplexing apparatus and a cell multiplexing method capable of multiplexing a high priority cell and a low priority cell while reducing delay fluctuation of the low priority cell.

  The cell multiplexing apparatus of the present invention is a cell multiplexing apparatus that multiplexes and transmits a high priority cell and a low priority cell having a lower priority than the high priority cell, and stores the high priority cell. A storage means; a second storage means for storing the low priority cell; and a first predetermined number of the high priority cells to be transmitted from the first storage means for each predetermined scheduling period, and the read high priority cell Scheduling means for performing a scheduling process in which each cell is stored in a time slot corresponding to a transmission point in a block composed of a time slot sequence having a length corresponding to the predetermined scheduling period, and outputting the block after the scheduling process And reading a second predetermined number of low priority cells to be transmitted from the second storage means for each predetermined scheduling period. A low-priority cell read by the read-out means in an empty time slot in which the high-priority cell does not exist in the block output from the scheduling means, and a placement of the low-priority cell Low-priority cell arrangement means for outputting the subsequent block as a multiplexed output, wherein the low-priority cell arrangement means assigns the block output from the scheduling means to the second predetermined number of sub-blocks in units of time slots. And the low-priority cells read by the reading unit are arranged one by one in the empty time slots of each of the sub-blocks.

  The cell multiplexing method of the present invention is a cell multiplexing method of a cell multiplexing apparatus that multiplexes and transmits a high priority cell and a low priority cell having a lower priority than the high priority cell, and has a predetermined scheduling period. Each time, a first predetermined number of the high priority cells to be transmitted are read from the first storage means storing the high priority cells, and each of the read high priority cells has a length corresponding to the predetermined scheduling period. A scheduling step of performing a scheduling process of storing in a time slot corresponding to a transmission time point in a block of time slot trains, and outputting the block after the scheduling process; and the low-priority cell for each predetermined scheduling period Read step for reading out a second predetermined number of low priority cells to be transmitted from the second storage means storing And placing the low-priority cell read by the read-out step in an empty time slot in which the high-priority cell does not exist in the block output in the scheduling step, and after the placement of the low-priority cell, A low-priority cell allocation step that outputs a block as a multiplexed output, wherein the low-priority cell allocation step divides the block output in the scheduling step into the second predetermined number of sub-blocks in units of time slots. The low priority cells read in the reading step are arranged one by one in the empty time slots of each of the sub blocks.

  According to the cell multiplexing apparatus and the cell multiplexing method of the present invention, the block generated by the scheduling process for the high priority cell is divided into the second predetermined number of subblocks in units of time slots, and the empty time slots of each of the subblocks are divided. One low priority cell is arranged at a time. Therefore, since low priority cells are distributed in time slots in which high priority cells are not arranged in the block, the delay fluctuation of the low priority cells should be reduced when multiplexing high priority cells and low priority cells. Can do.

It is a figure explaining insertion of the low priority cell in the conventional multiplexing apparatus. It is a figure explaining insertion of the low priority cell in the conventional multiplexing apparatus. It is a block diagram which shows the structure of the ATM cell multiplexing apparatus of the Example of this invention. It is a flowchart which shows operation | movement of the low priority cell arrangement | positioning part in the apparatus of FIG. It is a figure explaining the operation example of the low priority cell arrangement | positioning part of FIG. It is a figure explaining the other operation example of the low priority cell arrangement | positioning part of FIG. FIG. 10 is a diagram illustrating still another operation example of the low priority cell arrangement unit of FIG. 4.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows a schematic configuration of an ATM multiplexing apparatus according to an embodiment of the present invention. This ATM multiplexing apparatus has class queues 10 ₁ to 10 ₄ and scheduling units 11 _{1 to} 11 ₄ . In this embodiment, the classes are described as four types C1 to C4 having different priorities, so that four class queues 10 ₁ to 10 ₄ and four scheduling units 11 _{1 to} 11 ₄ are provided corresponding to the classes C1 to C4. It has been. Each of the class queues 10 ₁ to 10 ₄ is a buffer that stores cells in the order of input and outputs them in that order. Class queues 10 ₁ to 10 ₃ is a first storage means, the cell of the high priority class, i.e. while storing high priority cell, class queue 10 ₄ is the second storing means, a low-priority class cells, i.e., the output of the class queues ₁₀ 1 to 10 ₄ for storing low-priority cell scheduling unit ₁₁ 1 to 11 ₄ corresponding is connected. Each of the scheduling units 11 _{1 to} 11 ₄ reads out the number of cells in the band for each of the classes C ₁ to C ₄ from the corresponding class queues 10 ₁ to 10 ₄ , and transmits the cells for each read cell within a limited range. Is output at the timing. Limited range corresponds to a period predetermined scheduling period is when the scheduling unit 11 ₁ to 11 ₄ performs the scheduling process, as will be described later, a predetermined number of time slots (time slot columns) located within its limits To do. Highest priority is C1 In class C1~C4 high, C2, C3, since the order of priority of C4 becomes lower, most frequently scheduling unit 11 _1, namely it is possible to output the cell shape rate, the scheduling unit The shaping speed decreases in the order of 11 ₂ , 11 ₃ , and 11 ₄ .

The priority control unit 12 is connected to the outputs of the scheduling units 11 _{1 to} 11 ₃ . Priority control unit 12 outputs a high-priority cell read from the scheduling unit 11 ₁ to 11 ₃ separately from one output sequentially, the scheduling unit 11 ₁ to 11 ₃ high priority cell is temporally read from In case of contention, high priority cells are output in the priority order of classes C1 to C3. A high priority cell arrangement storage unit 13 is connected to the output of the priority control unit 12.

  The high-priority cell arrangement storage unit 13 stores the high-priority cells within one limit range in the order output from the priority control unit 12 (transmission order). A set of cells obtained in one limit range is referred to as one block. One block is, for example, cell data having a size corresponding to 16 time slots.

Note that the scheduling units 11 _{1 to} 11 ₃ , the priority control unit 12 and the high priority cell arrangement storage unit 13 correspond to scheduling means for high priority cells, and thereby a first predetermined number corresponding to each band of the classes C1 to C3. High priority cells are read out and scheduled. Further, the scheduling unit 11 ₄ corresponds to the read means, whereby the second predetermined number of low-priority cells corresponding to the band class C4 is read.

Low priority cell placement portion 14, which is a low priority cell placement means is connected to the output of the scheduling unit 11 ₄ is connected to the holding output of the high-priority cell placement storage unit 13. The low priority cells of low priority cell placement portion 14 scheduling unit 11 ₄ classes read by C4, arranged in idle time slots of one block obtained from the arrangement cell output of the high priority cells arranged storage unit 13, The arranged blocks are output in the order of time slots.

In the ATM multiplexing apparatus having such a configuration, the class queues 10 ₁ is supplied cell class C1, the class queues 10 ₂ is supplied cell classes C2, cell class C3 is the class queue 10 ₃ There is provided, in the class queues 10 ₄ cells of class C4 is supplied. The cell supply to each of the class queues 10 ₁ to 10 ₄ may be performed by distributing cells by a distribution unit (not shown). For example, if the service of ITU-T standard, the cell according to the DBR (Deterministic Bit Rate transfer capacity) is the class queue 10 ₁ as a class C1, the class queue 10 ₂ SBR (Statistical Bit Rate) as a class C2 the related cell, the cell according to the GFR / ABR (Guaranteed Frame Rate / Available Bit Rate) is the class queue 10 ₃ as a class C3, the class queue 10 ₄ cells of the U class of DBR as a class C4, distributes each It is possible. As described above, the cells of class C1 to C3 are high priority cells (high priority cells), and the class C4 cell is a low priority cell (low priority cells).

These class queues 10 ₁ to 10 ₄ are stored in the order in which cells of the same class are supplied. The cells stored in the class queues 10 ₁ to 10 ₄ are read out in the storage order (sending order) by the scheduling units 11 ₁ to 114 at a frequency (shaping speed) suitable for the band determined by each of the classes C _{1 to} C ₄ and transmitted. It is output to the priority control unit 12 at a timing corresponding to the time. The high priority cells output from the scheduling units 11 _{1 to} 11 ₃ for the classes C1 to C3 are arranged by the priority control unit 12 in the order of output. When the high priority cells output from the scheduling units 11 _{1 to} 11 ₃ compete in time, the priority control unit 12 arranges the high priority cells in the priority order of the classes C1 to C3.

  Further, the high priority cell arrangement storage unit 13 stores the arrangement of the high priority cells in a time slot corresponding to the time within the above-described limit range. In the time slot corresponding to the timing when the high priority cell is not supplied, an empty time slot in which no cell is arranged is generated. The high-priority cell arrangement storage unit 13 outputs, to the low-priority cell arrangement unit 14, the stored contents of one block including an empty time slot within the limit range every time the limit range has elapsed.

Low priority cell class C4 read by the scheduling unit 11 _4, the low-priority cell placement portion 14 is supplied, the supplied low-priority cells were are placed in the empty time slots corresponding in one limited range. The low-priority cell arrangement unit 14 detects the number of class C4 low-priority cells supplied to the one restricted range as m.

Low priority cell placement portion 14 is inserted into one block idle time slots of showing the high priority cell arrangement which is supplied with low priority cells supplied from the scheduling unit 11 ₄ from the high-priority cell located storage unit 13. As shown in FIG. 4, the low-priority cell placement unit 14 first divides the number n of one-block time slots by the number m of low-priority cells to create m sub-blocks (step S1). One sub-block consists of n / m or (n / m) +1 time slots. In addition, one sub-block is created sequentially from a time slot that is earlier in time than one block. For the remaining time slots of n / m, the first sub-block is set to (n / m) +1 time slot by adding the remaining one time slot, and if there are still more time slots, the second sub-block The sub-blocks are (n / m) +1 time slots. As described above, the sub-blocks corresponding to the number of the remaining time slots have (n / m) +1 time slots.

  Next, the low priority cell arrangement unit 14 detects the presence of an empty time slot in each sub-block (step S2). Then, it is determined whether or not there is an empty time slot in all sub-blocks (step S3). If there is an empty time slot in all the subblocks, one low priority cell is placed in an empty time slot for each subblock (step S4). On the other hand, if there is no empty time slot in any of the sub-blocks, that is, if there is a sub-block in which all the time slots are filled with high priority cells, only the sub-block in which the empty time slot exists is timed. These are combined in order to form a new block (step S5). In step S5, the total number of sub-blocks n 'of sub-blocks having empty time slots is set to the number n of new one-block time slots. That is, the number n of new time slots of one block is a number excluding the number of time slots of sub-blocks in which all time slots are filled with high priority cells.

  The low-priority cell arrangement unit 14 returns to step S1 after executing step S5 to create new m sub-blocks, and repeats the above operation.

  When the placement of the class C4 cell is completed in step S4, the low-priority cell placement unit 14 adds a sub-block in which all the time slots are filled with cells to the original position as a block including n time slots having initial values. The cells of the block are output in order of time (step S6). As a result, the low-priority cell placement unit 14 outputs one block in which a cell of class C4 is inserted after a lapse of at least one limit range after receiving one block of cell data from the high-priority cell placement storage unit 13 To do.

  Next, an example of the arrangement of class C4 low-priority cells, where the number of time slots in one block is 16, will be described with reference to FIGS.

FIG. 5A shows an example of one block output from the high priority cell arrangement storage unit 13. This one block includes a time slot (described as “cell” in FIG. 5) in which a cell (high priority cell) belonging to any of classes C1 to C3 exists, and a time slot in which no cell exists (“empty” in FIG. 5). And description). When the scheduling unit 11 ₄ 4 The number m of low priority cell class C4 in one limited range supplied from the block is divided into four sub-blocks 1 to 4 as shown in Figure 5 (b). The number of time slots in each of the four sub-blocks 1 to 4 obtained in step S1 is n / m = 16/4 = 4. As can be seen from the sub-blocks 1 to 4 in FIG. 5B, all the sub-blocks 1 to 4 have empty time slots. Accordingly, in step S3, since it is determined that there are empty time slots in all the sub-blocks, step S4 is executed. When scheduling result for low priority cells to be output from the scheduling unit 11 ₄ is to be as shown in FIG. 5 (c), as shown in step S4 FIG. 5 (d), the one of the sub-blocks 1-4 Class C4 low-priority cells (denoted as “C4” in FIG. 5) are sequentially arranged in the empty time slots. One block in which the C4 low priority cell is inserted for each of the sub-blocks 1 to 4 is output from the low priority cell arrangement unit 14 in step S6.

Incidentally, in the insertion of the low priority cells of C4 of FIG. 5 (d), the scheduling result for the low priority cells to be output from the scheduling unit 11 ₄ as shown in FIG. 5 (c), corresponding to the time slot 9 When the low priority cell shown in FIG. 5 (c) competes with the high priority cell in time by the code A, the cell is placed in the time slot 10 by the operation of the low priority cell placement unit 14.

FIG. 6A shows another example of a block output from the high priority cell arrangement storage unit 13. This one block includes a time slot in which a high-priority cell belonging to any of classes C1 to C3 exists (described as “cell” in FIG. 6) and a time slot in which no cell exists (indicated as “empty” in FIG. 6). And have. When the scheduling unit 11 ₄ 4 The number m of low priority cells in one limited range supplied from the block is divided into four sub-blocks 1 to 4 as shown in Figure 6 (b). The number of time slots of the four sub-blocks 1 to 4 obtained in step S1 is n / m = 16/4 = 4. As can be seen from the sub-blocks 1 to 4 in FIG. 6B, there are empty time slots in the sub-blocks 1, 2, and 4, and there are no empty time slots in the sub-block 3. Accordingly, in step S3, since the sub-block 3 in which no empty time slot exists is determined, step S5 is executed.

  As a result of the process in step S5, as shown in FIG. 6C, sub-blocks 1, 2, and 4 other than sub-block 3 are combined to form a new block. Since the block of FIG. 6 (c) consists of 12 time slots, as shown in FIG. 6 (d), the number of time slots of each of the four sub-blocks 1 to 4 obtained in step S1 is n / m = 12. / 4 = 3. As can be seen from the sub-blocks 1 to 4 in FIG. 6D, there are empty time slots in each of the sub-blocks 1 to 4. Therefore, in step S4, as shown in FIG. 6 (e), a low priority cell of class C4 (described as “C4” in FIG. 6) is sequentially arranged in one empty time slot of each of the sub-blocks 1 to 4. . One block in which the low-priority cells are inserted into the sub-blocks 1 to 4 is formed again in step S6 as shown in FIG. 6 (f), and the one block is output from the low-priority cell placement unit 14.

  In FIG. 6D, since the first time slot of each of the sub-blocks 1 to 4 is an empty time slot, a low priority cell of class C4 is arranged there, but it is not always necessary to be the first time slot. . However, it is preferable that the low-priority cells of class C4 do not continue when returning to a block consisting of 16 time slots as shown in FIG. 6 (f).

FIG. 7A shows another example of a block output from the high priority cell arrangement storage unit 13. This one block includes a time slot in which a high-priority cell belonging to any of classes C1 to C3 exists (described as “cell” in FIG. 7) and a time slot in which no cell exists (indicated as “empty” in FIG. 7). And have. When 3 the number m of low priority cell class C4 in one limited range which is supplied from the scheduling unit 11 _4, the block is divided into three sub-blocks 1-3 as shown in FIG. 7 (b). The number of time slots of the three sub-blocks 1 to 3 obtained in step S1 is n / m = 16/3 = 5, and the remainder is 1. Accordingly, the number of time slots in sub-block 1 is 6 including the remainder 1, and the number of time slots in sub-blocks 2 and 3 is 5. As can be seen from the sub-blocks 1 to 3 in FIG. 7B, all the sub-blocks 1 to 3 have empty time slots. Accordingly, in step S3, since it is determined that there are empty time slots in all the sub-blocks, step S4 is executed. Therefore, in step S4, as shown in FIG. 7 (c), low priority cells of class C4 (denoted as “C4” in FIG. 7) are sequentially arranged in one empty time slot of each of the sub-blocks 1 to 3. . One block in which this class C4 low-priority cell is inserted for each of the sub-blocks 1 to 3 is output from the low-priority cell arrangement unit 14 in step S6.

  In the above embodiment, the number of time slots of sub-block 1 of the young sub-block is added by 1 corresponding to the remainder of 1. However, the number of time slots of sub-block 2 or 3 is replaced with sub-block 1. Only 1 may be added. If the remainder is 2, the number of time slots in any two sub-blocks of sub-blocks 1 to 3 may be added by one.

  As described above, in the ATM multiplexing apparatus of the embodiment, the low priority cells can be efficiently distributed and arranged in empty time slots other than the time slot in which the high priority cells are arranged in each block. Therefore, a problem that a plurality of low-priority cells are fixedly arranged continuously or are not arranged within a restriction range to which the low-priority cells should belong is prevented, so that cell delay fluctuations for the low-priority cells can be reduced. .

Further, in the above embodiment, the low-priority scheduling unit 11 ₄ for scheduling cell is provided, but the number of cells corresponding the class queue 10 ₄ to band class C4 (second predetermined number) reading means May be simply read out and supplied to the low-priority cell placement unit 14 without performing scheduling processing.

  In the embodiment described above, the present invention is applied to an ATM cell multiplexing apparatus. However, the present invention can be applied to an apparatus that multiplexes other cells including Ethernet packets.

10 ₁ to 10 ₄ class queues 11 _{1 to} 11 ₄ Scheduling unit 12 Priority control unit 13 High priority cell arrangement holding unit 14 Low priority cell arrangement unit

Claims (5)

A cell multiplexing apparatus for multiplexing and transmitting a high priority cell and a low priority cell having a lower priority than the high priority cell,
First storage means for storing the high priority cell;
Second storage means for storing the low priority cell;
A first predetermined number of the high-priority cells to be transmitted from the first storage means are read every predetermined scheduling period, and each of the read high-priority cells is a time slot string having a length corresponding to the predetermined scheduling period. Scheduling processing for storing in a time slot corresponding to the transmission time of the block consisting of, and outputting the block after the scheduling processing;
Reading means for reading out a second predetermined number of the low-priority cells to be sent from the second storage means at each predetermined scheduling period;
The low-priority cell read by the reading unit is arranged in an empty time slot in which the high-priority cell does not exist among the blocks output from the scheduling unit, and the block after the arrangement of the low-priority cell is arranged. Low priority cell placement means for multiplexing output, and
The low-priority cell arrangement unit divides the block output from the scheduling unit into the second predetermined number of sub-blocks in units of time slots, and reads the empty time slots of each of the sub-blocks by the reading unit. A cell multiplexing apparatus, wherein the low priority cells are arranged one by one.   The low-priority cell arrangement means replaces the second predetermined number of sub-blocks with the empty sub-blocks when the second predetermined number of sub-blocks has a free sub-block with no empty time slot. Remove and combine to form a new block, divide the new block into the second predetermined number of sub-blocks in units of time slots, and read the read into the empty time slots of each of the sub-blocks of the new block 2. The cell multiplexing apparatus according to claim 1, wherein the low priority cells read by the means are arranged one by one.   The low-priority cell placement unit may determine the remainder of the second predetermined number of sub-blocks when the block is not divisible by the second predetermined number when the block is divided. 3. The cell multiplexing apparatus according to claim 1, wherein the number of time slots of the sub-block is increased by one time slot.   4. The cell multiplexing apparatus according to claim 1, wherein the high priority cell and the low priority cell are ATM cells. A cell multiplexing method of a cell multiplexer for multiplexing and transmitting a high priority cell and a low priority cell having a lower priority than the high priority cell,
For each predetermined scheduling period, a first predetermined number of the high priority cells to be transmitted are read from the first storage means storing the high priority cells, and each of the read high priority cells corresponds to the predetermined scheduling period. Performing a scheduling process of storing in a time slot corresponding to a transmission time point in a block composed of a time slot sequence having a length, and a scheduling step of outputting the block after the scheduling process;
A step of reading out a second predetermined number of the low priority cells to be transmitted from the second storage means storing the low priority cells for each predetermined scheduling period;
The low-priority cell read by the reading step is arranged in an empty time slot in which the high-priority cell does not exist among the blocks output in the scheduling step, and the block after the arrangement of the low-priority cell is arranged. A low-priority cell placement step for multiplexing output, and
The low-priority cell placement step divides the block output in the scheduling step into the second predetermined number of sub-blocks in units of time slots, and reads in the empty time slots of each of the sub-blocks in the reading step. A cell multiplexing method, wherein the low priority cells are arranged one by one.

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