JP3919341B2 - Asynchronous transfer mode switching device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an Asynchronous Transfer Mode (ATM) switching apparatus having a unicast function for switching and outputting input cells from an arbitrary port to one port and a multicast function for switching and outputting to a plurality of different ports. Specifically, the present invention relates to an improvement in cell transmission control for improving the efficiency of the multicast function.
[0002]
[Prior art]
As functions related to data transmission in a communication system, in addition to a unicast function that transmits data for each corresponding destination, a multicast function that transmits the same data to a plurality of different destinations is known.
[0003]
On the other hand, in recent years, as a construction form such as a railway management system and a road management system, a plurality of node devices having an ATM switching function are distributedly arranged via a transmission line such as an optical fiber, and the local communication connected to each of these node devices. There is known an ATM communication network in which data is transmitted and received between terminals via each node device. In this network, each of the node devices is connected via the input / output port with the transmission path realized by a two-level path of VP (Virtual Path) and VC (Virtual Channel), A fixed-length cell (ATM cell) input from an input port is output according to a VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier) included in the ATM cell. It is responsible for the function of exchange processing.
[0004]
The multicast function described above is also applied to this type of ATM communication, and is a very important function especially for realizing LAN emulation. Here, a multicast realization method in the conventional ATM switching apparatus corresponding to the node apparatus will be described with reference to FIGS. FIG. 5 is a diagram showing a schematic configuration of the entire conventional ATM switching apparatus, including an incoming header conversion unit 51-1 to 51-n, an incoming conversion table 52-1, to 52-n, and an ATM switch. 53, egress header conversion units 54-1 to 54-n, egress conversion tables 55-1 to 55-n, a cell duplication unit 56, and a duplication table 57.
[0005]
In this conventional apparatus, cells input from the respective ports (# 1,..., #N) are input to the incoming header conversion units 51-1 to 51-n. The ingress header conversion units 51-1 to 51-n retrieve the ingress conversion tables 52-1 to 52-n from the VPI / VCI or the like in the header portion of the input cell, and output destinations of the input cell And obtain a connection identifier.
[0006]
Next, the input cell is transferred to the ATM switch 53 together with information obtained from the input side conversion tables 52-1,..., 52-n. The output destination obtained from the input side conversion tables 52-1 to 52-n indicates an output destination for the ATM switch 53. The ATM switch 53 transfers the cells to the outgoing header converters 54-1 to 54-n according to the output destination obtained by the incoming header converters 51-1 to 51-n. The outgoing side header conversion units 54-1,..., 54-n search the outgoing side conversion tables 55-1,..., 55-n based on the connection identifier transferred together with the cell to obtain a new VPI / VCI. . Further, after the header portion of the transferred cell is replaced with the obtained VPI / VCI, the cell is output to each port (# 1,..., #N).
[0007]
The above is the basic operation related to the cell exchange in the conventional apparatus, but the cell duplicating unit 56 is responsible for the control related to the multicast function in the conventional apparatus. That is, in this conventional apparatus, for the multicast cell, the cell output destination and the connection identifier are set so that the output destination is the cell duplicating unit 56 in the input side conversion tables 52-1 to 52-n referred to. It is set in advance.
[0008]
Based on this setting, the multicast cell is transferred from the ingress header conversion units 51-1 to 51-n to the ATM switch 53 and routed in the ATM switch 53, and the cell duplicating unit 56, as in the normal cell. Forwarded to As can be seen from this point, in the conventional apparatus, the ATM switch 53 is realized with a functional configuration in which a cell is transferred according to an output destination input together with the cell without being conscious of whether it is a multicast cell. The cell duplicating unit 53 duplicates the multicast cell transferred from the ATM switch 53 and sends it to the ATM switch 53 to realize multicasting.
[0009]
For example, as shown in FIG. 6, the cell replication unit 56 includes an identifier buffer 561, a cell buffer 562, an address management unit 563, a selector 564, and an address latch 565. The cell duplicating unit 56 stores the cell in the cell buffer 562 at the address indicated by the write pointer managed by the address managing unit 563, and stores the connection identifier transferred along with the cell in the identifier buffer 561. To do. At the same time, the address management unit 563 updates the write pointer to indicate the next free area.
[0010]
Next, the stored connection identifier is read into the address latch 565 from the address indicated by the read pointer of the identifier buffer 561. At the same time, the address management unit 563 updates the read pointer to indicate the area where the next cell is stored.
[0011]
Further, the replication table 57 is searched by the address indicated by the address latch 565, and a new output destination, connection identifier, next address, and last cell display stored in the replication table 57 are acquired. Then, the cell is read from the area of the cell buffer 562 indicated by the read pointer of the address management unit 563, and is input again to the ATM switch 53 together with the new output destination and connection identifier.
[0012]
The cell duplication unit 56 latches the next address obtained by the immediately preceding cell, searches the duplication table 57 again, and similarly obtains a new output destination, connection identifier, next address, and last cell display. By repeating such duplication processing, it is possible to duplicate cells having different output destinations and transfer cells to different destinations although the contents of the cell data are the same.
[0013]
When the last cell display indicates that the cell is the last duplicate cell, after the cell is output, the connection identifier is read from the area indicated by the read pointer of the identifier buffer 561 to the address latch 565, as described above. Perform proper processing.
[0014]
As can be seen from the above operation, in the conventional apparatus, the cell duplication unit 56 duplicates the cell to realize the multicast function. For this reason, the following relationship is established between the input band and the output band of the cell duplication unit 56 depending on the number of times of duplication for one cell in the cell duplication unit 56.
[0015]
That is, assuming that n cells are duplicated for one cell input, and the input band of the cell duplicating unit 56 is mi and the output band is mo,
mo = mi × n (1)
Is established.
[0016]
Further, since the physical output band of the cell duplicating unit 56 is finite, in order to prevent the cell duplicating unit 56 from being overloaded, assuming that the physical maximum output band is moMAX, the cell duplicating unit 56 The input bandwidth mi to
mi ≦ moMAX / n
Will be limited.
[0017]
Therefore, when n is large, that is, when there are many partners to be multicast, traffic in a very small band is only seen in each multicast connection due to the bottleneck of the transfer part from the cell duplicating unit 56 to the ATM switch 53. I was unable to transfer.
[0018]
On the other hand, if traffic of a large band is input to the cell duplicating unit 56 in violation of the above conditions, the band required on the output side of the cell duplicating unit 56 exceeds the physical maximum band. In the cell buffer 562 in the duplicating unit 56, the cells stay with time, and there is a risk that the cells are eventually discarded.
[0019]
[Problems to be solved by the invention]
As described above, in the conventional apparatus, the multicast cell is transferred to the cell duplicating unit via the ATM switch, and the cell duplicating unit duplicates a required number of cells and returns to the ATM switch to perform the exchange process. Since the input bandwidth is limited by the output bandwidth of the cell duplicating unit and the number of partners to be multicast increases, it is necessary to reduce the input bandwidth accordingly from the viewpoint of preventing overload, that is, cell discard. In actuality, there was a problem that only a very small bandwidth could be multicast.
[0020]
The present invention eliminates the above-mentioned problems and provides an asynchronous transfer mode switching apparatus that can realize an efficient multicast function for traffic of a larger band, without limiting the input band of cells to be multicast. For the purpose.
[0021]
[Means for Solving the Problems]
In order to achieve the above object, claim 1 is provided. Description The present invention provides an asynchronous transfer mode switching apparatus having a unicast function for switching and outputting an input cell from an arbitrary port to one port and a multicast function for switching and outputting to a plurality of different ports. And a second output queue for the multicast cell, Multicast tag indicating the port to be multicast and the same port output indicating the number of cell transmissions to the same port from the route information added to the input cell and the information of the port to which the input cell is input and preset information Information conversion means for obtaining cell transmission control information including frequency information, and determining whether the input cell is a unicast cell or a multicast cell by referring to the multicast tag obtained by the information conversion means, and transmitting the cell of the input cell A wait queue related to control is distributed to the corresponding first or second output queue, and when the wait queue is distributed to the second output queue, the wait queue distributed to the first output queue Before sending the unicast cell based on the waiting queue allocated to the second output queue. When performing transmission control of a multicast cell, based on the multicast tag corresponding to the multicast cell and the same port output count information, the multicast cell is a cell that does not need to perform multicast multiple times for the same port, It is determined whether a cell needs to be multicasted multiple times for the same port, and a multicast cell that does not need to be multicasted multiple times to the same port is assigned to each port to be multicast indicated by the corresponding multicast tag. A multicast cell that is sent only once in the same cell cycle as the unicast cell and needs to be multicast to the same port multiple times corresponds to the corresponding port based on the same port output count information Output as many times as cell output That Cell delivery control means.
[0022]
Claim 2 Description The invention of claim 1 Description In the invention of Provided corresponding to the second output queue and distributed to the second output queue, which is performed after suppressing the transmission of the unicast cell based on the waiting queue allocated to the first output queue. Multicast scheduler means for restricting a cell transmission execution period of the multicast cell corresponding to each waiting queue between the waiting queues to a preset period It is characterized by that.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a schematic configuration of an ATM switching apparatus according to an embodiment of the present invention. This figure is an example of a configuration having an n × n switch structure that performs cell exchange between n input ports and n output ports. As shown in the figure, the ATM switching apparatus includes an input header conversion unit 11, an input conversion table 12, a cell buffer 13, an output header conversion unit 14, an output conversion table 15, a cell transmission control unit 16, a queue. A management table 17 is provided.
[0026]
The cell transmission control unit 16 includes a table control unit 161, a cell buffer control unit 162, an output cell determination unit 163, and a multicast control unit 164. The table control unit 161 controls the queue management table 17. The cell buffer control unit 162 provides an address when writing a cell to the cell buffer 13 or reading a cell from the cell buffer 13. The output cell determination unit 163 determines a cell to be output for each port (# 1,..., #N). The multicast control unit 164 has a built-in multicast timer that controls the output band of multicast, and sends whether or not multicast output is possible to the output cell determination unit 163.
[0027]
FIG. 2 is a schematic diagram showing a logical configuration of an output cell selection algorithm in the cell transmission control unit 16 of the ATM switching apparatus. In the cell transmission control unit 16 of the present embodiment, the table control unit 161 includes unicast queues 21-11 to 21-1m and 21-21 for each priority class for each port (# 1, to, #n). ,..., 21-2m,..., 21-n1,..., 21-nm and multicast queues 22-1 to 22-n according to priority classes for all ports (# 1,. Management. Here, of the unicast queues 21-11,..., 21-1m provided corresponding to port # 1, for example, the queue 21-11 is a queue for the cell of the highest priority class. Queues for lower priority class cells in order. The queues for each priority class are used in accordance with the unicast queues 21-21, ..., 21-2m, ..., 21-n1, ..., 21-nm corresponding to the ports # 2, ..., n, and the multicast queue 22-. The same applies to 1,..., 22-n.
[0028]
The output cell determination unit 163 is provided for each port (# 1,..., #N), and the unicast queues 21-11 to 21-1m, 21-21 to 21-2m,. port schedulers 23-1,..., 23-n for determining queues output from n1,..., 21-nm, and multicast scheduler 24 for determining queues output from multicast queues 22-1,. Output selectors 25-1,..., 25-n for selecting cells to be finally output for each port based on the output queues from the port schedulers 23-1,. And an output scheduler 26 for managing a transmission schedule of each output cell.
[0029]
The configuration of FIG. 2 is based on the output queues for unicast cells (21-11, ..., 21-1m, 21-21, ..., 21-2m, ...) for each port (# 1, ..., #n). , 21-n1,..., 21-nm) and output queues (22-1 to 22-n) for the multicast cells for all ports are logically provided. Needless to say, it can be physically provided.
[0030]
With the basic configuration of the output selection algorithm in mind, the basic cell switching operation of the ATM switching apparatus according to this embodiment will be described first with reference to FIG. In this ATM switching apparatus, cells input from the ports (# 1,..., #N) are input to the incoming header conversion unit 11. The ingress header conversion unit 11 searches the attached ingress conversion table 12 based on the VPI / VCI and input port number of the input cell, and determines the multicast tag, the same port output count, the priority class, the connection identifier, etc. Obtain information (see FIG. 3).
[0031]
The ingress header conversion unit 11 may be divided for each port (# 1,..., #N) as a physical structure, but in the present embodiment, it is handled as one physically. In this case, the incoming header conversion unit 11 performs the above-described processing on the input cells from the ports (# 1,..., #N) in a time-sharing manner for the ports (# 1,..., #N). When the incoming header conversion unit 11 is physically divided for each port (# 1,..., #N), the incoming conversion is performed based only on VPI / VCI in the above processing for the input cell. Search the table 12.
[0032]
FIG. 3 shows an example of the entry in the entry side conversion table 12 obtained by the search in the entry side header conversion unit 11 described above. The entries in the ingress conversion table 12 include valid 31, multicast tag 32, same port output count 33, priority class 34, and connection identifier 35. Valid 31 indicates whether or not this entry is a valid entry. The multicast tag 32 requires as many bits as the number of output ports. In the case of a switch having an n × n structure, n bits are assigned to the multicast tag 32 and “1” is assigned to the bit corresponding to the port to which the cell is to be output. "Is set. In the case of unicast, “1” is set only in one bit of the multicast tag 32, and in the case of multicast, “1” is set in a plurality of bits.
[0033]
The same port output count 33 is used when the cell needs to be output to different destinations of the same output port, and the required count is set for each output port (# 1,..., #N). The priority class 34 is used when there are a plurality of queues having different priorities for each output port, and the priority class of the cell is set.
[0034]
The connection identifier 35 is used by the outgoing header conversion unit 14 to identify the connection of the cell received from the incoming header conversion unit 11 through the cell buffer 13. However, since the connection can be identified if the egress header conversion unit 14 can refer to the input port number and VPI / VCI of the cell, if the input port number and VPI / VCI are transferred together with the cell, a special connection identifier is provided. You do not have to prepare. Each entry in the ingress conversion table 12 needs to be set by external control before the cell arrives.
[0035]
After searching the input side conversion table 12 in the input side header conversion unit 11 described above, the cell data itself is transferred to the cell buffer 13, and the information (see FIG. 3) obtained from the input side conversion table 12 is the table control unit 161. Forwarded to
[0036]
The table control unit 161 uses the queue management table 17 to store the cell buffer 13 in which cells input and output by the ATM switching apparatus are stored, and the priority class for each port (# 1,..., #N). Unicast queues 21-11,..., 21-1m, 21-21,..., 21-2m,..., 21-n1,. Manage queues.
[0037]
In this embodiment, each queue is managed in a linked list format, and each unicast queue 21-11,..., 21-1m21-21,. 21-n1,..., 21-nm, each multicast queue 22-1,..., 22-n is managed by the read pointer, write pointer, and the number of staying cells. Do with numbers.
[0038]
The read pointer for each queue indicates the head of each queue where the cells stay, and specifically indicates the address of the cell buffer in which the cell to be output next is stored for the corresponding queue. The write pointer indicates the tail end of the corresponding queue where the cell is retained. The number of staying cells indicates the number of cells staying in the corresponding queue, and the output cell determining unit 163 is notified of whether there is a cell to be output for the corresponding queue with reference to the number of staying cells. The head pointer of the empty queue indicates the head of the empty queue, and the tail pointer indicates the end of the empty queue. The number of empty queues indicates the remaining buffer amount of the current cell buffer in cell units, and is controlled so that no new cell is input when it is “0”.
[0039]
Here, the operation of the table control unit 161 will be described. The table control unit 161 transfers the head pointer of the empty queue to the cell buffer control unit 162 when the cell is written from the incoming header conversion unit 11 to the cell buffer 13, and updates the head pointer. At the same time, information transferred from the incoming header conversion unit 11 is stored in the same address of the queue management table 17 as shown in FIG. As can be seen from the figure, the entries in the queue management table 17 at the time of writing a cell to the cell buffer 13 include a multicast tag 41, the same port output count 42, a connection identifier 43, and a link identifier 44.
[0040]
However, this entry is an example in the case of a multicast cell. In the case of a unicast cell, the queue to be enqueued corresponds to the output port and the priority class on a one-to-one basis, and it is not necessary to output to the same port a plurality of times, so only the connection identifier 43 and the link identifier 44 need be stored.
[0041]
Further, the table control unit 161 determines a queue to enqueue the corresponding cell from the multicast tag 32 and the priority class 34 transferred from the ingress header conversion unit 11, and the queue control table 17 indicated by the write pointer of the queue. The address at which the corresponding cell is entered is written in the link identifier 44, and the write pointer of the queue is updated. That is, the link identifier 44 indicates the address of the queue management table 17 of the next cell linked by the linked list. Further, the number of staying cells in the queue is incremented by “1” in accordance with the update of the write pointer.
[0042]
When reading a cell from the cell buffer 13 to the outgoing header conversion unit 14, the table control unit 161 transfers the queue read pointer indicated by the output cell determination unit 163 to the cell buffer control unit 162. If the cell to be read is a unicast cell, the read pointer value is stored in the empty queue area indicated by the tail pointer of the empty queue in order to release the cell buffer area in which the unicast cell was stored after reading. The tail pointer is updated to the value of the read pointer. Furthermore, the read pointer of the queue is updated to the value of the link identifier 44 of the entry of the queue management table 17 indicated by the read pointer. Finally, the retained cell number counter of the queue is decremented by “1”.
[0043]
When a multicast cell that does not need to be multicast multiple times for the same port is output, the same processing as the processing of the unicast cell is performed. On the other hand, when it is necessary to perform multicasting for the same port a plurality of times, the table control unit 161 decrements the same port output count 42 in the entry of the queue management table 17 by “1” in the next cell cycle. The cell is output again. When the same port output count becomes “0” for all ports (# 1,..., #N), the cell buffer 13 in which the multicast cell is stored is released.
[0044]
The cell buffer control unit 162 instructs an address to the cell buffer 13 when a cell is input to or output from the cell buffer 13. The address that the cell buffer control unit 162 instructs the cell buffer 13 is given by the table control unit 161.
[0045]
The multicast control unit 164 sends a multicast output control signal generated by a multicast timer that controls the multicast output band to the output cell determination unit 163. The multicast timer is a timer that is decremented by 1 for each cell cycle. When the multicast timer reaches “0”, the output of the multicast cell is output cell determination unit 163. In Instruct. After the corresponding multicast cell is transmitted based on this instruction, an initial value designated from the outside is set in the multicast timer. Since the initial value of the multicast timer is set by external control, the multicast output band can be freely changed.
[0046]
The output cell determination unit 163 selects a queue to be output next for each port (# 1,..., #N), and stores a cell to be output to the cell buffer control unit 162 for the table control unit 161. A cell buffer address transfer instruction and a cell connection identifier transfer instruction to be output to the outgoing side conversion table 15 are issued.
[0047]
Next, an algorithm for determining an output cell in the ATM switching apparatus of the present invention will be described with reference to FIG. In the figure, the table control unit 161 includes unicast queues 21-11 to 21-1m, 21-21 to 21-2m, ... for each priority class for each port (# 1, ..., #n). 21-n1,..., 21-nm are managed, and the unicast queues 21-11,. , 21-21,..., 21-2m,..., 21-n1,. The table control unit 161 also manages the multicast queues 22-1,..., 22-n. The multicast queues 22-1,. The cell retention information for each n is also notified to the output cell determination unit 163.
[0048]
The queue distribution (enqueue) for each queue refers to the multicast tag 32 in the entry (see FIG. 3) of the entry conversion table 12 transferred from the entry header conversion unit 11 with respect to the input cell. Do. In other words, if there is only one port that outputs a cell on the multicast tag 32 (“1” is set in the port corresponding bit), it is determined as a unicast cell, and a waiting queue related to the cell is set. The unicast queues 21-11,..., 21-1m, 21-21,..., 21-2m, ..., 21-n1,. On the other hand, when there are a plurality of ports that output cells on the multicast tag 32, it is determined as a multicast cell, and the waiting queues related to the cell are distributed to the multicast queues 22-1, ..., 22-n.
[0049]
The output cell determination unit 163 determines a queue to be output by the port schedulers 23-1,..., 23-n arranged for each port (# 1,..., #N). When there are cells in a high priority queue, the port schedulers 23-1,..., 23-n always select a high priority queue and output a cell. However, when the multicast tag 32 indicates that a multicast cell is to be output, the back of the port scheduler 23-1, to 23-n does not select a unicast cell in order to prioritize the multicast cell. Control by pressure is performed. That is, since the output of a unicast cell is suppressed by using the back pressure by the multicast tag 32, in the case of a cell that multicasts only once to the same port, it is possible to simultaneously multicast to a desired port.
[0050]
For multicast cells, multicast queues 22-1,..., 22-n to be output are selected by multicast scheduler 24. Similarly to the port schedulers 23-1,..., 23-n, the multicast scheduler 24 adopts a fixed priority method. However, when the back pressure control by the multicast timer transferred from the multicast control unit 164 is performed, the multicast cell is not selected.
[0051]
The output cell selectors 25-1,..., 25-n finally determine the output cells for each port (# 1,..., #N). The output cell selectors 25-1,..., 25-n select unicast cells or multicast cells to be output. Finally, the cell to be output for each port (# 1,..., #N) is transferred in time division by the output scheduler 26. Actually, the queue number to be output from the output cell determination unit 163 to the table control unit 161 is transferred in a time division manner.
[0052]
Thereafter, the table controller 161 instructs the cell buffer controller 162 of the read pointer corresponding to the queue number. The cell buffer control unit 162 reads out the corresponding cell from the cell buffer 13 according to the read pointer and sends it to the output header conversion unit 14. The outgoing side header conversion unit 14 searches the outgoing side conversion table 15 according to the connection identifier transferred from the table control unit 161, replaces the VPI / VCI, and then outputs each output port (# 1 to #n). Output the cell. When a connection identifier is not specially prepared, the output side conversion table 15 is searched based on the input port number of the cell and VPI / VCI. In this embodiment, since the outgoing header conversion unit 14 is physically handled as one block, cell output to each port (# 1,..., #N) is performed in a time division manner.
[0053]
【The invention's effect】
As explained above, according to the present invention, When a wait queue is allocated to the second output queue, transmission of unicast cells based on the wait queue allocated to the first output queue is suppressed, and multicast based on the wait queue allocated to the second output queue is performed. When sending a cell preferentially, based on the multicast tag corresponding to the multicast cell and the same port output count information, a multicast cell that does not need to be multicast multiple times to the same port At the same time, multicast cells that can be multicast in the same cell cycle as unicast cells, do not need to limit the input bandwidth of the cells to be multicast, and need to perform multiple multicasts to the same port, The same port output count information indicates the corresponding port. Becomes multicast possible for a plurality of different destinations in the same port by outputting only the number of outputs, it is possible to achieve efficient multicast functionality of the ATM cell .
[0055]
Furthermore, in the present invention, in addition to the multicast tag, the same port output frequency information indicating the number of multicast times for each port is used together, and based on this information, a control function for outputting the same cell to the same port multiple times is provided. Since it is added, it is possible to multicast to a plurality of different destinations of the same port, and an efficient multicast function of ATM cells can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of an ATM switching apparatus according to the present invention.
FIG. 2 is a diagram showing a logical configuration of an output cell selection algorithm in a cell transmission control unit.
FIG. 3 is a diagram showing an example of a table entry of an entry side conversion table.
FIG. 4 is a diagram showing an example of a table entry in the queue management table.
FIG. 5 is a schematic configuration diagram of a conventional ATM switching apparatus.
FIG. 6 is a schematic configuration diagram of a cell duplicating unit in a conventional ATM switching apparatus.
[Explanation of symbols]
11 Incoming header converter
12 Incoming conversion table
13 Cell buffer
14 Outgoing header converter
15 Outgoing conversion table
16 Cell transmission controller
161 Cell buffer control unit
162 Table control unit
163 Output cell determination unit
164 Multicast controller
17 Queue management table
21-11, ..., 21-1m, ..., 21-n1, ..., 21-nm Multicast queue
22-1 to 22-n Multicast queue
23-1, ..., 23-n Port scheduler
24 Multicast scheduler
25-1, ..., 22-n Output cell selector
26 Output scheduler
31, 32, 33, 34, 35 Entry side conversion table entry
41, 42, 43, 44 Queue management table entry

Claims (2)

In an asynchronous transfer mode switching apparatus having a unicast function for switching and outputting input cells from an arbitrary port to one port and a multicast function for switching and outputting to a plurality of different ports,
A first egress queue for unicast cells;
A second output queue for the multicast cell;
Multicast tag indicating the port to be multicast and the same port output indicating the number of cell transmissions to the same port from the route information added to the input cell and the information of the port to which the input cell is input and preset information Information conversion means for obtaining cell transmission control information including number of times information;
It is determined whether the input cell is a unicast cell or a multicast cell by referring to the multicast tag obtained by the information conversion means, and the first or second queue corresponding to the cell transmission control of the input cell is applied. When the queue is allocated to the output queue, and when the waiting queue is allocated to the second output queue, the transmission of the unicast cell based on the waiting queue allocated to the first output queue is suppressed, and the second queue When performing transmission control of the multicast cell based on the wait queue allocated to the output queue, a plurality of multicast cells are assigned to the same port based on the multicast tag corresponding to the multicast cell and the same port output count information. It is a cell that does not need to be multicast multiple times, or it can be A multicast cell that does not need to perform multicast to the same port multiple times is the same as the unicast cell for each port to be multicast indicated by the corresponding multicast tag. Multicast cells that need to be transmitted only once in the cell cycle and that need to be multicast to the same port multiple times are output based on the same port output count information and output the corresponding cell output count for the corresponding port. An asynchronous transfer mode switching apparatus comprising: a transmission control unit; Provided corresponding to the second output queue and distributed to the second output queue, which is performed after suppressing the transmission of the unicast cell based on the waiting queue allocated to the first output queue. Multicast scheduler means for restricting a cell transmission execution period of the multicast cell corresponding to each waiting queue between the waiting queues to a preset period
The asynchronous transfer mode switching apparatus according to claim 1 , further comprising:

Images