JPH09168016A - Pakcet switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a packet switch solving a problem of head of line(HOL) blocking without increasing an amount of packets transferred from an input buffer to an output buffer in the case of multi-casting. SOLUTION: The switch has input buffers 12a-12n and common output buffers 16a-16c. In this case, plural buffer areas 17 used in common by plural output ports are provided to the output buffers 16a-16c and a logic queue 13 corresponding to combinations of the buffer areas 17 is provided to the input buffers 12a-12n, an input control section 11 is used to input a multi-cast packet to the logic queue 13 corresponding to the combinations including the buffer areas 17 corresponding to the destination output ports and a scheduling section 14 and a switch section 15 are used to transfer the packet to the buffer area 17 connecting to the destination output port and the packet is transferred from the buffer area 17 to the destination output port.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packet switch used for packet communication such as ATM communication, and more particularly to a packet switch having buffers on both input and output sides of a switch section.

[0002]

2. Description of the Related Art Packet communication, in particular ATM (Asynchronous T) that transfers and exchanges fixed length packets called cells.
ransfer Mode (Asynchronous Transfer Mode) communication is drawing attention as a means for realizing high-speed data communication. Recently, ATM NI for transmitting and receiving data as cells in terminals
C (Network Interface Card) and ATM switches for exchanging cells have been put to practical use one after another, and the cell relay service has started on the public network, and the importance of ATM communication is becoming more and more certain. .

Various architectures have been proposed for the ATM switch, which is the most important key device for realizing ATM communication. Among them, an input buffer for temporarily accumulating incoming packets is provided in the switch unit. It is known that the switch architecture arranged on the input side can relatively easily implement a large-capacity buffer, and can exhibit excellent performance for traffic with strong burstiness. For example, IEICE Technical Report SSE93-
6 "ATM switch with expandable buffer capacity: XATO
M "discloses an ATM switch architecture combining an inexpensive large-capacity low-speed input buffer and a small-capacity high-speed output buffer. This architecture achieves high throughput even when strong bursty traffic is input. It is said that you can do it.

However, considering a multicast function for selectively broadcasting the same packet to a plurality of desired destinations,
The above-described conventional ATM switch architecture including the input buffer has a problem in that some compromise is required in terms of realizing high throughput. Hereinafter, this problem will be specifically described.

FIG. 5 is a diagram showing a schematic structure relating to a multicast function of an ATM switch having a conventional input buffer and output buffer, and a switch section is omitted. As shown in the figure, the input buffer has a logical queue for multicast packets for each input port,
The output buffer has a multicast packet buffer area for each output port. The multicast packet input to the logical queue for multicast packets in the input buffer is judged by the back pressure signal from the output buffer that the multicast buffer areas of all the output buffers corresponding to the multiple output ports of the destination are empty. If it is, it is transferred to the output buffer corresponding to the plurality of destination output ports. In this way, multicast is realized.

Here, in the configuration of FIG. 5, the number of logical queues for multicast set in the input buffer is one regardless of the destination of the packet. Therefore, if the output buffer corresponding to the destination output port of the packet at the head of the multicast logical queue is crowded, the chance that the packet will be transferred to the output buffer decreases, so the transfer of other packets is also affected. However, this has the drawback of reducing the overall throughput. This phenomenon is generally called HOL (Head Of Line) blocking.

The cause of such HOL blocking is that multicast packets having different destinations are managed by one logical queue for multicast packets. Therefore, as shown in FIG. 6, for example, when a multicast packet is input to the input buffer, the multicast packet is copied to create a logical queue for the multicast packet for each destination of the packet, and the multicast packet is managed by these logical queues. It is considered. In this way, the logical queue for multicast packets in the input buffer is equivalent to the logical queue for unicast packets, and the conventional unicast HO
Just as L blocking does not occur, HOL blocking does not occur.

However, in order to realize the multicast function with the configuration as shown in FIG. 6, the multicast packet is transferred from the input buffer to the output buffer in the multicast in order to make a multicast packet logical queue for each destination by copying in the input buffer. The amount of packets increases by the number of copies. When the number of copies, that is, the number of destinations of multicast packets is large, the amount of transfer packets from the input buffer to the output buffer increases accordingly, so that the switching capacity of the switch unit cannot be fully utilized and the packet switch The problem arises that the overall throughput is reduced.

[0009]

As described above, the conventional method of realizing the multicast function in the packet switch, in which the multicast packets having different destinations are managed by one logical queue for the multicast packet, has a problem of HOL blocking. In addition, the method of copying a multicast packet in the input buffer and creating a logical queue for the multicast packet for each destination solves the problem of HOL blocking, but the amount of packets transferred from the input buffer to the output buffer increases during multicast. However, there is a problem in that the replacement capacity of the switch cannot be fully utilized.

An object of the present invention is to provide a packet switch capable of solving the problem of HOL blocking without increasing the amount of packets transferred from the input buffer to the output buffer during multicast.

[0011]

In order to solve the above problems, a first packet switch according to the present invention has an input buffer for temporarily accumulating packets arriving at an input port, and a packet to the input buffer. Corresponding to the input control means for controlling the input of the input buffer, the output buffer for temporarily storing the packet transferred from the input buffer and outputting it to the destination output port, and the packet accumulated in the input buffer for the destination output port. In the packet switch provided with the transfer means for transferring to the output buffer, the output buffer is
The input buffer has a plurality of buffer areas shared by a plurality of predetermined output ports, the input buffer has a logical queue corresponding to each of a plurality of combinations of the plurality of buffer areas, and the input control means receives an input from the input port. Input multicast packets to the logical queue corresponding to the combination including the buffer areas corresponding to the output ports of the destination, and the transfer means connects the multicast packets input to the logical queue to the output ports of the destination. It is characterized in that the data is transferred to the created buffer area.

In this case, it is preferable that the logical queues of the input buffers are provided corresponding to the same number of combinations of the plurality of buffer areas. In the first packet switch, the HO, which has been a problem in the related art, is obtained by inputting and managing the multicast packets having different destinations into a plurality of logical queues in the input buffer.
Performance degradation due to L blocking can be avoided.
In other words, when a multicast packet is input, even if a certain output buffer is congested, the effect of this is only the packet destined to the output port corresponding to that output buffer, and other packets are not affected. ,
The problem of HOL blocking does not occur.

Further, unlike the method of copying a multicast packet in the input buffer and creating a logical queue for the multicast packet for each destination, it is not necessary to repeatedly transfer the same multicast packet to the output buffer side, so that the transfer packet amount in the switch unit is reduced. Since the switching capacity is reduced, the exchange capacity of the switch unit is not wastefully used, and the throughput of the entire packet switch is improved.

Further, the logical queue for multicast packet provided in the input buffer may be a relatively small number depending on the combination of all or part of the buffer area for multicast packet in the output buffer shared by the plurality of output ports. It is good and easy to implement.

A second packet switch according to the present invention is
An input buffer that temporarily stores packets that have arrived at the input port, an input control unit that controls the input of packets to this input buffer, and an output port that is the destination that temporarily stores the packets transferred from the input buffer. In a packet switch equipped with an output buffer for outputting to an output buffer and a transfer means for transferring a packet accumulated in the input buffer to an output buffer corresponding to a destination output port, the output buffer is a buffer corresponding to each of the plurality of output ports. The input buffer has a region, the input buffer has logical queues respectively corresponding to a plurality of combinations of a plurality of output ports, and the input control means includes a plurality of output ports of the destination of the multicast packet input from the input port. Input to the logical queue corresponding to the combination, transfer means input to the logical queue And wherein the transfer of multicast packets in a buffer area corresponding to a plurality of output ports of the destination.

Also in this second packet switch,
Basically, by inputting and managing multicast packets with different destinations to multiple logical queues in the input buffer, performance degradation due to HOL blocking is mitigated, and the same multicast packet does not need to be repeatedly transferred to the output buffer side. The amount of transfer packets in the switch unit is reduced, the exchange capacity of the switch unit is not wasted, and the throughput of the entire packet switch is improved.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing a configuration relating to a multicast function of a packet switch according to a first embodiment of the present invention. Multiple input ports 10a-
10n, input control units 11a to 11n, input buffers 12a to 12n, and scheduling unit 14a to
14n is provided, and a switch unit 15 for performing packet transfer / exchange processing and output buffers 16a to 16c are provided.

The output buffers 16a to 16c are smaller in number than the output ports 18a to 18m, are shared by some output ports, and have a multicast packet buffer area 17 shared by those output ports. A back pressure signal line 19 is drawn from the output buffers 16a to 16c, and the signal line 19 depends on the empty state of each multicast packet buffer area 17 in the output buffers 16a to 16c. The back pressure signal for giving the packet output permission from 12n is transmitted to the scheduling units 14a to 14c.

More specifically, the output buffers 16a to 16c will be described in detail. In the case of a switch architecture in which the output buffers 16a to 16c are composed of shared buffer type unit switches of 8 inputs and 8 outputs, for example, half of the shared output buffer areas are provided. Is used as a buffer area for unicast packets, and the other half is used as a buffer area for multicast packets. The unicast packet buffer area is further divided into the number of output ports (e.g., 8), and each output port is made to correspond.

The output buffers 16a to 16c shown in FIG.
The multicast packet buffer area 17 is not directly related to the actual configuration of the logical queue in the output buffer. The present invention works effectively regardless of what kind of logical queue the buffer areas available for multicast packets in the output buffers 16a to 16c form.

On the other hand, each of the input buffers 12a to 12n has a multicast packet buffer area, and a plurality of multicast packets corresponding to various combinations of the multicast packet buffer areas 17 in the output buffers 16a to 16c are provided in each of these buffer areas. A logical queue 13 for use is provided. In this example, there are three multicast packet buffer areas 17 in the output buffers 16a to 16c indicated by buffer area numbers A, B, and C. Therefore, the combination is A, B,
A, B, C, A + B, B + C, C + A, including C alone
There may be seven types of A + B + C, but in the present embodiment, for the reasons described later, among these combinations, A + B and B
The multicast packet logical queue 13 is provided for only three combinations of + C and C + A.

Next, the operation relating to the multicast function in the packet switch of this embodiment will be described. Now, consider the case where a multicast packet arrives at any of the input ports 10a to 10n. The arrived multicast packet is first input to the input control units 11a to 11a.
n. Input control units 11a to 11n
Checks the destination (output port) of the packet from the contents of the header of the multicast packet that arrived at the input port, and the input buffers 12a to 12n corresponding to the buffer area for the multicast packet in the output buffer corresponding to the output port of the destination. The multicast packet is input to the logical queue 13 for multicast packet therein.

For example, if the destination of the arrived multicast packet is the output port 18i and the output port 18j, the output buffers 16b and 16c corresponding to them are provided.
Since the buffer area 17 for the multicast packet therein is B and C, the multicast packet is input to the logical queue 13 for the multicast packet corresponding to the combination of B + C.

The multicast packet input to the multicast packet logical queue 17 in the input buffers 12a to 12n in this way is scheduled by the scheduling unit 14a.
14n are input to the switch unit 15. Based on the back pressure signal transmitted from the output buffers 16a to 16c via the back pressure signal line 19, the scheduling units 14a to 14n are all in the multicast packet buffer area 17 in the output buffers 16a to 16c corresponding to the destination. If there is a free space, that is, if the packets cannot be simultaneously transferred to the multicast packet buffer areas 17, the head packet of the multicast packet logical queue 17 in the input buffers 12a to 12n is taken out and the switch unit Entering 15 is prohibited.

FIG. 2 shows an example of the format of the back pressure signal, and "0" or "1" is set corresponding to each buffer area number A, B, C of the multicast packet buffer area 17. Here, "0"
Is output permission, and “1” is output prohibition, “1” if the number of packets accumulated in the corresponding buffer areas A, B, C is equal to or more than a threshold value, otherwise “1”. It is set to 0 ". In the example of the figure, A = “1”, B =
Since "0" and C = "0", the packet output to the output buffer 16a is "output prohibited", the output buffer 16b,
Since the packet output to 16c is “output permitted”, the scheduling units 14a to 14n use the input buffer 12
Logical queue 1 for multicast packets in a to 12n
Of the three packets, packets are extracted from only the logical queue corresponding to the combination of B + C and input to the switch unit 15.

The switch unit 15 transfers the packet input via the scheduling units 14a to 14n to the multicast packet buffer area 17 in the output buffer corresponding to the destination. Here, the input port 10a-
If the packet arriving at 10n is a multicast packet to a plurality of output buffers, the switch unit 15
Is a multicast packet buffer area 17 corresponding to a plurality of destinations by copying the multicast packet.
You can transfer it to.

The multicast packets thus transferred from the switch unit 15 and temporarily stored in the multicast packet buffer area 17 corresponding to the destination are
It is output to the destination output port of the output ports 18a to 18m.

By the way, as described above, the output buffer 1
When there are three multicast packet buffer areas A, B, and C in 6a to 16c, the combinations are A, B, C, A + B, B + C, C + A, and A + B + C.
Therefore, it is conceivable to provide the same number of logical queues 13 for multicast packets in the input buffers 12a to 12n as the number of combinations of these multicast packet buffer areas.

However, as the multicast packet logical queue 13 in the input buffers 12a to 12n, the multicast packet buffer area 17 corresponding to the destination is provided.
Of a large number (in the above example, a logical queue corresponding to a combination of A + B + C) and a small number of multicast packet buffer areas 17 corresponding to a destination (in the above example, A, B, C , The logical queue with a large number of buffer areas corresponding to the destination has a smaller number of output opportunities, resulting in unfairness. This is because if the number of buffer areas corresponding to the destination is large, a packet cannot be output unless there is a vacancy in all the buffer areas.

On the other hand, if the multicast packet buffer areas corresponding to the destinations of all the multicast packet logical queues 13 have the same number, such unfairness is unlikely to occur. That is, only logical queues having the same number of multicast packet buffer areas corresponding to destinations, for example, A + B, B + C, and C + as described above.
By setting only the logical queues corresponding to the respective combinations of A in the input buffers 12a to 12c,
Such injustice is mitigated.

At this time, when the number of the multicast packet buffer areas 17 corresponding to the destination of the input packet does not match the number of the multicast packet buffer areas 17 corresponding to the destination of the multicast packet logical queue 13, The problem is how to determine which logical queue a packet should be input to. To solve this problem, if the destination of the packet is narrower than the destination of one logical queue, you can select one of the logical queues including the destination of the packet and input it, or vice versa. , The input buffers 12a to 12d are wider than the destinations of one logical queue.
The packet may be copied at the time of input to 12c and input to a plurality of logical queues for multicast packets.

As in the above example, A + B, B + C, C + A
When only the logical queues corresponding to the respective combinations are set in the input buffers 12a to 12c, for example, the multicast packet corresponding to only the buffer area with the destination A becomes the logical queue for the multicast packet corresponding to the combination of A + B or C + A. Just put it in. Further, the multicast packet corresponding to the buffer area with the destination of A + B + C may be copied and input into the two multicast packet logical queues corresponding to the respective combinations of A + B and B + C at the time of input. In this case, since the packet to be transferred to the buffer area B may be either the packet placed in the logical queue corresponding to the combination of A + B or the packet placed in the logical queue corresponding to the combination of B + C, the destination of the packet is Different for each logical queue.

Regarding the method of inputting the multicast packet corresponding to the buffer area of A + B + C, in addition to the method of putting in the two logical queues for the multicast packet corresponding to each combination of A + B and B + C as described above, It is possible to adopt various methods such as putting two logical queues for multicast packets corresponding to each combination, or two logical queues for multicast packet corresponding to each combination of A + B and C + A.

However, it should be noted that, especially in the case of ATM, it is not allowed to change the transfer procedure of cells of the same virtual connection. Simply, cells of the same virtual connection can avoid such a transfer order change by continuing to select the same logical queue for multicast packets.

As described above, according to the present embodiment, the multicast packets having different destinations are input to the input buffer 12a.
By inputting to and managing a plurality of logical queues 13 to 12n, it is possible to mitigate the decrease in throughput due to HOL blocking. In other words, when a multicast packet is input, even if a certain output buffer is congested, the effect of this is only the packet destined to the output port corresponding to that output buffer, and other packets are not affected. , HOL blocking does not occur.

Also, in the present embodiment, unlike the method shown in FIG. 4 in which a multicast packet is copied in the input buffer to create a logical queue for the multicast packet for each destination, it is not necessary to repeatedly transfer the same multicast packet to the output buffer side. Therefore, the switch unit 15
In this case, the amount of packets transferred in the packet is reduced, the exchange capacity of the switch unit 15 is not wasted, and the throughput of the packet switch is not reduced.

Further, in this embodiment, the input buffer 12
The multicast packet logical queues 13 provided in a to 12n may have a relatively small number corresponding to a combination of all or some of the multicast packet buffer areas in the output buffers 16a to 16c shared by a plurality of output ports. Since it is sufficient, it has the advantage of being easy to implement.

(Second Embodiment) FIG. 3 is a block diagram showing a configuration relating to a multicast function of a packet switch according to another embodiment of the present invention. The packet switch of this embodiment has a plurality of input ports 20a to 20n,
Input control units 21a to 21n and input buffers 22a to 22
n, scheduling units 24a to 24n, switch unit 2
5, output buffers 26a to 26d, output ports 28a to
28d and the back pressure signal line 29, and the input buffers 22a to 22n are provided with a multicast packet logical queue 23A and a unicast packet logical queue 23B, respectively, and an output buffer 26a.
26d to the multicast packet buffer area 2
7 are provided respectively.

This embodiment differs from the previous embodiments in the method of implementing the multicast packet function. That is,
In this embodiment, the multicast packet logical queue 23A in the input buffers 22a to 22n is provided corresponding to the combination of the output ports 28a to 28d of the destination of the multicast packet. For example, output port 2
If the port numbers of 8a, 28b, 28c, and 28d are 1, 2, 3, and 4, respectively, the logical queue for multicast packet 23A is 1 + 2 + 3 + 4, 1 + 2 + 3,2 + 3.
+ 4,1 + 3 + 4,1 + 2 + 4,1 + 2,2 + 3,3 +
It is provided corresponding to each combination of 4, 1 + 4, 2 + 4, 1 + 3.

On the other hand, the unicast packet logical queue 23B in the input buffers 22a to 22n is provided for each output port 28a to 28d of the destination of the unicast packet. In this example, the port numbers 1, 2, 3, 4 are provided. Are provided corresponding to each.

FIG. 4 shows an example of the format of the back pressure signal on the back pressure signal line 29 according to the present embodiment, in which "0" or "1" corresponds to the output port numbers 1, 2, 3 and 4. It is set. here,
“0” indicates output permission, “1” indicates output prohibition, “1” if the number of packets accumulated in the multicast packet buffer area connected to the corresponding output port is greater than or equal to the threshold value, If not, it is set to "0".
In the example in the figure, 1 = “0”, 2 = for each output port number
"1", 3 = "0", 4 = "1" are set, packet output to the output buffers 16b and 16c is "permitted", and packet output to the output buffer 16a is "prohibited".
Therefore, the scheduling units 14a to 14n take out packets from only the logical queues corresponding to the combination of B + C among the logical queues 13 for multicast packets in the input buffers 12a to 12n and input them to the switch unit 15.

As described above, also in this embodiment, basically, as in the first embodiment, the multicast packets having different destinations are input to the plurality of multicast packet logical queues 23 in the input buffers 22a to 22n to be managed. As a result, it is possible to mitigate the decrease in throughput due to HOL blocking. Further, since it is not necessary to repeatedly transfer the multicast packet to the output buffer side during the multicast, the transfer packet amount in the switch unit 25 is reduced, the exchange capacity of the switch unit 15 is not wastefully used, and the entire packet switch is not used. There is no reduction in throughput.

In this embodiment, the input buffer 22a is used.
22n to multicast packet logical queue 23
Are provided corresponding to the combination of the output ports 28a to 28d, the logical queue 2 becomes available when the number of output ports increases.
The number of 3 also increases, which makes implementation difficult. Therefore, the configuration of this embodiment is suitable when the number of output ports is relatively small.

[0044]

As described above, in the packet switch of the present invention, when realizing the multicast function, the output buffer is provided with a plurality of buffer areas shared by a plurality of output ports, and the input buffer is provided with a plurality of buffer areas. A logical queue corresponding to each combination of multiple types is provided, and the multicast packet input from the input port is input to the logical queue corresponding to the combination including the buffer areas corresponding to the output ports of the destination. The multicast packet input to the destination is transferred to the buffer area connected to the output ports of the destination, or the output buffer has buffer areas corresponding to the output ports, and the input buffer has multiple output ports. Compatible with multiple combinations A logical queue is provided, and the multicast packet input from the input port is input to the logical queue corresponding to the combination including multiple output ports of the destination, and the multicast packet input to the logical queue is output to the multiple output ports of the destination. Transfer to the corresponding buffer area.

With such a configuration, in the packet switch of the present invention, performance deterioration due to HOL blocking is alleviated, and the transfer packet amount in the switch unit is reduced, so that the exchange capacity of the switch unit is not wasted. Therefore, there is an effect that the throughput of the entire packet switch is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration related to a multicast function of a packet switch according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a format of a back pressure signal in the same embodiment.

FIG. 3 is a block diagram showing a configuration of a packet switch according to another embodiment of the present invention.

FIG. 4 is a diagram showing an example of a format of a back pressure signal in the same embodiment.

FIG. 5 is a block diagram showing a schematic configuration of a multicast function of a conventional packet switch.

FIG. 6 is a block diagram showing a schematic configuration of a multicast function of another conventional packet switch.

[Explanation of symbols]

 10a to 10n ... Input ports 11a to 11n ... Input control section 12a to 12n ... Input buffer 13 ... Multicast packet logical queue 14a to 14n ... Scheduling section 15 ... Switch section 16a to 16c ... Output buffer 17 ... Multicast packet shared buffer 18a -18m ... Output port 19 ... Back pressure signal line 20a-20n ... Input port 22a-22n ... Input control part 22a-22n ... Input buffer 23A ... Multicast packet logical queue 23B ... Unicast packet logical queue 24a-24n ... Scheduling Part 25 ... Switch part 26a-26d ... Output buffer 27 ... Multicast packet buffer 28a-28d ... Output port 29 ... Back pressure signal line

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshinada Saito 580-1 Horikawa-cho, Sachi-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Semiconductor System Technology Center

Claims (3)

[Claims] 1. An input buffer for temporarily accumulating packets arriving at an input port, input control means for controlling the input of packets to the input buffer, and temporarily accumulating packets transferred from the input buffer. In the packet switch provided with an output buffer for outputting to a destination output port, and a transfer unit for transferring the packet accumulated in the input buffer to an output buffer corresponding to the destination output port, the output buffer is A plurality of buffer areas shared by a plurality of predetermined output ports; the input buffer has logical queues respectively corresponding to a plurality of combinations of the plurality of buffer areas; Multicast packets input from a port are stored in the buffer area corresponding to multiple output ports of the destination. Is input to the logical queue corresponding to the combination including, and the transfer unit transfers the multicast packet input to the logical queue to the buffer area connected to a plurality of output ports of the destination. Packet switch to do. 2. An input buffer for temporarily storing a packet arriving at an input port, an input control means for controlling the input of the packet to the input buffer, and a buffer for temporarily storing the packet transferred from the input buffer. In the packet switch provided with an output buffer for outputting to a destination output port, and a transfer unit for transferring the packet accumulated in the input buffer to an output buffer corresponding to the destination output port, the output buffer is A plurality of buffer areas shared by a plurality of predetermined output ports, the input buffer has a logical queue respectively corresponding to the same number of combinations of the plurality of buffer areas, the input control means, The multicast packet input from the input port is stored in the buffer corresponding to the output ports of the destination. Inputting to the logical queue corresponding to the combination including an area, the transfer means transfers the multicast packet input to the logical queue to the buffer area connected to a plurality of output ports of the destination. And packet switch. 3. An input buffer for temporarily storing a packet arriving at an input port, an input control means for controlling the input of the packet to this input buffer, and a buffer for temporarily storing the packet transferred from the input buffer. In the packet switch provided with an output buffer for outputting to a destination output port, and a transfer unit for transferring the packet accumulated in the input buffer to an output buffer corresponding to the destination output port, the output buffer is The input buffer has logical queues respectively corresponding to a plurality of combinations of the plurality of output ports, and the input control means receives an input from the input port. Before the multicast packet corresponding to the combination including multiple output ports of its destination Enter the logical queue, said transfer means, a packet switch, characterized in that to transfer a multicast packet which is input to the logical queue in the buffer area corresponding to a plurality of output ports of the destination.