JP2000101591A - Cell scheduler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten packet transfer time while satisfying fairness between connections during communication sharing the same band and to set a priority order based on a packet length by estimating the queue length of each cell buffer in the case of assuming that plural cell buffers circularly send out cells. SOLUTION: A VCI identification part 1 discriminates whether or not an arriving cell is the EOP cell of the final cell of the plural cells transmitted by decomposing one packet into the plural cells. The cell buffers 61-6n store the arriving cell for every connection, and an information management part 2 estimates the buffer length of the respective cells in the case of assuming that the cell buffers 61-6n circularly send out the cells. When the EOP cell is included in the cell buffer for which the queue length estimated by the information management part 2 is below an actual queue length, a judging part 3 imparts a priority right to the cell buffer and further, the judgement part 3 sets a priority order corresponding to the length of the packet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ATM (Asynchronou).
s Transfer Mode). The present invention is suitable for use in ATM communication in which an upper layer packet is divided into a plurality of cells and transferred. The present invention relates to a technology for fairly using an ATM network.

[0002]

2. Description of the Related Art Although an ATM network is a cell network, recently, a number of controls have been proposed in consideration of a packet which is an upper layer. Among them, there is cell scheduling that is aware of upper layer packets. The purpose of packet-aware cell scheduling is to minimize the packet transfer time.

Here, simply shortening the cell transfer time,
FIG. 9 shows an example in which the packet transfer time cannot be reduced. FIG.
In this example, it is assumed that cells constituting a packet having a packet size of 4 arrive at the switch at t = 1, 2, 3, and 4, respectively.

At output A, the cells have t = 2 and t = 2, respectively.
3, t = 4 and t = 8, the cell transfer time of each cell is (2-1) = 1, (3-2) = 1, (4
-3) = 1, (8-4) = 4, and the average cell transfer time is (1 + 1 + 1 + 4) /4=1.75. Also,
When the packet transfer time is defined as the time from the arrival of the first cell constituting the packet to the output of the last cell constituting the packet, the packet transfer time is defined as:
(8-1) = 7.

At output B, the cells have t = 3 and t =
4, t = 5 and t = 6, the cell transfer time of each cell is (3-1) = 2, (4-2) = 2, (5
-3) = 2, (6-4) = 2, and the average cell transfer time is (2 + 2 + 2 + 2) / 4 = 2. The packet transfer time is (6-1) = 5.

That is, although the average cell transfer time is shorter for output A than output B, the packet transfer time for output B is shorter than output A. Therefore, in order to shorten the packet transfer time, it is necessary to perform packet-aware cell scheduling instead of conventional cell-aware cell scheduling. As such cell scheduling, there has been proposed a method of preferentially outputting a cell of a connection at which the last cell (EOP cell: Endof Packet cell) constituting a packet has arrived (Soda et al., A Study of ATM Cell Scheduling, "IEICE Communications Society Conference 1996 B-548). The procedure is described below. (1) When there is a queue including an EOP cell which is a packet break in all connection queues, one of the queues is selected by round robin. (2) The cells in the queue selected in (1) are transmitted continuously from the head to the first EOP cell. (3) Until the queue containing the EOP cell disappears
Continue (1) and (2). (4) When the queue including the EOP cell is exhausted, one of the queues including the cell is selected by round robin. (5) Transmit the cells in the queue selected in (4) to the end. However, when an EOP cell is queued in another queue on the way, (2) is executed in that queue. (6) Until there are no more queues containing cells, (4)
Continue with (5).

[0007]

As described above, the packet transfer time can be shortened by using the conventionally proposed method. However, the available bandwidth cannot be fairly distributed among the active connections that are currently communicating. That is, fairness cannot be satisfied. The reason is that, in the conventionally proposed method, the more the traffic is output, the more bandwidth can be obtained.

In other words, the conventionally proposed packet-aware cell scheduling has a problem that fairness cannot be satisfied and the packet transfer time cannot be shortened.

Accordingly, the applicant of the present application has filed Japanese Patent Application No. 10-25 / 1998.
No. 5,451 (not disclosed at the time of filing of the present application) makes it possible to perform packet-aware cell scheduling while satisfying fairness between communicating connections sharing the same band, and shortening the packet transfer time. A possible cell scheduler was proposed.

However, in the prior application, since the packet length is not consciously controlled, the packet transfer time of a connection transmitting a short packet is longer than that in the case of transmitting cells in a round robin manner. There was a problem.

That is, when a connection becomes a connection that can transmit cells preferentially, and if the number of cells to be transmitted is equal to or less than a certain value, the cell can be transmitted more preferentially among connections that can transmit cells preferentially. It is desired to perform hierarchical cell scheduling control such that the cell scheduling can be transmitted.

SUMMARY OF THE INVENTION The present invention has been made in such a background, and performs packet-aware cell scheduling while satisfying the fairness between communicating connections sharing the same band. It is another object of the present invention to provide a cell scheduler that can shorten the packet transfer time and also considers the packet length.

[0013]

SUMMARY OF THE INVENTION The present invention is a cell scheduler for identifying whether an arriving cell is the last cell of a plurality of cells transmitted by disassembling one packet into a plurality of cells. Identification means, a plurality of cell buffers for storing arriving cells for each connection, and a determination means for determining a cell buffer to which the priority of cell reading is to be given among the plurality of cell buffers. Is a cell scheduler including selection means for selecting a cell buffer including the last cell as a candidate to which the priority is given.

Here, the feature of the present invention is that a means for estimating the queue length of each cell buffer when the plurality of cell buffers are assumed to transmit cells cyclically is provided, Means for assigning the priority to the cell buffer when the last cell is included in a cell buffer whose queue length estimated by the estimation means is smaller than the actual queue length; The means for setting includes means for setting a priority according to the length of the packet.

[0015] The means for setting the priority may include means for setting a higher priority for a packet having a shorter packet length than a predetermined packet length as compared to a packet having a longer packet length than the predetermined packet length. It is desirable to include.

As described above, according to the present invention, while performing packet-aware cell scheduling, it is possible to satisfy the fairness between communicating connections sharing the same band and to shorten the packet transfer time. It is characterized by taking into account the packet length as well as being able to do so.

That is, by estimating the queue length of each cell buffer when it is assumed that the plurality of cell buffers transmit cells cyclically, the queue length is estimated by cell scheduling in a cell unit that is not aware of packets. can do. If the queue length estimated in this way is called a virtual queue length, comparing the actual queue length with the virtual queue length, the difference between cell-based cell scheduling and packet-aware cell scheduling is calculated. You can ask.

In other words, the virtual queue length is the queue length when the bandwidth is fairly distributed between the communicating connections. Thus, a connection whose actual queue length is longer than the virtual queue length is a connection that has obtained a bandwidth less than the fair bandwidth, while a connection whose actual queue length is shorter than the virtual queue length is
A connection that has obtained more bandwidth than fair bandwidth.

Therefore, the connection in which the actual queue length is longer than the virtual queue length, and the connection in which the EOP cell is stored in the cell buffer can be preferentially set as the connection capable of transmitting the cell,
The packet transfer time can be shortened while satisfying fairness.

At this time, the present invention takes into account the packet length, and solves the problem that the packet transfer time of a connection transmitting a short packet is longer than the case where cells are transmitted in a round robin manner. . That is,
When a plurality of cell buffers including EOP cells exist, this problem is solved by giving a high priority to a cell buffer including a packet having a short packet length.

[0021] It is preferable that the apparatus further comprises means for giving a transmission right to permit cell transmission until the last cell is transmitted to the cell buffer to which the priority is set by the priority setting means.

[0022] The means for granting the transmission right may include means for transferring the transmission right to another cell buffer when the cell buffer to which the transmission right has been granted has transmitted the last cell. desirable.

That is, when the transmission of a series of cells constituting one packet is completed, the transmission right is transferred to another cell buffer, so that a cell between a plurality of cell buffers having the same condition for obtaining the transmission right can be obtained. Equal sending opportunities can be ensured.

[0024]

Embodiments of the present invention will be described with reference to FIG. FIG. 1 is a block diagram of a main part of a cell scheduler according to an embodiment of the present invention.

The present invention relates to a cell scheduler, and FIG.
As shown in (1), a VCI identification unit 1 for identifying whether an arriving cell is an EOP cell of a plurality of cells transmitted by decomposing one packet into a plurality of cells, and an arriving cell for each connection. a plurality of cell buffers ₆₁ through 65 to be stored
_n and a determination unit 3 for determining a cell buffer 6 _i (any one of _{1 to n} ) to which the priority of cell reading is to be given among the cell buffers 6 _{1 to} 6 _n. ,
A cell scheduler that sets a cell buffer including the EOP cell as a candidate for giving the priority.

[0026] Here, it is an aspect of the present invention, the information management as a means of estimating the queue length of each cell buffer when the cell buffer 6 ₁ to 6 _n is assumed to perform the delivery of cyclically cell A determination unit for determining whether the EOP cell is included in a cell buffer in which the queue length estimated by the information management unit is smaller than the actual queue length; The determination unit 3
The priority is set according to the length of the packet.

The determining unit 3 sets a higher priority to a packet having a shorter packet length than a predetermined packet length as compared with a packet having a longer packet length than the predetermined packet length. There EOP cell to set the cell buffer 6 _i confer send right to allow delivery of the cell to be sent. This setting result is stored in the priority connection list section 7. Further, the judgment unit 3
, When the send right cell buffer 6 _i granted threw the last cell shifts the send right to the other cell buffer.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a diagram showing the recorded contents of the information management unit 2. FIG. 3 is a flowchart showing a procedure for determining a transmission cell according to the first embodiment of the present invention. FIG. 4 is a flowchart showing a procedure for shifting to a connection from which cells can be output preferentially. FIG. 5 is a diagram for explaining a specific operation example. FIG. 6 is a diagram showing the recorded contents of the information management unit. FIG. 7 is a diagram showing the recorded contents of the priority connection list section 7.

As shown in FIG. 1, the VCI identification unit 1 identifies the VCI of an arriving cell and whether the cell is an EOP cell. Queue length reading unit 4 reads the queue length of the cell buffer 6 ₁ to 6 _n provided for each connection.

The information management unit 2 determines, for each connection, whether the connection is a connection that can output cells preferentially, the number of EOP cells in the cell buffers 6 _{1 to} 6 _n , the position of the first EOP cell, cells in round-robin is managing virtual queue length is a queue length of each connection when it is sent from the cell buffer 6 ₁ to 6 _n.

The priority connection list unit 7 manages connections that can output cells preferentially in two lists, and determines which list the connection is registered in. If the actual queue length of a connection is equal to or longer than the virtual queue length, the determination unit 3 determines that the connection is a connection that can be output with priority. The control unit 5 controls a cell to be transmitted next.

The operation of the first embodiment of the present invention will be described below with reference to FIGS. Now, the time is t = 1, the number of connections in communication is 3, and each cell buffer 6
_{1 to} 6 _n have two cells each, the virtual queue length of each is _{1, 1} , 4, and each EOP
The number of cells is 1, 0, 0, and the connection that can output cells preferentially is only connection # 1, and connection # 1 is registered in the list. Whether a connection is registered in the list or in the list is determined if the position of the first EOP cell, that is, the number of cells to be transmitted is 3 or less, if the connection is registered in the list, otherwise the connection is registered in the list. I do. Connection # 2,
Suppose # 3 that the EOP cell arrives at the switch at t = 2. (T = 2) (Cell output) The control unit 5 recognizes that the priority connection list unit 7 has no registration in the list and that the connection # 1 is registered at the head of the list. Output a cell. As a result, the queue lengths of the respective connections are 1, 2, and 2, and the virtual queue lengths are 0, 1, and 4. The position of the first EOP cell of connection # 1 is 1.

Although the virtual queue of the connection # 1 has been subtracted, the determination unit 3 does not make a determination because the connection # 1 is already a connection that can output cells with priority. Further, since the output cell is not an EOP cell, the connection # 1 is not removed from the connection which can output the cell preferentially. (Cell input) When the EOP cells of the connections # 2 and # 3 arrive, the VCI identification unit 1 identifies the arriving cell and the arriving cell as an EOP cell, and notifies the information management unit 2 of the result. I do.

The information management unit 2 sends the VC
When the information indicating that the I number and the EOP cell have arrived is received, the virtual queue length and the number information of the EOP cells of the managed connection are increased by one. As a result, each virtual queue length is 0, 2, 5, and the number of each EOP cell is 1, 1, 1. Also,
The positions of the first EOP cells of the connections # 2 and # 3 are 3 and 3, respectively. EOP of connection # 2, # 3
Since the cell has arrived and the connections # 2 and # 3 are not connections that can send cells preferentially, the information management unit 2 sends the connection number and the virtual queue length of the connection to the determination unit 3.

When the information is received, the determination unit 3 requests the queue length reading unit 4 to send the actual queue length of the received connection number. Queue length reading unit 4, the queue length for the requested connection cell buffer ₆₁ through
It reads from _n and sends it to the determination unit 3. In the determination unit 3,
Based on the received queue length and virtual queue length, it is determined whether or not the connection becomes a connection for transmitting cells preferentially. In the first embodiment of the present invention, the connection # 2 has a real queue length of 3 and a virtual queue length of 2, so it is a connection for transmitting cells preferentially. Since the position of the first EOP cell is 3, the list 1 Registered in. On the other hand, since the actual queue length is 3 and the virtual queue length is 5, connection # 3 does not become a connection for preferentially transmitting cells.

Here, the meaning of comparing the actual queue length with the virtual queue length will be described. As described above, the virtual queue length is the queue length of each connection when a cell is always transmitted from the cell buffer in round robin. In other words, the virtual queue length is the queue length when the bandwidth is fairly distributed among the communicating connections. Therefore, a connection in which the actual queue length is longer than the virtual queue length is a connection that has obtained a bandwidth smaller than the fair bandwidth. On the other hand, a connection in which the actual queue length is shorter than the virtual queue length is a connection that has obtained a bandwidth higher than the fair bandwidth. Therefore, by setting a connection in which the actual queue length is longer than the virtual queue length as a connection capable of transmitting cells preferentially, it is possible to shorten the packet transfer time while satisfying fairness. (T = 3) (Cell output) The control unit 5 outputs the cell of the connection # 2 since the priority connection list unit 7 knows that the connection # 2 is registered at the head of the list. As a result, the queue length of each connection is 1, 2, and 3, and the virtual queue length is t
= 2, connection # 1 was selected, so connection # 2 was selected by round robin, and 0,
1,5. The position of the first EOP cell of connection # 2 is 2. Although the virtual queue of the connection # 2 has been subtracted, the determination unit 3 does not make a determination because the connection # 2 is already a connection that can output cells with priority. Further, since the output cell is not an EOP cell, the connection # 2 is not removed from the connection that can output the cell preferentially. (Cell input) No cell is input. (T = 4) (Cell output) The control unit 5 outputs the cell of the connection # 2 because the priority connection list unit 7 knows that the connection # 2 is registered at the head of the list. As a result, the queue length of each connection becomes 1, 1, 3 and the virtual queue length is t
= 3, connection # 2 was selected, so 0,
1 and 4. The position of the first EOP cell of connection # 2 is 1. Since the virtual queue of the connection # 3 has been subtracted, the determination unit 3 determines whether or not the connection # 3 is a connection that can transmit cells preferentially. However, since the actual queue length is 3 and the virtual queue is 4, However, it is not a connection that can preferentially transmit cells. Further, since the output cell is not an EOP cell, the connection # 2 is not removed from the connection that can output the cell preferentially. (Cell input) No cell is input. (T = 5) (Cell output) The control unit 5 outputs the cell of the connection # 2 because the priority connection list unit 7 knows that the connection # 2 is registered at the head of the list. As a result, the queue length of each connection is 1, 0, 3, and the virtual queue length is t
= 4, the connection # 3 was selected, so that it becomes 0, 0, 4 by round robin. (The virtual queue of connection # 1 is not selected because it is already 0.) The position of the first EOP cell of connection # 2 is 0. Although the virtual queue of the connection # 2 has been subtracted, since the connection # 2 has no EOP cell, the determination unit 3 does not make a determination. Since the output cell is an EOP cell, the connection # 2 is out of the connection which can output the cell preferentially. (Cell input) No cell is input.

Thereafter, cells are transmitted in accordance with the procedures shown in FIGS. As shown in FIG. 3, it is determined whether or not there is a connection that can output cells preferentially (S1). If not, a cell to be transmitted by round robin is determined from connections having cells in the cell buffer. (S2). If such a connection exists, it is determined whether there is a connection registered in the list from among such connections (S3). If there is a connection registered in the list, a transmission right is given to the connection registered at the top of the list (S
4). If there is no connection registered in the list, a transmission right is given to the connection registered at the head of the list (S5). The cell of the connection having the transmission right is transmitted (S6). If the transmitted cell is an EOP cell (S7), the connection having the transmitted cell is preferentially removed from the connection for outputting the cell (S7).
8).

As shown in FIG. 4, E of connection #i
When the OP cell arrives at the cell buffer 6 _i , or when the virtual queue length of the connection #i is reduced (S 9), the connection #i is connected to the cell buffer 6 i.
It is determined whether or not there is an EOP cell in _i and the connection can output the cell preferentially (S10). At this time, if the connection can output cells preferentially, the actual queue length of the connection #i is further compared with the virtual queue length. If the actual queue length exceeds the virtual queue length (S11), the connection is established. #I is set as a connection that can output cells preferentially (S1
2). If the number of cells up to the EOP cell appearing next to the connection #i is equal to or smaller than a preset value, (S
13) The connection #i is registered in the list of the priority connection list section 7 (S14). connection#
If the number of cells up to the EOP cell appearing after i exceeds a preset value (S13), the connection #i is registered in the list of the priority connection list section 7 (S15). (Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. 1, 2, and 4 to 8. FIG. A diagram showing a system configuration, a procedure for shifting to a connection capable of outputting cells preferentially, and a specific example are the same as those in the first embodiment of the present invention, and FIG. It is.

The operation of the second embodiment of the present invention will be described below with reference to FIGS. Now, the time is t = 1, the number of communicating connections is 3, and each cell buffer has:
There are two cells, each having a virtual queue length of 1, 1, 4, and the number of each EOP cell is:
1, 0, and 0, and the only connection that can output cells preferentially is connection # 1. It is assumed that connection # 1 is registered in the list and has a transmission right. Whether a connection is registered in the list or in the list is determined if the position of the first EOP cell, that is, the number of cells to be transmitted is 3 or less, if the connection is registered in the list, otherwise the connection is registered in the list. I do. In the connections # 2 and # 3, it is assumed that the EOP cell arrives at the switch at t = 2. (T = 2) (Cell output) The control unit 5 outputs the cell of the connection # 1 because the priority connection list unit 7 knows that the connection # 1 at the head of the list has the transmission right. As a result, the queue lengths of the respective connections are 1, 2, and 2, and the virtual queue lengths are 0, 1, and 4. EO at the beginning of connection # 1
The position of the P cell becomes 1. Although the virtual queue of the connection # 1 has been subtracted, the determination unit 3 does not make a determination because the connection # 1 is already a connection that can output cells preferentially. Further, since the output cell is not an EOP cell, the connection # 1 is not removed from the connection which can output the cell preferentially. (Cell input) When the EOP cells of the connections # 2 and # 3 arrive, the VCI identification unit 1 identifies the arriving cell and the arriving cell as an EOP cell, and notifies the information management unit 2 of the result. I do. When the information management unit 2 receives the information indicating that the VCI number and the EOP cell have arrived from the VCI identification unit 1, the information management unit 2 increases the virtual queue length of the managed connection and the number information of the EOP cells by one. As a result, each virtual queue length is
0, 2, 5, the number of each EOP cell is 1, 1,
It becomes 1. Also, the first EO of the connections # 2 and # 3
The positions of the P cells are 3 and 3, respectively. connection#
2, # 3 EOP cells arrive and connection #
Since information # 2 and # 3 are not connections that can transmit cells preferentially, the information management unit 2 sends the connection number and the virtual queue length of the connection to the determination unit 3.

Upon receiving the information, the judging unit 3 requests the queue length reading unit 4 to send the actual queue length of the received connection number. Queue length reading unit 4, the queue length for the requested connection cell buffer ₆₁ through
It reads from _n and sends it to the determination unit 3. In the determination unit 3,
Based on the received queue length and virtual queue length, it is determined whether or not the connection becomes a connection for transmitting cells preferentially. In the second embodiment of the present invention, the connection # 2 has a real queue length of 3 and a virtual queue length of 2, so it is a connection for transmitting cells preferentially. Since the position of the first EOP cell is 3, the connection # 2 is included in the list. be registered. On the other hand, since the actual queue length is 3 and the virtual queue length is 5, connection # 3 does not become a connection for preferentially transmitting cells. (T = 3) (Cell output) The control unit 5 outputs the cell of the connection # 1 because the connection # 1 at the head of the list in the priority connection list unit 7 has the transmission right. As a result, the queue lengths of the respective connections are 0, 2, and 3. The virtual queue length is t = 2 and the connection # 1 is selected. Therefore, the connection # 2 is selected by round robin, and 0 is selected. , 1 and 5. EO at the beginning of connection # 1
The position of the P cell becomes 0. Although the virtual queue length of the connection # 2 has been subtracted, since the connection # 2 is already a connection that can output cells preferentially, the determination unit 3
Does not make a determination. Since the output cell is an EOP cell, the connection # 1 is disconnected from the connection capable of outputting the cell preferentially and loses the transmission right. (Cell input) No cell is input. (T = 4) (Cell output) Since there is no connection having the transmission right in the priority connection list unit 7, the control unit 5 gives the transmission right to the connection # 2 at the head of the list, and assigns the cell of the connection # 2. Output. As a result, the queue lengths of the respective connections are 0, 2, and 3, and the virtual queue lengths are 0, 1, and 4 because t = 3 and the connection # 2 is selected. The position of the first EOP cell of connection # 2 is 2. Connection # 3
Is determined, the determination unit 3 determines whether or not the connection # 3 is a connection that can transmit cells preferentially. However, since the actual queue length is 3 and the virtual queue is 4, priority is given. Is not a connection that can send cells to The output cell is EO
Since it is not a PCell, the connection # 2 is not removed from the connection that can output cells preferentially. (Cell input) No cell is input. (T = 5) (Cell output) The control unit 5 outputs the cell of the connection # 2 since the priority connection list unit 7 knows that the connection # 2 is at the head of the list. As a result, the queue length of each connection is 0, 1, 3, and the virtual queue length is t = 4.
Since the connection # 3 is selected, the values are 0, 0, and 4 by round robin. Since the virtual queue of connection # 1 is already 0, it is not selected. The position of the first EOP cell of connection # 2 is 1. Since the connection # 2 is a connection that can already output cells with priority, the determination unit 3 does not make a determination. (Cell input) No cell is input.

Thereafter, cells are transmitted in accordance with the procedures shown in FIGS. FIG. 4 is as described above. As shown in FIG. 8, it is determined whether or not there is a connection that can output cells preferentially (S16). If not, a cell to be transmitted by round robin is determined from connections having cells in the cell buffer. (S17).
If such a connection exists, it is determined whether or not there is a connection having a transmission right among such connections (S18). If there is a connection that has the sending right,
The cell of the connection having the transmission right is transmitted (S2
2). If the transmitted cell is an EOP cell (S23),
The connection having the transmitted cell is preferentially removed from the connection for outputting the cell (S24).

When there is no connection having the transmission right (S18), it is determined whether or not there is a connection registered in the list (S19). If there is a connection registered in the list, a transmission right is given to the connection registered at the head of the list (S2).
1). If there is no connection registered in the list, a transmission right is given to the connection registered at the head of the list (S20). The cell of the connection having the transmission right is transmitted (S22). If the transmitted cell is an EOP cell (S23), the connection having the transmitted cell is preferentially removed from the connection for outputting the cell (S24).

[0043]

As described above, according to the present invention,
A cell scheduler that satisfies fairness between communicating connections sharing the same bandwidth while performing packet-aware cell scheduling, shortens packet transfer time, and considers packet length Can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a cell scheduler according to an embodiment of the present invention.

FIG. 2 is a diagram showing recorded contents of an information management unit.

FIG. 3 is a flowchart showing a transmission cell determination procedure according to the first embodiment of the present invention.

FIG. 4 is a flowchart showing a procedure for shifting to a connection from which cells can be output preferentially.

FIG. 5 is a diagram illustrating a specific operation example.

FIG. 6 is a diagram showing recorded contents of an information management unit.

FIG. 7 is a diagram showing recorded contents of a priority connection list section.

FIG. 8 is a flowchart showing a transmission cell determination procedure according to the second embodiment of the present invention.

FIG. 9 is a diagram illustrating an example in which a packet transfer time cannot be reduced only by shortening a cell transfer time.

[Explanation of symbols]

1 VCI identification unit 2 information management unit 3 determination unit 4 queue length reading unit 5 control unit 6 ₁ to 6 _n cell buffers 7 priority connection wrist portion

Claims (4)

[Claims] 1. An identification means for identifying whether or not an arriving cell is the last cell of a plurality of cells transmitted by decomposing one packet into a plurality of cells, and an arriving cell is identified for each connection. A plurality of cell buffers to be stored; and a judging means for judging a cell buffer to which a cell read priority is given from among the plurality of cell buffers. In a cell scheduler including a selection unit as a candidate to which a priority is given, a unit for estimating a queue length of each cell buffer when it is assumed that the plurality of cell buffers cyclically transmit cells is provided; The means includes, when the last cell is included in a cell buffer in which the queue length estimated by the estimating means is smaller than the actual queue length, stores the last cell in the cell buffer. A cell scheduler comprising: means for assigning a priority; means for assigning a priority includes means for setting a priority according to a length of the packet. 2. The priority setting means sets a higher priority for a packet having a shorter packet length than a predetermined packet length as compared to a packet having a longer packet length than the predetermined packet length. 2. The cell scheduler of claim 1, including means. 3. A method according to claim 2, further comprising the step of granting a transmission right to permit cell transmission until the last cell is transmitted to the cell buffer in which the priority is set by the priority setting means. Item 3. The cell scheduler according to Item 2. 4. The method according to claim 1, wherein said means for granting a transmission right includes means for transferring said transmission right to another cell buffer when said cell buffer to which said transmission right has been granted has transmitted the last cell. Item 3. The cell scheduler according to Item 3.