JP2001016223A - Shaping system in atm communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To warrant the quality of service QOS of uni-cast cells even in the case that multicast cells are continuously reached. SOLUTION: When cell output buffers 5, 6 have idle capacity, a traffic control section 12 gives a transmission permission to cell input buffers 1, 2, 3, 4 in order of precedence. The transmission permission has the priority in order of multicast > constant bit rate CBR > variable bit rate VBR > available bit rate ABR. When traffic is in congestion in the cell output buffers 5, 6 and the traffic control section 12 receives a back-pressure, the traffic control section 12 activates a shaping function with respect to the cell input buffer 1. That is, a cell output timing arrives from any input buffer, the cell input buffer 1 does not output cells continuously but the traffic control section 12 gives the transmission permission to the cell input buffer 1 at an interval to satisfy a minimum cell rate MCR.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AT in which multicast traffic and unicast traffic coexist.
QO required for each connection in the M communication system
It relates to a shaping method that guarantees S.

[0002]

2. Description of the Related Art In an ATM communication system, a communication quality (QOS: Quality of Quality) required for each connection.
Service) is provided. The following are defined as classes related to communication quality.

[0003] 1. Constant Bit Rate Service (Cons
tent Bit Rate (CBR): Used for transmitting traffic at a fixed bit rate having a fixed timing relationship between data and samples. It is intended for voice transmission.

[0004] 2. Real-time variable bit rate service (Variable Bit Rate-Real)
Time: VBR-rt): Has a fixed timing relationship between samples and is used to transmit variable bit rate traffic. It is intended for transmission of variable bit rate video data and the like.

[0005] 3. Non-real-time variable bit rate service (Variable BitRate-Non
Real Time: VBR-nrt): Used when transmitting variable bit rate traffic that has no timing relationship between samples but guarantees QOS in bandwidth or delay.

[0006] 4. Available Bit Rate Service (Available Bit Rate: ABR) Supports variable bit rate data transmission and does not guarantee any timing relationship between source and destination. Nor does it guarantee bandwidth.

[0007] 5. Undefined bit rate service (Uns
Specified Bit Rate: No quality assurance is performed.

[0008] Each class is defined based on the following traffic parameters. (1) Peak Cell Rate (PCR): The peak value of the speed at which data is transmitted. It is defined as the reciprocal of the minimum interval T between ATM cells entering the network.

(2) Cell Delay Varia
Tion Tolerance (CDVT): Allowable value of cell delay variation. This is a parameter indicating how much a change in the cell transfer interval T is allowed.

(3) Sustainable Cell
Rate (SCR): Average cell speed. This is a parameter for VBR.

(4) Burst Tolerance
(BT): The maximum burst size that can be transmitted in a continuous cell.
VBR class parameter indicates how much cells can be transmitted in bursts.

(5) Minimum Cell Rat
e (MCR): minimum value of cell transmission rate.

For example, in the CBR class, PCR and CV
The quality is defined by DT. In the VBR class,
Its quality is defined by SCR and BT. Guaranteeing QOS means that the connection of each class is (1)
It means that among the traffic parameters of (5) to (5), the traffic parameters corresponding to each class are always guaranteed.

In the ATM communication system, multicast communication is also possible. In the multicast communication, for example, many cells are copied and generated from one cell at an appropriate place in a network, and the same cell is sent to many destinations.

FIG. 3 is a system configuration diagram showing a shaping method applied to multicast communication. Shaping is control for restricting cell transmission according to some condition. In FIG. 3, unicast cells 62 and 6 are connected via an ATM switch (hereinafter referred to as a switch) 11.
3, 64 and the system to which the multicast cell 61 is transferred.

A unicast cell is a cell transmitted / received from one cell input buffer to one cell output buffer via the switch 11. In this example, a multicast cell is a cell transmitted and received from one cell input buffer to many cell output buffers via the switch 11. In this example, two cells are copied from the multicast cell.

The cells input to the system shown in FIG.
The data is input to any of the cell input buffers 2, 3, 4, and 10 in the FIFO configuration according to whether or not the cell is a multicast cell and the traffic class. The cell input buffers 2, 3, 4, and 10 correspond to traffic class CBR, VBR, ABR, and multicast, respectively. Each cell input buffer 2, 3, 4, 10
When a new cell is input, this is notified to the traffic control unit 21 via the path 17.

The traffic control unit 21 checks the cell output buffers 5 and 6 for vacancies through the path 18 and, if there is a vacancy in the cell output buffers 5 and 6,
A transmission permission is issued to 3, 4, and 10. Cells output from the cell input buffers 2, 3, 4, and 10 are input to the cell output buffers 5 and 6 via the switch 11.

When cells are output from the cell input buffer 10 in which the multicast cells are stored, the cells are copied and generated by the number N of output partners, and the same cells are transmitted. That is, the cell input buffer 10 needs to perform N times of copying and N times of sending processing. In the example shown in FIG. 3, N = 2. Therefore, transmission of the multicast cell 61 takes N times as long as transmission of the unicast cells 62, 63, 64. Therefore, generally, the transmission of the multicast cell 61 has a higher priority than the transmission of the unicast cells 62, 63, 64.

That is, the frequency band (= data transfer rate) that can be used for transmitting the multicast cell 61 is wider than the frequency band that can be used for transmitting the unicast cells 62, 63, and 64. Specifically, the output is controlled so that the priority of the cell output from the cell input buffer 10 in which the multicast cells 61 are stored is the highest.
Hereinafter, the cell input buffer 2 of the CBR class, VB
The priority is lower in the order of the R-class cell input buffer 3 and the ABR-class cell input buffer 4.

Therefore, when there is a vacancy in the cell output buffers 5 and 6, the traffic control unit 21 determines that the cells are stored in the cell input buffer 10 and the cell input buffer 1
A transmission permission is issued for 0.

[0022]

If the cell input buffer 10 in which the multicast cells 61 are stored does not become empty, no cells are transmitted from the cell input buffers 2, 3, and 4. In particular, when the multicast cells 61 arrive continuously, the cell input buffers 2, 3, 4
Cannot send cells from That is, the band that can be used for the unicast cell decreases. Therefore, there is a possibility that the connection of each traffic type cannot guarantee the traffic parameters to be originally satisfied.

For example, in the configuration shown in FIG. 3, when the multicast cells 61 (# 1 to # 4) arrive continuously, the priority is output and the cells 91 and 92 are sent to the cell output buffers 5 and 6 via the switch 11. Is entered as Although FIG. 3 shows the cell 61 and the cells 91 and 92, when the cells 91 and 92 are input to the cell output buffers 5 and 6, the multicast cell 61 does not exist in the cell input buffer 10.

A cell 62 of CBR and a cell 63 of VBR having lower priority than the multicast cell 61 are
Waiting for completion of transmission of 1, the cells are transmitted to the cell output buffers 5 and 6 as cells 93 and 94. Having to wait for a long time for cell output means that CDVT cannot be guaranteed for a CBR type connection. This poses a problem in the case of data that requires real-time properties, such as audio / moving image data. For example, a multicast cell continuously arrives during voice transmission using the BR class, and CDVT is not guaranteed. As a result, a cell arrival delay exceeds an allowable range, and voice is suddenly interrupted during a conversation. Would. Further, the ABR-type cell 64 having the lowest priority is not transmitted forever, causing a problem that MCR cannot be guaranteed.

FIG. 4 is an explanatory diagram showing an example of how the entire transmission band is used. FIG. 4 shows that when the total transmission band 59 is “100”, the multicast cell 61
Arrives continuously, for example, the bandwidth 56 of “80” is used for multicast transmission, and the bandwidth 5 of “20” is used for CBR type and VBR type connections.
Indicates that only 7,58 can be assigned. AB
Indicates that no bandwidth is allocated to R-type connections.

As described above, in the conventional ATM communication system for handling multicast cells, there is a problem that when the multicast cells continuously arrive, the QOS of the unicast cells cannot be guaranteed.

Therefore, the present invention provides a CBR, VBR, A even if a multicast cell arrives continuously.
QOS of connection of each traffic type such as BR
It is an object of the present invention to provide a shaping method in ATM communication that can guarantee the following.

[0028]

The shaping method in the ATM communication according to the present invention comprises a traffic control means for prioritizing multicast traffic over unicast traffic and lowering the priority of multicast traffic when traffic is congested. And

The traffic control means suppresses the transmission rate of the multicast traffic to, for example, MCR (the minimum value of the cell transmission rate in the traffic parameters) at the time of traffic congestion.

The shaping method in the ATM communication is as follows.
A multicast cell input buffer for temporarily storing multicast cells; and a unicast cell input buffer for temporarily storing unicast cells. The traffic control means gives priority to cell transmission from the multicast cell input buffer when traffic is not congested. At the time of congestion, the cell transmission rate from the multicast cell input buffer may be suppressed to MCR.

The shaping method in the ATM communication is as follows.
A cell output buffer for cell output may be provided, and the traffic control means may be configured to determine whether there is traffic congestion based on the amount of cells stored in the cell output buffer.

Then, a plurality of unicast cell input buffers according to the priority of the unicast cells may be provided.

[0033]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system configuration diagram showing an example of a shaping method in ATM communication according to the present invention. In FIG. 1, cell input buffers 1 to 4 having a FIFO structure temporarily store cells input from a line or another switch. In the example shown in FIG. 1, the cell input buffer 1 stores the multicast cells 61. The cell input buffer 2 stores cells 62 of the CBR type. The cell input buffer 3 stores cells 63 of the VBR type. The cell input buffer 4 stores cells 64 of the ABR type.

The cells 61, 62, 63, 64 stored in the cell input buffers 1 to 4 are stored in the traffic control unit 12.
Is output to the switch 11 in response to the transmission permission instruction. The switch 11 refers to the routing information in the ATM cell, and outputs the cell to the cell output buffers 5 and 6 according to the routing information.

The cell input buffers 1-4 have shaping functions 31-34. The shaping function is a function for regulating cell transfer, and is specifically realized by input buffer read control of the traffic control unit 12. When a cell cannot be input, the cell output buffers 5 and 6 notify the traffic control unit 12 via the path 18 of the situation. This notification is called back pressure. When receiving the back pressure from the cell output buffers 5 and 6, the traffic control unit 12
Cell input buffer 1 for storing multicast cells 61
From cell transmission to MCR.

Note that, specifically, the back pressure may be output from the cell output buffers 5 and 6 to the traffic control unit 12, or the traffic control unit 12 may output the back pressure to the cell output buffers 5 and 6. The configuration may be such that the back pressure is detected by checking the empty space. When the back pressure is notified from the cell output buffers 5 and 6, the cell output buffers 5 and 6 notify the back pressure when the cell storage amount exceeds a predetermined threshold value, for example.

Next, the operation will be described. The arriving cell is input to any of the cell input buffers 1, 2, 3, and 4 of the FIFO configuration according to whether or not the cell is a multicast cell and the traffic class. The cell input buffers 1, 2, 3, and 4 correspond to CBR, VBR, and ABR of multicast and traffic classes, respectively.

The traffic control unit 12 checks the vacancy of the cell output buffers 5 and 6 via the path 18 and, if there is a vacancy in the cell output buffers 5 and 6,
A transmission permission is issued to 2, 3, and 4. The transmission permission has a priority of multicast>CBR>VBR> ABR. This priority is the same as the priority in the system shown in FIG. 3, but in this embodiment, the cell input buffer 1 for storing the multicast cells 61 is also provided with the shaping function 31. 3 is different from the system shown in FIG.

When a cell is input, each of the cell input buffers 1, 2, 3, and 4 notifies the traffic control unit 12 via the path 17 that the cell is input. Then, the cells are stored until a transmission permission instruction is issued from the traffic control unit 12. In the example shown in FIG. 1, cells 61 (# 1 to # 4) are stored in the cell input buffer 1 that stores the multicast cells 61. The cell 62 is stored in the cell input buffer 2 and the cell 63 is stored in the cell input buffer 3. The cells 64 are stored in the cell input buffer 4.

If there is a vacancy in the cell output buffers 5 and 6, the traffic control unit 12 issues a transmission permission in order from the cell input buffer having the highest priority. Cell output buffers 5, 6
Traffic congestion in the traffic control unit 1
When 2 receives the back pressure, the traffic control unit 12 activates the shaping function for the cell input buffer 1. It should be noted that issuing a transmission permission means not only configuring the hardware so that each of the cell input buffers 1, 2, 3, and 4 outputs a cell by itself in response to the transmission permission from the traffic control unit 12, This means that the hardware may be configured such that the traffic control unit 12 reads cells from any of the cell input buffers 1, 2, 3, and 4 and inputs the cells to the switch 11.

When the traffic control unit 12 detects the back pressure, the traffic control unit 12 reduces the cell transmission rate from the cell input buffer 1 to MCR (minimum cell transmission rate). Specifically, when the cell output timing from the input buffer arrives, the cell input buffer 1 does not continuously output cells, but the MCR.
Cell input buffer 1 at discrete intervals to satisfy
Give transmission permission to. At other cell output timings, transmission permission is sequentially issued to the cell input buffers 2 to 4 according to the priority (CBR>VBR> ABR) of the traffic type excluding multicast cells.

Therefore, four cells 61 are not continuously transmitted from the cell input buffer 1 for storing the multicast cells 61. For example, as shown in FIG. , 6 and then a CBR-type cell 71, a VBR-type cell 72, and an ABR-type cell 73 are transmitted. In the example shown in FIG. 1, thereafter, the multicast cells 74 and 75 are transmitted to the cell output buffers 5 and 6.

The congestion of the cell output buffers 5 and 6 is considered to occur when a large number of copied and generated multicast cells are input to the cell output buffers 5 and 6. That is, when the multicast cells continuously arrive at the cell input buffer 1, the cell output buffers 5 and 6 become congested. In this case, cell transmission from the cell input buffer 1 is suppressed in accordance with the congestion of the cell output buffers 5 and 6. Therefore, when a large number of multicast cells are accumulated in the cell input buffer 1, CBR type cells 7
1. VBR type cell 72, ABR type cell 73
From the cell input buffers 2-4.
In the conventional method, when a large number of multicast cells are accumulated in the cell input buffer 1, unless the cell input buffer 1 becomes empty, cells cannot be transmitted from the cell input buffers 2 to 4, and the traffic of each traffic type cannot be transmitted. The QOS of the connection could not be maintained.

When a small number of multicast cells are stored in the cell input buffer 1, no congestion occurs in the cell output buffers 5 and 6, and the shaping function 31
Does not work. However, in such a case, the cell input buffer 1 becomes empty in a short time. Therefore, in a short time, CB
R type cell 71, VBR type cell 72, ABR
Since the cell 73 of the type can be transmitted from the cell input buffers 2 to 4, the QOS does not deteriorate.

FIG. 2 is an explanatory diagram showing an example of how the entire transmission band is used. FIG. 2 shows that when the total transmission band 55 is set to “100”, the multicast cell 61
Arrives continuously, for example, a bandwidth 51 of “60” is used for multicast transmission, and a bandwidth 52 of “20” is allocated to the connection of the CBR type,
"10" for VBR and ABR type connections
Are assigned.
However, these numerical values are merely examples for explanation.

The traffic control unit 12 controls the bandwidths 52, 5
3 and 54 are controlled so as to issue a transmission permission instruction to each of the cell input buffers 2 to 4 so as to satisfy the traffic parameters (CDVT, MCR, etc.) of each traffic type. However, traffic parameters can be guaranteed for each connection. That is, the Q of each connection
OS can always be guaranteed. As described above, according to this embodiment, even when the multicast cells arrive continuously, it is possible to guarantee the MCR and the like of each traffic type.

Hereinafter, the effect of the present invention will be described with reference to FIGS. In FIG. 3, the total number of cells transmitted to the cell output buffers 5 and 6 is ten. Among them, the number of the multicast cells 91 and 92 is eight.
The number of CBR type cells 93 is one, and the number of VBR type cells 94 is one. There are no ABR type cells. Therefore, as shown in FIG. 4, the allocation of the band in this time zone is performed by multicast: CBR: VBR: A
BR = 80: 10: 10: 0.

That is, the bandwidth 56 of the multicast cell
Occupies the majority, the bandwidths 57 and 58 of CBR and VBR type cells become very narrow, and the bandwidth of ABR type cells is not secured. That is, in this time zone, A
BR type cells are not transmitted at all.

On the other hand, in FIG. 1, the number of cells transmitted to the cell output buffers 5 and 6 is also 10 in total, of which the multicast cells 81, 82, 74 and
75 is six. The CBR type cell 71 has 2 cells.
And one VBR type cell 72 and one ABR type cell 73 are provided. Therefore, as shown in FIG. 2, the allocation of the band in this time zone is multicast: CBR: VBR: ABR = 60: 20: 1.
0:10. As described above, in this embodiment, even when the multicast cells continuously arrive, it is possible to allocate the bandwidth to the connections of all traffic types in the time zone.

As described above, in this embodiment, the shaping control is performed such that the transfer rate of the multicast cell is suppressed to MCR when the cell output buffers 5 and 6 are congested while the priority of the multicast cell is increased. Even when the multicast cells arrive continuously, the traffic parameters of each connection of the unicast cells can be guaranteed.

In this embodiment, the case where the number of the cell input buffers 1 to 4 at the input port is four and the number of the output ports is two has been described as an example. It is not limited to the value of.

[0052]

According to the present invention, the shaping method in the ATM communication is provided with the traffic control means for lowering the priority of the multicast traffic at the time of traffic congestion while giving priority to the multicast traffic over the unicast traffic. , Even if the multicast cells arrive continuously,
There is an effect that the QOS of the connection of each traffic type such as BR, VBR, and ABR can be guaranteed.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing an example of a shaping method in ATM communication according to the present invention.

FIG. 2 is an explanatory diagram showing an example of how the entire transmission band is used.

FIG. 3 is a system configuration diagram showing an example of a shaping method in conventional ATM communication.

FIG. 4 is an explanatory diagram showing a conventional example of how the entire transmission band is used.

[Explanation of symbols]

1-4 cell input buffer 5, 6 cell output buffer 11 switch 12 traffic controller 31-34 shaping function 61, 74, 75, 81, 82 cells (multicast cells) 62, 63, 64, 71, 72, 73 cells ( Unicast cell)

Claims (5)

[Claims] 1. A shaping method in an ATM communication system in which multicast traffic and unicast traffic coexist. A traffic control means for prioritizing multicast traffic over unicast traffic and lowering the priority of multicast traffic when traffic is congested. A shaping method in an ATM communication system, comprising: 2. A shaping method in an ATM communication system according to claim 1, wherein said traffic control means suppresses the transmission rate of the multicast traffic to MCR at the time of traffic congestion. 3. A multicast cell input buffer for temporarily storing a multicast cell, and a unicast cell input buffer for temporarily storing a unicast cell, wherein the traffic control means comprises a cell from the multicast cell input buffer when traffic is not congested. 3. A shaping method in an ATM communication system according to claim 2, wherein transmission is prioritized, and a cell transmission rate from said multicast cell input buffer is suppressed to MCR when traffic is congested. 4. A shaping method in an ATM communication system according to claim 3, further comprising a cell output buffer for cell output, wherein said traffic control means determines whether or not traffic is congested based on the amount of cells stored in said cell output buffer. 5. The shaping method in an ATM communication system according to claim 3, wherein a plurality of unicast cell input buffers are provided according to the priority of the unicast cells.