KR100319457B1 - Traffic control method for ATM switches - Google Patents

Abstract

The present invention is a cell of a shared buffer type ATM switch module to accommodate ABR (Available Bit Rate) and UBR (Unspecified Bit Rate) service in ATM (Asynchronous Transfer Mode) switching system. Its purpose is to provide a traffic control method for controlling traffic jams.

According to the present invention, there is provided a traffic control method for accommodating ABR (Availabel Bit Rate) and UBR (Unspecified Bit Rate) services in an asynchronous transmission mode switch comprising an input / output matching module and a central switching module. In order to calculate the scheduling speed in the ingress TCM (input traffic control module), the sum of the size of the output link buffers of all the unit switch elements inside the switching module through which the data cell passes is recorded in the header of the data cell and the Egress TCM ( After calculating the scheduling speed for each ABR and UBR connection from the sum of the output link buffer sizes of all the unit switch elements in the internal switching module recorded in the header of the data cell received from the Egress TCM, Send it to the Ingress TCM for that connection, and ABR and UB calculated and sent by the Egress TCM A traffic control method is provided, wherein the scheduling rate of a corresponding connection is changed at a scheduling rate for each R connection.

Description

Traffic control method for Asynchronous Transfer Mode Switch {Traffic control method for ATM switches}

The present invention relates to a traffic control method of an ATM switch, and more particularly, to a traffic control method of controlling cell accumulation of a shared buffer type ATM switch module to accommodate ABR and UBR services in an ATM exchange system.

In recent years, demand is growing rapidly and ATM's Available Bit Rate (ABR) and Unspecified Bit Rate (UBR) are unspecified to accommodate Internet services in ATM networks that are expected to account for more than 90% of total traffic in the near future. Bit rate) services are becoming prominent. The ABR service does not use the allocated bandwidth at the time of connection establishment, such as CBR (Constant Bit Rate) or VBR (Variable Bit Rate) service, Through flow control, the bandwidth dynamically allocated according to the situation of ATM network is used. Therefore, it is used for services that are not sensitive to cell delay and sensitive to cell loss.

In addition, UBR service is a concept of Best-effort such as Internet service. Since UBR service is used only when there is free bandwidth in the network, nothing can be guaranteed about the quality of service.

The flow control of the ABR service is performed by using a RM (Resource Management) cell that is generated in proportion to the transmission rate of the data cell.When the RM cell is generated at the source and reaches the destination through the network, the destination receives this again. Send back to the sender. At this time, the network may transmit the congestion state in the network to a transmitter or a receiver by using an internal field of the RM cell. Such ABR flow control can be largely divided into an Explicit Forward Congestion Indication (EFCI) method and an Explicit Rate (ER) method.

The EFCI method is a method of controlling the transmission data transmission rate by transmitting a congestion state in a network to a transmission source using the EFCI bit in the data cell. This method can accommodate the ABR service in the switch without a separate device, but there are problems such as impartiality between the ABR service connections or the rapid escape from the congestion.

On the other hand, ER flow control calculates the ER value according to the congestion state (buffer state) of the network and loads it in the ER field inside the RM cell, thereby efficiently adjusting the data transmission rate at the transmission source. Although it is superior to the EFCI scheme in terms of fairness and performance of bandwidth use, implementation is complicated, and there is a problem in that a separate apparatus and algorithm for implementing the same are required in the switch module to implement it.

ATM switches used in local area networks or private networks can implement complex devices and algorithms inside the switch module.However, in large-capacity switching systems used for public networks or backbones, due to the limitations of high-speed exchange and hardware integration, the internal switching modules Most of the traffic control functions including the ER value calculation of ABR traffic, with only a small common buffer, are performed by the Traffic Control Module (TCM) located in the input / output part of the switch module. The Ingress TCM located at the switch input includes a scheduling function to ensure fairness between ABR and UBR connections.

Most of these high-capacity exchanges are composed of multiple stage switch elements. When scheduling in an Ingress TCM, if the buffer state inside the unit switch element is not considered, due to the instantaneous burst of traffic, Congestion in the buffer will occur. In the conventional control method, the scheduling weight for each connection of ABR and UBR is specified only at connection establishment or release, and cell scheduling is performed only by a predetermined weight in the meantime. there was.

The present invention has been made to solve the problems of the prior art as described above, ABR (Available Bit Rate) and UBR (Unspecified Bit Rate, Unspecified Bit) in ATM (Asynchronous Transfer Mode) exchange system It is an object of the present invention to provide a traffic control method for controlling cell accumulation of a shared buffer type ATM switch module to accommodate a service).

1 is a block diagram showing the configuration of an ATM switching system to which the present invention is applied;

2 is a diagram illustrating a buffer management structure and a scheduling structure for accommodating a plurality of ATM traffic classes including ABR and UBR in a TCM according to an embodiment of the present invention;

3 is a diagram illustrating a data cell flow and a control mechanism of ABR and UBR traffic according to an embodiment of the present invention;

FIG. 4 is a diagram logically illustrating a process of obtaining the total buffer sum inside an switch module passed through an Nth connection in an Egress TCM M according to an embodiment of the present invention;

5 is a view showing the internal configuration of the Ingress and Egress TCM according to an embodiment of the present invention,

FIG. 6 is a diagram illustrating a process of calculating a scheduling rate for each connection to be carried in an ER field of a BRM cell in an Egress TCM when a BRM cell arrives according to an embodiment of the present invention.

♠ Description of the main parts of the drawing ♠

111,121: I / O matching module (Input Module, Output Module)

112,122: Line Interface

113,123: Traffic Control Module

131: Switch Module 141: Switch Port

211: queue by connection 212: scheduler by connection

221 ~ 223: Queue by class 231: Scheduler by class

311 input side traffic control module (Ingress TCM)

312 ~ 315: Class queue 316: Class scheduler

321: Switch Module

322 ~ 324: unit switch element

325: output link of the unit switch element

331 ~ 332: Output traffic control module (Egress TCM)

411 input traffic control module (Ingress TCM)

421: Switch Module

422 ~ 424: unit switch element

431: Output traffic control module (Egress TCM)

432: Output link queue in egress TCM

511: Ingress TCM

512: Means for classifying data cells by class (Demux)

513: Queue by ABR connection 514: Queue by UBR connection

515: queue by class 516: scheduler by class

According to the present invention for achieving the object as described above, ABR (Availabel Bit Rate) and UBR (Unspecified Bit Rate) in the asynchronous transmission mode switch is composed of the input and output matching module and the central switching module In a traffic control method for accommodating a service, the sum of the sizes of the output link buffers of all the unit switch elements inside the switching module through which the data cell passes, in order to calculate the scheduling speed in the ingress TCM (input side traffic control module) ABR and UBR from the sum of the output link buffer sizes of all unit switch elements inside the exchanging module recorded in the header of the data cell received from the Egress TCM and forwarded to the Egress TCM (output-side traffic control module). Calculate the scheduling rate per connection and send it to the Ingress TCM for that connection. A traffic control method is provided, wherein the ess TCM changes a scheduling rate of a corresponding connection to a scheduling rate for each ABR and UBR connection calculated and transmitted by an Egress TCM.

In the following, with reference to the accompanying drawings, a preferred embodiment according to the present invention will be described in detail.

1 is a block diagram illustrating a configuration of an ATM switching system to which the present invention is applied, and includes a plurality of matching modules 111 and 121 accommodating a plurality of subscribers or relay lines and a central exchange accommodating the matching modules 111 and 121. It consists of a Switch Module (131). The portion flowing into the exchange module 131 according to the data transmission direction is called an input module 111 and the portion output from the exchange module is called an output module 121.

Here, the matching modules 111 and 121, which are connected to a plurality of subscribers / relay lines, have a Line Interface (LI, 112) dedicated to processing the physical layer functions of ATMprotocol and a traffic dedicated to buffer management and traffic control functions for each ATM cell. It consists of Control Module (TCM, 113). The TCM 113 included in the input module 111 is called an ingress TCM, and the TCM 123 included in the output module 121 is called an egress TCM.

The central exchange module 131 has a plurality of input / output ports 141 and assumes a structure in which the unit switch module is configured in multiple stages. Each ATM unit switch module is a shared buffer type switch.

2 is a diagram illustrating a buffer management structure and a scheduling structure for accommodating a plurality of ATM traffic classes including ABR and UBR in a TCM according to an embodiment of the present invention.

Traffic requiring real-time processing such as CBR and VBR is stored in the class queue 221 having the highest priority, and non-real-time traffic such as ABR and UBR is first stored in the queue 211 allocated to each connection, and then connected. The scheduling is performed between the queues 212 and is transferred to the corresponding class queues 222 and 223. Between the class queues 222 and 223, cells having a high priority in the order of CBR, VBR, ABR, and UBR are first scheduled 231 by priority control.

At this time, the scheduling rate of each connection belonging to the ABR and UBR classes is determined by an ER (Explicit Rate) value carried in a backward RM cell (Backward RM; BRM) from the Egress TCM side to the transmitting source.

3 is a diagram illustrating a flow of data cells and a control mechanism of ABR and UBR traffic according to an embodiment of the present invention.

As the data cells of the ABR and UBR pass through the exchange, each switch unit element 322, 323, 324 accumulates and records the corresponding class queue value of the corresponding output link at a designated location within the data cell. Each of the unit switch elements 322, 323, and 324 has a class-specific queue for each of the output links 325, CBR, VBR, ABR, and UBR. For example, it is input from the ingress TCM1 311 to the exchange module 321 and output to the egress TCM M 332 via the unit switch elements 1 322, 5 323, and 12 324 inside the exchange module. For ABR connection 1, the ABR class buffer size at switch element 1 322 is q ₁ , the buffer size at switch element 5 323 is q ₅ , and the buffer size at switch element 12 324 is q ₁₂ . In the Egress TCM M 332, the total buffer size Q ₁ inside the switch for the ABR class can be obtained by the equation (Q ₁ = q ₁ + q ₂ + q ₃ ).

In addition, Q ₁ , ... Q _N may be obtained for N connections output to the Egress TCM M 332.

FIG. 4 is a diagram logically illustrating a process of obtaining the total buffer sum inside the switch module passed through the Nth connection in an Egress TCM M according to an embodiment of the present invention. In each Egress TCM, an ER for all received connections is illustrated. The value is calculated at every control time interval T.

If the sum of the number of currently active ABR and UBR connections is N, the allowable bandwidth for ABR and UBR traffic at time k can be obtained by subtracting the bandwidth allocated to CBR and VBR from the maximum link speed of the Egress TCM. If this is the available bandwidth A (k), under the same conditions, the fair bandwidth FS (k) to be allocated to ABR and UBR can be obtained by A (k) / N.

However, concatenation through congested unit switch elements in the internal buffer is to allocate a smaller bandwidth than FS (k), or otherwise allocate a larger bandwidth to prevent cell loss and increase link efficiency. The cell rate for the i < th > connection is determined by adding the increase and decrease determined by considering the buffer size inside the switch to the current cell rate.

In detail, to calculate the transfer rate, first, set the performance evaluation function J _i (k) as shown in [Equation 1] to minimize the difference between the target value Q _T of the queue value and the measured queue value, and maintain fairness. do.

Where FS (k) is Fair Share, A (k) is the available bandwidth at time k, and N is the total number of ABR and UBR connections going to the same Egress TCM. Obtaining a transmission rate that minimizes the performance evaluation function J _i (k) given above is equivalent to solving an optimization problem as shown in Equation 2 below.

Here, λ _i means the transmission rate of the i-th connection, λ _PCRi means the maximum transmission rate of the i-th connection.

On the other hand, if T is the control time interval, Equation 3 below is obtained.

Using the well-known Steepest descent method to find the optimal solution to the problem set out above, we obtain Equation 4 below.

Μ is a learning parameter that determines the convergence speed of the algorithm.

The rate determined by the above equation is allocated for constrainless connections. For connections with constrain for max-min fairness, that is, connections with only transmission rates below the Fair Share value due to bottlenecks at other nodes, connections without constrain bandwidth corresponding to the difference between Fair Share and its limited rate. Redistribute to It compares the input rate of each connection measured by the Ingress TCM with the calculated Fair Share (FS) value and determines whether it is constrained.

5 is a view showing the internal configuration of the Ingress and Egress TCM according to an embodiment of the present invention, which will be described in detail as follows.

Ingress and Egress TCMs are physically implemented on one board and support one full duplex port of the switch module.

Ingress TCM (511) is a Demux (512) part for classifying the received cell according to the class, connection-specific queue 513 of ABR, connection-specific queue 514 of UBR and class queue (515) for transmitting the cell to the exchange module ) And a class scheduler 516 portion.

The egress TCM 521 receives and processes a data cell output from a switch and an RM cell sent from the ingress TCM 511 for calculating a scheduling rate, and a queue for each class 523 existing for each physical link. It is composed of parts.

In the Demux 512 of the Ingress TCM, cells transmitted from the user side are classified into classes and stored in the connection-specific queues 513 and 514 of the ABR and UBR. When a BRM (Backward RM) cell of an ABR arrives from the receiver to the Ingress TCM 511, it is sent by the Demux 512 to the Egress TCM 521, and the Rate Controller 522 of the data cell. After recording the scheduling rate for each connection calculated from the queue state information in the switch module loaded in the header, it is loaded in the ER field of the Backward RM cell and transmitted to the switch module through the ABR VC queue of Ingress. The BRM cell is transmitted back to all Ingress TCMs that have transmitted data cells to the Egress TCM 521 through a switch module.

The Egress TCM 521 receiving the BRM cell passing through the switch module sends this to the Ingress TCM 511 physically present on one board, and the Ingress TCM 511 sends the BRM scheduling rate of the corresponding ABR and UBR connections. By changing to the ER value inside the cell, buffer congestion inside the switch module can be prevented. Since no BRM cell is transmitted from the receiver for UBR traffic, every time the Egress TCM 521 receives every N data cells, the BRM cell heads toward the Ingress TCM 511 that has transmitted the data cells. Generates. This is done in the Rate Controller 522. The BRM cell of the UBR connection thus generated is delivered to the Ingress TCM 511, which is a destination, so that the ER value therein is read and then discarded.

FIG. 6 is a diagram illustrating a process of calculating a scheduling rate for each connection that will be carried in the ER field of a BRM cell when an BRM cell arrives according to an embodiment of the present invention.

One of the periodically calculated ER value and the Fair Share value obtained from the measurement is recorded as the scheduling speed in the ER field inside the RM cell, which is determined by comparing the target link utilization with the measured link utilization.

Here, λ _i is the transmission rate of the i-th connection, and Load Factor is obtained by dividing the capacity of the TCM output link by the total amount of traffic measured. Compare this value with the Target Utilization value to determine the FS ( k) the value for a value of λ _i, the opposite is to determine a value of FS (k) value and λ _i with ER value. Target Utilization values are usually 0.9 or 0.95.

The present invention as described above is recorded on a computer-readable recording medium, and can be processed by a computer.

As described in detail above, the present invention provides a switch input in consideration of a buffer size for each class in a unit switch element inside an exchange module in a traffic control method for accommodating ABR and UBR services in an asynchronous transfer mode exchange system. By controlling the cell scheduling rate in the module, it is possible to efficiently control traffic using fewer buffers.

The technical spirit of the present invention has been described above with reference to the accompanying drawings, but this is by way of example only and not by way of limitation to the present invention. In addition, it is obvious that any person skilled in the art may make various modifications and imitations without departing from the scope of the technical idea of the present invention.

Claims (5)

In a traffic control method for accommodating ABR (Availabel Bit Rate) and UBR (Unspecified Bit Rate) services in an asynchronous transmission mode switch composed of an I / O matching module and a central switching module, In order to calculate the scheduling speed in the ingress TCM (input traffic control module), the sum of the size of the output link buffers of all unit switch elements in the switching module through which the data cell passes is recorded in the header of the data cell to output the Egress TCM (output side traffic). Control module), The scheduling rate for each ABR and UBR connection is calculated from the sum of the output link buffer sizes of all the unit switch elements in the exchange module recorded in the header of the data cell received from the Egress TCM, and then transmitted to the Ingress TCM of the connection. , A method of controlling traffic in an asynchronous transmission mode switch, wherein the ingress TCM changes the scheduling rate of a corresponding connection to a scheduling rate for each ABR and UBR connection calculated and transmitted by an Egress TCM. The method of claim 1, The scheduling rate for each ABR connection calculated by the Egress TCM is recorded in an ER (Explicit Rate) field of a RM (Resource Management) cell received for traffic control of the ABR service and is an Ingress TCM of the connection as a BRM (Backward RM) cell. Sent to, The scheduling rate for each UBR connection calculated in the Egress TCM is recorded in an ER field of a BRM cell generated by the Egress TCM at regular intervals for traffic control of the UBR service, and is transmitted to the Ingress TCM of the corresponding connection. Traffic control method of mode switch. The method according to claim 1 or 2, The scheduling rate for each ABR and UBR connection transmitted from the Egress TCM to the Ingress TCM of the connection is By comparing the target utilization and the measured load utilization, the target link utilization is less than the measured link utilization, and the transmission rate λi (k) and the fair bandwidth of each connection periodically calculated Determined by the smaller of the values FS (k), If the target link utilization is equal to or greater than the measured link utilization, the traffic control method of the asynchronous transfer mode switch is determined to be the larger of the transmission rate λ i (k) and the fair bandwidth value FS (k) of the periodically calculated connections. . The method of claim 3, The load factor is calculated by dividing the link capacity of the TCM output link by the measured load of the total traffic. A computer that records a program that performs traffic control to accommodate the ABR (Availabel Bit Rate) and UBR (Unspecified Bit Rate) services in an asynchronous transmission mode switch consisting of an I / O matching module and a central switching module. In the recording medium readable by In order to calculate the scheduling speed in the ingress TCM (input traffic control module), the sum of the size of the output link buffers of all unit switch elements in the switching module through which the data cell passes is recorded in the header of the data cell to output the Egress TCM (output side traffic). Control module), After calculating the scheduling rate for each ABR and UBR connection from the sum of the output link buffer sizes of all unit switch elements in the exchange module recorded in the header of the data cell received from the Egress TCM, the calculated scheduling rate for each ABR connection is ABR. Recorded in the ER (Explicit Rate) field of the received RM (Resource Management) cell for traffic control of the service, and transmits it to the ingress TCM of the connection as a BRM (Backward RM) cell, and the calculated scheduling rate for each UBR connection is UBR service. In order to control the traffic of the Egress TCM periodically recorded in the ER field of the BRM cell generated by itself transmits to the Ingress TCM of the connection, A computer-readable recording medium that records an executable program that changes the scheduling rate of an ABR and UBR connection, calculated by Egress TCM, and changes the scheduling rate for that connection.