KR100283391B1 - Buffer Allocation Method in ATM Switch_ - Google Patents

Abstract

The present invention relates to a buffer allocation method in an ATM switch that can increase buffer utilization efficiency by allocating a buffer variably according to traffic characteristics.

In the related art, there is a problem in that the buffer utilization efficiency is reduced by providing a constant buffer resource regardless of the characteristics of the traffic.

The present invention allocates ABR and UBR buffers for each virtual channel by dividing buffer resources obtained by subtracting the buffer occupied by VBR traffic over the SCR from the remaining extra buffers allocated to CBR and VBR by the number of calls of ABR and UBR. The buffer utilization efficiency can be improved by allocating the ABR and UBR buffers for each virtual channel by moving the value of the buffer excluding the buffer occupied by the VBR traffic over the SCR from the extra buffer remaining in the VBR in a predetermined direction.

Description

Buffer Allocation Method in ATM Switch

The present invention relates to a buffer allocation method in an ATM switch. More particularly, the present invention relates to a buffer allocation method in an ATM switch that can increase buffer utilization efficiency by variably assigning a buffer according to traffic characteristics.

In general, Asynchronous Transfer Mode (hereinafter referred to as ATM) is a transmission / switching technology that is the core of B-ISDN, a packet type transfer mode based on asynchronous time division multiplexing. . Here, the basic unit of ATM information transmission is a cell, and the ATM treats all information as a 53-byte fixed length cell composed of a 5-byte header and a 48-byte information field. This fixed length data string (packet) becomes a unit of multiplex and exchange. Meanwhile, in the header, a Virtual Channel Identifier (VCI) for identifying a connection to which a cell belongs, a Virtual Path Identifier (VPI), and a CLP indicating whether the cell is discarded during congestion. Functions such as cell priority identification), PT (cell type identification) for distinguishing network control information, and header error detection and control (HEC).

As described above, an ATM network using ATM supports various types of traffic. An ATM switch in which a user cell selects a path from an input module to an output module performs an operation process according to the characteristics of each traffic. do. This traffic is distinguished by three characteristics: bandwidth, rotational delay, and cell delay variation (CDV). The dual bandwidth is directly related to the buffer implementation in the ATM switch.

Therefore, the ATM switch is implemented by having a buffer for each virtual channel to have a separate buffer for each service class or to provide traffic independence for each virtual channel.

In the method of assigning a buffer to each service class, a maximum size of a buffer that can be used for each service class is determined. This method includes a constant bit rate (CBR) and a variable bit rate (VBR). Rate) When there is no traffic and a lot of variable bit rate (ABR) traffic occurs, a large number of buffers are allocated to ABR traffic, and thus a buffer that CVR and VBR cannot use is lost. Therefore, in this case, priority is given to CBR, VBR, and ABR in order, so that CBR has no limit on buffer usage, and VBR is authorized to use more buffers than ABR.

Meanwhile, a method of assigning a buffer for each virtual channel may be implemented by a common buffer type switch. The size of the buffer of each virtual channel may be determined by the central processing unit (CPU) when the virtual channel is set up. Will be given according to

1 is a diagram illustrating the structure of a buffer implemented by a conventional virtual channel-specific buffer allocation method. As shown in FIG. 1, the buffer implemented by the conventional virtual channel-specific buffer allocation method is provided with a CBR buffer, a VBR buffer, and an ABR buffer for each virtual channel.

The CBR buffer and the VBR buffer described above have a discard threshold that can determine the discard of ATM cells according to the value of CLP (Cell Priority) indicating cell discard when the network becomes congested. The ABR has thresholds for displaying an Early Packet Discard (EPD) and an Explicit Forward Congestion Indication (EFCI) for each virtual channel.

As described above, the buffer size of each virtual channel is given according to the bandwidth requirement of the traffic of the call. As a parameter describing the bandwidth that determines the characteristics of the traffic, a PCR (Peak Cell Rate) is used. , SCR (Sustainable Cell Rate), MBR (Maximum Burst Size), MCR (Minimum Cell Rate), and the like. Accordingly, CBR occupies a constant bandwidth corresponding to PCR, and VBR occupies bandwidth as much as PCR when MBS cells are transmitted. Here, the average of the total traffic transmitted is equal to or smaller than the SCR. ABR, on the other hand, does not require a constant bandwidth, but uses CBR and VBR traffic and uses the remaining bandwidth.

Therefore, applying the size of the buffer corresponding to PCR to VBR and ABR irrespective of the grade of service causes waste of buffer resources. That is, when a buffer corresponding to the PCR is assigned to the VBR, even when the VBR traffic is transmitted to the MCR, the buffer resource is allocated to correspond to the PCR, thereby causing a waste of available buffer resources. In addition, ABR transmits a large amount of data instantaneously due to the characteristics of the traffic, so giving a buffer having a constant size when setting up a call may cause a problem that the efficiency of using the buffer may be reduced.

That is, conventionally, there is a problem in that the buffer utilization efficiency is reduced by providing a constant buffer resource regardless of the characteristics of the traffic.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a buffer allocation method in an ATM switch capable of increasing the buffer utilization efficiency by allocating a buffer variably according to traffic characteristics.

A buffer allocation method in an ATM switch according to an embodiment of the present invention for achieving the above object allocates a CBR buffer for each virtual channel to the size of a buffer corresponding to a PCR and sets the size of a buffer corresponding to an SCR. Allocating a VBR buffer for each virtual channel by using; And dividing the buffer resources obtained by subtracting the buffer occupied by the VBR traffic over the SCR from the remaining extra buffers allocated to the CBR and VBR by the number of calls of ABR and UBR to allocate the ABR and UBR buffers for each virtual channel. Is done. Furthermore, the method may further include dividing the ABR and UBR buffers for each virtual channel by the threshold coefficients of the ABR and UBR to obtain ABR and UBR buffer thresholds for the virtual channels.

Meanwhile, a buffer allocation method in an ATM switch according to another embodiment of the present invention allocates a CBR buffer for each virtual channel to the size of a buffer corresponding to PCR when setting up a call, and VBR for each virtual channel to a buffer size corresponding to the SCR. Allocating a buffer; And allocating the ABR and UBR buffers for each virtual channel by moving a buffer value obtained by subtracting the buffer occupied by the VBR traffic over the SCR from the remaining extra buffers allocated to the CBR and the VBR in a predetermined direction. Furthermore, the method may further include obtaining the ABR and UBR buffer thresholds for the virtual channels by moving the values of the ABR and UBR buffers for each virtual channel in a predetermined direction.

1 is a diagram illustrating a structure of a buffer implemented by a conventional virtual channel-specific buffer allocation method.

2 is a diagram illustrating a buffer allocation method in an ATM switch according to an embodiment of the present invention.

3 is a diagram illustrating a buffer allocation method in an ATM switch according to another embodiment of the present invention.

4 is a diagram showing the size of a buffer applied to the present invention.

5 is a diagram showing the structure of a buffer implemented by a buffer allocation method in an ATM switch of the present invention.

Hereinafter, a buffer allocation method in an ATM switch according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a diagram illustrating a buffer allocation method in an ATM switch according to an embodiment of the present invention. Prior to the description, the CBR is allocated a buffer in a conventional manner. That is, the CBR is allocated a buffer resource corresponding to the PCR for each virtual channel by the CPU when the call is set up. On the other hand, the VBR is allocated a buffer resource corresponding to the SCR for each virtual channel.

As shown in FIG. 2, the ABR and unspecified bit rate (UBR) occupy VBR traffic over SCR in the remaining buffer (Excess Buffer Resource) allocated to CBR and VBR. It is possible to use a buffer resource (hereinafter referred to as a 'virtual buffer resource') minus the buffer resource (Excess VBR Buffer Resource). By dividing the possible virtual buffer resources by the number of calls of ABR and UBR, buffer resources of ABR and UBR per virtual channel are determined. Meanwhile, ABR and UBR perform an Early Packet Discard (EPD) or Explicit Forward Congestion Indication (EFCI) indication for efficient flow control and traffic control. It is determined by dividing the buffer per virtual channel of ABR and UBR by a certain ratio (threshold coefficient of ABR and UBR).

When a buffer is allocated using a buffer allocation method in an ATM switch according to an embodiment of the present invention as described above, an effect of obtaining a precise threshold value in real time occurs.

3 is a diagram illustrating a buffer allocation method in an ATM switch according to another embodiment of the present invention. CBR is allocated a buffer resource corresponding to PCR for each virtual channel when setting up a call, and VBR allocates a buffer resource corresponding to SCR (Desicated VBR Buffer Resoure (hereinafter referred to as 'VBR dedicated buffer resource') to each virtual channel. Assigned by channel.

As shown in FIG. 3, ABR and UBR can use virtual buffer resources that are allocated to CBR and VBR and subtract the excess VBR buffer resources occupied by VBR traffic over SCR from the remaining excess buffer resources. The buffer resources of the ABR and UBR are determined per virtual channel by moving the writeable virtual buffer resources based on the connection count received from the CPU. On the other hand, ABR and UBR perform EPD or EFCI indication for efficient flow control and traffic control. Also, the threshold of buffers is required for this, and various thresholds also include the threshold coefficients of the ABR and UBR buffers received from the CPU. And based on a predetermined threshold shift coefficient).

When the buffer is allocated by using the buffer allocation method in the ATM switch according to another embodiment of the present invention as described above, an effect of obtaining an approximation of the threshold in real time occurs.

4 is a diagram showing the size of a buffer applied to the present invention, Figure 5 is a diagram showing the structure of the buffer implemented by the buffer allocation method in the ATM switch of the present invention.

Hereinafter, a method of allocating a buffer in an ATM switch according to the present invention will be described with reference to FIGS. 2 to 5.

CBR is allocated a buffer resource corresponding to PCR for each virtual channel when setting up a call, and VBR allocates a buffer resource corresponding to SCR (Desicated VBR Buffer Resoure (hereinafter referred to as 'VBR dedicated buffer resource') to each virtual channel. Assigned by channel.

As described above, the remaining buffer resources after allocating CBR and VBR are used by ABR and UBR, and the threshold limit of ABR and UBR traffic can be raised and lowered according to the amount of VBR traffic exceeding the SCR. In other words, when the amount of VBR traffic exceeding the VBR dedicated buffer resource (hereinafter referred to as 'excess VBR traffic') is small, the buffer resources that ABR and UBR can use are increased, which increases the limit of ABR and UBR traffic. For example, if there is a lot of excess VBR traffic, the buffer resources that ABR and UBR can use are small, so the limit of ABR and UBR traffic is small.

By calculating the size of the excess buffer resource from the CPU every time the call is established, the excess VBR buffer resource occupied by the excess VBR traffic is obtained. This is a summary of the buffer resource calculation method.

Excess buffer resource = Total buffer resource-(CBR buffer resource + VBR dedicated buffer resource)

Virtual buffer resource = over buffer resource-over VBR buffer resource

In Equation 1, the excess VBR buffer resource is provided from a counter that counts the number of VBR cells (Excess VBR cells) beyond the VBR dedicated buffer resource.

As shown in FIG. 4, when there is no CBR or VBR traffic (the excess VBR buffer resource becomes the total buffer resource), as shown in FIG. 4, the ABR or UBR traffic occupies the entire buffer so that the CBR or VBR is occupied. It must have a minimum value to prevent blocking. On the other hand, the buffer resources that can be occupied by CBR and the buffer resources that can be occupied by VBR transferred to PCR to reserve buffer resources for ABR and UBR traffic (ABR and UBR dedicated buffer resources). ; Hereinafter referred to as 'VBR allocated buffer resource' must have a maximum value.

Since the size of the virtual buffer resource calculated by Equation 1 becomes the buffer resource of the entire ABR and UBR traffic, to separate and manage the ABR and UBR traffic, the virtual buffer resource needs to be divided into the ABR and UBR. Is a formula of ABR and UBR buffer resource calculation method. Here, the ABR and UBR are allocated buffer resources in proportion to the number of each connection, so that the ABR is allocated more than the UBR.

ABR buffer resource = VQ * k (0 <k <1)

UBR buffer resource = VQ * (1-k) (0 <k <1)

In Equation 2, VQ represents a partition coefficient where k is a virtual buffer resource.

This calculation is performed by the CPU, which delivers the division factor k at every call setup. Here, the partition coefficient k represents a moving value and should be a value that can be implemented by a simple moving operation. For example, if the partition coefficient is 0.5, the buffer resources of ABR and UBR can be obtained simply by moving the value of VQ to the right once.

By dividing the ABR buffer resource or the UBR buffer resource calculated by Equation 2 by the number of each currently connected call, the buffer resources for each virtual channel are determined. Equation 3 summarizes the method of calculating ABR and UBR buffer resources per virtual channel. One expression.

ABR buffer resource per virtual channel = ABR buffer resource / number of total ABR calls

UBR buffer resource per virtual channel = UBR buffer resource / number of total UBR calls

However, when the ABR buffer resource or the UBR buffer resource is divided into the number of connected calls as shown in Equation 3, real-time processing is not possible without complex hardware such as an arithmatic logic unit (ARU). This can be solved by performing the transfer operation by receiving the connection coefficient (c) for each call setup.

On the other hand, ABR and UBR are determined by dividing the buffer per virtual channel of ABR and UBR by a certain ratio (threshold coefficient of ABR and UBR) for the buffer required to perform EPD or EFCI indication for efficient flow control and traffic control. Equation 4 summarizes the buffer threshold calculation method of ABR and UBR per virtual channel.

EPD buffer threshold per virtual channel = Buffer resource / EPD threshold per virtual channel

EFCI display buffer threshold per virtual channel = Buffer resource / virtual display threshold per EFCI

However, as shown in Equation 4, when a buffer resource for each virtual channel is divided into threshold coefficients, real-time processing is impossible without complex hardware such as an ARU. This can be solved by performing a shift operation by receiving a threshold shift coefficient for each call setup from the CPU. have.

The buffer allocation method in the ATM switch of the present invention is not limited to the above-described embodiment, and can be modified in various ways within the scope of the technical idea of the present invention.

According to the buffer allocation method in the ATM switch of the present invention as described above, by allocating buffer resources according to the characteristics of the traffic, that is, varying the buffer resources occupied by the VBR according to the amount of traffic beyond the SCR of the VBR, ABR and UBR can use the remaining buffer resources except for the buffer resources occupied by CBR and VBR. When there is a lot of VBR traffic over SCR, ABR and UBR use less buffer resources and when there is less VBR traffic over SCR. Since many buffer resources can be used, there is an effect that the buffer resources can be used efficiently.

Claims (4)

Allocating a CBR buffer for each virtual channel with a size of a buffer corresponding to a PCR when setting up a call, and allocating a VBR buffer for each virtual channel with a size of a buffer corresponding to an SCR; And assigning ABR and UBR buffers for each virtual channel by dividing the buffer resources obtained by subtracting the buffer occupied by the VBR traffic over the SCR from the remaining extra buffers allocated to the CBR and VBR by the number of calls of ABR and UBR. Buffer Allocation Method in ATM Switch. The AMT switch of claim 1, further comprising dividing the ABR and UBR buffers for each virtual channel by the threshold coefficients of the ABR and UBR to obtain ABR and UBR buffer thresholds for the virtual channels. Buffer allocation method. Allocating a CBR buffer for each virtual channel with a size of a buffer corresponding to a PCR when setting up a call, and allocating a VBR buffer for each virtual channel with a size of a buffer corresponding to an SCR; AMT which comprises assigning ABR and UBR buffers for each virtual channel by moving the value of the buffer excluding the buffer occupied by the VBR traffic over the SCR from the extra buffers allocated to the CBR and VBR in a predetermined direction How buffers are allocated on the switch. 4. The buffer allocation of an AT switch according to claim 3, further comprising the step of moving the values of the ABR and UBR buffers for each virtual channel in a predetermined direction to obtain the ABR and UBR buffer thresholds for the virtual channels. Way.