KR20030056287A - An Apparatus and Method for scheduling the ATM cell using a Calendar - Google Patents

Abstract

PURPOSE: An ATM(Asynchronous Transfer Mode) cell scheduling apparatus using a calendar and a method therefor are provided to enhance switch efficiency by scheduling the transmission of a traffic according to a traffic state of a switch output port when a cell inputted in an ATM switch is switched and by restraining a temporary overload state of the traffic. CONSTITUTION: A VC(Virtual Connection) buffer(20) stores cells by a VC unit, and transmits a storing address of a primary cell among corresponding VC cells. If the storing addresses of the cells are received from the VC buffer(20), a plurality of calendar schedulers(30-33) calculate start times of the cells and store the storing addresses of the cells in corresponding slots. A service scheduling(40) schedules whether a certain storing address of the cell is primarily started among the storing addresses of the cells, which are outputted from the calendar schedulers(30-33). VCQs(Virtual Output Queues)(60-63) read and store cells corresponding to the storing addresses of the cells, which are outputted from the service scheduling(40). A scheduler schedules and outputs the cells stored in the VCQs(60-63) according to the state of an output port and a service level.

Description

An Apparatus and Method for scheduling the ATM cell using a Calendar}

The present invention relates to an asynchronous transmission mode cell scheduling apparatus using a calendar and a method thereof, and more particularly, to schedule cell traffic in terms of service class and virtual connection (VC) in a relatively simple structure using a calendar, and to negotiate a negotiated traffic parameter. The present invention relates to a traffic scheduling apparatus and a method thereof.

Asynchronous Transfer Mode (ATM) exchanges (hereinafter referred to as ATM exchanges) classify the communication quality according to each service type, and provide a service that meets the quality class when the subscriber requests the service. To this end, the ATM exchange negotiates the traffic parameters of the virtual connection (VC) when establishing a virtual connection (VC) with the subscriber, and receives the cell traffic sent by the subscriber, and observes the quality according to the negotiated value. Pass cell traffic. However, at this time, the ATM exchange is mixed with traffic from other subscribers and exchanged. A cell collision occurs, and the cell pushed by the collision delays departure, which makes it difficult to comply with the negotiated traffic parameters. In addition, when a subscriber randomly sends cell traffic such as Internet traffic, it often occurs that the link band is exceeded, resulting in transmission loss of cell traffic. When the link bandwidth is exceeded, high-quality cell traffic can be delivered, low-level traffic can be discarded, and high-quality traffic can be scheduled by collision-modified traffic patterns to comply with traffic parameters and maintain communication quality. Should be. To this end, cell traffic is scheduled according to the quality of service, and if necessary, scheduling for each virtual connection (VC) can be performed to properly service subscriber information.

The conventional cell scheduler schedules according to the service class and is not scheduled in the virtual connection (VC) unit. Therefore, for the service class such as the constant bit rate (CBR) or the variable bit rate (VBR), It was difficult to comply with the negotiation parameters in units of VC, and it was difficult to distribute the bands evenly in units of VC for best effort such as unspecified bit rate (UBR).

Another existing scheduler that schedules by class of service and VC unit combines several VCs of the same group into one group and schedules them by group of VC groups, and schedules cell traffic by group of each VC to meet the characteristics of the service. Because of the scheduling, the scheduling was very complicated and difficult because the scheduling method was different for each service.

Accordingly, the present invention, in order to solve the above problems of the prior art, has a buffer for each virtual connection (VC), scheduling to meet the requirements of the virtual connection (VC), virtual connection (VC) unit in case of overload It is able to service evenly, and it has several calendar schedulers with the same structure, and it can schedule and maintain the communication quality of each service according to the calendar access method, and also has a buffer for each output port, Accordingly, an object of the present invention is to provide a scheduling apparatus and method for controlling traffic delivery.

1 is a block diagram of an asynchronous transmission mode switching system to which the present invention is applied.

2 is a block diagram of a traffic scheduling apparatus according to the present invention.

3 is a detailed block diagram of a traffic scheduling apparatus according to the present invention.

Explanation of symbols on the main parts of the drawings

20: VC buffer 30, 31, 32: calendar scheduler

40: Service Scheduling 50: Copy Cell

60: virtual output port buffer (VOQ)

The present invention for achieving the above object, the virtual connection unit for storing the cell in the buffer, the virtual connection buffer for transferring the storage address of the first cell of the virtual connection cell;

A plurality of calendar schedulers, each of which has a corresponding service and a storage address of the cell transmitted from the virtual connection buffer, calculates a departure time of the cell and stores the storage address of the cell in a corresponding slot;

A first scheduler which schedules which of the storage addresses of cells output from the plurality of calendar schedulers should start first;

A plurality of virtual output port buffers provided for each service class and reading and storing cells corresponding to storage addresses of the cells output from the first scheduler; And

And a second scheduler configured to output the cells stored in the virtual output port buffer according to the state and service level of the output port.

The present invention also provides a method for scheduling an ATM cell,

A first step of storing a cell in a buffer on a virtual connection (VC) basis and transferring a storage address of a first cell among cells of the virtual connection to a calendar scheduler of a corresponding service;

A second step of the calendar scheduler calculating a time at which a cell starts and inserting a storage address of the first cell into a slot corresponding to the calculated start time;

A third step of rescheduling which cell storage address of the service scheduler of each service should start first, and outputting a cell storage address of a corresponding calendar scheduler;

If the virtual output port buffer to which the cell storage address is to be transmitted is not empty, transferring it to an input of the corresponding calendar scheduler;

A fifth step of reading a cell from the virtual connection buffer indicated by the cell storage address and storing it in the virtual output port buffer when the virtual output port buffer to which the cell storage address is to be transferred is empty; And

And a sixth step of scheduling and outputting the cells stored in the virtual output port buffer according to the state and service level of the output port.

The present invention also provides a processor comprising: a first function of storing a cell in a buffer in units of a virtual connection (VC) and transferring a storage address of a first cell among cells of the virtual connection to a calendar scheduler of a corresponding service;

A second function of the calendar scheduler calculating a time at which the cell starts and inserting a storage address of the first cell into a slot corresponding to the calculated start time;

A third function of rescheduling which cell storage address of the service scheduler of each service should start first, and outputting a cell storage address of a corresponding calendar scheduler;

A fourth function of transferring the virtual output port buffer to which the cell storage address is to be transferred to an input of the corresponding calendar scheduler;

A fifth function of reading a cell from the virtual connection buffer indicated by the cell storage address and storing it in the virtual output port buffer when the virtual output port buffer to which the cell storage address is to be transferred is empty; And

A computer-readable recording medium having recorded thereon a program for executing a sixth function of scheduling and outputting a cell stored in the virtual output port buffer according to a state and a service level of an output port.

The virtual link (VC) buffer is implemented as a memory, which consists of a cell buffer that stores cells, a VC management table that records the cell's storage status per VC, and an empty slot FIFO that points to a free space in memory. do. The VC management table records and manages the address of the cell buffer in which the first cell is stored, the address in which the last cell is stored, and the number of cells for each VC. A cell is stored in the memory of the address, and an address at which the next cell of the VC is stored is recorded at the end of the cell (linked list method). An empty slot FIFO has a list of addresses in which no cells are stored in the cell buffer, and when a new cell is saved, an empty slot is given. When a new cell is entered, an empty slot FIFO is assigned the cell's storage address, saves the cell there, writes the stored address to the VC management table, reads the last cell of that VC from the cell buffer, and writes it to the end of the cell. Change the storage address of to the address where the cell entered this time is saved. When outputting a cell stored in the cell buffer, read the cell from the memory where the first cell is stored and output it, and then read the address value stored in the next cell (the second cell) to the address value of the first cell recorded in the VC management table. Take it. In the VC buffer, an address value (head of line, hereinafter referred to as HOL) of a cell to be started first in VC units is transmitted to the calendar scheduler. When the cell outputs from the VC buffer and the next cell is designated as a new HOL of the corresponding VC, the VC buffer delivers the HOL to the calendar scheduler.

There are several calendar schedulers for service scheduling. Each calendar scheduler is assigned a service class. A calendar is a collection of several cell slots. In the cell slot, the address (HOL) of the first cell among the cells waiting in the VC buffer is recorded. Cell slots are accessed in different ways depending on the scheduling method. One typical example is the CBR service.

When the HOL of the cell corresponding to the CBR service is input to the calendar scheduler, the time at which the virtual connection (VC) of the cell should be output is calculated. The starting time of the cell starting from the previous starting cell is added by the peak cell interval (1 / PCR, PCR: peak cell rate). Record the HOL in the cell slot of the calendar corresponding to the calculated start time. On the other hand, the calendar accesses the cell slots one by one, and if there is a HOL in the accessed slot, the cell is read from the cell buffer and output. This outputs the first cell of the corresponding VC waiting in the VC buffer. If there is no HOL in the access slot, no cell is output. Therefore, the start time of the cell can be delayed by the difference between the time of storing the cell in the slot and the time of reading the cell. For cell departure time calculation, a virtual scheduling algorithm (VSA) engine is used to calculate a cell departure time based on PCR. When VCR service requires simultaneous calculation of peak cell rate (PCR) and sustainable cell rate (SCR), two VSA engines are used. VSA is an algorithm recommended by ITU-T that calculates and monitors PCR or SCR in units of VC.

As another example of calendar scheduling, the calendar slot access method is a real-time service for an available bit rate (ABR) service, which is known as a best effort service, an unspecified bit rate (UBR), or a guaranteed frame rate (GFR) service. It is different from CBR or VBR. The access method of the best effort service is as follows. If there is a cell (HOL) at the current access location, the cell is outputted. If there is no cell (HOL), the next slot is searched for a cell (HOL). If there is a cell HOL, the cell is output. If there is no cell HOL, the next slot is also found. This access method is called round robin (RR). In this access method, when there is a cell HOL recorded in a calendar, the cell is always output.

When recording a cell HOL in a calendar, the method of calculating the start time of the cell and the method of accessing the calendar when outputting differ according to the type of service. Therefore, the scheduler according to the present invention includes a plurality of calendars having the same structure, and each calendar separately designates a departure time calculation method and an access method to fit the service. Therefore, the present invention enables scheduling for various services even with the same calendar.

If the cell starting the calendar scheduler is a broadcast cell, the cell is copied. Cells belonging to the broadcast connection (VC) are copied, one is passed to the virtual output port buffer, and one is returned to the calendar scheduler to set the next departure time.

Cells delivered to a virtual output queue (VOQ) are stored in a virtual port buffer corresponding to the cell's class of service and the output port to which the cell should go. The ATM switch collects the cells input through the subscriber link, processes the cells at high speed, and delivers them to the switch module. The scheduler then controls the transfer of the cells according to the state of each output port of the switch. That is, do not forward the cell to the output port of the overloaded switch. In addition, the cell passing through the switch is distributed to each subscriber link in the ATM matching unit, and at this time, the subscriber link must be controlled so as not to overload the subscriber link. This function is performed by VOQ. VOQ also requires buffers for each output port, since the switch output port is the input port of the ATM matching unit and the subscriber link is the output unit of the ATM matching unit. There is a buffer for each virtual output port in each service buffer. The type of service class of VOQ should match the type of service class of switch output port or subscriber link port. In the VOQ, buffers for each port are accessed in a round robin manner or a weighted round robin (WRR) method, and cells are output in order of priority among a plurality of VOQs.

Therefore, the scheduler according to the present invention includes a VC buffer, a calendar scheduler, and a VOQ, so that various schedules according to service grades can be delivered fairly even for each VC even when overloaded.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 shows the location of the cell scheduler 13 in an ATM switch 10.

The cells input through the ATM matching unit 11 in the ATM switch 10 may pass through the switch module 12 and may be mixed and multiplexed with cells input from other places, resulting in an overload. The scheduler 13 suppresses cell traffic to the corresponding port when the output port of the switch is overloaded. In addition, when trying to output the traffic through the switch to the subscriber link, if more traffic is applied than the bandwidth of the link, the overload is also generated. In this case, the scheduler 13 suppresses the traffic output to the link. That is, the scheduler 13 is required for the receiving side and the transmitting side of the ATM matching section 11, respectively.

2 shows a schematic diagram of a scheduler 13 according to the present invention.

The scheduler 13 is composed of a VC buffer 20, multiple calendar schedulers 30, 31, 32, cell copy 50, and multiple virtual output port buffers (VOQs) 60, 61, 62. The schedulers 30, 31, 32 and VOQs 60, 61, 62 each have a scheduling function 40, 70 that selects one of a plurality of outputs. Once the cell is input it is stored in the VC buffer 20. Then, the address HOL indicating the storage location of the cell is transmitted to the calendar schedulers 30, 31, and 32. The calendar schedulers 30, 31, and 32 are respectively assigned a corresponding service. Therefore, the address HOL of the cell is transmitted to the calendar scheduler 30 to which the cell belongs, so as to schedule the start time of the cell. In addition, the calendar scheduler 30, 31, 32 outputs the cell at the start time. Since there are several calendar schedulers 30, 31, and 32, the schedule scheduler 30, 31, and 32 re-schedules which one should start first. This is the service scheduling function 40. After scheduling is performed between services, the cell is copied 50 when the cell is a broadcast cell. The copy function 50 of the cell is a function required only at the output side. The cell is then applied to VOQs 60, 61, 62. VOQ (60, 61, 62) is also composed of several depending on the type of service. When the scheduler 13 is applied to the input side, the VOQs 60, 61 and 62 are for controlling the output port of the switch and for the subscriber link port when applied to the output side. The VOQs 60, 61, and 62 schedule the cell 70 according to the state of the output port and the class of service.

3 shows a detailed block diagram of the scheduler 13 according to the present invention.

This further embodies Figure 2 and adds an operating principle. When the cell is input to the VC buffer 20, the VC buffer 20 stores the cell in the buffer in units of virtual connection (VC), and stores the storage address (HOL) of the first cell among the cells of the VC in the calendar scheduler 30, 31, 32). The calendar schedulers 30, 31, and 32 are respectively assigned a corresponding service. Thus, the address HOL of the cell is passed to the corresponding calendar scheduler 30 of the cell, so that the time at which the cell will start is calculated. The calendars 301, 311 in the calendar scheduler 30, 31 are a collection of several slots. Since each slot is accessed and output in turn, a departure time is determined for each slot. If the cell address (HOL) is put in the slot corresponding to the calculated start time, the cell will start at that time. Here, the access methods of the calendars 301 and 311 vary depending on the type of service. As described above, in the case of a real-time service such as CBR or real-time VBR, cell slots are accessed one by one to output cells. If there are no cells to be output, the time is rested. On the other hand, in the case of a best effort service such as ABR, UBR, or GFR, if there is no cell to start, the next slot in which the cell is located is found and the cell in the slot is output. Since there are several calendar schedulers 30, 31, and 32, it reschedules which of the cells (HOL) of the cell leaving the calendar scheduler should be departed first. This is an example of the present invention as the service scheduling function 40, which shows an example of self-clocked fair queuing (SCFQ) and priority. SCFQ is a method in which one service is selected equally with each other, with appropriate weights among each service. The priority is to output the high priority cell (HOL) first, and then the low priority cell. (HOL) is output. When scheduling is performed between services in the service scheduling function 40, the cell should now be delivered to the virtual output port buffers (VOQs) 60, 61, and 62. Before the cell is delivered, the VOQs (60, 61, 62) must be transferred. Check the buffer status. If the buffer is not empty where the cell is to be delivered, the cell is sent back to the input of the calendar scheduler 30, 31, 32 without passing it to the VOQs 60, 61, 62. If the VOQs 60, 61, 62 are empty, the cell is forwarded to the VOQs 60, 61, 62. Now, it is checked whether the broadcast is for broadcast. If broadcasting, copy the cell's address (HOL) and send the copied value back to the input of the calendar scheduler (30, 31, 32), while reading the cell from the VC buffer 20 and VOQ the cell itself. Pass it to (60, 61, 62). This is because the calendar scheduler has a cell address (HOL) and processes it like a cell, but VOQ stores and processes the cell itself.

First, there are several VOQs 60, 61, and 62 according to service class, and there is a buffer for each virtual output port in one VOQ 60 again. Cells delivered to VOQs 60, 61, and 62 are stored in the corresponding buffers according to the type of service and port number to be output. When the scheduler 13 is applied to the input side, the VOQs 60, 61 and 62 are for controlling the output port of the switch and for the subscriber link port when applied to the output side. Therefore, the type of service class of the VOQs 60, 61, and 62 should match the type of service class of the switch output port or the subscriber link port. VOQ (60, 61, 62) access between the port-specific buffers in a round robin (RR) or weighted round robin (WRR), the priority between several VOQ (60, 61, 62) The cell is output in accordance with 70).

As described above, when the cell input to the ATM exchanger is switched, the transfer of traffic is scheduled according to the traffic state of the switch output port, thereby suppressing a temporary overload state of the traffic, thereby increasing the switch efficiency. In addition, since the quality of the service is differently performed according to the grade, the quality of service can be kept. In addition, since control is performed in units of VC, fairness between VCs can be maintained. Since the scheduler according to the present invention performs various scheduling with the same basic structure of calendar according to the service type, the control structure of the buffer is simple and the operation reliability is high and the implementation is easy.

Claims (7)

A virtual connection buffer which stores cells in a virtual connection unit and transfers a storage address of the first cell among the virtual connection cells; A plurality of calendar schedulers, each of which has a corresponding service and a storage address of the cell transmitted from the virtual connection buffer, calculates a departure time of the cell and stores the storage address of the cell in a corresponding slot; A first scheduler which schedules which of the storage addresses of cells output from the plurality of calendar schedulers should start first; A plurality of virtual output port buffers provided for each service class and reading and storing cells corresponding to storage addresses of the cells output from the first scheduler; And And a second scheduler configured to output the cells stored in the virtual output port buffer according to the state and service level of the output port. The method of claim 1, And a cell copying means for copying the cell storage address and providing the cell storage address as an input of the calendar scheduler when the cell storage address output from the first scheduler is a broadcast cell. The method according to claim 1 or 2, The virtual connection buffer, A cell buffer for storing the cell; A virtual connection management table for recording a storage state of a cell for each virtual connection; And And an empty slot FIFO pointing to an empty portion of the cell buffer. The method of claim 3, wherein Wherein each of the calendar schedulers includes a calendar and the calendar is a collection of multiple cell slots. A method for scheduling an ATM cell, the method comprising: A first step of storing a cell in a buffer on a virtual connection (VC) basis and transferring a storage address of a first cell among cells of the virtual connection to a calendar scheduler of a corresponding service; A second step of the calendar scheduler calculating a time at which a cell starts and inserting a storage address of the first cell into a slot corresponding to the calculated start time; A third step of rescheduling which cell storage address of the service scheduler of each service should start first, and outputting a cell storage address of a corresponding calendar scheduler; If the virtual output port buffer to which the cell storage address is to be transmitted is not empty, transferring it to an input of the corresponding calendar scheduler; A fifth step of reading a cell from the virtual connection buffer indicated by the cell storage address and storing it in the virtual output port buffer when the virtual output port buffer to which the cell storage address is to be transferred is empty; And And a sixth step of outputting the cells stored in the virtual output port buffer according to the status and service level of the output port. The method of claim 5, And if the cell storage address output in step 3 is a broadcast cell, copying the cell storage address and providing the cell storage address as an input of the calendar scheduler. On the processor, A first function of storing a cell in a buffer in units of a virtual connection (VC) and transferring a storage address of a first cell among cells of the virtual connection to a calendar scheduler of a corresponding service; A second function of the calendar scheduler calculating a time at which the cell starts and inserting a storage address of the first cell into a slot corresponding to the calculated start time; A third function of rescheduling which cell storage address of the service scheduler of each service should start first, and outputting a cell storage address of a corresponding calendar scheduler; A fourth function of transferring the virtual output port buffer to which the cell storage address is to be transferred to an input of the corresponding calendar scheduler; A fifth function of reading a cell from the virtual connection buffer indicated by the cell storage address and storing it in the virtual output port buffer when the virtual output port buffer to which the cell storage address is to be transferred is empty; And A computer-readable recording medium having recorded thereon a program for executing a sixth function of scheduling and outputting a cell stored in the virtual output port buffer according to the state and service level of the output port.