KR20040048233A - Apparatus for queue scheduling using linear control and method therefor - Google Patents

Abstract

PURPOSE: A queue scheduling apparatus and method using linear control are provided to effectively utilize scheduling of a queue of a router by predicting an inflow speed of packets transmitted to the router. CONSTITUTION: e(t)(10) is the number of packets introduced during certain time. (d/dt)e(t)(12) is the changed amount of the number of introduced packets. A numerical formula(14) is the total amount of packets introduced during the certain time. A PID controller(200) generates certain control variable(20) through PID controlling according to the number of packets(10) introduced into a queue(300) during certain time, its changed amount(12) and the total amount of the number of packets(14). The control variable(20) is the number of discharged packets during the certain time, a threshold value of the queue, or a discard probability. The packet discarding unit(210) discards packets introduced into the queue(300) by using a certain discard algorithm.

Description

Apparatus for queue scheduling using linear control and method therefor}

The present invention relates to the transmission of data, and more particularly to efficient scheduling for packet processing and discarding of router queues on the Internet.

Conventional queue-related scheduling methods include tail dropping, random early detection (RED), red with in / out (RIO), and push-out (PO).

Tail Dropping Scheduling is used in the existing best-effort basis service. When the first-in first-out queue is full, the first dropping packet is discarded. However, QoS is not guaranteed because packets are discarded in the order in which they are queued, regardless of the importance of the packets.

RED scheduling is an active queue management technique that can discard input packets even before the queue is full. In RED, a certain threshold is set that is smaller than the maximum length of the queue. Scheduling that discards all packets according to a random probability P. RED solves the global synchronization problem of TCP traffic caused by Tail Dropping technique by randomly discarding packets before the queue overflows due to congestion, but there is a problem in that loss rate differentiation cannot be brought about according to the importance of packets.

RIO scheduling is a technique that applies each RED to In-Profile packets that comply with a predefined protocol and to Out-Profile packets that do not. Each RED applied to In-Profile packets and Out-Profile packets has a different threshold and discard probability (usually loose for RED for In-Profile packets and RED for Out-Profile packets). Is strictly applied), which has the disadvantage of low utilization.

The PO technique is a technique for selectively removing a packet already in the queue to receive a packet arriving when the queue is full. This technique has the advantage of minimizing the loss rate of high-utilization and high-priority packets compared to the methods of accepting packets based on thresholds (RED, RIO, etc.), but cannot solve the global synchronization problem. There is this.

In addition, conventional packet scheduling schemes commonly use a new packet transmitted to the router when the packet flowing into the router exceeds the queue capacity of the router, regardless of importance. There is a problem that it is discarded.

It is an object of the present invention to provide a queue scheduling apparatus and method which can minimize packet loss rate and solve global synchronization problem.

Another object of the present invention is to provide a network router including the above-described queue scheduling apparatus.

Another object of the present invention is to provide a computer-readable recording medium having recorded thereon a program for executing the above-described queue scheduling method on a computer.

1 is a block diagram of a control system by a PID controller to be applied to queue scheduling according to the present invention.

2 is a block diagram illustrating an apparatus for controlling queue scheduling according to the present invention.

3 is a conceptual diagram of a queue showing variables related to queue scheduling according to the present invention.

According to an aspect of the present invention, there is provided a queue scheduling apparatus, including: a PID controller configured to generate a predetermined control variable through PID control according to the number of packets introduced into a queue, a change amount, and a total amount of packets for a predetermined time; And a packet discarding unit for discarding packets introduced to the queue according to the control variable.

The control variable is preferably the discard count or discard probability of the packet for a predetermined time.

The PID controller may include a PI controller configured to generate a control variable so as to satisfy a predetermined requirement for a rise time of a change amount of the discarded number of packets according to the number of packets flowing into the queue, the amount of change, and the total amount of packets; And a PD control unit for generating a control variable so as to satisfy a predetermined requirement for the maximum amount of change in the discarded number of packets according to the number of packets flowing into the queue, the amount of change, and the total amount of packets. desirable.

According to an aspect of the present invention, there is provided a method for scheduling a queue, the method including: generating a predetermined control variable through PID control according to the number of packets flowing into the queue, a change amount, and a total amount of packets for a predetermined time; And discarding packets introduced to the queue according to the control variable.

According to another aspect of the present invention, there is provided a network router including: a packet queue configured to receive and store network packets; A PID controller configured to generate a predetermined control variable through PID control according to the number of packets flowing into the queue, a change amount thereof, and a total amount of packets for a predetermined time; And a packet discarding unit for discarding packets introduced into the queue according to the control variable.

Hereinafter, an apparatus and method for scheduling a queue according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a control system by a PID controller to be applied to queue scheduling according to the present invention.

The quality of service (QoS) that can be experienced on the network is characterized by delay, jitter and loss. Many network applications are sensitive to one or more of these parameters. For example, an interactive application may not be available if the total delay of the network exceeds a threshold. Streaming applications such as video can tolerate large fixed delays, but require more buffer space if the jitter or change in delay experienced by different packets exceeds a threshold. Other applications cannot tolerate dropped packets due to packet loss, such as excess congestion.

Most of today's Internet traffic is moderated as a single class of traffic delivered on a best-effort basis. That is, the network tries to deliver all packets in a reasonable time, but there is no guarantee of delay or loss. Because of the burst nature of network traffic, some packets may be delayed or dropped due to congestion, and the delays they experience vary considerably from packet to packet. The best effort delivery is sufficient for many types of traffic such as file delivery and web page access, but not for other types of traffic such as real time audio and video streams. In order to support traffic in real time and also provide premium quality services to specific customers, some networks divide traffic into segments and provide service guarantees for each class of traffic. For example, the traffic is divided into a first class in which the limited bit rate and a limited delay are guaranteed, a second class in which the minimum bit rate is guaranteed, and one or more best effort traffic classes in which different portions of the overall network bandwidth are allocated.

There are many ways in which the classification of the service traffic received by the delivery unit (packet, cell or frame) of the network is encoded in the unit. For example, the class of service in an Internet packet is encoded using an 8 bit Type of Service (ToS) field in the packet header. Or, the service class can be derived directly from the flow to which the packet belongs. In the case of an ATM network, the service class is associated with the virtual circuit through which the cell passes.

Service guarantees are implemented by a combination of input policing and output scheduling. Input cleanup ensures that all traffic arriving at the router matches the appropriate service connection. When the packet arrives at the router, a check is made to determine if its arrival time matches the service connection. If the packets match, they are processed normally. If the packets do not match, for example, a 10 Mbit / s bandwidth-guaranteed flow consumes 15 Mbit / s, an indication of packet inconsistency is provided, and once the packets are processed normally, the quality of service is degraded or the packets are dropped according to network policy. Can be.

Output scheduling determines the order in which packets leave the router on a particular output channel. Scheduling is a major factor in ensuring specific QoS. For example, to ensure a limited bit rate for a particular flow, packets of this flow must be scheduled in front of packets from a burst of best effort flow that may exceed the available capacity. To ensure low jitter on the streaming flow, each packet is scheduled to leave the router within a narrow window of time.

Output scheduling for guaranteed bit rate (GBR) traffic is often performed using multiple queue structures. Separate output queues are provided for each traffic class (class-based queuing, CBQ) or for each network flow (flow queuing). Each queue waits for some packets waiting for transmission on the output line. A counter indicating when the next packet leaves the queue is associated with each queue. For example, for queues associated with constant bit rate traffic, the counter indicates when the next packet should leave the queue. After the packet leaves the queue, the counter is updated in increments to reflect the length of the packet separated by the current time and bandwidth allocation. This update method corresponds to an ATM leak-bucket algorithm for constant bit rate QoS.

Output scheduling for the best effort traffic is also performed using weighted-fair queuing (WFQ). Such traffic is also scheduled using a separate queue for each traffic class or each flow. However, for best effort traffic, packets in the queue are not assigned a guaranteed bit rate on the output port. Rather, each queue allocates a portion of the available bandwidth, and packets are scheduled based on the best action according to the available bandwidth. In queues associated with this best-acting traffic, the counter associated with each queue is run according to a weighted pair queuing algorithm, where the queue associated with the smallest count is selected for transmission when the output bandwidth is available and its counter is bandwidth share Incremented by the inverse of the share.

In a conventional router, the process of searching for the lowest counter, selecting the appropriate queue, and updating the counter associated with the queue is performed by software running on the microprocessor. Because of the processing overhead required to transfer each packet with class-based queuing or per-flow queuing, these mechanisms are limited to use on low-speed links with an intermediate number of queues.

The queue scheduling algorithm applying the PID control theory according to the present invention is largely composed of a method of calculating a proportional coefficient, a derivative coefficient, an integral coefficient of a PID controller, and a method of applying a designed controller to an actual queue.

First, obtaining each coefficient of the PID controller is based on a method of obtaining each coefficient by designing a PID controller for queuing scheduling.

The transfer function of the PID controller shown in FIG. 1 is represented by Equation 1 below.

In Equation 1, K _p is a proportional coefficient, K _d is a derivative coefficient, K _i represents the integral coefficient.

When the transfer function of Equation 1 is expressed in the time domain, it may be expressed as Equation 2 below.

There may be various methods of designing the PID controller shown in FIG. 1, but in the present invention, each coefficient is obtained by using the following decomposition method using a PI controller and a PD controller design method.

The PID controller transfer function expressed in Equation 1 may be decomposed and used as in Equation 3 below.

Equation 3 shows that the PID controller is formed by serial connection of the PI control part and the PD control part. In the PID controller, three coefficients are required, so if the constant term of the PD control part is set to 1 in the right term of Equation 3, and the coefficients of both sides are compared and matched, the relations of Equations 4 to 6 are obtained.

First, the coefficients K _i2 and K _p2 are determined to design the PI control part. The integral coefficients increase the order of the system by one order to improve the steady-state error, so select the values K _i2 and K _p2 to satisfy the system's rise time requirements. This step does not matter even if the maximum exceeded because it can be adjusted by the following derivative control.

Then design the PD control section to reduce the maximum exceeded. K _d1 value is selected to meet the braking ratio requirement to satisfy the design target for the object including the PI control part designed earlier.

When K _i2 , K _p2 , and K _d1 values are determined by the above method, K _p , K _d , and K _i values are obtained using the relations of Equations 4 to 6.

In the method of designing the PID controller designed for the router queue system, the functions and variables of the PID controller described above are the control variables u (t) for making the system requiring the control signal stable. In order to apply this system to the purpose of discarding the packets stored in the queue according to the inflow rate of the packets flowing into the router on the Internet, the functions and variables of the controller designed above are applied to the system. You need to redefine it.

2 is a block diagram illustrating an apparatus for controlling queue scheduling according to the present invention.

First, referring to each variable and function illustrated in FIG. 2, e (t) 10 is the number of packets flowing in during a specific time period. (12) is the amount of change in the number of incoming packets. And, (14) means the total amount of packets introduced during a specific time, i.e., integral.

According to FIG. 2, a preferred embodiment of the packet queue scheduling apparatus according to the present invention includes a PID controller 200 and a portion (packet closure unit 210) for discarding a packet.

PID controller 200 according to the PID control as shown in FIG. 1 according to the number of packets 10, the amount of change 12, and the total amount 14 of the packets flowing into the queue 300 for a predetermined time, Generate the control variable u (t) 20.

The control variable u (t) 20 is the discard count of the packet, the threshold of the queue, or the discard probability for a specific time.

The packet discard unit 210 discards the packet introduced into the queue 300 using a predetermined discard algorithm according to the control variable u (t) 20.

3 is a conceptual diagram of a queue showing variables related to queue scheduling according to the present invention.

Looking at each variable with reference to Figure 3, it is defined as the following equation (7) to (10).

In the above equations, variables are respectively a time t, Pk (l) is a packet stored in the l-th queue stack, Pk (m) is a packet stored in the m-th queue stack, Pk (n) is an n-th queue stack Represents a packet stored in. 3, de (t) 36 is , se (t) (38) Means.

The present invention can be embodied as code that can be read by a computer (including all devices having an information processing function) in a computer-readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of computer-readable recording devices include ROM, RAM, CD-ROM, magnetic tape, floppy disks, optical data storage devices, and the like.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

According to the apparatus and method for scheduling a queue according to the present invention, by using the packet scheduling applying the PID control theory, the inflow rate of the packet transmitted to the router can be predicted, so that the scheduling of the queue inside the router can be more efficiently utilized. The packet may be discarded according to the inflow amount of the number of packets transmitted to the packet.

In addition, by detecting the change in the number of packets to be transmitted and actively classifying the packets stored in the queue can be selectively discarded, it is possible to solve the global synchronization problem of the existing scheduling methods and to minimize the packet loss rate.

Claims (12)

A PID controller configured to generate a predetermined control variable through PID control according to the number of packets flowing into the queue, a change amount thereof, and a total amount of the packets for a predetermined time; And And a packet discarding unit for discarding packets introduced to the queue according to the control variable. The apparatus of claim 1, wherein the control variable is a discard count of a packet during a predetermined time. 2. The apparatus of claim 1, wherein the control variable is a probability of discarding a packet for a predetermined time. The method of claim 1, wherein the PID control unit, A PI controller configured to generate a control variable so as to satisfy a predetermined requirement for a rise time of the change amount of the discarded number of packets according to the number of packets flowing into the queue, the amount of change, and the total amount of packets; And And a PD controller configured to generate a control variable so as to satisfy a predetermined requirement for the maximum amount of change in the discarded number of packets according to the number of packets flowing into the queue, the amount of change, and the total amount of packets. Packet queue scheduling apparatus. A packet queue for receiving and storing network packets; A PID controller configured to generate a predetermined control variable through PID control according to the number of packets flowing into the queue, a change amount thereof, and a total amount of packets for a predetermined time; And And a packet discarding unit for discarding packets introduced into the queue according to the control variable. 6. The network router according to claim 5, wherein the control variable is a discard count of a packet for a predetermined time. 6. The network router of claim 5, wherein the control variable is a probability of discarding a packet for a predetermined time. The method of claim 5, wherein the PID control unit, A PI controller configured to generate a control variable so as to satisfy a predetermined requirement for a rise time of the change amount of the discarded number of packets according to the number of packets flowing into the queue, the amount of change, and the total amount of packets; And And a PD controller configured to generate a control variable so as to satisfy a predetermined requirement for the maximum amount of change in the discarded number of packets according to the number of packets flowing into the queue, the amount of change, and the total amount of packets. Network router. (a) generating a predetermined control variable through PID control according to the number of packets flowing into the queue for a predetermined time, the amount of change thereof, and the total amount of packets; And and (b) discarding packets introduced to the queue according to the control variable. 10. The method of claim 9, wherein the control variable is a discard count of a packet for a predetermined time. 10. The method of claim 9, wherein the control variable is a probability of discarding a packet for a predetermined time. (a) generating a predetermined control variable through PID control according to the number of packets flowing into the queue for a predetermined time, the amount of change thereof, and the total amount of packets; And (b) a computer-readable recording medium having recorded thereon a program for causing a computer to discard a packet introduced into a queue according to the control variable.