KR100736908B1 - Method for data burst transmission in optical burst switching networks - Google Patents

Abstract

A method for transmitting data burst in an optical burst switching network is provided to allow an optical switching system to perform its maximum performance by controlling the length of data burst according to the amount of change in traffic without having to change a hardware system. A system parameter, including information about the number of input/output ports of an optical burst switching network, the number of wavelengths per port, the amount of traffic, the number of optical fiber delay lines, the length of initial data burst, and an initial unit delay time, is determined(500). An optimum unit delay time for which a core node can generate a minimum burst loss rate is determined according to the amount of change in traffic(502). The core node informs an entry node of the optimum unit delay time(504). The entry node calculates a new burst length according to the optimum unit delay time and corrects a threshold value of the burst length(506).

Description

Method for data burst transmission in optical burst switched networks

1 is a block diagram illustrating an optical burst switching network consisting of an inlet node and a core node;

2 is a block diagram illustrating an optical buffer implemented as a fiber forward delay line of a feed forward method in an optical exchange system;

3 is a configuration diagram illustrating an optical buffer implemented as a optical fiber delay line of a feedback method in an optical exchange system;

4 is a view for explaining an optical buffer implemented with an optical fiber delay line in an optical exchange system;

5 is a flowchart for explaining a data burst transmission method in an optical burst switched network according to a preferred embodiment of the present invention;

6 is a view for explaining the format of a control packet according to an embodiment of the present invention;

7 is a table showing the optimal unit delay time and burst length required according to each traffic amount obtained by the present invention;

8 is a graph showing a loss rate, a minimum loss rate, and an optimal unit delay time of a data burst according to each traffic amount;

FIG. 9 is a graph illustrating a loss rate of data bursts obtained by adjusting a data burst length according to a varying traffic amount in an optical switching system constructed according to an embodiment of the present invention.

TECHNICAL FIELD The present invention relates to optical burst switching networks, and in particular, the burst length is controlled by using a burst generator at the inlet node so that the already configured optical switching system always shows a minimum burst loss rate even under varying traffic loads. It relates to a data burst transmission method.

Optical Burst Switching (OBS) technology uses a one-way reservation scheme that sends control packets to the destination node first, reserves resources, and then sends them directly without checking them. Will be sent immediately.

In this optical burst switching network, which transmits data only in the optical signal domain between end-to-end nodes, since the core node does not have an electric buffer, collisions inevitably occur when a plurality of data bursts flow into one port (or wavelength) at the same time.

Various solutions have been proposed to resolve these conflicts, including the use of bypass paths, wavelength converters, class-specific priority discarding methods, class-specific wavelength groups, and fiber-optic delay lines (FDLs). Such as using an optical buffer.

Among these methods, an optical buffer using an optical fiber delay line (FDL) is the most useful method because it delays the burst in which the collision occurs by the collision time, and can effectively prevent burst loss as in the existing Internet network.

However, optical buffers, like conventional random access memory (RAM), do not adjust their buffering time freely, and consist of multiple optical fiber delay lines with different discrete lengths. Once configured and installed, the optical buffer is difficult to change easily. In addition, the optical buffer has a burst loss rate that varies depending on the number of optical fiber delay lines and the unit delay time, and there is a unit delay time (called an optimal unit delay time) showing a minimum loss rate. This optimal default delay depends on the amount of input traffic.

As described above, the optical buffer already configured may exhibit a minimum burst loss rate in a specific traffic amount, but the configured buffer does not show optimal performance as the amount of traffic varies.

The present invention has been made in view of the above, and in an optical burst switching network using an optical buffer utilizing an optical fiber delay line (FDL), the optical buffer provides optimal performance without changing the optical burst switching system that is already configured. The purpose is to provide a method of adjusting the length of the data burst to achieve.

)를 수학식

에 의해 계산하여 버스트 길이 임계치(T_H)를 수정하는 단계를 포함하는 것을 특징으로 한다. In order to achieve the above object, the present invention provides a data burst transmission method in an optical burst switched network comprising an inlet node and a core node, and having an optical buffer using an optical fiber delay line, the method comprising: (a) entering an optical burst switched network. Number of output ports (M), wavelength per port (W), traffic volume (ρ _B ), number of fiber delay lines (B), length of initial data burst (L _B ), initial unit delay time (D _P (B) determining an optimal unit delay time (D _R ) at which the core node generates the minimum burst loss rate according to the changed traffic amount, (c) the core node having the optimal unit delay Informing the ingress node of time D _R , and (d) the ingress node having a new burst length in accordance with the optimal unit delay time D _R (

) Equation

And modifying the burst length threshold T _H by calculating.

In step (b) of the present invention, the optimum unit delay time (D _R ) is the number of input / output ports (M), the number of wavelengths per port (W), the traffic amount (ρ _B ), the number of optical fiber delay lines (B). It can be determined according to.

In step (c) of the present invention, the core node delivers the control packet to the inlet node, and the control packet includes the number of input / output ports (M), the number of wavelengths per port (W), the number of optical buffers, It is preferable to include data for the length L _B of the initial data burst, the initial unit delay time D _P , the optimum unit delay time D _R , and the traffic amount ρ _B , preferably at a predetermined period. Do.

The inlet node of the optical burst switching network has a burst generator, and the burst length threshold T _{H in} step (d) is preferably applied to this burst generator.

The optical buffer of the optical burst switched network may include a feed forward scheme and a feed back scheme.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments are provided to those skilled in the art to fully understand the present invention, and may be modified in various forms, and the scope of the present invention is limited to the embodiments described below. It doesn't happen.

(Example)

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

FIG. 1 is a block diagram illustrating an optical burst switching network including an edge node and a core node.

Referring to FIG. 1, the entrance node 100 classifies the input traffic having bursty characteristics according to the same destination and service class of the same class, generates a data burst, and reserves resources to the destination. Generate and forward control packets. The core node 102 reserves the resource for the data burst according to the received control packet information and transmits the data burst to the next node.

In the inlet node 100, the control plane 100a includes a resource manager 104, a control packet processor 106, and a burst scheduler 108, and the optical switching system 100b includes a burst generator 110 and an optical switch fabric. (112). The burst generator 110 first classifies the input traffic into the same service class as the desired destination, and generates a data burst when the total length of the input traffic waiting in the queue exceeds a preset threshold T _H. The control packet processor 106 generates and processes routing information necessary to reserve resources to the destination. Burst scheduler 108 is responsible for scheduling data bursts so that conflicts do not occur at the output ports.

The number of input traffic sources flowing into a burst generator is N _P , the arrival rate of input traffic λ _P , the service rate of input traffic μ _P , the input packet length L _P , and the threshold limiting the data burst length T _{If H} , the arrival rate of the data burst is expressed by Equation 1.

 Then, the service rate of the data burst is expressed by the equation (2).

Where C _B is the bandwidth of the optical fiber wavelength.

Meanwhile, in the core node 102, the control plane 102a includes a resource manager 114, a control packet processor 116, and a burst scheduler 118, and the optical switching system 102b includes an optical switch fabric 120. Include. Reference numeral 122 denotes an optical buffer.

The core node 102 reserves resources for successful transmission of the data burst according to the information of the control packet received in advance. However, if multiple bursts of data attempt to transmit to one port (or wavelength) at the same time, collisions will occur between the data bursts, resulting in loss. Therefore, to solve this problem, the optical buffer based on the optical fiber delay line is utilized.

FIG. 2 is a block diagram illustrating an optical buffer implemented as a feed-forward optical fiber delay line in an optical exchange system, and FIG. 3 is implemented as a feedback optical fiber delay line in an optical exchange system. It is a block diagram for demonstrating the optical buffer.

2 shows a plurality of demultiplexers 200a ... 200m, multiplexers 202a ... 202m, combiners 204a ... 204n, 206a ... 206n, switches 208a ... 208c, wavelength converters 210a ... 210n, 212a. 202n), and feedforward buffers 214a and 214b. 3 includes components similar to those of FIG. 2 but includes a feedback buffer 304 instead of a feedforward buffer.

As shown in FIGS. 2 and 3, the optical buffer may be configured as a feed forward method or a feedback method. In addition, as shown in Figure 2 may be shared in each output port, as shown in Figure 3 may be shared in one node. As described above, the present invention is not limited to the optical buffer having a specific structure.

The feed-forward scheme gives only one chance to use a buffer. When data bursts collide at the output port, a fixed length buffer is used, exiting the buffer regardless of the success of the output resource. On the other hand, if the output buffer is not available even after one buffering, the feedback-type buffer causes the buffer to be cycled until the point at which the output resource is available or until the allowable number of buffering times.

4 is a view for explaining an optical buffer implemented as an optical fiber delay line in an optical switching system.

Referring to Fig. 4, each circle of arrows indicates an optical fiber delay line having a unit delay time 1, and the optical buffer is composed of B optical fiber delay lines having different delay times. Each delay line is configured by increasing the unit delay time (D), where the i-th delay line can delay the data burst by i * D time, and the maximum delay time is B * D. This unit delay is often expressed as a relative percentage of the data burst length. For example, if the data burst is 100KByte and the unit delay time is 0.2, the first delay line can be delayed by 20KByte, which is 0.2 times the burst length, the next delay line is increased to 40KByte, then 60KByte, etc. Done. In practice, we use fiber-optic delay lines that are capable of buffering that length of time.

However, in the optical buffer implemented with the optical fiber delay line, the burst loss rate is different according to the unit delay time. For example, if the unit delay time is very small, there is a high probability that there is no buffer of sufficient length to buffer the collision time between bursts. As the unit delay time increases, the burst loss rate decreases. On the other hand, if the unit delay time is very large, it not only needs to buffer a much longer time than the collision time between bursts, but also occupies resources. Therefore, reducing the unit delay time reduces the burst loss rate.

Thus, there is an optimal unit delay time D _R with a minimum burst loss rate. The optimal unit delay time depends on the number of input / output ports (M), wavelengths per port (W), number of fiber delay lines (B), and traffic volume (ρ _B = λ _B / μ _B ) in the optical switching system. Therefore, it is different. Therefore, the optical buffer should be designed in consideration of these characteristics.

Nevertheless, since the optimal unit time of the optical buffer is different according to the amount of traffic in the existing optical switching system, the dynamically changing traffic causes the optical buffer to not perform optimal performance. However, as described above, since the unit delay time of the optical buffer is expressed as a ratio of the length of the data burst, if the length of the data burst is adjusted according to the changed traffic amount using Equation 3 below, the pre-installed optical buffer always It can be emulated as if it were operating in a situation with optimal unit delay time.

Where L _B is the length of the initially set data burst, D _P is the unit delay time of the pre-installed fiber delay line, and D _R is the optimal unit delay time at the changed traffic amount.

For example, if the unit delay time in an optical switching system with an optical buffer is 0.2, and the initial data burst length is 100 KByte, the optimal unit delay time in the changed traffic is 0.5, the burst is 100 KByte * 0.2 / It should be created with a length modified to 0.5 = 40 Kbytes. The new data burst length thus obtained is immediately set to the threshold T _H of the burst generator to generate a data burst of the new length. It should be noted that changing the threshold of the burst generator will change the length of the data burst and thus the service rate of the burst, but the arrival rate of the burst will also change at the same rate, resulting in the bursting load (ρ _B = λ _B / μ _B ) becomes the same. That is, the present method only changes the length of the data burst in accordance with the changing traffic amount so that the optical switching system having the optical buffer can always achieve the target optimal performance in each traffic amount without changing the traffic amount.

5 is a flowchart for explaining a data burst transmission method in an optical burst switched network according to a preferred embodiment of the present invention.

First, a system parameter of the light exchange system is determined (step 500). That is, the number of input / output ports (M), the number of wavelengths per port (W), and the like are determined according to the target design requirements of the optical exchange system. Basically assume that each input wavelength has a wavelength converter. In addition, considering the target performance (burst loss rate and burst delay time), the number of fiber delay lines (B), the length of the initial data burst (L _B or T _H ), and the initial unit delay time (D _P ) are determined. The information determined in this way is owned by each core node.

Then, if the traffic amount changes, the core node determines the optimal unit delay time D _R , which generates the minimum burst loss rate in the optical switching system having the optical buffer configured as described above, according to the changed traffic amount (step 502). . The optimal unit delay time D _R can be obtained using a conventionally known method, and a method for determining the optimum unit delay time D _R is not within the scope of the present invention.

After operation 502, the core node notifies each inlet node of the changed optimal unit delay time D _R according to the changed traffic load (operation 504). That is, when the amount of traffic flowing into the core node changes so that the preset optical buffer does not show optimal performance in a given traffic situation, the core node changes the traffic information, the standard of the optical node's optical switching system, and Information on the unit delay time D _P of the set optical buffer is transmitted to each inlet node using a control packet.

6 illustrates a format of a control packet according to an embodiment of the present invention. Referring to FIG. 6, the control packet includes a port number, a wavelength number, a buffer number, L _B , in order to inform each ingress node of the optimal unit delay time according to the configuration of the optical buffer and the specific traffic amount in the core node. D _P , D _R , contains information about traffic volume. In addition, the control packet may be used for resource reservation for data burst transmission, for OAM used for operation / management of the optical switching network and optical switching system, and for resource information notification.

)를 계산하여 버스트 생성기의 버스트 길이 임계치(T_H)를 수정한다(제506단계). 즉, 제어 패킷을 수신한 입구노드는 수학식 3을 이용하여 새롭게 요구되는 버스트 길이(

)를 결정하여 버스트 생성기의 임계치(T_H)를 재설정한다. 이러한 방법을 통해 각 코어노드는 구성한 광 버퍼가 트래픽 양이 변함에 상관없이 각 트래픽 양에 대해서 최적의 성능을 제공할 수 있다. After operation 504, the inlet node may have a new burst length according to the changed optimal buffer delay time D _R.

In step 506, the burst length threshold T _H of the burst generator is modified. That is, the inlet node receiving the control packet newly uses the burst length (Equation 3).

To reset the threshold T _H of the burst generator. In this way, each core node can provide optimal performance for each traffic amount regardless of the amount of traffic.

7 is a table showing the optimal unit delay time and the burst length required according to each traffic amount obtained by the present invention.

)를 볼 수 있다. Referring to FIG. 7, when the number of input / output ports is 4, the optimum unit delay time D _R when the number of wavelengths W per port is 4 or 8, and the optical fiber delay line B is 4 or 8 and The resulting burst length (

) Can be seen.

8 is a graph showing the loss rate, the minimum loss rate, and the optimal unit delay time of the data burst according to each traffic amount. In FIG. 8, the small square boxes represent the optimal unit delay time showing the minimum burst loss rate in each traffic amount.

8 shows a structure in which the number of input / output ports is 4, the number of wavelengths per port, 8 feed-forward buffers are shared to each port, 8 optical fiber delay lines, input traffic has a Poisson distribution, and an initial burst length threshold is shown. As a graph when set to 100 KByte, it can be seen that the optimal unit delay time showing the minimum burst loss rate varies depending on the traffic load.

FIG. 9 is a graph illustrating a loss rate of data bursts obtained by adjusting a data burst length according to a varying traffic amount in an optical switching system constructed according to an embodiment of the present invention.

In FIG. 9, the initially set unit delay time is 0.3, and the remaining basic parameters are the same as those assumed in FIG. 8. As shown in FIG. 9, the optical buffer having the initially set unit delay time shows a very high burst loss rate especially at a high traffic load. This is because the optimal unit delay time for each traffic is different from the initially set unit time. The more you fly, the bigger you can see. In addition, when the dynamic data burst length adjustment scheme proposed in the present invention is applied, it can be seen that the optimal burst loss performance that can be provided in each traffic load is always close.

As described above, according to the present invention, since the unit delay time is expressed as a ratio with respect to the length of the data burst, by adjusting the length of the data burst according to the changed traffic amount, the amount of traffic is changed without changing the hardware system. There is an effect that can achieve the maximum performance that the optical exchange system can provide. That is, when a core node that detects a sudden change in the traffic volume does not perform the optimal performance of an already configured optical buffer or predicts that the performance will worsen in the future due to the continuous change in the traffic volume, By passing new data burst length information in accordance with the change of, it is always possible to approach the minimum burst loss performance that can be provided in each traffic load as shown in FIG. 8.

As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various deformation | transformation by a person of ordinary skill in the art within the scope of the technical idea of this invention is carried out. This is possible.

Claims (6)

A data burst transmission method in an optical burst switched network comprising an inlet node and a core node and having an optical buffer using an optical fiber delay line, (a) Number of input / output ports (M), wavelengths per port (W), traffic volume (ρ _B ), number of fiber delay lines (B), and length of initial data burst (L _B ) in an optical burst switched network. ), Determining a system parameter including an initial unit delay time D _P ; (b) determining an optimal unit delay time (D _R ) at which the core node generates a minimum burst loss rate according to the changed traffic amount; (c) the core node informing the inlet node of the optimum unit delay time D _R ; (d) the ingress node, a new burst length according to the optimized unit delay time (D _R) (

And modifying the threshold value T _H of the burst length by calculating Equation (4) according to Equation 4 below.

The method of claim 1, wherein in step (b), the optimum unit delay time (D _R ) is the number of input / output ports (M), the number of wavelengths per port (W), the traffic amount (ρ _B ), The data burst transmission method characterized in that it is determined according to the number (B). The method of claim 1, wherein step (c) comprises: The core node delivers the control packet to the entry node, The control packet includes the number of input / output ports (M), the number of wavelengths per port (W), the number of optical buffers, the length of the initial data burst (L _B ), the initial unit delay time (D _P ), and the optimum unit delay time ( D _R ), the data burst transmission method comprising the data for the traffic amount (ρ _B ). The data burst transmission method according to claim 1, wherein step (c) is performed at a predetermined cycle. The method of claim 1, wherein the inlet node includes a burst generator, and the burst length threshold T _H of step (d) is applied to the burst generator. 2. The method of claim 1, wherein the optical buffer includes a feed forward method and a feed back method.

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