KR100271524B1 - Multi-stage congestion control method - Google Patents

Abstract

In the present invention, the centralized multi-level congestion in an asynchronous transmission mode network that prevents congestion by using the optimal path and distributing the load imposed on the network in consideration of the state of all resources available between two end-to-end users In the control method, by defining the multi-level congestion level in the broadband integrated network and using the central controller, it is possible to find an efficient path considering the entire network resource state when searching for the path for the connection through the congested virtual path. According to the characteristics of the congestion in the congestion state by performing other congestion control to increase the utilization of network resources and improve the yield.

Description

Multistep Congestion Control Method in Asynchronous Transmission Mode Network

The present invention relates to a multi-stage congestion control method in an asynchronous transmission mode network, and more particularly, to divide congestion into multiple stages according to the state of all virtual paths in a broadband integrated telecommunication network, and to transfer or connect the congestion state to the central controller in each exchange. A multistep congestion control method in an asynchronous transmission mode network configured to perform congestion control in association with admission control.

Asynchronous transmission mode network (ATM network) can deliver a multimedia service having a variety of quality of service through the same transmission path.

In this asynchronous transmission mode network, there are three types of transmission paths: a virtual channel (VC) as a logical link, a virtual path (VP) as a bundle of a plurality of virtual channels, and a physical link. The relationship is as in FIG. 1 is a view showing the concept of a virtual path (VP) in a broadband integrated information network (B-ISDN), a virtual channel (VC) is a unit representing a connection between a user and a virtual path (VP) It is a bundle of multiple virtual channels (VC), the TP represents the transmission path of the physical layer, and the PDH (Plesiochronous Digital Hierarchy; check that the underlined parts are incorrectly written) and the Synchronous Digital Hierarchy (SDH). Used.

They are routed using their respective identifiers: VCI (VC Identifier), Virtual Path Identifier (VPI), and Transmission Path Identifier (TPI), and Virtual Path (VP) provides various services. Virtual channel (VC) connections with quality of service (QoS) can be accommodated, and an efficient congestion control scheme is required when congestion occurs in an ATM node or a transmission path.

In relation to congestion control, various methods have been proposed so far, including self-healing techniques for controlling congestion at the virtual path (VP) level and ABR flow control for non-real time connection. Both of these methods are congestion control techniques that have only one level of congestion. Self-Healing technique reroutes in virtual unit (VP) when congestion is very serious or network failure occurs. It is a method to guarantee the quality of service for traffic flowing through the (VP), and ABR flow control is a method of controlling congestion by adjusting the cell flow of the connection according to the state of network resources.

2 is a block diagram showing an example of a virtual path rerouting by the conventional self-healing method, Figure 3 is a flow chart of the self-healing method shown in Figure 2, the original passing through the links (L1, L2, L3) Assign an alternate virtual path passing through the virtual path (OVP: Original VP) and the links (L4, L5, L6), and monitor the virtual path (VP) in the normal state, as shown in (a) of FIG. If congestion or hardware damage occurs in the path OVP, the problem is solved through an alternative virtual path, as shown in FIG. And, if the problem solving by the alternate virtual path fails, find a new route and solve the problem.If the problem is solved in this way, the virtual in normal state after reallocating the alternate virtual path for each virtual path Return to the path status monitoring operation.

The conventional self-healing technique for performing this operation is performed when there is congestion or hardware damage in the link L2 when there is an original virtual path (OVP: Original VP) passing through the links L1, L2, and L3. The problem is solved by using an alternative virtual path (AVP) set through the links L4, L5, and L6. After increasing the bandwidth of the alternate virtual path (AVP) from "0" to the bandwidth of the original virtual path (OVP), the traffic passing through the original virtual path (OVP) is replaced with the alternate virtual path (AVP). Since bandwidth movement in units of virtual paths (VP) occurs, the links L4, L5, and L6 shown in FIG. 2 (b) must have sufficient free bandwidth to accommodate the bandwidth of the original virtual path (OVP). Due to the virtual path identifier (VPI) for the alternate virtual path (AVP), the shortage of the virtual path identifier (VPI) occurs.

That is, since the conventional self-healing technique is performed in units of virtual paths (VP), one or more alternative virtual paths (AVP) having a bandwidth of "0" are reserved for one or more virtual paths (VP) in advance. Also, when rerouting, an alternate virtual path (AVP) is used, and a transmission path (TP) accommodating the alternate virtual path (AVP) is less likely to have enough bandwidth to accommodate the required bandwidth. There is a disadvantage in that the probability of success of the route rerouting is very low.

4 is a block diagram showing an example of the congestion control by the conventional ABR flow control method, Figure 5 is a flow chart of the ABR flow control method shown in Figure 4, the originating node 5 of the virtual path (VP) In the case where the ATM cell 10 in the state passes through the ATM switch 16 and is delivered to the receiving node 7, the present state of the virtual path (VP) is monitored and congested, that is, the ATM switch 16 is congested. A phenomenon occurs that results in a runaway switch 18 and a cell 12 with runaway bits being applied to the receiving node 7 via a subsequent ATM switch 20. The receiving node 7 then in turn applies the congestion notification cell 14 to the originating node 5.

The ABR flow control technique that performs this operation is a reactive congestion control technique that controls the congestion by reducing the cell rate by an information source (calling node) that receives congestion from the network through the ATM cell. Fast and accurate information exchange is required, and due to the variable network conditions, there is a limit to accurate cell rate calculation and efficient use of network resources. In addition, when a certain virtual path (VP) is in a congested state, there is a problem that the overall resource utilization rate is low and the yield is lowered by not using the spare bandwidth of the other virtual path (VP).

That is, the conventional ABR flow control technique described above adjusts the cell rate by transmitting the network state to the information source, and it is difficult to obtain an accurate cell rate in consideration of the time taken to deliver the network state to the information source. The resource management cell to be identified needs to be transferred together with the data cell, thereby increasing the load on network resources. In addition, other available paths are not available even though they exist, reducing the overall cell yield by reducing the cell rate of the connection.

Accordingly, the present invention has been made to solve the above-mentioned conventional problem, and in consideration of the state of all resources available between two end-to-end users, two users can use optimal paths and distribute the load imposed on the network to prevent congestion. It is an object of the present invention to provide a multilevel congestion control method in an asynchronous transmission mode network.

In order to achieve the above object, a multi-stage congestion control method in an asynchronous transmission mode network according to a preferred embodiment of the present invention includes an ATM switch, an ATM cross connect, a transmission path, and a broadband having a path composed of a plurality of virtual paths. In the congestion control method in a comprehensive communication network,

Presetting the congestion level for the virtual path in multiple stages;

Determining a current congestion level for the virtual path based on the predetermined congestion level according to the amount of traffic passing through the virtual path;

And performing runaway control for the identified current runaway level.

1 is a diagram illustrating a relationship between three types of links, a virtual channel, a virtual path, and a transmission link used in a general broadband integrated information communication network;

2 is a view showing an example of a virtual path rerouting by a conventional self-healing technique,

3 is a flow chart of the self-healing technique shown in FIG.

4 is a view showing an example of performing congestion control by the conventional ABR flow control method;

5 is a flowchart of the ABR flow controller method shown in FIG. 4;

6 is a configuration diagram of a multi-stage congestion control apparatus in an asynchronous transmission mode network applied to an embodiment of the present invention;

7 is a flowchart illustrating a multistep congestion control method in an asynchronous transmission mode network according to an embodiment of the present invention;

8 is a view showing an example of congestion control by rerouting ABR connection at congestion level 3 according to an embodiment of the present invention;

9 is a flowchart illustrating a process of selecting a CSFR and finding a new path of the CSFR in the central controller of the present invention.

<Description of the symbols for the main parts of the drawings>

10: ATM cell 12: cell with congestion bits

14 congestion notification cell 16, 20: ATM switch

18: Runaway switch 22, 24, 26: ATM switch

28 ATM Cross Connect 30 Central Controller

VC: Virtual Channel VP: Virtual Path

TP: Transmission Path

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

6 is a configuration diagram of a multi-stage congestion control apparatus in an asynchronous transmission mode network employed in an embodiment of the present invention, wherein reference numeral 22 denotes a first ATM switch, reference numeral 24 denotes a second ATM switch, and reference numeral 26 A third ATM exchange is shown and reference numeral 28 denotes an ATM cross connect.

Reference numeral 30 collects and analyzes the reported network state information periodically, receives a congestion level of each virtual path VP1, VP2, VP3 from the network node, performs a congestion control algorithm that is periodically performed, and performs the worst of each pass. Determining the virtual path (VP) of the, represents the central controller to determine the priority of the path according to the congestion level of the virtual path (VP), and then take appropriate action according to the congestion level.

The network node providing the network state information to the central controller 30 enters each level due to the instantaneous traffic increase in determining the congestion level as shown in Table 1 according to the virtual path VP and the buffer state. Exponential Moving Average Technique (Y (n) = a X (n) + (1-a) Y (n-1), where 0 <a≤1, Y (0) ) = 0, Y (n-1) is the previous runaway level, X (n) is the currently measured sample value, and a is the weight. In addition, the network node collects input traffic and network state information and transmits it to the central controller 30. When there is a change in the congestion level, the network node transmits the changed congestion level to the central controller 30, It receives the rerouting information of the non-real time connection from 30) and performs a connection reset and transmits the result to the central controller 30.

TABLE 1

Runaway levels Network status (cell level measurement) measure Level 1 When more than T1 (eg 88%) of the transmission path is in use None, save and retain data Level 2 When T2 (eg 91%) or more of the transmission path is in use or Level 1 is sustained for a period of time (a1; 30 minutes to 1 hour) Reject new connection attempts from services like ABR Level 3 When T3 (eg 94%) or more of the transmission path is in use or Level 2 is sustained for a period of time (a2; 10-30 minutes) Attempt to reroute delayed tolerant services such as ABR / NRT-VBR Level 4 When more than T4 (e.g. 97%) of the transmission path is in use or level 3 is persistent for a period of time (e.g. 5 to 10 minutes) Reject all new connection attempts

That is, the central controller 30 controls to reject the non-real time connection through the connection admission control when the current congestion level is level 2, and sets the virtual path VP when the current congestion level is level 3. Passing non-real-time connections is rerouted in the order of last-in-first-out (LIFO), and reject all new connection attempts if the current congestion level is level 4.

In the case of FIG. 6, each node determines its own congestion state and takes appropriate measures according to the congestion state. When the congestion level 3 is reached, the node reports to the central controller 30 to perform rerouting for the non-real time connection. This increases the utilization of network resources and provides users with improved quality of service (QoS).

Next, a multistep congestion control operation in an asynchronous transmission mode network according to an embodiment of the present invention will be described with reference to the flowchart of FIG. 7.

The ATM switches 22, 24, and 26 periodically measure traffic data and network performance information (step 100), and transmit the measured traffic data and network performance information to the central controller 30 as the central controller 30 In step S110, traffic data and network performance information are collected (step 110). Subsequently, the ATM switch 22, 24, 26 determines its congestion level by monitoring the load of the virtual path VP and the buffer state (step 120).

Once the level of congestion is determined, if it is the same as the previous congestion level (YES at step 130), the traffic state monitoring of step 100 is returned, and if it is different (NO at step 130), the action according to the congestion level is determined. Will be taken. In case of congestion level 1 (YES in step 140), only relevant information (information about the network node or virtual path, congestion status and persistence) is maintained (step 150), and in congestion level 2 (YES in step 160), ABR_REJECT is set so that the ABR connection is rejected in connection acceptance control (step 170). In other words, when the ATM switch receives a congestion level 2 congestion status from the network node, the ATM node lowers the priority of the congested node or the route having the virtual path (VP) to determine the probability that a new connection passes through the virtual path (VP). Lower. Therefore, by using the flag according to the congestion state in the connection admission control (CAC), it is possible to control that the connection with a low quality of service (QoS) is rejected and that the quality of service (QoS) is accepted. .

If the determined runaway level is level 3 (YES at step 180), then the current runaway level is sent to central controller 30 (step 190) to allow for rerouting of the non-real time connection. If congestion level 4 (NO in step 180), ALL_REJECT is set to reject all new connection attempts (step 200). The congestion control of the congestion level 4 includes congestion control measures of the lower congestion levels 1, 2, and 3, and removes the control measures added to the corresponding level when there is a state change from the upper level to the lower level. Receiving congestion level 3 rerouting information from the node (step 210), the central controller 30 takes network configuration information and state information from the database and performs rerouting (step 220). From the ABR connections traversing the route (VP), a Connection Selected For Rerouting (CSFR) connection is selected (step 230), and a new path is selected for the selected CSFR connection (step 240). Accordingly, the optimal path for CSFR can be found using network configuration information and state information. The selected pass information is transmitted to the ATM switch 22, 24, and 26 to establish a new connection (step 250). The ATM switch 22, 24, and 26 uses the pass information to establish a new connection and then traffic. Is replaced with a new connection (step 260), and then the existing connection passing through the congested virtual path VP is released (step 270). The ATM switches 22, 24, and 26 then report the rerouting result to the central controller 30 (step 280), and the central controller 30 receives the execution result from the node (step 290). When the reporting of the rerouting result is completed, the ATM exchangers 22, 24, and 26 check if the congestion level of the congestion virtual path (VP) is lowered to level 2, and if the congestion level is not exceeded (step 300 in step 300). NO "), ABR flow control is performed (step 310).

8 is a diagram illustrating an example of congestion control by rerouting ABR connection in congestion level 3 according to an embodiment of the present invention, and between each ATM switch 22, 24, 26 and ATM cross connect 28; The transmission path TP is divided into two virtual paths VP2 and VP3, respectively, and the ATM switch 22 and the ATM switch 26 are directly connected through the virtual path VP1. At this time, when the congestion occurs in the virtual path VP1, the congestion is resolved by distributing the traffic passing through the virtual path VP1 into the virtual path VP2 and the virtual path VP3 in the central controller 30. That is, the traffic passing through the virtual path VP1 is reduced and the traffic passing through the virtual paths VP2 and VP3 is increased to solve the congestion in the virtual path VP1.

In other words, in the case of FIG. 8, when congestion occurs in the virtual path VP1, the congestion is controlled by rerouting the connection passing through the virtual path VP1 so as to pass through the virtual paths VP2 and VP3.

9 is a flowchart illustrating a process of selecting a CSFR and finding a new path of the CSFR in the central controller of the present invention. First, the number of ABR connections passing through the congested virtual path (VP) is calculated (step 400). After arranging these ABR connections by the set reverse order-in-first-out (LIFO) (step 410), the CSFRs are sequentially selected one by one (step 420), and a new path of CSFR for rerouting is selected (step 430). ). If there is a suitable pass ("success" in step 430), the bandwidth (VPB) of the congested virtual path (VP) is reduced by the CSFR bandwidth (CSFR_BAN) (step 440), and if there is no suitable pass (step 430). In case of "Fail", go to the next step 450, if the reduced bandwidth is less than the congestion level 2 threshold (Level2_T), or if all the ABR connections are checked, the pass selection process is finished; The operation from step 420 described above for selecting a connection to find a new path is repeated. When rerouting the CSFR, the best candidate pass is a pass in which all the virtual paths VP on the path are in a runaway state than the runaway virtual path VP and the cost is minimal.

According to the present invention as described above, the problem of the conventional self-healing (Self-Healing) technique and the flow control technique to improve the resource utilization rate and yield of the network, by defining a multi-step congestion step by step preventive and By implementing reactive congestion control techniques, the network remains stable.

In addition, preferred embodiments of the present invention are disclosed for the purpose of illustration, those skilled in the art will be able to make various modifications, changes, additions, etc. within the spirit and scope of the present invention, such modifications, changes, etc. fall within the scope of the claims Should be seen.

Claims (26)

A congestion control method in an asynchronous transmission mode network having an ATM switch, an ATM cross connect, and a transmission path composed of a plurality of virtual paths, for controlling a path for a connection passing through a congested virtual path, Presetting a congestion level of multiple levels according to the state of the virtual path; Determining a current congestion level for the virtual path based on the predetermined congestion level according to the amount of traffic passing through the virtual path; And distributing the load imposed on the network by performing differential congestion control according to the identified current congestion level. The method of claim 1, The predetermined congestion level is classified into four levels according to the traffic data and network status information, the multi-stage congestion control method. The method of claim 2, The congestion level in the fourth stage includes congestion level 1 when the transmission path between the exchanges is in use above the first threshold, congestion level 2 when the transmission path is in use above the second threshold, and the transmission path is in the third threshold. And a congestion level 3 when abnormally in use, and a congestion level 4 when the transmission path is in use above a fourth threshold value. The method of claim 3, The first threshold value is 88%, characterized in that the congestion control method. The method of claim 4, wherein And wherein the second threshold is 91%. The method of claim 5, And the third threshold value is 94%. The method of claim 6, And the fourth threshold value is 97%. The method of claim 3, And when the current congestion level for the virtual path is level 1, congestion information including time information of entering the level 1 is maintained. The method of claim 3, And if the current congestion level for the virtual path is level 2, rejecting an attempt for a new connection with low quality of service. The method of claim 3, And if the current congestion level for the virtual path is at level 3, rerouting of the non-real time connection. The method of claim 10, And rerouting the non-real time connection using a central controller configured to control the ATM switch, the ATM cross connect, and the transmission path. The method of claim 11, The rerouting process using the central controller calculates the number of non-real time connections passing through the congested virtual path, arranges the non-real time connections in the reverse order in which the connections are established, and sequentially CSFR one by one for the non-real time connections. Multi-step runaway control method characterized in that in order to reduce the load of the virtual path after selecting the path for the rerouting. The method of claim 3, And if the current congestion level for the virtual path is level 4, rejecting attempts for all new connections. The method of claim 2, The congestion level of the four stages is the congestion level 1 when the transmission path between the exchanges is in use above the first threshold value, the congestion level 2 when the transmission path continues within the first time range above the first threshold value, and the transmission. Multi-level congestion control, characterized in that the congestion level 3 when the path continues in the second time range above the second threshold value, and the congestion level 4 when the transmission path lasts in the third time range above the third threshold value. Way. The method of claim 14, The first threshold value is 88%, characterized in that the congestion control method. The method of claim 15, And the first time range is 30 minutes to 1 hour. The method of claim 16, And the second threshold value is 91%. The method of claim 17, And the second time range is 10 minutes to 30 minutes. The method of claim 18, And the third threshold value is 94%. The method of claim 19, And the third time range is 5 minutes to 10 minutes. The method of claim 14, And when the current congestion level for the virtual path is level 1, congestion information including time information of entering the level 1 is maintained. The method of claim 14, And if the current congestion level for the virtual path is level 2, rejecting an attempt for a new connection with low quality of service. The method of claim 14, And if the current congestion level for the virtual path is at level 3, rerouting of the non-real time connection. The method of claim 23, wherein And rerouting of the non-real time connection using a central controller configured to control the ATM switch, the ATM cross connector, and the transmission path. The method of claim 24, The rerouting process using the central controller calculates the number of non-real time connections passing through the congested virtual path, arranges the non-real time connections in the reverse order in which the connections are established, and sequentially CSFR one by one for the non-real time connections. Multi-step runaway control method characterized in that in order to reduce the load of the virtual path after selecting the path for the rerouting. The method of claim 14, And if the current congestion level for the virtual path is level 4, rejecting attempts for all new connections.