KR20050066468A - Detour path decision method for dual failures restoration on optical network system - Google Patents

Abstract

A method of setting up bypass for dual failover is disclosed. According to the present invention, a method for setting a detour for dual failure recovery may include: (a) setting a required LSP by receiving link information according to a predetermined network policy from nodes in a network; (B) calculating the detour while controlling to minimize the degree of sharing of the set detour, taking into account the link of the determinant, and (b) deciding the need for resource sharing. In this case, there can be many routes sharing the link, and the recovery path sharing the link can be removed to reduce the ripple effect of failure by distributing the share and efficiently use resources. . In addition, the share of each link is distributed, thereby increasing the recovery rate for any dual failures.

Description

Detour path decision method for dual failures restoration on optical network system

TECHNICAL FIELD The present invention relates to optical network systems, and more particularly, to a method of setting up bypass for dual failure recovery.

Network Survivability is a critical requirement for high speed optical based networks. This is a fast recovery capability that can counter SONET ring performance because optical link, path, and node failures mean much more information loss than electrical.

Recently, in order to accommodate the explosive growth of networks due to Internet services, transport networks based on WDM (Wavelength Division Multiplex) are gradually being developed in carrier networks. In optical transport networks, WDM technology can accommodate large bands of fiber by multiplexing hundreds of optical channels. Currently, point-to-point (P-T-P) WDM links that multiplex dozens of optical channels are accommodated in a carrier network.

A typical approach to providing network survivability is to consider only a single component, such as one link or node, at a time. In practice, however, disability in a network tends to occur simultaneously, and discussion for this is being actively conducted. Actual research shows that triple spare capacity is required for full-failure restorability. In other words, resource utilization is very inefficient in case of double failure of link or node.

In a network, there is a recovery path along with a working path to recover from a failure if normal data transfer is not possible due to a path or node error. There are two types of recovery paths: a protection switching model that prepares an alternate path before failure and a rerouting model that finds a new alternative path after failure.

The protection switching model establishes the recovery path before failure by network routing policy. When establishing a recovery path, the traffic requirements of the current work path are taken into account. If a failure is detected on the work path, the start node of the recovery path immediately replaces the traffic with the recovery path, enabling fast recovery. On the other hand, in the protection switching model, a failure signal should be transmitted to the start node of the recovery path that starts the recovery operation and switches to the recovery path. Therefore, a failure notification function is required for this.

In the rerouting model, after a failure, a request for traffic recovery establishes a new path or path segment. The new path is set by fault information, network routing policy, preset shape information and network topology information. If a failure occurs, a failure signal is sent to the recovery start node. At this time, the recovery start node may be a start node of a work path or a node that detects a failure after a network failure occurs.

The rerouting model is sometimes more suitable for network optimization because the recovery path is established based on the current network state and network policy. However, a lot of work must be done after a failure, and recovery paths are more difficult and slower than protection switching models in the event of a node failure or multiple links along the work path.

Meanwhile, the protection switching model and the rerouting model may be used together. For example, a recovery path preset by the protection switching model may be temporarily used while forming a new path by the path resetting model.

Traffic mapping from failed work paths to recovery paths includes 1 + 1 protection, 1: 1 protection, 1: n protection, and m: n protection. 1 + 1 protection doubles the resource consumption by sending the same traffic to both sides. 1: 1 also wastes resources in the recovery path, not just traffic. 1: n is also a special case of m: n, which also reduces some of the waste of resources by using several recovery paths, but reserves all resources for traffic for each of the work paths. Of waste occurs.

1 is a diagram illustrating an example of a network for explaining an example of a traffic mapping method.

Referring to FIG. 1, let LSP passing through A-B-C-D-E be referred to as LSP1 and LSP passing through A-I-J-K-E as LSP2. In this case, if LSP1 and LSP2 select both recovery paths as AFGHE using the 1: n method to map each recovery path in case of network failure, the two working paths can share one recovery path. have. If only one failure occurs in the network shown in FIG. 1, LSP1 and LSP2 do not use the recovery path at the same time. Resource allocation for the recovery paths of LSP1 and LSP2 on A-F-G-H-E can be selected by selecting the larger of the LSP1 and LSP2 traffic. Thus, if only one failure is assumed in the network and the work paths do not overlap each other, resources can be shared on the recovery path. Taking it a step further and sharing the wavelengths with each other in the recovery path by assuming the optical transmission network can save the wavelengths available in the optical transmission network where the number of available wavelengths is limited and increase the number of wavelengths that can be recovered.

Many recovery schemes that can be used in a general network, based on the rerouting scheme, include a link-based scheme as shown in FIG. 2A and a path-based scheme as shown in FIGS. 2B and 2C. ) Can be divided into On a link basis, rerouting refers to redirecting traffic issued by a fault around the point of failure. Pass-based, on the other hand, involves changing all paths between two failed stages. The link base must be able to identify the failed link at both ends of the failed link, and it may take up more capacity because it is difficult to recover in case of node failure, and the selection of recovery path is limited.

On the other hand, Per-Path-reserved Backup Sharing is a proactive restoration method that sets up a recovery path at the initial stage of setting the priority path and reserves the resources accordingly. It is a method of reserving RC (Restoration Channels) of each optical line group (OLG). Two or more recovery paths will then reserve the same RC, which is actually used when only one of these RCs fails. Thus, when an optical line group (OLG) on a link is used as a recovery path, the following considerations arise. Given a priority path, consideration should be given to whether specific OLGs are reserved for use as RCs or reused to share existing RCs in the route of the recovery path. This affects the price of the OLG's backup path calculation algorithm and how resources are distributed after the recovery path is selected. In the per-path-reserved approach, since the RCs reserved for one OLG do not carry the actual traffic, the number of these RCs is calculated as the network overhead required for recovery.

As a result, conventionally, fault information is propagated to the network by a signal, causing a load on the entire network.

Also, conventionally, hop length is not taken into account in the path calculation in the case of double failure recovery. (What problem arises?) In the hop calculation, a path calculation through a simple hop can recover between actual hops. Restoration average packet hop distance.

In addition, triple spare capacity may be required for complete dual-failure recovery.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a method for setting a bypass for dual failure recovery in an optical network system.

Another technical problem to be solved by the present invention is to provide a recording medium in which the detour setting method is recorded as program code executable by a computer.

In order to achieve the above object, in the optical network system according to the present invention, the detour setting method for dual failure recovery comprises the steps of (a) setting the required LSP by receiving link information according to a predetermined network policy from nodes in the network; (B) calculating the detours according to the set main LSP in consideration of the link of the main LSP, and (c) determining the detour while controlling to minimize the sharing degree of the set detour.

Hereinafter, an idle resource control method for dual failure recovery in an optical network system according to the present invention will be described with reference to the accompanying drawings.

3 is a diagram illustrating an example of a network topology composed of two-level SRLGs in consideration of hop distances.

3, the lower layer SRLG is for representing the SRLG (PSR) of the physical link of each node, and the upper layer SRLG serves as a means for controlling the hop limit of the network topology. do.

4 is a diagram illustrating an example of detour resource sharing when a double failure occurs in the present invention. 4 shows respective bypasses for two primary LSPs, and illustrates resource sharing of the bypass for when two link failures occur at any one time.

The main LSP A assumes a detour path for each span section through the paths a1 to e1. For example, as shown in the figure, Detour 1 is available for the failure of links b1-c1. Main LSP B also assumes a detour path at each span section through the paths a2 to e2. For example, as shown in the figure, detour 2 or detour 2 ' Available. If link b1-c1 and link b2-c2 fail at the same time, node b2 will try to recover link b2-c2 by selecting either detour 2 or detour 2 '. However, as shown in the figure, T1 (sharing two detours in one path) between links f and g and T2 (sharing one detour in one path) between links i and j are assigned. When considering, b2 selects Detour 2 'rather than Detour 2. In other words, if you try to use Detour 1 and Detour 2 at the same time, one of them is likely to be a disorder. Therefore, if you choose Detour 2 ', a bypass of T2 with a lower share, the likelihood of failure will be reduced. As such, the possibility of failure can be lowered by evenly sharing idle resources so that they are not concentrated on a specific detour.

Equation 1 shows the idle resource sharing described with reference to FIG. 4 as an equation.

,

here, : Set of detours in the network

: Set of detours at link i

: Length of link i

: Length of one bypass in link i belonging to parent SRLG j

: Length of upper SRLG j

: Maximum share in network

: Constant of link i

: Denotes λ used as bypass in link i, respectively.

In Equation 1, the object function is to evenly use a spare capacity for bypass in the event of a link failure in the entire network, thereby minimizing the sharing of one link. That is, F denotes a link having the largest degree of sharing of λ by the detours at link i.

Constraints for this objective function are given by the following equations (2) and (3).

Here, Equation 2 is for preserving the first fail, indicating that the sum of the detours shared on the link i is LA. Equation 3 is for the second fail preservation, and indicates that the recovery link of the link i is j.

As such, we define a constraint so that detour1 does not share with detour2 when two links fail.

Equation 4 below represents a hop limit function, which is one of constraints on the objective function.

Referring to Equation 4, in the case of the hop limit, the sharing degree of one link does not exceed the number of working paths of the upper SRLG.

Equation 5 below represents the degree of sharing constraints for the double failure among the constraints on the objective function.

In Equation 5, if link i and link j fail at the same time in case of shared constraints for double failure, detour for link i and link i for λ assigned to d are used as link j. Otherwise, a variable δ represented by 0 and a linkage of the variable R representing 1, otherwise link 0, j are the same lower SRLG groups. In Equation 5, C = 1 when one detour is assumed in the main LSP, and C = 2 when two detours are assumed.

In other words, assuming that links i and j fail at the same time, the bypasses for failover should not overlap each other, which should be less than the detour on link k.

FIG. 5 is a flowchart illustrating a process of flooding information by inputting and routing shape information of an upper SRLG number and a lower SRLG number for each link according to an operator's network policy.

Referring to FIG. 5, the operator allocates a higher SRLG for the link i that can control the hop limit according to the network plan or the network situation and policy (step 501). In addition, the number of the lower SRLG according to the wiring situation of the actual physical link i is allocated (step 502). Each allocated information adds SRLG information to link information during periodic information flooding of a routing protocol (step 503). Link information is encoded (step 504) for flooding routing information, and the encoded information is transmitted to nodes in the network (step 505).

6 is a flowchart illustrating a detour setting process according to the present invention for the availability of resources according to the present invention.

Referring to FIG. 6, when link information according to the network policy of FIG. 5 is received from nodes in a network (step 601), a required main LSP is set (step 602). Detours according to the main LSP are calculated in consideration of each link of the main LSP (step 603). Equations (1), (4) and (5) are calculated for sharing degree of each detour and optimal resource availability (step 604). Through the calculation result in step 604, the detour is determined while controlling the detour setting (step 605) so that the resource is usefully used (step 606).

As described above, in setting up the detour, the objective function of Equation 1 is used to uniformly use the idle resources of the entire network to overcome obstacles, minimize the sharing of one link, and the limit functions of Equations 4 and 5 The failure recovery rate can be increased by controlling detour1 and detour2 not to be shared when two links fail.

The invention can also be embodied as computer readable code on 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 media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like, which are also implemented in the form of a carrier wave (for example, transmission over the Internet). It also includes. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

The best embodiments have been disclosed in the drawings and specification above. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, according to the detour setting method for dual failure recovery of the present invention, in the case of a double failure in which resource sharing is desperately required, there may be many routes sharing a link. By distributing sharing by removing links with many recovery paths, the impact of failure can be reduced and resources can be used efficiently. In addition, the share of each link is distributed, thereby increasing the recovery rate for any dual failures.

1 is a diagram illustrating an example of a network for explaining an example of a traffic mapping method.

2 is a diagram illustrating an example of recovery schemes that can be used in a general network.

3 is a diagram illustrating an example of a network topology composed of two-level SRLGs in consideration of hop distances.

4 is a diagram illustrating an example of detour resource sharing when a double failure occurs in the present invention.

FIG. 5 is a flowchart illustrating a process of flooding information by inputting and routing shape information of an upper SRLG number and a lower SRLG number for each link according to an operator's network policy.

6 is a flowchart illustrating a detour setting process for dual failure recovery according to the present invention.

Claims (8)

(a) receiving link information according to a predetermined network policy from nodes in the network and setting a required main LSP; (b) calculating detours according to the established main LSP in consideration of a link of the main LSP; And and (c) determining the detour while controlling to minimize sharing of the set detour. The method of claim 1, wherein step (a) (a1) allocating a higher SRLG for link i that can control hop restriction in accordance with network planning or network conditions and policies; (a2) allocating the number of the lower SRLG according to the wiring situation of the actual physical link i; (a3) adding each piece of information to the SRLG information to link information during periodic information flooding of a routing protocol; And (a4) encoding the link information for the flooding of routing information, and transmitting the encoded information to nodes in the network. 2. The method of claim 1, wherein the step (c) minimizes the share of one link by using Equation 1 below. (Equation 1) , here, : Set of detours in the network : Set of detours at link i : Length of link i : Length of one bypass in link i belonging to parent SRLG j : Length of upper SRLG j : Maximum share in network : Constant of link i : Denotes λ used as bypass in link i, respectively. The method of claim 3, And limiting the limit function so as not to share the detours when two links fail. The method of claim 4, wherein The sum of the detours shared on link i equals LA Calculating; And The recovery link of link i is equal to j The method of setting a bypass for dual failover in the optical network system, characterized in that it comprises the step of calculating a. The method of claim 3, Equation The method of setting a bypass for dual failover in the optical network system, characterized in that it controls the sharing degree of one link so as not to exceed the number of working paths of the upper SRLG. The method of claim 3, Equation for limiting the degree of sharing for double failure (Where f is a variable that is set to 1 if link i and j are disabled at the same time, and δ is 1 if link j is a bypass for link i, otherwise 0 is set to 0) Where R represents a variable that represents 1 if the link i, j is the same sub-SRLG group, otherwise 0, C = 1 for assuming one bypass in the main LSP, C = 2 for assuming two bypass Each of which is set to a bypass configuration for dual failure recovery in an optical network system. A recording medium recorded with a program code executable on a computer, the method of setting a detour for recovering a double failure according to any one of claims 1 to 7.