Backup path convergence in the APS environment

• US 20070263532A1
• Filed: 05/10/2006
• Published: 11/15/2007
• Est. Priority Date: 05/10/2006
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Roy, Abhay, Mirtorabi, Sina, Shaikh, Mukhtiar, Hasan, Yousuf
• Granted Patent: US 8,040,795 B2
• Time in Patent Office: Days
• US Class Current: 370/228
• CPC Class Codes: H04J 3/14 Monitoring arrangements for SDH/SONET rings H04J3/085
• CPC Class Codes: H04L 45/00 Routing or path finding of packets in data switching networks routing or path finding in wireless networks H04W40/00
• CPC Class Codes: H04L 45/22 Alternate routing
• CPC Class Codes: H04L 45/28 using route fault recovery
• CPC Class Codes: H04L 45/54 Organization of routing tables

Abstract

A SONET network terminated by routers includes working paths and backup paths. The routers pre-establishes in their link state data bases the links in both for both the working and backup paths. However, the links involved in the backup paths are given higher costs, then the links working paths, that the routers select only the links in the working path. If there is a failure in a link in a working path, an APS arrangement provides rapid switchover of the optical links so as to substitute one or more links in the corresponding backup path. This is accomplished by changing the relative costs of the working and backup links involved, so that the routers select the backup links for their routing tables.

Claims

1. A method of shifting to a backup path in a SONET network including working links and backup links, each of said links being terminated at one end by a router, each router having a link state data base containing routes from a router and a routing table containing routes selected from the data base, the method comprising:

A) in each router

1. initially populating its link state data base with links that include both the working links extending from the router and the backup links extending therefrom,

2. attaching a higher cost to the backup links so that the router selects the working links and none of the backup links for its routing tables;

B) in the SONET network, when a failure of a working link is detected,

1. switching to a backup link to bypass the working link,

2. notifying the routers terminating the working and backup links by means of one or more overhead bytes in SONET frames that they should change the costs of the working and backup links so that the routers change their routing tables to specify the backup links instead of the working links.

2. The method of claim 1 in which the routers establish OSPF adjacencies by means of SONET DCC overhead bytes.

3. The method of claim 1 in which the routers

A. use IGP routines to communicate with adjacent routers,

B. populate their databases with both primary paths to the adjacent routers and, in addition, backup paths to said adjacent routers, said backup paths not being the shortest paths, and

C. initially assigning to the backup paths costs that are higher than the costs of the corresponding primary paths.

4. The method of claim 2 in which the routers

A. use IGP routines to communicate with adjacent routers,

B. populate their databases with both primary paths to the adjacent routers and, in addition, backup paths to said adjacent routers, said backup paths not being the shortest paths, and

C. initially assigning to the backup paths costs that are higher than the costs of the corresponding primary paths.

5. A SONET network capable of fast switch-over from a failed link to a backup link, said network comprising:

A. a first router connected to a working optical link connected in turn to an ADM;

B. a second router connected to a backup optical link connected in turn to the ADM;

C) each of said routers

1. having a link state data base of possible connections to adjacent routers, the possible connections including working links and backup links to the same routers and a routing table comprised of a list of connections selected from the database,

2. configured for shortest path first selection of connections, and

3. including in the database the costs of the respective paths;

D) means for detecting a failed optical link, switching from the failed link to a backup link and using the overhead bytes in SONET frames to instruct the routers connected to the failed and backup links to change the costs associated with the links so that the costs associated with the backup links are lower than those associated with the failed links, whereby the routers rebuild their databases with the paths including the backup links.

6. The network of claim 5 in which said routers establish adjacencies with neighboring routers to exchange link-state data base entries with each other, using SONET overhead bytes to carry the messages between said routers.

7. A SONET network capable of fast switch over from a failed path to a backup path, said network comprising:

A. a first router connected to a working optical link in said first path, said working link being connected in turn to an ADM;

B. a second router connected to a backup optical path including a backup optical link connected in turn to the ADM;

C. an optical link interconnecting said first and second routers;

D. means in said routers for establishing IGP adjacencies by means of SONET overhead bytes, said adjacencies including said first path and said second path;

E. each of said routers being configured for shortest path first selection of connections;

F. means for detecting a failed optical link, switching from the failed path to a backup path and using the overhead bytes in SONET frames to insert the routers connected to the field of backup paths to change the costs associated with the paths so that the costs associated with the backup paths are lower than those associated with the failed paths, whereby the routers rebuild their routing tables with the backup paths instead of the failed paths.

8. A router for shifting to a backup path in a synchronous optical network (SONET), the router comprising:

a first optical output line configured to transmit to a working link;

a second optical output line configured to transmit to a backup link for the working link;

a memory configured to store a routing table and a link state database, the link state database comprising a first cost associated with the working link and a second cost associated with the backup link, wherein the first cost is initially lower than the second cost; and

a processor configured to;

i) select the working link for the routing table in response to the lower first cost, ii) change one or more of the costs, in response to a failure of the working link, so that the second cost is lower than the first cost, and iii) select the backup link for the routing table in response to the lower second cost.

9. The router of claim 8 wherein the second cost is initially a maximum cost.

10. The router of claim 8 wherein the memory is further configured to store the first and second costs in response to a predetermined overhead byte in a SONET frame received at the router.

11. The router of claim 8 wherein the processor is further configured to change the one or more of the costs in response to a predetermined overhead byte in a SONET frame received at the router.

12. The router of claim 8 wherein the processor is further configured to detect the failure of the working link.

13. The router of claim 8 wherein the SONET network is configured to implement automatic protection switching (APS).

14. The router of claim 8 wherein the processor is further configured to establish a plurality of adjacencies with a plurality of corresponding routers over a plurality of corresponding links, wherein the plurality of corresponding links comprises the working and backup links.

15. The router of claim 14 wherein the plurality of adjacencies are open shortest path first (OSPF) adjacencies.

16. The router of claim 14 wherein a single link of the plurality of corresponding links comprises a first and a second adjacency, the first adjacency comprising the working link and the second adjacency comprising the backup link, and wherein the single link is a point-to-multipoint link.

17. The router of claim 14 wherein the processor is further configured to preestablish an adjacency over the backup link prior to failure of the working link.