Method for restoring a virtual path in an optical network using 1protection

[0001] This application is a continuation-in-part of patent application Ser. No. (______ Attorney Docket No. M-9829 US ______), filed May 16, 2001 and entitled A Resource Reservation Scheme For Path Restoration In An Optical Network, having A. N. Saleh, H. M. Zadikian, Z. Baghdasarian, and V. Parsi as inventors. This application is assigned to Cisco Technology, Inc the assignee of the present invention, and is hereby incorporated by reference, in its entirety and for all purposes.

[0002] This application is also related to following commonly-assigned applications:

[0003] 1. Patent application Ser. No. 09/232,397, entitled A Network Addressing Scheme For Reducing Protocol Overhead In An Optical Network, filed Jun. 4, 1999.

[0004] 2. Patent application Ser. No. 09/232,395, entitled A Configurable Network Router, filed Jan. 15, 1999.

[0005] 3. Patent application Ser. No. (______Attorney Docket No. M-07165-5P US ______), entitled A Virtual Path Restoration Scheme Using Fast Dynamic Mesh Restoration in an Optical Network, filed on Dec. 29, 2000.

[0006] 4. Patent application Ser. No. (______Attorney Docket No. M-9830 US ______), entitled A Method of Restoring a Virtual Path in an Optical Network Using Dynamic Unicast, filed on ______.

[0007] 5. Ppatent application Ser. No. (______Attorney Docket No. M-9832 US ______), entitled A Method of Restoring a Virtual Path in an Optical Network Using 1:N Protection, filed on ______.

[0008] Above mentioned applications are assigned to Cisco Technology, Inc., the assignee of the present invention, and are hereby incorporated by reference, in their entirety and for all purposes.

[0009] 1. Field of the Invention

[0010] This invention relates to the field of information networks, and more particularly relates to a protocol for configuring routes over a network.

[0011] 2. Description of the Related Art

[0012] Today's networks carry vast amounts of information. High bandwidth applications supported by these networks include streaming video, streaming audio, and large aggregations of voice traffic. In the future, these bandwidth demands are certain to increase. To meet such demands, an increasingly popular alternative is the use of lightwave communications carried over fiber-optic cables. The use of lightwave communications provides several benefits, including high bandwidth, ease of installation, and capacity for future growth.

[0013] Optical infrastructures are capable of transmission speeds in the gigabit range, which helps address the ever-increasing need for bandwidth mentioned above. Such infrastructures employ various topologies, including ring and mesh topologies. In order to provide fault protection, ring topologies normally reserve a large portion (e.g 50% or more) of the network's available bandwidth for use in restoring failed circuits. However, ring topologies are capable of quickly restoring failed circuits. This capability is important in providing reliable service to customers, and is particularly important in telephony applications, where a failure can result in alarms, dropped calls, and, ultimately, customer dissatisfaction and lost revenue. In a similar vein, because of bandwidth demands, protocol overhead related to provisioning, restoration, and other functions should be kept to a minimum in order to make the maximum amount of bandwidth available for use by customers.

[0014] An alternative to the ring topology, the mesh topology reduces the amount of bandwidth needed for protection. The mesh topology is a point-to-point topology, with each node in the network connected to one or more other nodes. Because a circuit may be routed through various combinations of the network's nodes and over the various links which connect them, excess capacity through a given node or over a given link can serve to protect several circuits. However, the restoration of a circuit following a failure in a mesh topology can consume a relatively large amount of time.

[0015] In one embodiment, the present invention restores a failed virtual path, provisioned on an active physical path, in a mesh topology optical network by providing an alternative link-and-node disjoint standby physical path protection. Each path is provisioned between the source and the destination node (the end nodes) using a different set of intermediary nodes. In case of a failure in the active physical path, the end nodes switch the virtual path to alternative standby physical path.

[0016] The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the present invention, as defined solely by the claims, will become apparent in the non-limiting detailed description set forth below.

[0017] The present invention may be better understood, and numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawing.

[0018] FIG. 1 illustrates an example of provisioning a virtual path using 11 restoration method.

[0019] FIG. 2 illustrates an example of the path integrity message packet.

[0020] FIG. 3 illustrates an example of the path update message packet.

[0021] FIG. 4 is a flowchart illustrating the actions performed by a node during 11 restoration.

[0022] The following is intended to provide a detailed description of an example of the invention and should not be taken to be limiting of the invention itself. Rather, any number of variations may fall within the scope of the invention which is defined in the claims following the description.

[0023] Provisioning of Network Nodes

[0024] A network can include multiple connected nodes. The nodes in a network can be configured in various topologies. Once a network topology has been defined, the user can configure one or more end-to-end connections that can span multiple nodes, an operation is referred to herein as provisioning. For end-to-end connection between two nodes, a physical path must be selected and configured. Each set of physical connections that are provisioned creates an end-to-end connection between the two end nodes that supports a virtual point-to-point link (referred to herein as a virtual path or VP). The resulting VP has an associated capacity and an operational state, among other attributes.

[0025] In a network, VPs may be provisioned statically or dynamically. For example, a user can identify the nodes which will comprise the virtual path and manually configure each node to support the given virtual path. The selection of nodes may be based on any number of criteria, such as Quality of Service (QoS), latency, cost, distance traveled in the network and the like. Alternatively, the VP may be provisioned dynamically using any one of a number of methods. The provisioning information may then be forwarded to all the nodes in the network to store information in each node's network topology database. Each node periodically updates this information to efficiently maintain resources and in case of path failure, effectively allocate appropriate resources needed for specific virtual path for path restoration.

[0026] The end nodes of a VP can be configured to have a master/slave relationship. The term source and destination are also used herein in referring to two such end-nodes. In such a relationship in one embodiment, the node with a numerically lower node ID typically assumes the role of the master (or source) node, while the other assumes the role of the slave (or destination) node, although the opposite arrangement is also acceptable. An intermediate node is referred to herein as tandem node. Generally, the source node assumes all provisioning responsibilities and the destination node simply waits for a message from the source node informing the destination node of the VP's new physical path. This information includes node identifications, if any, of tandem nodes of that path. In a zoned mesh network topology, if a virtual path spans over multiple zones, the border node or proxy node of each zone acts as source node for their particular zone. As will be apparent to one of skill in the art, the opposite convention or another paradigm could easily be employed.

[0027] During the provisioning, each VP is assigned a performance and restoration priority level. This priority, also referred to herein as Class of Service (CoS), determines VP's relative priority for performance within the network and restoration in the event of a failure within the network. The method of assigning CoS is described in commonly-assigned U.S. patent application Ser. No. (______ Attorney Docket No. M-9829 US ______), filed on , entitled A Resource Reservation Scheme for Path Restoration in an Optical Network, and is hereby incorporated by reference, in its entirety and for all purposes. In case of a VP failure at any node in the network (e.g., due to a failure of the physical path, high bit error rate or the like) the node determines how to restore the VP based on the CoS assigned to the VP. The assigned CoS defines the restoration method used by the node to restore the failed VP.

[0028] Provisioning of Virtual Path using 11 Protection

[0029] The 11 restoration method is typically assigned to mission critical data paths with higher CoS. Typically, the source node of a VP initiates the provisioning using Add Path Request packet. The an example of a method of initiating an Add Path request and the allocation of physical resources for a VP is described in commonly-assigned U.S. patent application Ser. No. (______ Attorney Docket No. M-9830 ______), filed on ______, entitled A Method For Restoring A Virtual Path In An Optical Network Using Dynamic Unicast, as previously incorporated herein.

[0030] In a 11 restoration method, two distinct physical paths are provisioned and assigned to a VP. Each provisioned physical path is preferably completely node and link disjoint, although the 11 restoration method described herein can be limited to only a section of a given path. The VP is provisioned by using two separate Add Path requests for two distinct physical paths. The provisioning of the VP is not considered successful unless two distinct physical paths are provisioned and assigned to the VP. One of the two assigned physical paths is designated as the primary path and the other physical path is designated as the secondary path. During the provisioning, each tandem node allocates specific ports at input and output links for each path. For 11 restoration scheme, these ports are not shared by any other VP. In case of a path failure, tandem nodes do not release these ports.

[0031] FIG. 1 illustrates an example of a VP provisioned using 11 restoration method. The network 100 includes seven nodes, nodes 101-107 and eleven optical links, links 111-121. Each node is connected to an adjacent node by one or more optical links. A virtual path VP 0 is provisioned in network 100. VP 0 originates at node 104 (the source node) and terminates at node 107 (the destination node). Two distinct physical paths are provisioned for VP 0. The primary path of VP 0 is provisioned over node 104, node 106 and node 107 using link 120 and link 121. The secondary path of VP 0 is provisioned over node 104, node 103 and node 107 using link 117 and link 119.

[0032] After the provisioning of VP 0, the reserved ports and the bandwidth of the secondary path at link 117 and link 119 are not used by any other VP in the network 100. The secondary path including link 117 and link 119 is dedicated to VP 0 for restoration purpose. The primary path and the secondary path stay active during the data transmission. However, one path is used as the transmission path and the other path is used as standby path in case of a failure.

[0033] Failure Detection, Propagation, and Restoration

[0034] Failure Detection and Propagation

[0035] In networks, failures are typically detected using the mechanisms provided by the underlying physical network. The failure detection mechanism in a mesh optical network is described in commonly-assigned U.S. patent application Ser. No. 09/232,397, filed Jan. 15, 1999 and entitled A Method For Routing Information Over A Network, which is hereby incorporated by reference, in its entirety and for all purposes.

[0036] 11 Restoration

[0037] The restoration using a 11 restoration scheme can be initiated either by the source node or the destination node of the VP. When the VP's active physical path fails at a tandem node, the tandem node initiates a path restoration request for the end nodes (the source node and the destination node) of the failed VP using a Restore_I request. The method of generating Restore_I requests and associated responses is described in commonly-assigned U.S. patent application Ser. No. (______ Attorney Docket No. M-7165-5P US ______), entitled A Virtual Path Restoration Scheme Using Fast Dynamic Mesh Restoration in an Optical Network, as previously incorporated herein. The tandem node sends Restore_I request upstream and down stream for the end nodes (the source node and the destination node). The Restore_I request is transmitted in both directions because due to the path failure, one of the source node and the destination node will not receive the failure message. When a tandem node receives a Restore_I request, the tandem node forwards the Restore_I request on appropriate link to the next node. Because the physical paths are reserved for the VP, the tandem nodes do not release the resources of the VP.

[0038] When an end node (either the source node or the destination node) receives a path failure message or a Restore_I request, the end node switches the VP to the standby physical path. Each end node can switch the physical path of the VP independent of the other. The end node switches the physical path of the VP without further command packet exchange. After switching the VP to the standby physical path, the end nodes exchange a path integrity message to ensure the integrity of the VP. The end nodes also exchange a path update message to update network topology database to reflect the physical path change of the VP.

[0039] FIG. 2 illustrates an example of a path integrity message packet 200. The end node, which switches the physical path of the VP, sends the path integrity message. A positive acknowledgment to the path integrity message indicates a valid physical path for the VP. Path integrity message packet 200 includes a VP-ID 210, the 32 bit ID of the VP. It will be apparent to one of the skill in the art that, while specific lengths are described, the fields discussed here may be of any appropriate length. A path integrity ID 220 stores a 16-bit path integrity check instance. A physical instance field 230 stores a 16-bit physical instance identifier for the VP. When a new path is selected for the VP, the source node increments physical instance identifier (e.g., by 1). Due to the distributed nature of path selection and multiple failures, several physical instances of the same VP may temporarily exist in the network at any given time. However, only one instance ultimately survives. A port ID 240, the 16-bit physical port ID is used to identify the specific port that is used to transmit the path integrity message. The path type field 250 is used to identify the type of physical path (primary or secondary) that is being checked for the integrity.

[0040] FIG. 3 illustrates an example of a path update message packet 300. Path update message is used to update the status of the VP in the network topology databases at each node. Path update message packet 300 includes a VP-ID 310, the VP's 32 bit ID. A current active path type field 320 is used to indicate the type of physical path (primary or secondary) that was active before the switching of the physical path. Path type field 330 indicates the type of physical path (primary or secondary) that is active after the switching of the physical path.

[0041] FIG. 4 is a flowchart illustrating the actions performed by a node when the node receives a notification of a VP failure. The node initially receives a path failure notification (step 410). The failure notification can be a local failure detection or a Restore_I request forwarded by another node. Upon receiving the failure notification, the node checks if the node is an end node of the VP (i.e., the source or the destination node) (step 415). If the node is not the end node of the VP (i.e., the node is a tandem node), the node checks if the path failure is a local failure (step 420). If the failure is not a local failure (i.e., the node receives a Restoer_I request from a remote node), the node forwards the failure notification upstream and downstream (step 430). The failure notifications are forwarded in both directions so the end node (either the source node or the destination node) can switch VP to the secondary path. If the failure is a local failure, the node generates a Restore_I request for the end nodes (step 425). The node forwards the request upstream and downstream for the end nodes (step 430). The resources of the VP at the tandem nodes are not released.

[0042] If the failure notification is received by the end node (the source node or the destination node) of the VP, the end node generates a local alarm (step 435). The failures can be major (e.g., failure of a link and the like) or minor (e.g., high bit rate error and the like). Generally, not every failure requires physical path switching. The node determines if the failure requires switching the physical path of the VP (step 440). If the failure does not require switching the physical path, the node needs not take any further action. If the failure requires switching the physical path, the node determines if the alternate physical path is available (step 445). If the alternate physical path is not available (i.e., due to a previous failure that has not been fixed), the node generates a major network alarm (step 450). The node changes the state of the VP to down (step 455).

[0043] If the alternate physical path is available, the node proceeds to switch the physical path (step 460). After switching the VP to the alternate physical path, the node sends a path integrity message to check the validity of the VP (step 465). The node also sends a port update message on the VP to update the active ports information in the network (step 470). After the switching of the physical path, the VP continues to use the alternate physical path until a failure occurs in the alternate physical path. In case of a failure on the alternate physical path, similar process is followed to switch the VP to the previous physical path provided that the previous physical path is restored.

[0044] While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this invention and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention. Furthermore, it is to be understood that the invention is solely defined by the appended claims.