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Rerouting High-Priority Diamond ASON Services Failed

Publication Date:  2012-07-25 Views:  65 Downloads:  0
Issue Description
In the network, two subnets interwork through two separate optical fibers. For details on the network topology, see the attachment ASON TOPO. The network carries diamond ASON services from certain NEs on one subnet to certain NEs on the other subnet. The diamond services are classified into two levels: high-priority level and low-priority level. When one of the two optical fibers fails, certain high-priority services fail to be rerouted whereas certain low-priority services are rerouted successfully. 
Alarm Information
On the T2000, the following abnormal events are reported:
? Rerouting diamond ASON services failed
? Services interrupted
The details indicate the source and sink timeslots and nodes of the services, the node where the rerouting fails, and the error code.
For details, see the attachment Abnormal Events. 
 
Handling Process
1. View the reported abnormal events to determine which ASON services between the two subnets fail to be rerouted. Then, query the ASON circuit management to check whether the services are interrupted. It is found that the services are interrupted. Query the TE link management to check whether the TE link usage between the two subnets reaches 100%. It is found that the TE link usage reaches 100%. This indicates that the TE link resources between the two subnets are insufficient. Thus, certain ASON services fail to be rerouted. In this case, the two subnets are connected through third-party equipment. The equipment assigns only 16 VC-4 timeslots to the routes between the two subnets. The NE manager proves that the 10 Gbit/s N1SF64 on the third-party equipment reserves 48 VC-4 timeslots. The assigned resources are insufficient to reroute the ASON services. Advise the customer to release the reserved resources. The ASON services are rerouted successfully.
2. Check whether the ASON services run from different source nodes to different sink nodes. It is found that the ASON services run from different source nodes in one subnet to different sink nodes in the other subnet. When one of the two optical fibers fails, ASON service rerouting occurs. The ASON services from the same source node are rerouted in a decreasing sequence of priority levels. This rerouting mechanism is inapplicable to the ASON services from different source nodes. The ASON services from different source nodes are rerouted according to the sequence in which the Notify messages are received. Therefore, when the link resources are insufficient to reroute the ASON services, certain high-priority ASON services fail to be rerouted though certain low-priority ASON services are rerouted successfully. Advise the customer to release the reserved resources. The ASON services of both the priority levels are rerouted successfully.
3. According to the ASON service configuration, re-plan the resources to ensure that sufficient resources are available to reroute the ASON services after an optical fiber between the two subnets fails. 
 
Root Cause
According to the abnormal events reported on the T2000, when one of the two optical fibers fails, ASON service rerouting fails. Certain high-priority services are interrupted whereas certain low-priority services are rerouted successfully. The possible causes are as follows:
1. The other optical fiber is insufficient to reroute the ASON services. Thus, certain ASON services fail to be rerouted.
2. The ASON services run from different source nodes to different sink nodes. ASON service rerouting works in this manner. When an optical link fails, the upstream and downstream nodes send the information on all the LSPs that traverse the link to the first nodes directly through Notify messages. Each Notify message contains the information on multiple LSPs. After receiving the Notify message, the first node sorts the LSPs mentioned in the message according to the priority level. The LSPs are then rerouted one by one in a decreasing sequence of priority levels. After an LSP is rerouted successfully, the old LSP is deleted. At one time, only the LSPs mentioned in one Notify message can be rerouted according to priority. Thus, when the ASON services run from different source nodes in one subnet to different sink nodes in the other subnet, this problem occurs. Certain high-priority services fail to be rerouted whereas certain low-priority services are rerouted successfully. 
 
Suggestions
Configure ASON link resources between subnets to ensure that if an optical fiber between the subnets fails, sufficient resources are available to reroute the ASON services. 

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