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Knowledge Base

Switching-Back Failure Reason of Silver-Level Service to the Original Routing and Its Solution

Publication Date:  2012-07-25  |   Views:  143  |   Downloads:  0  |   Author:  x48115  |   Document ID:  EKB0000357999


Issue Description

Two services fail to return to their original paths and the system prompts “inconsistent timeslots”.
ASON Trail: Source TNS00972005-28-N1SLQ4-4-VC4:2, Sink TNS09159007-28-N1SLQ4-3-VC4:3, Index 6
ASON Trail: Source TNS00972005-31-N1SLQ4-4-VC4:2, Sink TNS09159007-30-N1SLQ4-4-VC4:3, Index 25 

Alarm Information


Handling Process

This problem and the subsequent enable of similar classic server trail in the ASON domain can be solved in the following method:
Set timeslot 10 of slot 11 in NE 3004 and timeslot 10 in slot 8 of NE 9007 to reserved timeslots in the Topology shown in Figure 4 and Figure 5. That is, the timeslot should be reserved for static services and cannot be used in the IN service calculation. But the reserved timeslot has no effect on the establishment of static higher-order and lower-order cross-connect.
The operation is as follows: set the Reservation state of the timeslot to Yes and click Apply.
It should be noted, though the problem can be solved by reserving the timeslot of the idle end, users are suggested to reserve the timeslots of both ends of the link. Otherwise, when the service is deleted, the reservation states of the timeslots in the two ends will be inconsistent again.
In addition, this problem can also be solved by upgrading the server trail to the IN service circuit. This is because that after the IN service circuit is established, the egress timeslot of the first NE and the ingress timeslot of the last node will be labeled as occupied by the IN service, no matter whether the lower-order service is carried on the circuit. 

Root Cause

After analysis, the engineers find that the initial trails of the two services are the same, except that the timeslots are different, as shown in Figure 1. It should be noted that only the golden-level service can return to the original timeslot. The services of other types can only return to their original optical ports and cannot return to their timeslots.
The engineers compare the timeslot states of the service paths and find that timeslot 10 of slot 8 in NE 9007 is occupied statically, and timeslot 10 of slot 8 in NE 3004 of the peer end is in the idle state. Figure 2 shows the states of certain timeslots.
The engineers also check the states of the cross-connection in the T2000. It is found that timeslot 10 of slot 8 in NE 9007 includes the static cross-connection with the following service trails, as shown in Figure 3. It can be seen that the lower-order service is not enabled in the classic server trail. As a result, the source node timeslot is idle and the timeslot states of the two link ends become inconsistent.
When a service originates the return, the ASON trail calculates the path and allocates timeslots. From the timeslot conditions in Figure 1, it can be seen that timeslot 10 is the first idle timeslot. Hence, this timeslot is involved in the path calculation in service return. As a result, the timeslots are inconsistent and the service return fails. 


 Refer to the solution.