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The LCAS_TLCT and LCAS_TLCR Alarms Are Reported and the Services Are Interrupted Due to the Loopback of Certain Channels Bound in a VCTRUNK on the EGS4

Publication Date:  2012-07-25 Views:  35 Downloads:  0
Issue Description
Two OptiX OSN 3500 NEs, NE A and NE B, are interconnected through three STM-1 optical links. Either NE uses one VCTRUNK on the EGS4 to carry the Ethernet services between them. For the sake of security, the VC-12 channels bound in the VCTRUNK are distributed on the three STM-1 optical links and LCAS is enabled.
When the first STM-1 optical link becomes abnormal and reports a lot of error codes, the two NEs report the LCAS_PLCT and LCAS_PLCR alarms frequently. To identify the problem, conduct an inloop test on the first STM-1 optical link on NE A. In this case, however, the EGS4 reports the LCAS_TLCT and LCAS_TLCR alarms and the Ethernet services are interrupted. 
 
Alarm Information
LCAS_PLCT, LCAS_PLCR, LCAS_TLCT, and LCAS_TLCR 
Handling Process
Disable the loopback. The services are restored. 
Root Cause
The LCAS protocol functions on VCTRUNKs. There must be a one-to-one instead of one-to-many VCTRUNK mapping between interconnected NEs. During the inloop test on certain channels bound in the VCTRUNK on NE A, however, the VCTRUNK on NE A is mapped to the following two VCTRUNKs:
? VCTRUNK made up of the looped channels
? VCTRUNK made up of the unlooped channels
In this case, the LCAS protocol chooses one of the two VCTRUNKs at random and considers the other VCTRUNK unavailable.
? If the VCTRUNK made up of the looped channels is chosen, the LCAS_PLCT and LCAS_PLCR alarms are reported.
? If the VCTRUNK made up of the unlooped channels is chosen, due to the transient interruption during the loopback, the LCAS_TLCT and LCAS_TLCR alarms are reported and the WTR state is entered. The services, however, are actually interrupted. 
 
Suggestions
This problem can occur to all Ethernet boards. Therefore, when LCAS is enabled, do not conduct a loopback test on certain channels bound in a VCTRUNK. 

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