MSTP

Much Virtual concatenation delay lead to EoS service interrupt

Firstly, Eth service is running on MSTP link with virtual concatenation. And it’s configured with LCAS.

Customer complains the link interrupts occasionally for a short time.Alarm FCS_ERR,ALM_GFP_dLFD report at the same time. The issue happens 8 times in one month.
Topology as attached. Version of equipment and boards as below:

OSN3500: V100R008C01B01C

EGS4: 1.17

OSN8800: V100R006C01

EGSH: 3.05

Base on the alarm FCS_ERR,ALM_GFP_dLFD, we first check the configuration at both ends if the capsulation protocal is the same;
Then check the transmission link performance, at the faulty point there is no corresponding bit error or optical power alarm;
After replace the Ethernet boards the issue still exist;
Collect the information for R&D analysis, we found the time delay of virtual concatenation on different paths is different, and it’s beyond the limitatioin of delay range.
So we try to configure the service on the same physical path. Finally the issue resolved.
If the time delay of virtual concatenation is too much, some package can’t be framed when transmitted.But the FCS function can correct the bit error, so there is no obvious alarm. After accumulation, the bit error will be out of the limitaion and report FCS_ERRSolution: Put all service into one SDH path to avoid the the delay of Virtual concatenation.

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