Problem in CCSU/SIGU path reach ability in GCS due to which M3UA associations are down

ISSUE Description:

Signalling Unit (SIGU) and GCS are connected together and sometimes issues arrived between these two network elements which causes M3UA associations down between NE's.

Connectivity between GCS and SIGU can be interpreted as:

|GCS CCSU| -- |L2 SWITCH| --- |ROUTER-A| -- | ROUTER-B| -- |GGN SIGU-2|

Detailed Description: 

In this case NSS/switching team has found M3UA associations to be down which actually causes issues in signalling information to be traveled over MTP layer3.

Since layer 3 information is not travel-led, router issues is suspecting.

Troubleshooting Steps:

1. The router port connected to CCSU made shut and no-shut, suspecting port to be hanged.
2. When no information has found, another router port has been configured for the same.
3. Configuration changes with respect to the router has also changed.

But after above doing the above steps no issues has been detected at router end.

During more troubleshooting with core team, switching unit of NSS i.e ESB which connect the router has found faulty. The respective ESB card has found faulty and replaced.

After replacement of the card, IP connectivity restored and M3UA associations has also came up.