The roots of problem were found in NSS.
I am sorry for not mentioning during the problem description phase that the MSC that controls the E1 cell is in fact an MSC Server, 3GPP R4 core network.
May be I am not the right person to describe problem as I said it is in NSS, yet I will try my level best.
As we know that problem comes only when the MS moves from N1 to E1 or from a cell of Nokia MSC (here it is MSC only and not a MSC server) to a cell of Ericsson MSC Server.
An Inter MSC handover should occur and it do.
But this is the trigger of trouble.
The call at other end gets released, doesn’t matter with whom you are talking be it a landline or a GSM number.
And at your end you find your phone is hanged. It shows itself to be in dedicated mode.
Where is the problem? We are finding it difficult to get it done, as we have to deal with two different vendors for a single issue.
Then one day I got a call from NSS guy that vendor Nokia has solved the issue and I was asked to verify it.
After verifying when I asked the same NSS person to tell me what was the cause.
The reply he gave me was that…
In Nokia MSC the handovers are defined by defining two parameters, GT & SCP.
In our case the handover is defined with Ericsson MSC server by using both GT & SCP. That was causing problem. When they removed the SCP part and kept only GT part the problem got solved.
I am not sure whether the person was saying the word SCP or SCCP, whatever it may be but I believe it was a case of SS7 somewhere.
May be SS7 over TDM when get interfaced with SS7 over IP , SIGTRAN has got its own issues.