hi Ram,
Look for ABIS Rsl congestion. The SACCH itself, on the Air interface, cannot be congested. But the transfer through the Abis link might be a problem, especially with Abis over IP. I forgot the exact vocabulary they use in Ericsson…
Also, ensure your BSC is not overloaded at the signalling plane level.
Either Abis or BSC… that’s my guess.