here is what we have found out by now.
The appropriate (Nokia) counter (1075 “SDCCH Abis Failure Call” shows high values) is not only incremented if the timer T9103 expires. We made a trace and it shows that the “Channel Activation Ack” is sent by the BTS in question. So the problem occurs in the next step: BSC sends “Immediate Assignment” but the MS can not hear the BTS anymore and it does not answer with “SABM”. So the BTS will not send “Establish Indication” to the BSC. Therefore the SDCCH connection is released and the call setup fails.
We think that there might be a problem in the link balance after implementing EDGE in these cells.
Do you have any other ideas related to this topic ?