Hello SM.
In the Ericsson networks, the T3101 can indeed improve the SDCCH Assignment Failure. If you monitor the counter CESTIMMASS from the dbo_CELL_MAIN or dbo_CELL_MAIN_PEAK tables from the GRAN_seg1 server you will see that at least a 5% of the CCALLS correspond to the expiration of the T3101. The default value for Ericsson is 1,5 seconds. We found an improvement by moving it to 3 seconds.
Of course, ideally would be to have a Protocol Analyzer and measure the average time for the timer and see if the actual value is correct!
I think in Alcatel-Lucent is easy to set a new value. However in Ericsson, even a small restart is needed on a BSC level.
Regards,
SA