Since last year I have seen in my network random cells that for some hours have very high SDCCH access failures due to T3101 expiring without having established the connection. It happens regardless the BSS provider (we have Ericsson, Siemens and Nokia)
All these SDCCH attemps where caused by the location update procedure and it seems there is some kind of buggy phone out there that triggers these failures. The phone starts to send massive connection requests for location update without seizing the channel granted by the network.
Has anybody been able to detect which phone causes this problem? Since the failure happens before the SDCCH has been established there is no IMEI, IMSI or MSISDN info yet to identify it.