Toufic, in last time we also survey same problem on Ultrasites with BTS SW5.0 CD3.0. Please try find TRX with low MHT (2-3 sec.) on this cell and change corresponding BB2 card. As secondary reason – need made extention for LAPD links from 16kbps to 32 (strongly recomended Nokia if AMR use on cell). Gud luck.