when MS enters the cell in Idle mode it loses signal (No Service). After that it begins LU request (probably IMSI Attach as you said) and lasts 17 sec till LU accept. I don’t think so there is a jammer nearby, because we don’t have interference in idle measurements, UL quality HO is fine, so, we do not suspect in UL interference. Call drop is low. Sdcch drop, sdcch traffic and sdcch duraiton increased as well as IMSI detach rate. I thought maybe there’s other equipment than jammer such as, let’s say, anti-tapping equipment or something else.
during measurements we noticed that between LU Req and LU accept there is 4 seconds in cells with Legacy (SSP, RCP) and more than 16 seconds in cells within NGN (Call Server, Media Gateway). Which parameter or timer in NSS should consider in order to solve this.