1. increase number of sdcch static timeslots
does the congestion disappear ?
2. is the sdcch traffic very high (much higher than normal) ?
3. what is the cause of sdcch traffic (OC, TC, LU, SMS, Emerg call ?)
4. check the SDCCH traffic on each timeslot, or on each TRX. Do you notice some TRX with poor SDCCH usage (very short or very long SDCCH duration, low or high number of sdcch allocations, …)