As DangerousMinds said that TCH drop rate is lower than 1 % while SDCCH Drop rare is around 1.5/2 %.
If you know another formula of SD drop, pls share with me. We use NSN default sdr_4.
Its multivendor operator, NSN & Huawei. Its strange that NSN BSCs which connect Huawei MSC, SD Drop rate is lower than which connect to NSN MSC. There are some minor A interface SD drop in NSN-NSN system’ but our problem is still mainly in Radio part seem.
SDCCH drop during ciphering;
We have a kind trace sw which shows when connection failure comes that indicated SD Drop.
And when we analyze a call with this SW, most of radio SD drops happen during Ciphering phase. It’s explained as no reply one of side or connecion lost or messages not delivered. Shortly SD drops recorded at time of Ciphering, not before not after. There are still some drops during Imm assign, but no major.