About SDCCH and TCH drop rate

What are the reason for SDCCH and TCH drop rate can anyone say me. so what we have to do to overcome from that situation.

Hi;

There are many reasons for that, drops can happen because of overshooting, bad frequency plan, hardware issue, transmission issue, handover issue, ....
in attached files you can find more details about drop reasons, the pdf file is in french language.

B.R