What is the difference between Call Drop Rate (CDR) and Service Drop Rate (SDR)?
Depends which technology you talking about.
Until 4G, CDR was prime KPI used to show voice call drop rate (CDR).
In 4G, it really depends on your own definition.
Main KPI for 4G is Retainability - which RRC + eRAB drop rate.
4G voice drop rate can be drop of QCI-1 and/or QCi-5.
Service Drop Rate is per Service (QCI).
CDR generally considered for Voice.
Services for specific qci , call drop for all qci