This is done by RRC
Idle Mode: Reports used to construct to support cell-reselection process (UE Specific)
connected mode: Here UE also sends report to N/w .
Few times N/w may ask UE to send some reports.
Reports are of 7 types in general.
1) Intra frequency Reports
2) Inter Frequency Reports
3) InterRAT frequency Reports
4) UE Positioning requirements Reports
5) Traffic Volume measurements Reports
6) Quality measurements Reports
7) UE-Internal measurements Reports