LTE: What is the difference between connected mode mobility and idle mode mobility?

Question

Which messages eNodeB uses to configure connected mode DRX and idle mode DRX for an UE ?

Answer 1

Idle mode mobility relies on UE measurements and UE decisions whether to make a cell reselection or not. The MME keeps track of the UEs on a TA level.

Connected mode mobility relies on UE measurements and eNB decisions whether to make Handover or not. The UE position is known on cell level by the eNB.

Answer 2

In CONNECTED the UE on 99% is sending/reciving data, so its Radio Bearer is established with eNB. The other 1% is for cases when it stopped sending/reciving, but Inactivity timer on taking down the Radio Bearer has not exceeded.

In IDLE mode the UE's Radio Bearer was was released because the Inactivity timer on the radio side has exceeded.

CONNECTED - has Radio Bearer(s) established;
IDLE - no Radio Bearer(s) established.

Although the Bearers on the Core side still exist in both cases.