what all cases in which rrc connection reconfiguration is failed which leads to trigger restablishment

Question

Is DRX will by default present in UE?or will it be assigned by eNB?
If it is assigned by eNB,then in which message does it send to UE,in RRC setup or RRC reconfiguration or SIB2 message?

Answer 1

Case 1:Normal RRC Connection Reconfiguration Failure will lead to RRC Connection Re-establishment.Means In LTE RRC Connection Reconfiguration will be used To Setup/Release Measurements,To Setup/Modify/Release of Bearers.
In this case the RRC Connection Reconfiguration is sent to the UE by Including any of the Configuration mentioned above, But my UE is unable to comply with the configuration which is sent by eNB then UE will send RRC Connection Reconfiguration Failure then Immediately UE will do RRC Connection Re-establishment Procedure.

Case 2:RRC Connection Reconfiguration Failure while making HANDOVER Leads to RRC Connection Re-establishment.Means while Making Handover after Reserving Resources at T-eNB, SeNB will send RRC Connection Reconfiguration with Mobility Control Info(Target Cell PCI,Dedicated RACH Preamble Info,T-eNB security Info) to the UE.Then UE will access the Target Cell by using the information in RRC Connection Reconfiguration message,but UE is unable to access the Target cell because of RACH Failure then UE will send the RRC Connection Reconfiguration Failure Message then Immediately UE will do the RRC Connection Re-establishment.

Answer 2

Case 1:Normal RRC Connection Re-configuration Failure leads to RRC Connection Re-estabilshment. Means in LTE RRC Connection reconfiguration message is coming to Setup/Release Measurements,To Establish/Modify/Release Bearers.So the Configuration which is sent in RRC Connection Re-configuration message is unable to configure in the UE then UE will send RRC Connection Reconfiguration Failure then UE will Trigger RRC Connection Re-establishment.

Case 2:RRC Connection Reconfiguration message which is sent while making HANDOVER.
In Handover after reserving Resources in T-eNB. S-eNB will send RRC Connection Reconfiguration message with Mobility Control Info(Target Cell PCI,Dedicated RACH Preamble Info,T-eNB security Info) by using the information which is given in Reconfiguration message UE will access the T-eNB,in this process UE is unable to access the Target Cell because of RACH Failure then UE will send RRC Connection Reconfiguration Failure message then UE will do RRC Connection Re-establishment.