When does eNodeB send measurement gap configuration for the first time to a UE in live network?

Question

When does eNodeB comes to know that UE wants to do an IRAT handover in the live network?
Or, eNodeB always sends the measurement gap config info in the RRC connection reconfiguration message which has the measconfig IE?

Without knowing the measurement gap configuration, how does the UE perform inter frequency measurements?
Is it something like, the NodeB sends the meas gap config info to UE after succesful attach?Because UE needs to measure other frequency cells both during idle mode and connected mode.
Please clarify.

Answer 1

Hope I have understood your question correctly

Part 1: How to collect Measurements?
• Each Measurement Type will define on one or several Measurement Object(s) (Carrier Frequency).
• Reporting Configurations are defined on each Measurement Object (i.e. criteria like Event triggered, periodic or event triggered periodic reporting).
• Measurement quantities and Reporting Configurations are considered separately for each Measurement Type.
• Measurement Object and Measurement Configurations are related with the help of Measurement id.
• eNB configures each Measurement Type using a Measurement Identity and instructs the UE when to report the measurements results.
• Measurement commands are used by eNB to order the UE to start, modify or stop measurements specified by RRC as in UTRAN Measurement_Control.What UE measures?
• After instructions from eNB; UE measures two parameters on reference signal: cell RSSI & CPICH RSCP or CPICH En/lo.
• The handover measurement report triggering are based on cell RSSI & CPICH RSCP in GSM or CPICH Ec/Io for UMTS for inter-RAT.
• Serving Cell’s RSRP is degrading threshold 1, while neighbor cell RSSI or CPICH RSCP or CPICH En/lo increasing threshold 2 will trigger the event.

Call Flow of Inter Rat Handover

Now coming to specifics though measConfig is a optional IE but it is important to tell UE when/how measurement config to be done if operator is supporting it. Please comment if you are looking something different.

Answer 2

As per my understanding When UE will send the measurement report then on the basic of that eNB configures measurement GAP on UE that it need to measure inter RAT freq. But my question of confusion is always is if UE will not send measurent report eNB will not configure measurement GAP but until UE doesn't have measurement GAP how it can measure and send reports??