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LTE: What's relation between RRC-Connected and ECM-Connected ?

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LTE: What's relation between RRC-Connected and ECM-Connected ?
posted Jun 7, 2014 by Rupam

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1 Answer

+2 votes

RRC layer in LTE maintains two states i.e. RRC-IDLE and RRC-CONNECTED. Similarly MME node at core networks maintains two states "ECM-IDLE" and "ECM-CONNECTED".

When an UE establishes Radio connection with an eNodeB it's and eNodeB RRC layers move from RRC-IDLE to RRC-CONNECTED. This state transition doesn't mean that data flow can be done. RRC connection just provides a way or path to signalling messages between UE and eNodeB.
But when UE establishes at least one data bearer with network then only data flow can start.

In short, when UE is in ECM-CONNECTED state then data and signalling can flow but not true for RRC-CONNECTED state. RRC-CONNECTED is a sub set of ECM-CONNECTED.

answer Jun 7, 2014 by Alok
Just want to add if RRC connection is established RRC state transition will be from RRC_IDLE to RRC_CONNECTED. And once UE attaches to network ECM state transition will be from ECM_IDLE to ECM_CONNECTED.
And if there is no data over S1 path state can be change from ECM_CONNECTED to ECM_IDLE. This will also force RRC_CONNECTED state to move to RRC_IDLE
Please refer to EMM State Transition diagram in the link below.
http://www.netmanias.com/en/?m=view&id=techdocs&no=5909
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