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LTE : How does E-RAB setup procedrue work ?

+5 votes
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LTE : How does E-RAB setup procedrue work ?
posted May 5, 2014 by Neeraj Mishra

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3 Answers

+3 votes

Establishment of an E-RAB involves a number of control messaging among core network nodes.
Here I am assuming, UE requested bearer establishment scenario:

When UE figures out that existing bearer can not suffice new requirement. UE's NAS layer sends "Bearer Resource Allocation Request" message to MME. Once MME receives this NAS message, its sends "Bearer Resource Command" GTP-C message to SGW which in turns forward the same message to PGW/PCEF.
PCEF receives response message from PCRF and if response is positive, then PGW responds with either "Create bearer Request" or "Update bearer Request" GTP-C message.

when MME receives this response message (i.e. Create bearer Request) from SGW, it prepares "Activate dedicated EPS bearer context request" NAS message and send to eNodeB as piggybacked withing the S1-AP E-RAB setup Request message. MME also sends "Create bearer Response" GTP-C message to SGW and SGW in turn sends this message to PGW.

Once S1 E-RAB Setup Request message is received by eNodeB, it configuration its layers accordingly.
It prepares and sends "RRC Connection Reconfiguration" message to UE and wait for RRC Connection Reconfiguration complete message from UE. Then It sends S1 E-RAB setup response message to MME.

Once MME receives both "S1 E-RAB Setup Response from eNodeB" and "Activate dedicated EPS bearer context accept" NAS message from UE, It sends Modify bearer request to SGW and receives Modify bearer response from SGW.

This is how a dedicated bearer gets established.
Hope I have answered your query.

answer May 6, 2014 by Vimal Kumar Mishra
Hi..
In one of my troubleshoot I found that after enodeB sends rrc connection reconfiguration message and also received a rrc reconfiguration complete message for the development of a radio access bearer of qci 1 , just immediately after this again the enodeB sends out rrc connection reconfiguration message having that erab to be released.... is it an expected behaviour according to 3gpp specs or some issue is there....

the sequence is like this -

erab setup request (for qci1) -> rrc connection reconfiguration message(for qci establishment) -> rrc connection reconfiguration complete -..>   then again rrc connection reconfiguration(release of qci1) -> rrc connection reconfiguration complete -> erab release response..
0 votes

An established bearer can be requested to delete either from UE or network. Please check the wireshark logs for S1-AP interface.
You can get to know what is the reason behind sending the "rrc connection reconfiguration" message with the "drb release information" to UE.

RRM or the module which takes care of radio management at the eNodeB, decide to release the radio bearer on which data transmission is not happening. So it would be better to check wireshark log and then only problem can be resolved.

answer Sep 12, 2015 by Vimal Kumar Mishra
0 votes

does anyone have an idea about sudden increase in ERAB modification fail due to radio interface procedure in EnodeB Nokia FL15A ?

answer Jan 26, 2017 by Jalloul Bouchkara
Its a old thread may be ask a fresh question so that it can reach to larger audience.
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