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LTE : What is NAS recovery procedure ?

+3 votes

I am not able to find NAS Recovery message as such in 24.301 spec. Some weblink has talked about NAS recovery but I could not any reference in specification.
Would someone like to put some comment on this topic ?

posted Feb 17, 2014 by Harshita

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1 Answer

+1 vote

Consider this Scenario -
NAS Recovery Procedure

  1. ENB A Given Measurement Configuration to a UE and due to RLF Happened with UE so UE not sent measurement Report.
  2. UE will try to re-establish with other ENB (suppose ENB - B) nearer to him so he UE will send RRC Re-establishment message to ENB B , But at ENB B there is no context about this (As measurement report not reached and handover preparation also not sent from ENB A to ENB B)
  3. So here two case arises
    CASE 1: Either ENB B will bring context from ENB A (Known as Forward Handover procedure) and Proceed with re-establishment procedure .
    CASE 2: ENB B will send RRC Establishment Reject (As he is not able to find context of UE at ENB B and unable to get context from ENB A) . so UE will go to idle mode and later UE will start from beginning by synchronizing with the ENB B. In this case all older data of UE present at ENB A will be lost .
    This is known as NAS Recovery Procedure.

Reference :-,d.bmk&cad=rja

answer Feb 27, 2014 by Sachidananda Sahu
In that scenario, What UE shall do ? Does it maintain all previous session ?  What shall be impact of running data with respect to UE and Network ?
UE will only contain RLF report when RLF happened, When UE gets RRC Reestablishment then in reestablishment complete UE will tell that i have RLF report then ENB can ask for it and find out the reason of RLF for it.
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+1 vote

I was looking into NAS header. First four bits are used for security header type. Few values I understood but one value I could not understand which was 1100 saying "security header for service request message". I could not understand why such thing is defined only for service request message not for the other messages ?

+3 votes

When this message is sent by Network to an UE ? There are couple of optional IEs within the message, what significance of their presence within the message ?

+3 votes

There are couple of procedures are defined which consist of NAS as well as RRC signalling messages exchange.
Some of the NAS message sends to an UE through RRC Connection Reconfiguration message as piggybacked and some as DL Info transfer.

I want to know, Is there any procedure exists in lte when an UE receives RRC Connection Reconfiguration along with NAS message and responds back to network with NAS message first and then Reconfiguration Complete to eNodeB.

Usually, I saw UE sends RRC Connection Reconfiguration Complete message first then NAS response message.

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