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What is the combined attach procedure in LTE?

+3 votes
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I want to know combined attach procedure and how it is different between UMTS and LTE?

posted Oct 15, 2013 by anonymous

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Combined Attach meand UE performs registration for LTE network and Non-LTE network (e.g, WCDMA or GSM) simultaneously where in UMTS it is simultaneous attach to PS and CS network.

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When UE performs registration for LTE network and Non-LTE network (e.g, WCDMA or GSM) simultaneously.

Why do we need this kind of simultaneous registration for two different network ?
It is mainly for CS-Fallback. Unless a system operator/UE use Voice Over IMS, we use legacy network (e.g, WCDMA, GSM, C2K) for voice call. In this case, UE has to go through the registration for the legacy network. The idea of Combined Attach is to perform the attach process for LTE and Legacy Network simultaneously.

answer Oct 30, 2013 by Deepak Dasgupta
Similar Questions
+2 votes

During a combined attache, a UE can receive an ATTACH-REJECT if for the specific PLMN the EPS service are not allowed.
In this case, the EMM cause value received in the ATTACH REJECT message should be 14.
The 124.301 ETSI standard tells that in this situation, if the UE operates in CS/PS mode 1, it may select GERAN or UTRAN
radio access technology instead of LTE for the same PLMN.
The standards doesn't tell anything about UE's operating in CS/PS mode 2: must they choose another PLMN?

+1 vote

Can someone explain this step by step?

0 votes

In TS 24.301 5.5.1.3.4.2, if combined attach is success(i.e Combined attach successful for both EPS services and non-EPS), why core network contains IMSI in MS identity IE of combined attach accept, and why not just allocate a new TMSI?
In what situation will core network use IMSI in MS identity?

+1 vote

Several messages are exchanged between UE and network nodes (eNodeB and MME) during attach procedure. I want to know in which all stages timers are used to guard various sub procedures of LTE attach procedure.

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