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what is mme tau (3g to 4g)

+3 votes
what is mme tau (3g to 4g)
posted Oct 20, 2014 by Ramilo

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@Romilo: Can not understand the question, are you looking for TAU procedure. Please describe in detail...

2 Answers

+1 vote

When an UE primarily attaches to LTE network with the "combined attach type" , UE can move to 3G network while keeping context at MME. As part of combined attach, MME establishes a session with the relevant SGGN based on the mapping of LTE tracking area <-> UMTS routing area. In that case if UE is moving to a geographical location where only 3G coverage is there, then UE handed over to SGSN. When UE again moves to an LTE area, it perform tracking area update.

answer Oct 21, 2014 by Harshita
0 votes

TAU means "Tracking Area Update" which is used in LTE which is known as RAU i.e. Routing Area Update in GERAN/UTRAN/3G. These procedures are initiated by UE when it detects a new tracking area or routing area.

Whenever UE moves from 3g to 4G-LTE then TAU procedure is initiated, but could not understand your query fully so dont know what to answer. Please check 23.401 or provide input so that it can be answered.

answer Oct 20, 2014 by Nikhil Pandey
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The whole purpose of TA is to know where the UE is situated so that it can be pagged. In connected mode, the eNB and MME already know which cell the UE is connected to so why TAU is neeeded in connected mode? Note that location area update is not required in 2G/3G in connected mode. In legacy 2G/3G, LAU only happens after the call is released so why in LTE the TAU is needed in connected mode?

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