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EMM Procedure 8 & 9. Handover and Cell Reselection with TAU
May 07, 2014 | By Netmanias (tech@netmanias.com)
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Comments (6)
This document will describe two types of EMM procedures: i) handover where UE in Connected state (EMM-Registered, ECM-Connected, RRC-Connected) moves to a non-registered TA (EMM Case 8) and ii) cell reselection where UE in Idle state (EMM-Registered, ECM-Idle, RRC-Idle) moves to a non-registered TA (EMM Case 9). The handover and cell reselection procedures are the same as in EMM Case 6 (Handover without TAU) and Case 7 (Cell Reselection without TAU), respectively, except that a TAU procedure is required after handover/cell reselection as this time UE moves to a non-registered TA. As in EMM Cases 6 and 7, we will discuss intra-LTE handover and intra-frequency cell reselection only.
Page 1 of 5

Table of Contents  

1. Introduction
2. EMM Case 8. Handover with TAU

3. EMM Case 9. Cell Reselection without TAU

4. EPS Entity Information

5. Closing



1. Introduction


When UE accesses the network, a group of Tracking Areas (TAs) is assigned by the network (MME) through the Tracking Area Identity (TAI) list. The UE then can move within these TAs without having to report its location to the network. The network does not know which cell the UE is camping on, but knows it is in one of the assigned TAs. So, if a call/packet arrives for UE in Idle state, the network initiates paging within these TAs where the UE is registered. The TAI list assigned to the UE is a list of the areas where the UE has been registered. Because of this, if UE moves to a TA not in the TAI list, it must perform a TAU procedure, requesting for TA update, so that the network can update the UE’s TAI list and assign the updated list accordingly. 


This document concerns the EMM cases, where UE moves to a TA that it is not registered to, specifically “EMM Case 8. Handover with TAU” and “EMM Case 9. Cell Reselection with TAU” in [1].


[1] Netmanias Technical Document, Eleven EMM Cases in an EMM Scenario


In EMM Case 8, UE moves to another TA while it stays in Connected state (EMM-Registered, ECM-Connected, RRC-Connected). During this move, the procedure for handover from the source eNB to the target eNB is the same as described in our EMM Case 6. Handover without TAU documents [2][3][4]. What is different from the previous case is that thereafter the UE performs a TAU procedure at the new cell in the target eNB.


[2] Netmanias Technical Document, “LTE EMM Procedure 6. Handover without TAU – Part 1. Overview of Handover
[3] Netmanias Technical Document, “LTE EMM Procedure 6. Handover without TAU – Part 2. X2 Handover
[4] Netmanias Technical Document, “LTE EMM Procedure 6. Handover without TAU – Part 3. S1 Handover



On the other hand, in EMM Case 9, UE moves while in Idle state (EMM-Registered, ECM-Idle, RRC-Idle). Here, the procedure for cell reselection at the serving cell is the same as in EMM Case 7. Cell Reselection without TAU [5]. Again, this time however the UE, after cell reselection, must perform a TAU procedure before it camps on the new cell.


[5] Netmanias Technical Document, “LTE EMM Procedure 7. Cell Reselection without TAU



This document is organized as follows:


Chapter 2 explains the EMM Case 8 procedure, and

Chapter 3 discusses the EMM Case 9 procedure.

In Chapter 4, we will learn how information elements in EPS entities are different before and after the procedures. 





Page 1 of 5
yuanjiantao 2014-11-16 10:51:55

thanks  very much 

yuanjiantao 2014-11-23 17:37:27

Hi,I have read almost all the documents about EMM topic,thanks for your summary ,it's very useful for me.

there is a typo in this document,"Abbreviations  KSI  ...." 

thanks again.

ohyong 2015-03-02 14:58:16

Many thanks for good material on HO with TAU. I am wondering about whether ENB-UE-S1AP-ID for both S1 Handover and TAU should be identical or not under HO with TAU. Target eNB has its ENB-UE-S1AP-ID during HO execution. And it also has its ENB-UE-S1AP-ID for TAU right after S1 HO.

So should ENB-UE-S1AP-ID be totally identical to both equal eNB(Target) and equal UE under above uttered two phases? Am I thinking right? Otherwise they should be different ENB-UE-S1AP-ID.
Please make sure whether equal or different ENB-UE-S1AP-ID should be related to Target eNB under HO with TAU.

Faisal Adeem Siddiqui 2015-06-24 19:26:12

Why the TAU is necessary after HO if the new cell belongs to different TA ? This can happen after the PS call ends as it happens in 2G/3G (LAC update happens at the end of CS call if LAC is changed during HO).

Ankush Taneja 2020-06-10 22:54:12

Hyperlink in point 3 for table of contents is wrong. It says "Cell reselection without TAU" whereas it should be with TAU

Mohanavamsi Gorantla 2020-07-09 15:05:14

While Cell Reselection , was with TAU .. 

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