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.