Table of Contents
4.1 Before Periodic TAU
4.2 After Periodic TAU
This document describes the periodic TAU (Tracking Area Update) procedure defined as EMM Case 5 in our technical document, “Eleven EMM Cases in an EMM Scenario” . This procedure is performed when a UE which entered ECM/RRC-Idle state in the network due to no traffic periodically updates the network (MME) with its current location.
A TAU procedure is initiated when a UE enters a new TA that is not in the list of TAIs allocated by the MME at the time of the UE’s attach, or when the TAU timer expires. The EMM Case 5 presented in this document is related to the periodic TAU procedure performed by a UE upon expiration of the TAU timer. A UE in Idle state reports its current location to the MME by sending a TAU Request message when the TAU timer expires. After transiting to ECM/RRC-Connected state, and performing the periodic TAU procedure, the UE returns to Idle state.
This document explains the periodic TAU procedure performed by a UE in Idle state in an LTE network.
Chapter 2 explains the concept of periodic TAU, and
Chapter 3 describes its specific procedures. Finally,
Chapter 4 summarizes how information elements in EPS entities are different before and after the procedure.
Thanks for such a wonderful blog on LTE procedures. Very useful for those who are trying to get an end to end picture. Once again, amazing work and kudos to your team!
Also, I would like to point out a small error in Section "III. Procedure of Periodic TAU", steps "4), 5), 6) [UE → MME] ECM Connection Establishment Request and TA Report" as below:
>>> "TAU Request message is sent integrity-protected with the NAS integrity key (KNASint) and encrypted with the encryption key (KNASenc)."
As I know, at UE Initial NAS messages(Specifically, TAU and Attach Request are never sent Ciphered) are sent only Integrity Protected and not ciphered. Please refer to TS 24.301, Section 4.4.5 for further reference.
no E-RAB (between UE and MME) ---- I think E-RAB always set up in between UE-eNodeB -SGW....
Please clarrify me this procedure,
UE is in Attached to Netowrk with Some HPLMN(111-210) and in Equilent HPLMN list (112-210) is present , same has been configured in USIM as well
So , my question is when UE moved from (111-210) to (112-210) what could be the UE behaviour ?
Does UE intiate TAU procedure or Attach request ?
I have tried with Samsung Mobile it is intiating TAU when in the case UE is already attached with HPLMN(111-210) then UE moved from HPLMN - to Equilent HPLMN(112-210) since its already configured in USIM as well as Mobile configuration
But in the case if i removed Equilent HPLMN(112-210) in mobile NAs configuration UE will intiate Attach reuqest in this case
where as when i tried with other mobile like LG and other mobile altair ..it's intiating attach request procedure when UE changed from HPLMN(111-210) to Equilent HPLMN(112-210) instead of TAU even though SIM configured E-HPLMN list (111-210 && 112-210)
what is the ideal Behaviour ?
please share your valuable comments ..
(ii) During the procedure, the UE stays in EMM-Registered, ECM-Connected and RRC-Connected state. The periodic TAU procedure is different from procedures for initial attach or service request in that no E-RAB (between UE and MME) is set up, and only the signaling connection (ECN signaling connection) for delivering periodic TAU-related NAS messages is set up during this procedure.
In above paragraph, small typo mistake.(ECN signaling connection) should be (ECM signaling connection)
Outstanding description and neat sequence diagram.
But, if I'm not wrong, it looks like that is missing any reference to timer T3440, that's letting the NAS Signalling Connection Release after the TAU.
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