EMM Procedure 2. Detach

January 21, 2014 | By Netmanias (tech@netmanias.com)

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SUMMARY

This document, as the second of the EMM Procedure series, will discuss detach procedures required for cases where a user detaches/is detached from the LTE network he attached to, as in EMM Case 2 in “Eleven EMM Cases in an EMM Scenario”. Depending on where detach triggering is detected, we will categorize detach into three types: UE-initiated Detach, MME-initiated Detach and HSS-initiated Detach. Then we will describe detach procedures required in each type. Finally, we will look into what changes are made in the information EPS entities have after detach.

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Table of Contents

1. Introduction
2. Cases of Detach
3. UE-initiated Detach
4. MME-initiated Detach
5. HSS-initiated Detach
6. EPS Entity Information: Before/After Detach
7. Closing

1. Introduction

This document discusses detach procedures defined as EMM Case 2 in our previous document, “Eleven EMM Cases in an EMM Scenario”[1]. During this phase, a user is detached/detaches from the network he attached to. A user, initially attached to the network after going through the initial attach procedures as in EMM Case 1, uses LTE services in EMM-Registered state. After using the services, the user may be detached by the network or UE, while in ECM/RRC-Connected or ECM/RRC-Idle state. In any case, once detach procedures are completed, the user’s EPS bearer(s) are released, and his state is cleared.

This document is about detach procedures in an LTE network, and is organized as follows:

Chapter 2 identifies detach types depending on where the detach is triggered.

Chapters 3 through 5 describe detach procedures required in each detach type.

In Chapter 6, we will look into what kinds of information in each EPS entity are changed after the detach procedures in EMM Case 2.

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Hector 2014-05-18 08:58:45

Hi guys, great information, congrats!
About the UE initiated detach reasons "UE is attempting to use a non-EPS service (e.g. CS fallback, SMS, etc.)". In this case, does the mobile sends explcitly a detach? (For CS Fallback, the mobile starts a detach procedure?)

Rahul Mishra 2015-10-16 23:56:00

Hi,

I've one question.

If UE initiates Detach with cause as Switch off, does the network stiil sends RRCConnectionRelease to UE.

yuvraj patil 2017-10-11 18:07:06

Hi,

when UE gets switch off, UE stops sending a periodic tracking area updates and N/W will read this situation as UE is not reachable and in this case, N/W will initiate detach procedure.

Michael 2015-10-19 13:02:18

The MME transmits the UE context release command to eNB to release the UE-associated logical connection. Then, the eNB transmits the RRC connection release to the UE, releases the eNB resource, and transmits the UE context release complete to the MME to complete the call release procedure.
An MME-initiated call release occurs in the following cases.
1. A procedure between UE and MME is completed (e.g. Detach).
2. A call in the source eNB is released due to successful handover.
3. A call in the target eNB is released due to cancelled handover.
4. The old logical connection is to be released when 2 logical connections are established for a specific UE (e.g. when UE duplication occurs in the MME).
5. The UE is not a CSG member of the CSL cell.

TianMing 2016-10-20 18:19:12

Hi, if ue combined attached to lte , if imsi detach, whether only deactive the cs

domain security and authentication?

yuvraj patil 2017-10-11 19:26:52

Hi,

can anyone tell about PCC Rule Removal?

Sachin Vishwasrao 2018-01-20 21:02:39

After Step 16 in case of MME initiated Detach is the UE expected to ack the RRC Connection release message? I think since UE has released all the resources after sending the Detach Accept it cannot send the Ack. But in one of the operator specs it is expecting the RRC Connection release ACK. Please comment.

Tushar Waman 2019-01-29 18:27:27

Hi,

I would like to know, what happens when the battery is removed from the UE, how does the detach scenario play out ?

I believe the UE is not able to send any detach request when the battery is removed abruptly, but I would like to know how does the NW perform a detach in this case(if at all it perfoms a deatch). Tried reading the specification, but I could not find this Use Case. Any help would be appreciated.

sasi.reddy@Ltts.com 2019-03-22 01:42:30

Not able to register since my company email id has "." Eg. sasi.reddy@Ltts.com

bala nagarjuna 2019-09-04 19:05:19

Hi Tushar,

if Battery is removed UE doesnt send detach request to Network. Network doesn't know status of UE thinks it is in IDLE.

here 2 things may let the Network about UE.

1. paging message sent by Network, there will be no RRC connection from UE so Network may think UE is in out of coverage. based on this Network can trigger internal detach.

2. There will be no Periodic TAU after perodic timer expiry, so Netowrk considers UE is in out of coverage and implicitly Detaches the UE

Inder Chand 2020-02-28 19:51:32

Why do UE get Detach type=3 and attach type = 2 in LTE detach and attach process

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