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LTE EMM and ECM States
September 20, 2013 | By Netmanias (tech@netmanias.com)
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Comments (20)
A UE can attach to a network and use services regardless of its location by exchanging control signaling messages with the network using NAS signaling between the UE and an MME. EPS Mobility Management (EMM) and EPS Session Management (ESM) functions are two major NAS functions, and this document will cover EMM states and their transitions to help understand the EMM procedures to be discussed in details in the documents to be presented later on. EMM connection management is performed through EPS Connection Management (ECM) function, and an ECM connection consists of an RRC (Radio Resource Control) connection over the radio interface and an S1 signaling connection over the S1-MME interface. Thus, ECM and RRC states will also be explained when discussing the EMM states of a UE in this document.
Page 1 of 6



Table of Contents  

1. Introduction
2. EMM, ECM and RRC States 
3. EMM State Transition
4. EMM Features

5. EMM User Information

6. Closing



1. Introduction 


Through the previous technical documents, we have studied the LTE network architecture and LTE identifications, the fundamentals of LTE technology, and LTE security operation required for a user to attach to an LTE network and communicate securely. Now, we will look further into the detailed LTE procedures based on our previous studies.


Once a user attaches to an LTE network (or EPS system), i) the user is authenticated and registered at the network, ii) an EPS session and bearer(s) are established for using services and iii) mobility management functions for supporting the user’s movement are triggered. And at this time, it is a Mobility Management Entity (MME) in the network that takes care of all the foregoing three tasks by establishing signaling connection with the user and exchanging control messages.


Mobility and session management between a user and a network are controlled in accordance with the NAS protocols in the Non-Access Stratum (NAS) layer located in the control plane of UE and MME. The two entities communicate with each other using NAS messages. The NAS protocols are defined in 3GPP TS 24.301[1]. NAS features can roughly be classified into EPS Mobility Management (EMM) and EPS Session Management (ESM) features.


Through a series of technical documents, we will describe these two procedures, EMM and ESM.


This document is the first document of the series, and will provide descriptions of i) EMM state, and ii) what user information is kept in EPS entities (See “LTE Network Architecture” [2]) once an EMM procedure is initiated, to help understand the EMM procedure.


This document is organized as follows:


In Chapter 2, types of EMM procedures and EMM-related states (EMM/ECM/RRC) are explained.

Chapter 3 will describe the transition among these states, and

Chapter 4 will summarize the characteristics of EMM in EPS entities.

Finally, Chapter 5 will discuss what user information is kept in EPS entities in different combinations of EMM/ECM/RRC states.




Page 1 of 6
Netmanias 2015-05-25 03:10:12

There is an error in Figure 2 and it will be fixed later.

Find comments belows (from Jakub Bluszcz in LinkedIn):

RLF doesn’t necessarily result in transition from RRC-CONNECTED to RRC-IDLE [3GPP 36.331 5.3.11].

If cell selection and reestablishment procedures are successful the UE remains in RRC-CONNECTED. In case there is no suitable cell or reestablishment fails the UE goes to RRC-IDLE.

Some selected cases are presented here: http://www.sploty.com/en/rlf-and-connection-reestablishment

Moreover, the RLF and subsequent transition to RRC-IDLE doesn’t result in transition from EMM-REGISTERED to EMM-DEREGISTERED. The correct state should be EMM-REGISTERED substate NO-CELL-AVAILABLE [see 24.301], which means that after new cell selection followed by new RRC Connection Establishment the EMM Service Request procedure can be successful (i.e. no Attach nor default EPS bearer establishment is necessary). 

Deepak 2016-09-14 22:51:17


Lajos Pajtas 2015-06-11 17:20:48

Probably the best description available on net.

Keep up the good work!

Mateenuddin 2015-09-09 01:43:12

The best document ever to read for begginers.

Thanks for effort, please keep it up.

vidyasagarrao7 2017-01-10 22:11:21



Can you please share this document? I am unable to download that..

Mail id: vidyasagarrao7@gmail.com

Netmanias 2017-01-11 13:10:21

You can download PDF file after login.

santoshi 2016-01-29 00:20:18

how cna we attach a ue to network through coding?

Basheer 2016-04-12 15:54:28

Explanation on UE transitions are awsome...Thank you very much

MANOJ 2016-05-04 13:58:13



Thanx for very good docs for LTE..


Can you explain in which order we should read LTE docs

Nikita Raju Nikrad 2017-06-13 16:19:47



You can find the index with above link for the LTE Technical Documents.

CHEN 2016-10-14 14:29:45

Thank you for your every good documents for LTE, easy to understand :)

ANTONIO ALONSO 2016-10-21 05:23:39

I think there is an error when explaining transition from D to C. Current text provides two conditions [numbered as "i)" and "ii)"] and use "AND" between both (so it means the two conditions must be fulfilled) ... should it not be an "OR" instead? Any of them means transtioning from D (EEM-Registered, ECM-Idle/RRC-Idle)  to C (EEM-Registered, ECM-Connected/RRC-Connected).

Thierry Van de Velde 2017-03-01 04:23:46

This article has become a timeless classic and a must-read for any 4G and 5G network engineer.

jullien 2017-03-02 20:46:14

Dear Netmanias;

From where i can download all the technical documents ? Thanks.

Netmanias 2017-03-04 10:04:57

Thank you for your interest and inquiry. 

Unfortunately, you can't download all documents at a single location at once.
Instead, each page provides a red box saying "Download PDF File", and you can simply click it and download the document on the page. 

Hope it helps.

CHEN 2017-05-25 17:03:27

Dear Netmanias,

There is a question, what will the LTE client do if the network will drop the LTE PDP context because the inactivity timer in the P-GW has expired and therefore release the client IP address?

Apparently, there is a 24-hr inactivity timer in the P-GW. Will the LTE client re-establish a new PDP Context activation request to the network to keep LTE connected?





justin king 2020-02-04 16:03:40

Wonderful document that can be understood even by beginners thanks a lot


jassim.mohamed@asiacell.com 2020-04-05 18:09:30


firstly thanks alot for sharing such vlauble, comprehensive doucment.

I would like to asking if there are a way to find out all documntes related to LTE basic detials sequentially arranged.

thanks in advance


Yijie 2020-10-15 15:32:08

Thanks for your effort, it is super useful.

HMK 2020-10-23 19:37:18

Anyone can u pls help Im confusing on below two things I would like to know what is 
1.Number of Dynamic 4G bearers(This parameter indicates the number of activated 4G bearers) and
2. Number of dynamic 4G MMs(This parameter indicates the number of attached 4G users. The users are those in the ECM-CONNECTED and ECM-IDLE states)

Thank you for visiting Netmanias! Please leave your comment if you have a question or suggestion.
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