Table of Contents
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. 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” ) 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.
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 24.301 220.127.116.11.4.7], 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).
Probably the best description available on net.
Keep up the good work!
The best document ever to read for begginers.
Thanks for effort, please keep it up.
Can you please share this document? I am unable to download that..
Mail id: email@example.com
Thanx for very good docs for LTE..
Can you explain in which order we should read LTE docs
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).
This article has become a timeless classic and a must-read for any 4G and 5G network engineer.
From where i can download all the technical documents ? Thanks.
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.