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EMM Procedure 1. Initial Attach - Part 2. Call Flow of Initial Attach
January 16, 2014 | By Netmanias (tech@netmanias.com)
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This document, Part 2 of Initial Attach, discusses detailed initial attach procedures in EMM Case 1. EMM Case 1 concerns initial attach procedures for a user attaching to a network for the first time, as categorized as Attach Case 1 in Part 1. Below, we will provide a description of those procedures and their related function blocks explained in Part 1. We will also summarize what kinds of information are set in the EPS entities after the procedures.
Page 1 of 4

Table of Contents  

1. Introduction
2. Initial Attach Procedure 

        2.1 IMSI Acquisition
        2.2 Authentication
        2.3 NAS Security Setup
        2.4 Location Update
        2.5 EPS Session Establishment
3. EPS Entity Information

        3.1 Before Initial Attach
        3.2 After Initial Attach
4. Closing



1. Introduction


Now, we will look into EMM Case 1: Initial Attach by Unknown UE in "Eleven EMM Cases in an EMM Scenario"[1]. This case is when a user turns on his UE and attempts to attach to a network for the first time after subscribing to the LTE network/service. It was previously categorized as Attach Case 1 in Part 1 [2].


This document, Part 2, is organized as follows:


Chapter 2 explains the detailed procedures in EMM Case 1 (Initial Attach with IMSI), focusing on the functions required in the case, as described in Part 1.

Chapter 3 summaries what information is changed in each EPS entity after initial attach in Attach Case 1.





Page 1 of 4
fanrui 2014-07-08 19:20:50

Very good document. I have a question.

In the attach accept message, the IP address allocated to UE is mandatory. However, there is no DNS related information. I checked spec, in the PCO (protocol configuration options) DNS server address can be included. However PCO is optional. So I just wonder, without DNS server in PCO, how could UE access the internet?

nn 2018-01-21 22:21:29

Hi, Did you find the answer anywhere ? 


Hi Netmania ,


Can you please clarify points put by fanrui. Thanks in advance.



Nagarjuna 2014-09-18 22:07:16

Hi Netmanias,


                   First i have to thank you ,that you shred a very valuable document with us regarding lte stuffs , but here i have one small suggestion , in point of initial attach part-1 &2 ,document maily focusing on core network rather on RRC messages (i.e., between UE and Enodeb).can you please add one more document(which highlits UE and Enodeb messages and transcations) related also,so that end-to-end connection would be clear for us.






Vijayakumar 2015-04-12 21:45:11

Hi Netmanias,


Really appreciate the depth of the information provided. Can you please also add "Selection of MME" in the eNodeB (using static/DNS queried)?

HUAWENJIAN 2015-07-19 12:59:52

Very Excellent!Thanks for your sharing! I have got lot of information about my concern topic.

Siva Dugana 2015-10-20 11:58:00

Thanks for the detailed explanation. Appriciate to have a thought to share the knowledge like this...

DAniel 2016-04-05 09:37:32

Man, congratulations and thank you

Chandru 2016-05-25 18:40:09

Really Really Super. Thanks Guys

Netmanias 2016-05-29 04:15:31

Glad you liked it. And thank you for your interest!

Stay tuned!

Markus 2016-09-21 20:03:50

Great explanation! Thank you very much.

venkat 2016-10-17 13:31:10

Good explanation!!


bijukumar 2017-05-23 15:17:34

good explanation and  well explained in main areas of call flows

Ken Hu 2017-07-21 10:53:06

There is typo in "Figure 7. Procedure for EPS Session Establishment (1)" step 14 : "Receive S5 TEID (DL)" should be "Receive S5 TEID (UL)".

Marcin 2017-09-29 18:43:43

I was thinking same as you. Thank you for notice so I know i wasn't wrong.

Above all - good explanation

netti 2017-10-05 15:47:07

Can somebody help me with the softwares required in this simulation?

yasin akar 2017-12-19 23:24:37

hi everyone,


Is it possible to establish more than 1 default bearers? I mean within an initial attach procedure the EPS can setup more than one APN default bearers for example one for internet and other one is IMS bearers? Or only one default bearer can be setup within an initial attach procedures and other additional default bearers can be setup upon demanded?


thanks for your supports.

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