ProDeveloperTutorial.com

Tutorials and Programming Solutions
Menu
  • Shell Scripting
  • System Design
  • Linux System Programming
  • 4g LTE
  • Coding questions
  • C
  • C++
  • DSA
  • GIT
  • 450 DSA Cracker
  • 5G NR
  • O-RAN

S1 based inter eNB handover

prodevelopertutorial September 7, 2020

In the previous chapter we saw X2 based inter eNB HO.

In this chapter we shall learn S1 based HO.

Scenarios where we need S1 HO.

1. If X2 interface is busy to perform HO.
2. If X2 interface is not present in between 2 eNB.

This handover is based on 3 steps as below:

1. HO Preparation
2. HO Execution
3. HO Completion

s1 handover lte
1. HO Preparation

Step 1:
Some thresholds will be met and UE will send Measurement report. It will include “rsrpResult” and “rsrqResult”.
Source eNB will decide if HO should happen or not.
Here source eNB will not talk to target eNB because of lack of X2 interface.
Hence source eNB will talk with MME and MME will talk with target eNB.

Step 2:
HO Required from source eNB to MME.
It will include “ERAB to be established: QCI, ARP, AMBR related info, target-eNB ID, S1 SGW TEID”

Step 3:
“HANDOVER REQUEST” from MME to Target eNB.
It will include “ERAB to be established: QCI, ARP, AMBR related info, target-eNB ID”

Step 4:
Target eNB will receive “S1 SGWTEID (a)”, now t-eNB will be able to send packet to SGW.
It will create “S1 t-eNBTEID (b)”, “s1 t-eNBTEID (c)”, allocate DRB ID and CRNTI

Step 5:
“HANDOVER REQUEST ACKNOWLEDGE” from Target eNB to MME. It will include above ID’s crated by t-eNB.

Step 6:
Create Indirect Data Forwarding Tunnel Request, MME -> SGW. It will send “S1 t-eNBTEID (b)”

Step 7:
Create Indirect Data Forwarding Tunnel Response, SGW -> MME. It will receive “S1 t-eNBTEID (b)”, it will create a tunnel towards t-eNB.
It will also create “S1 SGWTEID (d)” and send it to MME.

Step 8:
“HANDOVER COMMAND” MME -> source eNB. It will include “DRB, CRNTI, S1 SGWTEID (d)”.

Now s-eNB will create a bearer towards SGW.

Now “s-eNB -> SGW -> t-eNB” path is established.

 

2. HO Execution

Step 1:
“RRCConnectionReconfiguration” from “source-eNB (s-eNB)” to “UE”. Now there is no connection between UE and s-eNB.

Step 2:
“eNB STATUS TRANSFER” from “s-eNB” to “MME”. It will have UL/DL count.
It helps to know from which packet number t-eNB should send to UE.

Step 3:
“MME STATUS TRANSFER” from MME to t-eNB.

Step 4:
Now there will be indirect data transfer as
“SGW -> s-eNB -> t-eNB -> SGW -> t-eNB -> buffer”

Step 5:
Detach from old cell/Synchronize to new cell

Step 6:
“RRCConnectionReconfigurationComplete” UE -> -eNB.
Now DRB will be established from UE to t-eNB.
UL is already established.
But downlink will take a long path “SGW -> s-eNB -> t-eNB -> SGW -> t-eNB -> buffer”.
This will be taken in HO complete.

 

3. HO Completion

Step 1:
“HANDOVER NOTIFY” t-eNB to MME.

Step 2:
“Modify Bearer Request” from MME to SGW

Step 3:
“Modify Bearer Response” from SGW to MME

Step 4:
“End marker” from SGW to s-eNB.

Step 5:
“End marker” from s-eNB to t-eNB

Share
Email
Tweet
Linkedin
Reddit
Stumble
Pinterest
Prev Article

About The Author

prodevelopertutorial

Follow this blog to learn more about C, C++, Linux, Competitive Programming concepts, Data Structures.

Leave a Reply Cancel Reply

You must be logged in to post a comment.

ProDeveloperTutorial.com

Tutorials and Programming Solutions
Copyright © 2023 ProDeveloperTutorial.com
We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept”, you consent to the use of ALL the cookies.
Do not sell my personal information.
Cookie SettingsAccept
Manage consent

Privacy Overview

This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may affect your browsing experience.
Necessary
Always Enabled
Necessary cookies are absolutely essential for the website to function properly. These cookies ensure basic functionalities and security features of the website, anonymously.
CookieDurationDescription
cookielawinfo-checkbox-analytics11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Analytics".
cookielawinfo-checkbox-functional11 monthsThe cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional".
cookielawinfo-checkbox-necessary11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookies is used to store the user consent for the cookies in the category "Necessary".
cookielawinfo-checkbox-others11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other.
cookielawinfo-checkbox-performance11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Performance".
viewed_cookie_policy11 monthsThe cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. It does not store any personal data.
Functional
Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features.
Performance
Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors.
Analytics
Analytical cookies are used to understand how visitors interact with the website. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc.
Advertisement
Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. These cookies track visitors across websites and collect information to provide customized ads.
Others
Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet.
SAVE & ACCEPT