inter rat handover 2

7/29/2019 Inter Rat Handover 2

1/17

IRAT Handover LTE

Name: Vivek Pal

Student # 38978983


2/17

Types of LTE Handover

Intra LTE

- X2 handover

- S1 handover Inter LTE

Inter RAT

- with 3GPP technologies- with Non- 3GPP technologies


3/17

Need for Inter-RAT

LTE, primarily was available only in hot spots, hence mobility

across radio access technology is essential.

Non real-time data should not be lost during the handoverprocedure.

Tearing down and setting up new connection may cause

significant degradation of user experience.


4/17

What is I-RAT Handover

Inter RAT HO is network controlled through source accesssystem.

The source access system decides about starting thepreparation and provides the necessary information to the

target system in the format required by the target system. The handover execution is decided in the source system.

Inter RAT HO is backwards handover, i.e. radio resources areprepared in the target 3GPP access system before the UE iscommanded by the source 3GPP access system


5/17

What is I-RAT Handover(cont.)

To enable backwards handover, a control interface exists in CN

level. In Inter RAT HO involving E-UTRAN access, this interface

is between 2G/3G SGSN and corresponding MME/Serving

Gateway

The target access system will be responsible for giving exact

guidance for the UE on how to make the radio access there.

This information is given during the handover preparation

and should be transported completely transparently through

the source access system to the UE


6/17

What is I-RAT Handover(cont.)

The handover procedure should not require any UE to CN

signalling in order for data to start to flow in the target

system. This requires that the security context, UE capability

context and QoS context is transferred within the networkbetween source and target system


7/17

LTE to UMTS IRAT Handover

The source eNodeB connects to the S-MME and S-SGW while

the target RNC connects to the T-SGSN and T-SGW

Source and target SGWs connect to the same PGW

Procedure is divided into:- Preparation

- Resources are reserved in the target network

- Execution

-The UE is handed over to the target network fromthe source network.


8/17

Preparation Phase


9/17

Preparation Phase (cont.)

Once the inter-RAT handover is decided at the S-eNB based

on the measurement report procedure, it prepares and sends

a HANDOVER REQUIRED message to the S-MME.

The S-MME detects that it is an Inter-RAT handover from the

message contents, retrieves the target SGSN details from the

database based on the information in the message. It now

prepares and sends a FORWARD RELOCATION REQUEST to

the T-SGSN

The T-SGSN detects the change of SGW and creates thebearer resources in the T-SGW by initiating the CREATE

SESSION procedure


10/17


Once the resources are reserved at the T-SGW, it responds tothe T-SGSN with a GTP: CREATE SESSION RESPONSE message.

The T-SGSN now reserves the resources at the T-RNC bysending a RANAP: RELOCATION REQUEST message to it

The T-RNC reserves the radio resources and responds to theT-SGSN with a RANAP: RELOCATION REQUEST ACK message.

The T-SGSN creates the indirect data forwarding tunnels inthe T-SGW for the DL packets transfer from the S-SGW to T-SGW during the handover


11/17


After the Indirect Data forwarding tunnel creation, the T-SGSN

responds with a GTP: FORWARD RELOCATION RESPONSE

message to the S-MME.

The S-MME has to create the indirect data forwarding tunnels

as the resources are reserved successfully in the target

network to forward the DL packets to the target network.

With this, the preparation phase is complete.


12/17

Execution Phase


13/17

Execution Phase (cont.)

The S-MME sends the HANDOVER COMMAND message to the

S-eNB with the target to source transparent container (i.e., it

has the reserved resource information at the target).

The S-eNB prepares and sends the MOBILITY FROM EUTRA

COMMAND message to prepare the UE for the handover

toward the target network.

After accessing the target UMTS cell, the UE sends a HO TO

UTRAN COMPLETE message to the T-RNC signaling the

successful handover.


14/17


The S-eNB forwards the DL data packets toward the T-SGW via theS-SGW during the handover. This step can happen any time after itreceives the S1AP HANDOVER COMMAND message from the S-MME. This step is executed in case a direct forwarding path is not

available with the T-RNC, otherwise it will forward the DL datapackets to the T-RNC directly.

Once the T-RNC detects the UE in its area, it notifies the T-SGSNabout the completion of the handover by sending a RANAP:

RELOCATION COMPLETE message. The S-MME acknowledges thismessage and proceeds with release of the resources associatedwith this UE at the S-SGW and S-eNB


15/17


The T-SGSN modifies the E-RAB resources at the T-SGW by

initiating the GTP MODIFY BEARER procedure.

The T-SGW notifies the bearer parameters with the PGW by

initiating the GTP MODIFY BEARER procedure


16/17

Reference

LNA 108 7020 R6B_3 -ericsson

Interworking LTE with WCMDAalcatel lucent

http://lib.tkk.fi/Dipl/2011/urn100472.pdf http://go.radisys.com/rs/radisys/images/pape

r-lte-interoperable.pdf
http://lib.tkk.fi/Dipl/2011/urn100472.pdfhttp://lib.tkk.fi/Dipl/2011/urn100472.pdfhttp://lib.tkk.fi/Dipl/2011/urn100472.pdf


17/17

Thank You.

inter rat handover 2

Documents