rrc-procedures-in-lte

RRC PROCEDURES IN LTE
Version 0.1

Revision History:

© Hughes Systique India Private Limited, India

Version Date Description Author
0.1 22-APR-2008 Initial Draft Praveen Kumar
0.2 23-APR-2008 Incorporated Praveen Kumar
pradeep’s comment

ntents


1 Introduction.......................................................................................................................6
2 Purpose..............................................................................................................................6
3 Important Changes in RRC specification for LTE and its difference with legacy 3G-
RNC system.........................................................................................................................6
4 Architecture.......................................................................................................................9
4.1 RRC State...................................................................................................................9
4.2 Signaling Radio Bearers............................................................................................9
4.3 RRC Functions.........................................................................................................10
4.4 RRC Procedures.......................................................................................................11
4.4.1 Paging...............................................................................................................11
4.4.2 RRC Connection establishment........................................................................12
4.4.3 RRC Connection Reconfiguration....................................................................14
4.4.4 RRC Connection Re-establishment .................................................................16
4.4.5 Initial Security Activation.................................................................................17
4.4.6 RRC Connection Release..................................................................................18
4.4.7 DL Information Transfer...................................................................................18
4.4.8 UL Information Transfer...................................................................................19
4.4.9 Handover Procedure..........................................................................................20
..........................................................................................................................................22

Reference
Document Name References in Document Date Version
RRC Specification 33.331 v


from 3GPP – 8.1.0
Release 8

Abbreviations:

ARQ Automatic Repeat Query
HARQ Hybrid Automatic Repeat Query
AM Acknowledged Mode
ASN.1 Abstract Syntax Notation.1
ARQ Automatic Repeat Request
AS Access Stratum
BCCH Broadcast Control Channel
BCH Broadcast Channel
CCCH Common Control Channel
CCO Cell Change Order
CP Control Plane
C-RNTI Cell RNTI
CSG Closed Subscriber Group
DCCH Dedicated Control Channel
DRB (user) Data Radio Bearer
DRX Discontinuous Reception
DTCH Dedicated Traffic Channel
DTX Discontinuous Transmission
DL Downlink
DL-SCH Downlink Shared Channel
E-UTRA Evolved Universal Terrestrial Radio Access
E-UTRAN Evolved Universal Terrestrial Radio Access Network
ENB Evolved Node B
EPC Enhanced Packet Core
EPS Enhanced Packet System
FDD Frequency Division Duplex
FFS For Further Study
GERAN GSM/EDGE Radio Access Network
GSM Global System for Mobile Communications
HARQ Hybrid Automatic Repeat Request
HRPD CDMA2000 High Rate Packet Data
IE Information element
IMEI International Mobile Equipment Identity
IMSI International Mobile Subscriber Identity
L1 Layer 1
L2 Layer 2
L3 Layer 3
MAC Media Access Control
MBMS Multimedia Broadcast Multicast Service
MCCH MBMS point-to-multipoint Control Channel
MIB Master Information Block


MTCH MBMS point-to-multipoint Traffic Channel
N/A Not Applicable
NACC Network Assisted Cell Change
NAS Non Access Stratum
PCCH Paging Control Channel
PDU Protocol Data Unit
PDCP Packet Data Convergence Protocol
PLMN Public Land Mobile Network
PTM-MC Point-to-Multipoint, Multi-Cell
PTM-SC Point-to-Multipoint, Single-Cell
PTP Point-to-Point
QoS Quality of Service
RACH Random Access Channel
RA-RNTI Random Access RNTI
RAT Radio Access Technology
RB Radio Bearer
RLC Radio Link Control
RNTI Radio Network Temporary Identifier
RRC Radio Resource Control
RSCP Received Signal Code Power
RSRP Reference Signal Received Power
RSSI Received Signal Strength Indicator
SAE System Architecture Evolution
SAP Service Access Point
SI Scheduling Information
SIB System Information Block
SI-RNTI Scheduling Information Change RNTI
SI-RNTI Scheduling Information RNTI
SRB Signaling Radio Bearer
S-TMSI SAE Temporary Mobile Station Identifier
TA Tracking Area
TDD Time Division Duplex
TM Transparent Mode
UE User Equipment
UICC Universal Integrated Circuit Card
UL Uplink
UM Unacknowledged Mode
UL-SCH Uplink Shared Channel
UP User Plane


1 Introduction
This document provides the details of RRC procedures as specified in 3GPP 36.331
for LTE.

2 Purpose
The purpose of this document is to understand RRC Procedures and RRC IEs for
LTE. It will help developers and testing engineer to understand the feature better and
utilize their knowledge in various customer sites. This document will also help developer
to start thinking design of RRC in LTE.

3 Important Changes in RRC specification for LTE and
its difference with legacy 3G-RNC system
Following is the important changes in RRC specification for LTE and its difference
with legacy 3G-RNC system. Procedure specific difference is mentioned in specific
procedure section.

• RRC State: - In LTE there is only 2 RRC states i.e. RRC_IDLE and
RRC_CONNECTED whereas in 3G-RNC system RRC has a 5 state i.e.
IDLE, CELL_FACH, CELL_DCH, CELL_PCH, URA_PCH. In LTE, there
is no concept of common and dedicated transport channel, that’s why there is
no need of CELL_FACH and CELL_DCH state. In LTE there is only shared
transport channel are defined. CELL_PCH and URA_PCH is also removed
because in LTE. Therefore this will simplifies the RRC State machine
handling and improves RRC performance. This will also simplify the RRM
algorithm which decides RRC states.
• Signaling Radio Bearers: - In LTE there is only three SRB is defined i.e.
SRB0, SRB1 and SRB2. Still SRB2 is on FFS, whereas in 3G-RNC system
RRC has 4 SRBs i.e. SRB0, SRB1, SRB2 and SRB3 (optional).
• SRB 0: - In LTE SRB 0 is used RLC TM entity over CCCH logical channel
in DL whereas in 3G-RNC system RLC UM entity over CCCH logical
channel in DL.
• MAC entity: - In LTE there is only one MAC entity which needs to
configured whereas in 3G-RNC system there is 4 different MAC entity based
on different type of transport channel i.e MAC-d (DCH), MAC-c/sh (FACH,
DSCH), MAC-hs (HS-DSCH) and MAC-e (E-DCH). In 3G-RNC system the
state machine which is handling MAC configuration is quite complex. During
state transition CELL_FACH->CELL_DCH or CELL_DCH->CELL_FACH
lots of signaling was involved. In LTE, since there is only one MAC entity
which is easier and simple to configure and have very simple State Machine.


• Radio Bearer mapping: - In LTE Radio bearer mapping would be much
simpler than the 3G-RNC system because of there is no common and
transport channel defined in LTE.
• In LTE there is no RRC connection mobility defined like cell update and ura
update.
• Domain Identity: - In LTE, there is only one domain identity i.e. PS domain
and which is implicit no need to specify anywhere in signaling where as in
3G-RNC system there is two domain identity i.e. CS domain and PS domain
identity. Because of these two identities, there was lot of signaling overhead
and complexity in RRC design. Now in LTE, there is no Initial UE Message
is defined because only one domain identity is there.
• System Broadcast Information:- In LTE, MIB includes a limited number of
most frequently transmitted parameters and SIB Type 1containing the
scheduling information that mainly indicates when the SI messages are
transmitted where as in 3G-RNC system, MIB includes the frequently
transmitted parameters was well as scheduling information.
• In LTE, only shared channel is defined, so UE is always listening/decoding to
the radio frame at L1 and L2 layer, there is no need to define the downlink
transport channel configuration in the RRC Reconfiguration message. This
will reduce signaling message size effectively. All DL-SCH transport channel
information is broadcasted in system information.
• The above point introduces another very critical feature of DRX calculation
since all DL data is on the shared channel. ENB can tell the UE when to
decode/listen over the radio frame. This will optimize UE power consumtion.
• Paging Type: - In LTE there is only one type of paging required where as in
3G-RNC system there is two type of paging defined. This is because there is
no CELL_FACH and CELL_DCH state in LTE.
• Less signaling message in case of Reconfiguration: - In LTE there is only one
reconfiguration message to reconfigure all logical, transport and physical
channel where as in 3G-RNC system there are number of reconfiguration
message i.e. RB reconfiguration , TRCH configuration, PHY configuration.
• In LTE there is no NBAP protocol, this reduces the latency of the RRC
connection establishment and RB management procedure.
• There is no need to define URNTI, ERNTI, HRNTI, SRNTI in LTE, since
there is only one shared MAC entity.
• In LTE, there in no need to define activation time. Because of this there are
lots of synchronizing complexity in 3G-RNC systems i.e. Synchronizing
Radio link procedure based on activation time, synchronizing between the
various MAC entity. This reduces significantly latency during establishment
and reconfiguration of radio bearers.
• In LTE, there in no need to specify the RRC State in RRC message.
• For network control mobility, there is one feature which become very
important and critical i.e. CQI Reporting. CQI reporting should be fast and
correct for taking decision for mobility.


• There is no signaling connection release procedure in LTE, since there is only
one domain i.e. PS domain and the UE context is shared between the MME
and ENB and if UE is active in ENB then it should be active in MME also.


4 Architecture

4.1 RRC State
UE has two RRC state
• RRC_IDLE:- This state indicates that there is not signaling radio bearer is
established i.e. no RRC connection is established. RRC_IDLE state can
further characterized as follows
o Transfer of broadcast/multicast data to UE.
o A UE specific DRX may be configured by upper layers.
o UE controlled mobility.
o The UE:
 Monitors control channels associated with the shared data
channel to determine if data is scheduled for it.
 Performing neighboring cell measurements and measurement
reporting.
 Acquires system information.

• RRC_CONNECTED: - This state indicates that there is signaling radio
bearer established i.e. RRC connection is established. RRC_CONNECTED
state can be further characterized as follows
o Transfer of unicast data to/from an UE, transfer of
broadcast/multicast data to UE.
o At the lower layers, the UE may configure with a UE specific
DRX/DTX.
o Network Control Mobility, i.e. handover and cell change order with
network assistance (NACC) to GEREN.
o The UE:
 Monitors control channels associated with the shared data
channel to determine if data is scheduled for it
 Provides channel quality and feedback information.
 Performing neighboring cell measurements and measurement
reporting.
 Acquires system information.

4.2 Signaling Radio Bearers
"Signaling Radio Bearers" (SRBs) are defined as Radio Bearers (RB) that are used only
for the transmission of RRC and NAS messages. More specifically, the following three
SRBs are defined:
- SRB0 is for RRC messages using the CCCH logical channel;
- SRB1 is for NAS messages and for most RRC messages, all using DCCH logical
channel;
- SRB2 is for high-priority RRC messages, using DCCH logical channel.


CCCH DCCH DCCH

TM- SRB 0 TM- AM- SRB 1 AM- AM- SRB 2 AM-
UL DL DL UL DL UL

Figure 1 Signalling radio Bearer Configuration

Figure 1 shows the SRB configuration CCCH, DCCH are the logical channel between the
RRC and RLC layer. TM-UL is the transparent mode RLC entity used in uplink, UM-DL
is the unacknowledgement mode RLC entity used in DL, AM –DL is the
acknowledgement entity used in DL, AL-UL is the acknowledgement entity used in
uplink.

4.3 RRC Functions
The RRC protocol includes the following main functions:
- Broadcast of system information
o Including NAS common information;
o Information applicable to the UEs in RRC_IDLE e.g. cell (re-selection)
parameters, neighbouring cell information and information (also)
applicable for UEs in RRC_CONNECTED e.g. common channel
configuration information.
- RRC Connection Control
o Paging
o Establishment/Modification/release of RRC Connection, including e.g.
assignment/modification of UE identity (C-RNTI),
establishment/modification/release of SRB1 and SRB2, access class
barring;
o Initial security activation, i.e. initial configuration of AS integrity
protection (CP) and AS ciphering (CP, UP);
o RRC connection mobility including e.g. intra-frequency and inter-
frequency handover, associated security handling, i.e. key and/or
algorithm change, specification of RRC Context information transferred
between network nodes.


o Establishment/modification/release of point to point RBs carrying user
data.
o Radio configuration control including e.g. assignment/modification of
ARQ configuration, HARQ configuration , DRX configuration;
o QoS Control including assignment/modification of semi-persistent
configuration information of DL/UL assignment/modification of
parameters for UL rate control in the UE, i.e. allocation of a priority and
a prioritized bit rate (PBR) for each RB.
o Recovery from Radio link Failure.
- Inter-RAT mobility including e.g. security activation, transfer of RRC
context information.
- Measurement configuration control and reporting:
o Establishment/modification/release of measurements (e.g. Intra
frequency, inter frequency and inter RAT mobility, Quality, UE
internal, positioning)
o Configuration and deactivation of measurement gaps;
o Measurement Reporting
- Other functions including e.g. transfer of dedicated NAS Information and
non-3GPP dedicated information, transfer of UE Radio access capability
information, and support for E-UTRAN sharing (multiple PLMN
identities).
- Multicast/Broadcast
- Support of self configuration and self-optimisation.

4.4 RRC Procedures

4.4.1 Paging

UE EUTRAN

PAGING

Figure 2 Paging Procedure

The purpose of paging
- Transmit paging information to the UE in RRC_IDLE state.
- To inform UEs in RRC_IDLE about the system information change.

Paging message include paging records for UE which is to be paged. RRC needs
to configure the one TM RLC entity over PCCH logical channel to send the
paging message to the UE.


4.4.1.1 Differences with 3G-RNC System in Paging
In 3G-RNC system, there is two type of paging is defined i.e. paging Type 1 (idle,
CELL_PCH, URA_PCH) and paging Type 2 (CELL_DCH, CELL_FACH) and these
paging are specific to the CN Domain. In LTE this has become simpler because there is
only one domain and there is no state like CELL_PCH and URA_PCH. In LTE paging is
handled in RRC_IDLE state.

4.4.2 RRC Connection establishment

UE EUTRAN

RRC CONNECTION REQUEST

RRC CONNECTION SETUP

RRC CONNECTION SETUP COMPLETE

Figure 3 Successful Scenario of RRC Connection Establishment

The purpose of RRC Connection establishment
- To establish SRB1 only.
This procedure is initiated by the UE when the upper layer request the establishment
of a signalling connection while UE is in RRC_IDLE state. UE sends RRC Connection
Request message to ENB on SRB 0 and the US shall continue cell re-selection related
measurement as well as cell-reselection evaluation. If the contention resolution of the
RRC Connection Request is successful, as indicated by the lower layer, wait for RRC
Connection Setup Response from ENB. Otherwise retry to send the RRC Connection
Request message.
ENB performs the Admission Control based on its RRM algorithm. If ENB
permits the admission of the UE, ENB sends the RRC Connection Setup message to the
UE. RRC Connection setup message contains all the RLC (logical channel) and MAC
(transport layer) parameters to establish the SRB1. UE applies the configuration informed
in RRC Connection setup message. UE enters into RRC_CONNTECTED state and stop
the cell-reselection procedure.
After successfully applying the configuration UE sends the RRC Connection
setup complete message.

Ue-identity = UE_CONTENTION_RESOLUTION_IDENTITY.

Setting of UE_CONTENTION_RESOLUTION_IDENTITY


- If upper layer provides an S-TMSI. Upper layer will provide the S-TMSI if
the UE is registered in the TA of the current cell.
o Set Identity Type to “S-TMSI”
o Set the “S-TMSI” to the value received from upper layer.
- Else
o Set the identity type to “random number”
o Draw a random value and set the “Random number” to the selected value.

UE EUTRAN

RRC CONNECTION REQUEST

RRC CONNECTION REJECT

Figure 4 RRC connection establishment, network reject

ENB can reject the RRC connection establishment based on its admission control
algorithm. In this case ENB sends RRC Connection Reject message to the UE.

4.4.2.1 Difference with 3G-RNC system in RRC Connection
Establishment Procedure
• RRC Connection Request is very small in size in LTE as compared to 3G-
RNC. The main difference in both cases is the usage of UE identity. In LTE
UE identity is used as contention resolution identity because this is first
message from UE on the shared uplink channel where as in 3G RNC UE
identity is the initial UE identity. In LTE many IE have been removed from
RRC Connection Request message i.e. CN Domain Identity, Call type, HS-
PDSCH in CELL_FACH, MAC-ehs support, Access Stratum release
indicator, support of F-DPCH, UE mobility state indicator, Measured result
on RACH.
• In LTE UE identity is used as contention resolution identity. It is possible
that contention failure can happen; in this case UE will try again the RRC
connection request based on its timer and counter. RRC will come to know
about the contention result from random access response message from peer
MAC layer. In this procedure there is interaction with the MAC layer where
as in 3G-RNC there is no such interaction with the MAC layer.
• In LTE C-RNTI is indirectly allocated by MAC layer where as in 3G-RNC
system C-RNTI is allocated by the RRC layer and indicates to the MAC
layer. During random access procedure MAC Layer provides T-CRNTI to
the UE and UE uses this T-CRNTI as a CRNTI after successfully
completion of the RRC Connection establishment procedure.


• In LTE the default configuration is used for the radio bearer parameters.
There is no explicit configuration possible for RB where as in 3G-RNC
system explicit configuration is possible. The number of default
configuration in LTE is under FFS.
• RRC Connection Setup Complete message include the
nasDedicationInfomation IE which will reduce the NAS signalling delay. In
3G-RNC system the nas information is sent via uplink direct transfer
message.

Question
• Why there is no UE capabilities information in RRC Connection Setup
Complete message
• There is no START value defined in RRC Connection Setup Complete. In
3G-RNC system START value is defined for each domain. But I do not
know how this is handled in the LTE.

4.4.3 RRC Connection Reconfiguration

The purpose of this procedure
- Establish/modify/release RBs,
- To perform Handover
- To configure/modify measurements
- NAS dedicated information may be transferred from ENB to UE.

If AS-Security is enabled then only include Mobility Control Information IE and IEs
related to the RB establishment.

UE EUTRAN

RRC CONNECTION RECONFIGURATION

COMPLETE
Figure 5 RRC connection reconfiguration, successful


UE EUTRAN


FAILURE

Figure 6 RRC connection reconfiguration, failure

RRC Connection Reconfiguration message is used to establish one or more RBs. In this
procedure following broad level IEs are included.
• Measurement Configuration
• Nas dedicated information.
• Radio Resource Configuration.
• Mobility Control information.
• Security Configuration
• UE Related Information.

If UE successfully applied the configuration, It sends RRC Connection Reconfiguraion
Complete, otherwise RRC Connection Reconfiguration Fail

Reconfiguration Procedure

• In LTE, the prioritized bit rate is introduced in Uplink. The UE has an uplink
rate control function which manages the sharing of uplink resources between
radio bearers. RRC controls the uplink rate control function by giving each
bearer a priority and a prioritized bit rate (PBR). PBR is a parameter set
internal to the ENodeB and is not signaled over the S1 interface as QoS
parameter. The uplink rate control function ensures that the UE serves its
radio bearer(s) in the following sequence:
o All the radio bearer(s) in decreasing priority order up to their PBR;
o All the radio bearer(s) in decreasing priority order for the remaining
resources assigned by the grant
NOTE: In case the PBRs are all set to zero, the first step is skipped and the
radio bearer(s) are served in strict priority order: the UE maximizes the
transmission of higher priority data
• Since LTE is having only one state in RRC connected mode i.e.
RRC_CONNECTED, that’s why the complexity is reduced significantly as
compared to the 3G-RNC.
• In LTE there is only one message define for the reconfiguration where as in
3G-RNC system 3 procedures are there to change the radio bearer


configurations i.e radio bearer reconfiguration, transport channel
reconfiguration and physical channel reconfiguration.
• RB mapping Info is much simpler as compared to the 3G-RNC system.
• Transport channel and physical channel information IE is significantly
reduced as compared to the 3G-RNC system due to use of shared transport
and physical channel. There is no common and dedicated transport and
physical channel define in LTE.
• In LTE, at RRC level only one RNTI is maintained i.e. CRNTI which is
generated by MAC layer and informed to RRC Layer.
• In LTE, there is provision to change the security configuration using RRC
Connection Reconfiguration where as in 3G-RNC system, it was handled
using security mode command procedure.
• In LTE, RRC Connection reconfiguration can be also used to send NAS
dedicated signalling to the MS to reduce the latency where as this option is not
in 3G-RNC system.

4.4.4 RRC Connection Re-establishment

The purpose of this procedure is re-establish the RRC connection, which involved
resumption of SRB1 operation and re-activation of security.
A UE in RRC_CONNECTED, for which security has been activated, may initiate
the procedure in order to continue the RRC connection. The connection re-establishment
succeeds only if the concerned cell is prepared i.e. has a valid UE context. In case E-
UTRAN accepts the re-establishment, SRB1 operation resumes while the operation of
other radio bearers remains suspended. E-UTRAN applies the procedure as follows:
- to reconfigure SRB1 and to resume data transfer only for this RB;
- to re-activate security without changing algorithms.

UE EUTRAN

RRC CONNECTION RE-ESTABLISHMENT
REQUEST


COMPLETE

Figure 7 RRC connection re-establishment, successful


UE EUTRAN

REQUEST

REJECT
Figure 8 RRC connection re-establishment, successful

The UE shall initiate this procedure when security as been activated. The UE initiates the
procedure when one of the following conditions is met:
- Upon re-entry of the service area after having detected radio link failure;
- Upon handover failure
- When lower layers detect problems, as specified in TS 36.322 [7];

Reestablishment Procedure
• In 3G-RNC System, for indicating radio link failure and lower layers failure
CELL UPDATE procedure is used where as in LTE RRC Connection
reestablishment procedure is used.
• The handling of Radio Link Failure case is still FFS. There are various
proposals for handling radio link failure going on.

4.4.5 Initial Security Activation

The purpose of this procedure is to activate AS security upon RRC connection
establishment. ENB initiates the security mode command procedure to a UE in
RRC_CONNECTED. Moreover, ENB applies the procedure as follows:
- When only SRB1 is established, i.e. prior to establishment of SRB2 and/ or
DRBs.

UE EUTRAN

SECURITY MODE COMMAND

SECURITY MODE COMPLETE

Figure 9 Security mode command, successful


UE EUTRAN

SECURITY MODE COMMAND

SECURITY MODE FAILURE

Figure 10 Security Mode command, failure

RRC Specification for LTE does not specify about the START value. The security
specification is also under FFS.

4.4.6 RRC Connection Release
The purpose of this procedure is to release the RRC connection, which includes the
release of the signaling connection, the established EPS bearers as well as all radio
resources. E-UTRAN initiates the RRC connection release procedure to a UE in
RRC_CONNECTED. It is FFS if redirection can be done from E-UTRAN before
security is activated.

UE EUTRAN

RRC CONNECTION RELEASE

Figure 11 RRC connection release, successful

4.4.7 DL Information Transfer
The purpose of this procedure is to transfer NAS or (tunnelled) non-3GPP dedicated
information from E-UTRAN to a UE in RRC_CONNECTED. E-UTRAN initiates the
DL information transfer procedure whenever there is a need to transfer NAS or non-
3GPP dedicated information. E-UTRAN initiates the DL information transfer procedure
by sending the DL INFORMATION TRANSFER message.

UE EUTRAN

DL INFORMATION TRANSFER


4.4.8 UL Information Transfer
The purpose of this procedure is to transfer NAS or (tunnelled) non-3GPP dedicated
information from the UE to E-UTRAN. A UE in RRC_CONNECTED initiates the UL
information transfer procedure whenever there is a need to transfer NAS or non-3GPP
dedicated information. The UE initiates the UL information transfer procedure by
sending the UL INFORMATION TRANSFER message.

UE EUTRAN

UL INFORMATION TRANSFER


4.4.9 Handover Procedure

4.4.9.1 Handover from E-UTRA to other RAT
(UTRAN/GERAN/CDMA2000)

UE E-UTRA MME Inter RAT Inter RAT
AS NAS
Decision for HO

HO Required

UN known Message?

Relocation Request

Relocation Request Ack

Un known Message?
HO Command

HO Preparation failure

Forwarding of Data

1. Mobility from EUTRA in RRC Container of ENB

2. HO From E UTRA Preparation request (CDMA
2000) in RRC Container of ENB

Figure 12Protocol Message Flow between UE, ENB and MME in case of HO
The purpose of this procedure is to move a UE in RRC_CONNECTED to a cell using
another Radio Access Technology (RAT), e.g. GERAN, UTRA or CDMA2000 systems.
The mobility from E-UTRA procedure covers both:
- Handover, i.e. the MOBILITY FROM E-UTRA message includes radio resources
that have been allocated for the UE in the target cell and
- Cell change order, i.e. the MOBILITY FROM E-UTRA message may include
information facilitating access of and/ or connection establishment in the target cell, e.g.
system information. Cell change order is applicable only to GERAN.
The mobility from E-UTRA procedure applies when signaling radio bearers are
established, possibly in combination with EPS bearers.


4.4.9.2 Handover From other RAT (UTRAN/GERAN/CDMA2000) to
E-UTRA

UE E-UTRA MME Inter RAT Inter RAT
AS NAS

Decision for HO

Relocation Request
Un known Message ?

HO Request

HO Request Ack

HO Failure
Un known Message ?

Relocation Command

Forwarding of Data

RRC Connection Reconfiguration in RRC Container of other RAT

HO Notify

RRC Connection Reconfiguration Complete

Figure 13 Protocol Message Flow between UE, ENB and MME in case of HO

The purpose of this procedure is to, under the control of the network; transfer a
connection between the UE and another Radio Access Network (e.g. GERAN or
UTRAN) to E-UTRAN. The handover to E-UTRA procedure applies when signaling
radio bearers are established, possibly in combination with (EPS) bearers. In case only
signaling radio bearers are established, it is FFS if the default EPS bearer is established
during handover. It is FFS if handover to E-UTRAN may be initiated while security is
not activated in the other RAT.


4.4.9.3 Intra Handover A2000) to E-UTRA

eNB source eNB target
UE
sector sector

UL allocation
1. Measurement reports

eNB source sector makes
HO decision to move UE to a
eNB target sector

2. Context data (UE RAN
context + intra-eNB flag)

Intra-eNB
handover Store UE RAN context,
(proprietary) reserve C-RNTI

3. Context confirm
(new C-RNTI...)
DL allocation

4. Handover command
(new C-RNTI etc. + intra-
eNB flag)

Detach from old cell and Deliver buffered and in
synchronize to new cell transit packets + RLC,
MAC, and HARQ
context to target sector

Deliver data

Buffer packets from
target sector

Synchronisation
UL allocation + TA for UE
6. Handover confirm
7. Handover completed


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