Lte_system_basic_signaling_procedure.pptx
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- Words: 2,449
- Pages: 37
Security Level:
2011-5-9
LTE Basic Signaling Procedure www.huawei.com
HUAWEI TECHNOLOGIES CO., LTD.
Huawei Confidential
Training Objectives
After completing this course, you will be able to:
Understand the concept of the E-UTRAN.
Understand the basic LTE signaling procedure.
Understand the typical signaling procedures such as the attach procedure, paging, and handover.
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Service Bearer Architecture
The radio bearer is used to transmit evolved packet system (EPS) data packets between the UE and the eNodeB, which indicates the one-to-one relationship between the EPS bearer and radio bearer. The S1 bearer is used to transmit the EPS packets between the eNodeB and the serving GW. The eNodeB saves the one-to-one mapped relationship between the radio bearer and the S1 interface, and therefore the radio bearer and the S1 interface are bound in the uplink and downlink.
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QoS Bearers QCI
Type
Priority
Packet Delay Budget (ms)
Packet Error Rate
Example Service
1
GBR
2
100
10-2
Conversational Voice
2
GBR
4
150
10-3
Conversational Video
3
GBR
3
50
10-3
Real Time Gaming
4
GBR
5
300
10-6
Non-Conversational Voice
5
Non-GBR
1
100
10-6
IMS Signaling
6
Non-GBR
6
300
10-6
Video, TCP Based
7
Non-GBR
7
100
10-3
Voice, Video, Interactive Gaming
8
Non-GBR
8
300
10-6
Video, TCP Based
9
Non-GBR
9
300
10-6
Video, TCP Based
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Default and Dedicated Bearers Default EPS Bearer
UE
TFT
PDN-GW
Dedicated EPS Bearer (Maximum of 7)
TFT
Each Dedicated EPS Bearers has an associated TFT (Traffic Flow Template)
Default and dedicated bearers In the EPS system, when the PDN connected, the default bearer provides the UE with a permanent online IP connection continuously . The dedicated bearers are the different EPS bearers which connected to the same PDN. To establish or modify the dedicated bearers is completed only by the network side and the QoS parameter value of bearer is allocated by the EPC. Scenario for setting up dedicated bearers When the UE needs to provide a special service, the dedicated bearers are set up between the UE and the EPC. To establish the dedicated bearers is completed only by the network side, but the UE could trigger to establish the dedicated bearers at network side(Such as Samsung phone ).
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identify of Application Protocol EPS Bearer Identity
The EPS bearer Identity is used to identify the EPS bearers when the UE access the attach procedure through
the E-UTRAN.
The MME allocates the EPS bearer identifiers.
There exists a one-to-one mapping between the EPS RB and the EPS bearers and the mapping is provided by
the E-UTRAN. eNB UE S1AP ID The
eNodeB UE S1AP ID identifies the unique UE corresponding to the S1 interface at the same eNodeB.
MME UE S1AP ID The
MME UE S1AP ID identifies the unique UE corresponding to the S1 interface in the MME.
Old eNB UE X2AP ID The
Old eNB UE X2AP ID identifies the unique UE corresponding to the X2 interface in the original eNodeB.
News eNB UE X2AP ID The
New eNB UE X2AP ID identifies the unique UE corresponding to the X2 interface in the target eNodeB.
C-RNTI The
C-RNTI identifies the unique UE when the eNB cell indicates UE in the RRC connection and scheduling
procedure, It’s unique in one cell.
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Contents 1. E-UTRAN Concept 2. E-UTRAN Signaling Procedure
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Contents 1. E-UTRAN Concept 2. E-UTRAN Signaling Procedure 1. UE Attach Procedure
2. Paging Procedure
3. Handover Procedure
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UE Attach Procedure Description Cell search
When the UE power on, the first thing UE to do is searching the available network. Actually, it is a downlink synchronization procedure.
Random Access
The random access is aimed to resolve the contention between different UEs and achieve the uplink synchronization.
Attach
establish the same mobility context between the UE and the MME establish the default bearers between the UE and the PDN GW the UE obtains the IP address allocated by the network through the EPS attach procedure.
Common Procedure
The common procedure consists of the authentication and security mode. Not necessary
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UE Attach Procedure 文档密级
文档名称
+ UE
MME
eNode RRC Connection Request
B
RRC Connection Setup RRC Connection Setup Complete SRB1 signal, with Nas signal in it DL Information Transfer
Establish UE context， SRB1 resource admission and resource distribution Initial UE Message
NAS signal： Attach Request、 PDN Connectivity Request
DL NAS Transfer Authenticati
UL Information Transfer
on UL NAS Transfer UL NAS Transfer
DL Information Transfer
NAS
UL Information Transfer
encryption UL NAS Transfer NAS signal： Attach Accept、 Active Default EPS Bearer context Request
Initial Context Setup Request Security Mode Command
Uu interface encryption
Security Mode Complete UE Capability Enquiry UE Capability Information
UE capability information transfer
UE Capability Information Indication RRC Connection Reconfiguration RRC Connection Reconfiguration Complete Initial Context Setup Response UL Information Transfer
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NAS signal: Attach complete, Active Default EPS Bearer context
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RRC Connection Setup RRC Connection Request UE Identity Cause
UE
eNB RRC Connection Request RRC Connection Setup RRC Connection Setup Complete
RRC Connection Setup Radio Resource Config Dedicated - srb-ToAddModList - drb-ToAddModList - drb-ToReleaseList - MAC Main Config - SPS Config - Physical Config Dedicated
RRC Connection Setup Complete Selected PLMN-Identity Registered MME Dedicated Info NAS
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S1 Initial Context Setup Request
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S1 Initial Context Setup Request Message analysis
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RRC Security Mode Command
UE
eNB
Security Mode Command Ciphering Algorithm Integrity Protection Algorithm
Security Mode Command Security Mode Complete Security Mode Failure
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UE Capability Information Reports UE
EUTRAN
UECapabilityEnquiry
UECapabilityInformation
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RRC Connection Reconfiguration The RRC connection reconfiguration is used for establishing the SRB2 and default bearer DRB1. UE
EUTRAN
RRCConnectionReconfiguration
RRCConnectionReconfigurationComplete
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Initial Context Setup
eNB
Initial Context Setup Response MME UE S1AP ID eNB UE S1AP ID E-RAB Setup List - E-RAB ID - Transport Layer Address - GTP-TEID E-RAB Failed to Setup List (O) Criticality Diagnostics (O)
MME
S-GW
Initial Context Setup Request Modify Bearer
Initial Context Setup Response eNB Address and TEID
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S-GW Address and TEID
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UE Attach Procedure Uu interface signaling trace
S1 interface signaling trace
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Contents 1. E-UTRAN Concept 2. E-UTRAN Signaling Procedure 1. UE Attach Procedure
2. Paging Procedure
3. Handover Procedure
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Paging Procedure When the UE is in the idle state and there arrives the downlink data, the paging procedure is started at the network side.
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Paging Procedure
Uu interface trace signaling at the eNodeB side
S1 interface trace signaling at the eNodeB side
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Contents 1. E-UTRAN Concept 2. E-UTRAN Signaling Procedure 1. UE Attach Procedure
2. Paging Procedure
3. Handover Procedure
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Handover Description Three Types of Intra-RAT Handover
S1
S1
X2 Handover
Uu
Handover
Uu
Intra-eNodeB Handover
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Handover
Uu
Inter-eNodeB handover based on X2 Interface
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Uu
Uu
Inter-eNodeB handover based on S1 Interface
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Handover Description A handover consists of three steps: handover measurement, handover decision, and handover execution. In the step of handover measurement: the UE executes related measurements according to the measurement configuration messages(RRC-CONN-RECFG) received by the eNodeB, then UE sends measurement results(MR) to the eNodeB. In the step of handover decision: the eNodeB evaluates the measurement results
reported by the UE and determines whether to start a handover. In the step of handover execution: the eNodeB notifies the UE to handover to the target cell based on the handover decision. The whole handover procedure includes six steps which are the measure control delivery, measure report, handover decision, handover resource preparation,
handover execution, and original cell resource release.
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Measurement Events
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Handover Description (Measurement Control)
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Handover Description (Measurement Reports)
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Handover Description (Handover Decision)
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Intra-eNodeB Handover The intra-eNodeB handover procedure is relatively simple. the intra-eNodeB handover only upgrade the resources of uu interface. the resources application between the source cells and the target cells completed through the internal eNodeB messages. and the resources release in the source cells also completed by the
internal eNodeB messages. In this procedure, there is no data retransmit at the inter-eNodeB, and no message exchange at the EPC.
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Intra-eNodeB Handover UE
Source Cell
Target Cell
eNB
Serving Gateway
MME/MMEs
Area Restriction Provided
1. Measurement Control packet data
packet data
packet data The UE reports the Measurement result message in the source cell. Legend
UL allocation 2. Measurement Reports Measurement Reports
L1/L2 signalling
Handover Pre paration
L3 signalling
The eNodeB sends a handover command after User Data completing admission and radio resource allocation 3. HO decision in the target cell. Handover Command DL allocation 4. Handover Command
packet data
Detach from old cell and synchronize to new cell
The UE accesses the target cell. 5. Synchronization 6. UL allocation + TA for UE
Handover Execution
Buffer packets from MME
The handover is complete, and the cell resources are released in the source cell.
7. Handover Confirm
Handover Completion
Handover Confirm
Flush DL buffer, continue delivering in transit packets
packet data
packet data
packet data
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Handover Signaling at the eNodeB
Uu trace signaling at the UE side
Uu trace signaling at the eNodeB side
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Inter-eNodeB Handover on the X2 Interface The handover on the X2 interface is triggered by the event A3 report , the target cell and the source cell must belong to the two different eNodeBs which exist the X2 links. when the source eNodeB receives the measurement reports by the UE and decides UE to hand over to the target eNodeB . The source eNodeB applies for resources through the X2 interface from the target eNodeB and completes the resource preparation for the target eNodeB . then, the source eNodeB notifies the UE to hand over to the target eNodeB by the reconfiguration message through the Uu interface. After the handover has completed, the target eNodeB notifies the source
eNodeB to release the radio resources in the source eNodeB . In addition, the data which is not transmitted entirely from the source eNodeB will retransmit to the target eNodeB and update node relationship between the user plane and control plane.
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Inter-eNodeB Handover On the X2 Interface (I) The source eNodeB delivers measurement control information to UE and notifies UE Source eNB the UE to start the neighbor cell measurement.
The users access the network Target eNB
Serving
MME
Gateway
0. Area Restriction Provided 1. Measurement Control
After detecting the cell measurement thatmessage meet theto theLegend UL allocation start the handover preparation procedure, the source eNodeB transmits the Handover result Request target threshold, the UE reports the Measurement Reports. L3 signalling eNodeB and carries the current service information and otherThe access information encryption, integrality, and source eNodeBincluding makes handover decision based 2. Measurement Reports measurement. on the handover algorithm and current state. L1/L2 signalling 3. HO decision
The target eNodeB returns the admission and Userresults Data resource configuration information to the source eNodeB. In this step, the preparation of handover Admission Control has5.completed. The source eNodeB transmits the handover message from the target 4.
6. Handover Request Ack eNodeB through the Uu interface to the UE and notifies that the UE executes the handover command.
DL allocation
Detach from old cell and synchronize to new cell
Handover Command Deliver buffered and in transit packets to target eNB 8.
SN Status Transfer
Handover Execution
7.
Handover Request radio
After receiving the HandoverReq message from the source eNodeB, the target eNodeB starts admission based on the carried service information then configures radio resources. Handover Preparation
packet data
packet data
The data starts to be forwarding
Data Forwarding
Buffer packets from Source eNB 9. 10.
Synchronisation UL allocation
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TA for UE
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Inter-eNodeB Handover on the X2 Interface(II) After UE and the target eNodeB complete the random access, the Handover Confirm message is transmitted to the target eNodeB.
UE
Source eNB
Target eNB
Serving
MME
Gateway
After receiving the HandoverConfirm message from the UE, the target eNodeB starts the PathSwitch procedure to the MME to complete the user plane handover.
11. Handover Confirm 13. User Plane update request
After completing the user plane handover End Marker from the S-GW, the MME transmits the Switch DL path 14. PathSwitchRsp message to the target eNodeB to notify that the user plane 15.User Plane update handover is complete. response 16.Path Switch RequestisAck After the PathSwitch message complete, the target eNB notifies the source eNodeB of releasing resources, and in this step the handover procedure has completed. 17. Release Resource Flush DL buffer, continue delivering in -transit packets
Data Forwarding End Marker
18. Release Resources packet data
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Handover Completion
12. Path Switch Request
Inter-eNodeB Handover on the X2 Interface
Uu trace signaling at the UE
Uu interface trace signaling at the source eNodeB side
X2 interface trace signaling at the source eNodeB side
Uu interface trace signaling at the eNodeB side
S1 interface trace signaling at the target eNodeB side
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Inter-eNodeB Handover on the S1 Interface The S1 handover is similar to the X2 handover. The difference is that there is no direct link between eNodeBs. So Handover Request, Handover Request Acknowledge and data retransmit messages
requires to be retransmit by the S1 interface .
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Thank you www.huawei.com
2011-5-9
LTE Basic Signaling Procedure www.huawei.com
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Huawei Confidential
Training Objectives
After completing this course, you will be able to:
Understand the concept of the E-UTRAN.
Understand the basic LTE signaling procedure.
Understand the typical signaling procedures such as the attach procedure, paging, and handover.
HUAWEI TECHNOLOGIES CO., LTD.
Huawei Confidential
Page 2
Service Bearer Architecture
The radio bearer is used to transmit evolved packet system (EPS) data packets between the UE and the eNodeB, which indicates the one-to-one relationship between the EPS bearer and radio bearer. The S1 bearer is used to transmit the EPS packets between the eNodeB and the serving GW. The eNodeB saves the one-to-one mapped relationship between the radio bearer and the S1 interface, and therefore the radio bearer and the S1 interface are bound in the uplink and downlink.
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QoS Bearers QCI
Type
Priority
Packet Delay Budget (ms)
Packet Error Rate
Example Service
1
GBR
2
100
10-2
Conversational Voice
2
GBR
4
150
10-3
Conversational Video
3
GBR
3
50
10-3
Real Time Gaming
4
GBR
5
300
10-6
Non-Conversational Voice
5
Non-GBR
1
100
10-6
IMS Signaling
6
Non-GBR
6
300
10-6
Video, TCP Based
7
Non-GBR
7
100
10-3
Voice, Video, Interactive Gaming
8
Non-GBR
8
300
10-6
Video, TCP Based
9
Non-GBR
9
300
10-6
Video, TCP Based
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Default and Dedicated Bearers Default EPS Bearer
UE
TFT
PDN-GW
Dedicated EPS Bearer (Maximum of 7)
TFT
Each Dedicated EPS Bearers has an associated TFT (Traffic Flow Template)
Default and dedicated bearers In the EPS system, when the PDN connected, the default bearer provides the UE with a permanent online IP connection continuously . The dedicated bearers are the different EPS bearers which connected to the same PDN. To establish or modify the dedicated bearers is completed only by the network side and the QoS parameter value of bearer is allocated by the EPC. Scenario for setting up dedicated bearers When the UE needs to provide a special service, the dedicated bearers are set up between the UE and the EPC. To establish the dedicated bearers is completed only by the network side, but the UE could trigger to establish the dedicated bearers at network side(Such as Samsung phone ).
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identify of Application Protocol EPS Bearer Identity
The EPS bearer Identity is used to identify the EPS bearers when the UE access the attach procedure through
the E-UTRAN.
The MME allocates the EPS bearer identifiers.
There exists a one-to-one mapping between the EPS RB and the EPS bearers and the mapping is provided by
the E-UTRAN. eNB UE S1AP ID The
eNodeB UE S1AP ID identifies the unique UE corresponding to the S1 interface at the same eNodeB.
MME UE S1AP ID The
MME UE S1AP ID identifies the unique UE corresponding to the S1 interface in the MME.
Old eNB UE X2AP ID The
Old eNB UE X2AP ID identifies the unique UE corresponding to the X2 interface in the original eNodeB.
News eNB UE X2AP ID The
New eNB UE X2AP ID identifies the unique UE corresponding to the X2 interface in the target eNodeB.
C-RNTI The
C-RNTI identifies the unique UE when the eNB cell indicates UE in the RRC connection and scheduling
procedure, It’s unique in one cell.
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Contents 1. E-UTRAN Concept 2. E-UTRAN Signaling Procedure
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Contents 1. E-UTRAN Concept 2. E-UTRAN Signaling Procedure 1. UE Attach Procedure
2. Paging Procedure
3. Handover Procedure
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UE Attach Procedure Description Cell search
When the UE power on, the first thing UE to do is searching the available network. Actually, it is a downlink synchronization procedure.
Random Access
The random access is aimed to resolve the contention between different UEs and achieve the uplink synchronization.
Attach
establish the same mobility context between the UE and the MME establish the default bearers between the UE and the PDN GW the UE obtains the IP address allocated by the network through the EPS attach procedure.
Common Procedure
The common procedure consists of the authentication and security mode. Not necessary
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UE Attach Procedure 文档密级
文档名称
+ UE
MME
eNode RRC Connection Request
B
RRC Connection Setup RRC Connection Setup Complete SRB1 signal, with Nas signal in it DL Information Transfer
Establish UE context， SRB1 resource admission and resource distribution Initial UE Message
NAS signal： Attach Request、 PDN Connectivity Request
DL NAS Transfer Authenticati
UL Information Transfer
on UL NAS Transfer UL NAS Transfer
DL Information Transfer
NAS
UL Information Transfer
encryption UL NAS Transfer NAS signal： Attach Accept、 Active Default EPS Bearer context Request
Initial Context Setup Request Security Mode Command
Uu interface encryption
Security Mode Complete UE Capability Enquiry UE Capability Information
UE capability information transfer
UE Capability Information Indication RRC Connection Reconfiguration RRC Connection Reconfiguration Complete Initial Context Setup Response UL Information Transfer
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UL NAS Transfer
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NAS signal: Attach complete, Active Default EPS Bearer context
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RRC Connection Setup RRC Connection Request UE Identity Cause
UE
eNB RRC Connection Request RRC Connection Setup RRC Connection Setup Complete
RRC Connection Setup Radio Resource Config Dedicated - srb-ToAddModList - drb-ToAddModList - drb-ToReleaseList - MAC Main Config - SPS Config - Physical Config Dedicated
RRC Connection Setup Complete Selected PLMN-Identity Registered MME Dedicated Info NAS
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S1 Initial Context Setup Request
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S1 Initial Context Setup Request Message analysis
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RRC Security Mode Command
UE
eNB
Security Mode Command Ciphering Algorithm Integrity Protection Algorithm
Security Mode Command Security Mode Complete Security Mode Failure
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UE Capability Information Reports UE
EUTRAN
UECapabilityEnquiry
UECapabilityInformation
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RRC Connection Reconfiguration The RRC connection reconfiguration is used for establishing the SRB2 and default bearer DRB1. UE
EUTRAN
RRCConnectionReconfiguration
RRCConnectionReconfigurationComplete
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Initial Context Setup
eNB
Initial Context Setup Response MME UE S1AP ID eNB UE S1AP ID E-RAB Setup List - E-RAB ID - Transport Layer Address - GTP-TEID E-RAB Failed to Setup List (O) Criticality Diagnostics (O)
MME
S-GW
Initial Context Setup Request Modify Bearer
Initial Context Setup Response eNB Address and TEID
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S-GW Address and TEID
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UE Attach Procedure Uu interface signaling trace
S1 interface signaling trace
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Contents 1. E-UTRAN Concept 2. E-UTRAN Signaling Procedure 1. UE Attach Procedure
2. Paging Procedure
3. Handover Procedure
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Paging Procedure When the UE is in the idle state and there arrives the downlink data, the paging procedure is started at the network side.
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Paging Procedure
Uu interface trace signaling at the eNodeB side
S1 interface trace signaling at the eNodeB side
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Contents 1. E-UTRAN Concept 2. E-UTRAN Signaling Procedure 1. UE Attach Procedure
2. Paging Procedure
3. Handover Procedure
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Handover Description Three Types of Intra-RAT Handover
S1
S1
X2 Handover
Uu
Handover
Uu
Intra-eNodeB Handover
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Uu
Handover
Uu
Inter-eNodeB handover based on X2 Interface
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Uu
Uu
Inter-eNodeB handover based on S1 Interface
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Handover Description A handover consists of three steps: handover measurement, handover decision, and handover execution. In the step of handover measurement: the UE executes related measurements according to the measurement configuration messages(RRC-CONN-RECFG) received by the eNodeB, then UE sends measurement results(MR) to the eNodeB. In the step of handover decision: the eNodeB evaluates the measurement results
reported by the UE and determines whether to start a handover. In the step of handover execution: the eNodeB notifies the UE to handover to the target cell based on the handover decision. The whole handover procedure includes six steps which are the measure control delivery, measure report, handover decision, handover resource preparation,
handover execution, and original cell resource release.
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Measurement Events
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Handover Description (Measurement Control)
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Handover Description (Measurement Reports)
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Handover Description (Handover Decision)
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Intra-eNodeB Handover The intra-eNodeB handover procedure is relatively simple. the intra-eNodeB handover only upgrade the resources of uu interface. the resources application between the source cells and the target cells completed through the internal eNodeB messages. and the resources release in the source cells also completed by the
internal eNodeB messages. In this procedure, there is no data retransmit at the inter-eNodeB, and no message exchange at the EPC.
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Intra-eNodeB Handover UE
Source Cell
Target Cell
eNB
Serving Gateway
MME/MMEs
Area Restriction Provided
1. Measurement Control packet data
packet data
packet data The UE reports the Measurement result message in the source cell. Legend
UL allocation 2. Measurement Reports Measurement Reports
L1/L2 signalling
Handover Pre paration
L3 signalling
The eNodeB sends a handover command after User Data completing admission and radio resource allocation 3. HO decision in the target cell. Handover Command DL allocation 4. Handover Command
packet data
Detach from old cell and synchronize to new cell
The UE accesses the target cell. 5. Synchronization 6. UL allocation + TA for UE
Handover Execution
Buffer packets from MME
The handover is complete, and the cell resources are released in the source cell.
7. Handover Confirm
Handover Completion
Handover Confirm
Flush DL buffer, continue delivering in transit packets
packet data
packet data
packet data
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packet data
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Handover Signaling at the eNodeB
Uu trace signaling at the UE side
Uu trace signaling at the eNodeB side
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Inter-eNodeB Handover on the X2 Interface The handover on the X2 interface is triggered by the event A3 report , the target cell and the source cell must belong to the two different eNodeBs which exist the X2 links. when the source eNodeB receives the measurement reports by the UE and decides UE to hand over to the target eNodeB . The source eNodeB applies for resources through the X2 interface from the target eNodeB and completes the resource preparation for the target eNodeB . then, the source eNodeB notifies the UE to hand over to the target eNodeB by the reconfiguration message through the Uu interface. After the handover has completed, the target eNodeB notifies the source
eNodeB to release the radio resources in the source eNodeB . In addition, the data which is not transmitted entirely from the source eNodeB will retransmit to the target eNodeB and update node relationship between the user plane and control plane.
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Inter-eNodeB Handover On the X2 Interface (I) The source eNodeB delivers measurement control information to UE and notifies UE Source eNB the UE to start the neighbor cell measurement.
The users access the network Target eNB
Serving
MME
Gateway
0. Area Restriction Provided 1. Measurement Control
After detecting the cell measurement thatmessage meet theto theLegend UL allocation start the handover preparation procedure, the source eNodeB transmits the Handover result Request target threshold, the UE reports the Measurement Reports. L3 signalling eNodeB and carries the current service information and otherThe access information encryption, integrality, and source eNodeBincluding makes handover decision based 2. Measurement Reports measurement. on the handover algorithm and current state. L1/L2 signalling 3. HO decision
The target eNodeB returns the admission and Userresults Data resource configuration information to the source eNodeB. In this step, the preparation of handover Admission Control has5.completed. The source eNodeB transmits the handover message from the target 4.
6. Handover Request Ack eNodeB through the Uu interface to the UE and notifies that the UE executes the handover command.
DL allocation
Detach from old cell and synchronize to new cell
Handover Command Deliver buffered and in transit packets to target eNB 8.
SN Status Transfer
Handover Execution
7.
Handover Request radio
After receiving the HandoverReq message from the source eNodeB, the target eNodeB starts admission based on the carried service information then configures radio resources. Handover Preparation
packet data
packet data
The data starts to be forwarding
Data Forwarding
Buffer packets from Source eNB 9. 10.
Synchronisation UL allocation
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TA for UE
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Inter-eNodeB Handover on the X2 Interface(II) After UE and the target eNodeB complete the random access, the Handover Confirm message is transmitted to the target eNodeB.
UE
Source eNB
Target eNB
Serving
MME
Gateway
After receiving the HandoverConfirm message from the UE, the target eNodeB starts the PathSwitch procedure to the MME to complete the user plane handover.
11. Handover Confirm 13. User Plane update request
After completing the user plane handover End Marker from the S-GW, the MME transmits the Switch DL path 14. PathSwitchRsp message to the target eNodeB to notify that the user plane 15.User Plane update handover is complete. response 16.Path Switch RequestisAck After the PathSwitch message complete, the target eNB notifies the source eNodeB of releasing resources, and in this step the handover procedure has completed. 17. Release Resource Flush DL buffer, continue delivering in -transit packets
Data Forwarding End Marker
18. Release Resources packet data
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packet data
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Handover Completion
12. Path Switch Request
Inter-eNodeB Handover on the X2 Interface
Uu trace signaling at the UE
Uu interface trace signaling at the source eNodeB side
X2 interface trace signaling at the source eNodeB side
Uu interface trace signaling at the eNodeB side
S1 interface trace signaling at the target eNodeB side
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Inter-eNodeB Handover on the S1 Interface The S1 handover is similar to the X2 handover. The difference is that there is no direct link between eNodeBs. So Handover Request, Handover Request Acknowledge and data retransmit messages
requires to be retransmit by the S1 interface .
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