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LTE – Handover &
Mobility Overview
LTE Nodes & Interfaces (Logical View)
S1 Handover - Source eNB
S1 Handover - Target eNB
X2 Handover - Source eNB
X2 Handover - Target eNB
Intra-LTE HO (within one MME pool).
S1
X2
S1
eNode BeNode B
MME/S-GW
VI
III
II
IV
I
V
eNode BeNode B
I. Handover RequestII. Handover Request AckIII. Handover CommandIV. “Start Packet Forwarding”V. Handover ConfirmVI. Path SwitchVII. Path Switch AckVIII. Release Resource
VII
Source Target
VII
S/P-GW
CP & UP message sequence flow
Interworking with 2G/3G.
Handover
CELL_PCH
URA_PCH
CELL_DCH
UTRA_Idle
E-UTRA
RRC_CONNECTED
E-UTRA
RRC_IDLE
GSM_Idle/GPRS
Packet_Idle
GPRS Packet
transfer mode
GSM_Connected
Handover
ReselectionReselection
Reselection
Connection
establishment/release
Connection
establishment/release
Connection
establishment/release
CCO,
Reselection
CCO with
NACC
CELL_FACH
CCO, Reselection +
PDP context est*
PMM_CONNECTED
PMM_IDLE
* PDP Context establishment is needed if no PDP context exists
Reselection +
PDP context est*
EMM_CONNECTED
EMM_IDLE
PMM_DETACHED EMM_DETACHED Idle
Cell change
(without signaling)
Cell change
(without signaling)
LTE to 3G Handover
SGSN
RNC
Node B
MME
eNode B
sourceS-GW
PDN-GW
targetS-GW
1
1. Handover Required2. Forward Relocation Request3. Create PDP Context Request4. Create PDP Context Response
5. Relocation Request6. Relocation Request Ack7. Update PDCP Context Request
8. Update PDP Context Response9. Forward Relocation Response10. Create Bearer Request
11. Create Bearer Response12. HO Command13. HO from E-UTRAN Command14. HO to UTRAN Complete
15. Relocation Complete16. Forward Relocation Complete17. Forward Relocation Complete Ack
18. Update PDP Context Request19. Update Bearer Request20. Update Bearer Response21. Update PDP Context Response
2
34
5 6
78
9
10
11
12
1314
15
16
1718
19
20
21
SGSNSGSN
RNC
Node BNode B
MME
eNode BeNode B
sourceS-GW
PDN-GW
targetS-GW
1
1. Handover Required2. Forward Relocation Request3. Create PDP Context Request4. Create PDP Context Response
5. Relocation Request6. Relocation Request Ack7. Update PDCP Context Request
8. Update PDP Context Response9. Forward Relocation Response10. Create Bearer Request
11. Create Bearer Response12. HO Command13. HO from E-UTRAN Command14. HO to UTRAN Complete
15. Relocation Complete16. Forward Relocation Complete17. Forward Relocation Complete Ack
18. Update PDP Context Request19. Update Bearer Request20. Update Bearer Response21. Update PDP Context Response
2
34
5 6
78
9
10
11
12
1314
15
16
1718
19
20
21
LTE to 3G Cell-reselection
SGSN
RNC
Node B
MME
eNode B
PDN-GW
S-GW
1a. Routing Area Update Request
1b. Routing Area Update Request2. Context Request
3. Context Response
4. Context Acknowledge
5. Update Bearer Request6. Update Bearer Request
7. Update Bearer Response8. Update Bearer Response
9. Routing Area Update Accept
10. Routing Area Update Complete
2
1b 3
1a
6
7
4
58
9
10
SGSNSGSN
RNC
Node BNode B
MME
eNode BeNode B
PDN-GW
S-GW
1a. Routing Area Update Request
1b. Routing Area Update Request2. Context Request
3. Context Response
4. Context Acknowledge
5. Update Bearer Request6. Update Bearer Request
7. Update Bearer Response8. Update Bearer Response
9. Routing Area Update Accept
10. Routing Area Update Complete
2
1b 3
1a
6
7
4
58
9
10
