The document discusses different types of handovers in wireless networks, including hard handovers, soft handovers, and inter-RAT (radio access technology) handovers. It explains that hard handovers involve breaking the connection in the old network or cell before making it in the new one, while soft handovers make the connection in the new network or cell first via techniques like softer handover between cells of the same NodeB or soft handover between different NodeBs. The document also notes that inter-frequency and inter-RAT handovers are always hard since they require changing the wireless technology. Diagrams and call flows are provided to illustrate the handover signaling processes.

1. Simplified Call Flow Signaling:
Handovers
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2. Handover: Basic Concepts
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A1 A2 A3 A4
B1 B2f2
f1

3. Handover: Basic Concepts
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A1 A2 A3 A4
B1 B2f2
f1
Break before make – Hard Handover

4. Handover: Basic Concepts
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A1 A2 A3 A4
B1 B2f2
f1
Break before make – Hard Handover
Make before break – Soft Handover

5. Handover: Basic Concepts
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AS
CS NAS
Voice (PSTN)
Network
Data (IP)
Network
Radio
Access
Network
Core
Network
Air
Interface
PS NAS
Backhaul
AS
• Softer Handover – between cells
belonging to same NodeB

6. Handover: Basic Concepts
©3G4G
AS
CS NAS
Voice (PSTN)
Network
Data (IP)
Network
Radio
Access
Network
Core
Network
Air
Interface
PS NAS
Backhaul
AS
• Softer Handover – between cells
belonging to same NodeB
• Soft Handover – between cells
belonging to different NodeB

7. Handover: Basic Concepts
©3G4G
A1 A2 A3 A4
B1 B2f2
f1
Inter-frequency Handover – Always hard handover

8. What is Radio Access Technology (RAT)?
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BSC
BTS
MSC
Voice (PSTN)
Network
SGSN
Data (IP)
Network
RNC
Node BeNodeB
MME
GGSN
Access
Network
Core
Network
Air
Interface
MSUEUE
BSSRNS
S-GW
P-GW
2G 2.5G
3G 4G
EPC

9. Handover: Basic Concepts
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A1 A2 A3 A4
B1 B2RAT 2
RAT 1
Inter-RAT Handover – Always hard handover
(Also known as Inter-System Hard Handover)

10. Handover (same RAT)
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UE AN2 CS CN PS CN
Access Network Core Network
Measurement Report
Hello, AN1 told me to handover to you
I was already informed, welcome
AN1
UE 1 will be better served by you, OK for handover?
Ok.
Handover to AN2
UE1 is now connected to me. You can release its context

11. Handover (Inter-RAT)
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UE AN2 PS CN
RAT1
PS CN
RAT2
Measurement Report
Hello, AN1 told me to handover to you
I was already informed, welcome
AN1
UE 1 will be better served by AN2, OK for handover?
Handover to AN2 using <…>
Handover succeeded. You can release UE 1 context
AN1 wants to handover UE1 to AN2. Ok?
Ok. Use <…>
UE 1 wants to connect to you. OK for handover?
Yes, please use these parameters <…>
OK for handover, tell UE to use <…>
Success
You can release UE 1 context

12. Thank You
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