How does handover work in LTE and 5G?

[Kajal_Gupta]

Handover is the process of transferring an active user session (call or data) from one cell to another to maintain seamless connectivity when the user moves or signal conditions change.

Handover in LTE

In LTE, handover is mainly a hard handover (break-before-make). This means the connection with the source cell is released before connecting to the target cell. The process is controlled by the eNodeB, based on UE measurement reports (RSRP/RSRQ).

Basic steps:

• UE measures neighbor cells and sends reports

• Source eNodeB decides handover (based on events like A3)

• Target eNodeB prepares resources

• UE switches to target cell and resumes session

LTE supports:

• Intra-frequency

• Inter-frequency

• Inter-RAT handovers

Key goal: Seamless mobility with minimal interruption

Handover in 5G

5G handover builds on LTE but is more advanced due to dense networks, beamforming, and dual connectivity.

Key enhancements:

• Supports dual connectivity (LTE + NR) for smoother transitions

• Uses beam-level mobility (not just cell-level)

• Introduces features like conditional handover for better reliability

• More complex due to ultra-dense deployments and diverse scenarios

Goal in 5G: Ultra-reliable, low-latency mobility even at high speeds

Final Thought

LTE handover focuses on efficiency and simplicity, while 5G takes it further with intelligence, flexibility, and reliability to support next-gen applications.

For detailed LTE handover call flow:
https://techlteworld.com/handover-in-lte/

[jsidra]

Handover is the process of transferring an active call or data session from one cell tower to another without dropping the connection as a user moves through a network.

In LTE, the network mainly controls this process. The serving base station (eNodeB) monitors signal quality. When the signal drops below a certain level, it checks neighboring cells, chooses the best one, and coordinates the transfer. This whole process takes about 50 milliseconds, and the user hardly notices it.

In 5G, the same basic idea applies but with some notable differences. 5G networks run on much higher frequencies, especially mmWave. This means that signal coverage per tower is much smaller. As a result, handovers occur more frequently as users move. To manage this, 5G introduced a smarter system where the core network handles more decision-making, easing the burden on individual towers. This makes handovers faster and more reliable.

A key feature in 5G is Dual Connectivity. This allows a device to keep connections to both a 4G LTE base station and a 5G node during the handover period. Instead of disconnecting from one and connecting to another, the device maintains both connections for a short time. This almost completely removes any service gap.

The main goal for both LTE and 5G is the same: seamless continuity for the user. However, 5G is built to achieve this goal more quickly, more often, and in much more complex multi-layer network environments than LTE was designed for.

[VijayHI]

Hi,

The Truth About “Handover” in Telecom — What It Really Means

There is a massive misconception in the industry about the term handover. Many engineers casually apply it to any mobility event, but that is technically wrong.
Let’s set the record straight.

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1. Handover is a Voice‑Continuity Concept — Not a Data Concept

The term handover exists because of voice calls, not data sessions.

Why?

A voice call:

• is real‑time

• is stateful

• has strict latency requirements

• cannot tolerate interruption

• must maintain an unbroken RTP stream

If the radio link drops even briefly, the call drops.

Therefore, the network must perform a seamless, controlled transfer of the call from one cell or RAT to another.

This is what handover means.

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2. Data Sessions Do NOT Need Handover

Data is packet‑switched, meaning:

• short disruptions are invisible to the user

• TCP retransmits

• HTTP/QUIC recovers

• apps buffer and retry

So the network does not need to perform a seamless transfer.

Data mobility is handled by:

• cell reselection (idle mode)

• RRC handover (connected mode, but only radio-level)

• TAU / RAU

• GTP tunnel relocation

• PDU session anchor mobility

These are mobility procedures, not handover in the voice sense.

This is why we call it a Packet‑Switched (PS) network — interruptions are acceptable.

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3. Legacy (2G/3G) Handover Was Purely About Voice

In GSM/UMTS days, handover was defined by voice domain boundaries:

• Intra‑BSC handover

• Inter‑BSC handover

• Intra‑MSC handover

• Inter‑MSC handover

All of these existed to keep a circuit‑switched voice call alive while the UE moved.

Data (GPRS/EDGE/UMTS PS) did not require seamless continuity.

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4. 4G Changed Everything — Voice Became Packet‑Based

When LTE arrived:

• the network became data‑anchored

• initial attach was to the packet core (EPC)

• voice moved to IMS over data tunnels

• fallback to 3G was used when IMS was unavailable

This created a challenge:

• 3G voice was CS‑anchored

• 4G voice was PS‑anchored

Moving a live call between these two worlds required a new mechanism.

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5. SRVCC Was Invented to Bridge 3G ↔ 4G Voice

SRVCC (Single Radio Voice Call Continuity) was created to allow:

• VoLTE → 3G CS voice

• 3G CS voice → VoLTE

It was needed because:

• 3G voice lived in the MSC/CS core

• 4G voice lived in the IMS/PS core

SRVCC ensured the call moved seamlessly, preserving the SIP dialog and RTP stream.

This was the dominant mobility method until 3G shutdown.

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6. 5G SA Simplified Voice Mobility Again

In 5G SA:

• everything is packet‑switched

• IMS voice works over 5G NR, 4G LTE, or Wi‑Fi

• the core network doesn’t care which access the UE uses

Voice continuity between:

• 5G ↔ 4G

• 5G ↔ Wi‑Fi

• 4G ↔ Wi‑Fi

is handled by IMS Access Transfer (ATCF/ATGW), not by radio handover.

The RAN only handles radio mobility.
The IMS handles voice continuity.

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7. Idle Mode “Handover” Does Not Exist

People often say “idle mode handover,” but this is incorrect.

In idle mode:

• the UE is not in RRC_CONNECTED

• there is no bearer to transfer

• the UE performs cell reselection, not handover

• the network does not control mobility

Correct term: Idle Mode Mobility, not handover.

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8. Final Summary

Handover = Seamless continuity of a live voice call

Data sessions do not need handover

Idle mode has no handover — only cell reselection

Legacy handover was CS‑voice anchored

LTE introduced IMS voice and SRVCC for 3G ↔ 4G

5G SA unified everything under packet‑switched voice

RAN handles radio mobility; IMS handles voice continuity