Multi-Device Sync

Modern messaging apps support

• Phone

• Laptop

• Tablet

• Desktop

All devices stay synchronized.

How?

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Device Registration

Every device is registered to the account.

Example

User

↓

Phone

Laptop

Tablet

Each device maintains its own secure connection.

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Synchronization Flow

Each linked device receives the same message independently.

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Why Not Sync From Phone?

Suppose your phone battery dies.

Your laptop should still receive new messages.

This is why every linked device maintains its own secure session.

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Offline Devices

If your laptop is offline,

the server temporarily stores pending events.

When the laptop reconnects,

it requests missing messages.

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Synchronization

Devices periodically synchronize

• Messages

• Read receipts

• Delete events

• Edit events

This ensures every device eventually reaches the same state.

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Interview Notes

Interviewer

Why doesn't the laptop fetch everything from the phone?

Answer

Because every linked device communicates independently with the backend.

The phone is not a dependency.

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Key Takeaways

✔ Every device has its own connection.

✔ Devices synchronize independently.

✔ Offline devices catch up later.

✔ Event ordering is maintained during synchronization.

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