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**When a UDP packet is lost, nothing "special" happens - it is simply lost.**
UDP **does not try to detect the loss and does not recover the data**.

In short:
**the packet is gone, and UDP moves on as if nothing happened**.

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## What exactly happens, step by step

1. **The sender sends a UDP packet**
2. On the network, the packet can:
  - get lost
  - be dropped due to congestion
  - get corrupted
3. **The receiver does not get the packet**
4. **UDP does nothing about it**:
  - no ACK
  - no timeouts
  - no retransmission

That is all.

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## What does NOT happen when a UDP packet is lost

Important for the interview.
UDP **does not**:

- retransmit
- notify the sender
- restore the order
- compensate for the loss

UDP works on a **best effort** basis.

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## Who is responsible for the consequences of the loss

If data loss is **critical**, it has to be handled by:

### **Application logic**

The application can:

- resend the data
- ignore the loss
- interpolate the data
- request an updated state

UDP **deliberately shifts responsibility to the application**.

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## Why this is considered normal

For many scenarios:

- **losing one packet is not critical**
- delay is worse than loss

Examples:

- voice → a small "dropout"
- video → a dropped frame
- a game → a missed position update

Retransmission would be **worse** than the loss.

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## Comparison with TCP

- **TCP**:
  - detects loss
  - retransmits data
  - slows down transmission
- **UDP**:
  - does not detect loss
  - does not retransmit
  - works as fast as possible

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