Quiz Entry - updated: 2026.07.14
What does OSI Layer 4 (Transport) do?
OSI Layer 4 (Transport) provides end-to-end data transfer — segmentation/reassembly, flow control, and (with TCP) reliable error recovery.
Layer 4 = Transport Layer
Provides end-to-end communication and data transfer services.
Key functions:
| Function | Description |
|---|---|
| Segmentation | Breaks data into segments |
| Reassembly | Puts segments back together |
| Flow control | Manages transmission rate |
| Error recovery | Retransmits lost data (TCP) |
Protocols:
- TCP (reliable, connection-oriented)
- UDP (fast, connectionless)
Memory tip: Layer 4 "Transports" data reliably - it's the delivery service!
Go deeper:
Transport layer — end-to-end transfer, segmentation, flow control, and TCP vs UDP.