2. Physical Layer

2.3. Transport Layer (Layer

4. Transport Layer (Layer 4)

Function: Provides reliable or unreliable end-to-end data transfer between hosts, ensuring data arrives complete, in order, or quickly as needed.

Key Responsibilities:

Segments and reassembles data for transmission.

Manages flow control (e.g., TCP windowing).

Performs error detection and retransmission (for reliable protocols).

Supports connection-oriented (e.g., TCP) or connectionless (e.g., UDP) communication.

Uses port numbers to identify applications.

Examples:

Protocols: Transmission Control Protocol (TCP), User Datagram Protocol (UDP).

Port Numbers: 80 (HTTP), 443 (HTTPS), 53 (DNS).

Technologies: TCP three-way handshake, UDP for streaming.

Analogy: A courier service ensuring all packages arrive correctly and in order (TCP) or sending them quickly without guarantees (UDP).