The Transport Layer is the fourth layer of the OSI model. While the Network Layer is responsible for moving a packet from one computer to another, the Transport Layer is responsible for moving data from a specific process (application) on the sender machine to a specific process on the receiver machine.

It provides logical end to end communication. This means that from the perspective of the communicating applications, it appears as though they are connected by a direct, reliable link, completely hiding the complex physical network underneath.

For connection oriented communication, the Transport Layer must establish a dedicated logical connection before any actual data is transmitted. This is accomplished using a strict 3 Way Handshake to guarantee both the client and server are fully ready.

Why exactly three steps? A simple two step process would leave the server unsure if the client actually received its acknowledgement. The third step provides mandatory mutual confirmation.

TCP is a strictly connection oriented and highly reliable protocol. It guarantees that all data sent will eventually reach the destination without errors and in the exact correct order. It achieves this by tracking sequence numbers, forcing acknowledgements, and strictly retransmitting lost packets.

UDP is a connectionless and unreliable protocol. It blindly fires data packets (called user datagrams) at the destination without establishing a connection and without waiting for any acknowledgements.

Because it skips the complex error checking and handshake processes of TCP, UDP is significantly faster. It is used in scenarios where speed is critical and a few lost packets are acceptable, for example, during live video streaming or online fast paced gaming.

SCTP is an advanced protocol that combines the best features of both TCP and UDP. It provides reliable, connection oriented transport but is highly optimized for scenarios involving multiple IP addresses (multi homing) and simultaneous data streams.