The Transport Layer operates exactly between the Application Layer and the Network Layer. While the Network Layer successfully routes packets between different devices, the Transport Layer ensures that data reaches the specific software process running on those devices.

To achieve this process to process delivery, the Transport Layer relies on 16 bit port numbers and specialized protocols that dictate exactly how data is managed, ordered, and delivered.

UDP is a connectionless transport protocol. It is incredibly fast but highly unreliable. It does not establish a connection before sending data, it does not check if the data arrived, and it never retransmits lost packets.

Because it skips all error checking and connection overhead, it is used when raw speed is far more important than perfect accuracy. For example, during a live video call or online gaming, dropping a few frames of data is acceptable, but waiting for retransmissions would cause terrible lag.

TCP is the exact opposite of UDP. It is a strictly connection oriented protocol that provides guaranteed, reliable, and error free data delivery. It establishes a virtual connection using a three way handshake before any data is sent.

For example, when you download a file or load a webpage, every single byte must arrive perfectly. If a packet is lost, TCP automatically detects the loss and forces a retransmission until the data is whole.

SCTP is a modern, reliable, connection oriented protocol that combines the speed of UDP with the reliability of TCP.

Its greatest feature is Multihoming. If a computer has multiple network connections (like wired and wireless simultaneously), SCTP can use multiple paths for a single connection. For example, if the wireless connection suddenly drops during a secure telephony call, SCTP will seamlessly failover to the wired connection without dropping the call.