Source: The English Department at the University of Virginia, Lindsey Kordis

The Transport Layer “ensures the reliable arrival of messages and provides error checking mechanisms and data flow controls”

May be connexionless (e.g., User Datagram Protocol, UDP) or connection oriented (e.g., Transport Control Protocol, TCP).

TCP and UDP both have a source and destination port

Source ports are chosen arbitrarily, usually above 1024

Destination ports usually defined in /etc/services and are fixed

UDP/TCP Headers contains 16 bit source and destination ports, checksum, sequence number, etc.