Final answer:
TCP and UDP are both transport-layer protocols, use IP for packet delivery, and employ port numbers to differentiate services on devices.
Step-by-step explanation:
Common elements to both Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) include that they are both transport-layer protocols used in Internet Protocol (IP) networks to send data between devices. Furthermore, both TCP and UDP are built on top of IP, which means they are used for sending data packets over the network using IP addresses to identify source and destination. Additionally, both protocols utilize port numbers to distinguish between different user requests or services on a single device.