Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are the two primary types of transport protocols used for data transmission across the internet. Data travels over the internet in packets, which are transmitted using the IP network. Imagine sending a letter: you need an envelope to make sure it is delivered to its destination untouched and without delay. TCP and UDP are two kinds of envelopes you can use, and they both carry digital signals in the form of data packets.