What is an example of a stateful protocol?

A stateful protocol is one that maintains information about the state of a connection or session over time, allowing it to manage and track the data exchanged between systems. In this context, the Transmission Control Protocol (TCP) exemplifies a stateful protocol because it establishes a connection between a sender and receiver and maintains that connection throughout the data transmission process. TCP uses a three-way handshake to initiate a connection, tracks the order of packets, manages retransmission of lost packets, and ensures that data is received in the correct sequence. This capability to maintain and manage state information through the session is what defines it as stateful.

In comparison, other options like Post Office Protocol version 3 (POP3) and Hypertext Transfer Protocol (HTTP) are considered stateless protocols. They do not retain session information between requests. Each request is treated independently, with no awareness of previous interactions. The Domain Name System (DNS) also acts statelessly, resolving domain names to IP addresses without maintaining information about past queries or sessions.

Thus, in the realm of networking protocols, TCP stands out as the quintessential example of stateful communication, enabling reliable and ordered delivery of data through a sustained connection.