Which of the following is considered a connectionless protocol?

The User Datagram Protocol (UDP) is a core member of the Internet protocol suite and is fundamentally connectionless. Unlike connection-oriented protocols, UDP does not establish a dedicated end-to-end connection before sending data. It sends packets, called datagrams, to a destination with no prior handshake or session setup. This approach minimizes overhead and latency, making it ideal for time-sensitive applications like DNS, VoIP, and online gaming, where speed is prioritized over the guaranteed delivery and ordering of packets.

A. SSH: Secure Shell (SSH) operates over TCP to establish a persistent and reliable session for secure remote access, making it connection-oriented.
B. TCP: Transmission Control Protocol (TCP) is the quintessential connection-oriented protocol, using a three-way handshake to establish a reliable connection before data transfer.
C. HTTPS: Hypertext Transfer Protocol Secure (HTTPS) relies on TCP to ensure the reliable and ordered delivery of web data, making it a connection-oriented protocol.

1. Postel, J. (1980). RFC 768: User Datagram Protocol. Internet Engineering Task Force (IETF). Section "Introduction". This document defines UDP and states, "This protocol provides a procedure for application programs to send messages to other programs with a minimum of protocol mechanism," which describes its connectionless nature.

2. Postel, J. (1981). RFC 793: Transmission Control Protocol. Internet Engineering Task Force (IETF). Section 1.5 "Operation". This document defines TCP as a "reliable, connection-oriented" protocol that requires a logical connection to be established.

3. Kurose, J., & Ross, K. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson. Chapter 3, Section 3.3, "Connectionless Transport: UDP," explicitly describes UDP as a protocol that provides an "unreliable, connectionless service." This textbook is widely used in university computer science curricula.

4. Stanford University. (n.d.). CS144: Introduction to Computer Networking, Lecture 5: Transport. Stanford Engineering Everywhere. The lecture notes and video clearly distinguish between TCP as a "reliable, in-order, connection-oriented" protocol and UDP as an "unreliable, unordered, connectionless" protocol.