A. Telnet
B. TCP/IP
C. FTP
D. Point-to-Point protocol (PPP)

Solution

A. Telnet

Explanation

<p>The terminal emulation protocol that allows users to log on to a host computer from remote computers is Telnet.</p><p><span style="font-size: 1rem; letter-spacing: 0.01rem;"><b>Key Points about Telnet:</b></span></p><p><b>Full Name:</b> Teletype Network</p><p><span style="font-size: 1rem; letter-spacing: 0.01rem;"><b>Function: </b>Provides a bidirectional interactive text-based communication facility using a virtual terminal connection.</span></p><p><span style="font-size: 1rem; letter-spacing: 0.01rem;"><b>Port: </b>Operates typically over TCP port 23.</span></p><p><span style="font-size: 1rem; letter-spacing: 0.01rem;"><b>Usage: </b>Allows users to remotely access and manage devices and servers, often for configuration or troubleshooting.</span></p><p><span style="font-size: 1rem; letter-spacing: 0.01rem;"><b>Security Note:</b> Telnet transmits data, including usernames and passwords, in plaintext, making it insecure for use over untrusted networks.</span></p>