Application-layer
The TCP/IP application-layer combines layers 5–7 (session, presentation, and application) of the OSI model. Most of these protocols use a client-server architecture, where a client (eg, ssh) connects to a listening server (called a daemon on UNIX systems), such as sshd. The clients and servers use either TCP or UDP (and sometimes both) as a transport layer protocol. TCP/IP application-layer protocols include secure shell (SSH), Telnet, and FTP, among many others.