Xshell FAQ

Answer
The Secure Shell(SSH) protocol provides secure authentication and encryption replacing insecure login protocols such as telnet, rlogin and r-commands. It also supports the port forwarding of the X11 connections and arbitrary TCP/IP protocols.

SSH is based on the protocol documented by the SECSH Working group of IETF where many standard documents of network protocols are maintained by network designers, operators, vendors, and researchers.