Obsolete

• One thing Telnet and SSH have in common is that they were both superseded because of their security weaknesses. Telnet has no security features. Although the user requires a login to the remote computer, Telnet carries the username and password unencrypted, making them visible to wire tappers. SSH made Telnet obsolete, because it did the same job, but with added encryption. However, SSH's encryption procedures were flawed and transmissions were susceptible to a variety of intrusion attacks. SSH was scrapped when SSH2 was produced.
  
  

Telnet

• Telnet is one of the oldest applications on the Internet. In fact, it pre-dates the Internet. It was first created for ARPANET, which was the pre-cursor of the Internet. It first appeared in 1969, whereas the Internet was created with the publication of the TCP/IP protocol suite in 1974. Telnet was also one of the first client-server applications. In client-server, the client is where the user sits and requires something from a remote computer, which is the server. The pair engage in a simple request/response exchange, which is called “connectionless,” or they establish a connection within which several messages are conveyed. Telnet is connection-oriented.
  
  

SSH

• Secure Shell was created at the Helsinki University of Technology in 1995 after they experience a number of security failures in their internal network. SSH performed exactly the same tasks as Telnet, except communication was encrypted.
  
  

Similarities

• Telnet and SSH are text-based protocols: mouse movements cannot be transferred, only keystrokes. Both are connection-oriented and both use the Transmission Control Protocol for a transport protocol and connect to TCP ports. The commands entered into a Telnet screen, or an SSH screen are not native to those applications, but are commands understood by the remote computer where they are executed. Both Telnet and SSH are client-server protocols, each has a client program, which includes a user interface and both have a server program, which interacts with the remote computer's operating system on behalf of the client program.
  
  

Operating Systems

• Telnet and SSH were intended for Unix and Unix- like environments. SSH was also adapted for Linux, which didn't exist when Telnet was in operation. The general public are less likely to use these programs, as graphics-based, windows-compatible terminal emulators and “virtualization” packages are more prevalent in user-oriented environments.