In a similar manner to ftp allowing a user to transfer files across the Internet, telnet allows users to log onto and work on remote machines as if they were sitting at one of its terminals. How usable this remote login is depends on how well the machines are connected and how well your terminal is recognized by the foreign machine. You can measure this round trip time with the ping command as discussed in Chapter 2 . If the ping times are greater than 500 milliseconds, the remote machine will seem unresponsive and you will find it hard to be productive.
Slow connections are common when using machines at far-removed different sites.
Telnet has very few options and is simple to use. Telnet will automatically try to set your TERM variable for you so the foreign machine knows your terminal type, but nevertheless, you may have to correct it if the remote machine does not know about the name it was sent as your terminal type. To end the telnet session, log off the remote machine. You will also get the telnet prompt if telnet does not recognize the remote hostname you use. In this case you are not connected to the foreign machine but are just running telnet.