UNIX for Advanced & Expert Users

We have about 300 users in the systeme , they mainly use the software called "netterm" to telnet our RH server to access the db in our internal network , I know there are some secure program like ssh , that is more secure for connection , do you think it is good idea to replace the software in our case ? what it the advantage and impact ? could provide any recommendation ? thx in advance.

ssh would definitely be more secure. the password in telnet is sent over the connection in an unencrypted manner; while ssh encrypts it. However, this encryption is an additional load on the server...

thx reply , we have firewall to block the external network , do you think it is neccssary to use ssh in the internal network ? thx