Have anyone idea, how to authenticate user info given at client side on the server side with real users database. Actually i want to make a remote shell like telnet which also require user authentication

Are you asking how to authenticate the user using the existing system authentication (/etc/shadow on Linux, etc), or how to design your own authentication scheme?

http://www.mindcontrol.org/~hplus/authentication.html talks about various kinds of authentication.

Doing authentication for the system is fairly complicated, and requires the root/setuid privilege on Linux, and Administrator privileges on Windows. The actual procedure can be found by reading the source for telnetd/login on Linux, or on MSDN for Windows.