I have got three computers at my home[A,B,C] ( all connected to each other), now I connect to B from A using telnet( $telnet ip_B) , but when I try to connect to C using this telnet session( telnet > open ip_C) , I get this error, "already connected to xxx". Is it possible to connect A to B and then use that session to connect to C, so that C finds that the request is being asked by B.
Can telnet do this, or is there any other service, that might be helpful.

Please do not mention ssh.

Telnet already does that. But you don't say how you're doing this telnet session (command line, or from a program???) If you connect from A to B, then go from B to C, C will see you as coming from address B.

This all depends on your network setup, firewalls, etc. And if you don't like people mentioning SSH....too bad. SSH replaced telnet years ago, for a wide variety of reasons. Telnet is BAD to use, period, so upgrading is always going to be suggested. If you don't like the suggestions, then don't post the question.

Thanks for your suggestion.
I don't have anything against ssh, I know it's more secure and a great service. What I am trying to do is, using the command line telnet to B from A, this connects me to the B, now since ''[' is the escape character, pressing ctrl+[ , sends me to the telnet command prompt while I am still connected to B, now how can I connect to C using this command prompt, since on doing "telnet> open xxx" , I get the error, already connected to yyy. Is it possible to achieve this? I don't have any firewalls on any of the three systems.
Or if there is any other method , can you explain it to me ?

sounds like you're still trying to open a connection from A. ctrl+[ seems arbitrary and possibly the root cause. When you're telnetted into another machine you should be able to run from the shell. Such as previous poster stated.

Maybe I am not making myself clear, what I want is to connect A to B,
A> telnet B
connected to B
Escape character is '^]'.
now 'pressing ctrl+]'
telnet> open C
error?already connected to B.

so how can I achieve this using telnet.

Telnet can only open one connection at a time. When you escape back to the telnet prompt, the connection is still open, unless you issue the close command.
--- rod.

theNbomr explained it well.

And you're very clear, but are obviously having problems with basic concepts. Kind of like saying "I want to call my friend Bob, and when I get him on the phone, I want him to call Sally. So when Bob answers, I hang up....."

oh thanks ,got it.