Some little questions ..

Please answer :
What Unix file contain the connection between IP and host name ?
/etc/host.conf or
/etc/networks ?

Then, what is the Unix command which allow to open a remote session ?
rlogin ADDR_IP
rhost ADDR_IP or
login ADDR_IP ?

This depends on what name resolution mechanism you are using - files, NIS/NIS++, DNS? From your question I will assume you are using files in which case hostnames are mapped to IP addresses in /etc/hosts thus:

[ip_address] [hostname] [alias]

A remote login can be done via a number of ways, rlogin is one. If you have the hostname mapped to an ip address in /etc/hosts the syntax would be

rlogin [hostname]

You could also use telnet

telnet [hostname]

Or rsh and ssh in exactly the same way.

Of course routes and networking has to be set up in order for you to be able to talk to the other machine, and if you are sitting in an infrastructure where firewalls determine access control certain forms of communication between machine may be disallowed by firewall rules (i.e. certain ports blocked).

Hope this helps.