> Besides the cases you pointed out, there is the case of client lost
> conection.
>
> But I think that this is the easiest way to do it...
>
> The OP could tell us some more info like:
> Do you want to count the simultaneous connections or the number of users
> ? (ex. the costumer could have 10 valid users but are allowed to use
> just 5 at a time)
>

My purpose is very simple. The users can install the program on any
number of computers connected to a Firebird server, and I want to limit
the number of simultaneous connections.
So they could install it on 5 computers but, if they payed for 2
connections, they will be able to use the program only on 2 computers at
the same time.

Fulvio