"when I use pconnect, I have to connect only ONE time (at the start of my script)"
Uhm.. what does that have to do with pconnect??
Pconnect is a PHP Internal thing, you have NO control over it.
If you need a database connection, you MUST use OCIPLogon, allways, no matter if you use pconnect or not.
And if you tell php to connect twice, it will connect twice.
The ONLY thing that pconnect does it keep existing connections between the PHP engine and the database open. It does NOT keep connections between your SCRIPT and the database open.