First, when connecting, the function would first try to find a (persistent) link that's already open with the same host, username and password. If one is found, an identifier for it will be returned instead of opening a new connection.
Second, the connection to the SQL server will not be closed when the execution of the script ends. Instead, the link will remain open for future use (sybase_close() will not close links established by sybase_pconnect()).
This type of links is therefore called 'persistent'.
The servername argument has to be a valid servername that is defined in the 'interfaces' file.
Sybase user name
Password associated with username.
Specifies the charset for the connection