+ <li><a name="port">port</a> - individual port on a <a href="#nas">nas</a>
+ <ul>
+ <li>portnum - primary key
+ <li>ip - IP address of this port
+ <li>nasport - port number on the NAS
+ <li>nasnum - <a href="#nas">NAS</a>
+ </ul>
+ <li><a name="prepay_credit">prepay_credit</a>
+ <ul>
+ <li>prepaynum - primary key
+ <li>identifier - text or numeric string used to receive this credit
+ <li>amount - amount of credit
+ </ul>
+ <li><a name="session">session</a>
+ <ul>
+ <li>sessionnum - primary key
+ <li>portnum - <a href="#port">Port</a>
+ <li>svcnum - <a href="#svc_acct">Account</a>
+ <li>login - timestamp indicating the beginning of this user session.
+ <li>logout - timestamp indicating the end of this user session. May be null, which indicates a currently open session.
+ </ul>
+