During installation of Oracle Internet Directory, Oracle Identity Management 11g Installer follows specific steps in assigning the SSL and non-SSL port. First, it attempts to use 3060 as the non-SSL port. If that port is unavailable, it tries ports in the range 3061 to 3070, then 13060 to 13070. Similarly, it attempts to use 3131 as its SSL port, then ports in the range 3132 to 3141, then 13131 to 13141.
If you want Oracle Internet Directory to use privileged ports, you can override the defaults ports during installation by using staticports.ini.