http://www.cisco.com/en/US/tech/tk801/tk379/technologies_tech_note09186a008012e95f.shtml
http://www.cisco.com/en/US/docs/ios/11_3/debug/command/reference/disdn.html
http://networking.ringofsaturn.com/RemoteAccess/isdncausecodes.php
http://www.cisco.com/en/US/tech/tk801/tk379/technologies_tech_note09186a0080093c1a.shtml
http://networking.ringofsaturn.com/RemoteAccess/isdncausecodes.php