Number Portability in the Global Switched Telephone Network (GSTN): An Overview
RFC 3482

2002-11-04 - suggested sec consid sect from authors

"In the PSTN, the NPDB queries are generated by the PSTN switches and
carried over the SS7 networks to reach the NPDBs and back to the switches.
The SS7 networks are operated by telecommunications operators and signaling
transport service providers in such a closed environment that make them
difficult for the hackers to penetrate.  However, when VoIP operators need
the NP information and have to launch the NP queries from their
softswitches, media gateway controllers or call managers, there would be
security concerns if the NP queries and responses are transported over
Internet.  If the routing number or routing prefix in the response is
altered during the message transport, the call will be routed to the wrong
place.  It is recommended that the NPDB queries be transported via a secure
transport layer or with added security mechanisms to ensure the data
integrity."

2002-11-03 - note to chairs
this looks like a very useful document but I think it need a better
Security Considerations section -
        mention the security model of NP in the PSTN ( walled garden)
        mention what the security issues might be for IP telephony
                work in the IETF relating to NP