True Number Portability and Advanced Call Screening in a SIP-Based IP Telephony System

0163-6804/99/$10.00 © 1999 IEEE or many years, the public switched telephone network (PSTN) has provided custom local area signaling service (CLASS) features to residential customers, such as call blocking, caller ID, and call forwarding. However, these services have certain limitations, primarily due to the closed PSTN signaling architecture which does not allow access to network signaling protocols by terminal devices. The adoption of IP telephony will enable the development and deployment of a new paradigm of services and features that are not possible to implement in today’s PSTN. This is especially the case for services that make use of personal, trusted information. Personal digital assistants (PDAs) are very suited to providing such information, because they store personal data and are carried by their owner most of the time. We have designed and built an experimental system to investigate how personal information can be coupled with an IP telephony network service to provide user-customized call handling by the network. In particular, we use a PDA which supplies personal information to an Ethernet-attached phone running the Internet Engineering Task Force (IETF) Session Initiation Protocol (SIP) [1] (from here on referred to as a SIPEtherphone). By synchronizing the owner information on the PDA with the SIP-Etherphone, the owner of the PDA registers with the phone. This allows for true number portability, since the call is forwarded to the SIP-Etherphone where the owner of the PDA was registered most recently. Furthermore, the address book data and the appointment book data in the PDA can be synchronized with the SIP-Etherphone to program an advanced call screening service in the local SIP server. For example, the user may opt to accept calls from only those callers who are in the address book with a certain priority, and to forward calls from everyone else to a third party or to voice mail. More sophisticated services could check the appointment book. If the current meeting is of lower priority than the current call, the phone would ring; otherwise, the call would be forwarded. Moreover, the PDA can provide the user with a flexible user interface to customize and control the phone services. CURRENT TELEPHONY SERVICES