IETF RFC 3910 PDF

This document describes the Services in PSTN (Public Switched Telephone Network) requesting Internet Services (SPIRITS) protocol. The purpose of the SPIRITS protocol is to support services that originate in the cellular or wireline PSTN and necessitate interactions between the PSTN and the Internet. On the PSTN side, the SPIRITS services are most often initiated from the Intelligent Network (IN) entities. Internet Call Waiting and Internet Caller-ID Delivery are examples of SPIRITS services, as are location-based services on the cellular network. The protocol defines the building blocks from which many other services can be built.