scope:

The future of Emergency Services network architectures predicts that some network interconnections will continue to rely on the existence of a legacy selective routing function (TN-based routing) for some time. The RFAI architecture was developed to meet the needs of interconnection to functional entities that provide legacy selective routing while they are still needed in the network.

This document defines an ATIS Standard for an emergency Request For Assistance Interface (RFAI). This interface is a SIP-based interface between an IP Selective Routing (IPSR) Function, which is part of the ES-NGN functionality, and a Request For Assistance SIP User Agent (RFAUA) Function located in a Public Safety Answering Point (PSAP) or other authorized agencies as defined in the context of NG9-1- 1. This document uses the term PSAP to mean both PSAP and other authorized agencies.

The RFAI specification supports the transition from today's legacy technology into IP-based technology which includes functionality in the ES-NGN and the PSAP CPE. The RFAI specification supports the transition to NENA's i3 stage of evolution by delivering location routing keys (e.g., Telephone Number [TN], Emergency Services Routing Key [ESRK], or Emergency Services Query Key [ESQK]) to the PSAP that allow the PSAP to query for Automatic Location Identification (ALI). The RFAI specification has been developed to support the transitional period that begins with the introduction of IP-based technology in the ES-NGN and the PSAP. The RFAI specification is fully evolvable to NENA's i3 stage of evolution architecture. This interface specification will support emergency call delivery to a PSAP and also provide bridging capability among PSAPs.

Purpose

The purpose of the RFAI specification is to define an interoperable SIP-based interface between the ATIS Emergency Services Next Generation Network (ES-NGN) and SIP User Agents in the PSAP CPE call processing equipment (typically located within a PSAP). The RFAUA Function in the PSAP contains these SIP User Agents, or the SIP proxy that serves them.

Specifically, the RFAI architecture is intended to define a new interface between the new functional network elements, IPSR and RFAUA. These new functional elements serve to provide a transitional step from a legacy TDM environment to an IP environment that serves a PSAP. The transitional signaling is accomplished via the RFAI defined IPSR. In the transitional network, the IPSR takes incoming TDM signaling, does TN based routing and converts it to SIP protocol for communication to the RFAUA. The IPSR also includes the ability to accept incoming SIP signaling and to route based on TN information.

NENA has defined the primary transition path as using a Legacy Selective Router Gateway between an existing Selective Router and a PSAP upgraded with an i3 interface. ATIS ESIF envisions a different transition strategy, where the existing selective router is replaced with a new selective router with new capability (an IPSR) and the PSAP is upgraded with a different interface (RFAI) rather than the NENA defined i3 interface. Ultimately, IPSR functionality will be replaced by i3 ESRP functionality once the PSAP has upgraded to full i3 PSAP functionality. This specification supports migration of IPSR functionality  to i3 ESRP functionality, but the exact migration path is an implementation decision.