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Public Safety Answering Point (PSAP) Callback
RFC 7090

Internet Engineering Task Force (IETF)                    H. Schulzrinne
Request for Comments: 7090                           Columbia University
Category: Standards Track                                  H. Tschofenig
ISSN: 2070-1721
                                                             C. Holmberg
                                                                Ericsson
                                                                M. Patel
                                      Huawei Technologies (UK) Co., Ltd.
                                                              April 2014

             Public Safety Answering Point (PSAP) Callback

Abstract

   After an emergency call is completed (terminated either prematurely
   by the emergency caller or normally by the call taker), the call
   taker may feel the need for further communication.  For example, the
   call may have been dropped by accident without the call taker having
   sufficient information about the current state of an accident victim.
   A call taker may trigger a callback to the emergency caller using the
   contact information provided with the initial emergency call.  This
   callback could, under certain circumstances, be treated like any
   other call and, as a consequence, it may get blocked by authorization
   policies or may get forwarded to an answering machine.

   The IETF emergency services architecture specification already offers
   a solution approach for allowing Public Safety Answering Point (PSAP)
   callbacks to bypass authorization policies in order to reach the
   caller without unnecessary delays.  Unfortunately, the specified
   mechanism only supports limited scenarios.  This document discusses
   shortcomings of the current mechanisms and illustrates additional
   scenarios where better-than-normal call treatment behavior would be
   desirable.  We describe a solution based on a new header field value
   for the SIP Priority header field, called "psap-callback", to mark
   PSAP callbacks.

Schulzrinne, et al.          Standards Track                    [Page 1]
RFC 7090                      PSAP Callback                   April 2014

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7090.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Schulzrinne, et al.          Standards Track                    [Page 2]
RFC 7090                      PSAP Callback                   April 2014

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................5
   3. Callback Scenarios ..............................................5
      3.1. Routing Asymmetry ..........................................5
      3.2. Multi-Stage Routing ........................................7
      3.3. Call Forwarding ............................................8
      3.4. Network-Based Service URN Resolution ......................10
      3.5. PSTN Interworking .........................................11
   4. SIP PSAP Callback Indicator ....................................12
      4.1. General ...................................................12
      4.2. Usage .....................................................12
      4.3. Syntax ....................................................12
           4.3.1. General ............................................12
           4.3.2. ABNF ...............................................12
   5. Security Considerations ........................................12
      5.1. Security Threat ...........................................12

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