Telephony Routing over IP (TRIP) Attribute for Resource Priority
RFC 5115

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Network Working Group                                        K. Carlberg
Request for Comments: 5115                                           G11
Category: Standards Track                                    P. O'Hanlon
                                                                     UCL
                                                            January 2008

    Telephony Routing over IP (TRIP) Attribute for Resource Priority

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This document defines a new attribute for the Telephony Routing over
   IP (TRIP) protocol.  The attribute associates protocols/services in
   the PSTN offering authorized prioritization during call setup that
   are reachable through a TRIP gateway.  Current examples of
   preferential service in the Public Switched Telephone Network (PSTN)
   are Government Emergency Telecommunications Service (GETS) in the
   U.S. and Government Telephone Preference Scheme (GTPS) in the U.K.
   The proposed attribute for TRIP is based on the NameSpace.Value tuple
   defined for the SIP Resource-Priority field.

1.  Introduction

   An IP telephony gateway allows nodes on an IP-based network to
   communicate with other entities on the circuit switched telephone
   network.  The Telephony Routing over IP (TRIP) protocol [rfc3219]
   provides a way for nodes on the IP network to locate a suitable
   gateway through the use of Location Servers.  TRIP is a policy-
   driven, inter-administrative domain protocol for advertising the
   reachability, negotiating the capabilities, and specifying the
   attributes of these gateways.

   The TRIP protocol is modeled after BGP-4 [rfc4271] and uses path-
   vector advertisements distributed in a hop-by-hop manner (resembling
   a Bellman-Ford routing algorithm) via Location Servers.  These
   Location Servers are grouped in administrative clusters known as
   Internet Telephony Administrative Domains (ITADs).  A more extensive
   framework discussion on TRIP can be found in [rfc2871].

Carlberg & O'Hanlon         Standards Track                     [Page 1]
RFC 5115              Resource Priority Attribute           January 2008

   This document defines a new attribute that has been registered with
   IANA.  The purpose of this new attribute, and the rationale behind
   its specification, is explained in the following sections.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [rfc2119].

2.  Emergency Telecommunications Service

   Emergency Telecommunications Service is a broad term that refers to
   the services provided by systems used to support emergency
   communications.  One example of these systems is the U.S. Government
   Emergency Telecommunications Service (GETS).  This system currently
   operates over the U.S. Public Switched Telephone Network (PSTN) as a
   pay-per-use system by authorized personnel.  It uses the T1.631-1993
   ANSI standard [ANSI] to signal the presence of the National Security
   / Emergency Preparedness (NS/EP) codepoint in an ISDN User Part
   (ISUP) Initial Address Message (IAM) for Signaling System No. 7
   (SS7).  A key aspect of GETS is that a signaling standard in the U.S.
   PSTN is used to convey the activation/request of the GETS service.

   From a protocol perspective, other examples of priority (and which
   can be argued as emergency/disaster related) standards are the
   H.460.4 ITU [itu460] standard on Call Priority designation for H.323
   calls, and the I.255.3 [itu255] ITU standard on Multi-Level
   Precedence and Preemption Service.  The latter has been integrated
   into private telephony systems like AUTOVON.  In both cases,
   signaling codepoints exist to distinguish telephony calls by
   authenticated and prioritized end-user from the normal end-user.  The
   form of this distinction varies and is outside the scope of this
   document.  [rfc3689] and [rfc3690] provide additional information on
   ETS and its requirements.

3.  SIP Resource-Priority Effort

   The initial discussions in the IEPREP working group list, along with
   the presentation at the Adelaide IETF [ADEL00], led to strawman
   requirements to augment SIP to have the ability to prioritize call
   signaling.  This effort was then advanced formally in the SIPPING
   working group so that SIP would be able to prioritize access to
   circuit-switched networks, end systems, and proxy resources for
   emergency preparedness communication [rfc3487].

   The requirements in [rfc3487] produced the corresponding document