1. RFC 3690
Network Working Group                                        K. Carlberg
Request for Comments: 3690                                           UCL
Category: Informational                                      R. Atkinson
                                                        Extreme Networks
                                                           February 2004

                     IP Telephony Requirements for
               Emergency Telecommunication Service (ETS)

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.


   This document presents a list of requirements in support of Emergency
   Telecommunications Service (ETS) within the context of IP telephony.
   It is an extension to the general requirements presented in RFC 3689.
   Solutions to these requirements are not presented in this document.

1.  Introduction

   Effective telecommunications capabilities can be imperative to
   facilitate immediate recovery operations for serious disaster events,
   such as, hurricanes, floods, earthquakes, and terrorist attacks.
   Disasters can happen unexpectedly, at any time or place.  Quick
   response for recovery operations requires immediate access to any
   public telecommunications capabilities at hand.  These capabilities
   include:  conventional telephone, cellular phones, and Internet
   access via online terminals, IP telephones, and wireless Personal
   Digital Assistants (PDAs).  The commercial telecommunications
   infrastructure is rapidly evolving to Internet-based technology.
   Therefore, the Internet community needs to consider how it can best
   support emergency management and recovery operations.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [1].

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1.1.  Problem

   Standards have been developed by other standards bodies concerning
   emergency communications.  As discussed in [3], some of these
   standards, such as T1.631 [5], define specific indicators or labels
   for emergency communications in Signaling System 7 (SS7) networks.
   Certain requirements must be defined in order to achieve peering
   across hybrid networks (networks that communicate between IP and
   other types of networks, such as that realized by the Public Switched
   Telephone Network) in order to achieve an interworking of services.

2.  Scope

   [3] has defined a set of general system requirements to support
   Emergency Telecommunications Service (ETS).  This document defines an
   additional set of system requirements to achieve support for ETS
   within the specific context of IP telephony (note that this document
   views IP telephony within the context of an end-to-end application
   layer service).  Solutions to requirements are not defined.  The
   document does not specify protocol enhancements or specifications.

   Note that [4], Requirements for Resource Priority Mechanisms for the
   Session Initiation Protocol (SIP), is an RFC that shares some overlap
   with this document.  However, [4] only applies to SIP and is not
   meant to be applied to a more general perspective of IP telephony as
   it relates to ETS.

2.1.  Out of Scope

   An item that is not in scope of this document is mandating acceptance
   and support of the requirements presented in this document.  The IETF
   does not mandate requirements or capabilities to independent networks
   that comprise the Internet.  As an example, Internet Service
   Providers (ISP) may choose not to operate any telephony-related
   gateways or services.  The IETF cannot and does not mandate that an
   ISP deploy either telephony-related gateways or telephony-related
   services.  There is an expectation that business contracts, for
   example Service Level Agreements (SLA), will be used to satisfy those
   following requirements that apply to service providers.  Absence of
   an SLA implies best effort service is provided.

   It is assumed that some ISPs will choose to offer ETS services and
   that other carriers will choose not to offer ETS services.  These
   requirements do not apply to ISPs that have chosen not to offer ETS

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3.  IP Telephony Requirements

   The requirements in this section relate only to Telephony Signaling
   as used in Internet-based telephony services.  They are an extension
   to the general requirements specified in [3].  The following
   requirements explicitly do not relate to IP-layer mechanisms, such as
   Differentiated Services or Integrated Services.

   1) Telephony signaling applications used with Internet-based
      telephony MUST be able to carry labels.

   2) The ability to carry labels MUST be extensible to support various
      types and numbers of labels.  A single binary value will not be
      sufficient given the various labeling standards in existence

   3) Telephony signaling labels SHOULD have a mapping with the various
      emergency related labels/markings used in other telephony based
      networks, such as the Public Switched Telephone Network (PSTN).
      This ensures that a telephone call placed over a hybrid
      infrastructure (traditional PSTN over some portion(s) of the path,
      Internet telephony over some other portion(s) of the path) can
      carry the labels end-to-end with appropriate translation at
      PSTN/Internet boundaries.  Absence of a mapping means that the
      signaling reverts to a default service (presumably one attributed
      to the general public).

   4) Application layer IP telephony capabilities MUST NOT preclude the
      ability to do application layer accounting.

      Accounting is a useful feature in support of billing and tracking
      down abuse of service.  If specific solutions or protocols in
      support of ETS require accounting, then this will be articulated
      in future document(s).

   5) Application layer mechanisms in gateways and stateful proxies that
      are specifically in place to recognize ETS type labels MUST be
      able to support "best available" service (this will probably be
      realized as better than best effort).  These labels MAY exist in
      the application layer headers of data (i.e., bearer) traffic or
      signaling traffic used for call completion.

      The support for best available service SHOULD focus on probability
      of forwarding packets.  Probability MAY reach 100% depending on
      the local policy associated with the label.  Local policy MUST
      also be used to determine if better than best effort is to be
      applied to a specific label (or related set of labels).

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      Additional comments on this topic are presented below in item 2 of
      section 4.

      The above paragraphs MUST be taken in their entirety.  The ability
      to support best available service does not mean that the
      application layer mechanism is expected to be activated.  Further,
      we do not define the means by which best available service is
      realized.  Application layer mechanisms that do not recognize ETS
      type labels are not subject to this requirement.

4.  Issues

   This section presents issues that arise in considering solutions for
   the telephony requirements that have been defined for ETS.  This
   section does not specify solutions, nor is it to be confused with
   requirements.  Subsequent documents that articulate a more specific
   set of requirements for a particular service may make a statement
   about the following issues.

   1) Alternate paths

      Experience with The Government Emergency Telecommunications
      Service (GETS) over the PSTN has shown the utility of alternate
      paths to a destination to help facilitate emergency-related
      communications.  From the perspective of the Internet, this
      utility may be difficult to achieve and have a more limited
      benefit.  Unlike the PSTN, which creates a fixed path during call
      setup phase, the Internet uses dynamic routing for IP packets.
      This dynamic routing capability automatically causes IP packets to
      travel the best current path.  The Internet network infrastructure
      does not have the concept of a "call" or the concept of "call
      setup", though IP telephony applications might have application
      layer awareness of calls or the call setup concept.

   2) Application of Best Available Service

      In item 5 of section 3 above, we discuss the requirement of
      supporting best available service.  We note that in this document,
      the scope of that support is constrained to the application layer
      and flows that traverse that layer.  This may involve direct
      support for the flow containing the ETS type label, or may involve
      indirect support (e.g., ETS labels in signaling messages that
      cause an effect on corresponding data or bearer flows).

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      It is critical to understand that how the support for best
      available service can be realized is outside the scope of this
      document.  In addition, the perceived effectiveness of a given
      approach or implementation is also outside the scope of this

5.  Security

   Only authorized users or operators SHOULD be able to create non-
   ordinary Labels (i.e., labels that may alter the default best effort
   service).  Labels SHOULD be associated with mechanisms to provide
   strong end-to-end integrity during their transmission through the
   telephony systems.  Finally, in cases where labels are expected to be
   acted upon by operators, these operators SHOULD have the capability
   of authenticating the label on a received message or transmission in
   order to prevent theft of service and reduce risk of denial of
   service (e.g., by unauthorized users consuming any limited

   Security is also discussed in the general requirements of [3], which
   applies to section 3 above.

6.  References

6.1.  Normative Reference

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

6.2.  Informative References

   [2]  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
        9, RFC 2026, October 1996.

   [3]  Carlberg, K. and R. Atkinson, "General System Requirements for
        Emergency Telecommunications Service", RFC 3689, February 2004.

   [4]  Schulzrinne, H., "Requirements for Resource Priority Mechanisms
        for the Session Initiation Protocol (SIP)", RFC 3487, February

   [5]  ANSI, "Signaling System No. 7(SS7): High Probability of
        Completion (HPC) Network Capability", ANSI T1.631, 1993.

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7.  Authors' Addresses

   Ken Carlberg
   University College London
   Department of Computer Science
   Gower Street
   London, WC1E 6BT
   United Kingdom

   EMail: k.carlberg@cs.ucl.ac.uk

   Ran Atkinson
   Extreme Networks
   3585 Monroe Street
   Santa Clara, CA
   95051  USA

   EMail: rja@extremenetworks.com

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8.  Full Copyright Statement

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
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   or assist in its implementation may be prepared, copied, published
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an


   Funding for the RFC Editor function is currently provided by the
   Internet Society.

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  1. RFC 3690