stir B. Rosen
Internet-Draft March 9, 2020
Intended status: Standards Track
Expires: September 10, 2020
Non-Interactive Emergency Calls
draft-rosen-stir-emergency-calls-00
Abstract
Emergency calls from citizens to authorities, and call back of such
emergency calls by authorities to citizens need assurances that
headers intended to get appropriate priority from the networks they
traverse, and in some cases, appropriate routing. Protection of the
SIP Resource Priority Header and the SIP Priority header is needed
for such calls. This document describes the environment for placing
emergency calls and call backs which motivate the need and use of the
mechanisms described in other documents
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Emergency Calls . . . . . . . . . . . . . . . . . . . . . . . 3
4. Emergency Call-backs . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
[RFC6643] describes how devices use the Internet to place emergency
calls and how Public Safety Answering Points (PSAPs) handle Internet
emergency calls. In traditional telephone networks, emergency calls
are not afforded any priority in the network. Emergency calls are
marked with a Service URN, [RFC5031].
Sometimes, the emergency services need to call the person that placed
an emergency call after the original emergency call was terminated.
This is a case of "call-back". [RFC7090] discusses using SIP
Priority to mark a call as a call back. The Resource Priority
Header, [RFC4412] defines a way to request the network afford
priority in resources: The 'Priority' header field describes the
importance that the SIP request should have for the receiving human
or its agent. For example, that header may be factored into
decisions about call routing to mobile devices and assistants and
about call acceptance when the call destination is busy. The
'Priority' header field does not affect the usage of PSTN gateway or
proxy resources, for example. In addition, any User Agent Client
(UAC) can assert any 'Priority' value, and usage of 'Resource-
Priority' header field values is subject to authorization.
This document describes the environment for placing emergency calls
on the Internet, which has different capabilities than the PSTN, as
well as call backs across the Internet and describes the requirements
for protecting them with the "stir" mechanism.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
SIP is the Session Initiation Protocol [RFC3261]
PSAP is a Public Safety Answering Point, the call center for
emergency calls.
3. Emergency Calls
SIP signaling for emergency calls is defined in [RFC6881]. An
emergency call is marked with a Service URN [RFC5031] in the Request-
URI field. RFC6881 does not have any recommendations for the
Resource Priority Header. Emergency calls will make use of the stir
mechanism to assure the PSAP that the calling party identifier is
accurate. There are numerous cases of what is called "swatting"
where an emergency call with a spoofed identity is placed and the
caller fraudulently reports serious criminal activity at some
address, prompting the authorities to respond with significant force
(SWAT team). By validating the identity, authorities hope swatting
will become much less possible.
It is desirable in some networks to be able to provide some priority
in the call handling network for emergency calls, even though the
PSTN does not do that. [RFC7135] defines the "esnet" namespace, and
4 priority levels "for local emergency session establishment to a
public safety answering point (PSAP), between PSAPs, and between a
PSAP and first responders and their organizations. ". There is
presently no recommendation for what priority level to assign to
emergency calls. There are other documents [i3] that describe how to
use the esnet values within an Emergency Services IP Network, which
is distinct from the originating service provider networks, over
which emergency calls may be placed.
This document recommends that emergency calls from outside an
Emergency Services IP Network be assigned esnet.0. This document
makes no recommendations on what originating service provider
networks actually provide for resource priority other than to note
the obvious: emergency calls should receive some priority for
resources.
Whatever the network does with the RPH value, it is desirable to
protect it from manipulation and
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[I-D.ietf-stir-rph-emergency-services] provides the mechanism to
accomplish that.
4. Emergency Call-backs
After an emergency call is placed, it is sometimes necessary for the
PSAP, or a responder, to call the caller back. This call is placed
by the authorities back to the original caller. [RFC7090] describes
the use of the SIP Priority header field, with the value "psap-
callback" to mark such calls and describes how called networks may
use that marking. RFC7090 does not describe any priority, and does
not mention use of the Resource Priority header field. There is no
protection against misuse of the SIP Priority field, and because, as
RFC7090 illustrates, it may affect routing, it is very desirable to
protect it from modification.
This document recommends that emergency calls-backs from authorities
outside an ESInet contain a Resource Priority header field and be
assigned esnet.0. This document makes no recommendations on what
service provider networks actually provide for resource priority
other than to note the obvious: emergency calls-backs should receive
some priority for resources.
Many countries are starting to adopt the emergency calling paradigms
promulgated by the IETF. For example, in North America, the [i3]
standard defines IP based emergency calling networks, drawing from
IETF work. In those systems, a PKI is being created, with a trusted
root, the "PSAP Credentialing Agency" (PCA). The PCA provides a root
of trust that could be used to sign call-backs protecting the SIP
Priority and Resource Priority header fields.
5. IANA Considerations
There are no actions requested of IANA in this document
6. Security Considerations
TBD
7. Acknowledgments
TBD
8. References
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8.1. Normative References
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informative References
[i3] NENA, "Detailed Functional and Interface Standards for the
NENA i3 Solution", September 2016,
<https://www.nena.org/resource/resmgr/standards/NENA-STA-
010.2_i3_Architectu.pdf>.
[RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for
Emergency and Other Well-Known Services", RFC 5031,
DOI 10.17487/RFC5031, January 2008,
<https://www.rfc-editor.org/info/rfc5031>.
[RFC4412] Schulzrinne, H. and J. Polk, "Communications Resource
Priority for the Session Initiation Protocol (SIP)",
RFC 4412, DOI 10.17487/RFC4412, February 2006,
<https://www.rfc-editor.org/info/rfc4412>.
[RFC6643] Schoenwaelder, J., "Translation of Structure of Management
Information Version 2 (SMIv2) MIB Modules to YANG
Modules", RFC 6643, DOI 10.17487/RFC6643, July 2012,
<https://www.rfc-editor.org/info/rfc6643>.
[RFC7090] Schulzrinne, H., Tschofenig, H., Holmberg, C., and M.
Patel, "Public Safety Answering Point (PSAP) Callback",
RFC 7090, DOI 10.17487/RFC7090, April 2014,
<https://www.rfc-editor.org/info/rfc7090>.
[RFC7135] Polk, J., "Registering a SIP Resource Priority Header
Field Namespace for Local Emergency Communications",
RFC 7135, DOI 10.17487/RFC7135, May 2014,
<https://www.rfc-editor.org/info/rfc7135>.
[RFC6881] Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in Support of Emergency Calling",
BCP 181, RFC 6881, DOI 10.17487/RFC6881, March 2013,
<https://www.rfc-editor.org/info/rfc6881>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/info/rfc3261>.
[I-D.ietf-stir-rph-emergency-services]
Dolly, M. and C. Wendt, "Assertion Values for a Resource
Priority Header Claim in Support of Emergency Services
Networks", draft-ietf-stir-rph-emergency-services-00 (work
in progress), January 2020.
Author's Address
Brian Rosen
470 Conrad Dr
Mars, PA 16046
US
Phone:
Email: br@brianrosen.net
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