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rfc:rfc7135

Internet Engineering Task Force (IETF) J. Polk Request for Comments: 7135 Cisco Systems Category: Informational May 2014 ISSN: 2070-1721

   Registering a SIP Resource Priority Header Field Namespace for
                   Local Emergency Communications

Abstract

 This document creates the new Session Initiation Protocol (SIP)
 Resource Priority header field namespace 'esnet' and registers this
 namespace with IANA.  The new header field namespace allows for local
 emergency session establishment to a public safety answering point
 (PSAP), between PSAPs, and between a PSAP and first responders and
 their organizations.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 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).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see 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/rfc7135.

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.

Polk Informational [Page 1] RFC 7135 Emergency RPH Namespace May 2014

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
 2.  Rules of Usage of the Resource Priority Header Field . . . . .  4
 3.  "esnet" Namespace Definition . . . . . . . . . . . . . . . . .  6
   3.1.  Namespace Definition Rules and Guidelines  . . . . . . . .  6
   3.2.  The 'esnet' Namespace  . . . . . . . . . . . . . . . . . .  6
 4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   4.1.  IANA Resource-Priority Namespace Registration  . . . . . .  7
   4.2.  IANA Priority-Value Registrations  . . . . . . . . . . . .  7
 5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
 6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
 7.  Normative References . . . . . . . . . . . . . . . . . . . . .  9

1. Introduction

 This document creates the new Session Initiation Protocol (SIP)
 Resource Priority header (RPH) field namespace 'esnet' for local
 emergency usage and registers this namespace with IANA.  The SIP
 Resource-Priority header field is defined in RFC 4412 [RFC4412].  The
 new 'esnet' namespace is to be used for inbound calls towards a
 public safety answering point (PSAP), between PSAPs, and between a
 PSAP and first responders or their organizations within managed IP
 networks.  This namespace is not for use on the open public Internet
 because it can be trivially forged.
 Adding an RPH with the 'esnet' namespace can be differentiated from
 the marking of an emergency call using a service URN as defined in
 [RFC5031] in that the RPH specifically requests preferential
 treatment in networks that honor it, while the marking merely
 identifies an emergency call without necessarily affecting resources
 allocated to it.  It is appropriate to use both where applicable.
 RPH with 'esnet' may also be used within public safety networks for
 SIP sessions that are not emergency calls and thus not marked per RFC
 5031.
 This new namespace is included in SIP requests to provide an explicit
 priority indication within controlled environments, such as an IP
 Multimedia Subsystem (IMS) infrastructure or Emergency Services
 network (ESInet) where misuse can be reduced to an acceptable level
 because these types of networks have controls in place.  The function
 facilitates differing treatment of emergency SIP requests according
 to local policy, or more likely, a contractual agreement between the
 network organizations.  This indication is used solely to
 differentiate certain SIP requests, transactions, or dialogs from
 other SIP requests, transactions, or dialogs that do not have the
 need for priority treatment.  If there are differing, yet still
 understandable and valid Resource-Priority header values in separate

Polk Informational [Page 2] RFC 7135 Emergency RPH Namespace May 2014

 SIP requests, then this indication can be used by local policy to
 determine which SIP request, transaction, or dialog receives which
 treatment (likely better or worse than another).
 Application Service Providers (ASPs) that are securely connected to
 an ESInet may have sufficient controls policing the header, and a
 trust relationship with the entities inside the ESInet.  SIP requests
 from such ASPs could make use of this 'esnet' namespace for
 appropriate treatment when requests are passed from the ASP to the
 ESInet.
 The 'esnet' namespace may also be used on calls from a PSAP or other
 public safety agency on an ESInet towards a private or public
 network, ASP or User Agent ("call back") when priority is needed.
 Again, the request for priority is not for use on the public Internet
 due to the ease of forging the header.
 This document merely creates the namespace, per the rules within
 [RFC4412] as updated by [RFC7134], which necessitates that new RPH
 namespaces and their relative priority-value order be IETF reviewed
 before being registered with IANA.
 There is the possibility that within emergency services networks,
 Multilevel Precedence and Preemption (MLPP)-like behavior can be
 achieved (likely without the 'preemption' part), provided the local
 policy supports enabling this function.  For example, calls placed
 between law enforcement agents could be marked similarly to MLPP
 systems used by military networks, and some of those calls could be
 handled with higher priority than an emergency call from an ordinary
 user.  Therefore, the 'esnet' namespace is given five priority-levels
 instead of just one.  This document does not define MLPP-like SIP
 signaling for emergency calls like those using emergency service
 numbers (such as 911, 112, and 999), but it is not prevented either.
 Within the ESInet, there will be emergency calls requiring different
 treatments, according to the type of call.  Does a citizen's call to
 a PSAP require the same, a higher, or a lower relative priority than
 a PSAP's call to a police department or the police chief?  What about
 either relative to a call from within the ESInet to a national
 government's department responsible for public safety, disaster
 relief, national security/defense, etc.?  For these additional
 reasons, the 'esnet' namespace has multiple priority levels.
 This document does not define any of these behaviors, outside of
 reminding readers that the rules of RFC 4412 apply - though examples
 of usage are included for completeness.  This document registers the
 'esnet' RPH namespace with IANA for use within any emergency services
 networks, not just of those from citizens to PSAPs.

Polk Informational [Page 3] RFC 7135 Emergency RPH Namespace May 2014

 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. Rules of Usage of the Resource Priority Header field

 This document retains the behaviors of the SIP Resource Priority
 header field, defined in [RFC4412], when choosing between the
 treatment options surrounding this new 'esnet' namespace.  Given the
 environment this is to be used within (i.e., within an ESInet), the
 usage of the 'esnet' namespace does not have a 'normal' or routine
 call level; that is left for local jurisdictions to define within
 their respective parts of the ESInet, which could be islands of local
 administration.
 The 'esnet' namespace MUST only be used where at least one end of the
 signaling, setting aside the placement of B2BUAs (Back-to-Back User
 Agents), is within a local emergency organization.  In other words,
 if either the originating human caller's User Agent (UA) or the
 destination human callee's UA is part of the local emergency
 organization, this is a valid use of 'esnet'.
 The 'esnet' namespace has 5 priority-values, in a specified relative
 priority order, and is registered as a queue-based namespace in
 compliance with [RFC4412].  SIP entities that support preemption
 treatment (see Section 5 of [RFC4412]) can be configured according to
 local policy.  Display names for the 'esnet' values displayed can
 likewise be set according to local policy.

Polk Informational [Page 4] RFC 7135 Emergency RPH Namespace May 2014

 The following network diagram provides one example of local policy
 choices when using the 'esnet' namespace:
                                               |<-'esnet' namespace->|
                                               |        is used      |
 'esnet' namespace                             |        ,-------.
 usage out of scope                            |      ,'         `.
    |<------------>|<---'esnet' namespace ---->|     /             \
 +----+            |       can be used      +-----+ |    ESInet     |
 | UA |---         |    --------------------|Proxy|-+    ------     |
 +----+   \        |   /                    +-----+ |               |
           \  ,-------+           ,-------.    |    |   +------+    |
 +----+     ,'         `.       ,'         `.  |    |   |PSAP-1|    |
 | UA |--- /  User       \     / Application \ |    |   +------+    |
 +----+   (    Network    +---+    Service    )|    |               |
           \             /     \   Provider  / |    |   +------+    |
 +----+    /`.         ,'       `.         .+-----+ |   |PSAP-2|    |
 | UA |----   '-------'           '-------' |Proxy|-+   +------+    |
 +----+            |                        +-----+ |               |
                   |                           |    |               |
 +----+            |                        +-----+ |   +------+    |
 | UA |---         |    --------------------|Proxy|-+   |PSAP-3|    |
 +----+   \        |   /                    +-----+ |   +------+    |
           \  ,-------+           ,-------.    |    |               |
 +----+     ,'         `.       ,'         `.  |    |               |
 | UA |--- /  User       \     / Application \ |    |   +------+    |
 +----+   (    Network    +---+    Service    )|    |   |PSAP-4|    |
           \             /     \   Provider  / |    |   +------+    |
 +----+    /`.         ,'       `.         .+-----+ |               |
 | UA |----   '-------'           '-------' |Proxy|-+    ANY can    |
 +----+            |                        +-----+ |   xfer/call   |
                   |                           |     \    | | |    /
                                                      `.  | | |  ,'
                                                        '-|-|-|-'
                                                          | | |
                                   Police  <--------------+ | |
                                            Fire <----------+ |
                                      National Agency <-------+
      A Possible Network Architecture Using the 'esnet' Namespace
 In the figure, the 'esnet' namespace is used within the ESInet on the
 right side of the diagram.  How it is specifically utilized is out of
 scope for this document and is left to local jurisdictions to define.
 Whether preemption is implemented in the ESInet and the values
 displayed to the ESInet users is likewise out of scope.  Adjacent
 ASPs to the ESInet may have a trust relationship that includes
 allowing this/these neighboring ASP(s) to use the 'esnet' namespace

Polk Informational [Page 5] RFC 7135 Emergency RPH Namespace May 2014

 to differentiate SIP requests and dialogs within the ASP's network.
 The exact mapping between the internal and external sides of the edge
 proxy at the ESInet boundaries is out of the scope of this document.

3. "esnet" Namespace Definition

 The 'esnet' namespace is not generic for all emergencies because
 there are a lot of different kinds of emergencies, some on a military
 scale ([RFC4412] defines 3 of these), some on a national scale
 ([RFC4412] defines 2 of these), and some on an international scale.
 Each type of emergency can also have its own namespace(s); although
 there are many defined for other uses, more are possible -- so using
 the public emergency service number (such as 911, 112, or 999) to
 call for police officers, firefighters, or emergency medical
 technicians (etc.) does not have a monopoly on the word "emergency".
 The namespace 'esnet' has been chosen, roughly to stand for
 "Emergency Services NETwork", for a citizen's call for help from a
 public authority type of organization.  This namespace will also be
 used for communications between emergency authorities, and it MAY be
 used by emergency authorities to call public citizens.  An example of
 the latter is a PSAP operator calling back someone who previously
 called an emergency service number (such as 911, 112, or 999) and the
 communication was terminated before it -- in the PSAP operator's
 judgment -- should have been.
 Below is an example of a Resource-Priority header field using the
 'esnet' namespace:
       Resource-Priority: esnet.0

3.1. Namespace Definition Rules and Guidelines

 This specification defines one unique namespace for emergency calling
 scenarios, 'esnet' and registers this namespace with IANA.  This IANA
 registration contains the facets defined in Section 9 of [RFC4412].

3.2. The 'esnet' Namespace

 Per the rules of [RFC4412], each namespace has a finite set of
 relative priority-value(s), listed (below) from lowest priority to
 highest priority.  In an attempt to not limit this namespace's use in
 the future, more than one priority-value is assigned to the 'esnet'
 namespace.  This document does not recommend which Priority-value is
 used where in which situation or scenario.  That is for another
 document to specify.  To be effective, the choice within a national

Polk Informational [Page 6] RFC 7135 Emergency RPH Namespace May 2014

 jurisdiction needs to be coordinated by all sub-jurisdictions to
 maintain uniform SIP behavior throughout an emergency calling system
 of that nation.
 The relative priority order for the 'esnet' namespace is as follows:
       (lowest)  esnet.0
                 esnet.1
                 esnet.2
                 esnet.3
       (highest) esnet.4
 The 'esnet' namespace will have priority queuing registrations for
 these levels per Section 4.5.2 of [RFC4412].  Although no preemption
 is specified in this document for any levels of 'esnet', local
 jurisdiction(s) MAY configure their SIP infrastructure to use this
 namespace with preemption, as defined in RFC 4412.
 The remaining rules that originated in RFC 4412 apply with regard to
 an RP actor who understands more than one namespace, and must
 maintain its locally significant relative priority order.

4. IANA Considerations

4.1. IANA Resource-Priority Namespace Registration

 The following entry has been added to the "Resource-Priority
 Namespaces" registry of the sip-parameters section of IANA (created
 by [RFC4412]):
                                     Intended       New     New resp.
    Namespace  Levels   Algorithm     Code      warn-code   Reference
    ---------  ------  -----------  ---------   ---------   ---------
      esnet      5       queue         no          no       RFC 7135

4.2. IANA Priority-Value Registrations

 The following entry has been added to the "Resource-Priority
 Priority-values" registry of the sip-parameters section of IANA:
    Namespace: esnet
    Reference: (this document)
    Priority-Values (least to greatest): "0", "1","2", "3", "4"

Polk Informational [Page 7] RFC 7135 Emergency RPH Namespace May 2014

5. Security Considerations

 The Security considerations that apply to RFC 4412 [RFC4412] apply
 here.
 For networks that act on the SIP Resource-Priority header field,
 incorrect use of namespaces can result in traffic that should have
 been given preferential treatment not receiving it, and vice versa.
 This document does not define a use case where an endpoint outside
 the ESInet marks its call for preferential treatment.  Precautions
 need to be taken to prevent granting preferential treatment to
 unauthorized users not calling for emergency help even if they are in
 the ESInet, as well as to prevent misuse by callers outside the
 ESInet.
 A simple means of preventing this usage is to not allow traffic
 marked 'esnet' to get preferential treatment unless the destination
 is towards the local/regional ESInet.  This is not a consideration
 for internetwork traffic within the ESInet, or generated out of the
 ESInet.  Calling an emergency service number (such as 911, 112, or
 999) is fairly local in nature, with a finite number of URIs that are
 likely to be considered valid within a portion of a network receiving
 SIP signaling.
 This namespace is not intended for use on the Internet because of the
 difficulty in detecting abuse; specifically, it can trivially be
 forged and used on a non-emergency session to obtain resource
 priority.  Some networks may determine that it can reasonably prevent
 abuse and/or that the consequences of undetected abuse is not
 significant.  In such cases, use of 'esnet' on the Internet MAY be
 allowed.

6. Acknowledgements

 Thanks to Ken Carlberg, Janet Gunn, Fred Baker, and Keith Drage for
 help and encouragement with this effort.  Thanks to Henning
 Schulzrinne, Ted Hardie, Hannes Tschofenig, and Marc Linsner for
 constructive comments.  A big thanks to Robert Sparks for being
 patient with the author and Brian Rosen for completing the final
 edits.

Polk Informational [Page 8] RFC 7135 Emergency RPH Namespace May 2014

7. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC4412]  Schulzrinne, H. and J. Polk, "Communications Resource
            Priority for the Session Initiation Protocol (SIP)", RFC
            4412, February 2006.
 [RFC5031]  Schulzrinne, H., "A Uniform Resource Name (URN) for
            Emergency and Other Well-Known Services", RFC 5031,
            January 2008.
 [RFC7134]  Rosen, B., "The Management Policy of the Resource Priority
            Header (RPH) Registry Changed to "IETF Review"", RFC 7134,
            March 2014.

Author's Address

 James Polk
 Cisco Systems
 3913 Treemont Circle
 Colleyville, TX  76034
 USA
 Phone: +1-817-271-3552
 EMail: jmpolk@cisco.com

Polk Informational [Page 9]

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