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Versions: 00 01 02 03 04 05 RFC 7135

Network Working Group                                        James Polk
Internet-Draft                                            Cisco Systems
Expires: August 8, 2013                                 February 8,2013
Intended Status: Informational

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


   This document creates the new Session Initiation Protocol (SIP)
   Resource Priority header field namespace "esnet" for local emergency
   usage to a public safety answering point (PSAP), between PSAPs, and
   between a PSAP and first responders and their organizations, and
   places this namespace in the IANA registry.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 8, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
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Table of Contents

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

1.  Introduction

   This document creates the new Session Initiation Protocol (SIP)
   Resource Priority header (RPH) field namespace "esnet" for local
   emergency usage and places this namespace in the IANA registry.  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 a RPH with the "esnet" namespace can be differentiated from
   the marking of an emergency call using a service urn as defined in
   RFC 5031 in that the RPH specifically requests preferential
   treatment in networks which 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 IMS infrastructure or Emergency Services network (ESInet) where
   misuse can be reduced to a minimum 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

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   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 (ASP) directly attached to an ESInet
   would need to have a trust relationship with the ESInet such that
   within these networks, SIP requests (thereby the session(s) they
   establish) could make use of this "esnet" namespace for appropriate

   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 UA ("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 [draft-rosen-rph-reg-policy], necessitating
   IETF review for IANA registering new RPH namespaces and their
   relative priority-value order.

   There is the possibility that within emergency services networks a
   Multilevel Precedence and Preemption (MLPP)-like behavior can be
   achieved  (likely without the 'preemption' part), provided 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.  MLPP-like SIP signaling is not defined in this
   document for 911/112/999 style emergency calling, 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 was given 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 IANA
   registers the "esnet" RPH namespace for use within any emergency
   services networks, not just of those from citizens to PSAPs.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   "OPTIONAL" in this document are to be interpreted as described

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   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], during the treatment options
   surrounding this new "esnet" namespace. The usage of the "esnet"
   namespace does not have a 'normal', or routine call level, given the
   environment this is to be used within (i.e., within an ESInet).
   That is left for local jurisdictions to define within their
   respective parts of the ESInet, which could be islands of local

   The "esnet" namespace MUST only be used where at least one end of
   the signaling, setting aside the placement of B2BUAs, is within a
   local emergency organization. In other words, if either the
   originating human caller's UA, or the destination human callee's UA
   is part of the local emergency organization, this is a valid use of

   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.

   The following network diagram provides one example of local policy
   choices for the use of the "esnet" namespace:

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                                                |<-"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 <-------+

   Figure 1: A possible network architecture using "esnet" namespace

   In Figure 1., 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 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 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 scope of this

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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), some on an international
   scale.  Each type of emergency can also have its own namespace(s),
   and although there are 45 defined for other uses, more are possible
   - so the 911/112/999 style of public user emergency calling for
   police or fire or ambulance (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 MAY be
   used for the ESInet to emergency authorities calling public
   citizens.  An example of the latter is a PSAP operator calling back
   someone who previously called 911/112/999 and the communication was
   terminated before it -in the PSAP operator's judgment - should have

   Here 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", constituting its registration with IANA.
   This IANA registration contains the facets defined in Section 9 of

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 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

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      (highest) esnet.4

   The "esnet" namespace will be designated into the priority queuing
   algorithm (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 originated in RFC 4412 apply with regard to an
   RP actor who understands more than one namespace, and is must
   maintain its locally significant relative priority order.

4.  IANA Considerations

4.1  IANA Resource-Priority Namespace Registration

   Within the "Resource-Priority Namespaces" of the sip-parameters
   section of IANA (created by [RFC4412]), the following entries will
   be added to this table:

                        Intended      New warn-   New resp.
   Namespace  Levels    Algorithm     code        code      Reference
   ---------  ------  --------------  ---------   --------- ---------
     esnet      5        queue           no          no     [This doc]

4.2  IANA Priority-Value Registrations

   Within the Resource-Priority Priority-values registry of the
   sip-parameters section of IANA, the following (below) is to be added
   to the table:

   Namespace: esnet
   Reference: (this document)
   Priority-Values (least to greatest): "0", "1","2", "3", "4"

5.  Security Considerations

   The Security considerations that apply to RFC 4412 [RFC4412] apply

   For networks that act on the SIP Resource-Priority header field,
   incorrect use of namespace can result in traffic that should have
   been given preferential treatment not be given it and vice versa.
   This document does not define a use case where an endpoint outside
   the ESInet marks its call for preferential treatment.  Protections
   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

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   A simple means of preventing this usage into an ESInet is to not
   allow "esnet" marked traffic 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.  911/112/999 type of calling 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

   This namespace is not intended for use on the Internet because of
   the difficulty in detecting abuse.  Some networks may determine that
   it can reasonably prevent abuse and/or the consequences of
   undetected abuse is not significant.  In such cases, use of esnet
   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, Brian Rosen, Janet Gunn
   and Marc Linsner for constructive comments. A big thanks to Robert
   Sparks for being patient with the author.

7.  References

7.1  Normative References

 [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
           Requirement Levels", RFC 2119, March 1997

 [RFC4412] Schulzrinne, H., Polk, J., "Communications Resource
           Priority for the Session Initiation Protocol (SIP)", RFC
           4412, Feb 2006

 [RFC5031] H. Schulzrinne, "A Uniform Resource Name (URN) for Emergency
           and Other Well-Known Services", RFC 5031, January 2008

 [draft-rosen-rph-reg-policy]  Rosen, B, "Resource-Priority Header
           Registry Policy to IETF Review, draft-rosen-rph-policy-00
           (work in progress), Feb 2013

7.2  Informative References


Author's Address

   James Polk

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   3913 Treemont Circle
   Colleyville, Texas  76034
   Phone: +1-817-271-3552
   Email: jmpolk@cisco.com

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