ECRIT Working Group                                          James Polk
Internet-Draft                                            Cisco Systems
Expires: September 9, 24, 2009                                Mar 9, 24, 2009
Intended Status: Standards Track (as PS)
Updates: RFC4412 (if published as an RFC)

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

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   This documents and the information contained therein are provided on


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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .  3  2
   2.  Rules of Usage of the Resource Priority Header  . . . . . . .  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.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     7.1   Normative References  . . . . . . . . . . . . . . . . . .  8
     7.2   Informative References  . . . . . . . . . . . . . . . . .  8
       Author's Address  . . . . . . . . . . . . . . . . . . . . . .  8

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   "OPTIONAL" in this document are to be interpreted as described
   in [RFC2119].

1.  Introduction

   This document creates and IANA registers the new Session Initiation
   Protocol (SIP) Resource Priority header (RPH) namespace "esnet" for
   local emergency usage.  The SIP Resource-Priority header is defined
   in RFC 4412 [RFC4412]. This new namespace is to be used within
   public safety answering point (PSAP) networks.  This new namespace
   can be used for inbound calls towards PSAPs, between PSAPs, and
   between a PSAP and first responders or their organizations.

   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 great controls in
   place, this namespace can be to provide an explicit priority
   indication that facilitates differing treatment of emergency SIP
   messages according to local policy, or more likely, a contractual
   agreement between the network organizations.  This indication is
   used to differentiate SIP requests, or dialogs, from other requests
   or dialogs that do not have the need for priority treatment.

   It can also be imagined that Voice Service Providers (VSP) directly
   attached to an ESInet can have a trust relationship with the ESInet
   such that within these networks, SIP requests (thereby the session
   they establish) make use of this "esnet" namespace for appropriate

   Usage of the "esnet" namespace is to be defined in a future
   document(s). This document merely creates the namespace, per the
   rules within [RFC4412], necessitating a Standards Track RFC for
   IANA registering new RPH namespaces and their relative
   priority-value order.   Section 8 of [RFC4412] further states that
   modifying the order or the number of priority-values to a registered
   namespace SHOULD NOT occur, due to interoperability issues with
   dissimilar implementations.

   There is a possibility that within emergency services networks, a
   Multilevel Precedence and Preemption (MLPP)-like behavior can be
   achieved (likely without the 'preemption' part, which will always be
   a matter of local policy, and not defined here) - ensuring more
   important calls are established or retained, the "esnet" namespace
   is given 5 priority-levels.  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
   federal government's department of national security, such as the US
   Department of Homeland Security?  For this reason, the "esnet"
   namespace is 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 emergency
   services networks, not just of those from citizens to PSAPs.

2.  Rules of Usage of the Resource Priority Header

   This document updates the behaviors of the SIP Resource Priority
   header, defined in [RFC4412], during the treatment options
   surrounding this new "esnet" namespace only. The usage of the
   "esnet" namespace does not have a normal, 'normal', or routine call level,
   defined in
   given the environment this document. is to be used within (i.e., within an
   ESInet).  That is for local jurisdictions to define within their
   respective parts of the ESInet- which could be islands of local

   RFC4412 states that modifying the relative priority ordering or the
   number of priority-values to a registered namespace is not
   recommended across the same administrative domain, due to
   interoperability issues with dissimilar implementations.

   Every use of this namespace will be in times of an emergency, where
   at least one end of the signaling is within a local emergency

   The "esnet" namespace has 5 priority-values, in a specified relative
   priority order, and is a queue-based treatment namespace [RFC4412].
   Individual jurisdictions MAY configure their SIP entities for
   preemption treatment, but this is optional, and a local policy

   Conceivably, this could be an example network diagram where the
   "esnet" namespace is used:

                                                |<-"esnet" namespace->|
                                                |    *WILL* be used   |
  "esnet" namespace                             |        ,-------.
  usage out of scope                            |      ,'         `.
     |<------------>|<---"esnet" namespace ---->|     /             \
  +----+            |       can be used      +-----+ |    ESINet     |
  | UA |---         |    --------------------|Proxy|-+    ------     |
  +----+   \        |   /                    +-----+ |               |
            \  ,-------+           ,-------.    |    |   +------+    |
  +----+     ,'         `.       ,'         `.  |    |   |PSAP-1|    |
  | UA |--- /  User       \     /   Service   \ |    |   +------+    |
  +----+   (    Network    +---+    Network    )|    |               |
            \             /     \             / |    |   +------+    |
  +----+    /`.         ,'       `.         .+-----+ |   |PSAP-2|    |
  | UA |----   '-------'           '-------' |Proxy|-+   +------+    |
  +----+            |                        +-----+ |               |
                    |                           |    |               |
  +----+            |                        +-----+ |   +------+    |
  | UA |---         |    --------------------|Proxy|-+   |PSAP-3|    |
  +----+   \        |   /                    +-----+ |   +------+    |
            \  ,-------+           ,-------.    |    |               |
  +----+     ,'         `.       ,'         `.  |    |               |
  | UA |--- /  User       \     /   Service   \ |    |   +------+    |
  +----+   (    Network    +---+    Network    )|    |   |PSAP-4|    |
            \             /     \             / |    |   +------+    |
  +----+    /`.         ,'       `.         .+-----+ |               |
  | UA |----   '-------'           '-------' |Proxy|-+    ANY can    |
  +----+            |                        +-----+ |   xfer/call   |
                    |                           |     \    | | |    /
                                                       `.  | | |  ,'
                                                           | | |
                                    Police  <--------------+ | |
                                             Fire <----------+ |
                                        Federal Agency <-------+

       Figure 1: Where 'esnet' Namespace Can or Will be used

   In Figure 1., the "esnet" namespace is intended for usage 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.  Adjacent VSPs to the ESInet MAY have a
   trust relationship that includes allowing this/these neighboring
   VSP(s) to use the "esnet" namespace to differentiate SIP requests
   and dialogs within the VSP's network.  How this namespace is
   utilized is out of scope for this document.  Because the more
   important usage of the "esnet" namespace occurs within the ESInet,
   the edge proxy, called an Emergency Services Routing Proxy (ESRP)
   can modify or delete this namespace. This is a normative change to
   the allowed behavior within  [RFC4412] which only applies to the
   "esnet" namespace, and MUST only be considered valid in this usage
   at the ESInet boundary for this one RP namespace (and associated
   priority-value).  The exact mapping between the
   internal and external sides of the ESRP edge proxy at the ESInet
   boundaries are is out of scope of this document.

   To be clear, the use of an edge proxy in any network, the rules
   within the document that create a (i.e., each) namespace apply, and
   because the "esnet" namespace is allowed to be modified or deleted
   at the edge proxy of the ESInet does not allow any edge proxy to
   modify or delete any other Resource-Priority namespace.  This
   document's target market is for the "esnet" namespace only.

3.  "esnet" Namespace Definition

   One thing to keep in mind for now is the fact that this namespace
   is not to be considered just "EMERGENCY" 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.  These types of
   emergencies can also have their own namespaces, and although there
   are 5 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".

   Therefore, the namespace "esnet" has been chosen, as it is most
   recognizable as that of 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 emergency authorities calling public citizens.  An example of
   the later is a PSAP operator calling back someone who previously
   called 9111/112/999 and the communication was terminated before it
   should have been (in the operator's judgment).

   Here is an example of a Resource-Priority header using the esnet

      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.  That is for another document to
   specify.  This document does RECOMMEND the choice within a national
   jurisdiction is coordinated by all sub-jurisdictions to maintain
   uniform SIP behavior throughout an emergency calling system.

   The relative priority order for the "esnet" namespace is as follows:

      (lowest)  esnet.0
      (highest) esnet.4

   The "esnet" namespace will be assigned into the priority queuing
   algorithm (Section 4.5.2 of [RFC4412]) from the public user to the
   PSAP.  This does not limit its usage to only the priority queue
   algorithm; meaning the preemption algorithm can be used where the is a policy decision for
   local jurisdiction preferred to preempt normal calls in lieu of
   completing emergency calls. jurisdictions.  This document is not RECOMMENDING this
   usage, merely pointing out those behaviors is a matter of local

   The rules originated in RFC 4412 remain with regard to an RP actor,
   who understands more than one namespace, MUST maintain its locally
   significant relative priority order.

   NOTE: at this time, there has not been sufficient discussion about
   whether or not preemption will be used for communications between
   PSAPs or between PSAPs and First responders (and their

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

   The implications of using this header-value incorrectly can cause a
   large impact on a network - given that this indication is to give
   preferential treatment of marked traffic great preference within the
   network than other traffic.  This document does not indicate this
   marking is intended for use by endpoints, yet protections need to be
   taken to prevent granting preferential treatment to unauthorized
   users not calling for emergency help.

   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 considered

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.

7.  References

7.1  Normative References

 [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
 [RFC4412] Schulzrinne, H., Polk, J., "Communications Resource
           Priority for the Session Initiation Protocol (SIP)", RFC

7.2  Informative References


Author's Address

   James Polk
   3913 Treemont Circle
   Colleyville, Texas  76034
   Phone: +1-817-271-3552