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

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7135.
Author James Polk
Last updated 2012-08-16 (Latest revision 2012-07-12)
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IESG IESG state Became RFC 7135 (Informational)
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Responsible AD Robert Sparks
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Network Working Group                                        James Polk
Internet-Draft                                            Cisco Systems
Expires: January 12, 2013                                 July 12, 2012
Intended Status: Standards Track 

          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
   Task Force (IETF).  Note that other groups may also distribute
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   reference material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 12, 2013.

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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

   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 the new Session Initiation Protocol (SIP) 
   Resource Priority header 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 envisioned for use on the open 
   public Internet because it can be trivially forged.  

   This new namespace can be 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 great controls in place.  The function is to facilitate 
   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
   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).

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

   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.

   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,. This will ensure more the 
   important calls are established or retained; 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 
   federal government's department of national security, such as the US
   Department of Homeland Security?  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.

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 for local jurisdictions to define within their respective 
   parts of the ESInet, which could be islands of local administration.

   RFC 4412 states that modifying the relative priority ordering or the
   number of priority-values to a registered namespace SHOULD NOT occur
   within the same administrative domain due to interoperability issues
   with dissimilar implementations and backwards compatibility of past 

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   The "esnet" namespace MUST only be used in times of an emergency, 
   where at least one end, setting aside the placement of B2BUAs, of 
   the signaling 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 "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]. Individual jurisdictions MAY configure 
   their SIP entities for preemption treatment. This is OPTIONAL, 
   subject to local policy decisions.

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

                                                |<-"esnet" namespace->|
                                                |    *WILL* be 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 <----------+ |
                                        Federal Agency <-------+

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

   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 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 document.

3.  "esnet" Namespace Definition

   The "esnet" namespace SHOULD NOT to be considered 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 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 been. 

   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 

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   "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.  This document does RECOMMEND 
   the choice within a national jurisdiction be coordinated by all 
   sub-jurisdictions to maintain uniform SIP behavior throughout an 
   emergency calling system of that country.

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

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

   The "esnet" namespace will be designated into the priority queuing 
   algorithm (Section 4.5.2 of [RFC4412]).  However, as a policy 
   decision, local jurisdiction(s) MAY configure their SIP 
   infrastructure to use the this namespace in a preemption algorithm 
   way, defined in RFC 4412. This document does not recommend this 
   usage, but it is permissible according to this specification.

   The remaining rules 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

   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"

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5.  Security Considerations

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

   Within a network that is enabled to act on the Resource-Priority 
   header field within SIP requests, the implications of using this 
   namespace within the field incorrectly can potentially cause a large
   impact on a network, given that this indication is to give 
   preferential treatment of marked traffic great preference within the
   network verses 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 likely to be 
   considered valid within a portion of a network receiving SIP 

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 
           4411, Feb 2006

7.2  Informative References


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Author's Address

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

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