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

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Document Type Active Internet-Draft (individual in rai area)
Author James Polk 
Last updated 2013-02-18
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Network Working Group                                        James Polk
Internet-Draft                                            Cisco Systems
Expires: August 15, 2013                               February 15,2013
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 in the following cases: to a public safety answering point 
   (PSAP), between PSAPs, and between a PSAP and first responders and 
   their organizations.  The document also puts this namespace into the
   IANA registry.

Status of this Memo

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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 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

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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) and ESInets that interact need 
   to specifically trust one another to correctly use this header. 

   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 
   in [RFC2119].

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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 (5 in [RFC4412] and
   40 in [RFC5478]), 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 in 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, 
   an incorrect use of a 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 

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   outside the ESInet.  

   A simple means of preventing this usage in 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

 [RFC5478] J. Polk, "IANA Registration of New Session Initiation 
           Protocol (SIP) Resource-Priority Namespaces", RFC 5478, 
           March 2009

 [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


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Author's Address

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

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