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
draft-polk-local-emergency-rph-namespace-02
Abstract
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
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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
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"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
configurations.
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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
[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
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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
esnet.1
esnet.2
esnet.3
(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
here.
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
signaling.
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
none
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Author's Address
James Polk
3913 Treemont Circle
Colleyville, Texas 76034
USA
Phone: +1-817-271-3552
Email: jmpolk@cisco.com
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