ECRIT Working Group James Polk
Internet-Draft Cisco Systems
Intended Status: Standards Track (as PS) Oct 27, 2008
Expires: April 27, 2009
IANA Registering a SIP Resource Priority Header
Namespace for Local Emergency Communications
draft-ietf-ecrit-local-emergency-rph-namespace-00
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
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
organizations.
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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 . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1 Normative References . . . . . . . . . . . . . . . . . . 7
7.2 Informative References . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . 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 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 can be from a caller in
distress, or added at the entry server into an emergency services
managed network, towards a public safety answering point (PSAP),
i.e., the 911 or 112-based emergency services call taker. This
new namespace can be used between PSAPs, and between a PSAP and
first responders and their organizations.
Within controlled environments, such as an IMS infrastructure or
Emergency Services network (ESINet), where misuse can be reduced to
a minimum where possible, providing an explicit priority indication
facilitates treatment of emergency SIP messages according to local
policy. This indication is used to differentiate SIP signaling
requests, or dialogs, from other requests or dialogs.
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. [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 - perhaps separated by timing of each
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implementation.
From this fact about RFC 4412, and the possibility that within
emergency services networks, a Multilevel Precedence and Preemption
(MLPP)-like behavior can be achieved - 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 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, or routine call level.
Every use of this namespace will be in times of an emergency, where
at least one end of the signaling is with a local emergency
organization.
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
decision.
Conceivably, this could be an example of a generic network diagram
where the "esnet" namespace is used:
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|<-"esnet" namespace->|
| *WILL* be used |
"esnet" namespace | ,-------.
can be used | ,' `.
|<------------>|<---"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 a call |
| | \ | | | /
`. | | | ,'
'-|-|-|-'
| | |
Police <--------------+ | |
Fire <----------+ |
Federal Agency <-------+
Figure 1: Where 'esnet' Namespace Can or Will be used
In Figure 1., UAs connect to service providers that can have SIP
proxies. When calling for emergency help, the UAs MAY include a
"esnet" namespace in the SIP request. Use of this new namespace is
OPTIONAL, and likely is not trustworthy, unless SIP signaling is
within a managed environment starting at the originating UAC. This
namespace, therefore, MAY be overwritten or deleted, contrary to the
rules of RFC 4412 [RFC4412]. These proxies in the service provider
MAY either
o accept the existing RPH value with "esnet" in it, if one is
present, and grant relative preferential treatment to the request
when forwarding it to the ESINet.
o replace any existing RPH value, if one is present, and insert an
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"esnet" namespace and give relative preferential treatment to the
request when forwarding it to the ESINet.
o insert an "esnet" namespace in a new RPH and give relative
preferential treatment to the request when forwarding the SIP
request towards the ESINet.
Adjacent service providers can have a trust relationship in regards
to emergency calling, and the receiving service provider can accept
the inbound 'esnet' RPH namespace value and give preferential
treatment to the request when forwarding it to the ESINet.
On the other hand, SPs can choose to process each inbound SIP
requests with its own policies, based on the type of request it is,
in addition to the nature of the request. If the request is
destined for a PSAP, according to the receiving SP, it MAY treat the
request as if it were coming directly from a UA, and act according
to the 3 bullets above.
Ultimately, the edge proxy at the ESINet will receive emergency SIP
request, and process the request according to its rules. Regardless
of what RPH indications there are in the message, and what
treatments the message has received, the ESINet edge proxy will
ensure there is an RPH with the "esnet" namespace in the request.
Local policy will dictate the priority-value to be assigned within
the ESINet. This document makes no recommendations.
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 calling 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
namespace:
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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
"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
esnet.1
esnet.2
esnet.3
(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
local jurisdiction preferred to preempt normal calls in lieu of
completing emergency calls. This document is not RECOMMENDING this
usage, merely pointing out those behaviors is a matter of local
policy.
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
organizations).
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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
here. This document introduces no new security issues relative to
RFC 4412.
That said, since this SIP header, used for emergency calling can
have a great impact on local communications, providers SHOULD use
caution when deciding if they want to use a preemption algorithm
within the public space for 911/112/999 type calling. As
potentially already limited communications bandwidth might starve
out all other types of calls in a location. This decision might be
desired; but this effect might not be desired.
6. Acknowledgements
Thanks to Ken Carlberg, Janet Gunn, Fred Baker and Keith Drage for
help and encouragement with this effort.
7. References
7.1 Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997
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[RFC4412] Schulzrinne, H., Polk, J., "Communications Resource
Priority for the Session Initiation Protocol (SIP)", RFC
4411, Feb 2006
7.2 Informative References
none
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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