Network Working Group James Polk
Internet-Draft Cisco Systems
Expires: August 8, 2013 February 8,2013
Intended Status: Informational
IANA Registering a SIP Resource Priority Header Field
Namespace for Local Emergency Communications
draft-polk-local-emergency-rph-namespace-03
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
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 a minimum 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) directly attached to an ESInet
would need to have a trust relationship with the ESInet such that
within these networks, SIP requests (thereby the session(s) they
establish) could make use of this "esnet" namespace for appropriate
treatment.
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
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described
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in [RFC2119].
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
administration.
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
"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]. 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
document.
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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, 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
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
"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
esnet.1
esnet.2
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esnet.3
(highest) esnet.4
The "esnet" namespace will be designated into 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
here.
For networks that act on the SIP Resource-Priority header field,
incorrect use of 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 outside the
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ESInet.
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.
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
[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
none
Author's Address
James Polk
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3913 Treemont Circle
Colleyville, Texas 76034
USA
Phone: +1-817-271-3552
Email: jmpolk@cisco.com
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