One document matched: draft-winterbottom-ecrit-direct-00.txt
ECRIT J. Winterbottom
Internet-Draft M. Thomson
Intended status: BCP Andrew Corporation
Expires: April 22, 2010 H. Tschofenig
Nokia Siemens Networks
H. Schulzrinne
Columbia University
October 19, 2009
ECRIT Direct Emergency Calling
draft-winterbottom-ecrit-direct-00.txt
Status of this Memo
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Abstract
This document describes a generic emergency calling client.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. The Jurisdictional Problem . . . . . . . . . . . . . . . . . . 5
4. Network Reference model . . . . . . . . . . . . . . . . . . . 6
5. ESRP Route Determination . . . . . . . . . . . . . . . . . . . 7
6. Emergency Client Registration . . . . . . . . . . . . . . . . 8
7. Emergency Client Call Intitiation . . . . . . . . . . . . . . 12
8. Call Termination Control . . . . . . . . . . . . . . . . . . . 13
9. SIP Feature Restrictions . . . . . . . . . . . . . . . . . . . 14
10. Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Test Registration . . . . . . . . . . . . . . . . . . . . 15
10.2. Format . . . . . . . . . . . . . . . . . . . . . . . . . 15
11. PSAP Callback . . . . . . . . . . . . . . . . . . . . . . . . 16
12. Security Considerations . . . . . . . . . . . . . . . . . . . 17
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
15.1. Normative References . . . . . . . . . . . . . . . . . . 20
15.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
The current IETF ECRIT architecture, as described in
[I-D.ietf-ecrit-phonebcp] and in [I-D.ietf-ecrit-framework], focuses
on devices where emergency calls are routed primarily through the
subscriber's home VSP and the direct signaling communication between
the end host and the PSAP that contains the IP-based PSAP is only an
exception. This is a convenient assumption if one considers the
regular communication patterns of the device and the potential
proprietary protocol implementations used between the end host and
the VSP and the ability to move the interoperability challenges away
from the end device and closer to VSPs. There are, however,
challenges for regulators to enforce emergency services functionality
when the VSP is located in a different jurisdiction with the current
model. Inclusion of a VSP introduces unnecessary elements into the
emergency call path making the overall solution more cumbersome.
This document describes the regulatory challenge and illustrates a
model for direct communication between the end host and the PSAP that
is supported by the basic SIP communication patterns. With the help
of the Location-to-Service Translation protocol a PSAP URI is
discovered that allows the end device to directly send SIP
communication requests towards the PSAP.
Note that the information returned by LoST may not necessarily be the
address of the PSAP itself but might rather be an entity that gets
the emergency call closer to the PSAP by returning the address of an
Emergency Services Routing Proxy (ESRP).
This memo attempts to address the issues raised above and describe
the requirements, procedures and operations necessary for a generic
IP emergency calling client. The intent of this client is that it
will be able to use the available ECRIT building blocks to allow any
IP enabled device with access to the Internet to make an emergency
call without requiring a voice service subscription. Further more, a
means for call-back in the event of a dropped call is also described.
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2. Terminology
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].
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3. The Jurisdictional Problem
The jurisdictional problem is illustrated with Figure 1 that
highlights that providing the data in the Location Information Server
(LIS) and the LoST server are correct, that the caller and the PSAP
are assured of being in the same regulatory jurisdiction. This is
important, because it shows that it is the access component of the
network and not the service component against which reguatory
obligations can be imposed with any hope of enforcement. Regulation
without the possibility of enforcement is challenging as there is
very little coordination between regulators world wide in this area,
consequently any emergency calling procedure should ensure that all
nodes against which the procedures apply fall within the same
regulatory boundary.
+-----+
| VSP |
| # |
+-----+
o-------------o----------------------o-------------o
/ \
/ +---------+ +--------+ \
/ | Access \ ASSURED / ESINet \ \
o | Network \ / \ o
| + + COMMON + O + |
| / O | / <P\ | |
| + <C\ o REGULATORY + /'\ + |
| | /'\ / | PSAP / o
o + Caller + JURISDICTION + +-------+ + /
\ \ __________| \ / \/ /
\ /
o--------------o----------------------o---------------o
Figure 1: Jurisdictional Boundaries in Internet Emergency Calling
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4. Network Reference model
In many deployments today the emergency calling device is located
behind a NAT or a firewall, and there is no assumption or requirement
for a VSP subscription to exist. Figure 2 illustrates such a typical
scenario. Indeed any subscription of this nature is immaterial to
the operation described in this memo.
.... ....
,' ',' ',
+----------+ ; ;
+--------+ | Firewall | ; ; +------+
| Device |--->| NAT | --->: ISP :----->| ESRP |
+--------+ +----------+ ; ; +------+
`, ,', ,'
{ } { }
```` ````
Figure 2: Network Configuration
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5. ESRP Route Determination
The ESRP is discovered by the emergency client obtaing its location
from a LIS, for example, using HELD, and then using LoST to resolve
the location and 'urn:services.sos' Service URN to the ESRP URI.
When the emergency client is started the device needs to perform LIS
and LoST server discovery, as described in Section 7 of
[I-D.ietf-ecrit-phonebcp].
The emergency client MUST support location acquisition and the LCPs
described in Section 6.5 of [I-D.ietf-ecrit-phonebcp]. The
description in Section 6.5 and 6.6 of [I-D.ietf-ecrit-phonebcp]
regarding the interaction between the device and the LIS applies to
this document.
The emergency client MUST use LoST [RFC5222] to obtain an ESRP URI.
The exact timing of individual LoST lookups may vary based on a
number of factors, including the design of the user interface. For
example, a hypothetical user interface may offer an emergency call
button that triggers a <listServicesByLocation> interaction to learn
about the available emergency services (potentially using the
serviceListBoundary extension defined in
[I-D.ietf-ecrit-lost-servicelistboundary]). The service options may
be presented to the emergency caller in a graphical fashion and once
a specific service is selected a LoST query would be initiated
(unless a cached mapping is available that makes this request
obsolete). The LoST <findService> query to obtain the ESRP URI for
the selected service is in this example initiated at the time the
emergency call setup is performed. It is recommended that ESRP
discovery occurs at call time.
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6. Emergency Client Registration
Emergency registration is only necessary when an emergency call
procedure is initiated. Immediately prior to making an emergency
call, the emergency client performs a SIP emergency registration with
the registrar in the ESRP, the ESRP-registrar. The emergency
registration is a SIP registration with specific options and headers
which are required in order to guard the emergency network and ensure
callback should it be required.
Each emergency client MUST provide an instance-id, as defined in
[I-D.ietf-sip-outbound], this allows the ESRP-registrar to generate a
GRUU [I-D.ietf-sip-gruu] that can be used as a callback identifier.
A GRUU is necessary as the callback identifier because the emergency
client does not provide a longer-term contact address to the ESRP-
registrar prior to registration, and the GRUU provides a handle by
which the PSAP can identify the calling emergency client. To
simplify the emergency client and ESRP-registrar implementations,
only public GRUUs are provided by the ESRP-registrar. The public
GRUU is guaranteed to be the same for a device regardless of re-
registration with a different call-id, which may occur if the device
unexpectedly reboots. This is not true for temporary GRUUs, which
makes temporary GRUUs undesriable in the scope of this application
space.
The PSAP is able to define and mandate the time over which callback
is possible. This needs to be a reasonable period of time, nominally
10s of minutes, as the device may well be transient with regards to
network attachment. The ESRP-registrar reflects the regulatory
callback period in the expiry value of emergency registration
responses. Emergency clients claiming compliance to this
specification MUST honour the value in the registration response from
the ESRP-registrar, up to a maximum of 60 minutes. An emergency
client SHOULD respect a registration expiry of longer than 60
minutes, but MAY terminate its registration with and ESRP-registrar
at 60 minutes if the expiry value provided by the ESRP-registrar was
longer.
In the event that a registration is lost by the emergency client
prior to reaching registration expiry then the emergency client MUST
re-register with the ESRP-registrar and SHOULD use the same call-id.
In this circumstance the ESRP-registrar SHOULD match the instance-id
and the call-id to recognize that it is a re-registration for a
dropped connection, and expiry time in the registration response
SHOULD be set to the time remaining from the original registration
occurred.
[I-D.ietf-sip-outbound] requires a device to support at least 2
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registrations to different proxies. The emergency client
requirements in this memo relax this requirement down to one
registration, but more than one is allowed. There are several
reasons for relaxing the connection redundancy requirement. Firstly,
ESRPs are expected to have inbuilt redundancy, so if a connection is
dropped due to a failed proxy in the ESRP, then a new connection or
registration will automatically be directed to an active proxy in the
ESRP cluster. If the connection dropped because of some other
failure along the path from the emergency client to the ESRP, then
multiple SIP registrations are unlikely to provide any measurable
reliability improvements since single points of failure in this path
are inherently likely. Secondly, re-registrations only occur
immediately prior to call placement, so any outbound failure will
also likely result in the call dropping. If this occurs then the
emergency client MUST re-register with the ESRP-registrar, and since
instance-id and public GRUU will remain unchanged as a result of
this, the emergency client can either receive a callback from the
PSAP, or it can initiate a new call to the emergency network.
Location information is critical to emergency calling. Providing
location information to the calling-entity with sufficient
granularity to allow ESRP route determination is crucial. Since this
must occur prior to the emergency client registering with the ESRP-
registrar, the emergency client must have access to a certain amount
of location information (and the amount varies depending on the
specific emergency services deployment architecture).
The device SHOULD include all the location information it has when
registering with the ERSP-registrar. Inclusion of location
information in SIP REGISTER messages is specified in
[I-D.ietf-sipcore-location-conveyance]. There are three possible
execution paths for the ESRP-registrar when receiving a REGISTER
message:
1. If the REGISTER message does not include location information the
ESRP-registrar MUST use HELD identity
[I-D.ietf-geopriv-held-identity-extensions] to obtain the
location of the device as both a location value and reference.
In order to contact the LIS the ESRP-registrar SHOULD determine
the LIS address using the mechanism described in
[I-D.thomson-geopriv-res-gw-lis-discovery]. The ESRP-registrar
MAY use other methods for LIS determination where available.
2. If the REGISTER message contains a location URI then the ESRP-
registrar MUST dereference it so that it has a location available
to route the impending emergency call. The ESRP-registrar MAY
validate the LIS address in the location URI with that of the LIS
serving the network from which the REGISTER message originated.
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LIS determination MAY be performed using the methods described in
[I-D.thomson-geopriv-res-gw-lis-discovery].
3. The REGISTER message contains location information by value. Any
actions performed by the ESRP-registrar to valid this information
are specific to the jurisdiction in which the ESRP operates and
are out of the scope of this document.
Where location conveyance is used confidentiality protection SHOULD
be provided using Transport Layer Security (TLS).
Figure 3 show the registration message exchange graphically.
+--------+ +-----+ +------+ +------+
| Device | | LIS | | LoST | | ESRP |
+--------+ +-----+ +------+ +------+
| | | |
+<----LIS Discovery---->+ | |
| | | |
+----locationRequest--->+ | |
| | | |
+<---locationResponse---| | |
| | | |
+------------------findService------------->+ |
| | | |
+<--------------findServiceResponse---------+ |
| | | |
+------------------------REGISTER------------------------>+
| | | |
| +<------locationRequest-----------+
| | | |
| +-------locationResponse--------->+
| | | |
+<-------------------------200 OK ------------------------+
| | | |
Figure 3: Registration message flow
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REGISTER sip:sos.example.com SIP/2.0
Via: SIP/2.0/TCP 192.0.2.2;branch=z9hG4bKnashds7
Max-Forwards: 70
From: anon <sip:anon@sos.example.com>;tag=7F94778B653B
To: anon <sip:anon@sos.example.com>
Call-ID: 16CB75F21C70
CSeq: 1 REGISTER
Geolocation: <https://lis.access.example.com:9192/suXweu838737d72>
;inserted-by="anon@192.0.2.2"
;routing-allowed=yes
Geolocation: <cid:target123@192.0.2.2>
;inserted-by="anon@192.0.2.2"
;routing-allowed=no
Require: gruu, geolocation
Supported: outbound, gruu
Contact: <sip:anon@192.0.2.2;transport=tcp>
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
Figure 4: Sample REGISTER message
Since the emergency client does not have a nominal domain, it MUST
register in the same domain as the ESRP. This is illustrated in the
example REGISTER message show in Figure 4.
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7. Emergency Client Call Intitiation
Immediately subsequent to the registration a SIP INVITE request is
sent to the ESRP in the following form:
1. The Request URI MUST be the service URN [RFC5031] in the "sos"
tree.
2. The To header MUST be a service URN in the "sos" tree.
3. The From header MUST be present and MUST be the public GRUU
returned from the registration with the ESRP-registrar.
4. A Route header MUST be present with an ESRP URI, obtained from
LoST.
5. A Contact header MUST be present and contain the public GRUU
[I-D.ietf-sip-gruu], and be valid for several minutes following
the termination of the call, provided that the UAC remains
registered with the same registrar, to permit an immediate call-
back to the specific device which placed the emergency call.
6. A SDP offer MUST be included in the INVITE. If voice is
supported the offer MUST include the G.711 codec, see Section 14
of [I-D.ietf-ecrit-phonebcp].
7. SIP Caller Preferences [RFC3841] SHOULD be used to signal how the
PSAP should handle the call. For example, a language preference
expressed in an Accept-Language header may be used as a hint to
cause the PSAP to route the call to a call taker who speaks the
requested language. SIP Caller Preferences may also be used to
indicate a need to invoke a relay service for communication with
people with disabilities in the call.
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8. Call Termination Control
The description in [I-D.rosen-ecrit-premature-disconnect-rqmts] is
relevant for this document.
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9. SIP Feature Restrictions
The functionality defined in Section 9.3 in [I-D.ietf-ecrit-phonebcp]
regarding disabling of certain features is relevant for this document
and an emergency client MUST NOT implement the the features listed in
ED-70, and ED-71.
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10. Testing
The description in Section 15 of [I-D.ietf-ecrit-phonebcp] regarding
emergency call testing is used by this specification. Since this
specification mandates a registration with the ESRP-registrar a
similar tagging URI to that described in
[I-D.patel-ecrit-sos-parameter] is used to indicate a test
registration.
Test registrations SHALL be of short durations, but MUST be long
enough to allow completion of a "test call" as described in
[I-D.ietf-ecrit-phonebcp].
10.1. Test Registration
When the emergency client sends a REGISTER request for emergency test
registration, the "sos.test" URI parameter MUST be appended to the
URI in the Contact header. This indicates to the ESRP-registrar that
the request is for emergency test registration.
...
Contact: <sip:anon@192.0.2.2;transport=tcp;sos.test>
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
Figure 5: Test REGISTER Message Fragment
Only one Contact header field SHOULD be included in the emergency
REGISTER test request. If more than one Contact header is included
then the presence of the "sos.test" URI in any of the Contact fields
SHALL result in the ESRP-registrar treating the registration as a
test registration.
10.2. Format
The following syntax specification uses the augmented Backus-Naur
Form (BNF) as described in [RFC5234].
The "sos.test" URI parameter is a "uri-parameter", as defined by
[RFC3261].
uri-parameter =/ sos-param-test
sos-param-test = "sos.test"
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11. PSAP Callback
PSAP callback occurs as described in
[I-D.schulzrinne-ecrit-psap-callback].
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12. Security Considerations
TBD
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13. IANA Considerations
This specification defines one new SIP URI parameter, as per the
registry created by [RFC3969].
Parameter Name: sos.test
Predefined Values: none
Reference: [RFCXXXX]
[NOTE TO IANA: Please replace XXXX with the RFC number of this
specification.]
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14. Acknowledgements
Thanks to Elaine Quah for being a sounding board.
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15. References
15.1. Normative References
[I-D.ietf-ecrit-phonebcp]
Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in support of Emergency Calling",
draft-ietf-ecrit-phonebcp-13 (work in progress),
July 2009.
[I-D.ietf-geopriv-held-identity-extensions]
Winterbottom, J., Thomson, M., Tschofenig, H., and R.
Barnes, "Use of Device Identity in HTTP-Enabled Location
Delivery (HELD)",
draft-ietf-geopriv-held-identity-extensions-01 (work in
progress), October 2009.
[I-D.ietf-sip-gruu]
Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-15 (work in progress),
October 2007.
[I-D.ietf-sip-outbound]
Jennings, C., "Managing Client Initiated Connections in
the Session Initiation Protocol (SIP)",
draft-ietf-sip-outbound-20 (work in progress), June 2009.
[I-D.ietf-sipcore-location-conveyance]
Polk, J. and B. Rosen, "Location Conveyance for the
Session Initiation Protocol",
draft-ietf-sipcore-location-conveyance-01 (work in
progress), July 2009.
[I-D.schulzrinne-ecrit-psap-callback]
Schulzrinne, H. and H. Tschofenig, "Marking of Calls
initiated by Public Safety Answering Points (PSAPs)",
draft-schulzrinne-ecrit-psap-callback-00 (work in
progress), March 2009.
[I-D.thomson-geopriv-res-gw-lis-discovery]
Thomson, M. and R. Bellis, "Location Information Server
(LIS) Discovery From Behind Residential Gateways",
draft-thomson-geopriv-res-gw-lis-discovery-02 (work in
progress), July 2009.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004.
[RFC3969] Camarillo, G., "The Internet Assigned Number Authority
(IANA) Uniform Resource Identifier (URI) Parameter
Registry for the Session Initiation Protocol (SIP)",
BCP 99, RFC 3969, December 2004.
[RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for
Emergency and Other Well-Known Services", RFC 5031,
January 2008.
[RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A Location-to-Service Translation
Protocol", RFC 5222, August 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
15.2. Informative References
[I-D.ietf-ecrit-framework]
Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
"Framework for Emergency Calling using Internet
Multimedia", draft-ietf-ecrit-framework-10 (work in
progress), July 2009.
[I-D.ietf-ecrit-lost-servicelistboundary]
Wolf, K., "Location-to-Service Translation Protocol (LoST)
Extension: ServiceListBoundary",
draft-ietf-ecrit-lost-servicelistboundary-00 (work in
progress), October 2009.
[I-D.patel-ecrit-sos-parameter]
Patel, M., "SOS Uniform Resource Identifier (URI)
Parameter for Marking of Session Initiation Protocol
(SIP) Requests related to Emergency Services",
draft-patel-ecrit-sos-parameter-06 (work in progress),
May 2009.
[I-D.rosen-ecrit-premature-disconnect-rqmts]
Rosen, B., "Requirements for handling abandoned calls and
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premature disconnects in emergency calls on the
Internet", draft-rosen-ecrit-premature-disconnect-rqmts-02
(work in progress), January 2009.
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Authors' Addresses
James Winterbottom
Andrew Corporation
Andrew Building (39)
University of Wollongong, NSW 2500
AU
Email: james.winterbottom@andrew.com
Martin Thomson
Andrew Corporation
Andrew Building (39)
University of Wollongong, NSW 2500
AU
Email: martin.thomson@andrew.com
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo, 02 600
Finland
Email: Hannes.Tschofenig@gmx.net
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US
Phone: +1 212 939 7004
Email: hgs+ecrit@cs.columbia.edu
URI: http://www.cs.columbia.edu
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