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GEOPRIV M. Garcia-Martin
Internet-Draft Ericsson
Intended status: Standards Track H. Tschofenig
Expires: April 29, 2010 Nokia Siemens Networks
H. Schulzrinne
Columbia University
M. Thomson
Andrew Corporation
October 26, 2009
Indirect Presence Publication with the Session Initiation Protocol(SIP)
draft-garcia-geopriv-indirect-publish-01
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Abstract
A method for indirectly publishing presence information is described.
This allows a presentity user agent to publish a URI that can be used
by the presence agent to retrieve presence information. A presence
agent is then better able to acquire dynamic presence information
without relying on the presentity user agent. This also allows a
presentity user agent to delegate responsibility for managing
changing presence data to the source of that information.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Geolocation Protocols Relationship . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2. Indirect Presence Publish . . . . . . . . . . . . . . . . . . 6
2.1. Multiple Presence Sources . . . . . . . . . . . . . . . . 6
3. Location header . . . . . . . . . . . . . . . . . . . . . . . 7
4. Indicating and Requiring Support of Indirect Publish . . . . . 8
5. De-reference Errors . . . . . . . . . . . . . . . . . . . . . 8
6. The Geolocation Header . . . . . . . . . . . . . . . . . . . . 9
7. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Security considerations . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
10.2. Informational References . . . . . . . . . . . . . . . . . 14
Appendix A. Alternative Solutions Considered . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
The Session Initiation Protocol (SIP) [RFC3261] is extended by the
SIP-events [RFC3265] framework to provide subscriptions and
notifications of SIP events. One example of such event notification
mechanism is 'presence' and this presence information is carried in
Presence Information Data Format (PIDF) [RFC3863] documents.
Two sources of presence information have been established. The
presence agent might be able to acquire presence data independently,
or it might rely on the presentity user agent providing that
information. Use of the SIP PUBLISH method for the purpose of
informing the presence agent of state is described in RFC 3903
[RFC3903].
Many existing elements of presence information, such as the Presence
Data Model [RFC4479], Rich Presence Extensions to PIDF (RPID)
[RFC4480], or the Contact Information to the Presence Information
Data Format (CIPID) [RFC4481], are acquired directly from the
presentity user agent. However, there are cases when the presentity
user agent is not the direct source of the presence information.
One such example is location information. A presentity user agent
might acquire location information from a Location Information Server
(LIS). Due to the dynamic nature of location information, a LIS
might provide location information by reference rather than value.
One of these cases occurs when a presentity user agent acquires its
own location information from a LIS using HELD
[I-D.ietf-geopriv-http-location-delivery]. A reference in the form
of a location URI allows the holder of the reference to obtain
location information at any time directly from the LIS.
This document describes a means for a presentity user agent to
publish presence information indirectly using a URI. The presence
agent is then able to obtain information directly from the source of
the data. This removes some of the burden of managing dynamic
content from the presentity user agent, as they do not need to
monitor changes to presence data and publish updates as changes
occur.
Presence agents might provide a complex presence document that is
assembled from multiple sources. A means is provided where the
presence agent is able to assemble a presence document.
The mechanism in this document was originally designed with location
information in mind, but it can be equally applied to any other form
of dynamic presence data.
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1.1. Geolocation Protocols Relationship
[ED: move these pictures out of here. We need pictures that aren't
location-specific so that readers don't mistakenly think that this is
just about location. That's already compounded by using "Location",
so this needs to be very clear. Maybe this could be made an
appendix.]
The PIDF location object (PIDF-LO) [RFC4119] establishes location
information as a form of presence information. Therefore, a presence
agent might provide location information along with other information
such as status or mood ([RFC4480]).
A presence service commonly needs to rely on other entities to
provide it with location information. A presentity user agent might
be able to provide location information, or it might interact with a
Location Information Server (LIS) [I-D.ietf-geopriv-arch] to acquire
that information.
Figure 1 depicts the geolocation protocol relationship. A location
URI points to a resource on a LIS that is able to provide location of
a specific Target. The LIS is able to associate the Location URI to
the location of the Target inside its administrative domain. In this
case, the Target in question is the presentity user agent.
+-----------+ +------------+
| | | Location |
| LIS | | Recipient/ |
| | | Presence |
| | | Agent |
+-----------+ +------------+
^ ^ ^
| | //
Location | | Location //
Configuration| | Dereference //
Protocol | | Protocol //
(1) | | (2) //
| | // Location Conveyance
v v // Protocol (e.g., SIP)
+------------+ // (3)
| | //
| Target / | //
| Presentity |<
| |
+------------+
Figure 1: Presence and Geolocation Protocols (Values)
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The following three steps are followed in Figure 1:
(1). The presentity user agent (or Target) acquires a location URI
from the Location Information Server (LIS) using a Location
Configuration Protocol (LCP).
(2). Before publishing location information to the presence agent,
the target must first de-reference the location URI to acquire
a location value. Alternatively, location information might be
acquired from the LIS by value.
(3). Finally, the presentity user agent assembles an updated
presence document and publishes this to the presence agent.
A location URI [I-D.ietf-geopriv-lbyr-requirements] provides
additional flexibility that this process does not take advantage of.
A location URI provides a way for a location recipient to have
control over when and how location information is acquired. A
location URI can be used by the presence agent to acquire location
information according to the needs of the watchers that require the
information.
This document enables the scenario shown in Figure 2, where the
presentity user agent is able to acquire a location URI (step 1) and
publish the URI (step 2). The presence agent is then able to acquire
location information directly from the LIS (step 3).
+-----------+ +------------+
| | Location | Location |
| LIS |<------------->| Recipient/ |
| | Dereference | Presence |
| | Protocol (3) | Agent |
+-----------+ +------------+
^ ^
| //
| Location //
| Configuration //
| Protocol //
| (1) //
| // Location Conveyance
v // Protocol (e.g., SIP)
+-------------+ // (2)
| | //
| Target / | //
| Presentity |<
| |
+-------------+
Figure 2: Presence and Geolocation Protocols (References)
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1.2. 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 BCP 14, RFC 2119
[RFC2119].
This document uses SIP events terminology from [RFC3265], presence
terminology from [RFC3903], and Geopriv terminology from
[I-D.ietf-geopriv-arch].
2. Indirect Presence Publish
A presentity user agent first acquires a reference to presence
information in the form of a URI.
For location information, a location URI can be obtained using a
location configuration protocol, such as HELD
[I-D.ietf-geopriv-http-location-delivery]. For HELD, this is done
by including a "locationType" element with the value set to
"locationURI".
The presentity user agent then publishes the URI (or URIs) to a
presence agent, using the "Location" header (see Section 3).
This header is not specific to physical location information. Do
not confuse the "Location:" header with the "Geolocation:" header.
The former inherits its meaning from the HTTP [RFC2616] header of
the same name, the name being a logical location or address. The
latter is specifically restricted to physical location
information.
The presence agent de-references URIs to acquire the referenced
information. A "sip:", "sips:" or "pres:" URI is dereferenced by
subscribing for the presence event package at the given URI; a
"http:" or "https:" URI is dereferenced following the rules in
[I-D.winterbottom-geopriv-deref-protocol]. Other URIs MUST not be
used unless a method is defined for that URI that produces a presence
document.
2.1. Multiple Presence Sources
Indirect publish establishes multiple presence sources for a presence
agent. In addition to the presentity user agent, multiple indirect
sources of presence data can be identified using the "Location"
header.
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The presence agent acquires presence information from each source.
This results in multiple presence documents. These documents are
combined to produce a single document.
The single presence document contains the union of the set of tuples
(or the [RFC4479] equivalents of "device" or "person") from every
presence document thus obtained. Tuple identifiers are modified as
necessary to prevent collisions in the identifier namespace; this
might be done be prefixing each tuple with the source identifier.
The presentity identifier in the final document is the presentity
identifier in any presence document provided by the presentity user
agent itself. Presentity identifiers from other sources are ignored.
The presence agent then monitors the state of the referenced presence
document according to the needs of watchers. The presence agent
updates its own copy of the presence data from each source. As
presence state provided by each source changes, this is combined with
data from other sources and watchers are notified accordingly.
A partial presence document [RFC5264] MAY be used if the presence
agent supports this format. In this case, partial differences
("pidf-diff" documents) provided from a given source are applied the
information retrieved previously from the same source.
3. Location header
The "Location" header includes a URI for information that might
otherwise be included in the body of a request. It is defined by the
following ABNF [RFC5234], using the conventions and definitions in
[RFC3261]:
location-header = "Location" HCOLON location-header-value
location-value = (location-item *(COMMA location-item))
location-item = LAQUOT location-URI RAQUOT
/ *(SEMI location-param)
location-URI = absoluteURI
location-param = location-src-param / generic-param
location-src-param = "src" EQUAL token
This document defines the "Location" header field as valid in SIP
PUBLISH [RFC3903] requests only.
Each URI in the "Location" header MAY be tagged with a "src"
parameter, identifying the source of the data that is found at the
URI. This identifier is an opaque tag that is used to identify
different URIs as having the same source. An included URI with no
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"src" parameter is considered to have a different "src" parameter to
any other included URI. URIs with identical "src" parameters
indicate that they are alternative URIs (possibly with different
schemes) for the same information.
A presence agent MUST only attempt to use a single URI from each set
with a unique "src" parameter. Presence information from any given
URI can only be updated or replaced with presence information from a
URI with the same "src" parameter.
Each PUBLISH message contains a complete set of URIs. The presence
agent MUST NOT use a URI if the most recent "Location" header
received does not include that URI. The "Location" header can be
omitted in a request, which does not alter the set of URIs used by
the presence agent. Providing an empty "Location" header stops the
presence agent from using any URIs.
4. Indicating and Requiring Support of Indirect Publish
A SIP option tag of "indirectpub" is created for use in the "Require"
header. This is used by a presentity user agent to provide surety
that any request to indirectly publish presence data has been
understood by the presence agent.
Attempts to publish indirectly MUST use this option tag in the
"Require" header. If an attempt to publish information indirectly
fails, the presence agent includes the tag in the "Unsupported"
header of a 420 (Bad Extension) response. Upon receiving this
response, the presentity user agent SHOULD attempt to de-reference
the URI and re-attempt the request with the presence information
included directly unless it is unable or local policy dictates
otherwise.
5. De-reference Errors
Indirect publish adds an additional de-reference step to the publish
process. This adds additional failure scenarios. The presence agent
might be unable to de-reference a URI for a number of reasons:
o the indicated host might be unreachable
o the URI might be badly formed or it might refer to a non-existent
destination
o the URI schemes - and the de-reference mechanisms they indicate -
provided might not be supported by the presence agent
o the URI might produce information that is not presence data
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o the presence agent might not be authorized to retrieve the
indicated data and the de-reference request might be rejected by
the server
Some of these errors might be detected during the processing of the
request. Others might be encountered later by the presence agent. A
mechanism is provided to indicate to the presentity user agent when
the presence agent detects an error while processing the request.
[TBD: need to work out how to do this. Either way, it's almost
essential to indicate to the presentity user agent that something has
failed. There are many reasons that a URI might not be accessible,
in many cases, it might be useful if the presentity user agent could
fall back on providing information by value if the URI can't be used.
It might be that the presentity user agent is more able to
dereference the URI, or might be able to look for alternative sources
for the information.]
[The lessons of the Geolocation header might be of some use here.]
6. The Geolocation Header
[ED: Useful? Unnecessary complication? Initial inclination is
toward the latter.]
A presence agent MAY choose to treat a Geolocation header
[I-D.ietf-sipcore-location-conveyance] in a PUBLISH request as though
it were a "Location" header. The "Require" header of the request
MUST include "indirectpub" in this case; if it does not, the presence
agent cannot assume that the information was intended to be
published.
The contents of the "Geolocation" header MUST be ignored if a
"Location" header is present.
7. Example
In the Figure 3, the presentity user agent (PUA) acquires and
publishes a reference to presence data that is served by a presence
source (PS). The presence agent (PA) provides this information to a
watcher along with information included by the presentity user agent.
Only request messages are shown for clarity.
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PUA PS PA WATCHER
| | | |
|<-- Acquire -->| |<-- Establish -->|
| Reference | | Subscription |
| | | |
|------- M1: Publish Reference ----->| |
| | | |
| |<-- M2: Subscribe --| |
| | | |
| |--- M3: Notify ---->| |
| | | |
| | |-- M4: Notify -->|
| | | |
| | ... | |
| | | |
| |----- Notify ------>| |
| | | |
| | |---- Notify ---->|
| | | |
. . . .
Figure 3
A presentity user agent acquires a URI that refers to presence
information. In this example, it is also assumed that the watcher
has also established a subscription.
The presentity user agent publishes this information to a presence
agent. The SIP PUBLISH might also include information that the
presentity user agent directly provides, such as the status.
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M1:
PUBLISH sip:presentity@example SIP/2.0
To: <sip:presentity@example>
From: <sip:presentity@example>;tag=1234wxyz
Call-ID: 81818181@pua.example
CSeq: 1 PUBLISH
Max-Forwards: 70
Event: presence
Location: <pres:3cy89sckl@source.example>;src=abc123,
<https://source.example/presence/3cy89sckl>;src=abc123
Contact: presentity@pua.example
Content-Type: application/pidf+xml
Content-Length: ...
<presence entity="pres:presentity@example">
<tuple id="status>
<!-- status tuple contents-->
</tuple>
</presence>
The presence agent selects one location from each source and de-
references this URI. For a SIP URI ("sip:", "sips:", or "pres:")
this requires a presence event package subscription.
M2:
SUBSCRIBE pres:3cy89sckl@source.example SIP/2.0
To: <pres:3cy89sckl@source.example>
From: <pres:pa.example>;tag=4567qwer
Call-ID: 111222@example
CSeq: 1 SUBSCRIBE
Max-Forwards: 70
Event: presence
Expires: 3600
Contact: sip:pa.example
Content-Length: 0
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The presence source provides a notification containing presence
information selects one location from each source and de-references
this URI. For a SIP URI ("sip:", "sips:", or "pres:") this requires
a presence event package subscription.
M3:
NOTIFY pa.example SIP/2.0
To: <pres:pa.example>
From: <pres:3cy89sckl@source.example>;tag=7678fghj
Call-ID: 111222@example
CSeq: 1 NOTIFY
Max-Forwards: 70
Event: presence
Subscription-State: active; expires=3599
Contact: sip:source.example
Content-Type: application/pidf+xml
Content-Length: ...
<presence entity="pres:3cy89sckl@source.example">
<tuple id="geolocation">
<!-- geolocation tuple contents -->
</tuple>
</presence>
The presence agent then provides a notification to the watcher with
this new presence data.
M4:
NOTIFY watcher@example SIP/2.0
To: <pres:watcher@example>
From: <pres:presentity@example>;tag=asd234
Call-ID: 789678@example
CSeq: 1 NOTIFY
Max-Forwards: 70
Event: presence
Subscription-State: active; expires=3207
Contact: sip:pa.example
Content-Type: application/pidf+xml
Content-Length: ...
<presence entity="pres:presentity@example">
<tuple id="status>
<!-- status tuple contents-->
</tuple>
<tuple id="abc123-geolocation">
<!-- geolocation tuple contents -->
</tuple>
</presence>
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From this point, changes in presence state at the source trigger
notifications to the presence agent. This in turn triggers
notifications to any watchers.
8. IANA Considerations
TBD: register SIP header, "indirectpub" option tag and establish
parameter registry (pah).
9. Security considerations
The security considerations described in SIP Location Conveyance
[I-D.ietf-sip-location-conveyance]are applicable to this document.
Privacy protections are extremely important for presence information.
Indirect publish potentially provides watchers and presence agents
greater access to a user's private data. A presence source
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[I-D.winterbottom-geopriv-deref-protocol]
Winterbottom, J., Tschofenig, H., Schulzrinne, H.,
Thomson, M., and M. Dawson, "A Location Dereferencing
Protocol Using HELD",
draft-winterbottom-geopriv-deref-protocol-04 (work in
progress), July 2009.
[I-D.ietf-sipcore-location-conveyance]
Polk, J. and B. Rosen, "Location Conveyance for the
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Session Initiation Protocol",
draft-ietf-sipcore-location-conveyance-01 (work in
progress), July 2009.
10.2. Informational References
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3863] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr,
W., and J. Peterson, "Presence Information Data Format
(PIDF)", RFC 3863, August 2004.
[RFC3903] Niemi, A., "Session Initiation Protocol (SIP) Extension
for Event State Publication", RFC 3903, October 2004.
[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.
[RFC4479] Rosenberg, J., "A Data Model for Presence", RFC 4479,
July 2006.
[RFC4480] Schulzrinne, H., Gurbani, V., Kyzivat, P., and J.
Rosenberg, "RPID: Rich Presence Extensions to the Presence
Information Data Format (PIDF)", RFC 4480, July 2006.
[RFC4481] Schulzrinne, H., "Timed Presence Extensions to the
Presence Information Data Format (PIDF) to Indicate Status
Information for Past and Future Time Intervals", RFC 4481,
July 2006.
[RFC5264] Niemi, A., Lonnfors, M., and E. Leppanen, "Publication of
Partial Presence Information", RFC 5264, September 2008.
[W3C.REC-xml-20060816]
Yergeau, F., Paoli, J., Sperberg-McQueen, C., Maler, E.,
and T. Bray, "Extensible Markup Language (XML) 1.0 (Fourth
Edition)", World Wide Web Consortium FirstEdition REC-xml-
20060816, August 2006,
<http://www.w3.org/TR/2006/REC-xml-20060816>.
[W3C.REC-xmlschema-0-20041028]
Walmsley, P. and D. Fallside, "XML Schema Part 0: Primer
Second Edition", World Wide Web Consortium
Recommendation REC-xmlschema-0-20041028, October 2004,
<http://www.w3.org/TR/2004/REC-xmlschema-0-20041028>.
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[I-D.ietf-sip-location-conveyance]
Polk, J. and B. Rosen, "Location Conveyance for the
Session Initiation Protocol",
draft-ietf-sip-location-conveyance-13 (work in progress),
March 2009.
[I-D.ietf-geopriv-http-location-delivery]
Barnes, M., Winterbottom, J., Thomson, M., and B. Stark,
"HTTP Enabled Location Delivery (HELD)",
draft-ietf-geopriv-http-location-delivery-16 (work in
progress), August 2009.
[I-D.ietf-geopriv-lbyr-requirements]
Marshall, R., "Requirements for a Location-by-Reference
Mechanism", draft-ietf-geopriv-lbyr-requirements-08 (work
in progress), September 2009.
[I-D.ietf-geopriv-arch]
Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
Tschofenig, H., and H. Schulzrinne, "An Architecture for
Location and Location Privacy in Internet Applications",
draft-ietf-geopriv-arch-00 (work in progress), July 2009.
Appendix A. Alternative Solutions Considered
[ED: this section is a mess; it should be cleaned up and moved to an
appendix.]
The following alternative solutions were considered in the design of
this solution:
1. Rather than using a header, additional SIP bodies could be
defined. This could be a PIDF extension, or a specialized
format. This has a number of advantages, particularly in terms
of good protocol hygiene. This potentially runs afoul of the shy
support for multipart MIME in SIP agents. As a PIDF extension,
it's possible that multipart support is not required, but it
would potentially be difficult to ensure that it is the presence
agent that is performing the de-reference.
2. Integration with partial presence publish [RFC5264] was
considered. Including a URI in a "pidf-diff" document would
provide an elegant way to integrate indirectly published data.
However, RFC 5264 defines a format that cannot be extended. The
scheme chosen also provides less flexibility and is consequently
significantly simpler.
3. It's possible that a mechanism is not necessary at all. Presence
sources could be given the information necessary to PUBLISH the
information. Mechanisms would need to be provided for this
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purpose. Aside from the complexity of managing this
relationship, it does not benefit from the ability to use an
event-based subscription. It is also more difficult to ensure
that the presence source publishes when the presence agent (and
watchers) need the information.
4. The SIP Location Conveyance [I-D.ietf-sip-location-conveyance]
defines a Geolocation header field that could be used for
indirect publish. Limiting this solution to location information
would be a constraint that would prevent this from use for other
types of information.
Authors' Addresses
Miguel A. Garcia-Martin
Ericsson
Calle Via de los Poblados 13
Madrid, ES 28033
Spain
Email: miguel.a.garcia@ericsson.com
Hannes Tschofenig
Nokia Siemens Networks
Otto-Hahn-Ring 6
Munich, Bavaria 81739
Germany
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
USA
Phone: +1 212 939 7042
Email: schulzrinne@cs.columbia.edu
URI: http://www.cs.columbia.edu/~hgs
Garcia-Martin, et al. Expires April 29, 2010 [Page 16]
Internet-Draft SIP Indirect Presence Publication October 2009
Martin Thomson
Andrew Corporation
PO Box U40
University of Wollongong, NSW 2500
AU
Phone: +61 242 212915
Email: martin.thomson@andrew.com
URI: http://www.andrew.com/
Garcia-Martin, et al. Expires April 29, 2010 [Page 17]
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