SIMPLE WG M. Lonnfors
Internet-Draft J. Costa-Requena
Expires: April 24, 2006 E. Leppanen
Nokia
H. Khartabil
Telio
October 21, 2005
Session Initiation Protocol (SIP) extension for Partial Notification of
Presence Information
draft-ietf-simple-partial-notify-06
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
By default, presence delivered using the Presence Event Package for
the Session Initiation Protocol is represented in the Presence
Information Data Format (PIDF). A PIDF document contains a set of
elements, each representing a different aspect of the presence being
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reported. When any subset of the elements change, even just a single
element, a new document containing the full set of elements is
delivered. This memo defines an extension allowing delivery of
presence data that has actually changed.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Introduction to the partial notification mechanism . . . . . . 3
3.1. Basic presence agent operation . . . . . . . . . . . . . . 4
3.2. Operation with partial notification . . . . . . . . . . . 4
4. Client and server operations . . . . . . . . . . . . . . . . . 4
4.1. Content-type for partial notifications . . . . . . . . . . 5
4.2. Watcher generation of SUBSCRIBE requests . . . . . . . . . 5
4.3. Presence agent processing of SUBSCRIBE requests . . . . . 5
4.4. Presence agent generation of partial notifications . . . . 5
4.5. Watcher processing of NOTIFY requests . . . . . . . . . . 6
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
8. Normative references . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 15
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1. Introduction
A presence event package for Session Initiation Protocol (SIP) [4]
allow users ('watchers') to subscribe to other users'
('presentities') presence information. The presence information is
composed of multiple pieces of data that are delivered to the
watcher. The size of the presence information document can be large
(i.e. the presence document can contain an arbitrary number of
elements called presence tuples that convey data). As specified in
RFC2778 [3] and presence event package for SIP [4], a Presence Agent
(PA) always delivers in presence notifications all the presence data
that has been authorized for a certain watcher. This is done
regardless of what presence data has changed compared to last
notification. It may not be reasonable to send the complete presence
information over low bandwidth and high latency links when only part
of the presence information has actually changed. This may end up
degrading the presence service and causing bad perception at the
watcher side.
This document defines a partial notification approach where the
presence server delivers to the watchers only those parts of the
presence information that have changed compared to the presence
information sent in the previous notifications. This reduces the
amount of data that is transported over the network.
This mechanism utilizes the presence event package for SIP [4] and a
new MIME type for carrying partial Presence Information Data Format
documents [2].
2. Conventions
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
indicate requirement levels for compliant implementations.
This document makes use of the vocabulary defined in RFC2778 [3],
RFC3265 [7], the presence event package for SIP [4], and the PIDF
extension for Partial Presence [2].
3. Introduction to the partial notification mechanism
This chapter briefly introduces the regular functionality of the
presence service, and gives an overview of the partial notification
solution. This section is informational in nature. It does not
contain any normative statements.
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3.1. Basic presence agent operation
The presence service normally operates so that a watcher sends a SIP
SUBSCRIBE request targeted to the presentity. The request is routed
to the presence agent where the presentity's presence information is
stored. The SUBSCRIBE request can include an Accept header field
that indicates the supported content types.
The presence agent receives the SUBSCRIBE request and if there is no
Accept header indicating the supported content types or the Accept
header contains the default PIDF content type, the PA will generate
presence notifications using the default PIDF format [6]. The PIDF
document can contain one or multiple XML elements. The PIDF document
include a set of elements defined in RFC2778 [3] and its extensions
for representing the presence information. This PIDF document will
be carried in the body of a NOTIFY request constructed as per RFC3265
[7]. During basic operation, the presence document always contains
the full state corresponding to the presence status of the
presentity, as determined by the PA local policy and authorization
rules.
3.2. Operation with partial notification
The partial notification mechanism allows a watcher to request that,
whenever possible, notifications contain only presence information
that has actually changed. A watcher that wants to receive partial
notifications according to this document, creates a SIP SUBSCRIBE
request similar to that of a regular presence subscription. However,
the SIP SUBSCRIBE request contains an Accept header field whose value
contains the "application/pidf-diff+xml" tag.
When the presence agent receives the subscription, it examines the
Accept header field value and if the "application/pidf-diff+xml"
value is present, it can decide to use the partial notifications
mechanism specified in this memo. The presence agent builds NOTIFY
requests that contain the Content-Type header field set to
"application/pidf-diff+xml". The first NOTIFY request that contains
presence information will contain a full presence document.
Subsequent NOTIFY requests can contain partial presence documents.
This behavior is described in detail in Section 4.
4. Client and server operations
Unless otherwise specified in this document, the regular watcher and
presence agent behavior is applied as defined in the SIP presence
event package [4].
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4.1. Content-type for partial notifications
Entities supporting the partial notification extension described in
this document MUST support the 'application/pidf-diff+xml' content-
type specified in the PIDF extension for partial presence [2].
4.2. Watcher generation of SUBSCRIBE requests
A SUBSCRIBE request can be used to negotiate the preferred content
type to be used in the notifications. The Accept header field is
used for this purpose as specified in RFC2161 [5]. When a watcher
wants to allow the presence agent to send partial notifications the
watcher MUST include an Accept header field in its SUBSCRIBE request.
The value of the Accept header field MUST contain 'application/
pidf-diff+xml' (in addition to 'application/pidf+xml' required by the
SIP presence event package [4]). The watcher MAY include a "q"
parameter with each Accept value to indicate the relative preference
of that value.
4.3. Presence agent processing of SUBSCRIBE requests
The presence agent receives subscriptions from watchers and generates
notifications according to the SIP presence event package [4]. If
the watcher has indicated the supported content types in the Accept
header field of the SUBSCRIBE request, the presence agent compares
the values included in the Accept header field with the supported
ones, and decides which one to use. If the watcher has indicated
preferred accept values by means of "q" parameters, the presence
agent SHOULD base the decision on those preferences, unless otherwise
indicated by the presence agent local policy.
4.4. Presence agent generation of partial notifications
Once a subscription is accepted and installed, the PA MUST deliver
the full state of the presence information in the first partial
notification that contains a presence document. If the presence
agent decides to send notifications that include a presence document
according to this specification, the presence agent MUST build a
presence document according to the PIDF extension for Partial
Presence [2] and MUST set the Content-Type header field to the value
'application/pidf-diff+xml'.
When using the 'application/pidf-diff+xml' MIME type the PA MUST
include a "version" attribute and for the first partial notification
(within a given subscription) the PA MUST initialize version to value
one (1). This version counter is scoped to the subscription, and is
incremented by one within each partial notification. The version
value is only reset when the given subscription is terminated. It is
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not reset when the subscription is refreshed.
When the PA generates a partial presence document, the PA SHOULD
include only that presence information that have changed compared to
the previous notifications. It is up to the PA's local policy to
determine what is considered as a change to the previous state.
The PA MUST construct the partial presence document according to the
following logic:
o The PA MUST construct the presence information according to the
PIDF extension for Partial Presence [2]. All the information that
have been added to the presence document are listed inside <add>
elements. All information that have been removed from the
presence document are listed inside <remove> elements and all
information that have been changed are listed under <replace>
elements.
o The PA MUST include a "version" attribute in the presence
document. The PA MUST increment the version number by one
compared to the earlier successfully send presence document in the
PIDF extension for Partial Presence [2] format to the watcher
associated with a certain subscription.
The PA MUST NOT send a new NOTIFY request that contains a partial
notification for the same Request-URI until it has received a final
response from the watcher for the previous one or the previous NOTIFY
request has timed out.
When the PA receives a SUBSCRIBE request (refresh or termination)
within the associated subscription, it SHOULD send a NOTIFY request
containing the full presence document.
4.5. Watcher processing of NOTIFY requests
Watcher processes all NOTIFY requests that contain 'application/
pidf+xml' content type as specified in RFC3856 [4].
When the watcher receives the first notification containing the
'application/pidf-diff+xml' MIME body the watcher MUST initialize an
internal version counter, related to this subscription, to the value
of the "version" included in the presence document. This version
counter is scoped to the subscription. The watcher MUST also store
the received full presence presence document as its local copy.
When the watcher receives a subsequent 'application/pidf-diff+xml'
encoded presence document the watcher MUST compare the received
"version" attribute with the local version counter. If the watcher
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receives a presence document with the "version" attribute value equal
or lower than the locally stored version number, it is considered a
PA failure and the watcher SHOULD discard the document without
further processing. Otherwise the watcher MUST modify its locally
stored information according to the following logic:
o If the root element of the presence document is <pidf-full>, the
watcher must replace its local copy of the presence document with
the presence document received in the 'application/pidf-diff+xml'
body and set the internal version value to the value of the
"version" attribute included in the presence document.
o If the root element of the presence document is <pidf-diff> and
the received version number is incremented by one compared with
the local version counter, the watcher MUST apply the changes to
its local copy of the full presence document indicated in the
received 'application/pidf-diff+xml' document as specified in PIDF
extension for Partial Presence [2]. The watcher MUST increment
the local version counter by one.
o If the root element of the presence document is <pidf-diff> and
the received "version" value is higher by more than one with the
locally stored value the watcher assumes that one or more NOTIFYs
were lost. The watcher SHOULD either refresh the subscription in
order to receive a full presence document or terminate the
subscription.
If the PA changes the content type used in notifications within the
existing subscription the watcher MUST discard all the previously
received presence information (except local version counter) from
that particular presentity and process the new content as specified
for that content type. Local version counter MUST NOT be discarded
because if PA changes back to 'application/pidf-diff+xml' MIME type
version counter will continue to increase from the last version
value.
5. Examples
The following message flow shows an example applying the partial
notifications mechanism.
A watcher sends a SUBSCRIBE request declaring support for the default
presence format ('application/pidf+xml) and for the partial
notification format ('application/pidf-diff+xml') in the Accept
header field value. The watcher uses the "q" parameter to set the
preference for receiving partial notifications. The PA accepts the
subscription and, based on the "q" parameter value, selects to send
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partial notifications in NOTIFY requests. The first NOTIFY request
includes the full state of presence information. The following
notifications only include information about delta of the presence
information from the previous NOTIFY requests.
Watcher Presence Agent PUA
| F1 SUBSCRIBE | |
|-------------------------->| |
| F2 200 OK | |
|<--------------------------| |
| F3 NOTIFY | |
|<--------------------------| |
| F4 200 OK | |
|-------------------------->| |
| | |
| | Update presence |
| |<----------------------- |
| | |
| F5 NOTIFY | |
|<--------------------------| |
| F6 200 OK | |
|-------------------------->| |
Message Details
F1 SUBSCRIBE watcher->example.com server
SUBSCRIBE sip:resource@example.com SIP/2.0
Via: SIP/2.0/TCP watcherhost.example.com;
branch=z9hG4bKnashds7
To: <sip:resource@example.com>
From: <sip:watcher@example.com> ;tag=xfg9
Call-ID: 2010@watcherhost.example.com
CSeq: 17766 SUBSCRIBE
Max-Forwards: 70
Event: presence
Accept: application/pidf+xml;q=0.3,
application/pidf-diff+xml;q=1
Contact: <sip:user@watcherhost.example.com>
Expires: 3600
Content-Length: 0
The PA accepts the subscription and generates a 200 OK response
to the SUBSCRIBE request
F2 200 OK example.com server ->watcher
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SIP/2.0 200 OK
Via: SIP/2.0/TCP watcherhost.example.com;
branch=z9hG4bKnashds7
;received=192.0.2.1
To: <sip:resource@example.com>;tag=ffd2
From: <sip:watcher@example.com>;tag=xfg9
Call-ID: 2010@watcherhost.example.com
CSeq: 17766 SUBSCRIBE
Event: presence
Expires: 3600
Contact: <sip:server.example.com>
Content-Length: 0
The PA, based on the "q" parameter value in the Accept header
of the SUBSCRIBE request (F1), decides to use partial
notifications. The PA creates the first NOTIFY request that
includes the full presence document.
F3 NOTIFY example.com server -> watcher
NOTIFY sip:user@watcherhost.example.com SIP/2.0
Via: SIP/2.0/TCP server.example.com;
branch=z9hG4bKna998sk
To: <sip:watcher@example.com>;tag=xfg9
From: <sip:resource@example.com>;tag=ffd2
Call-ID: 2010@watcherhost.example.com
Event: presence
Subscription-State: active;expires=3599
Max-Forwards: 70
CSeq: 8775 NOTIFY
Contact: <sip:server.example.com>
Content-Type: application/pidf-diff+xml
Content-Length: [replace with real content length]
<?xml version="1.0" encoding="UTF-8"?>
<p:pidf-full xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:p="urn:ietf:params:xml:ns:pidf-diff"
xmlns:r="urn:ietf:params:xml:ns:pidf:rpid"
xmlns:c="urn:ietf:params:xml:ns:pidf:caps"
xmlns:cp="urn:ietf:params:xml:ns:pidf:cipid"
xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
entity="pres:someone@example.com"
version="1">
<tuple id="sg89ae">
<status>
<basic>open</basic>
</status>
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<c:servcaps>
<c:audio>true</c:audio>
<c:video>false</c:video>
<c:message>true</c:message>
</c:servcaps>
<r:relationship><r:assistant/></r:relationship>
<contact priority="0.8">tel:09012345678</contact>
</tuple>
<tuple id="cg231jcr">
<status>
<basic>open</basic>
</status>
<contact priority="1.0">im:pep@example.com</contact>
</tuple>
<tuple id="r1230d">
<status>
<basic>closed</basic>
</status>
<cp:homepage>http://example.com/~pep/</cp:homepage>
<cp:icon>http://example.com/~pep/icon.gif</cp:icon>
<cp:card>http://example.com/~pep/card.vcd</cp:card>
<contact priority="0.9">sip:pep@example.com</contact>
</tuple>
<note xml:lang="en">Full state presence document</note>
<dm:person id="fdkfj">
<r:activities>
<r:on-the-phone/>
<r:busy/>
</r:activities>
</dm:person>
<dm:device id="u00b40c7">
<c:devcaps>
<c:mobility>
<c:supported>
<c:mobile/>
</c:supported>
</c:mobility>
</c:devcaps>
<dm:deviceID>mac:xxx</dm:deviceID>
</dm:device>
</p:pidf-full>
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F4 200 OK watcher -> example.com server
SIP/2.0 200 OK
Via: SIP/2.0/TCP server.example.com;
branch=z9hG4bKna998sk
;received=192.0.2.2
To: <sip:watcher@example.com>;tag=xfg9
From: <sip:resource@example.com>;tag=ffd2
Call-ID: 2010@watcherhost.example.com
CSeq: 8775 NOTIFY
Content-Length: 0
At a later time, the presentity's presence information
changes. The PA generates a NOTIFY request
that includes information about the changes.
F5 NOTIFY example.com server -> watcher
NOTIFY sip:user@watcherhost.example.com SIP/2.0
Via: SIP/2.0/TCP server.example.com;
branch=z9hG4bKna998sl
To: <sip:watcher@example.com>;tag=xfg9
From: <sip:resource@example.com>;tag=ffd2
Call-ID: 2010@watcherhost.example.com
CSeq: 8776 NOTIFY
Event: presence
Subscription-State: active;expires=3543
Max-Forwards: 70
Contact: <sip:server.example.com>
Content-Type: application/pidf-diff+xml
Content-Length: [replace with real content length]
<?xml version="1.0" encoding="UTF-8"?>
<p:pidf-diff xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:p="urn:ietf:params:xml:ns:pidf-diff"
xmlns:r="urn:ietf:params:xml:ns:pidf:rpid"
xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
entity="pres:someone@example.com"
version="2">
<p:add sel="presence/note" pos="before"><tuple id="ert4773">
<status>
<basic>open</basic>
</status>
<contact priority="0.4">mailto:pep@example.com</contact>
<note xml:lang="en">This is a new tuple inserted
between the last tuple and note element</note>
</tuple>
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</p:add>
<p:replace sel="*/tuple[@id='r1230d']/status/basic/text()"
>open</p:replace>
<p:remove sel="*/dm:person/r:activities/r:busy"/>
<p:replace sel="*/tuple[@id='cg231jcr']/contact/@priority"
>0.7</p:replace>
</p:pidf-diff>
F6 200 OK watcher-> example.com server
SIP/2.0 200 OK
Via: SIP/2.0/TCP server.example.com;
branch=z9hG4bKna998sl
;received=192.0.2.2
To: <sip:watcher@example.com>;tag=xfg9
From: <sip:resource@example.com>;tag=ffd2
Call-ID: 2010@watcherhost.example.com
CSeq: 8776 NOTIFY
Content-Length: 0
6. Security Considerations
This specification relies on the presence event package for SIP [4].
Partial notifications can reveal information about what has changed
compared to the previous notification. This can make it easier for
eavesdropper to know what kind of changes are happening in the
presentity's presence information. However, the same information can
be found if the presence event package is used with baseline PIDF
[6].
A third party can inject a NOTIFY request with partial state that
will cause the watcher to think it has missed a partial notification
and to request a new full presence document. This is no worse than
what we have without this extension since a party that could perform
such action could also send a NOTIFY with Subscription-State:
terminated and achieve the same effect without knowing about the
extension. Partial Notification does not make the situation any
worse, and the protection mechanisms from the existing system apply
to preventing this attack against the partial notification mechanism.
Presence related security considerations are extensively discussed in
the presence event package for SIP [4] and all those identified
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security considerations apply to this document as well. Issues
described in the presence event package for SIP [4], including
confidentiality, message integrity and authenticity, outbound
authentication, replay prevention, DoS attacks against thirst parties
and DoS attacks against servers all apply here without any change.
It is RECOMMENDED that TLS [8] be used between elements to provide
hop by hop confidentially protection. Furthermore, S/MIME MAY be
used for integrity and authenticity of SUBSCRIBE and NOTIFY requests.
This is described in Section 23 of RFC 3261.
7. Acknowledgments
The authors would like to thank Jari Urpalainen, Jyrki Aarnos,
Jonathan Rosenberg, Dean Willis, Kriztian Kiss, Juha Kalliokulju,
Miguel Garcia, Anders Kristensen, Yannis Pavlidis, Ben Cambell,
Robert Sparks, and Tim Moran for their valuable comments.
8. Normative references
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Lonnfors, M., Khartabil, H., Leppanen, E., and J. Urpalainen,
"Presence Information Data Format (PIDF) Extension for Partial
Presence", draft-ietf-simple-partial-pidf-format-05 (work in
progress), October 2005.
[3] Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[4] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", RFC 3856, August 2004.
[5] 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.
[6] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and
J. Peterson, "Presence Information Data Format (PIDF)",
RFC 3863, August 2004.
[7] Roach, A., "SIP-Specific Event Notification", RFC 3265,
June 2002.
[8] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
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Authors' Addresses
Mikko Lonnfors
Nokia
P.O. Box 321
Helsinki
Finland
Phone: +358 71 8008000
Email: mikko.lonnfors@nokia.com
Jose Costa-Requena
Nokia
Valimotie 9 00380
Helsinki
Finland
Phone: +358 71 8008000
Email: jose.costa-requena@nokia.com
Eva Leppanen
Nokia
P.O. Box 785
Tampere
Finland
Phone: +358 71 8008000
Email: eva-maria.leppanen@nokia.com
Hisham Khartabil
Telio
P.O. Box 1203
Oslo
Norway
Phone: +47 2167 3544
Email: hisham.khartabil@telio.no
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