Session Initiation Protocol (SIP) User Agent Capability Extension to Presence Information Data Format (PIDF) :: RFC5196
Network Working Group M. Lonnfors
Request for Comments: 5196 K. Kiss
Category: Standards Track Nokia
September 2008
Session Initiation Protocol (SIP) User Agent Capability Extension to
Presence Information Data Format (PIDF)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
Presence Information Data Format (PIDF) defines a common presence
data format for Common Profile for Presence (CPP) compliant presence
protocols. This memo defines a PIDF extension to represent SIP User
Agent capabilities.
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Table of Contents
1. Introduction ....................................................3
1.1. Motivation .................................................3
1.2. Scope ......................................................4
2. Conventions .....................................................4
3. Extension for "Indicating User Agent Capabilities in the
Session Initiation Protocol (SIP)" in PIDF Documents ............4
3.1. Overview of Operation ......................................4
3.2. Service capabilities .......................................5
3.2.1. Element ..................................5
3.2.2. Element .....................................5
3.2.3. Element ...............................5
3.2.4. Element ......................................6
3.2.5. Element ...................................6
3.2.6. Element .....................................6
3.2.7. Element ......................................6
3.2.8. Element ...................................7
3.2.9. Element ......................................7
3.2.10. Element .................................7
3.2.11. Element ....................................7
3.2.12. Element ...................................8
3.2.13. Element ..............................8
3.2.14. Element ...........................9
3.2.15. Element .................................9
3.2.16. Element .................................10
3.2.17. Element ..............................11
3.2.18. Element .................................11
3.2.19. Element ...................................12
3.2.20. Element .................................12
3.2.21. Element ...............................13
3.3. Device Capabilities .......................................13
3.3.1. Element ..................................13
3.3.2. Element .................................14
3.3.3. Element ..............................14
4. Usage Guidelines ...............................................15
4.1. Use of and Elements ............15
5. Examples .......................................................16
6. XML Schema Definitions .........................................17
7. IANA Considerations ............................................26
7.1. URN Sub-Namespace Registration for ........................26
7.2. Schema Registration for Schema ............................27
8. Security Considerations ........................................27
9. Acknowledgments ................................................27
10. References ....................................................27
10.1. Normative References .....................................27
10.2. Informative References ...................................28
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1. Introduction
Common Profile for Presence (CPP) [RFC3859] and Common Profile for
Instant Messaging (CPIM) [RFC3860] define common operations and
formats that all presence and instant messaging services must agree
upon so that basic interoperability is possible. The actual base
format for the presence is defined in the Presence Information
Document Format (PIDF) [RFC3863]. The PIDF has been designed to
reduce the need for gatewaying and to allow end-to-end security of
presence information. It has taken a very minimalistic approach to
support such operations. In order to make the PIDF usable by
different presence applications, these applications usually must
extend the basic PIDF by standard XML mechanisms as defined in PIDF
[RFC3863].
The aim of this memo is to introduce a SIP-specific extension
mechanism to the PIDF that conveys the same SIP media feature tags as
described in [RFC3840]. With this extension, presence applications
based on SIP can have richer and more usable presence information
compared to the baseline PIDF.
1.1. Motivation
The PIDF [RFC3863] defines a element that may appear once
inside every element. The content of the element
encodes the CONTACT ADDRESS and CONTACT MEANS as defined in
[RFC2778]. The element is defined to be a URI of any
scheme. In some implementations, the URI scheme can uniquely
identify the service the tuple intends to describe (e.g., im: URI
scheme usually represents Instant Messaging service). However, this
may not be the case in all implementations. For example in SIP, a
SIP URI scheme can represent different kinds of services. A SIP URI
scheme can be used to contact voice services, video services, or
messaging services. If it is not known by other means, it might be
hard for applications processing the presence information containing
only a SIP URI contact addresses to know what particular service the
tuple intends to describe. Also, watchers receiving presence
information would probably benefit from getting more descriptive
information about what particular communication means or services are
supported by the presentity.
The User Agent Capabilities extension [RFC3840] defines a set of
extensions that allow user agents to express preferences about
request handling in SIP servers. The same information can provide
value to watchers as well so that they can make more rational
decisions on how a presentity should be contacted if a presence
document contained this information.
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1.2. Scope
This document defines a PIDF extension, which enables SIP presence
implementations to represent User Agent Capabilities [RFC3840] within
presence information.
This extension does not replace media negotiation mechanisms defined
for SIP (e.g., SDP [RFC4566]). The purpose of this extension is for
a presentity to give watchers hints about the presentity's
preferences, willingness, and capabilities to communicate before
watchers initiate communication with the presentity.
2. Conventions
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].
This memo makes use of the vocabulary defined in [RFC2778] and
[RFC3863].
3. Extension for "Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)" in PIDF Documents
This section presents the extension elements, attributes, their
values, and semantics. This section also describes how this
extension can be further extended.
This extension is intended to be used within the PIDF [RFC3863] and
that particular usage is described here. This extension may also be
used with other XML documents if appropriate.
3.1. Overview of Operation
This document defines how the features presented in [RFC3840] can be
provided as part of presence information. Additionally, this memo
includes the "type" feature tag [RFC2913], "message" media type
feature tag [RFC4569], and the "language" feature tag [RFC4646]
definitions. Adding these features to the PIDF means mapping them to
an XML formatted structure.
The presence data model [RFC4479] defines presence information
consisting of three types of data elements: person, service, and
device. This memo follows this model so that one XML extension is
defined to describe device capabilities and another one to describe
service capabilities.
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The namespace URIs for elements defined by this document are URNs
using the namespace identifier 'ietf' defined by [RFC2648] and
extended by [RFC3688].
When these extension namespaces are congregated with the PIDF
document, the combined document MUST follow the same general
formatting rules as specified in Section 4.1 of [RFC3863].
3.2. Service capabilities
Elements belonging to service capabilities are used to describe
dynamic characteristics of a service. These capabilities are
enclosed within the element which SHOULD be located in the
PIDF document as a child element of urn:ietf:params:xml:ns:pidf
namespace [RFC3863] element.
The namespace identifier for these elements is:
urn:ietf:params:xml:ns:pidf:caps
3.2.1. Element
The root element of service capabilities is . The root
element always has to be present. This element can contain the
following child elements: , , , ,
, , , , , , ,
, , , , ,
, , , and followed by any number
of optional extension elements from other namespaces.
A element can contain any number of optional extension
attributes from other namespaces.
3.2.2. Element
The element indicates that the service supports audio as a
streaming media type as defined in [RFC3840].
The element is a boolean type and does not have any
attributes. The value 'true' indicates that service supports audio
media type, and the value 'false' indicates that service does not
support audio media type.
3.2.3. Element
The element indicates that the service supports
application as a streaming media type as defined in [RFC3840].
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The element is a boolean type and does not have any
attributes. The value 'true' indicates that service supports
application media type, and the value 'false' indicates that service
does not support application media type.
3.2.4. Element
The element indicates that the service supports data as a
streaming media type as defined in [RFC3840].
The element is a boolean type and does not have any
attributes. The value 'true' indicates that service supports data
media type, and the value 'false' indicates that service does not
support data media type.
3.2.5. Element
The element indicates that the service supports control as
a streaming media type as defined in [RFC3840].
The element is a boolean type and does not have any
attributes. The value 'true' indicates that service supports control
media type, and the value 'false' indicates that service does not
support control media type.
3.2.6. Element
The element indicates that the service supports video as a
streaming media type as defined in [RFC3840].
The element is a boolean type and does not have any
attributes. The value 'true' indicates that service supports video
media type, and the value 'false' indicates that service does not
support video media type.
3.2.7. Element
The element indicates that the service supports text as a
streaming media type as defined in [RFC3840].
The element is a boolean type and does not have any
attributes. The value 'true' indicates that service supports text
media type, and the value 'false' indicates that service does not
support text media type.
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3.2.8. Element
The element indicates that the service supports messaging
as a streaming media type as defined in [RFC4569].
The element is a boolean type and does not have any
attributes. The value 'true' indicates that service supports message
media type, and the value 'false' indicates that service does not
support message media type.
3.2.9. Element
The element indicates a MIME media content type (i.e., that
appears in a 'Content-type:' header of the corresponding MIME-
formatted data) as defined in [RFC2913].
The element is a string type and does not have any attributes.
It MUST be a string of the form "type/subtype", where 'type' and
'subtype' are defined by the MIME specification [RFC2045]. Only
lowercase letters SHOULD be used.
3.2.10. Element
The element indicates whether the service represents an
automaton (such as a voicemail server, conference server, or
recording device) or a human as defined in [RFC3840].
The element is a boolean type and does not have any
attributes. The value 'true' indicates that the service represents
an automaton, and the value 'false' indicates that it represents a
human.
3.2.11. Element
The element indicates the setting, business or personal, in
which a communications service is used as defined in [RFC3840].
The element can contain two elements: and
. Classes that are supported by the service can be
listed under the element, and classes that are not
supported by the service can be listed under the
element.
and elements can contain and
elements followed by any number of optional extension
elements from other namespaces. The semantics of business and
personal are defined in [RFC3840] as:
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o : The service is used for business communications.
o : The service is used for personal communications.
Any value that is registered with IANA for the SIP media feature tag
registration tree as a sip.class media feature tag can be used as a
value of an extension element. If the appropriate value is not
registered, it SHOULD be registered as defined in [RFC3840].
3.2.12. Element
The element lists whether a communications service can
simultaneously send and receive media ("full"), alternate between
sending and receiving ("half"), only receive ("receive-only"), or
only send ("send-only") as defined in [RFC3840].
The element can contain two elements: and
. Duplex modes that are supported by the service can
be listed under the element, and duplex modes that are
not supported by the service can be listed under the
element.
and elements can contain , ,
, and elements followed by any number of
optional extension elements from other namespaces. The semantics of
these elements are defined in [RFC3840] as:
o : The service can simultaneously send and receive media.
o : The service can alternate between sending and receiving
media.
o : The service can only receive media.
o : The service can only send media.
Any value that is registered with IANA for the SIP media feature tag
registration tree as a sip.duplex media feature tag can be used as a
value of an extension element. If the appropriate value is not
registered, it SHOULD be registered as defined in [RFC3840].
3.2.13. Element
The element provides a textual description of the
service as defined in [RFC3840].
The element is of string type and does not have any
attributes.
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The element SHOULD be labeled with the 'xml:lang'
attribute to indicate its language and script. The specification
allows multiple occurrences of this elements so that the presentity
can convey elements in multiple scripts and languages.
If no 'xml:lang' attribute is provided, the default value is
"i-default" as defined in [RFC2277].
3.2.14. Element
The element lists the event packages supported by a
service.
The element can contain two elements:
and . Event packages that are supported by the service
can be listed under the element, and event packages that
are not supported by the service can be listed under the
element.
The and elements can contain any values
from the IANA SIP event types namespace registry followed by any
number of optional extension elements from other namespaces. As of
this writing, the IANA SIP event types namespace registry includes
the following packages: , , ,
, , , , ,
, , , and
.
3.2.15. Element
The element indicates the call priorities the service is
willing to handle as defined in [RFC3840].
The element can contain two elements: and
. Priority values that are supported by the service
can be listed under the element, and priority values that
are not supported by the service can be listed under the
element.
The and elements can contain any number of
, , , and elements followed by
any number of optional extension elements from other namespaces.
3.2.15.1. Element
The element has a single attribute called "maxvalue".
The "maxvalue" attribute is used to give the highest priority value
that the service is willing to support. All values equal and below
that value are supported.
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3.2.15.2. Element
The element has a single attribute called "minvalue".
The "minvalue" attribute is used to give the lowest priority value
that the service is willing to support. All values equal and above
that value are supported.
3.2.15.3. Element
The element is used to indicate the exact priority value
that the service is willing to handle. The element has a
single attribute called "value". The "value" attribute is used to
indicate the exact supported priority value.
3.2.15.4. Element
The element is used to indicate the priority range that the
service is willing to handle. The element has two attributes
called "minvalue" and "maxvalue". The value of the "minvalue"
attribute indicates the lowest priority value supported by the
service, and the value of the "maxvalue" attribute indicates the
highest priority value supported by the service.
3.2.16. Element
The element indicates the SIP methods supported by a
service. In this case, "supported" means that the service can
receive requests with this method. In that sense, it has the same
connotation as the Allow header field as defined in [RFC3840].
The element can contain two elements: and
. Methods that are supported by the service can be
listed under the element, and methods that are not
supported by the service can be listed under the
element.
The and elements can contain any values
from the methods table of the IANA SIP parameters registry table
followed by any number of optional extension elements from other
namespaces. As of this writing, the IANA SIP parameters registry
includes the following methods:, , , ,
, , , , , ,
, , , and .
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3.2.17. Element
The element is a list of SIP extensions (each of which
is defined by an option-tag registered with IANA) that are understood
by the service. Understood, in this context, means that the option
tag would be included in a Supported header field in a request as
defined in [RFC3840].
The element can contain two elements: and
. Extensions that are supported by the service can be
listed under the element, and extensions that are not
supported by the service can be listed under the
element.
The and elements can contain any values
from the option tags table of the IANA SIP parameters registry table
followed by any number of optional extension elements from other
namespaces. As of this writing, the IANA SIP parameters registry
includes the following option tags: , ,
, , , , , ,
, , , , ,
, , , , , , and .
3.2.18. Element
The element provides the set of URI schemes that are
supported by a service. "Supported" implies, for example, that the
service would know how to handle a URI of that scheme in the Contact
header field of a redirect response as defined in [RFC3840].
The element can contain two elements: and
. Schemes that are supported by the service can be
listed under the element, and schemes that are not
supported by the service can be listed under the
element.
and elements can contain any number of
elements, which can be used to describe individual schemes supported
by the service.
3.2.18.1. Element
The element is of string type and is used to describe an
individual scheme supported by the service. Values that can be used
here are scheme names that are registered to the IANA URI scheme
registry.
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3.2.19. Element
The element indicates the type of entity that is available at
this URI as defined in [RFC3840].
The element can contain two elements: and
. Actor types that are supported by the service can be
listed under the element, and actor types that are not
supported by the service can be listed under the
element.
The and elements can contain ,
, , and elements followed by any
number of optional extension elements from other namespaces.
The semantics of these elements are defined in [RFC3840] as:
o : The service provides communication with the principal
that is associated with the service. Often this will be a
specific human being, but it can be an automaton (for example,
when calling a voice portal).
o : The service provides communication with an automaton
or a person that will act as an intermediary in contacting the
principal associated with the service, or a substitute.
o : The service provides communication with an automaton
or a person that will take messages and deliver them to the
principal.
o : The service provides communication with an
automaton or a person that will provide information about the
principal.
Any value that is registered with IANA for the SIP media feature tag
registration tree as a sip.actor media feature tag can be used as a
value of an extension element. If the appropriate value is not
registered, it SHOULD be registered as defined in [RFC3840].
3.2.20. Element
The element indicates that the service is a conference
server, also known as a focus as defined in [RFC3840].
The element is of boolean type and does not have any
attributes. The value 'true' indicates that service is a conference
server and the value 'false' indicates that service does not support
conferencing.
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3.2.21. Element
The element indicates the ability to display particular
human languages as defined in [RFC4646].
The element can contain two elements: and
. Languages that are supported by the service can be
listed under the element, and languages that are not
supported by the service can be listed under the
element.
