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.
Lonnfors & Kiss Standards Track [Page 1]
RFC 5196 User Agent Capability Presence Status September 2008
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. <servcaps> Element ..................................5
3.2.2. <audio> Element .....................................5
3.2.3. <application> Element ...............................5
3.2.4. <data> Element ......................................6
3.2.5. <control> Element ...................................6
3.2.6. <video> Element .....................................6
3.2.7. <text> Element ......................................6
3.2.8. <message> Element ...................................7
3.2.9. <type> Element ......................................7
3.2.10. <automata> Element .................................7
3.2.11. <class> Element ....................................7
3.2.12. <duplex> Element ...................................8
3.2.13. <description> Element ..............................8
3.2.14. <event-packages> Element ...........................9
3.2.15. <priority> Element .................................9
3.2.16. <methods> Element .................................10
3.2.17. <extensions> Element ..............................11
3.2.18. <schemes> Element .................................11
3.2.19. <actor> Element ...................................12
3.2.20. <isfocus> Element .................................12
3.2.21. <languages> Element ...............................13
3.3. Device Capabilities .......................................13
3.3.1. <devcaps> Element ..................................13
3.3.2. <mobility> Element .................................14
3.3.3. <description> Element ..............................14
4. Usage Guidelines ...............................................15
4.1. Use of <supported> and <notsupported> 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
Lonnfors & Kiss Standards Track [Page 2]
RFC 5196 User Agent Capability Presence Status September 2008
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 <contact> element that may appear once
inside every <tuple> element. The content of the <contact> element
encodes the CONTACT ADDRESS and CONTACT MEANS as defined in
[RFC2778]. The <contact> 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.
Lonnfors & Kiss Standards Track [Page 3]
RFC 5196 User Agent Capability Presence Status September 2008
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.
Lonnfors & Kiss Standards Track [Page 4]
RFC 5196 User Agent Capability Presence Status September 2008
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 <servcaps> element which SHOULD be located in the
PIDF document as a child element of urn:ietf:params:xml:ns:pidf
namespace <tuple> [RFC3863] element.
The namespace identifier for these elements is:
urn:ietf:params:xml:ns:pidf:caps
3.2.1. <servcaps> Element
The root element of service capabilities is <servcaps>. The root
element always has to be present. This element can contain the
following child elements: <audio>, <application>, <data>, <control>,
<video>, <text>, <message>, <type>, <automata>, <class>, <duplex>,
<description>, <event-packages>, <priority>, <methods>, <extensions>,
<schemes>, <actor>, <isfocus>, and <languages> followed by any number
of optional extension elements from other namespaces.
A <servcaps> element can contain any number of optional extension
attributes from other namespaces.
3.2.2. <audio> Element
The <audio> element indicates that the service supports audio as a
streaming media type as defined in [RFC3840].
The <audio> 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. <application> Element
The <application> element indicates that the service supports
application as a streaming media type as defined in [RFC3840].
Lonnfors & Kiss Standards Track [Page 5]
RFC 5196 User Agent Capability Presence Status September 2008
The <application> 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. <data> Element
The <data> element indicates that the service supports data as a
streaming media type as defined in [RFC3840].
The <data> 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. <control> Element
The <control> element indicates that the service supports control as
a streaming media type as defined in [RFC3840].
The <control> 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. <video> Element
The <video> element indicates that the service supports video as a
streaming media type as defined in [RFC3840].
The <video> 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. <text> Element
The <text> element indicates that the service supports text as a
streaming media type as defined in [RFC3840].
The <text> 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.
Lonnfors & Kiss Standards Track [Page 6]
RFC 5196 User Agent Capability Presence Status September 2008
3.2.8. <message> Element
The <message> element indicates that the service supports messaging
as a streaming media type as defined in [RFC4569].
The <message> 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. <type> Element
The <type> 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 <type> 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. <automata> Element
The <automata> 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 <automata> 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. <class> Element
The <class> element indicates the setting, business or personal, in
which a communications service is used as defined in [RFC3840].
The <class> element can contain two elements: <supported> and
<notsupported>. Classes that are supported by the service can be
listed under the <supported> element, and classes that are not
supported by the service can be listed under the <notsupported>
element.
<supported> and <notsupported> elements can contain <business> and
<personal> elements followed by any number of optional extension
elements from other namespaces. The semantics of business and
personal are defined in [RFC3840] as:
Lonnfors & Kiss Standards Track [Page 7]
RFC 5196 User Agent Capability Presence Status September 2008
o <business>: The service is used for business communications.
o <personal>: 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. <duplex> Element
The <duplex> 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 <duplex> element can contain two elements: <supported> and
<notsupported>. Duplex modes that are supported by the service can
be listed under the <supported> element, and duplex modes that are
not supported by the service can be listed under the <notsupported>
element.
<supported> and <notsupported> elements can contain <full>, <half>,
<receive-only>, and <send-only> elements followed by any number of
optional extension elements from other namespaces. The semantics of
these elements are defined in [RFC3840] as:
o <full>: The service can simultaneously send and receive media.
o <half>: The service can alternate between sending and receiving
media.
o <receive-only>: The service can only receive media.
o <send-only>: 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. <description> Element
The <description> element provides a textual description of the
service as defined in [RFC3840].
The <description> element is of string type and does not have any
attributes.
Lonnfors & Kiss Standards Track [Page 8]
RFC 5196 User Agent Capability Presence Status September 2008
The <description> 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 <description> 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. <event-packages> Element
The <event-packages> element lists the event packages supported by a
service.
The <event-packages> element can contain two elements: <supported>
and <notsupported>. Event packages that are supported by the service
can be listed under the <supported> element, and event packages that
are not supported by the service can be listed under the
<notsupported> element.
The <supported> and <notsupported> 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: <conference>, <dialog>, <kpml>,
<message-summary>, <poc-settings>, <presence>, <reg>, <refer>,
<Siemens-RTP-Stats>, <spirits-INDPs>, <spirits-user-prof>, and
<winfo>.
3.2.15. <priority> Element
The <priority> element indicates the call priorities the service is
willing to handle as defined in [RFC3840].
The <priority> element can contain two elements: <supported> and
<notsupported>. Priority values that are supported by the service
can be listed under the <supported> element, and priority values that
are not supported by the service can be listed under the
<notsupported> element.
The <supported> and <notsupported> elements can contain any number of
<lowerthan>, <higherthan>, <equals>, and <range> elements followed by
any number of optional extension elements from other namespaces.
3.2.15.1. <lowerthan> Element
The <lowerthan> 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.
Lonnfors & Kiss Standards Track [Page 9]
RFC 5196 User Agent Capability Presence Status September 2008
3.2.15.2. <higherthan> Element
The <higherthan> 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. <equals> Element
The <equals> element is used to indicate the exact priority value
that the service is willing to handle. The <equals> element has a
single attribute called "value". The "value" attribute is used to
indicate the exact supported priority value.
3.2.15.4. <range> Element
The <range> element is used to indicate the priority range that the
service is willing to handle. The <range> 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. <methods> Element
The <methods> 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 <methods> element can contain two elements: <supported> and
<notsupported>. Methods that are supported by the service can be
listed under the <supported> element, and methods that are not
supported by the service can be listed under the <notsupported>
element.
The <supported> and <notsupported> 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:<ACK>, <BYE>, <CANCEL>, <INFO>,
<INVITE>, <MESSAGE>, <NOTIFY>, <OPTIONS>, <PRACK>, <PUBLISH>,
<REFER>, <REGISTER>, <SUBSCRIBE>, and <UPDATE>.
Lonnfors & Kiss Standards Track [Page 10]
RFC 5196 User Agent Capability Presence Status September 2008
3.2.17. <extensions> Element
The <extensions> 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 <extensions> element can contain two elements: <supported> and
<notsupported>. Extensions that are supported by the service can be
listed under the <supported> element, and extensions that are not
supported by the service can be listed under the <notsupported>
element.
The <supported> and <notsupported> 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: <rel100>, <early-session>,
<eventlist>, <from-change>, <gruu>, <histinfo>, <join>, <norefersub>,
<path>, <precondition>, <pref>, <privacy>, <recipient-list-invite>,
<recipient-list-subscribe>, <replaces>, <resource-priority>, <sdp-
anat>, <sec-agree>, <tdialog>, and <timer>.
3.2.18. <schemes> Element
The <schemes> 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 <schemes> element can contain two elements: <supported> and
<notsupported>. Schemes that are supported by the service can be
listed under the <supported> element, and schemes that are not
supported by the service can be listed under the <notsupported>
element.
<supported> and <notsupported> elements can contain any number of <s>
elements, which can be used to describe individual schemes supported
by the service.
3.2.18.1. <s> Element
The <s> 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.
Lonnfors & Kiss Standards Track [Page 11]
RFC 5196 User Agent Capability Presence Status September 2008
3.2.19. <actor> Element
The <actor> element indicates the type of entity that is available at
this URI as defined in [RFC3840].
The <actor> element can contain two elements: <supported> and
<notsupported>. Actor types that are supported by the service can be
listed under the <supported> element, and actor types that are not
supported by the service can be listed under the <notsupported>
element.
The <supported> and <notsupported> elements can contain <principal>,
<attendant>, <msg-taker>, and <information> elements followed by any
number of optional extension elements from other namespaces.
The semantics of these elements are defined in [RFC3840] as:
o <principal>: 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 <attendant>: 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 <msg-taker>: The service provides communication with an automaton
or a person that will take messages and deliver them to the
principal.
o <information>: 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. <isfocus> Element
The <isfocus> element indicates that the service is a conference
server, also known as a focus as defined in [RFC3840].
The <isfocus> 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.
Lonnfors & Kiss Standards Track [Page 12]
RFC 5196 User Agent Capability Presence Status September 2008
3.2.21. <languages> Element
The <languages> element indicates the ability to display particular
human languages as defined in [RFC4646].
The <languages> element can contain two elements: <supported> and
<notsupported>. Languages that are supported by the service can be
listed under the <supported> element, and languages that are not
supported by the service can be listed under the <notsupported>
element.
<supported> and <notsupported> elements can contain any number of <l>
elements which can be used to describe individual languages supported
by the service.
3.2.21.1. <l> Element
The <l> element is of string type and is used to describe an
individual language supported by the service. Values that can be
used here are language subtags that are registered to the IANA
language subtag registry as per [RFC4646].
3.3. Device Capabilities
Elements belonging to device capabilities are used to describe
dynamic characteristics of a device. These capabilities are enclosed
within the <devcaps> element, which SHOULD be located in the PIDF
document as a child element of the
urn:ietf:params:xml:ns:pidf:data-model namespace <device> element
[RFC4479].
The namespace identifier for these elements is urn:
ietf:params:xml:ns:pidf:caps
3.3.1. <devcaps> Element
The root element of device capabilities is <devcaps>. The root
element always has to be present. This element can contain the
following child elements: <mobility> and <description> followed by
any number of optional extension elements from other namespaces.
A <devcaps> element can contain any number of optional extension
attributes from other namespaces.
Lonnfors & Kiss Standards Track [Page 13]
RFC 5196 User Agent Capability Presence Status September 2008
3.3.2. <mobility> Element
The <mobility> element indicates whether the device is fixed (meaning
that it is associated with a fixed point of contact with the network)
or mobile (meaning that it is not associated with a fixed point of
contact). Note that cordless phones are fixed, not mobile, based on
this definition as defined in [RFC3840].
The <mobility> element can contain two elements: <supported> and
<notsupported>. Mobility modes that are supported by the device can
be listed under the <supported> element and mobility modes that are
not supported by the device can be listed under the <notsupported>
element.
The <supported> and <notsupported> elements can contain <fixed> and
<mobile> elements followed by any number of optional extension
elements from other namespaces.
The semantics of these elements are defined in [RFC3840] as:
o <fixed>: The device is stationary.
o <mobile>: The device can move around with the user.
Any value that is registered with IANA to the SIP media feature tag
registration tree as sip.mobility 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].
3.3.3. <description> Element
The <description> element provides a textual description of the
device as defined in [RFC3840].
The <description> element is of string type and does not have any
attributes.
The <description> element SHOULD be labeled with the 'xml:lang'
attribute to indicate its language and script. The specification
allows multiple occurrences of this element so that the presentity
can convey <description> elements in multiple scripts and languages.
If no 'xml:lang' attribute is provided, the default value is
"i-default" as defined in [RFC2277].
Lonnfors & Kiss Standards Track [Page 14]
RFC 5196 User Agent Capability Presence Status September 2008
4. Usage Guidelines
The User Agent Capabilities extension [RFC3840] recommends that a UA
provides complete information in its contact predicate. However, it
may be that the presentity is not willing to publish presence
information that would be consistent with actual device or service
capabilities (e.g., presentity may not want to indicate that he/she
supports voice when the service actually is able to support it).
Authorization rules or policies in the presence server may limit or
modify the presence information published by the presentity. Also,
combining presence information from multiple sources may result in
loss or mismatch of information.
It is RECOMMENDED that Presence User Agents (PUAs) using this
extension provide as complete presence information as they can. If
the PUA is publishing sensitive information using this extension, it
SHOULD obtain permission from the presentity. PUAs can indicate the
explicitly supported capabilities using the <supported> element, and
the capabilities that are explicitly not supported using the
<notsupported> element.
It is not mandated that presence information be consistent with
actual service or device capabilities. However, it is in the
presentity's best interest to avoid publishing false presence
information and provide accurate information to help minimize
unsuccessful communication invitations. Otherwise, watchers may
conclude that communication cannot be established with the
presentity, but in reality it would be possible; or watchers may
conclude that certain communication capabilities are available, but
in reality a communication establishment attempt would fail using
those capabilities. In any case, watchers should not expect the
presence information represented by this extension to be fully
aligned with the actual presentity's service or device capabilities.
As explained in Section 1.2, presence of this extension does not
replace the use of SIP signaling for capability negotiation.
4.1. Use of <supported> and <notsupported> Elements
PUAs should add information under <supported> and <notsupported>
elements only when they believe it may affect the decision making in
the watcher's end, i.e., information should be relevant and valuable
for the watcher. Listing all possible information under <supported>
and <notsupported> is rarely needed.
For example, if the PUA wants to advertise a message service that
supports the MESSAGE method, it should add it under the <supported>
element in the <methods> element. Even if the service does not
Lonnfors & Kiss Standards Track [Page 15]
RFC 5196 User Agent Capability Presence Status September 2008
support other methods, it is unlikely that listing all the methods
not supported under the <notsupported> element would provide any
value to the watcher.
In case of conflicting information, i.e., the same child element
appears under the <supported> and <notsupported> elements with the
same value, the watcher can safely assume that the listed capability
is supported regardless of the inclusion of the capability under the
<notsupported> element.
5. Examples
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:caps="urn:ietf:params:xml:ns:pidf:caps"
xmlns:mod="urn:ietf:params:xml:ns:pidf:data-model"
entity="pres:someone@example.com">
<tuple id="joi9877866786ua9">
<status>
<basic>open</basic>
</status>
<caps:servcaps>
<caps:audio>true</caps:audio>
<caps:description xml:lang="en">
Example service
</caps:description>
<caps:description xml:lang="hu">
Pe'lda szolga'ltata's
</caps:description>
<caps:duplex>
<caps:supported>
<caps:full/>
</caps:supported>
</caps:duplex>
<caps:message>true</caps:message>
<caps:methods>
<caps:supported>
<caps:ACK/>
<caps:BYE/>
<caps:INVITE/>
<caps:MESSAGE/>
</caps:supported>
</caps:methods>
<caps:priority>
<caps:supported>
<caps:lowerthan maxvalue="10"/>
</caps:supported>
Lonnfors & Kiss Standards Track [Page 16]
RFC 5196 User Agent Capability Presence Status September 2008
</caps:priority>
<caps:schemes>
<caps:supported>
<caps:s>sip</caps:s>
</caps:supported>
</caps:schemes>
<caps:video>false</caps:video>
</caps:servcaps>
<contact>sip:someone@example.com</contact>
</tuple>
<mod:device id="hgt67">
<caps:devcaps>
<caps:mobility>
<caps:supported>
<caps:mobile/>
</caps:supported>
</caps:mobility>
</caps:devcaps>
<mod:deviceID
>urn:uuid:d27459b7-8213-4395-aa77-ed859a3e5b3a</mod:deviceID>
</mod:device>
</presence>
6. XML Schema Definitions
This section gives the XML schema definitions for the extensions
defined in this document. The namespace identifier for this schema
is urn:ietf:params:xml:ns:pidf:caps.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:tns="urn:ietf:params:xml:ns:pidf:caps"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="urn:ietf:params:xml:ns:pidf:caps"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- This import brings in the XML language
attribute xml:lang-->
<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<!-- ROOT -->
<xs:element name="servcaps" type="tns:servcapstype"/>
<xs:complexType name="servcapstype">
<xs:sequence>
<xs:element name="actor" type="tns:actortype"
minOccurs="0"/>
Lonnfors & Kiss Standards Track [Page 17]
RFC 5196 User Agent Capability Presence Status September 2008
<xs:element name="application" type="tns:applicationtype"
minOccurs="0"/>
<xs:element name="audio" type="tns:audiotype" minOccurs="0"/>
<xs:element name="automata" type="tns:automatatype"
minOccurs="0"/>
<xs:element name="class" type="tns:classtype"
minOccurs="0"/>
<xs:element name="control" type="tns:controltype"
minOccurs="0"/>
<xs:element name="data" type="tns:datatype"
minOccurs="0"/>
<xs:element name="description" type="tns:descriptiontype"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="duplex" type="tns:duplextype"
minOccurs="0"/>
<xs:element name="event-packages" type="tns:event-packagestype"
minOccurs="0"/>
<xs:element name="extensions" type="tns:extensionstype"
minOccurs="0"/>
<xs:element name="isfocus" type="tns:isfocustype"
minOccurs="0"/>
<xs:element name="message" type="tns:messagetype"
minOccurs="0"/>
<xs:element name="methods" type="tns:methodstype"
minOccurs="0"/>
<xs:element name="languages" type="tns:languagestype"
minOccurs="0"/>
<xs:element name="priority" type="tns:prioritytype"
minOccurs="0"/>
<xs:element name="schemes" type="tns:schemestype"
minOccurs="0"/>
<xs:element name="text" type="tns:texttype"
minOccurs="0"/>
<xs:element name="type" type="tns:typetype"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="video" type="tns:videotype"
minOccurs="0"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>
<xs:element name="devcaps" type="tns:devcaps"/>
<xs:complexType name="devcaps">
<xs:sequence>
<xs:element name="description" type="tns:descriptiontype"
minOccurs="0" maxOccurs="unbounded"/>
Lonnfors & Kiss Standards Track [Page 18]
RFC 5196 User Agent Capability Presence Status September 2008
<xs:element name="mobility" type="tns:mobilitytype"
minOccurs="0"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>
<!-- AUDIO -->
<xs:simpleType name="audiotype">
<xs:restriction base="xs:boolean"/>
</xs:simpleType>
<!-- APPLICATION -->
<xs:simpleType name="applicationtype">
<xs:restriction base="xs:boolean"/>
</xs:simpleType>
<!-- DATA -->
<xs:simpleType name="datatype">
<xs:restriction base="xs:boolean"/>
</xs:simpleType>
<!-- CONTROL -->
<xs:simpleType name="controltype">
<xs:restriction base="xs:boolean"/>
</xs:simpleType>
<!-- VIDEO -->
<xs:simpleType name="videotype">
<xs:restriction base="xs:boolean"/>
</xs:simpleType>
<!-- TEXT -->
<xs:simpleType name="texttype">
<xs:restriction base="xs:boolean"/>
</xs:simpleType>
<!-- MESSAGE -->
<xs:simpleType name="messagetype">
<xs:restriction base="xs:boolean"/>
</xs:simpleType>
<!-- TYPE -->
<xs:simpleType name="typetype">
<xs:restriction base="xs:string"/>
</xs:simpleType>
Lonnfors & Kiss Standards Track [Page 19]
RFC 5196 User Agent Capability Presence Status September 2008
<!-- AUTOMATA -->
<xs:simpleType name="automatatype">
<xs:restriction base="xs:boolean"/>
</xs:simpleType>
<!-- CLASS -->
<xs:complexType name="classtype">
<xs:sequence>
<xs:element name="supported" type="tns:classtypes"
minOccurs="0"/>
<xs:element name="notsupported" type="tns:classtypes"
minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="classtypes">
<xs:sequence>
<xs:element name="business" type="xs:string"
minOccurs="0"/>
<xs:element name="personal" type="xs:string"
minOccurs="0"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<!-- DUPLEX -->
<xs:complexType name="duplextype">
<xs:sequence>
<xs:element name="supported" type="tns:duplextypes"
minOccurs="0"/>
<xs:element name="notsupported" type="tns:duplextypes"
minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="duplextypes">
<xs:sequence>
<xs:element name="full" type="xs:string"
minOccurs="0"/>
<xs:element name="half" type="xs:string"
minOccurs="0"/>
<xs:element name="receive-only" type="xs:string"
minOccurs="0"/>
<xs:element name="send-only" type="xs:string"
minOccurs="0"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
Lonnfors & Kiss Standards Track [Page 20]
RFC 5196 User Agent Capability Presence Status September 2008
</xs:complexType>
<!-- DESCRIPTION -->
<xs:complexType name="descriptiontype">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute ref="xml:lang"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<!-- EVENT-PACKAGES -->
<xs:complexType name="event-packagestype">
<xs:sequence>
<xs:element name="supported" type="tns:eventtypes"
minOccurs="0"/>
<xs:element name="notsupported" type="tns:eventtypes"
minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="eventtypes">
<xs:sequence>
<xs:element name="conference" type="xs:string"
minOccurs="0"/>
<xs:element name="dialog" type="xs:string"
minOccurs="0"/>
<xs:element name="kpml" type="xs:string"
minOccurs="0"/>
<xs:element name="message-summary" type="xs:string"
minOccurs="0"/>
<xs:element name="poc-settings" type="xs:string"
minOccurs="0"/>
<xs:element name="presence" type="xs:string"
minOccurs="0"/>
<xs:element name="reg" type="xs:string"
minOccurs="0"/>
<xs:element name="refer" type="xs:string"
minOccurs="0"/>
<xs:element name="Siemens-RTP-Stats"
type="xs:string" minOccurs="0"/>
<xs:element name="spirits-INDPs"
type="xs:string" minOccurs="0"/>
<xs:element name="spirits-user-prof"
type="xs:string" minOccurs="0"/>
<xs:element name="winfo" type="xs:string"
minOccurs="0"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
Lonnfors & Kiss Standards Track [Page 21]
RFC 5196 User Agent Capability Presence Status September 2008
</xs:sequence>
</xs:complexType>
<!-- PRIORITY -->
<xs:complexType name="prioritytype">
<xs:sequence>
<xs:element name="supported" type="tns:prioritytypes"
minOccurs="0"/>
<xs:element name="notsupported" type="tns:prioritytypes"
minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="prioritytypes">
<xs:sequence>
<xs:element name="equals" type="tns:equalstype"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="higherhan" type="tns:higherthantype"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="lowerthan" type="tns:lowerthantype"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="range" type="tns:rangetype"
minOccurs="0" maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="lowerthantype">
<xs:attribute name="maxvalue" type="xs:integer"
use="required"/>
</xs:complexType>
<xs:complexType name="higherthantype">
<xs:attribute name="minvalue" type="xs:integer"
use="required"/>
</xs:complexType>
<xs:complexType name="equalstype">
<xs:attribute name="value" type="xs:integer"
use="required"/>
</xs:complexType>
<xs:complexType name="rangetype">
<xs:attribute name="minvalue" type="xs:integer"
use="required"/>
<xs:attribute name="maxvalue" type="xs:integer"
use="required"/>
</xs:complexType>
<!-- METHODS -->
<xs:complexType name="methodstype">
<xs:sequence>
Lonnfors & Kiss Standards Track [Page 22]
RFC 5196 User Agent Capability Presence Status September 2008
<xs:element name="supported" type="tns:methodtypes"
minOccurs="0"/>
<xs:element name="notsupported" type="tns:methodtypes"
minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="methodtypes">
<xs:sequence>
<xs:element name="ACK" type="xs:string" minOccurs="0"/>
<xs:element name="BYE" type="xs:string" minOccurs="0"/>
<xs:element name="CANCEL" type="xs:string" minOccurs="0"/>
<xs:element name="INFO" type="xs:string" minOccurs="0"/>
<xs:element name="INVITE" type="xs:string" minOccurs="0"/>
<xs:element name="MESSAGE" type="xs:string" minOccurs="0"/>
<xs:element name="NOTIFY" type="xs:string" minOccurs="0"/>
<xs:element name="OPTIONS" type="xs:string" minOccurs="0"/>
<xs:element name="PRACK" type="xs:string" minOccurs="0"/>
<xs:element name="PUBLISH" type="xs:string" minOccurs="0"/>
<xs:element name="REFER" type="xs:string" minOccurs="0"/>
<xs:element name="REGISTER" type="xs:string" minOccurs="0"/>
<xs:element name="SUBSCRIBE" type="xs:string" minOccurs="0"/>
<xs:element name="UPDATE" type="xs:string" minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<!-- EXTENSIONS -->
<xs:complexType name="extensionstype">
<xs:sequence>
<xs:element name="supported" type="tns:extensiontypes"
minOccurs="0"/>
<xs:element name="notsupported" type="tns:extensiontypes"
minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="extensiontypes">
<xs:sequence>
<xs:element name="rel100" type="xs:string" minOccurs="0"/>
<xs:element name="early-session" type="xs:string" minOccurs="0"/>
<xs:element name="eventlist" type="xs:string" minOccurs="0"/>
<xs:element name="from-change" type="xs:string" minOccurs="0"/>
<xs:element name="gruu" type="xs:string" minOccurs="0"/>
<xs:element name="hist-info" type="xs:string" minOccurs="0"/>
<xs:element name="join" type="xs:string" minOccurs="0"/>
<xs:element name="norefersub" type="xs:string" minOccurs="0"/>
<xs:element name="path" type="xs:string" minOccurs="0"/>
<xs:element name="precondition" type="xs:string" minOccurs="0"/>
Lonnfors & Kiss Standards Track [Page 23]
RFC 5196 User Agent Capability Presence Status September 2008
<xs:element name="pref" type="xs:string" minOccurs="0"/>
<xs:element name="privacy" type="xs:string" minOccurs="0"/>
<xs:element name="recipient-list-invite" type="xs:string"
minOccurs="0"/>
<xs:element name="recipient-list-subscribe" type="xs:string"
minOccurs="0"/>
<xs:element name="replaces" type="xs:string" minOccurs="0"/>
<xs:element name="resource-priority" type="xs:string" minOccurs="0"/>
<xs:element name="sdp-anat" type="xs:string" minOccurs="0"/>
<xs:element name="sec-agree" type="xs:string" minOccurs="0"/>
<xs:element name="tdialog" type="xs:string" minOccurs="0"/>
<xs:element name="timer" type="xs:string" minOccurs="0"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<!-- SCHEMES -->
<xs:complexType name="schemestype">
<xs:sequence>
<xs:element name="supported" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element name="s" type="xs:string" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="notsupported" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element name="s" type="xs:string" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
<!-- ACTOR -->
<xs:complexType name="actortype">
<xs:sequence>
<xs:element name="supported" type="tns:actortypes"
minOccurs="0"/>
<xs:element name="notsupported" type="tns:actortypes"
minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="actortypes">
<xs:sequence>
Lonnfors & Kiss Standards Track [Page 24]
RFC 5196 User Agent Capability Presence Status September 2008
<xs:element name="attendant" type="xs:string" minOccurs="0"/>
<xs:element name="information" type="xs:string" minOccurs="0"/>
<xs:element name="msg-taker" type="xs:string" minOccurs="0"/>
<xs:element name="principal" type="xs:string" minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<!-- ISFOCUS -->
<xs:simpleType name="isfocustype">
<xs:restriction base="xs:boolean"/>
</xs:simpleType>
<!-- LANGUAGES -->
<xs:complexType name="languagestype">
<xs:sequence>
<xs:element name="supported" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element name="l" type="xs:string" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="notsupported" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element name="l" type="xs:string" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
<!-- MOBILITY -->
<xs:complexType name="mobilitytype">
<xs:sequence>
<xs:element name="supported" type="tns:mobilitytypes"
minOccurs="0"/>
<xs:element name="notsupported" type="tns:mobilitytypes"
minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="mobilitytypes">
<xs:sequence>
<xs:element name="fixed" type="xs:string"
minOccurs="0"/>
<xs:element name="mobile" type="xs:string"
Lonnfors & Kiss Standards Track [Page 25]
RFC 5196 User Agent Capability Presence Status September 2008
minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:schema>
7. IANA Considerations
IANA has registered one new XML namespace URN and one schema as
defined in [RFC3688].
7.1. URN Sub-Namespace Registration for
'urn:ietf:params:xml:ns:pidf:caps'
URI:
urn:ietf:params:xml:ns:pidf:caps
Description:
This is the XML namespace for XML elements defined by RFC 5196 to
describe service and device capabilities in application/pidf+xml
content type.
Registrant Contact:
IETF, SIMPLE working group, <simple@ietf.org>
Mikko Lonnfors, <mikko.lonnfors@nokia.com>
XML:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html> xmlns="http://www.w3.org/1999/xhtml"
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Namespace for PIDF user agent capability
extension</title>
</head>
<body>
<h1>Namespace for PIDF service capability extension</h1>
<h2>urn:ietf:params:xml:ns:pidf:caps</h2>
<p>
See <a href="http://www.rfc-editor.org/rfc/rfc5196.txt">RFC
5196</a>.
</p>
</body>
Lonnfors & Kiss Standards Track [Page 26]
RFC 5196 User Agent Capability Presence Status September 2008
</html>
END
7.2. Schema Registration for Schema
'urn:ietf:params:xml:schema:pidf:caps'
URI:
urn:ietf:params:xml:schema:pidf:caps
Registrant Contact:
IESG
XML:
See Section 6
8. Security Considerations
All security considerations specified in [RFC3859] and [RFC3863]
apply to this document. Compared to PIDF [RFC3863], this presence
document format may reveal additional information about user's
service and device capabilities. Thus, the PUA SHOULD always obtain
permission from the presentity when publishing sensitive information
using this extension.
9. Acknowledgments
Authors of this document would like to thank the following people for
their contributions and valuable comments: Paul Kyzivat, Jonathan
Rosenberg, Markus Isomaki, Eva Leppanen, Miguel Garcia, Jari
Urpalainen, and Hisham Khartabil.
10. References
10.1. Normative References
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) part one: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
[RFC2913] Klyne, G., "MIME Content Types in Media Feature
Expressions", RFC 2913, September 2000.
Lonnfors & Kiss Standards Track [Page 27]
RFC 5196 User Agent Capability Presence Status September 2008
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC3840] Schulzrinne, H., Rosenberg, J., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, August 2004.
[RFC3859] Peterson, J., "Common Profile for Presence (CPP)",
RFC 3859, August 2004.
[RFC3863] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr,
W., and J. Peterson, "Presence Information Data Format
(PIDF)", RFC 3863, August 2004.
[RFC4479] Rosenberg, J., "A Data Model for Presence", RFC 4479,
July 2006.
[RFC4646] Phillips, A. and M. Davis, "Tags for Identifying
Languages", BCP 47, RFC 4646, September 2006.
10.2. Informative References
[RFC2648] Moats, R., "A URN namespace for IETF documents", RFC 2648,
August 1999.
[RFC2778] Day, M., Rosenberg, J., and H. Sugano, "A Model for
Presence and Instant Messaging", RFC 2778, February 2000.
[RFC3860] Peterson, J., "Common Profile for Instant Messaging
(CPIM)", RFC 3860, August 2004.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC4569] Camarillo, G., "Internet Assigned Numbers Authority (IANA)
Registration of the Message Media Feature Tag", RFC 4569,
July 2006.
Lonnfors & Kiss Standards Track [Page 28]
RFC 5196 User Agent Capability Presence Status September 2008
Authors' Addresses
Mikko Lonnfors
Nokia
P.O. Box 321
Helsinki
Finland
Phone: +358 71 8008000
EMail: mikko.lonnfors@nokia.com
Krisztian Kiss
Nokia
313 Fairchild Dr
Mountain View, CA 94043
US
Phone: +1 650 391 5969
EMail: krisztian.kiss@nokia.com
Lonnfors & Kiss Standards Track [Page 29]
RFC 5196 User Agent Capability Presence Status September 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Lonnfors & Kiss Standards Track [Page 30]