Network Working Group M. Garcia-Martin

Network Working Group M. Garcia-Martin
Request for Comments: 4354 Nokia
Category: Informational January 2006

A Session Initiation Protocol (SIP) Event Package and Data Format
for Various Settings in Support
for the Push-to-Talk over Cellular (PoC) Service

Status of This Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2006).

Abstract

The Open Mobile Alliance (OMA) is defining the Push-to-talk over
Cellular (PoC) service where SIP is the protocol used to establish
half-duplex media sessions across different participants, to send
instant messages, etc. This document defines a SIP event package to
support publication, subscription, and notification of additional
capabilities required by the PoC service. This SIP event package is
applicable to the PoC service and may not be applicable to the
general Internet.

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Table of Contents

1. Introduction ....................................................3
2. Terminology .....................................................5
3. Applicability Statement .........................................5
4. Requirements ....................................................5
5. The "poc-settings" Event Package ................................6
5.1. Package Name ...............................................6
5.2. Event Package Parameters ...................................7
5.3. SUBSCRIBE Bodies ...........................................7
5.4. Subscription Duration ......................................7
5.5. NOTIFY Bodies ..............................................7
5.6. Notifier Processing of SUBSCRIBE Requests ..................8
5.6.1. Authentication ......................................8
5.6.2. Authorization .......................................8
5.7. Notifier Generation of NOTIFY Requests .....................8
5.8. Subscriber Processing of NOTIFY Requests ...................9
5.9. Handling of Forked Requests ...............................10
5.10. Rate of Notifications ....................................10
5.11. State Agents .............................................10
5.12. Examples .................................................10
5.13. Use of URIs to Retrieve State ............................10
5.14. PUBLISH Bodies ...........................................11
5.15. PUBLISH Response Bodies ..................................11
5.16. Multiple Sources for Event State .........................11
5.17. Event State Segmentation .................................11
5.18. Rate of Publication ......................................12
6. PoC-Settings Document ..........................................12
6.1. XML Schema ................................................14
6.2. Example ...................................................16
7. Security Considerations ........................................17
8. Acknowledgements ...............................................17
9. IANA Considerations ............................................17
9.1. Registration of the "poc-settings" Event Package ..........17
9.2. Registration of the "application/poc-settings+xml"
MIME type .................................................18
10. References ....................................................19
10.1. Normative References .....................................19
10.2. Informative References ...................................20

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1. Introduction

The Open Mobile Alliance (OMA) (http://www.openmobilealliance.org) is
currently specifying the Push-to-talk over Cellular (PoC) service.
This service allows a SIP User Agent (PoC terminal) to establish a
session to one or more SIP User Agents (UAs) simultaneously, usually
initiated when the initiating user pushes a button.

OMA has defined a collection of very stringent requirements in
support of the PoC service. In order to provide the user with a
satisfactory experience, the initial session establishment (from the
time the user presses the button to the time they get an indication
to speak) must be minimized.

The PoC terminal may support hardware capabilities such as a
speakerphone and/or headset and software that provide the capability
for the user to configure the PoC terminal to accept session
initiations immediately and play out the media as soon as it is
received without requiring the intervention of the called user. This
mode of operation is known as Auto-Answer mode or automatic mode.
The user may alternatively configure the PoC terminal to first alert
the user and require the user to accept the session invitation
manually before media is accepted. This mode of operation is known
as Manual-Answer mode. The PoC terminal may support both or only one
of these modes of operation. The user may change the Answer Mode
(AM) configuration of the PoC terminal frequently based on their
current circumstances and preference (perhaps because the user is
busy or in a public area where she cannot use a speaker phone, etc.).

SIP PoC terminals can support various SIP-based communication
services in addition to Push-to-talk (e.g., VoIP telephony, presence
services, messaging services, etc.). The user may at times wish to
disable the acceptance of Push-to-talk sessions whilst still
remaining SIP registered for one or more other SIP-based services.
When the PoC terminal is configured to not accept any incoming Push-
to-talk sessions, this is known as Incoming Session Barring (ISB).

A user may wish to contact another user who has a PoC terminal with
Incoming Session Barring enabled. A user may send an Instant
Personal Alert to another user to inform him that he wishes to engage
him in a PoC Session. This Instant Personal Alert is received even
when the destination PoC terminal has enabled Incoming Session
Barring. If a user wishes to disable the acceptance of Instant
Personal Alerts, he can configure his PoC terminal not accept any
incoming Instant Personal Alerts. This is known as Instant Personal
Alert Barring (IPAB).

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Some PoC terminals may provide support for handling multiple PoC
sessions simultaneously whereas other terminals are only able to
handle one PoC session at time. Or, even if the terminal is able to
handle multiple PoC sessions simultaneously, the user may desire to
have just one single PoC session at a time. This indication of
support for multiple PoC sessions simultaneously is known as
Simultaneous PoC Sessions Support (SSS).

The OMA PoC Architecture utilizes SIP servers within the network that
may perform roles such as a conference focus [12], an RTP translator,
or a policy server. A possible optimization to minimize the delay in
providing the caller with an indication to speak consist of the SIP
network server to perform buffering of media packets in order to
provide an early or unconfirmed indication to the caller and allow
the caller to start speaking before the called PoC terminal has
answered. This optimization only is appropriate when the called PoC
terminal is currently accepting PoC sessions and its Answer Mode is
set to Auto-Answer. This optimization therefore requires the network
SIP server to have knowledge of the current ISB and AM settings of
the called PoC terminal.

Similarly, in order to avoid unnecessary transmission of Instant
Personal Alerts across the radio interface, the network SIP server
needs to have knowledge of the current IPAB setting at the terminal.

When the UA supports multiple PoC sessions simultaneously the server
needs to act as a B2BUA in order to multiplex media and floor control
signaling between multiple sessions using a single bandwidth limited
radio bearer. When handling of multiple PoC sessions simultaneously
is not needed the server can act as a SIP proxy. It is therefore
advantageous for the server to be informed whether the UA currently
intends to support multiple PoC sessions simultaneously.

This document proposes additional SIP capabilities to enable the
communication of the ISB, AM, IPAB, and SSS settings between the SIP
PoC terminal and the SIP network server.

We define a SIP event package that allows a SIP Event Publication
Agent (EPA) to publish the user's settings at that particular EPA
which may impact some specific session attempts. This allows
subscribers to subscribe to the Event State Compositor to this event
package to gather this information, and anticipate to the user's
needs when a session is attempted to that user. It is believed that
the SIP event package defined here is not applicable to the general
Internet: it has been designed to serve the architecture of the PoC
service. In particular, and in the context defined by RFC 3903 [8],
it is the intention of OMA to make PoC terminals behave as Event
Publication Agents (EPA), and network servers behave as Event State

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Compositors (ESC). It is possible that PoC terminals and network
servers may also subscribe to the user's PoC related settings, so
that changes in this state made in one terminal are kept in
synchronization across all different terminals or with the network
server for a particular user.

This document defines a PoC-settings document that allows an EPA to
convey its ISB, AM, IPAB, and SSS settings to an ESC. The EPA sends
a PoC-settings document in PUBLISH requests [8]. The PoC-settings
document contain represents the settings view at that particular EPA.
The ESC can collect PoC-settings document for the same user at
different EPAs, apply a composition policy, and provide
notifications. Notifications can contain a composed view of the
settings or a list of settings per EPA, depending on whether the ESC
is able to resolve conflicts. A subscriber can receive notifications
of changes in this document according to the procedures specified in
RFC 3265 [5]. The aim of this memo is to follow the procedure
indicated in RFC 3427 [6] and to register a new poc-settings event
package with IANA.

2. Terminology

In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [1] and indicate requirement levels for
compliant implementations.

3. Applicability Statement

The event package defined in this document is intended for use with
network-based application servers that provide a Push-to-Talk over
Cellular service.

4. Requirements

A comprehensive description of all the requirements that affect the
Push-to-Talk over Cellular service developed by the Open Mobile
Alliance can be found in the Open Mobile Alliance web page at
http://www.openmobilealliance.org.

For the sake of simplicity, we briefly discuss here those
requirements that affect the solution described in this document.
These requirements can be summarized as follows:

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1. There must be a mechanism that reduces the session setup time as
much as possible.
2. In order to allow proper usage of scarce resources, there must be
a mechanism that saves the air interface from being congested
with unneeded or undesired traffic.
3. The mechanism should not involve the implementation of new
protocols, unless strictly needed.

These requirements lead to a solution whereby the user can indicate
to a network node his ability to accept or reject sessions or certain
types of messages. Pushing these settings to a network node allows
the network node to produce a faster response to the originator,
perhaps even declining or filtering some SIP requests towards the
destination. This approaches the goal of reducing the session setup
time.

5. The "poc-settings" Event Package

RFC 3265 [5] defines a SIP extension for subscribing to remote nodes
and receiving notifications of changes (events) in their states. It
leaves the definition of many aspects of these events to concrete
extensions, known as event packages. This document qualifies as an
event package. This section fills in the information required for
all event packages by RFC 3265 [5].

Additionally, RFC 3903 [8] defines an extension that allows SIP User
Agents to publish event state. According to RFC 3903 [8], any event
package intended to be used in conjunction with the SIP PUBLISH
method has to include a considerations section. This section also
fills the information for all event packages to be used with PUBLISH
requests.

We define a new "poc-settings" event package. Event Publication
Agents (EPA) use PUBLISH requests to inform an Event State Compositor
(ESC) of changes in the poc-settings event package. Acting as a
notifier, the ESC notifies subscribers to the user's poc-settings
information when changes occur.

5.1. Package Name

The name of this package is "poc-settings". As specified in RFC 3265
[5], this value appears in the Event header field present in
SUBSCRIBE and NOTIFY requests. As specified in RFC 3903 [8], this
value also appears in the Event header field present in PUBLISH
requests.

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5.2. Event Package Parameters

RFC 3265 [5] allows event packages to define additional parameters
carried in the Event header field. This event package,
"poc-settings", does not define additional parameters.

5.3. SUBSCRIBE Bodies

According to RFC 3265 [5], a SUBSCRIBE request can contain a body.
The purpose of the body depends on its type. Subscriptions to the
poc-settings event package will normally not contain bodies.

The Request-URI of the SUBSCRIBE request identifies the user about
whose poc-settings the subscriber wants to be informed.

5.4. Subscription Duration

The default expiration time for subscriptions within this package is
3600 seconds. As per RFC 3265 [5], the subscriber MAY specify an
alternate expiration in the Expires header field.

5.5. NOTIFY Bodies

As described in RFC 3265 [5], the NOTIFY message will contain bodies
describing the state of the subscribed resource. This body is in a
format listed in the Accept header field of the SUBSCRIBE request, or
a package-specific default format if the Accept header field was
omitted from the SUBSCRIBE request.

In this event package, the body of the notification contains a PoC-
settings document (see Section 6). The ESC has gathered PoC-
settings documents for the user at different EPAs. The ESC applies a
composition policy and composes a PoC-settings document with a common
view of all these settings across different EPAs. In case the ESC is
not able to resolve a conflict, due to contradictory information
provided by two different EPAs, the ESC provides a PoC-settings
document containing the settings at each terminal so that the
subscriber can resolve the conflict.

All subscribers and notifiers of the "poc-settings" event package
MUST support the "application/poc-settings+xml" data format described
in Section 6. The SUBSCRIBE request MAY contain an Accept header
field. If no such header field is present, it has a default value of
"application/poc-settings+xml" (assuming that the Event header field
contains a value of "poc-settings"). If the Accept header field is
present, it MUST include "application/poc-settings+xml" and MAY
include any other types capable of representing user settings for
PoC.

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5.6. Notifier Processing of SUBSCRIBE Requests

The contents of a PoC-settings document can contain sensitive
information that can reveal some privacy information. Therefore,
PoC-settings documents MUST only be sent to authorized subscribers.
In order to determine if a subscription originates in an authorized
user, the user MUST be authenticated as described in Section 5.6.1
and then he MUST be authorized to be a subscriber as described in
Section 5.6.2.

5.6.1. Authentication

Notifiers MUST authenticate all subscription requests. This
authentication can be done using any of the mechanisms defined in RFC
3261 [4] and other authentication extensions.

5.6.2. Authorization

Once authenticated, the notifier makes an authorization decision. A
notifier MUST NOT accept a subscription unless authorization has been
provided by the user. The means by which authorization are provided
are outside the scope of this document. Authorization may have been
provided ahead of time through access lists, perhaps specified in a
web page. Authorization may have been provided by means of uploading
some kind of standardized access control list document.

5.7. Notifier Generation of NOTIFY Requests

RFC 3265 [5] details the formatting and structure of NOTIFY messages.
However, packages are mandated to provide detailed information on
when to send a NOTIFY, how to compute the state of the resource, how
to generate neutral or fake state information, and whether state
information is complete or partial. This section describes those
details for the poc-settings event package.

A notifier MAY send a NOTIFY at any time. Typically, it will send
one when the poc-settings stage of a user changes. The NOTIFY
request MAY contain a body containing a PoC-settings document. The
times at which the NOTIFY is sent for a particular subscriber, and
the contents of the body within that notification, are subject to any
rules specified by the authorization policy that governs the
subscription. However, typically the NOTIFY will contain an
indication of those PoC-related services for which a change has
occurred.

In the case of a pending subscription, when final authorization is
determined, a NOTIFY can be sent. If the result of the authorization
decision was success, a NOTIFY SHOULD be sent and SHOULD contain a

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complete PoC-settings document with the current state of the user's
PoC settings. If the subscription is rejected, a NOTIFY MAY be sent.
As described in RFC 3265 [5], the Subscription-State header field
indicates the state of the subscription.

The body of the NOTIFY MUST be sent using one of the types listed in
the Accept header field in the most recent SUBSCRIBE request, or
using the type "application/poc-settings+xml" if no Accept header
field was present.

Notifiers will typically act as Event State Compositors (ESC) and
thus will learn the poc-settings event state via PUBLISH requests
sent from the user's Event Publication Agent (EPA) when the user
changes one of those settings. It is possible that the notifier
generates a NOTIFY request for a user for which no publication has
taken place. In that case, the PoC-settings document will not
contain any <entity> element (see Section 6.1 for a detailed
description of the <entity> element).

For reasons of privacy, it will frequently be necessary to encrypt
the contents of the notifications. This can be accomplished using
S/MIME [9]. The encryption can be performed using the key of the
subscriber as identified in the From field of the SUBSCRIBE request.
Similarly, integrity of the notifications is important to
subscribers. As such, the contents of the notifications MAY provide
authentication and message integrity using S/MIME [9]. Since the
NOTIFY is generated by the notifier, which may not have access to the
key of the user represented by the poc-settings user, often the
NOTIFY will be signed by a third party. The NOTIFY request SHOULD be
signed by an authority over the domain of the user. In other words,
for a user whose SIP URI is sip:[email protected], the signator of the
NOTIFY SHOULD be the authority for example.com.

5.8. Subscriber Processing of NOTIFY Requests

RFC 3265 [5] leaves it to event packages to describe the process
followed by the subscriber upon receipt of a NOTIFY request,
including any logic required to form a coherent resource state.

In this specification, each NOTIFY request contains either no PoC-
settings document, or a document representing one or more PoC related
settings for a given user. Within a dialog, the PoC-settings
document in the NOTIFY request with the highest CSeq header field
value is the current one. When no document is present in that
NOTIFY, the PoC-settings document present in the NOTIFY with the next
highest CSeq value is used.

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5.9. Handling of Forked Requests

RFC 3265 [5] requires each package to describe handling of forked
SUBSCRIBE requests.

This specification only allows a single dialog to be constructed as a
result of emitting an initial SUBSCRIBE request. This guarantees
that only a single subscriber is generating notifications for a
particular subscription to a particular user. The result of this is
that a user can have multiple SIP User Agents active, but these
should be homogeneous, so that each can generate the same set of
notifications for the user's poc-settings.

5.10. Rate of Notifications

RFC 3265 [5] requires each package to specify the maximum rate at
which notifications can be sent.

Poc-settings notifiers SHOULD NOT generate notifications for a single
user at a rate of more than once every five seconds.

5.11. State Agents

RFC 3265 [5] requires each package to consider the role of state
agents in the package and, if they are used, to specify how
authentication and authorization are done.

This specification allows state agents to be located in the network.
Publication of PoC-settings document is linked to a user. However, a
user may be simultaneously logged in at different PoC terminals. If
a user changes her PoC settings from a terminal, it will send a
PUBLISH request containing a PoC-settings document. These settings
are applicable to the user independently of the terminal at which she
is logged in. In other words, PoC settings changes done in a
terminal affect all the PoC terminals where the user is logged. It
is RECOMMENDED that each of the terminals where the user is logged in
subscribes to its own PoC-settings document in order to keep a
coherent state view with the state agent.

5.12. Examples

An example of a PoC-setting document is provided in Section 6.2.

5.13. Use of URIs to Retrieve State

RFC 3265 [5] allows packages to use URIs to retrieve large state
documents.

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PoC-settings documents are fairly small. This event package does not
provide a mechanism to use URIs to retrieve large state documents.

5.14. PUBLISH Bodies

RFC 3903 [8] requires event packages to define the content types
expected in PUBLISH requests.

In this event package, the body of a PUBLISH request contains a PoC-
settings document (see Section 6). This PoC-settings document
describes the PoC-related settings of a user at an EPA. EPAs SHOULD
include their own information in a PoC-settings document; i.e., there
SHOULD be a single <entity> element in the body of the PUBLISH
request (See Section 6.1 for a detailed description of the <entity>
element).

All EPAs and ESCs MUST support the "application/poc-settings+xml"
data format described in Section 6 and MAY support other formats.

5.15. PUBLISH Response Bodies

This specification does not associate semantics to a body in a
PUBLISH response.

5.16. Multiple Sources for Event State

RFC 3903 [8] requires event packages to specify whether multiple
sources can contribute to the event state view at the ESC.

This event package allows different EPAs to publish the PoC settings
for a particular user. Each EPA publishes its own settings grouped
in an <entity> element. The EPA provides a globally unique
identifier for a given address of record. This allows the ESC to
differentiate EPAs and either compose a state resolving conflicts or
provide the union of the states of all the EPAs that contributed to
it. The composition policy at the ESC is outside the scope of this
document.

5.17. Event State Segmentation

RFC 3903 [8] defines segments within a state document. Each segment
is defined as one of potentially many identifiable sections in the
published event state.

This event package defines, for a given EPA, four segments identified
by the elements <isb-settings>, <am-settings>, <ipab-settings>, and
<sss-settings>, respectively. Each of them refers to different
states of the EPA.

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5.18. Rate of Publication

RFC 3903 [8] allows event packages to define their own rate of
publication.

There are no rate-limiting recommendations for poc-settings
publication. Since changes in a PoC-settings document are typically
triggered by interaction with a human user, there is not periodicity,
nor a minimum or maximum rate of publication.

6. PoC-Settings Document

PoC-settings is an XML document [10] that MUST be well-formed and
SHOULD be valid. PoC-settings documents MUST be based on XML 1.0 and
MUST be encoded using UTF-8 [7]. This specification makes use of XML
namespaces for identifying PoC-settings documents. The namespace URI
for elements defined by this specification is a URN [2], using the
namespace identifier 'oma'. This URN is:

urn:oma:params:xml:ns:poc:poc-settings

PoC-settings documents are identified with the MIME type
"application/poc-settings+xml" and are instances of the XML schema
defined in Section 6.1.

A PoC-settings document begins with the root element tag
<poc-settings>. It consists of zero or more <entity> elements, each
one including an 'id' attribute that contains a globally unique
identifier for a given address of record that represents an EPA. An
<entity> element represents an EPA, and it is uniquely identified by
the 'id' attribute. EPAs SHOULD include a single <entity> element in
a PoC-settings document. ESCs MAY include several <entity> elements
in a PoC-settings document, typically when the ESC is unable to
resolve conflicts due to incongruent publication from different
sources.

A valid PoC-settings document can include zero <entity> elements
if the ESC provides a notification for which no publication has
occurred.

The <entity> element MAY contain other elements and attributes from
different namespaces for the purposes of extensibility; elements or
attributes from unknown namespaces MUST be ignored.

The <entity> element consists of zero or one <isb-settings> elements,
zero or one <am-settings> elements, zero or one <ipab-settings>, and
zero or one <sss-settings> elements. Other elements and attributes

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from different namespaces MAY be present for the purposes of
extensibility; elements or attributes from unknown namespaces MUST be
ignored.

An <isb-settings> element contains a single <incoming-session-
barring> element that contains a boolean 'active' attribute. The
'active' attribute indicates whether incoming sessions are barred at
the UA, depending on the user's preferences for this setting. Other
elements and attributes from different namespaces MAY be present for
the purposes of extensibility; elements or attributes from unknown
namespaces MUST be ignored.

An <am-settings> element contains an <answer-mode> element, whose
value can be set to either "automatic" or "manual". Other elements
and attributes from different namespaces MAY be present for the
purposes of extensibility; elements or attributes from unknown
namespaces MUST be ignored.

A server such as a URI-list server [11] receives a SIP request
addressed to one or more recipients. If the intended recipient set
the <answer-mode> to "manual", the URI-list server proceeds with the
session attempt. If she set it to "automatic", the URI-list server
generates a 200-class response prior to contacting the intended
recipient.

An <ipab-settings> element contains a single <incoming-personal-
alert-barring> element that contains a boolean 'active' attribute.
The 'active' attribute indicates whether incoming personal alert
messages are barred at the UA, depending on the user's preferences
for this setting. Other elements from different namespaces MAY be
present for the purposes of extensibility; elements or attributes
from unknown namespaces MUST be ignored.

An <sss-settings> element contains a single <simultaneous-sessions-
support> element that contains a boolean 'active' attribute. The
'active' attribute indicates whether the SIP UA is willing to handle
more than one PoC session simultaneously. If the 'active' attribute
is set to "false" or "0", then when the SIP UA is engaged in a PoC
session, and the SIP UA receives an second incoming request for a SIP
PoC session, the UA will decline the invitation. If the 'active'
attribute is set to "true" or "1", then when the SIP UA is engaged in
a PoC session, and the SIP UA receives an second incoming request for
a SIP PoC session, the UA will possibly accept the invitation. Other
elements and attributes from different namespaces MAY be present for
the purposes of extensibility; elements or attributes from unknown
namespaces MUST be ignored.

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6.1. XML Schema

Implementations according to this specification MUST comply to the
following XML Schema, which defines the constraints of the PoC-
settings document:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:oma:params:xml:ns:poc:poc-settings"
xmlns="urn:oma:params:xml:ns:poc:poc-settings"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">

<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:annotation>
<xs:documentation xml:lang="en">
XML Schema Definition in support of the Incoming Session
Barring, Answer Mode, Incoming Personal Alert Barring,
and Simultaneous Sessions Support in the Push-to-talk
over Cellular (PoC) service.
</xs:documentation>
</xs:annotation>

<xs:element name="poc-settings" type="poc-settingsType"/>

<xs:complexType name="poc-settingsType">
<xs:sequence>
<xs:element name="entity" type="entityType"
minOccurs="0" maxOccurs="unbounded" />
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

<xs:complexType name="entityType">
<xs:sequence>
<xs:element name="isb-settings" type="isbSettingType"
minOccurs="0"/>
<xs:element name="am-settings" type="amSettingType"
minOccurs="0"/>
<xs:element name="ipab-settings" type="ipabSettingType"
minOccurs="0"/>
<xs:element name="sss-settings" type="sssSettingType"
minOccurs="0"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>

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</xs:sequence>
<xs:attribute name="id" type="xs:string" use="required"/>
<xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

<xs:complexType name="isbSettingType">
<xs:sequence>
<xs:element name="incoming-session-barring">
<xs:complexType>
<xs:attribute name="active" type="xs:boolean"
use="required" />
</xs:complexType>
</xs:element>
<xs:any namespace="##any" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

<xs:complexType name="amSettingType">
<xs:sequence>
<xs:element name="answer-mode">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="automatic"/>
<xs:enumeration value="manual"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:any namespace="##any" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

<xs:complexType name="ipabSettingType">
<xs:sequence>
<xs:element name="incoming-personal-alert-barring">
<xs:complexType>
<xs:attribute name="active" type="xs:boolean"
use="required" />
</xs:complexType>
</xs:element>
<xs:any namespace="##any" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

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RFC 4354 PoC Settings Event Package January 2006

<xs:complexType name="sssSettingType">
<xs:sequence>
<xs:element name="simultaneous-sessions-support">
<xs:complexType>
<xs:attribute name="active" type="xs:boolean"
use="required"/>
</xs:complexType>
</xs:element>
<xs:any namespace="##any" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

</xs:schema>

6.2. Example

The following is an example of a PoC-settings document:

<?xml version="1.0" encoding="UTF-8"?>

<poc-settings xmlns="urn:oma:params:xml:ns:poc:poc-settings">
<entity id="do39s8zksn2d98x">
<isb-settings>
<incoming-session-barring active="true"/>
</isb-settings>
<am-settings>
<answer-mode>automatic</answer-mode>
</am-settings>
<ipab-settings>
<incoming-personal-alert-barring active="false"/>
</ipab-settings>
<sss-settings>
<simultaneous-sessions-support active="true"/>
</sss-settings>
</entity>
</poc-settings>

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7. Security Considerations

The "poc-settings" event package defined by this document is meant to
be transported with SIP PUBLISH requests. Therefore, the Security
Considerations (Section 14) in RFC 3903 [8] apply to this document.
In particular, the settings contained in the "poc-settings" event
package are applicable to the user that generated the SIP PUBLISH
request. Therefore, servers that receive SIP PUBLISH requests
containing a "poc-settings" event package SHOULD authenticate the
user prior to authorizing the event publication (as required by RFC
3903 [8]).

Authentication and authorization of subscriptions have been discussed
in Section 5.6. Lack of authentication or authorization may provide
poc-settings information to unauthorized parties, who can use that
information for creating attacks. For example, an unauthorized
recipient of a PoC-settings document can learn that the publisher's
terminal is set to answer PoC sessions in automatic answer mode and
then create a malicious session containing inappropriate media that
the UAS will play automatically. Or the attacker can learn that the
terminal is willing to receive simultaneous PoC sessions and then try
to exhaust resources in the SIP UA by creating bogus PoC sessions
that leave hung states in the attacked SIP UA.

Integrity protection and confidentiality of notifications are also
discussed in Section 5.7. If a notifier does not encrypt bodies of
NOTIFY requests, an eavesdropper could learn the status of a SIP user
agent and use it to create malicious PoC sessions. If the notifier
does not integrity protect the bodies of NOTIFY requests, a man-in-
the-middle attacker or malicious SIP proxy could modify the contents
of the poc-settings event package notification. Although this does
not cause harm, it can create annoyances (e.g., media clip due to
lack of buffering) when PoC sessions are delivered to the user.

8. Acknowledgements

The author wants to thank Ilkka Westman, Andrew Allen, Chinmay
Padhye, Gonzalo Camarillo, Paul Kyzivat, Haris Zisimopoulos, Joel M.
Halpern, and Russ Housley for their comments.

9. IANA Considerations

9.1. Registration of the "poc-settings" Event Package

This specification registers an event package, based on the
registration procedures defined in RFC 3265 [5]. The following is
the information required for such a registration:

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RFC 4354 PoC Settings Event Package January 2006

Package Name: poc-settings

Package or Template-Package: This is a package.

Published Document: RFC 4354

Person to Contact: Miguel A. Garcia-Martin,
[email protected]

9.2. Registration of the "application/poc-settings+xml" MIME type

To: [email protected]

Subject: Registration of MIME media type application/
poc-settings+xml

MIME media type name: application

MIME subtype name: poc-settings+xml

Required parameters: (none)

Optional parameters: charset; Indicates the character encoding of
enclosed XML. Default is UTF-8 [7].

Encoding considerations: Uses XML, which can employ 8-bit
characters, depending on the character encoding used. See RFC
3023 [3], Section 3.2.

Security considerations: This content type is designed to carry
information about current PoC user settings, which in some cases
may be considered private information. Appropriate precautions
should be adopted to limit disclosure of this information.

Interoperability considerations: This content type provides a
common format for exchange of PoC settings information.

Published specification: RFC 4354 (this document).

Applications which use this media type: Push-to-talk over Cellular
systems in compliance with the Open Mobile Alliance (OMA) PoC
specifications.

Additional information: The Open Mobile Alliance publishes the
Push-to-talk over Cellular specifications in the OMA web site at
http://www.openmobilealliance.org

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RFC 4354 PoC Settings Event Package January 2006

Person & email address to contact for further information: Miguel
A. Garcia-Martin, [email protected]

Intended usage: Limited use, restricted to PoC terminals and
servers.

Author/Change controller: Open Mobile Alliance
(http://www.openmobilealliance.org), PoC working group.

Other information: This media type is a specialization of
application/xml RFC 3023 [3], and many of the considerations
described there also apply to application/poc-settings+xml.

10. References

10.1. Normative References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

[2] Moats, R., "URN Syntax", RFC 2141, May 1997.

[3] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types",
RFC 3023, January 2001.

[4] 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.

[5] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.

[6] Mankin, A., Bradner, S., Mahy, R., Willis, D., Ott, J., and B.
Rosen, "Change Process for the Session Initiation Protocol
(SIP)", BCP 67, RFC 3427, December 2002.

[7] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
STD 63, RFC 3629, November 2003.

[8] Niemi, A., "Session Initiation Protocol (SIP) Extension for
Event State Publication", RFC 3903, October 2004.

[9] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Message Specification", RFC 3851,
July 2004.

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[10] Paoli, J., Sperberg-McQueen, C., Bray, T., and E. Maler,
"Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
FirstEdition REC-xml-20001006, October 2000.

10.2. Informative References

[11] Camarillo, G. and A. Roach, "Requirements and Framework for
Session Initiation Protocol (SIP) Uniform Resource Identifier
(URI)-List Services", Work in Progress, April 2005.

[12] Rosenberg, J., "A Framework for Conferencing with the Session
Initiation Protocol (SIP)", RFC 4353, January 2006.

Author's Address

Miguel A. Garcia-Martin
Nokia
P.O.Box 407
NOKIA GROUP, FIN 00045
Finland

EMail: [email protected]

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RFC 4354 PoC Settings Event Package January 2006

Full Copyright Statement

Copyright (C) The Internet Society (2006).

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
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