Network Working Group J. Rosenberg

Network Working Group J. Rosenberg
Request for Comments: 3680 dynamicsoft
Category: Standards Track March 2004

A Session Initiation Protocol (SIP) Event Package for Registrations

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.

Copyright Notice

Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

This document defines a Session Initiation Protocol (SIP) event
package for registrations. Through its REGISTER method, SIP allows a
user agent to create, modify, and delete registrations.
Registrations can also be altered by administrators in order to
enforce policy. As a result, these registrations represent a piece
of state in the network that can change dynamically. There are many
cases where a user agent would like to be notified of changes in this
state. This event package defines a mechanism by which those user
agents can request and obtain such notifications.

Table of Contents

1. Introduction ................................................. 2
2. Terminology .................................................. 3
3. Usage Scenarios .............................................. 3
3.1. Forcing Re-Authentication .............................. 3
3.2. Composing Presence ..................................... 3
3.3. Welcome Notices ........................................ 4
4. Package Definition ........................................... 4
4.1. Event Package Name ..................................... 4
4.2. Event Package Parameters ............................... 5
4.3. SUBSCRIBE Bodies ....................................... 5
4.4. Subscription Duration .................................. 5
4.5. NOTIFY Bodies .......................................... 6
4.6. Notifier Processing of SUBSCRIBE Requests .............. 6
4.7. Notifier Generation of NOTIFY Requests ................. 7
4.7.1. The Registration State Machine ................. 7

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4.7.2. Applying the state machine ..................... 9
4.8. Subscriber Processing of NOTIFY Requests ............... 9
4.9. Handling of Forked Requests ............................ 9
4.10. Rate of Notifications .................................. 10
4.11. State Agents ........................................... 10
5. Registration Information ..................................... 10
5.1. Structure of Registration Information .................. 10
5.2. Computing Registrations from the Document .............. 14
5.3. Example ................................................ 15
5.4. XML Schema ............................................. 16
6. Example Call Flow ............................................ 18
7. Security Considerations ...................................... 21
8. IANA Considerations .......................................... 21
8.1. SIP Event Package Registration ......................... 21
8.2. application/reginfo+xml MIME Registration .............. 22
8.3. URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:reginfo ......................... 23
9. References ................................................... 23
9.1. Normative References ................................... 23
9.2. Informative References ................................. 24
10. Contributors ................................................. 25
11. Acknowledgements ............................................. 25
12. Author's Address ............................................. 25
13. Full Copyright Statement ..................................... 26

1. Introduction

The Session Initiation Protocol (SIP) [1] provides all of the
functions needed for the establishment and maintenance of
communications sessions between users. One of the functions it
provides is a registration operation. A registration is a binding
between a SIP URI, called an address-of-record, and one or more
contact URIs. These contact URIs represent additional resources that
can be contacted in order to reach the user identified by the
address-of-record. When a proxy receives a request within its domain
of administration, it uses the Request-URI as an address-of-record,
and uses the contacts bound to the address-of-record to forward (or
redirect) the request.

The SIP REGISTER method provides a way for a user agent to manipulate
registrations. Contacts can be added or removed, and the current set
of contacts can be queried. Registrations can also change as a
result of administrator policy. For example, if a user is suspected
of fraud, their registration can be deleted so that they cannot
receive any requests. Registrations also expire after some time if
not refreshed.

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Registrations represent a dynamic piece of state maintained by the
network. There are many cases in which user agents would like to
know about changes to the state of registrations. The SIP Events
Framework [2] defines a generic framework for subscription to, and
notification of, events related to SIP systems. The framework
defines the methods SUBSCRIBE and NOTIFY, and introduces the notion
of a package. A package is a concrete application of the event
framework to a particular class of events. Packages have been
defined for user presence [9], for example. This specification
defines a package for registration state.

2. Terminology

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

3. Usage Scenarios

There are many applications of this event package. A few are
documented here for illustrative purposes.

3.1. Forcing Re-Authentication

It is anticipated that many SIP devices will be wireless devices that
will be always-on, and therefore, continually registered to the
network. Unfortunately, history has shown that these devices can be
compromised. To deal with this, an administrator will want to
terminate or shorten a registration, and ask the device to
re-register so it can be re-authenticated. To do this, the device
subscribes to the registration event package for the
address-of-record that it is registering contacts against. When the
administrator shortens registration (for example, when fraud is
suspected) the registration server sends a notification to the
device. It can then re-register and re-authenticate itself. If it
cannot re-authenticate, the expiration will terminate shortly
thereafter.

3.2. Composing Presence

An important concept to understand is the relationship between this
event package and the event package for user presence [9]. User
presence represents the willingness and ability of a user to
communicate with other users on the network. It is composed of a set
of contact addresses that represent the various means for contacting
the user. Those contact addresses might represent the contact
address for voice, for example. Typically, the contact address

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listed for voice will be an address-of-record. The status of that
contact (whether its open or closed) may depend on any number of
factors, including the state of any registrations against that
address-of-record. As a result, registration state can be viewed as
an input to the process which determines the presence state of a
user. Effectively, registration state is "raw" data, which is
combined with other information about a user to generate a document
that describes the user's presence.

In fact, this event package allows for a presence server to be
separated from a SIP registration server, yet still use registration
information to construct a presence document. When a presence server
receives a presence subscription for some user, the presence server
itself would generate a subscription to the registration server for
the registration event package. As a result, the presence server
would learn about the registration state for that user, and it could
use that information to generate presence documents.

3.3. Welcome Notices

A common service in current mobile networks are "welcome notices".
When the user turns on their phone in a foreign country, they receive
a message that welcomes them to the country, and provides information
on transportation services, for example.

In order to implement this service in a SIP system, an application
server can subscribe to the registration state of the user. When the
user turns on their phone, the phone will generate a registration.
This will result in a notification being sent to the application that
the user has registered. The application can then send a SIP MESSAGE
request [10] to the device, welcoming the user and providing any
necessary information.

4. Package Definition

This section fills in the details needed to specify an event package
as defined in Section 4.4 of [2].

4.1. Event Package Name

The SIP Events specification requires package definitions to specify
the name of their package or template-package.

The name of this package is "reg". As specified in [2], this value
appears in the Event header present in SUBSCRIBE and NOTIFY requests.

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Example:

Event: reg

4.2. Event Package Parameters

The SIP Events specification requires package and template-package
definitions to specify any package specific parameters of the Event
header that are used by it.

No package specific Event header parameters are defined for this
event package.

4.3. SUBSCRIBE Bodies

The SIP Events specification requires package or template-package
definitions to define the usage, if any, of bodies in SUBSCRIBE
requests.

A SUBSCRIBE for registration events MAY contain a body. This body
would serve the purpose of filtering the subscription. The
definition of such a body is outside the scope of this specification.

A SUBSCRIBE for the registration package MAY be sent without a body.
This implies that the default registration filtering policy has been
requested. The default policy is:

o Notifications are generated every time there is any change in
the state of any of the registered contacts for the resource
being subscribed to. Those notifications only contain
information on the contacts whose state has changed.

o Notifications triggered from a SUBSCRIBE contain full state
(the list of all contacts bound to the address-of-record).

Of course, the server can apply any policy it likes to the
subscription.

4.4. Subscription Duration

The SIP Events specification requires package definitions to define a
default value for subscription durations, and to discuss reasonable
choices for durations when they are explicitly specified.

Registration state changes as contacts are created through REGISTER
requests, and then time out due to lack of refresh. Their rate of
change is therefore related to the typical registration expiration.
Since the default expiration for registrations is 3600 seconds, the

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default duration of subscriptions to registration state is slightly
longer, 3761 seconds. This helps avoid any potential problems with
coupling of subscription and registration refreshes. Of course,
clients MAY include an Expires header in the SUBSCRIBE request asking
for a different duration.

4.5. NOTIFY Bodies

The SIP Events specification requires package definitions to describe
the allowed set of body types in NOTIFY requests, and to specify the
default value to be used when there is no Accept header in the
SUBSCRIBE request.

The body of a notification of a change in registration state contains
a registration information document. This document describes some or
all of the contacts associated with a particular address-of-record.
All subscribers and notifiers MUST support the
"application/reginfo+xml" format described in Section 5. The
subscribe request MAY contain an Accept header field. If no such
header field is present, it has a default value of
"application/reginfo+xml". If the header field is present, it MUST
include "application/reginfo+xml", and MAY include any other types
capable of representing registration information.

Of course, the notifications generated by the server MUST be in one
of the formats specified in the Accept header field in the SUBSCRIBE
request.

4.6. Notifier Processing of SUBSCRIBE Requests

The SIP Events framework specifies that packages should define any
package-specific processing of SUBSCRIBE requests at a notifier,
specifically with regards to authentication and authorization.

Registration state can be sensitive information. Therefore, all
subscriptions to it SHOULD be authenticated and authorized before
approval. Authentication MAY be performed using any of the
techniques available through SIP, including digest, S/MIME, TLS or
other transport specific mechanisms [1]. Authorization policy is at
the discretion of the administrator, as always. However, a few
recommendations can be made.

It is RECOMMENDED that a user be allowed to subscribe to their own
registration state. Such subscriptions are useful when there are
many devices that represent a user, each of which needs to learn the
registration state of the other devices. We also anticipate that
applications and automata will frequently be subscribers to the

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registration state. In those cases, authorization policy will
typically be provided ahead of time.

4.7. Notifier Generation of NOTIFY Requests

The SIP Event framework requests that packages specify the conditions
under which notifications are sent for that package, and how such
notifications are constructed.

To determine when a notifier should send notifications of changes in
registration state, we define a finite state machine (FSM) that
represents the state of a contact for a particular address-of-record.
Transitions in this state machine MAY result in the generation of
notifications. These notifications will carry information on the new
state and the event which triggered the state change. It is
important to note that this FSM is just a model of the registration
state machinery maintained by a server. An implementation would map
its own state machines to this one in an implementation-specific
manner.

4.7.1. The Registration State Machine

The underlying state machine for a registration is shown in Figure 1.
The machine is very simple. An instance of this machine is
associated with each address-of-record. When there are no contacts
registered to the address-of-record, the state machine is in the init
state. It is important to note that this state machine exists, and
is well-defined, for each address-of-record in the domain, even if
there are no contacts registered to it. This allows a user agent to
subscribe to an address-of-record, and learn that there are no
contacts registered to it. When the first contact is registered to
that address-of-record, the state machine moves from init to active.

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+------------+
| |
| Init |
| |
+------------+
|
V
+------------+
| |
| Active |
| |
+------------+
|
V
+------------+
| |
| Terminated |
| |
+------------+

Figure 1: Registration State Machine

As long as there is at least one contact bound to the address-of-
record, the state machine remains in the active state. When the last
contact expires or is removed, the registration transitions to
terminated. From there, it immediately transitions back to the init
state. This transition is invisible, in that it MUST NOT ever be
reported to a subscriber in a NOTIFY request.

This allows for an implementation optimization whereby the
registrar can destroy the objects associated with the registration
state machine once it enters the terminated state and a NOTIFY has
been sent. Instead, the registrar can assume that, if the objects
for that state machine no longer exist, the state machine is in
the init state.

In addition to this state machine, each registration is associated
with a set of contacts, each of which is modeled with its own state
machine. Unlike the FSM for the address-of-record, which exists even
when no contacts are registered, the per-contact FSM is instantiated
when the contact is registered, and deleted when it is removed. The
diagram for the per-contact state machine is shown in Figure 2. This
FSM is identical to the registration state machine in terms of its
states, but has many more transition events.

When a new contact is added, the FSM for it is instantiated, and it
moves into the active state. Because of that, the init state here is
transient. There are two ways in which it can become active. One is

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through an actual SIP REGISTER request (corresponding to the
registered event), and the other is when the contact is created
administratively, or through some non-SIP means (the created event).

+------+
| | refreshed
| | shortened
V |
+------------+ +------------+ +------------+
| | | | | |
| Init |----------->| Active |----------->| Terminated |
| | | | | |
+------------+ registered +------------+ expired +------------+
created deactivated
probation
unregistered
rejected

Figure 2: Contact State Machine

The FSM remains in the active state so long as the contact is bound
to the address-of-record. When a contact is refreshed through a
REGISTER request, the FSM stays in the same state, but a refreshed
event is generated. Likewise, when an administrator modifies the
expiration time of a binding (without deleting the binding) to
trigger the contact to re-register and possibly re-authenticate, the
FSM stays in the active state, but a shortened event is generated.

When the contact is no longer bound to the address-of-record, the FSM
moves to the terminated state, and once a NOTIFY is sent, the state
machine is destroyed. As a result, the terminated state is
effectively transient. There are several reasons this can happen.
The first is an expiration, which occurs when the contact was not
refreshed by a REGISTER request. The second reason is deactivated.
This occurs when the administrator has removed the contact as a valid
binding, but still wishes the client to attempt to re-register the
contact. In contrast, the rejected event occurs when an active
contact is removed by the administrator, but
re-registrations will not help to re-establish it. This might occur
if a user does not pay their bills, for example. The probation event
occurs when an active contact is removed by the administrator, and
the administrator wants the client to re-register, but to do so at a
later time. The unregistered event occurs when a REGISTER request
sets the expiration time of that contact to zero.

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4.7.2. Applying the state machine

The server MAY generate a notification to subscribers when any event
occurs in either the address-of-record or per-contact state machines,
except for the transition from terminated to init in the address-of-
record state machine. As noted above, a notification MUST NOT be sent
in this case. For other transitions, whether the server sends a
notification or not is policy dependent. However, several guidelines
are defined.

As a general rule, when a subscriber is authorized to receive
notifications about a set of registrations, it is RECOMMENDED that
notifications contain information about those contacts which have
changed state (and thus triggered a notification), instead of
delivering the current state of every contact in all registrations.
However, notifications triggered as a result of a fetch operation (a
SUBSCRIBE with Expires of 0) SHOULD result in the full state of all
contacts for all registrations to be present in the NOTIFY.

4.8. Subscriber Processing of NOTIFY Requests

The SIP Events framework expects packages to specify how a subscriber
processes NOTIFY requests in any package specific ways, and in
particular, how it uses the NOTIFY requests to construct a coherent
view of the state of the subscribed resource. Typically, the NOTIFY
will only contain information for contacts whose state has changed.
To construct a coherent view of the total state of all registrations,
the subscriber will need to combine NOTIFYs received over time. The
details of this process depend on the document format used to convey
registration state. Section 5 outlines the process for the
application/reginfo+xml format.

4.9. Handling of Forked Requests

The SIP Events framework mandates that packages indicate whether or
not forked SUBSCRIBE requests can install multiple subscriptions.

Registration state is normally stored in some repository (whether it
be co-located with a proxy/registrar or in a separate database). As
such, there is usually a single place where the contact information
for a particular address-of-record is resident. This implies that a
subscription for this information is readily handled by a single
element with access to this repository. There is, therefore, no
compelling need for a subscription to registration information to
fork. As a result, a subscriber MUST NOT create multiple dialogs as
a result of a single subscription request. The required processing
to guarantee that only a single dialog is established is described in
Section 4.4.9 of the SIP Events framework [2].

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4.10. Rate of Notifications

The SIP Events framework mandates that packages define a maximum rate
of notifications for their package.

For reasons of congestion control, it is important that the rate of
notifications not become excessive. As a result, it is RECOMMENDED
that the server not generate notifications for a single subscriber at
a rate faster than once every 5 seconds.

4.11. State Agents

The SIP Events framework asks packages to consider the role of state
agents in their design.

State agents have no role in the handling of this package.

5. Registration Information

5.1. Structure of Registration Information

Registration information is an XML document [4] that MUST be
well-formed and SHOULD be valid. Registration information documents
MUST be based on XML 1.0 and MUST be encoded using UTF-8. This
specification makes use of XML namespaces for identifying
registration information documents and document fragments. The
namespace URI for elements defined by this specification is a URN
[5], using the namespace identifier 'ietf' defined by [6] and
extended by [7]. This URN is:

urn:ietf:params:xml:ns:reginfo

A registration information document begins with the root element tag
"reginfo". It consists of any number of "registration" sub-elements,
each of which contains the registration state for a particular
address-of-record. The registration information for a particular
address-of-record MUST be contained within a single "registration"
element; it cannot be spread across multiple "registration" elements
within a document. Other elements from different namespaces MAY be
present for the purposes of extensibility; elements or attributes
from unknown namespaces MUST be ignored. There are two attributes
associated with the "reginfo" element, both of which MUST be present:

version: This attribute allows the recipient of registration
information documents to properly order them. Versions
start at 0, and increment by one for each new document
sent to a subscriber. Versions are scoped within a

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subscription. Versions MUST be representable using a
32 bit integer.

state: This attribute indicates whether the document contains
the full registration state, or whether it contains
only information on those registrations which have
changed since the previous document (partial).

Note that the document format explicitly allows for conveying
information on multiple addresses-of-record. This enables
subscriptions to groups of registrations, where such a group is
identified by some kind of URI. For example, a domain might define
sip:[email protected] as a subscribable resource that generates
notifications when the state of any address-of-record in the domain
changes.

The "registration" element has a list of any number of "contact"
sub-elements, each of which contains information on a single contact.
Other elements from different namespaces MAY be present for the
purposes of extensibility; elements or attributes from unknown
namespaces MUST be ignored. There are three attributes associated
with the "registration" element, all of which MUST be present:

aor: The aor attribute contains a URI which is the address-of-
record this registration refers to.

id: The id attribute identifies this registration. It MUST be
unique amongst all other id attributes present in other
registration elements conveyed to the subscriber within the
scope of their subscription. In particular, if two URI
identifying an address-of-record differ after their
canonicalization according to the procedures in step 5 of
Section 10.3 of RFC 3261 [1], the id attributes in the
"registration" elements for those addresses-of-record MUST
differ. Furthermore, the id attribute for a "registration"
element for a particular address-of-record MUST be the same
across all notifications sent within the subscription.

state: The state attribute indicates the state of the
registration. The valid values are "init", "active" and
"terminated".

The "contact" element contains a "uri" element, an optional
"display-name" element, and an optional "unknown-param" element.
Other elements from different namespaces MAY be present for the
purposes of extensibility; elements or attributes from unknown
namespaces MUST be ignored. There are several attributes associated
with the "contact" element which MUST be present:

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id: The id attribute identifies this contact. It MUST be
unique amongst all other id attributes present in other
contact elements conveyed to the subscriber within the
scope of their subscription. In particular, if the URI for
two contacts differ (based on the URI comparison rules in
RFC 3261 [1]), the id attributes for those contacts MUST
differ. However, unlike the id attribute for an address-
of-record, if the URI for two contacts are the same, their
id attributes SHOULD be the same across notifications.
This requirement is at SHOULD strength, and not MUST
strength, since it is difficult to compute such an id as a
function of the URI without retaining additional state. No
hash function applied to the URI can, in fact, meet a MUST
requirement. This is because equality of the SIP URI is
not transitive. However, a hash function which includes
unknown URI parameters (that is, any not defined in RFC
3261), will always result in a value that is the different
if two URI are different, and usually the same if the URI
are equal.

state: The state attribute indicates the state of the contact.
The valid values are "active" and "terminated".

event: The event attribute indicates the event which caused the
contact state machine to go into its current state. Valid
values are registered, created, refreshed, shortened,
expired, deactivated, probation, unregistered and rejected.

If the event attribute has a value of shortened, the "expires"
attribute MUST be present. It contains an unsigned long integer
which indicates the number of seconds remaining until the binding is
due to expire. This attribute MAY be included with any event
attribute value for which the state of the contact is active.

If the event attribute has a value of probation, the "retry-after"
attribute MUST be present. It contains an unsigned long integer
which indicates the amount of seconds after which the owner of the
contact is expected to retry its registration.

The optional "duration-registered" attribute conveys the amount of
time that the contact has been bound to the address-of-record, in
seconds. The optional "q" attribute conveys the relative priority of
this contact compared to other registered contacts. The optional
"callid" attribute contains the current Call-ID carried in the
REGISTER that was last used to update this contact, and the optional
"cseq" attribute contains the last CSeq value present in a REGISTER
request that updated this contact value.

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The "uri" element contains the URI associated with that contact. The
"display-name" element contains the display name for the contact.
The "display-name" element MAY contain the xml:lang attribute to
indicate the language of the display name.

The "unknown-param" element is used to convey contact header field
parameters that are not specified in RFC 3261. One example are the
user agent capability parameters specified in [11]. Each "unknown-
param" element describes a single contact header field parameter.
The name of the parameter is contained in the mandatory name
attribute of the "unknown-param" element, and the value of the
parameter is the content of the "unknown-param" element. For contact
header field parameters that have no value, the content of the
"unknown-param" element is empty.

5.2. Computing Registrations from the Document

Typically, the NOTIFY for registration information will only contain
information about those contacts whose state has changed. To
construct a coherent view of the total state of all registrations, a
subscriber will need to combine NOTIFYs received over time. The
subscriber maintains a table for each registration it receives
information for. Each registration is uniquely identified by the
"id" attribute in the "registration" element. Each table contains a
row for each contact in that registration. Each row is indexed by
the unique ID for that contact. It is conveyed in the "id" attribute
of the "contact" element. The contents of each row contain the state
of that contact as conveyed in the "contact" element. The tables are
also associated with a version number. The version number MUST be
initialized with the value of the "version" attribute from the
"reginfo" element in the first document received. Each time a new
document is received, the value of the local version number, and the
"version" attribute in the new document, are compared. If the value
in the new document is one higher than the local version number, the
local version number is increased by one, and the document is
processed. If the value in the document is more than one higher than
the local version number, the local version number is set to the
value in the new document, the document is processed, and the
subscriber SHOULD generate a refresh request to trigger a full state
notification. If the value in the document is less than the local
version, the document is discarded without processing.

The processing of the document depends on whether it contains full or
partial state. If it contains full state, indicated by the value of
the "state" attribute in the "reginfo" element, the contents of all
tables associated with this subscription are flushed. They are
re-populated from the document. A new table is created for each
"registration" element, and a new row in each table is created for

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each "contact" element. If the reginfo contains partial state, as
indicated by the value of the "state" attribute in the "reginfo"
element, the document is used to update the existing tables. For
each "registration" element, the subscriber checks to see if a table
exists for that registration. This check is done by comparing the
value in the "id" attribute of the "registration" element with the ID
associated with the table. If a table doesn't exist for that
registration, one is created. For each "contact" element in the
registration, the subscriber checks to see whether a row exists for
that contact. This check is done by comparing the ID in the "id"
attribute of the "contact" element with the ID associated with the
row. If the contact doesn't exist in the table, a row is added, and
its state is set to the information from that "contact" element. If
the contact does exist, its state is updated to be the information
from that "contact" element. If a row is updated or created, such
that its state is now terminated, that entry MAY be removed from the
table at any time.

5.3. Example

The following is an example registration information document:

<?xml version="1.0"?>
<reginfo xmlns="urn:ietf:params:xml:ns:reginfo"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
version="0" state="full">
<registration aor="sip:[email protected]" id="as9"
state="active">
<contact id="76" state="active" event="registered"
duration-registered="7322"
q="0.8">
<uri>sip:[email protected]</uri>
</contact>
<contact id="77" state="terminated" event="expired"
duration-registered="3600"
q="0.5">
<uri>sip:[email protected]</uri>
</contact>
</registration>
</reginfo>

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5.4. XML Schema

The following is the schema definition of the reginfo format:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:reginfo"
xmlns:tns="urn:ietf:params:xml:ns:reginfo"
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/2001/03/xml.xsd"/>
<xs:element name="reginfo">
<xs:complexType>
<xs:sequence>
<xs:element ref="tns:registration" minOccurs="0"
maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="version" type="xs:nonNegativeInteger"
use="required"/>
<xs:attribute name="state" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="full"/>
<xs:enumeration value="partial"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name="registration">
<xs:complexType>
<xs:sequence>
<xs:element ref="tns:contact" minOccurs="0" maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="aor" type="xs:anyURI" use="required"/>
<xs:attribute name="id" type="xs:string" use="required"/>
<xs:attribute name="state" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="init"/>
<xs:enumeration value="active"/>
<xs:enumeration value="terminated"/>
</xs:restriction>

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</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name="contact">
<xs:complexType>
<xs:sequence>
<xs:element name="uri" type="xs:anyURI"/>
<xs:element name="display-name" minOccurs="0">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute ref="xml:lang" use="optional"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name="unknown-param" minOccurs="0"
maxOccurs="unbounded">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="name" type="xs:string" use="required"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="state" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="active"/>
<xs:enumeration value="terminated"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="event" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="registered"/>
<xs:enumeration value="created"/>
<xs:enumeration value="refreshed"/>
<xs:enumeration value="shortened"/>
<xs:enumeration value="expired"/>
<xs:enumeration value="deactivated"/>
<xs:enumeration value="probation"/>

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<xs:enumeration value="unregistered"/>
<xs:enumeration value="rejected"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="duration-registered" type="xs:unsignedLong"/>
<xs:attribute name="expires" type="xs:unsignedLong"/>
<xs:attribute name="retry-after" type="xs:unsignedLong"/>
<xs:attribute name="id" type="xs:string" use="required"/>
<xs:attribute name="q" type="xs:string"/>
<xs:attribute name="callid" type="xs:string"/>
<xs:attribute name="cseq" type="xs:unsignedLong"/>
</xs:complexType>
</xs:element>
</xs:schema>

6. Example Call Flow

User Registrar Application
| |(1) SUBSCRIBE |
| |Event:reg |
| |<------------------|
| |(2) 200 OK |
| |------------------>|
| |(3) NOTIFY |
| |------------------>|
| |(4) 200 OK |
| |<------------------|
|(5) REGISTER | |
|------------------>| |
|(6) 200 OK | |
|<------------------| |
| |(7) NOTIFY |
| |------------------>|
| |(8) 200 OK |
| |<------------------|
|(9) MESSAGE | |
|<--------------------------------------|

Figure 3: Example Call Flow

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This section provides an example call flow, shown in Figure 3. It
shows an implementation of the welcome notice application described
in Section 3.3. First, the application SUBSCRIBEs to the
registration event package for the desired user (1):

SUBSCRIBE sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP app.example.com;branch=z9hG4bKnashds7
From: sip:app.example.com;tag=123aa9
To: sip:[email protected]
Call-ID: [email protected]
CSeq: 9887 SUBSCRIBE
Contact: sip:app.example.com
Event: reg
Max-Forwards: 70
Accept: application/reginfo+xml

The registrar (which is acting as the notifier for the registration
event package) generates a 200 OK to the SUBSCRIBE:

SIP/2.0 200 OK
Via: SIP/2.0/UDP app.example.com;branch=z9hG4bKnashds7
;received=192.0.2.1
From: sip:app.example.com;tag=123aa9
To: sip:[email protected];tag=xyzygg
Call-ID: [email protected]
CSeq: 9987 SUBSCRIBE
Contact: sip:server19.example.com
Expires: 3600

The registrar then generates a notification (3) with the current
state. Since there is no active registration, the state of the
registration is "init":

NOTIFY sip:app.example.com SIP/2.0
Via: SIP/2.0/UDP server19.example.com;branch=z9hG4bKnasaii
From: sip:[email protected];tag=xyzygg
To: sip:app.example.com;tag=123aa9
Call-ID: [email protected]
CSeq: 1288 NOTIFY
Contact: sip:server19.example.com
Event: reg
Max-Forwards: 70
Content-Type: application/reginfo+xml
Content-Length: ...

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<?xml version="1.0"?>
<reginfo xmlns="urn:ietf:params:xml:ns:reginfo"
version="0" state="full">
<registration aor="sip:[email protected]" id="a7" state="init" />
</reginfo>

Later on, the user registers (5):

REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP pc34.example.com;branch=z9hG4bKnaaff
From: sip:[email protected];tag=99a8s
To: sip:[email protected]
Call-ID: [email protected]
CSeq: 9976 REGISTER
Contact: sip:[email protected]

This results in a NOTIFY being generated to the application (7):

NOTIFY sip:app.example.com SIP/2.0
Via: SIP/2.0/UDP server19.example.com;branch=z9hG4bKnasaij
From: sip:[email protected];tag=xyzygg
To: sip:app.example.com;tag=123aa9
Call-ID: [email protected]
CSeq: 1289 NOTIFY
Contact: sip:server19.example.com
Event: reg
Max-Forwards: 70
Content-Type: application/reginfo+xml
Content-Length: ...

<?xml version="1.0"?>
<reginfo xmlns="urn:ietf:params:xml:ns:reginfo"
version="1" state="partial">
<registration aor="sip:[email protected]" id="a7" state="active">
<contact id="76" state="active" event="registered"
duration-registered="0">
<uri>sip:[email protected]</uri>
</contact>
</registration>
</reginfo>

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The application can then send its instant message to the device (9):

MESSAGE sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP app.example.com;branch=z9hG4bKnashds8
From: sip:app.example.com;tag=123aa10
To: sip:[email protected]
Call-ID: [email protected]
CSeq: 82779 MESSAGE
Max-Forwards: 70
Content-Type: text/plain
Content-Length: ...

Welcome to the example.com service!

7. Security Considerations

Security considerations for SIP event packages are discussed in RFC
3265 [2], and those considerations apply here.

Registration information is sensitive, potentially private,
information. Subscriptions to this event package SHOULD be
authenticated and authorized according to local policy. Some policy
guidelines are suggested in Section 4.6. In addition, notifications
SHOULD be sent in such a way to ensure confidentiality, message
integrity and verification of subscriber identity, such as sending
subscriptions and notifications using a SIPS URL or protecting the
notification bodies with S/MIME.

8. IANA Considerations

This document registers a new SIP Event Package, a new MIME type
(application/reginfo+xml), and a new XML namespace.

8.1. SIP Event Package Registration

Package name: reg

Type: package

Contact: Jonathan Rosenberg, <[email protected]>

Published Specification: RFC 3680.

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8.2. application/reginfo+xml MIME Registration

MIME media type name: application

MIME subtype name: reginfo+xml

Mandatory parameters: none

Optional parameters: Same as charset parameter application/xml
as specified in RFC 3023 [8].

Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023 [8].

Security considerations: See Section 10 of RFC 3023 [8] and
Section 7 of this specification.

Interoperability considerations: none.

Published specification: This document.

Applications which use this media type: This document type is
being used in notifications to alert SIP user agents that
their registrations have expired and must be redone.

Additional Information:

Magic Number: None

File Extension: .rif or .xml

Macintosh file type code: "TEXT"

Personal and email address for further information: Jonathan
Rosenberg, <[email protected]>

Intended usage: COMMON

Author/Change controller: The IETF.

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8.3. URN Sub-Namespace Registration for urn:ietf:params:xml:ns:reginfo

This section registers a new XML namespace, as per the guidelines in
[7].

URI: The URI for this namespace is
urn:ietf:params:xml:ns:reginfo.

Registrant Contact: IETF, SIMPLE working group,
<[email protected]>, Jonathan Rosenberg
<[email protected]>.

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>Registration Information Namespace</title>
</head>
<body>
<h1>Namespace for Registration Information</h1>
<h2>urn:ietf:params:xml:ns:reginfo</h2>
<p>See <a href="ftp://ftp.rfc-editor.org/in-notes/rfc3680.txt">
RFC3680</a>.</p>
</body>
</html>
END

9. References

9.1. Normative References

[1] 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.

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

[3] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", BCP 14, RFC 2119, March 1997.

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[4] W. W. W. C. (W3C), "Extensible markup language (xml) 1.0." The
XML 1.0 spec can be found at
http://www.w3.org/TR/1998/REC-xml-19980210.

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

[6] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
August 1999.

[7] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January
2004.

[8] Murata, M., St. Laurent, S. and D. Kohn, "XML media types", RFC
3023, January 2001.

9.2. Informative References

[9] Rosenberg, J., "Session initiation protocol (SIP) extensions for
presence", Work In Progress.

[10] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C. and D.
Gurle, "Session Initiation Protocol (SIP) Extension for Instant
Messaging", RFC 3428, December 2002.

[11] Schulzrinne, H. and J. Rosenberg, "Session initiation protocol
(SIP) caller preferences and callee capabilities", Work In
Progress.

[12] Mayer, G. and M. Beckmann, "Registration event package", Work In
Progress.

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10. Contributors

This document is based heavily on the registration event package
originally proposed by Beckmann and Mayer in [12]. They can be
contacted at:

Georg Mayer
Siemens AG
Hoffmannstr. 51
Munich 81359
Germany

EMail: [email protected]

Mark Beckmann
Siemens AG
P.O. Box 100702
Salzgitter 38207
Germany

EMail: [email protected]

Rohan Mahy provided editorial work in order to progress this
specification. His contact address is:

Rohan Mahy
Cisco Systems
170 West Tasman Dr, MS: SJC-21/3/3

Phone: +1 408 526 8570
EMail: [email protected]

11. Acknowledgements

We would like to thank Dean Willis for his support.

12. Author's Address

Jonathan Rosenberg
dynamicsoft
600 Lanidex Plaza
Parsippany, NJ 07054

EMail: [email protected]

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13. Full Copyright Statement

Copyright (C) The Internet Society (2004). 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 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 [email protected].

Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

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