A Session Initiation Protocol (SIP) Event Package for Registrations
RFC 3680

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:allusers@example.com 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:user@example.com" id="as9"
 state="active">
 <contact id="76" state="active" event="registered"
 duration-registered="7322"
 q="0.8">
 <uri>sip:user@pc887.example.com</uri>
 </contact>
 <contact id="77" state="terminated" event="expired"
 duration-registered="3600"
 q="0.5">
 <uri>sip:user@university.edu</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">
 <!-- 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/2001/03/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:joe@example.com SIP/2.0
 Via: SIP/2.0/UDP app.example.com;branch=z9hG4bKnashds7
 From: sip:app.example.com;tag=123aa9
 To: sip:joe@example.com
 Call-ID: 9987@app.example.com
 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:joe@example.com;tag=xyzygg
 Call-ID: 9987@app.example.com
 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:joe@example.com;tag=xyzygg
 To: sip:app.example.com;tag=123aa9
 Call-ID: 9987@app.example.com
 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:joe@example.com" 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:joe@example.com;tag=99a8s
 To: sip:joe@example.com
 Call-ID: 88askjda9@pc34.example.com
 CSeq: 9976 REGISTER
 Contact: sip:joe@pc34.example.com
 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:joe@example.com;tag=xyzygg
 To: sip:app.example.com;tag=123aa9
 Call-ID: 9987@app.example.com
 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:joe@example.com" id="a7" state="active">
 <contact id="76" state="active" event="registered"
 duration-registered="0">
 <uri>sip:joe@pc34.example.com</uri>
 </contact>
 </registration>
 </reginfo>
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 The application can then send its instant message to the device (9):
 MESSAGE sip:joe@pc34.example.com SIP/2.0
 Via: SIP/2.0/UDP app.example.com;branch=z9hG4bKnashds8
 From: sip:app.example.com;tag=123aa10
 To: sip:joe@example.com
 Call-ID: 9988@app.example.com
 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, <jdrosen@jdrosen.net>
 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, <jdrosen@jdrosen.net>
 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,
 <simple@ietf.org>, Jonathan Rosenberg
 <jdrosen@jdrosen.net>.
 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: Georg.Mayer@icn.siemens.de
 Mark Beckmann
 Siemens AG
 P.O. Box 100702
 Salzgitter 38207
 Germany
 EMail: Mark.Beckmann@siemens.com
 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: rohan@cisco.com
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: jdrosen@dynamicsoft.com
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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 ietf-ipr@ietf.org.
Acknowledgement
 Funding for the RFC Editor function is currently provided by the
 Internet Society.
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