Request for Comments: 2446 Microsoft
Category: Standards Track S. Mansour
Netscape
F. Dawson
Lotus
R. Hopson
ON Technologies
November 1998
iCalendar Transport-Independent Interoperability Protocol
(iTIP)
Scheduling Events, BusyTime, To-dos and Journal Entries
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 (1998). All Rights Reserved.
Abstract
This document specifies how calendaring systems use iCalendar objects
to interoperate with other calendar systems. It does so in a general
way so as to allow multiple methods of communication between systems.
Subsequent documents specify interoperable methods of communications
between systems that use this protocol.
The document outlines a model for calendar exchange that defines both
static and dynamic event, to-do, journal and free/busy objects.
Static objects are used to transmit information from one entity to
another without the expectation of continuity or referential
integrity with the original item. Dynamic objects are a superset of
static objects and will gracefully degrade to their static
counterparts for clients that only support static objects.
This document specifies an Internet protocol based on the iCalendar
object specification that provides scheduling interoperability
between different calendar systems. The Internet protocol is called
the "iCalendar Transport-Independent Interoperability Protocol
(iTIP)".
iTIP complements the iCalendar object specification by adding
semantics for group scheduling methods commonly available in current
calendar systems. These scheduling methods permit two or more
calendar systems to perform transactions such as publish, schedule,
reschedule, respond to scheduling requests, negotiation of changes or
cancel iCalendar-based calendar components.
iTIP is defined independent of the particular transport used to
transmit the scheduling information. Companion memos to iTIP provide
bindings of the interoperability protocol to a number of Internet
protocols.
Table of Contents
1 INTRODUCTION...................................................5
1.1 FORMATTING CONVENTIONS .....................................5
1.2 RELATED DOCUMENTS ..........................................6
1.3 ITIP ROLES AND TRANSACTIONS ................................6
2 INTEROPERABILITY MODELS........................................8
2.1 APPLICATION PROTOCOL .......................................9
2.1.1 Calendar Entry State ...................................9
2.1.2 Delegation .............................................9
2.1.3 Acting on Behalf of other Calendar Users ..............10
2.1.4 Component Revisions ...................................10
2.1.5 Message Sequencing ....................................11
3 APPLICATION PROTOCOL ELEMENTS.................................12
3.1 COMMON COMPONENT RESTRICTION TABLES .......................13
3.2 METHODS FOR VEVENT CALENDAR COMPONENTS ....................14
3.2.1 PUBLISH ...............................................15
3.2.2 REQUEST ...............................................17
3.2.2.1 Rescheduling an Event..............................19
3.2.2.2 Updating or Reconfirmation of an Event.............19
3.2.2.3 Delegating an Event to another CU..................19
3.2.2.4 Changing the Organizer.............................20
3.2.2.5 Sending on Behalf of the Organizer.................20
3.2.2.6 Forwarding to An Uninvited CU......................20
3.2.2.7 Updating Attendee Status...........................21
3.2.3 REPLY .................................................21
3.2.4 ADD ...................................................23
3.2.5 CANCEL ................................................25
3.2.6 REFRESH ...............................................26
3.2.7 COUNTER ...............................................28
3.2.8 DECLINECOUNTER ........................................29
3.3 METHODS FOR VFREEBUSY COMPONENTS ..........................31
3.3.1 PUBLISH ...............................................32
3.3.2 REQUEST ...............................................33
3.3.3 REPLY .................................................34
3.4 METHODS FOR VTODO COMPONENTS ..............................35
3.4.1 PUBLISH ...............................................35
3.4.2 REQUEST ...............................................37
3.4.2.1 REQUEST for Rescheduling a VTODO...................39
3.4.2.2 REQUEST for Update or Reconfirmation of a VTODO....39
3.4.2.3 REQUEST for Delegating a VTODO.....................40
3.4.2.4 REQUEST Forwarded To An Uninvited Calendar User....40
3.4.2.5 REQUEST Updated Attendee Status....................41
3.4.3 REPLY .................................................41
3.4.4 ADD ...................................................43
3.4.5 CANCEL ................................................44
3.4.6 REFRESH ...............................................46
3.4.7 COUNTER ...............................................48
3.4.8 DECLINECOUNTER ........................................49
3.5 METHODS FOR VJOURNAL COMPONENTS ...........................50
3.5.1 PUBLISH ...............................................51
3.5.2 ADD ...................................................52
3.5.3 CANCEL ................................................53
3.6 STATUS REPLIES ............................................55
3.7 IMPLEMENTATION CONSIDERATIONS .............................57
3.7.1 Working With Recurrence Instances .....................57
3.7.2 Attendee Property Considerations ......................58
3.7.3 X-Tokens ..............................................59
4 EXAMPLES......................................................59
4.1 PUBLISHED EVENT EXAMPLES ..................................59
4.1.1 A Minimal Published Event .............................60
4.1.2 Changing A Published Event ............................60
4.1.3 Canceling A Published Event ...........................61
4.1.4 A Rich Published Event ................................62
4.1.5 Anniversaries or Events attached to entire days .......63
4.2 GROUP EVENT EXAMPLES ......................................63
4.2.1 A Group Event Request .................................64
4.2.2 Reply To A Group Event Request ........................65
4.2.3 Update An Event .......................................65
4.2.4 Countering an Event Proposal ..........................66
4.2.5 Delegating an Event ...................................68
4.2.6 Delegate Accepts the Meeting ..........................70
4.2.7 Delegate Declines the Meeting .........................71
4.2.8 Forwarding an Event Request ...........................72
4.2.9 Cancel A Group Event ..................................72
4.2.10 Removing Attendees ...................................74
4.2.11 Replacing the Organizer ..............................75
4.3 BUSY TIME EXAMPLES ........................................76
4.3.1 Request Busy Time .....................................77
4.3.2 Reply To A Busy Time Request ..........................77
4.4 RECURRING EVENT AND TIME ZONE EXAMPLES ....................78
4.4.1 A Recurring Event Spanning Time Zones .................78
4.4.2 Modify A Recurring Instance ...........................79
4.4.3 Cancel an Instance ....................................81
4.4.4 Cancel Recurring Event ................................81
4.4.5 Change All Future Instances ...........................82
4.4.6 Add A New Instance To A Recurring Event ...............82
4.4.7 Add A New Series of Instances To A Recurring Event ....83
4.4.8 Counter An Instance Of A Recurring Event ..............87
4.4.9 Error Reply To A Request ..............................88
4.5 GROUP TO-DO EXAMPLES ......................................89
4.5.1 A VTODO Request .......................................90
4.5.2 A VTODO Reply .........................................90
4.5.3 A VTODO Request for Updated Status ....................91
4.5.4 A Reply: Percent-Complete .............................91
4.5.5 A Reply: Completed ....................................92
4.5.6 An Updated VTODO Request ..............................92
4.5.7 Recurring VTODOs ......................................92
4.5.7.1 Request for a Recurring VTODO......................93
4.5.7.2 Calculating due dates in recurring VTODOs..........93
4.5.7.3 Replying to an instance of a recurring VTODO.......93
4.6 JOURNAL EXAMPLES ..........................................94
4.7 OTHER EXAMPLES ............................................94
4.7.1 Event Refresh .........................................94
4.7.2 Bad RECURRENCE-ID .....................................95
5 APPLICATION PROTOCOL FALLBACKS................................97
5.1 PARTIAL IMPLEMENTATION ....................................97
5.1.1 Event-Related Fallbacks ...............................97
5.1.2 Free/Busy-Related Fallbacks ...........................99
5.1.3 To-Do-Related Fallbacks ...............................99
5.1.4 Journal-Related Fallbacks ............................101
5.2 LATENCY ISSUES ...........................................102
5.2.1 Cancellation of an Unknown Calendar Component. .......102
5.2.2 Unexpected Reply from an Unknown Delegate ............103
5.3 SEQUENCE NUMBER ..........................................103
6 SECURITY CONSIDERATIONS......................................103
6.1 SECURITY THREATS .........................................103
6.1.1 Spoofing the "Organizer" .............................103
6.1.2 Spoofing the "Attendee" ..............................103
6.1.3 Unauthorized Replacement of the Organizer ............104
6.1.4 Eavesdropping ........................................104
6.1.5 Flooding a Calendar ..................................104
6.1.6 Procedural Alarms ....................................104
6.1.7 Unauthorized REFRESH Requests ........................104
6.2 RECOMMENDATIONS ..........................................104
6.2.1 Use of [RFC-1847] to secure iTIP transactions ........105
6.2.2 Implementation Controls ..............................105
7 ACKNOWLEDGMENTS..............................................106
8 BIBLIOGRAPHY.................................................106
9 AUTHORS' ADDRESSES...........................................107
10 FULL COPYRIGHT STATEMENT....................................109
1 Introduction
This document specifies how calendaring systems use iCalendar objects
to interoperate with other calendar systems. In particular, it
specifies how to schedule events, to-dos, or daily journal entries.
It further specifies how to search for available busy time
information. It does so in a general way so as to allow multiple
methods of communication between systems. Subsequent documents
specify transport bindings between systems that use this protocol.
This protocol is based on messages sent from an originator to one or
more recipients. For certain types of messages, a recipient may
reply, in order to update their status and may also return
transaction/request status information. The protocol supports the
ability for the message originator to modify or cancel the original
message. The protocol also supports the ability for recipients to
suggest changes to the originator of a message. The elements of the
protocol also define the user roles for its transactions.
1.1 Formatting Conventions
In order to refer to elements of the calendaring and scheduling
model, core object or interoperability protocol defined in [iCAL] and
[iTIP] several formatting conventions have been utilized.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this
document are to be interpreted as described in [RFC-2119].
Calendaring and scheduling roles are referred to in quoted-strings of
text with the first character of each word in upper case. For
example, "Organizer" refers to a role of a "Calendar User" (CU)
within the scheduling protocol defined by [iTIP]. Calendar components
defined by [iCAL] are referred to with capitalized, quoted-strings of
text. All calendar components start with the letter "V". For example,
"VEVENT" refers to the event calendar component, "VTODO" refers to
the to-do calendar component and "VJOURNAL" refers to the daily
journal calendar component. Scheduling methods defined by [iTIP] are
referred to with capitalized, quoted-strings of text. For example,
"REQUEST" refers to the method for requesting a scheduling calendar
component be created or modified, "REPLY" refers to the method a
recipient of a request uses to update their status with the
"Organizer" of the calendar component.
Properties defined by [iCAL] are referred to with capitalized,
quoted-strings of text, followed by the word "property". For example,
"ATTENDEE" property refers to the iCalendar property used to convey
the calendar address of a "Calendar User". Property parameters
defined by this memo are referred to with lower case, quoted-strings
of text, followed by the word "parameter". For example, "value"
parameter refers to the iCalendar property parameter used to override
the default data type for a property value. Enumerated values defined
by this memo are referred to with capitalized text, either alone or
followed by the word "value".
In tables, the quoted-string text is specified without quotes in
order to minimize the table length.
1.2 Related Documents
Implementers will need to be familiar with several other memos that,
along with this one, describe the Internet calendaring and scheduling
standards. This document, [iTIP], specifies an interoperability
protocol for scheduling between different implementations. The
related documents are:
[iCAL] - specifies the objects, data types, properties and
property parameters used in the protocols, along with the
methods for representing and encoding them;
[iMIP] specifies an Internet email binding for [iTIP].
This memo does not attempt to repeat the specification of concepts or
definitions from these other memos. Where possible, references are
made to the memo that provides for the specification of these
concepts or definitions.
1.3 ITIP Roles and Transactions
ITIP defines methods for exchanging [iCAL] objects for the purposes
of group calendaring and scheduling between "Calendar Users" (CUs).
CUs take on one of two roles in iTIP. The CU who initiates an
exchange takes on the role of "Organizer". For example, the CU who
proposes a group meeting is the "Organizer". The CUs asked to
participate in the group meeting by the "Organizer" take on the role
of "Attendee". Note that "role" is also a descriptive parameter to
the _ATTENDEE_ property. Its use is to convey descriptive context to
an "Attendee" such as "chair", "req-participant" or "non-participant"
and has nothing to do with the calendaring workflow.
The ITIP methods are listed below and their usage and semantics are
defined in section 3 of this document.
+================+==================================================+
| Method | Description |
|================+==================================================|
| PUBLISH | Used to publish a calendar entry to one or more |
| | Calendar Users. There is no interactivity |
| | between the publisher and any other calendar |
| | user. An example might include a baseball team |
| | publishing its schedule to the public. |
| | |
| REQUEST | Used to schedule a calendar entry with other |
| | Calendar Users. Requests are interactive in that |
| | they require the receiver to respond using |
| | the Reply methods. Meeting Requests, Busy |
| | Time requests and the assignment of VTODOs to |
| | other Calendar Users are all examples. |
| | Requests are also used by the "Organizer" to |
| | update the status of a calendar entry. |
| | |
| REPLY | A Reply is used in response to a Request to |
| | convey "Attendee" status to the "Organizer". |
| | Replies are commonly used to respond to meeting |
| | and task requests. |
| | |
| ADD | Add one or more instances to an existing |
| | VEVENT, VTODO, or VJOURNAL. |
| | |
| CANCEL | Cancel one or more instances of an existing |
| | VEVENT, VTODO, or VJOURNAL. |
| | |
| REFRESH | The Refresh method is used by an "Attendee" to |
| | request the latest version of a calendar entry. |
| | |
| COUNTER | The Counter method is used by an "Attendee" to |
| | negotiate a change in the calendar entry. |
| | Examples include the request to change a |
| | proposed Event time or change the due date for a |
| | VTODO. |
| | |
| DECLINE- | Used by the "Organizer" to decline the proposed |
| COUNTER | counter-proprosal. |
+================+==================================================+
Group scheduling in iTIP is accomplished using the set of "request"
and "response" methods described above. The following table shows the
methods broken down by who can send them.
+================+==================================================+
| Originator | Methods |
|================+==================================================|
| Organizer | PUBLISH, REQUEST, ADD, CANCEL, DECLINECOUNTER |
| | |
| Attendee | REPLY, REFRESH, COUNTER |
| | REQUEST only when delegating |
+================+==================================================+
Note that for some calendar component types, the allowable methods
are a subset of the above set.
2 Interoperability Models
There are two distinct protocols relevant to interoperability: an
"Application Protocol" and a "Transport Protocol". The Application
Protocol defines the content of the iCalendar objects sent between
sender and receiver to accomplish the scheduling transactions listed
above. The Transport Protocol defines how the iCalendar objects are
sent between the sender and receiver. This document focuses on the
Application Protocol. Binding documents such as [iMIP] focus on the
Transport Protocol.
The connection between Sender and Receiver in the diagram below
refers to the Application Protocol. The iCalendar objects passed from
the Sender to the Receiver are presented in Section 3, Application
Protocol Elements.
+----------+ +----------+
| | iTIP | |
| Sender |<-------------------->| Receiver |
| | | |
+----------+ +----------+
There are several variations of this diagram in which the Sender and
Receiver take on various roles of a "Calendar User Agent" (CUA) or a
"Calendar Service" (CS).
The architecture of iTIP is depicted in the diagram below. An
application written to this specification may work with bindings for
the store-and-forward transport, the real time transport, or both.
Also note that iTIP could be bound to other transports.
+------------------------------------------+
| iTIP |
+------------------------------------------+
|Real-time | Store-and-Fwd | Other |
|Transport | Transport | Transports... |
+------------------------------------------+
2.1 Application Protocol
In the iTIP model, a calendar entry is created and managed by an
"Organizer". The "Organizer" interacts with other CUs by sending one
or more of the iTIP messages listed above. "Attendees" use the
"REPLY" method to communicate their status. "Attendees" do not make
direct changes to the master calendar entry. They can, however, use
the "COUNTER" method to suggest changes to the "Organizer". In any
case, the "Organizer" has complete control over the master calendar
entry.
2.1.1 Calendar Entry State
There are two distinct states relevant to calendar entries: the
overall state of the entry and the state associated with an
"Attendee" to that entry.
The state of an entry is defined by the "STATUS" property and is
controlled by the "Organizer." There is no default value for the
"STATUS" property. The "Organizer" sets the "STATUS" property to the
appropriate value for each calendar entry.
The state of a particular "Attendee" relative to an entry is defined
by the "partstat" parameter in the "ATTENDEE" property for each
"Attendee". When an "Organizer" issues the initial entry, "Attendee"
status is unknown. The "Organizer" specifies this by setting the
"partstat" parameter to "NEEDS-ACTION". Each "Attendee" modifies
their "ATTENDEE" property "partstat" parameter to an appropriate
value as part of a "REPLY" message sent back to the "Organizer".
2.1.2 Delegation
Delegation is defined as the process by which an "Attendee" grants
another CU (or several CUs) the right to attend on their behalf. The
"Organizer" is made aware of this change because the delegating
"Attendee" informs the "Organizer". These steps are detailed in the
REQUEST method section.
2.1.3 Acting on Behalf of other Calendar Users
In many organizations one user will act on behalf of another to
organize and/or respond to meeting requests. ITIP provides two
mechanisms that support these activities.
First, the "Organizer" is treated as a special entity, separate from
"Attendees". All responses from "Attendees" flow to the "Organizer",
making it easy to separate a calendar user organizing a meeting from
calendar users attending the meeting. Additionally, iCalendar
provides descriptive roles for each "Attendee". For instance, a role
of "chair" may be ascribed to one or more "Attendees". The "chair"
and the "Organizer" may or may not be the same calendar user. This
maps well to scenarios where an assistant may manage meeting
logistics for another individual who chairs a meeting.
Second, a "sent-by" parameter may be specified in either the
"Organizer" or "Attendee" properties. When specified, the "sent-by"
parameter indicates that the responding CU acted on behalf of the
specified "Attendee" or "Organizer".
2.1.4 Component Revisions
The "SEQUENCE" property is used by the "Organizer" to indicate
revisions to the calendar component. The rules for incrementing the
"SEQUENCE" number are defined in [iCAL]. For clarity, these rules are
paraphrased here in terms of how they are applied in [iTIP]. For a
given "UID" in a calendar component:
. For the "PUBLISH" and "REQUEST" methods, the "SEQUENCE" property
value is incremented according to the rules defined in [iCAL].
. The "SEQUENCE" property value MUST be incremented each time the
"Organizer" uses the "ADD" or "CANCEL" methods.
. The "SEQUENCE" property value MUST NOT be incremented when using
"REPLY", "REFRESH", "COUNTER", "DECLINECOUNTER", or when sending a
delegation "REQUEST".
In some circumstances the "Organizer" may not have received responses
to the final revision sent out. In this situation, the "Organizer"
may wish to send an update "REQUEST", and set "RSVP=TRUE" for all
"Attendees", so that current responses can be collected.
The value of the "SEQUENCE" property contained in a response from an
"Attendee" may not always match the "Organizer's" revision.
Implementations may choose to have the CUA indicate to the CU that
the response is to an entry that has been revised and allow the CU to
decide whether or not to accept the response.
2.1.5 Message Sequencing
CUAs that handle the [iTIP] application protocol must often correlate
a component in a calendar store with a component received in the
[iTIP] message. For example, an event may be updated with a later
revision of the same event. To accomplish this, a CUA must correlate
the version of the event already in its calendar store with the
version sent in the [iTIP] message. In addition to this correlation,
there are several factors that can cause [iTIP] messages to arrive in
an unexpected order. That is, an "Organizer" could receive a reply
to an earlier revision of a component AFTER receiving a reply to a
later revision.
To maximize interoperability and to handle messages that arrive in an
unexpected order, use the following rules:
1. The primary key for referencing a particular iCalendar component
is the "UID" property value. To reference an instance of a
recurring component, the primary key is composed of the "UID" and
the "RECURRENCE-ID" properties.
2. The secondary key for referencing a component is the "SEQUENCE"
property value. For components where the "UID" is the same, the
component with the highest numeric value for the "SEQUENCE"
property obsoletes all other revisions of the component with
lower values.
3. "Attendees" send "REPLY" messages to the "Organizer". For
replies where the "UID" property value is the same, the value of
the "SEQUENCE" property indicates the revision of the component
to which the "Attendee" is replying. The reply with the highest
numeric value for the "SEQUENCE" property obsoletes all other
replies with lower values.
4. In situations where the "UID" and "SEQUENCE" properties match,
the "DTSTAMP" property is used as the tie-breaker. The component
with the latest "DTSTAMP" overrides all others. Similarly, for
"Attendee" responses where the "UID" property values match and
the "SEQUENCE" property values match, the response with the
latest "DTSTAMP" overrides all others.
Hence, CUAs must persist the following component properties: "UID",
"RECURRENCE-ID", "SEQUENCE", and "DTSTAMP". Furthermore, for each
"ATTENDEE" property of a component CUAs must persist the "SEQUENCE"
and "DTSTAMP" property values associated with the "Attendee's"
response.
3 Application Protocol Elements
ITIP messages are "text/calendar" MIME entities that contain
calendaring and scheduling information. The particular type of [iCAL]
message is referred to as the "method type". Each method type is
identified by a "METHOD" property specified as part of the
"text/calendar" content type. The table below shows various
combinations of calendar components and the method types that this
memo supports.
+=================================================+
| | VEVENT | VTODO | VJOURNAL | VFREEBUSY |
|=================================================|
|Publish | Yes | Yes | Yes | Yes |
|Request | Yes | Yes | No | Yes |
|Refresh | Yes | Yes | No | No |
|Cancel | Yes | Yes | Yes | No |
|Add | Yes | Yes | Yes | No |
|Reply | Yes | Yes | No | Yes |
|Counter | Yes | Yes | No | No |
|Decline- | | | | |
|Counter | Yes | Yes | No | No |
+=================================================+
Each method type is defined in terms of its associated components and
properties. Some components and properties are required, some are
optional and others are excluded. The restrictions are expressed in
this document using a simple "restriction table". The first column
indicates the name of a component or property. Properties of the
iCalendar object are not indented. Properties of a component are
indented. The second column contains "MUST" if the component or
property must be present, "MAY" if the component or property is
optional, and "NOT" if the component or property must not be present.
Entries in the second column sometimes contain comments for further
clarification.
3.1 Common Component Restriction Tables
The restriction table below applies to properties of the iCalendar
object. That is, the properties at the outermost scope. The presence
column uses the following values to assert whether a property is
required, is optional and the number of times it may appear in the
iCalendar object.
Presence Value Description
--------------------------------------------------------------
1 One instance MUST be present
1+ At least one instance MUST be present
0 Instances of this property Must NOT be present
0+ Multiple instances MAY be present
0 or 1 Up to 1 instance of this property MAY be present
---------------------------------------------------------------
The tables also call out "X-PROPERTY" and "X-COMPONENT" to show
where vendor-specific properties and components can appear. The
tables do not lay out the restrictions of property parameters. Those
restrictions are defined in [iCAL].
Component/Property Presence
------------------- ----------------------------------------------
CALSCALE 0 or 1
PRODID 1
VERSION 1 Value MUST be "2.0"
X-PROPERTY 0+
DateTime values MAY refer to a "VTIMEZONE" component. The property
restrictions in the table below apply to any "VTIMEZONE" component in
an ITIP message.
Component/Property Presence
------------------- ----------------------------------------------
VTIMEZONE 0+ MUST be present if any date/time refers
to timezone
DAYLIGHT 0+ MUST be one or more of either STANDARD or
DAYLIGHT
COMMENT 0 or 1
DTSTART 1 MUST be local time format
RDATE 0+ if present RRULE MUST NOT be present
RRULE 0+ if present RDATE MUST NOT be present
TZNAME 0 or 1
TZOFFSET 1
TZOFFSETFROM 1
TZOFFSETTO 1
X-PROPERTY 0+
LAST-MODIFIED 0 or 1
STANDARD 0+ MUST be one or more of either STANDARD or
DAYLIGHT
COMMENT 0 or 1
DTSTART 1 MUST be local time format
RDATE 0+ if present RRULE MUST NOT be present
RRULE 0+ if present RDATE MUST NOT be present
TZNAME 0 or 1
TZOFFSETFROM 1
TZOFFSETTO 1
X-PROPERTY 0+
TZID 1
TZURL 0 or 1
X-PROPERTY 0+
The property restrictions in the table below apply to any "VALARM"
component in an ITIP message.
Component/Property Presence
------------------- ----------------------------------------------
VALARM 0+
ACTION 1
ATTACH 0+
DESCRIPTION 0 or 1
DURATION 0 or 1 if present REPEAT MUST be present
REPEAT 0 or 1 if present DURATION MUST be present
SUMMARY 0 or 1
TRIGGER 1
X-PROPERTY 0+
3.2 Methods for VEVENT Calendar Components
This section defines the property set restrictions for the method
types that are applicable to the "VEVENT" calendar component. Each
method is defined using a table that clarifies the property
constraints that define the particular method.
The following summarizes the methods that are defined for the
"VEVENT" calendar component.
+================+==================================================+
| Method | Description |
|================+==================================================|
| PUBLISH | Post notification of an event. Used primarily as |
| | a method of advertising the existence of an |
| | event. |
| | |
| REQUEST | Make a request for an event. This is an explicit |
| | invitation to one or more "Attendees". Event |
| | Requests are also used to update or change an |
| | existing event. Clients that cannot handle |
| | REQUEST may degrade the event to view it as an |
| | PUBLISH. |
| | |
| REPLY | Reply to an event request. Clients may set their |
| | status ("partstat") to ACCEPTED, DECLINED, |
| | TENTATIVE, or DELEGATED. |
| | |
| ADD | Add one or more instances to an existing event. |
| | |
| CANCEL | Cancel one or more instances of an existing |
| | event. |
| | |
| REFRESH | A request is sent to an "Organizer" by an |
| | "Attendee" asking for the latest version of an |
| | event to be resent to the requester. |
| | |
| COUNTER | Counter a REQUEST with an alternative proposal, |
| | Sent by an "Attendee" to the "Organizer". |
| | |
| DECLINECOUNTER | Decline a counter proposal. Sent to an |
| | "Attendee" by the "Organizer". |
+================+==================================================+
3.2.1 PUBLISH
The "PUBLISH" method in a "VEVENT" calendar component is an
unsolicited posting of an iCalendar object. Any CU may add published
components to their calendar. The "Organizer" MUST be present in a
published iCalendar component. "Attendees" MUST NOT be present. Its
expected usage is for encapsulating an arbitrary event as an
iCalendar object. The "Organizer" may subsequently update (with
another "PUBLISH" method), add instances to (with an "ADD" method),
or cancel (with a "CANCEL" method) a previously published "VEVENT"
calendar component.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST equal "PUBLISH"
VEVENT 1+
DTSTAMP 1
DTSTART 1
ORGANIZER 1
SUMMARY 1 Can be null.
UID 1
RECURRENCE-ID 0 or 1 only if referring to an instance of a
recurring calendar component. Otherwise
it MUST NOT be present.
SEQUENCE 0 or 1 MUST be present if value is greater than
0, MAY be present if 0
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of
values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1 Can be null
DTEND 0 or 1 if present DURATION MUST NOT be present
DURATION 0 or 1 if present DTEND MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PRIORITY 0 or 1
RDATE 0+
RELATED-TO 0+
RESOURCES 0 or 1 This property MAY contain a list of values
RRULE 0+
STATUS 0 or 1 MAY be one of TENTATIVE/CONFIRMED/CANCELLED
TRANSP 0 or 1
URL 0 or 1
X-PROPERTY 0+
ATTENDEE 0
REQUEST-STATUS 0
VALARM 0+
VFREEBUSY 0
VJOURNAL 0
VTODO 0
VTIMEZONE 0+ MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
3.2.2 REQUEST
The "REQUEST" method in a "VEVENT" component provides the following
scheduling functions:
. Invite "Attendees" to an event;
. Reschedule an existing event;
. Response to a REFRESH request;
. Update the details of an existing event, without rescheduling it;
. Update the status of "Attendees" of an existing event, without
rescheduling it;
. Reconfirm an existing event, without rescheduling it;
. Forward a "VEVENT" to another uninvited CU.
. For an existing "VEVENT" calendar component, delegate the role of
"Attendee" to another CU;
. For an existing "VEVENT" calendar component, changing the role of
"Organizer" to another CU.
The "Organizer" originates the "REQUEST". The recipients of the
"REQUEST" method are the CUs invited to the event, the "Attendees".
"Attendees" use the "REPLY" method to convey attendance status to the
"Organizer".
The "UID" and "SEQUENCE" properties are used to distinguish the
various uses of the "REQUEST" method. If the "UID" property value in
the "REQUEST" is not found on the recipient's calendar, then the
"REQUEST" is for a new "VEVENT" calendar component. If the "UID"
property value is found on the recipient's calendar, then the
"REQUEST" is for a rescheduling, an update, or a reconfirm of the
"VEVENT" calendar component.
For the "REQUEST" method, multiple "VEVENT" components in a single
iCalendar object are only permitted when for components with the same
"UID" property. That is, a series of recurring events may have
instance-specific information. In this case, multiple "VEVENT"
components are needed to express the entire series.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
-----------------------------------------------------------------
METHOD 1 MUST be "REQUEST"
VEVENT 1+ All components MUST have the same UID
ATTENDEE 1+
DTSTAMP 1
DTSTART 1
ORGANIZER 1
SEQUENCE 0 or 1 MUST be present if value is greater than 0,
MAY be present if 0
SUMMARY 1 Can be null
UID 1
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1 Can be null
DTEND 0 or 1 if present DURATION MUST NOT be present
DURATION 0 or 1 if present DTEND MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PRIORITY 0 or 1
RDATE 0+
RECURRENCE-ID 0 or 1 only if referring to an instance of a
recurring calendar component. Otherwise it
MUST NOT be present.
RELATED-TO 0+
REQUEST-STATUS 0+
RESOURCES 0 or 1 This property MAY contain a list of values
RRULE 0+
STATUS 0 or 1 MAY be one of TENTATIVE/CONFIRMED
TRANSP 0 or 1
URL 0 or 1
X-PROPERTY 0+
VALARM 0+
VTIMEZONE 0+ MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
VFREEBUSY 0
VJOURNAL 0
VTODO 0
3.2.2.1 Rescheduling an Event
The "REQUEST" method may be used to reschedule an event. A
rescheduled event involves a change to the existing event in terms of
its time or recurrence intervals and possibly the location or
description. If the recipient CUA of a "REQUEST" method finds that
the "UID" property value already exists on the calendar, but that the
"SEQUENCE" (or "DTSTAMP") property value in the "REQUEST" method is
greater than the value for the existing event, then the "REQUEST"
method describes a rescheduling of the event.
3.2.2.2 Updating or Reconfirmation of an Event
The "REQUEST" method may be used to update or reconfirm an event. An
update to an existing event does not involve changes to the time or
recurrence intervals, and might not involve a change to the location
or description for the event. If the recipient CUA of a "REQUEST"
method finds that the "UID" property value already exists on the
calendar and that the "SEQUENCE" property value in the "REQUEST" is
the same as the value for the existing event, then the "REQUEST"
method describes an update of the event details, but no rescheduling
of the event.
The update "REQUEST" method is the appropriate response to a
"REFRESH" method sent from an "Attendee" to the "Organizer" of an
event.
The "Organizer" of an event may also send unsolicited "REQUEST"
methods. The unsolicited "REQUEST" methods may be used to update the
details of the event without rescheduling it, to update the
"partstat" parameter of "Attendees", or to reconfirm the event.
3.2.2.3 Delegating an Event to another CU
Some calendar and scheduling systems allow "Attendees" to delegate
their presence at an event to another calendar user. ITIP supports
this concept using the following workflow. Any "Attendee" may
delegate their right to participate in a calendar VEVENT to another
CU. The implication is that the delegate participates in lieu of the
original "Attendee"; NOT in addition to the "Attendee". The delegator
MUST notify the "Organizer" of this action using the steps outlined
below. Implementations may support or restrict delegation as they
see fit. For instance, some implementations may restrict a delegate
from delegating a "REQUEST" to another CU.
The "Delegator" of an event forwards the existing "REQUEST" to the
"Delegate". The "REQUEST" method MUST include an "ATTENDEE" property
with the calendar address of the "Delegate". The "Delegator" MUST
also send a "REPLY" method to the "Organizer" with the "Delegator's"
"ATTENDEE" property "partstat" parameter value set to "delegated". In
addition, the "delegated-to" parameter MUST be included with the
calendar address of the "Delegate".
In response to the request, the "Delegate" MUST send a "REPLY" method
to the "Organizer" and optionally, to the "Delegator". The "REPLY"
method " SHOULD include the "ATTENDEE" property with the "delegated-
from" parameter value of the "Delegator's" calendar address.
The "Delegator" may continue to receive updates to the event even
though they will not be attending. This is accomplished by the
"Delegator" setting their "role" attribute to " NON-PARTICIPANT" in
the "REPLY" to the "Organizer"
3.2.2.4 Changing the Organizer
The situation may arise where the "Organizer" of a VEVENT is no
longer able to perform the "Organizer" role and abdicates without
passing on the "Organizer" role to someone else. When this occurs the
"Attendees" of the VEVENT may use out-of-band mechanisms to
communicate the situation and agree upon a new "Organizer". The new
"Organizer" should then send out a new "REQUEST" with a modified
version of the VEVENT in which the "SEQUENCE" number has been
incremented and value of the "ORGANIZER" property has been changed to
the calendar address of the new "Organizer".
3.2.2.5 Sending on Behalf of the Organizer
There are a number of scenarios that support the need for a calendar
user to act on behalf of the "Organizer" without explicit role
changing. This might be the case if the CU designated as "Organizer"
was sick or unable to perform duties associated with that function.
In these cases iTIP supports the notion of one CU acting on behalf of
another. Using the "sent-by" parameter, a calendar user could send an
updated "VEVENT" REQUEST. In the case where one CU sends on behalf of
another CU, the "Attendee" responses are still directed back towards
the CU designated as "Organizer".
3.2.2.6 Forwarding to An Uninvited CU
An "Attendee" invited to an event may invite another uninvited CU to
the event. The invited "Attendee" accomplishes this by forwarding the
original "REQUEST" method to the uninvited CU. The "Organizer"
decides whether or not the uninvited CU is added to the attendee
list. If the "Organizer" decides not to add the uninvited CU no
further action is required, however the "Organizer" MAY send the
uninvited CU a "CANCEL" message. If the "Organizer" decides to add
an uninvited CU, a new "ATTENDEE" property is added for the uninvited
CU with its property parameters set as the "Organizer" deems
appropriate. When forwarding a "REQUEST" to another CU, the
forwarding "Attendee" MUST NOT make changes to the VEVENT property
set.
3.2.2.7 Updating Attendee Status
The "Organizer" of an event may also request updated status from one
or more "Attendees. The "Organizer" sends a "REQUEST" method to the
"Attendee" and sets the "ATTENDEE;RSVP=TRUE" property parameter. The
"SEQUENCE" property for the event is not changed from its previous
value. A recipient will determine that the only change in the
"REQUEST" is that their "RSVP" property parameter indicates a request
for updated status. The recipient SHOULD respond with a "REPLY"
method indicating their current status with respect to the "REQUEST".
3.2.3 REPLY
The "REPLY" method in a "VEVENT" calendar component is used to
respond (e.g., accept or decline) to a "REQUEST" or to reply to a
delegation "REQUEST". When used to provide a delegation response, the
"Delegator" SHOULD include the calendar address of the "Delegate" on
the "delegated-to" property parameter of the "Delegator's" "ATTENDEE"
property. The "Delegate" SHOULD include the calendar address of the
"Delegator" on the "delegated-from" property parameter of the
"Delegate's" "ATTENDEE" property.
The "REPLY" method may also be used to respond to an unsuccessful
"REQUEST" method. Depending on the value of the "REQUEST-STATUS"
property no scheduling action may have been performed.
The "Organizer" of an event may receive the "REPLY" method from a CU
not in the original "REQUEST". For example, a "REPLY" may be received
from a "Delegate" to an event. In addition, the "REPLY" method may be
received from an unknown CU (a "Party Crasher"). This uninvited
"Attendee" may be accepted, or the "Organizer" may cancel the event
for the uninvited "Attendee" by sending a "CANCEL" method to the
uninvited "Attendee".
An "Attendee" can include a message to the "Organizer" using the
"COMMENT" property. For example, if the user indicates tentative
acceptance and wants to let the "Organizer" know why, the reason can
be expressed in the "COMMENT" property value.
The "Organizer" may also receive a "REPLY" from one CU on behalf of
another. Like the scenario enumerated above for the "Organizer",
"Attendees" may have another CU respond on their behalf. This is done
using the "sent-by" parameter.
The optional properties listed in the table below (those listed as
"0+" or "0 or 1") MUST NOT be changed from those of the original
request. If property changes are desired the COUNTER message must be
used.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "REPLY"
VEVENT 1+ All components MUST have the same UID
ATTENDEE 1 MUST be the address of the Attendee
replying.
DTSTAMP 1
ORGANIZER 1
RECURRENCE-ID 0 or 1 only if referring to an instance of a
recurring calendar component. Otherwise
it must NOT be present.
UID 1 MUST be the UID of the original REQUEST
SEQUENCE 0 or 1 MUST if non-zero, MUST be the sequence
number of the original REQUEST. MAY be
present if 0.
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1
DTEND 0 or 1 if present DURATION MUST NOT be present
DTSTART 0 or 1
DURATION 0 or 1 if present DTEND MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PRIORITY 0 or 1
RDATE 0+
RELATED-TO 0+
RESOURCES 0 or 1 This property MAY contain a list of values
REQUEST-STATUS 0+
RRULE 0+
STATUS 0 or 1
SUMMARY 0 or 1
TRANSP 0 or 1
URL 0 or 1
X-PROPERTY 0+
VTIMEZONE 0 or 1 MUST be present if any date/time refers
to a timezone
X-COMPONENT 0+
VALARM 0
VFREEBUSY 0
VJOURNAL 0
VTODO 0
3.2.4 ADD
The "ADD" method in a "VEVENT" calendar component is used to add one
or more instances to an existing "VEVENT". Unlike the "REQUEST"
method, when using issuing an "ADD" method, the "Organizer" does not
send the full "VEVENT" description; only the new instance(s). The
"ADD" method is especially useful if there are instance-specific
properties to be preserved in a recurring "VEVENT". For instance, an
"Organizer" may have originally scheduled a weekly Thursday meeting.
At some point, several instances changed. Location or start time may
have changed, or some instances may have unique "DESCRIPTION"
properties. The "ADD" method allows the "Organizer" to add new
instances to an existing event using a single ITIP message without
redefining the entire recurring pattern.
The "UID" must be that of the existing event. If the "UID" property
value in the "ADD" is not found on the recipient's calendar, then the
recipient SHOULD send a "REFRESH" to the "Organizer" in order to be
updated with the latest version of the "VEVENT". If an "Attendee"
implementation does not support the "ADD" method it should respond
with a "REQUEST-STATUS" value of 3.14 and ask for a "REFRESH".
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "ADD"
VEVENT 1
DTSTAMP 1
DTSTART 1
ORGANIZER 1
SEQUENCE 1 MUST be greater than 0
SUMMARY 1 Can be null
UID 1 MUST match that of the original event
ATTACH 0+
ATTENDEE 0+
CATEGORIES 0 or 1 This property MAY contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1 Can be null
DTEND 0 or 1 if present DURATION MUST NOT be present
DURATION 0 or 1 if present DTEND MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PRIORITY 0 or 1
RDATE 0+
RELATED-TO 0+
RESOURCES 0 or 1 This property MAY contain a list of values
RRULE 0+
STATUS 0 or 1 MAY be one of TENTATIVE/CONFIRMED
TRANSP 0 or 1
URL 0 or 1
X-PROPERTY 0+
RECURRENCE-ID 0
REQUEST-STATUS 0
VALARM 0+
VTIMEZONE 0+ MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
VFREEBUSY 0
VTODO 0
VJOURNAL 0
3.2.5 CANCEL