"VALARM" Extensions for iCalendarApple Inc.1 Infinite LoopCupertinoCA95014United States of Americacyrus@daboo.namehttp://www.apple.com/Fastmail US LLC1429 Walnut StSuite 1201PhiladelphiaPA19102United States of Americamurch@fastmailteam.comhttp://www.fastmail.com/
ART
alarmscalendaringiCalendarCalDAVThis document defines a set of extensions to the iCalendar
"VALARM" component to enhance the use of alarms and improve
interoperability between clients and servers.This document updates RFC 5545.Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
() in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
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Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
Table of Contents
. Introduction
. Conventions Used in This Document
. Extensible Syntax for VALARM
. Alarm Unique Identifier
. Alarm Related To
. Alarm Acknowledgement
. Acknowledged Property
. Snoozing Alarms
. Relationship Type Property Parameter
. Example
. Alarm Proximity Trigger
. Proximity Property
. Example
. Security Considerations
. Privacy Considerations
. IANA Considerations
. Property Registrations
. Relationship Types Registry
. Proximity Values Registry
. References
. Normative References
. Informative References
Acknowledgements
Authors' Addresses
IntroductionThe iCalendar specification
defines a set of components used to describe calendar data. One
of those is the "VALARM" component, which appears as a
subcomponent of the "VEVENT" and "VTODO" components. The "VALARM"
component is used to specify a reminder for an event or
task. Different alarm actions are possible, as are different
ways to specify how the alarm is triggered.As iCalendar has become more widely used and as client-server
protocols, such as Calendaring Extensions to WebDAV
(CalDAV), have
become more prevalent, several issues with "VALARM" components
have arisen. Most of these relate to the need to extend the
existing "VALARM" component with new properties and behaviors to
allow clients and servers to accomplish specific tasks in an
interoperable manner. For example, clients typically need a way
to specify that an alarm has been dismissed by a calendar user
or has been "snoozed" by a set amount of time. To date, this has
been done through the use of custom "X-" properties specific to
each client implementation, leading to poor
interoperability.This specification defines a set of extensions to "VALARM"
components to cover common requirements for alarms not currently
addressed in iCalendar. Each extension is defined in a separate
section below. For the most part, each extension can be
supported independently of the others; though, in some cases, one
extension will require another. In addition, this specification
describes mechanisms by which clients can interoperably
implement common features, such as "snoozing".Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14
when, and only when, they appear in all capitals, as shown here.
The notation used in this memo to (re-)define iCalendar elements is the ABNF notation of as used by .
Any syntax elements shown below that are not explicitly defined in this specification come from iCalendar .When XML element types in the namespaces "DAV:" and
"urn:ietf:params:xml:ns:caldav" are referenced in this document
outside of the context of an XML fragment, the string "DAV:" and
"CALDAV:" will be prefixed to the element type names,
respectively.Extensible Syntax for VALARM defines the syntax
for "VALARM" components and properties within them. However, as
written, it is hard to extend this, e.g., by adding a new
property common to all types of alarms. Since many of the
extensions defined in this document need to extend the base
syntax, an alternative form for the base syntax is defined here,
with the goal of simplifying specification of the extensions
while augmenting the existing functionality defined in
to allow for nested subcomponents
(as required by
proximity alarm triggers).A "VALARM" calendar component is redefined by the following notation:
alarmcext = "BEGIN" ":" "VALARM" CRLF
*alarmprop *alarm-subcomp
"END" ":" "VALARM" CRLF
alarmprop = (
;
; the following are REQUIRED
; but MUST NOT occur more than once
;
action / trigger /
;
; one set of action properties MUST be
; present and MUST match the action specified
; in the ACTION property
;
actionprops /
;
; the following are OPTIONAL
; and MAY occur more than once
;
x-prop / iana-prop
;
)
actionprops = *audiopropext / *disppropext / *emailpropext
audiopropext = (
;
; 'duration' and 'repeat' are both OPTIONAL
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
;
duration / repeat /
;
; the following is OPTIONAL
; but MUST NOT occur more than once
;
attach
;
)
disppropext = (
;
; the following are REQUIRED
; but MUST NOT occur more than once
;
description /
;
; 'duration' and 'repeat' are both OPTIONAL
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
;
duration / repeat
;
)
emailpropext = (
;
; the following are all REQUIRED
; but MUST NOT occur more than once
;
description / summary /
;
; the following is REQUIRED
; and MAY occur more than once
;
attendee /
;
; 'duration' and 'repeat' are both OPTIONAL
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
;
duration / repeat
;
; the following is OPTIONAL
; and MAY occur more than once
;
attach
;
)
alarm-subcomp = (
;
; the following are OPTIONAL
; and MAY occur more than once
;
x-comp / iana-comp
;
)
Alarm Unique IdentifierThis extension adds a "UID"
property to "VALARM" components to allow a unique identifier to
be specified. The value of this property can then be used to refer
uniquely to the "VALARM" component.The "UID" property defined here follows the definition in
with the security
and privacy updates in .
In particular, it MUST be a globally unique identifier that does
not contain any security- or privacy-sensitive information.The "VALARM" component defined in is
extended here as:
alarmprop =/ (
;
; the following is OPTIONAL
; but MUST NOT occur more than once
;
uid
;
)
Alarm Related ToIt is often convenient to relate one or more "VALARM"
components to other "VALARM" components (e.g., see ). This can be accomplished if the "VALARM"
components each have their own "UID" property (as per ).This specification updates the usage of the "RELATED-TO"
property defined in
to enable its use with "VALARM" components. Specific types of
relationships between "VALARM" components can be identified by
registering new values for the "RELTYPE" property parameter
defined in .The "VALARM" component defined in is
extended here as:
alarmprop =/ (
;
; the following is OPTIONAL
; and MAY occur more than once
;
related
;
)
Alarm AcknowledgementThere is currently no way for a "VALARM" component to
indicate whether it has been triggered and acknowledged. With
the advent of a standard client/server protocol for calendaring
and scheduling data (), it is quite
possible for an event with an alarm to exist on multiple clients
in addition to the server. If each of those is responsible for
performing the action when an alarm triggers, then multiple
"alerts" are generated by different devices. In such a
situation, a calendar user would like to be able to "dismiss"
the alarm on one device and have it automatically dismissed on
the others, too.Also, with recurring events that have alarms, it is important
to know when the last alarm in the recurring set was
acknowledged so that the client can determine whether past
alarms have been missed.To address these needs, this specification adds an
"ACKNOWLEDGED" property to "VALARM" components to indicate when
the alarm was last acknowledged (or sent, if acknowledgement is
not possible).
This is defined by the
syntax below.
alarmprop =/ (
;
; the following is OPTIONAL
; but MUST NOT occur more than once
;
acknowledged
;
)
Acknowledged Property
Property Name:
ACKNOWLEDGED
Purpose:
This property specifies the UTC
date and time at which the corresponding alarm was last
sent or acknowledged.
Value Type:
DATE-TIME
Property Parameters:
IANA and nonstandard
property parameters can be specified on this property.
Conformance:
This property can be specified
within "VALARM" calendar components.
Description:
This property is used to
specify when an alarm was last sent or acknowledged. This
allows clients to determine when a pending alarm has been
acknowledged by a calendar user so that any alerts can be
dismissed across multiple devices. It also allows clients
to track repeating alarms or alarms on recurring events or
to-dos to ensure that the right number of missed alarms
can be tracked.Clients SHOULD set this property to the current
date-time value in UTC when a calendar user acknowledges a
pending alarm.
Certain kinds of alarms, such as email-based alerts, might
not provide feedback as to when the calendar user sees them.
For those kinds of alarms, the
client SHOULD set this property when the alarm is
triggered and the action is successfully carried out.
When an alarm is triggered on a
client, clients can check to see if an "ACKNOWLEDGED"
property is present. If it is, and the value of that
property is greater than or equal to the computed trigger
time for the alarm, then the client SHOULD NOT trigger the
alarm. Similarly, if an alarm has been triggered and an
"alert" has been presented to a calendar user, clients can monitor
the iCalendar data to determine whether an "ACKNOWLEDGED" property
is added or changed in the alarm component. If the value
of any "ACKNOWLEDGED" property in the alarm changes and is greater
than or equal to the trigger time of the alarm, then
clients SHOULD dismiss or cancel any "alert" presented to
the calendar user.
Format Definition:
This property is defined
by the following notation:
acknowledged = "ACKNOWLEDGED" *acknowledgedparam ":" datetime CRLF
acknowledgedparam = (
;
; the following is OPTIONAL
; and MAY occur more than once
;
(";" other-param)
;
)
Example:
The following is an example of this property:
ACKNOWLEDGED:20090604T084500Z
Snoozing AlarmsUsers often want to "snooze" an alarm, and this specification
defines a standard approach to accomplish that.To "snooze" an alarm that has been triggered, clients MUST do
the following:
Set the "ACKNOWLEDGED" property
(see ) on the triggered alarm.
Create a new "VALARM" component (the "snooze" alarm) within
the parent component of the triggered alarm
(i.e., as a "sibling" component of the triggered alarm).
The new "snooze" alarm MUST be set to trigger
at the user's chosen "snooze" interval after the original alarm is
triggered. Clients SHOULD use an absolute "TRIGGER" property
with a "DATE-TIME" value specified in UTC.
The new "snooze" alarm MUST have a "RELATED-TO" property
(see )
with a value set to the "UID" property value of the original
"VALARM" component that was triggered.
If the triggered "VALARM" component does not
already have a "UID" property, the client MUST add one. The
"RELATED-TO" property added to the new "snooze" alarm MUST
include a "RELTYPE" property parameter with a value set to
"SNOOZE" (see ).
When the "snooze" alarm is triggered, the client MUST do the
following:
Update the "ACKNOWLEDGED" property on the original related
alarm.
If the "snooze" alarm is itself "snoozed", the client MUST
remove the "snooze" alarm component and return to step 2.
Otherwise, if the "snooze" alarm is dismissed, the client
MUST do one of the following:
Set the "ACKNOWLEDGED" property on the "snooze" alarm.
Remove the "snooze" alarm component.
Note that regardless of the final disposition of the "snooze"
alarm when triggered, the original "VALARM" component is left
unchanged other than updating its "ACKNOWLEDGED" property.Relationship Type Property Parameter
This specification adds the "SNOOZE" relationship type for
use with the "RELTYPE" property defined in
. This is used when relating a
"snoozed" "VALARM" component to the original alarm that
the "snooze" was generated for.
ExampleThe following example shows the "snoozing", "re-snoozing", and
dismissal of an alarm. Note that the encompassing
"VCALENDAR" component has been omitted for brevity and that the
line breaks surrounding the "VALARM" components are for clarity
only and would not be present in the actual iCalendar data.Assume that we have the following event with an alarm set
to trigger 15 minutes before the meeting:
BEGIN:VEVENT
CREATED:20210302T151004Z
UID:AC67C078-CED3-4BF5-9726-832C3749F627
DTSTAMP:20210302T151004Z
DTSTART;TZID=America/New_York:20210302T103000
DTEND;TZID=America/New_York:20210302T113000
SUMMARY:Meeting
BEGIN:VALARM
UID:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
TRIGGER:-PT15M
DESCRIPTION:Event reminder
ACTION:DISPLAY
END:VALARM
END:VEVENT
When the alarm is triggered, the user decides to "snooze" it
for 5 minutes. The client acknowledges the original alarm and
creates a new "snooze" alarm as a sibling of, and relates it
to, the original alarm (note that both occurrences of "VALARM" reside within the
same "parent" VEVENT):
BEGIN:VEVENT
CREATED:20210302T151004Z
UID:AC67C078-CED3-4BF5-9726-832C3749F627
DTSTAMP:20210302T151516Z
DTSTART;TZID=America/New_York:20210302T103000
DTEND;TZID=America/New_York:20210302T113000
SUMMARY:Meeting
BEGIN:VALARM
UID:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
TRIGGER:-PT15M
DESCRIPTION:Event reminder
ACTION:DISPLAY
ACKNOWLEDGED:20210302T151514Z
END:VALARM
BEGIN:VALARM
UID:DE7B5C34-83FF-47FE-BE9E-FF41AE6DD097
TRIGGER;VALUE=DATE-TIME:20210302T152000Z
RELATED-TO;RELTYPE=SNOOZE:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
DESCRIPTION:Event reminder
ACTION:DISPLAY
END:VALARM
END:VEVENT
When the "snooze" alarm is triggered, the user decides to
"snooze" it again for an additional 5 minutes. The client
once again acknowledges the original alarm, removes the triggered
"snooze" alarm, and creates another new "snooze" alarm as a
sibling of, and relates it to, the original alarm (note the
different UID for the new "snooze" alarm):
BEGIN:VEVENT
CREATED:20210302T151004Z
UID:AC67C078-CED3-4BF5-9726-832C3749F627
DTSTAMP:20210302T152026Z
DTSTART;TZID=America/New_York:20210302T103000
DTEND;TZID=America/New_York:20210302T113000
SUMMARY:Meeting
BEGIN:VALARM
UID:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
TRIGGER:-PT15M
DESCRIPTION:Event reminder
ACTION:DISPLAY
ACKNOWLEDGED:20210302T152024Z
END:VALARM
BEGIN:VALARM
UID:87D690A7-B5E8-4EB4-8500-491F50AFE394
TRIGGER;VALUE=DATE-TIME:20210302T152500Z
RELATED-TO;RELTYPE=SNOOZE:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
DESCRIPTION:Event reminder
ACTION:DISPLAY
END:VALARM
END:VEVENT
When the second "snooze" alarm is triggered, the user
decides to dismiss it. The client acknowledges both the
original alarm and the second "snooze" alarm:
BEGIN:VEVENT
CREATED:20210302T151004Z
UID:AC67C078-CED3-4BF5-9726-832C3749F627
DTSTAMP:20210302T152508Z
DTSTART;TZID=America/New_York:20210302T103000
DTEND;TZID=America/New_York:20210302T113000
SUMMARY:Meeting
BEGIN:VALARM
UID:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
TRIGGER:-PT15M
DESCRIPTION:Event reminder
ACTION:DISPLAY
ACKNOWLEDGED:20210302T152507Z
END:VALARM
BEGIN:VALARM
UID:87D690A7-B5E8-4EB4-8500-491F50AFE394
TRIGGER;VALUE=DATE-TIME:20210302T152500Z
RELATED-TO;RELTYPE=SNOOZE:8297C37D-BA2D-4476-91AE-C1EAA364F8E1
DESCRIPTION:Event reminder
ACTION:DISPLAY
ACKNOWLEDGED:20210302T152507Z
END:VALARM
END:VEVENT
Alarm Proximity TriggerCurrently, a "VALARM" is triggered when a specific date-time value is
reached. It is also desirable to be able to trigger alarms based
on location, e.g., when arriving at or departing from a
particular location.This specification adds the following elements to "VALARM"
components to indicate when an alarm can be triggered based on
location.
"PROXIMITY" property:
indicates that a location-based trigger is to
be used and which action is used for the trigger
"VLOCATION" component(s):
used to indicate the actual
location(s) to trigger off of, specified with a URL property containing a
'geo' URI, which allows for two or three
coordinate values with an optional uncertainty
alarmprop =/ (
;
; the following is OPTIONAL
; but MUST NOT occur more than once
;
proximity
;
)
alarm-subcomp =/ (
;
; the following is OPTIONAL
; and MAY occur more than once but only
; when a PROXIMITY property is also present
;
locationc
;
)
Typically, when a "PROXIMITY" property is used, there is no
need to specify a time-based trigger using the "TRIGGER"
property. However, since "TRIGGER" is defined as a required
property for a "VALARM" component, for backwards compatibility,
it has to be present but ignored. To indicate a "TRIGGER"
that is to be ignored, clients SHOULD use a value a long time
in the past. A value of "19760401T005545Z" has been commonly
used for this purpose.
Proximity Property
Property Name:
PROXIMITY
Purpose:
This property indicates that a
location-based trigger is applied to an alarm.
Value Type:
TEXT
Property Parameters:
IANA and nonstandard
property parameters can be specified on this property.
Conformance:
This property can be specified
within "VALARM" calendar components.
Description:
This property is used to
indicate that an alarm has a location-based trigger.
Its value identifies the action that will trigger the alarm.When the property value is set to "ARRIVE", the alarm
is triggered when the calendar user agent arrives in the
vicinity of one or more locations. When set to
"DEPART", the alarm is triggered when the calendar user
agent departs from the vicinity of one or more locations.
Each location MUST be specified with a "VLOCATION"
component.
Note that the meaning of "vicinity" in this
context is implementation defined.When the property value is set to "CONNECT", the alarm
is triggered when the calendar user agent connects to an
automobile to which it has been paired via
Bluetooth.
When set to "DISCONNECT", the alarm is
triggered when the calendar user agent disconnects from an
automobile to which it has been paired via Bluetooth.
Note that neither current implementations of proximity
alarms nor this document have a mechanism to target a
particular automobile.
Such a mechanism may be specified in a future extension.
Format Definition:
This property is defined
by the following notation:
proximity = "PROXIMITY" *proximityparam ":" proximityvalue CRLF
proximityparam = (
;
; the following is OPTIONAL
; and MAY occur more than once
;
(";" other-param)
;
)
proximityvalue = "ARRIVE" / "DEPART" /
"CONNECT" / "DISCONNECT" / iana-token / x-name
ExampleThe following example shows a "VALARM" component with a
proximity trigger set to trigger when the device running the
calendar user agent leaves the vicinity defined by the
URL property in the "VLOCATION" component. Note use of the "u=" parameter
with the 'geo' URI to define the uncertainty of the location
determination.
BEGIN:VALARM
UID:77D80D14-906B-4257-963F-85B1E734DBB6
ACTION:DISPLAY
TRIGGER;VALUE=DATE-TIME:19760401T005545Z
DESCRIPTION:Remember to buy milk
PROXIMITY:DEPART
BEGIN:VLOCATION
UID:123456-abcdef-98765432
NAME:Office
URL:geo:40.443,-79.945;u=10
END:VLOCATION
END:VALARM
Security ConsiderationsIn addition to the security properties of iCalendar
(see ),
a "VALARM", if not monitored properly, can be used to disturb
users and/or leak personal information. For instance, an
undesirable audio alert could cause embarrassment; an
unwanted display alert could be considered an annoyance; or an
email alert could be used to leak a user's location to a third
party or to send unsolicited email to multiple users.
Therefore, CalDAV clients and servers that accept iCalendar data
from a third party (e.g., via iCalendar Transport-Independent Interoperability Protocol (iTIP) ,
a subscription feed, or a shared calendar) SHOULD remove each
"VALARM" from the data prior to storing in their calendar system.Security considerations related to unique identifiers for "VALARM"
are discussed in .Privacy ConsiderationsA proximity "VALARM", if not used carefully, can leak a
user's past, present, or future location. For instance,
storing an iCalendar resource containing proximity "VALARM"s to a
shared calendar on CalDAV server can expose to anyone that has
access to that calendar the user's intent to leave
from or arrive at a particular location at some future time.
Furthermore, if a CalDAV client updates the shared iCalendar
resource with an "ACKNOWLEDGED" property when the alarm is
triggered, this will leak the exact date and time that the user left
from or arrived at the location.
Therefore, CalDAV clients that implement proximity alarms
SHOULD give users the option of storing and/or acknowledging the
alarms on the local device only and not storing the alarm and/or
acknowledgement on a remote server.Privacy considerations related to unique identifiers for "VALARM"
are discussed in .IANA ConsiderationsProperty RegistrationsThis document defines the following new iCalendar
properties that have been added to the "Properties" registry defined in
and located here:
.
Additions to the Properties Registry
Property
Status
Reference
ACKNOWLEDGED
Current
RFC 9074,
PROXIMITY
Current
RFC 9074,
Relationship Types RegistryThis document defines the following new iCalendar
relationship type that has been added to the "Relationship Types" registry defined in
and located here:
.
Addition to the Relationship Types Registry
Relationship Type
Status
Reference
SNOOZE
Current
RFC 9074,
Proximity Values RegistryA new iCalendar registry for values
of the "PROXIMITY" property has been created and is located here:
.Additional values MAY be used, provided the process described in
is used to
register them, using the template in
.
The following table has been used to initialize the
Proximity Value Registry.
Initial Contents of the Proximity Values Registry
Value
Status
Reference
ARRIVE
Current
RFC 9074,
DEPART
Current
RFC 9074,
CONNECT
Current
RFC 9074,
DISCONNECT
Current
RFC 9074,
ReferencesNormative ReferencesKey words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Augmented BNF for Syntax Specifications: ABNFInternet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK]Internet Calendaring and Scheduling Core Object Specification (iCalendar)This document defines the iCalendar data format for representing and exchanging calendaring and scheduling information such as events, to-dos, journal entries, and free/busy information, independent of any particular calendar service or protocol. [STANDARDS-TRACK]A Uniform Resource Identifier for Geographic Locations ('geo' URI)This document specifies a Uniform Resource Identifier (URI) for geographic locations using the 'geo\' scheme name. A 'geo' URI identifies a physical location in a two- or three-dimensional coordinate reference system in a compact, simple, human-readable, and protocol-independent way. The default coordinate reference system used is the World Geodetic System 1984 (WGS-84). [STANDARDS-TRACK]New Properties for iCalendarThis document defines a set of new properties for iCalendar data and extends the use of some existing properties to the entire iCalendar object.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.Event Publishing Extensions to iCalendarInformative ReferencesBluetooth Core Specification Version 5.0 Feature OverviewBluetooth Special Interest GroupCalendaring Extensions to WebDAV (CalDAV)This document defines extensions to the Web Distributed Authoring and Versioning (WebDAV) protocol to specify a standard way of accessing, managing, and sharing calendaring and scheduling information based on the iCalendar format. This document defines the "calendar-access" feature of CalDAV. [STANDARDS-TRACK]iCalendar Transport-Independent Interoperability Protocol (iTIP)This document specifies a protocol that uses the iCalendar object specification to provide scheduling interoperability between different calendaring systems. This is done without reference to a specific transport protocol so as to allow multiple methods of communication between systems. Subsequent documents will define profiles of this protocol that use specific, interoperable methods of communication between systems.The iCalendar Transport-Independent Interoperability Protocol (iTIP) complements the iCalendar object specification by adding semantics for group scheduling methods commonly available in current calendaring systems. These scheduling methods permit two or more calendaring systems to perform transactions such as publishing, scheduling, rescheduling, responding to scheduling requests, negotiating changes, or canceling. [STANDARDS-TRACK]AcknowledgementsThis specification came about via discussions at The
Calendaring and Scheduling Consortium. Also, thanks to the
following for providing feedback: , , , , , ,
and .Authors' AddressesApple Inc.1 Infinite LoopCupertinoCA95014United States of Americacyrus@daboo.namehttp://www.apple.com/Fastmail US LLC1429 Walnut StSuite 1201PhiladelphiaPA19102United States of Americamurch@fastmailteam.comhttp://www.fastmail.com/