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Network Working Group                                           C. Daboo
Internet-Draft                                                     Apple
Intended status: Standards Track                           July 12, 2010
Expires: January 13, 2011


                    VALARM Extensions for iCalendar
                    draft-daboo-valarm-extensions-01

Abstract

   This document defines a set of extensions to the iCalendar VALARM
   component to enhance use of alarms and improve interoperability
   between clients and servers.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on January 13, 2011.

Copyright Notice

   Copyright (c) 2010 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
   3.  Extensible syntax for VALARM . . . . . . . . . . . . . . . . .  3
   4.  VALARM Unique Identifier . . . . . . . . . . . . . . . . . . .  5
   5.  VALARM URI Action  . . . . . . . . . . . . . . . . . . . . . .  6
   6.  VALARM Agent Property  . . . . . . . . . . . . . . . . . . . .  7
     6.1.  Alarm Agent Property . . . . . . . . . . . . . . . . . . .  8
     6.2.  URI Property Parameter . . . . . . . . . . . . . . . . . .  9
   7.  VALARM Status Property . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Last Triggered Property  . . . . . . . . . . . . . . . . . 11
   8.  Snoozing Alarms  . . . . . . . . . . . . . . . . . . . . . . . 12
   9.  Default Alarms in CalDAV . . . . . . . . . . . . . . . . . . . 12
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 14
     13.2. Informative References . . . . . . . . . . . . . . . . . . 14
   Appendix A.  Change History (To be removed by RFC Editor
                before publication) . . . . . . . . . . . . . . . . . 14
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15




























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1.  Introduction

   The iCalendar [I-D.ietf-calsify-rfc2445bis] specification defines a
   set of components used to describe calendar data.  One of those is
   the "VALARM" component which appears as a sub-component of "VEVENT"
   and "VTODO" components.  The "VALARM" component is used to specify a
   reminder for an event or to-do.  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 CalDAV [RFC4791] have become more popular, 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".


2.  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
   [RFC2119].

   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.


3.  Extensible syntax for VALARM

   Section 3.6.6 of [I-D.ietf-calsify-rfc2445bis] defines the syntax for
   "VALARM" components and properties within them.  However, as written,



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   it is hard to extend this by adding, e.g., a new property common to
   all types of alarm.  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.

   A "VALARM" calendar component is re-defined by the following
   notation:

        alarmcext  = "BEGIN" ":" "VALARM" CRLF
                     alarmprop
                     "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 is 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




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                   )

        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

                   )



4.  VALARM Unique Identifier

   Several of the other extensions in this specification require
   identifying a specific instance of a "VALARM" component in an
   iCalendar stream.  To aid that, this extension adds a "UID" property
   to "VALARM" components to allow a unique identifier to specified.
   The value of this unique identifier can then be used to refer
   uniquely to the "VALARM" component.




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   The "UID" property defined here follows the definition in Section
   3.8.4.7 of [I-D.ietf-calsify-rfc2445bis].  In particular it MUST be a
   globally unique identifier.

   The "VALARM" component defined in Section 3 is extended here as:

           alarmprop  /= *(

                      ; the following is OPTIONAL,
                      ; but MUST NOT occur more than once

                      uid

                      )


5.  VALARM URI Action

   Currently "VALARM" components have actions for audio, display and
   email.  New types of action are of interest, e.g., SMS, instant
   messaging, etc.  Rather then specify separate actions for these, an
   alternative is to define a "URI" action that allows any URI scheme to
   be used as an action, where it makes sense.  Thus URI schemes for IM
   [RFC3860], SIP [RFC3261], TEL [RFC3966] etc could be used.

   This extension defines a new "URI" property value for use with the
   "ACTION" property in "VALARM" components.  A new set of action
   properties is defined for "VALARM" components based on this new
   action as defined by the syntax below.






















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           actionvalue /= "URI"
                       ; Adds a new action for a "VALARM"

           actionprop  /= uriprop
                       ; Re-defines the "VALARM" component to include
                       ; "uriprop" as a new set of action properties

           uriprop     = *(

                       ; the following is REQUIRED,
                       ; but MUST NOT occur more than once

                       uri /

                       ; 'duration' and 'repeat' are both OPTIONAL,
                       ; and MUST NOT occur more than once each,
                       ; but if one occurs, so MUST the other

                       duration / repeat

                       )



6.  VALARM Agent Property

   With the advent of a standard client/server protocol for calendaring
   and scheduling data ([RFC4791]) there is a need to specify which
   client or server should handle the presentation of an alarm when it
   is triggered.  For example, calendar users want to be able to receive
   alarms at all times, even when their desktop client might be
   unavailable.  Since the server is "always on", a service running on
   the server could monitor alarm status and, when appropriate, trigger
   those alarms.  In addition it may be important for only the server or
   the client to be set to handle an alarm - and in some cases only
   specific servers or clients.

   To address this need, this specification defines an "ALARM-AGENT"
   iCalendar property that can be added to any "VALARM" component.  This
   property specifies whether a client or server or both should be
   responsible for processing the alarm when it triggers.  In addition,
   a "URI" property parameter can be added to uniquely identify the
   client or server that should process the alarm.  This is defined by
   the syntax below.







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           alarmprop  /= *(

                      ; the following is OPTIONAL,
                      ; and MAY occur more than once

                      alarm-agent

                      )

6.1.  Alarm Agent Property

   Property Name:  ALARM-AGENT

   Purpose:  This property specifies whether a client, server, both or
      none gets to process an alarm when it is triggered.

   Value Type:  TEXT

   Property Parameters:  IANA, non-standard, and URI 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 who is responsible for
      processing an alarm when it is triggered.  When the value "SERVER"
      is specified, only a server that has a copy of the event is
      responsible.  When the value "CLIENT" is specified, only a client
      that has a copy of the event is responsible.  When the value
      "BOTH" is specified, either a client or server is responsible.
      When the value "NONE" is specified, neither a client nor server is
      responsible (i.e., the alarm action is never carried out when it
      triggers).

      If the "URI" property parameter is specified for "SERVER" or
      "CLIENT" values, then only the client or server identified by the
      "URI" value is responsible.  Clients or servers that are not
      responsible for the alarm SHOULD NOT process the alarm action when
      it is triggered.  If multiple clients or servers need to be
      specified, then the "ALARM-AGENT" property should be included
      multiple times in the "VALARM" component, with each one containing
      the appropriate "URI" property parameter value to identify each
      client or server.

      In the absence of this property clients and servers can choose to
      process the alarm themselves as appropriate when it triggers.

      This property MAY occur more than once to allow multiple



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      processors of an alarm.

   Format Definition:  This property is defined by the following
      notation:

        alarm-agent     = "ALARM-AGENT" alarmagentparam ":"
                        alarmagentvalue CRLF

        alarmagentparam = *(

                        ; the following is OPTIONAL,
                        ; but MUST NOT occur more than once

                        (";" uriparam) /

                        ; the following is OPTIONAL,
                        ; and MAY occur more than once

                        (";" other-param)

                        )

        alarmagentvalue = "SERVER" / "CLIENT" / "BOTH" / "NONE"
                        / iana-token / x-name

   Example:  The following is an example of this property:

        ALARM-AGENT:SERVER

6.2.  URI Property Parameter

   Property Name:  URI

   Purpose:  This property parameter specifies a URI that is related to
      the property it is applied to.

   Format Definition:  This property is defined by the following
      notation:

        uriparam   = "URI" "=" DQUOTE uri DQUOTE

   Description:  This property parameter is used to specify a URI that
      is associated with the property it is applied to.  Each property
      that allows this parameter to be specified MUST indicate what the
      value of the URI represents.






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   Example:  The following is an example of this property:

        ALARM-AGENT;URI="http://calendar.example.com":SERVER


7.  VALARM Status Property

   There is currently no way for a "VALARM" component to indicate the
   status of the alarm (e.g., whether it has been triggered or not).
   With the advent of a standard client/server protocol for calendaring
   and scheduling data ([RFC4791]) 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 dismissed on the
   others too.

   Finally, with recurring events that have alarms, it is important to
   know when the last alarm in the recurring set was triggered, so that
   the client can determine whether past alarms have been missed.

   To address these needs, this specification adds the following:

   o  a "STATUS" property to "VALARM" components with values to indicate
      wether an alarm is active, inactive, or completed (dismissed).

   o  a "LAST-TRIGGERED" property to "VALARM" components to indicate
      when the alarm was last triggered.

   This is defined by the syntax below.




















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           alarmprop       /= *(

                           ; the following are OPTIONAL,
                           ; but MUST NOT occur more than once

                           status / last-triggered

                           )

           statvalue       /= statvalue-alarm

           statvalue-alarm = "ACTIVE"    ; Indicates alarm is active and
                                         ; waiting to be triggered.
                           / "CANCELLED" ; Indicates alarm is inactive
                                         ; and won't be triggered.
                           / "COMPLETED" ; Indicates alarm has triggered
                                         ; and been dismissed.
           ; Status values for a "VALARM"


7.1.  Last Triggered Property

   Property Name:  LAST-TRIGGERED

   Purpose:  This property specifies the UTC date and time at which the
      corresponding alarm was last triggered.

   Value Type:  DATE-TIME

   Property Parameters:  IANA and non-standard 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
      triggered.  This 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.

   Format Definition:  This property is defined by the following
      notation:









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       last-triggered = "LAST-TRIGGERED" lasttrigparam ":" datetime CRLF

       lasttrigparam  = *(

                        ; the following is OPTIONAL,
                        ; and MAY occur more than once

                        (";" other-param)
                        )

   Example:  The following is an example of this property:

        LAST-TRIGGERED:20090604T084500Z


8.  Snoozing Alarms

   Users often want to "snooze" an alarm.  That process effectively
   creates a new alarm to be triggered a set amount of time after the
   original being "snoozed".  To accomplish this, clients SHOULD create
   a new "VALARM" component within the same component of the "VALARM"
   that was triggered and is being "snoozed".  The new "VALARM" MUST be
   set to trigger by the user's chosen "snooze" interval after the
   original alarm triggered.


9.  Default Alarms in CalDAV

   Users often want to have a default alarm applied to new events that
   they create or to new invitations that arrive on a CalDAV [RFC4791]
   server.  Since this behavior is expected to occur no matter which
   client a user is using, it is beneficial if the server itself is
   responsible for managing the creation of the default alarm.

   This specification defines four new WebDAV properties that can be
   used to specify different sets of default alarms.  Clients can store
   "VALARM" components in these properties to setup the defaults.  When
   a new event or todo is created on the server, the server will
   automatically add the default, as appropriate.  When a new event or
   todo invitation is delivered to the calendar user, the server will
   automatically add the default alarm, as appropriate.

   The four new WebDAV properties are:

   CALDAV:default-alarm-vevent-datetime  A default alarm applied to
      "VEVENT" components whose "DTSTART" property value is "DATE-TIME"





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   CALDAV:default-alarm-vevent-date  A default alarm applied to "VEVENT"
      components whose "DTSTART" property value is "DATE"

   CALDAV:default-alarm-vtodo-datetime  A default alarm applied to
      "VTODO" components whose "DUE" or "DTSTART" property value is
      "DATE-TIME"

   CALDAV:default-alarm-vtodo-date  A default alarm applied to "VTODO"
      components whose "DUE" or "DTSTART" property value is "DATE", or
      when neither of those properties is present

   The WebDAV properties are defined on a calendar user's "calendar
   home" collection, or on individual calendar collections.  When events
   or tasks are created in a calendar, the server will first inspect the
   WebDAV properties on the calendar collection to see if the
   appropriate property is present.  If it is, the server will use the
   value of that property to set the default in the new component.  If
   the property is not present on the calendar collection, the server
   will determine whether the property is present on the calendar home
   collection that contains the calendar collection.  If present on the
   calendar home, the property value there is used as the default.

   The WebDAV property value MUST be one or more "VALARM" components or
   the empty string.  If an empty string is used, no default alarms are
   applied.  TODO: more detail here


10.  Security Considerations

   TODO:talk about importance of stripping VALARMs from incoming iTIP.
   Talk about VALARMs being used to "spam" - particularly nasty if the
   server handles it.


11.  IANA Considerations

   TODO: tables registering new properties, parameters and values.


12.  Acknowledgments

   This specification came about via discussions at the Calendaring and
   Scheduling Consortium.  Also, thanks to the following for providing
   feedback: Bernard Desruisseaux, Mike Douglass, Ciny Joy.


13.  References




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13.1.  Normative References

   [I-D.ietf-calsify-rfc2445bis]
              Desruisseaux, B., "Internet Calendaring and Scheduling
              Core Object Specification (iCalendar)",
              draft-ietf-calsify-rfc2445bis-10 (work in progress),
              April 2009.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4791]  Daboo, C., Desruisseaux, B., and L. Dusseault,
              "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
              March 2007.

13.2.  Informative References

   [RFC3261]  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.

   [RFC3860]  Peterson, J., "Common Profile for Instant Messaging
              (CPIM)", RFC 3860, August 2004.

   [RFC3966]  Schulzrinne, H., "The tel URI for Telephone Numbers",
              RFC 3966, December 2004.


Appendix A.  Change History (To be removed by RFC Editor before
             publication)

   Changes in -01:

   1.  Removed DESCRIPTION as an allowed property in the URI alarm.

   2.  Added statement about what to do when ALARM-AGENT is not present.

   3.  Allow multiple ALARM-AGENT properties to be present.

   4.  Removed SNOOZE-UNTIL - snoozing now accomplished by creating a
       new VALARM.

   5.  Remove VALARM by reference section.

   6.  Added more detail to CalDAV default alarms.





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Author's Address

   Cyrus Daboo
   Apple Inc.
   1 Infinite Loop
   Cupertino, CA  95014
   USA

   Email: cyrus@daboo.name
   URI:   http://www.apple.com/









































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