Network Working Group                       Steve Silverberg, Microsoft
INTERNET-DRAFT                                  Steve Mansour, Netscape
Calendaring and Scheduling Working Group            Frank Dawson, Lotus
<draft-ietf-calsch-itip-01.txt>
<ietf-draft-calsch-itip-02.txt>            Ross Hopson, ON Technologies
Expires in six months from                              October 24,1997                             November 21,1997

       iCalendar Transport-Independent Interoperability Protocol
                                 (iTIP)
        Scheduling Events, BusyTime, To-dos and Journal Entries

Status of this Memo

   This document is an Internet-Draft. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups. Note that other groups MAY also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months. Internet-Drafts MAY be updated, replaced, or made obsolete by
   other documents at any time. It is not appropriate to use Internet-
   Drafts as reference material or to cite them other than as a "working
   draft" or "work in progress".

   To learn the current status of any Internet-Draft, please check the
   1id-abstracts.txt listing contained in the Internet-Drafts Shadow
   Directories on ds.internic.net (US East Coast), nic.nordu.net
   (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific
   Rim).

   Distribution of this document is unlimited.

   Copyright (C) The Internet Society 1997. 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.

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   Table of Contents

1    7
Introduction    8
Introduction   9
 1.1 Formatting Conventions  8   9
 1.2 Related Documents  9   10
 1.3 Calendar Roles9 Roles 10
 1.4 iTIP Transactions  10   11
2 Interoperability Models     11     12
 2.1 Application Protocol    11     12
  2.1.1 Calendar Entry State 12  13
3 Application Protocol Elements    12    13
 3.1 Methods For "VEVENT" Calendar Component13 Component 15
  3.1.1 PUBLISH    14     15
  3.1.2 REQUEST    15     16
    3.1.2.1 REQUEST for Rescheduling an Event    16     18
    3.1.2.2 REQUEST for Update or Reconfirmation of an Event    16     18
    3.1.2.3 REQUEST for Delegating an Event from an "Attendee" to
    another CU17 CU 18
    3.1.2.4 REQUEST for Delegating role of "Organizer" to another CU 17  19
    3.1.2.5 REQUEST for Changing the "Organizer" from one CU to another
     18
     19
    3.1.2.6 REQUEST for Changing the "Owner"18 "Owner" 19
    3.1.2.7 REQUEST Forwarded To An Uninvited Calendar User18 User 20
    3.1.2.8 REQUEST Updated Attendee Status 18  20
  3.1.3 REPLY 18  20
  3.1.4 CANCEL19 CANCEL 21
  3.1.5 REFRESH    20     22
  3.1.6 COUNTER    21     23
  3.1.7 DECLINECOUNTER  22   24
 3.2 Methods For VFREEBUSY Component   23    25
  3.2.1 PUBLISH    24     26
  3.2.2 REQUEST    25     27
  3.2.3 REPLY 26  28
 3.3 Methods For VTODO Component  27   29
  3.3.1 PUBLISH    28     30
  3.3.2 REQUEST    29     31
    3.3.2.1 REQUEST for Rescheduling a VTODO30 VTODO 32
    3.3.2.2 REQUEST for Update or Reconfirmation of a VTODO30 VTODO 33
    3.3.2.3 REQUEST for Delegating a VTODO  31   33
    3.3.2.4 REQUEST Forwarded To An Uninvited Calendar User31 User 34
    3.3.2.5 REQUEST Updated Attendee Status 32  34
  3.3.3 REPLY 32  35
  3.3.4 CANCEL33 CANCEL 36
  3.3.5 REFRESH    34     37
  3.3.6 COUNTER    35     37
  3.3.7 DECLINECOUNTER  36   38
 3.4 Methods For VJOURNAL Component    37     39
  3.4.1 PUBLISH    37     40
  3.4.2 CANCEL38 CANCEL 41
  3.4.3 REFRESH    39     41
 3.5 Status Replies39
 3.6 Implementation Considerations41 Replies 42

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 3.6 Implementation Considerations 44
  3.6.1 Working With Recurrence Instances   41    44
  3.6.2 Attendee Property Considerations    42     45
  3.6.3 When To Refresh An Event  43   46
  3.6.4 Timezones  43   46
  3.6.5 Alarms43 Alarms 46
  3.6.6 SUMMARY Property43 Property 46
  3.6.7 X-Tokens   43    47
4 Examples     44     47
 4.1 Published Event Examples44 Examples 47
  4.1.1 A Minimal Published Event 44  47
  4.1.2 Changing A Published Event45 Event 48
  4.1.3 Canceling A Published Event    45     49
  4.1.4 A Rich Published Event    46     49
  4.1.5 Anniversaries or Events attached to entire days    47     51
 4.2 Group Event Examples    48     51
  4.2.1 A Group Event Request48 Request 52
  4.2.2 Reply To A Group Event Request 49  52
  4.2.3 Update An Event 49  53
  4.2.4 Countering an Event Proposal   50    53
  4.2.5 Delegate An Event    51     55
  4.2.6 Delegate Accepts the Meeting   54    58
  4.2.7 Delegate Declines the Meeting  54   58
  4.2.8 Forwarding an Event Request    55     59
  4.2.9 Cancel A Group Event 55  59
 4.3 Busy Time Examples 56  60
  4.3.1 Request Busy Time    56     60
  4.3.2 Reply To A Busy Time Request   57    61
 4.4 Recurring Event and Time Zone Examples 57  61
  4.4.1 A Recurring Event Spanning Time Zones    57     61
  4.4.2 Modify A Recurring Instance    59     63
  4.4.3 Cancel A Recurring Instance    60     64
  4.4.4 Cancel An Exception  60   65
  4.4.5 Cancel Recurring Event    61     65
  4.4.6 Change All Future Instances    61     65
  4.4.7 Add A New Instance To A Recurring Event  62   66
  4.4.8 Counter An Instance Of A Recurring Event 62  67
  4.4.9 Error Reply To A request  63   67
 4.5 Group To-do Examples    64     68
  4.5.1 A VTODO Request 65  69
  4.5.2 A VTODO Reply   65    70
  4.5.3 A VTODO Refresh 65  70
  4.5.4 A Refresh Reply: Percent-Complete   66    71
  4.5.5 A Refresh Reply: Completed66 Completed 71
  4.5.6 An Updated VTODO Request  66   71
  4.5.7 A Recurring VTODOs   67    72
    4.5.7.1 Request for a Recurring VTODO   67    72
    4.5.7.2 Calculating due dates in recurring VTODOs 68  72
    4.5.7.3 Replying to an instance of a recurring VTODO   68    73
 4.6 Journal Examples   68    73
 4.7 Other Examples69 Examples 74
  4.7.1 Event Refresh   69    74
  4.7.2 Bad RECURRENCE-ID    69     74
5 Application Protocol Fallbacks   70
 5.1 Partial Implementation  70   75

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 5.1 Partial Implementation   75
  5.1.1 Event-Related Fallbacks   70    76
  5.1.2 To-Do-Related Fallbacks   72    77
  5.1.3 Journal-Related Fallbacks 74  79
 5.2 Latency Issues75 Issues 80
  5.2.1 Cancellation of an Unknown Calendar Component.75 Component. 80
  5.2.2 Unexpected Reply from an Unknown Delegate75 Delegate 80
 5.3 Sequence Number    76     81
6 Security Considerations     76     81
 6.1 Security Threats   76    81
  6.1.1 Spoofing the "Organizer"  76   81
  6.1.2 Spoofing the "Attendee"   76    82
  6.1.3 Eavesdropping   77    82
  6.1.4 Flooding a Calendar  77   82
  6.1.5 Procedural Alarms    77     82
 6.2 Recommendations    77     82
  6.2.1 Use of [RFC1847] to secure iTIP transactions  77   82
  6.2.2 Implementation Controls   77    83
7 Acknowledgments   78   83
8 Bibliography 78 83
9 Authors Addresses 79 84
10 Full Copyright Statement   80   85

1

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   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 interoperable methods of communications between systems that
   use this protocol.

   This protocol is based on requests sent from an originator and
   conveyed to one or more recipients. A recipient of a request MAY
   reply, in order to update their status and MAY also return
   transaction/request status information. The protocol also supports
   the ability for the entry originator to modify or cancel the original
   entry. The elements of the protocol also include the notion of user
   roles.

1.1 Formatting Conventions

   In order to refer to elements of the calendaring and scheduling
   model, core object or interoperability protocol defined in [ICMS],
   [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 interopreted as described in [RFC 2119].

   Calendaring and scheduling roles defined by [ICMS] 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"
   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

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   by this memo are referred to with capitalized text, either alone or
   followed by the word "value".

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   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;

     [ICMS] - describes the abstract model and defines common terms and
     concepts;

     [ICAL] - specifies the objects, data types, properties and property
     parameters used in the protocols, along with the methods for
     representing and encoding them;

     [IRIP] - specifies an Internet real time protocol binding for
     [ITIP].

     [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 Calendar Roles

   Roles are a behavior or set of activities performed by particular
   groups of users or agents at a given state of the calendar
   transaction. This specification describes 4 roles that determine a
   range of actions and responsibilities specific to each role.

+=====================================================================+
|  Role Name   |  Description                                         |
|=====================================================================|
| Owner        | The calendar entry owner is the only Calendar User   |
|              | allowed to directly modify an entry using the iTIP   |
|              | protocol. However, the Owner MAY delegate or         |
|              | assign an Organizer to manage the entry on their     |
|              | behalf. Usually, a calendar entry Owner is also the  |
|              | Organizer.                                           |
|              |                                                      |
| Organizer    | The Organizer controls manipulation of the calendar  |
|              | entry. In most cases, the Owner and the Organizer    |
|              | are the same Calendar User.                          |
|              |                                                      |
| Attendee     | An Attendee is a Calendar User associated with       |

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|              | a calendar entry via a Request method issued by an   |
|              | Organizer or another Attendee. Attendees are not     |
|              | capable of directly manipulating calendar entries,   |
|              | but MUST act through the Organizer.                  |
|              |                                                      |
| Delegate     | A Delegate is a proxy that acts on behalf of another |
|              | Calendar User. ITIP addresses two forms of           |

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|              | delegation:                                          |
|              | 1) An Owner MAY delegate or re-assign an Organizer   |
|              | to manage a calendar entry                           |
|              | 2) An Attendee MAY delegate a calendar entry request |
|              | to another Calendar User.                            |
+=====================================================================+

1.4 iTIP Transactions

   This protocol defines seven methods for exchanging [ICAL] objects for
   the purposes of group calendaring and scheduling between "Calendar
   Users". The methods are defined below and their usage and semantics
   are outlined 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 MAY require the receiver to respond using   |
|                | the 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.                               |
|                |                                                  |
| CANCEL         | The Cancel method is used to cancel an existing  |
|                | calendar entry such as a VEVENT or VTODO.        |
|                |                                                  |
| 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         |

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|                | proposed Event time or change the due date for a |
|                | VTODO.                                           |
| DECLINE-       |                                                  |
| COUNTER        | Used by the "Organizer" to decline the proposed  |
|                | counter-proprosal by an "Attendee"               |
+================+==================================================+

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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
   in section 1.4. The Transport Protocol defines how the iCalendar
   objects are sent between the sender and receiver. This document
   focuses on the Application Protocol.

   The connection between Sender and Receiver in the diagram below
   refers to the Application Protocol. In particular, the iCalendar
   objects passed from the Sender to the Receiver which conform to those
   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 "CUA"  or CS. These variants are
   detailed in the Model document [ICMS]

   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. If a
   capability is not available on a particular transport binding, iTIP
   provides a mechanism for indicating so.

              +------------------------------------------+
              |                   iTIP                   |
              +------------------------------------------+
              |Real-time | Store-and-Fwd | Other         |
              |Transport | Transport     | Transports... |
              +------------------------------------------+

2.1 Application Protocol

   The model for the application protocol is centered with the
   "Organizer" of the calendar entry. That is, the "Organizer" of a

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   Calendar entry sends a request to one or more "Attendees". The
   "Attendees" then reply to the "Organizer". The "Organizer" maintains
   the status of the event.

   The "Owner" is usually the "Organizer" of the calendar entry.
   However, the "Owner" MAY delegate or assign an "Organizer" to manage
   the calendar entry on their behalf. In cases where the "Owner" has
   delegated to another "Organizer", the "Owner" must still be specified
   in associated "REQUEST" and "COUNTER" methods.

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   The data sources for the application protocol are the "Calendar
   Users". Examples of these users are the "Organizer" and "Attendees"
   of an iCalendar event. The data objects are the iCalendar objects
   that are exchanged between "Calendar Users".

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" MAY either set the "STATUS"
   property to TENTATIVE or CONFIRMED values. The "Organizer" MAY also
   set the "STATUS" property to CANCELLED value by sending a "CANCEL"
   method to each "Attendee".

   The state of a particular "Attendee" relative to an entry is defined
   by the "STATUS" property parameter in the "ATTENDEE" property for
   that "Attendee". When an "Organizer" sends out an entry, the state
   associated with each "Attendee" is NEEDS-ACTION. Each "Attendee" MAY
   modify their "ATTENDEE" property "STATUS" parameter to an appropriate
   value and send it back to the "Organizer" in a "REPLY" message.

3 Application Protocol Elements

   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  |  Yes     |   No      |
          |Cancel   |  Yes   |  Yes  |  Yes     |   No      |
          |Reply    |  Yes   |  Yes  |  No      |   Yes     |
          |Counter  |  Yes   |  Yes  |  No      |   No      |

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          |Decline- |        |       |          |           |
          |Counter  |  Yes   |  Yes  |  No      |   No      |
          +=================================================+

   Each method type is defined in terms of its associated properties.
   Some properties are required, some are optional and others are
   excluded. The property restrictions are expressed in this memo using
   the following formal notation:

     prop-restriction    = "(" description component method
               1*MUST-component *MAY-component *not-component ")"

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     description    = "DESCRIPTION" *ws text
     component      = "COMPONENT" *ws ("CALPROPOS" / "VEVENT" /
                      "VTODO" / "VJOURNAL")
     method         = "METHOD" *ws <any of the methods defined in this
                       memo for the associated calendar component>

     MUST-component = "MUST COMPONENT =" *ws ("VEVENT" / "VTODO" /
                      "VJOURNAL" / "VTIMEZONE" / "VALARM" /
                      "VFREEBUSY" / "X-TOKEN")
                      *ws "(" [ws] 1*MUST-props *ws
                      *MAY-props *ws *not-props *ws ")"

     MAY-component  = "MAY COMPONENT =" *ws ("VEVENT" / "VTODO" /
                      "VJOURNAL" / "VTIMEZONE" / "VALARM" /
                      "VFREEBUSY" / "X-TOKEN")
                      *ws "(" [ws] ((*MUST-props *ws
                      *MAY-props *ws *not-props *ws) / any) ")"

     not-component  = "NOT COMPONENT =" *ws ("VEVENT" / "VTODO" /
                      "VJOURNAL" / "VTIMEZONE" / "VALARM" /
                      "VFREEBUSY" /"X-TOKEN")

     MUST-props     = "MUST PROPERTY =" *ws restriction-list
     MAY-props      = "MAY PROPERTY =" *ws (restriction-list / any)
     not-props      = "NOT PROPERTY =" *ws (restriction-list)

     restriction-list    = restriction
                         / restriction *ws "," *ws restriction
     restriction    = property-name
                      [*ws "{" parm-or-val-restriction "}"]
     property-name  = <any of the valid properties for the component>
     parm-or-val-restriction  = <a text string description of a
                    constraint on the property parameters
                    or values>
     any       = "ANY"  -- Specifies that any permissible
                 properties are allowed - -

     ws        = HTAB / SPACE

     HTAB      = <Horizontal TAB character>
     SPACE     = <Required Space character>

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3.1 Methods For "VEVENT" Calendar Component

   This section defines the property set restrictions for the method
   types that are applicable to the "VEVENT" calendar component. Each of
   the methods is defined using a grammar that clarifies the property
   constraints that define the particular method.

   The following summarizes the methods that are defined for the
   "VEVENT" calendar component.

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   +================+==================================================+
   | 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 MAYdegrade the event to view it as an    |
   |                | PUBLISH.                                         |
   | REPLY          | Reply to an event request. Clients MAYset their  |
   |                | status to                                        |
   |                | ACCEPTED, DECLINED, TENTATIVE, DELEGATED.        |
   | CANCEL         | Cancel an existing event request.                |
   | REFRESH        | A request sent to an  by an "Attendee"           |
   |                | "Organizer" asking                               |
   |                | for the latest version of an event to be resent  |
   |                | to the requester.                                |
   | COUNTER        | Counter a REQUEST with an alternative proposal.  |
   | DECLINECOUNTER | Decline a counter proposal by an "Attendee".     |
   +================+==================================================+

3.1.1     PUBLISH

   The "PUBLISH" method in a "VEVENT" calendar component provides an
   unsolicited posting of an iCalendar object. Any "Calendar User" MAY
   add the published components to their calendar. It requires and
   accepts no responses to the "Organizer". Its expected usage is for
   encapsulating an arbitrary event or to-do as an iCalendar object. The
   "Organizer" MAY subsequently update (with another "PUBLISH" 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:

     (DESCRIPTION "Event - Publish" COMPONENT "VEVENT" METHOD "PUBLISH

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     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"PUBLISH"})
     MUST COMPONENT = VEVENT (
          MUST PROPERTY = ATTENDEE{ROLE=OWNER and ORGANIZER if
               different}, DESCRIPTION{MAY BE NULL},DTSTAMP, DTSTART,
               SEQUENCE{IF NE 0}, UID
          MAY PROPERTY = ATTACH, ATTENDEE{other than ROLE=OWNER |
               ORGANIZER}, CATEGORIES, CLASS, COMMENT, CONTACT
               CREATED, DTEND, EXDATE, EXRULE, GEO, LAST-MODIFIED,
               LOCATION,PRIORITY, RELATED-TO, RDATE, RECURRENCE-ID,
               RESOURCES, RRULE, SEQUENCE{IF EQ 0},
               STATUS{TENTATIVE/CONFIRMED/CANCELLED},
               SUMMARY{MAYBE NULL}, URL

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          NOT PROPERTY = REQUEST-STATUS, TRANSP)
     MAY COMPONENT = VTIMEZONE (
          MUST PROPERTY = DTSTART, TZOFFSET
          MAY PROPERTY = COMMENT, DAYLIGHT, (RDATE / RRULE), TZNAME,
          NOT PROPERTY = CREATED)
     MAY COMPONENT = VALARM (
          MUST PROPERTY = CATEGORIES, DTSTART, DSTART, DURATION, REPEAT
          MAY PROPERTY = ATTACH, DESCRIPTION, SUMMARY
          NOT PROPERTY = COMMENT, CREATED, LAST-MODIFIED, RELATED-TO,
               URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VTODO
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     )

3.1.2     REQUEST

   The "REQUEST" method in a "VEVENT" calendar component provides the
   following scheduling functions:

      

      . Invite "Attendees" to an event;

      

      . Reschedule an existing event;

      

      . 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;

      

      . For an existing "VEVENT" calendar component, delegate the role
        of "Attendee" to another "Calendar User";

      

      . For an existing "VEVENT" calendar component, delegate the role
        of "Organizer" to another "Calendar User".

Silverberg/Mansour/Dawson/Hopson  14                   Expires MAY 1998
   The originator of the "REQUEST" method is the "Organizer" of the
   event. Normally this is the "Owner" of the event. The recipient of
   the "REQUEST" method is the "Calendar User" invited to the event,
   called the "Attendee". The "Attendee" uses the "REPLY" method to
   convey their attendance status to the "Organizer" of a VEVENT
   "REQUEST".

   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 either a rescheduling, an update, or a reconfirm of
   the "VEVENT" calendar component.

   If the "Organizer" of the "REQUEST" method is not authorized to make
   an event request on the "Attendee's" calendar system, then an
   exception is returned in the "REQUEST-STATUS" property of a
   subsequent "REPLY" method, but no scheduling action is performed.

Silverberg/Mansour/Dawson/Hopson  13                   Expires MAY 1998

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "Event - Request" COMPONENT "VEVENT" METHOD "REQUEST"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"REQUEST"})
     MUST COMPONENT = VEVENT (
          MUST PROPERTY = ATTENDEE{ ROLE=OWNER and ORGANIZER if
               different and "STATUS parameter absent or
               STATUS=NEEDS-ACTION on Attendees}, DESCRIPTION{MAYBE
               NULL}, DTSTAMP,DTSTART,SEQUENCE{IF NE 0}, UID
          MAY PROPERTY = ATTACH, CATEGORIES, CLASS, COMMENT, CONTACT, CREATED,
               DTEND, EXDATE, EXRULE, GEO, LAST-MODIFIED, LOCATION,
               PRIORITY, RDATE, RECURRENCE-ID, RELATED-TO, RESOURCES,
               RRULE, SEQUENCE{IF EQ 0}, STATUS{TENTATIVE/CONFIRMED
               /CANCELLED}, SUMMARY {MAYBE NULL}, TRANSP, URL
          NOT PROPERTY = REQUEST-STATUS)
     MAY COMPONENT = VTIMEZONE (
          MUST PROPERTY = DTSTART, TZOFFSET
          MAY PROPERTY = COMMENT, DAYLIGHT, (RDATE / RRULE), TZNAME
          NOT PROPERTY = CREATED)
     MAY COMPONENT = VALARM (
          MUST PROPERTY = CATEGORIES, DTSTART, DSTART, DURATION, REPEAT
          MAY PROPERTY = ATTACH, DESCRIPTION, SUMMARY
          NOT PROPERTY = COMMENT, CREATED, LAST-MODIFIED, RELATED-TO,
               URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VTODO
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     )

Silverberg/Mansour/Dawson/Hopson  15                   Expires MAY 1998

3.1.2.1   REQUEST for 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 it's 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" 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.

3.1.2.2   REQUEST for Update 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

Silverberg/Mansour/Dawson/Hopson  14                   Expires MAY 1998
   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.

   Unsolicited "REQUEST" methods MAY also be sent by the "Organizer" of
   an event. The unsolicited "REQUEST" methods MAY be used to either
   update the details of the event, without rescheduling it, to update
   the "STATUS" property parameter of "Attendees", or to reconfirm the
   event.

3.1.2.3   REQUEST for Delegating an Event from an "Attendee" to another
      CU

   The "REQUEST" method MAY be used to delegate an event to another
   "Calendar User". The method is used to delegate the "Attendee's" role
   (i.e., "Organizer" or "Attendee") for an event. The "REQUEST" method
   for delegation is sent by one of the "Attendees" of an existing event
   request to some other "Calendar User". In order to avoid scheduling
   loops, the method MUST NOT be sent from an "Attendee" back to the
   "Organizer" of the event. An "Attendee" MAY NOT delegate to the
   "Organizer" of the event.

   For the purposes of this description, the "Attendee" delegating the
   event is referred to as the "delegator". The "Attendee" receiving the
   delegation request is referred to as the "delegatee".

Silverberg/Mansour/Dawson/Hopson  16                   Expires MAY 1998
   The "delegator" of an event MUST forward the existing "REQUEST"
   method for an event to the "delegatee". The event description MUST
   include the "delegator's" up-to-date event definition. The "REQUEST"
   method MUST also include an "ATTENDEE" property with the calendar
   address of the "delegatee". The "delegator" MUST also send a "REPLY"
   method back to the "Organizer" with the "delegator's" "Attendee"
   property "STATUS" parameter value set to DELEGATED. In addition, the
   "DELEGATED-TO" parameter SHOULD be included with the calendar address
   of the "delegatee". A response to the delegation "REQUEST" is sent
   from the "delegatee" to the "Organizer" and optionally, to the
   "delegator". The "REPLY" method from the "delegatee" SHOULD include
   their "ATTENDEE" property with the "DELEGATED-FROM" parameter value
   of the "delegator's"calendar address.

   The delegation "REQUEST" method MUST assign the values of the "RSVP"
   and "EXPECT" property parameters associated with the "delegator's"
   "ATTENDEE" property to that of the "delegatee's" "ATTENDEE" property.
   For example if the "delegator's" "ATTENDEE" property specifies
   "RSVP=TRUE;EXPECT=REQUEST", then the "delegatee's" "ATTENDEE"
   property MUST specify "RSVP=TRUE;EXPECT=REQUEST".

3.1.2.4   REQUEST for Delegating role of "Organizer" to another CU

   If the "Owner" of an existing "VEVENT" calendar component wishes to
   delegate the role of "Organizer" to another CU, they MAY issue

Silverberg/Mansour/Dawson/Hopson  15                   Expires MAY 1998
   another "REQUEST" method that notifies all "Attendees" and the new
   "Organizer" of this change. The "Owner MUST modify several property
   parameters of the "ATTENDEE" property including the "ROLE", where the
   role of "Owner" and "Organizer" MUST be specified. Additionally, the
   "DELEGATED-TO" and "DELEGATED-FROM" parameters MUST specify the
   "Organizer" and "Owner" calendar addresses. The "Owner" MAY request
   reconfirmation by incrementing the "SEQUENCE" property and setting
   the "RSVP" property parameter to TRUE. This will cause a
   reconfirmation to be sent to the new organizer.

3.1.2.5   REQUEST for Changing the "Organizer" from one CU to another

   An "Owner" of an existing "VEVENT" calendar component MAY change the
   "Organizer" from one "CU" to another by sending a "REQUEST" method.
   The "ROLE" property parameter value of ORGANIZER MUST be assigned to
   the new "Organizer". If the old "Organizer" is still an "Attendee"
   then "ROLE" property parameter for that "CU" MUST be set to ATTENDEE.

3.1.2.6   REQUEST for Changing the "Owner"

   This memo does not support the notion of changing ownership of a
   "VEVENT" calendar component.

Silverberg/Mansour/Dawson/Hopson  17                   Expires MAY 1998

3.1.2.7   REQUEST Forwarded To An Uninvited Calendar User

   An "Attendee" invited to an event MAY invite another uninvited
   "Calendar User" to the event. The invited "Attendee" accomplishes
   this scheduling action by forwarding the original "REQUEST" method to
   the uninvited "Calendar User". The forwarded "REQUEST" method need
   not include a new "ATTENDEE" property for the uninvited "Attendee".
   Whether the uninvited "Calendar User" is added to the attendee list,
   and thus informed of changes to the "VEVENT" calendar component is an
   implementation issue.

3.1.2.8   REQUEST Updated Attendee Status

   An "Organizer" of an event MAY also request an updated status from
   one of the "Attendees". This is achieved by the "Organizer" sending a
   "REQUEST" method to the "Attendee" with the "ATTENDEE;RSVP=TRUE"
   property sequence. 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 an updated status. The recipient SHOULD
   respond with a "REPLY" method indicating their current status with
   respect to the "REQUEST".

   This capability MAY also be achieved by the "Organizer" sending the
   "REFRESH" method to the "Attendees".

3.1.3     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 in to provide a delegation response,

Silverberg/Mansour/Dawson/Hopson  16                   Expires MAY 1998
   the "delegator" SHOULD include the calendar address of the
   "delegatee" on the "DELEGATED-TO" property parameter of the
   "delegator's" "ATTENDEE" property. The "delegatee" SHOULD include the
   calendar address of the "delegator" on the "DELEGATED-FROM" property
   parameter of the "delegatee'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
   "Calendar User" not in the original "REQUEST". For example, a "REPLY"
   method MAY be received from a "delegatee" to an event. In addition,
   the "REPLY" method MAY be received from an unknown "Calendar User",
   forwarded the "REQUEST" from an invited "Attendee". This uninvited
   "Attendee" MAY be accepted, or the "Organizer" MAY cancel the event
   for the uninvited "Attendee" by sending them a "CANCEL" method to the
   univited "Attendee".

Silverberg/Mansour/Dawson/Hopson  18                   Expires MAY 1998
   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "Event - Reply" COMPONENT "VEVENT" METHOD "REPLY"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"REPLY"})
     MUST COMPONENT = VEVENT (
          MUST PROPERTY = ATTENDEE{MUST be address of ATTENDEE
               replying}, DTSTAMP, SEQUENCE{IF NE 0}, UID{UID
               associated with original REQUEST}
          MAY PROPERTY = COMMENT{provides comment from ATTENDEE to
               "Organizer"}, EXDATE, EXRULE, RECURRENCE-ID, REQUEST-
               STATUS, SEQUENCE{IF EQ 0}, SUMMARY {MAYBE NULL}, URL
          NOT PROPERTY = ATTACH, CATEGORIES, CLASS, CONTACT, CREATED,
               DESCRIPTION, DTSTART, DTEND, GEO, LAST-MODIFIED,
               PRIORITY, RELATED-TO, RESOURCES, RDATE, RRULE, STATUS,
               SUMMARY, TRANSP) TRANSP, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VTODO
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     NOT COMPONENT = VTIMEZONE
     NOT COMPONENT = VALARM
     )

3.1.4     CANCEL

   The "CANCEL" method in a "VEVENT" calendar component is used to send
   a cancellation notice of an existing event request to the
   "Attendees". The message is sent by the "Organizer" of an event to
   the "Attendees" of the event. For a recurring event, either the whole
   event or instances of an event MAY be cancelled. To cancel the
   complete range of recurring event, the "UID" property value for the
   event MUST be specified in the "CANCEL" method. In order to cancel an
   individual instance of the event, the "RECURRENCE-ID" property value

Silverberg/Mansour/Dawson/Hopson  17                   Expires MAY 1998
   for the event MUST be specified in the "CANCEL" method. In order to
   cancel a sequence of recurring events, either the"RECURRENCE-ID"
   property for the first event instance in the sequence MUST be
   specified with the "RANGE" property parameter value of THISANDPRIOR
   or THISANDFUTURE to indicate cancellation of the event instances
   before and after the first event instance, respectively. Lastly,
   individual recurrence instances MAY be cancelled by specifying
   multiple"RECURRENCE-ID" properties corresponding to the instances to
   be cancelled.

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "Event - Cancel" COMPONENT "VEVENT" METHOD "CANCEL"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"CANCEL"})

Silverberg/Mansour/Dawson/Hopson  19                   Expires MAY 1998
     MUST COMPONENT = VEVENT (
          MUST PROPERTY = DTSTAMP, SEQUENCE{IF NE 0}, UID{UID
               associated with original REQUEST}
          MAY PROPERTY = COMMENT{provides comment from "Organizer" to
               ATTENDEE}, EXDATE, EXRULE, RECURRENCE-ID, SEQUENCE{IF EQ
               0}, STATUS{CANCELLED}
          NOT PROPERTY = ATTACH, ATTENDEE, CATEGORIES, CLASS, CONTACT, CREATED,
               DESCRIPTION, DTSTART, DTEND, GEO, LAST-
               MODIFIED, LAST-MODIFIED,
               PRIORITY, RDATE, RELATED-TO, RESOURCES, REQUEST-STATUS,
               RRULE, SUMMARY, TRANSP, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VTODO
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     NOT COMPONENT = VTIMEZONE
     NOT COMPONENT = VALARM
     )

3.1.5     REFRESH

   The "REFRESH" method in a "VEVENT" calendar component is used by
   "Attendees" of an existing event to request an updated description
   from the event "Organizer". The "REFRESH" method MUST specify the
   "UID" property corresponding to the event needing update. A
   recurrence instance of an event MAY be requested by specifying the
   "RECURRENCE-ID" property corresponding to the associated event. The
   "Organizer" MUST respond with the latest description and version of
   the event. This method is intended to facilitate machine processing
   of event update requests by an "Attendee".

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "Event - Refresh" COMPONENT "VEVENT" METHOD "REFRESH"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"REFRESH"})
     MUST COMPONENT = VEVENT (

Silverberg/Mansour/Dawson/Hopson  18                   Expires MAY 1998
               MUST PROPERTY = ATTENDEE{address of requestor}, DTSTAMP,
               SEQUENCE{IF NE 0}, UID{UID associated with original
               REQUEST}
          MAY PROPERTY = COMMENT{provides comment from ATTENDEE to
               "Organizer"}, RECURRENCE-ID, SEQUENCE{IF EQ 0}
          NOT PROPERTY = ATTACH, CATEGORIES, CLASS, CONTACT, CREATED,
               DESCRIPTION, DTSTART, DTEND, EXDATE, EXRULE, GEO,
               LAST-MODIFIED, PRIORITY, RDATE,RELATED-TO, RESOURCES,
               REQUEST-STATUS, RRULE,SUMMARY, STATUS, TRANSP, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VTODO
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     NOT COMPONENT = VTIMEZONE
     NOT COMPONENT = VALARM

Silverberg/Mansour/Dawson/Hopson  20                   Expires MAY 1998
     )

3.1.6     COUNTER

   The "COUNTER" method in a "VEVENT" calendar component is used by an
   "Attendee" of an existing event to submit to the "Organizer" a
   counter proposal to the event description. The "Attendee" MUST send
   the message to the "Organizer" of the event.

   The counter proposal is an iCalendar object consisting of a VEVENT
   calendar component describing the complete description of the
   alternate event.

   The "Organizer" rejects the counter proposal by sending the
   "Attendee" a VEVENT "DECLINECOUNTER" "DECLINE-COUNTER" method. The "Organizer" accepts
   the counter proposal by sending all of the "Attendees" to the event a
   VEVENT "REQUEST" method rescheduling the event. In the later case,
   the "Organizer" SHOULD reset the individual "RSVP" property parameter
   values to TRUE on each "ATTENDEE" property in order to force a
   response by the "Attendees".

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "Event - Counter Proposal" COMPONENT "EVENT"
     METHOD "COUNTER"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"COUNTER"})
     MUST COMPONENT = VEVENT (
          MUST PROPERTY = ATTENDEE{STATUS parameter absent or
               STATUS=NEEDS ACTION, Owner and Organizer if different,
               MAY also be used to propose other  "Attendees"},
               DESCRIPTION{MAYBE NULL}, DTSTAMP, DTSTART,
               SEQUENCE{IF NE 0}, UID{MUST be the UID associated with
               the REQUEST being countered}
          MAY PROPERTY = ATTACH, CATEGORIES, CLASS, COMMENT{provides a
               comment from the ATTENDEE to the "Organizer"}, CONTACT, CREATED,
               DTEND, EXDATE, EXRULE, GEO, LAST-
               MODIFIED, LAST-MODIFIED, LOCATION,
               PRIORITY, RDATE, RECURRENCE-ID,

Silverberg/Mansour/Dawson/Hopson  19                   Expires MAY 1998 RELATED-TO, RESOURCES,
               RRULE, SEQUENCE{IF EQ 0},
               STATUS{TENTATIVE/CONFIRMED/CANCELLED} STATUS{TENTATIVE/CONFIRMED/
               CANCELLED} , SUMMARY {MAYBE NULL}, TRANSP, URL
          NOT PROPERTY = COMPLETED, DUE, DURATION, REQUEST-STATUS)
     MAY COMPONENT = VTIMEZONE (
          MUST PROPERTY = DTSTART, TZOFFSET
          MAY PROPERTY = COMMENT, DAYLIGHT, (RDATE / RRULE), TZNAME
          NOT PROPERTY = CREATED)
     MAY COMPONENT = VALARM (IF COMPONENT EXISTS
          MUST PROPERTY = CATEGORIES, DTSTART, DSTART, DURATION, REPEAT
          MAY PROPERTY = ATTACH, DESCRIPTION, SUMMARY
     NOT PROPERTY = COMMENT, CREATED, LAST-MODIFIED, RELATED-TO, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VTODO

Silverberg/Mansour/Dawson/Hopson  21                   Expires MAY 1998
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     )

3.1.7     DECLINECOUNTER

   The "DECLINECOUNTER" "DECLINE-COUNTER" method in a "VEVENT" calendar component is used
   by the "Organizer" of an event to reject a counter proposal submitted
   by an "Attendee". The "Organizer" MUST send the "DECLINECOUNTER" "DECLINE-COUNTER"
   message to the "Attendee" that sent the "COUNTER" method to the
   "Organizer".

   The counter proposal is an iCalendar object consisting of a VEVENT
   calendar component describing the complete description of the
   alternate event.

   The "Organizer" rejects the counter proposal by sending the
   "Attendee" a "DECLINECOUNTER" "DECLINE-COUNTER" method. The "Organizer" accepts the
   counter proposal by sending all of the "Attendees" to the event a
   "REQUEST" method; rescheduling the event. Since this is a rescheduled
   event, the "SEQUENCE" property value will be incremented. In the
   later case, the "Organizer" SHOULD reset the individual "RSVP"
   parameter values to TRUE on all of the "ATTENDEE" properties; in
   order to force a response by the "Attendees".

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "Event - Cancel" COMPONENT "VEVENT" METHOD
          "DECLINECOUNTER"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"},METHOD{
          "DECLINECOUNTER"})
     MUST COMPONENT = VEVENT (
          MUST PROPERTY = DTSTAMP, SEQUENCE{IF NE 0}, UID{same UID
               specified In Original REQUEST and subsequent COUNTER}
          MAY PROPERTY = COMMENT{provides comment from "Organizer" to
               ATTENDEE}, RECURRENCE-ID, REQUEST-STATUS, SEQUENCE{IF EQ
               0}
          NOT PROPERTY = ATTACH, ATTENDEE, CATEGORIES, CLASS, CONTACT,

Silverberg/Mansour/Dawson/Hopson  20                   Expires MAY 1998 CREATED,
               DESCRIPTION, DTSTART, DTEND, EXDATE, EXRULE, GEO,
               LAST-MODIFIED, PRIORITY, RDATE, RELATED-TO, RESOURCES,
               RRULE,STATUS, SUMMARY, TRANSP, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VTODO
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     NOT COMPONENT = VTIMEZONE
     NOT COMPONENT = VALARM
     )

Silverberg/Mansour/Dawson/Hopson  22                   Expires MAY 1998

3.2 Methods For VFREEBUSY Component

   This section defines the property set for the methods that are
   applicable to the "VFREEBUSY" calendar component. Each of the methods
   is defined using a grammar that specifies the property constraints
   that define the particular method.

   This memo only addresses the transfer of busy time information.
   Applications desiring free time information MUST infer this from
   available busy time information.

   The busy time information within the iCalendar object MAY be grouped
   into more than one "VFREEBUSY" calendar component. This capability
   allows busy time periods to be grouped according to some common
   periodicity, such as a calendar week, month, or year. In this case,
   each "VFREEBUSY" calendar component MUST include the "ATTENDEE",
   "DTSTART" and "DTEND" properties in order to specify the source of
   the busy time information and the date and time interval over which
   the busy time information covers.

   The "FREEBUSY" property value MAY include a list of values, separated
   by the COMMA character (ASCII decimal 44). Alternately, multiple busy
   time periods MAY be specified with multiple instances of the
   "FREEBUSY" property. Both forms MUST be supported by implementations
   conforming to this document. Duplicate busy time periods SHOULD NOT
   be specified in an iCalendar object. However, two different busy time
   periods MAY overlap.

   "FREEBUSY" properties SHOULD be sorted such that their values are in
   ascending order, based on the start time, and then the end time, with
   the earliest periods first. For example, today's busy time
   information SHOULD appear after yesterday's busy time information.
   And the busy time for this half hour SHOULD appear after the busy
   time for earlier today.

   Since events MAY span a day boundary, free busy time period MAY also
   span a day boundary. Individual "A" requests busy time from
   individuals "B", "C" and "D". Individual "B" and "C" replies with
   busy time data to individual "A". Individual "D" does not support
   busy time requests and does not reply with any data. If the transport
   binding supports exception messages, then a "unsupported capability"
   message is returned by individual "D" to individual "A".

   The following summarizes the methods that are defined for the
   "VFREEBUSY" calendar component.

Silverberg/Mansour/Dawson/Hopson  21                   Expires MAY 1998

 |================|==================================================|
 | Method         |  Description                                     |
 |================|==================================================|
 | PUBLISH        | Publish unsolicited busy time data.              |
 | REQUEST        | Request busy time data.                          |
 | REPLY          | Reply to a busy time request.                    |
 |================|==================================================|

Silverberg/Mansour/Dawson/Hopson  23                   Expires MAY 1998

3.2.1     PUBLISH

   The "PUBLISH" method in a "VFREEBUSY" calendar component is used to
   publish busy time data. The method MAY be sent from one "Calendar
   User" to any other. The purpose of the method is to provide a message
   for sending unsolicited busy time data. That is, the busy time data
   is not being sent as a "REPLY" to the receipt of a "REQUEST" method.

   Busy time intervals are represented by individual instances of the
   "FREEBUSY" property. There is one occurrence of the property for each
   busy time interval. Duplicate busy time periods SHOULD NOT be
   returned. However, two different busy time periods MAY overlap.

   The "FREEBUSY" property value MAY include a list of values, separated
   by the COMA character (ASCII decimal 44).

   "FREEBUSY" properties SHOULD be sorted such that their values are in
   ascending order, from the most recent to past. For example, today's
   busy time information SHOULD appear after yesterday's busy time
   information. And the busy time for this half hour SHOULD appear after
   the busy time for earlier today.

   Since events MAY span a day boundary, free busy time period MAY also
   span a day boundary.

   The busy time periods MAY be grouped into more than one "VFREEBUSY"
   calendar component. This capability allows busy time periods to be
   grouped according to some common periodicity, such as a calendar
   week, month, or year. In this case, each "VFREEBUSY" calendar
   component MUST include the "ATTENDEE", "DTSTART" and "DTEND"
   properties in order to specify the originator and date and time
   interval for the busy time information.

   The "ATTENDEE" property MUST be specified in the busy time
   information. The value is the "Calendar User" address of the
   originator of the busy time information.

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "Busy - Busy Time Publish" COMPONENT "VFREEBUSY"
          METHOD "PUBLISH"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"PUBLISH"})
     MUST COMPONENT = VFREEBUSY (
          MUST PROPERTY = ATTENDEE{address of originator of busy time

Silverberg/Mansour/Dawson/Hopson  22                   Expires MAY 1998
               data},FREEBUSY{values MUST all be of the same data type.
               Multiple instances are allowed. Multiple instances MUST
               be sorted in ascending order. Values MAY NOT overlap},
               RELATED-TO{refers to another related VFREEBUSY

Silverberg/Mansour/Dawson/Hopson  24                   Expires MAY 1998
               component},
          MAY PROPERTY = COMMENT{comment from attendee to originator of
               request}, CREATED{specifies when the busy time data was
               created}, DTSTART{represents start of interval for busy
               time data}, DTEND{represents end of interval for busy
               time data},LAST-MODIFIED{specifies when busy time data
               was last modified}, SEQUENCE{IF EQ 0}, URL{specifies busy
               time URL}
          NOT PROPERTY = DTSTAMP, DURATION, REQUEST-STATUS, SEQUENCE,
               UID)
     MAY COMPONENT = VTIMEZONE (
          MUST PROPERTY = DTSTART, TZOFFSET
          MAY PROPERTY = COMMENT, DAYLIGHT, (RDATE / RRULE), TZNAME
          NOT PROPERTY = CREATED)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VEVENT
     NOT COMPONENT = VTODO
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VALARM
     )

3.2.2     REQUEST

   The "REQUEST" method in a "VFREEBUSY" calendar component is used to
   ask a "Calendar User" for their busy time information. The request
   MAY be for a busy time information bounded by a specific date and
   time interval.

   This message only permits requests for busy time information. The
   message is sent from a "Calendar User" requesting the busy time
   information to one or more intended recipients.

   An "ATTENDEE" property MUST be included for the originator of the
   request and each of the intended recipients that the method is sent
   to. The originator is indicated with an "ATTENDEE" property parameter
   sequence of ";ROLE=ORGANIZER". The recipients are indicated with an
   "ATTENDEE" property parameter sequence of ";ROLE=ATTENDEE". The
   requests MAY be fanned out in separate messages to the recipients,
   with each "REQUEST" method only including the associated "ATTENDEE"
   properties for the recipients of the message.

   If the originator of the "REQUEST" method is not authorized to make a
   busy time request on the recipient's calendar system, then an
   exception message is returned in a "REPLY" method, but no busy time
   data need be returned.

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "FREEBUSY - Request For Busy Time" COMPONENT
          "VFREEBUSY" METHOD "REQUEST"

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     MUST COMPONENT = CALPROPS (

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          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"REQUEST"})
     MUST COMPONENT = VFREEBUSY (
          MUST PROPERTY = ATTENDEE{Attendee instances for the Owner and
               Organizer if different and the intended recipient of the
               request}, DTSTAMP, DTSTART, DTEND,SEQUENCE{IF NE 0}, UID
          MAY PROPERTY = SEQUENCE{IF EQ 0}
          NOT PROPERTY = COMMENT, CREATED, DURATION, FREEBUSY,
               LAST-MODIFIED, RELATED-TO, URL, REQUEST-STATUS)
     MAY COMPONENT = VTIMEZONE (
          MUST PROPERTY = DTSTART, TZOFFSET
          MAY PROPERTY = COMMENT, DAYLIGHT, (RDATE / RRULE), TZNAME
          NOT PROPERTY = CREATED)
     MAY COMPONENT X-TOKENS (ANY)
     NOT COMPONENT = VEVENT
     NOT COMPONENT = VTODO
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VALARM
     )

3.2.3     REPLY

   The "REPLY" method in a "VFREEBUSY" calendar component is used to
   respond to an existing busy time request. The method is sent from a
   recipient of a busy time request back to the originator of the
   request. The originator of the request is specified by the "ATTENDEE"
   property parameter sequence of ";ROLE=ORGANIZER".

   The "REPLY" method MAY also be used to respond to an unsuccessful
   "REQUEST" method. Depending on the "REQUEST-STATUS" value, no busy
   time information MAY be returned.

   Busy time intervals are represented by individual instances of the
   "FREEBUSY" property. There is one occurrence of the property for each
   busy time interval. Duplicate busy time periods SHOULD NOT be
   returned. However, two different busy time periods MAY overlap.

   The "FREEBUSY" property value MAY include a list of values, separated
   by the COMA character (ASCII decimal 44).

   "FREEBUSY" properties SHOULD be sorted such that their values are in
   ascending order, from the most recent to past. For example, today's
   busy time information SHOULD appear after yesterday's busy time
   information. And the busy time for this half hour SHOULD appear after
   the busy time for earlier today.

   Since events MAY span a day boundary, free busy time period MAY also
   span a day boundary.

   The busy time periods MAY be grouped into more than one "VFREEBUSY"
   calendar component. This capability allows busy time periods to be
   grouped according to some common periodicity, such as a calendar
   week, month, or year. In this case, each "VFREEBUSY" calendar
   component MUST include the "ATTENDEE", "DTSTART" and "DTEND"

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   properties in order to identify the source and date and time range
   for the busy time data.

Silverberg/Mansour/Dawson/Hopson  24                   Expires MAY 1998

   The "ATTENDEE" property MUST be specified in the busy time reply. The
   value is the fully qualified RFC 822 address of the recipient
   replying to the busy time request.

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "FreeBusy - Busy Time Reply" COMPONENT "VFREEBUSY"
     METHOD "REPLY"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"REPLY"})
     MUST COMPONENT = VFREEBUSY (
          MUST PROPERTY = ATTENDEE{address of recipient replying},
               DTSTAMP, DTSTART, DTEND, FREEBUSY{values MUST all be of
               the same data type. Multiple instances are allowed.
               Multiple instances MUST be sorted in ascending order.
               Values MAY NOT overlap}, RELATED-TO{refers to another
               related VFREEBUSY component}, REQUEST-STATUS, UID
          MAY PROPERTY = COMMENT{comment from attendee to originator of
               request}, CREATED{specifies when the busy time data was
               created}, DTSTART{represents start of interval for busy
               time data}, DTEND{represents end of interval for busy
               time data},LAST-MODIFIED{specifies when busy time data
               was last modified}, SEQUENCE{IF EQ 0}, URL{specifies busy
               time URL}
          NOT PROPERTY = DURATION, SEQUENCE)
     MAY COMPONENT = VTIMEZONE (
          MUST PROPERTY = DTSTART, TZOFFSET
          MAY PROPERTY = COMMENT, DAYLIGHT, (RDATE / RRULE), TZNAME
          NOT PROPERTY CREATED)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VEVENT
     NOT COMPONENT = VTODO
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VALARM
     )

3.3 Methods For VTODO Component

   This section defines the property set for the methods that are
   applicable to the "VTODO" calendar component . Each of the methods is
   defined using a grammar that specifies the property constraints that
   define the particular method.

   The following summarizes the methods that are defined for the "VTODO"
   calendar component .

+================+==================================================+

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| Method         |  Description                                     |
|================+==================================================|
| PUBLISH        | Post notification of a VTODO. Used primarily as  |
|                | a method of advertising the existence of a VTODO.|
| REQUEST        | Assign a VTODO. This is an explicit assignment to|

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|                | one or more Calendar Users.VTODO REQUEST method  |
|                | is also used to update or change an existing     |
|                | VTODO. Clients that cannot handle REQUEST MAY    |
|                | degrade the method to view it as a PUBLISH.      |
| REPLY          | Reply to a VTODO request. Attendees MAY set MAYset       |
|                | status to ACCEPTED, DECLINED, TENTATIVE,         |
|                | DELEGATED, PARTIAL, and COMPLETED.               |
| CANCEL         | Cancel an existing VTODO assignment.             |
| REFRESH        | A request sent to a VTODO "Organizer" asking for |
|                | the latest version of a                          |
| COUNTER        | Counter a REQUEST with an alternative proposal.  |
| DECLINECOUNTER | Decline a counter proposal by an attendee.       |
+================+==================================================+

3.3.1     PUBLISH

   The "PUBLISH" method in a "VTODO" calendar component has no reply
   response associated with it. Instead, it is simply a posting of an
   iCalendar object that MAY be added to a calendar by a "Calendar
   User". It requires and accepts no responses to the "Organizer". It's
   expected usage is for encapsulating an arbitrary "VTODO" calendar
   component as an iCalendar object. The "Organizer" MAY subsequently
   update (with another "PUBLISH" method) or cancel (with a "CANCEL"
   method) a previously published "VTODO" calendar component .

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "VTODO - Publish" COMPONENT "VTODO" METHOD "PUBLISH

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"PUBLISH"})
     MUST COMPONENT = VTODO(
          MUST PROPERTY = ATTENDEE{only Owner and Organizer if
               different}, DESCRIPTION{MAYBE NULL}, DTSTAMP, DTSTART,
               PRIORITY, SEQUENCE{IF NE 0}, UID
          MAY PROPERTY = ATTACH, ATTENDEE{other than ROLE=OWNER |
               ORGANIZER}, CATEGORIES, CLASS, COMMENT, COMPLETED,
               CONTACT, CREATED, DUE,
               EXDATE, EXRULE, GEO, LAST-
               MODIFIED, LOCATION,PERCENT-COMPLETE, LAST-MODIFIED, LOCATION,PERCENT-
               COMPLETE, RELATED-TO, RDATE, RECURRENCE-ID, RESOURCES,
               RRULE, SEQUENCE{IF EQ 0},
               STATUS{TENTATIVE/CONFIRMED/CANCELLED}, STATUS{TENTATIVE/CONFIRMED
               /CANCELLED}, SUMMARY{MAYBE NULL}, URL
          NOT PROPERTY = REQUEST-STATUS)
     MAY COMPONENT = VTIMEZONE (
          MUST PROPERTY = DTSTART, TZOFFSET
          MAY PROPERTY = COMMENT, DAYLIGHT, (RDATE / RRULE), TZNAME
          NOT PROPERTY = CREATED)

Silverberg/Mansour/Dawson/Hopson  28                   Expires MAY 1998
     MAY COMPONENT = VALARM (
          MUST PROPERTY = CATEGORIES, DTSTART, DSTART, DURATION, REPEAT
          MAY PROPERTY = ATTACH, DESCRIPTION, SUMMARY
     NOT PROPERTY =  COMMENT, CREATED, LAST-MODIFIED, RELATED-TO, URL)
     MAY COMPONENT = X-TOKENS (ANY)

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     NOT COMPONENT = VEVENT
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     )

3.3.2     REQUEST

   The "REQUEST" method in a "VTODO" calendar component provides the
   following scheduling functions:

      

      . Assign a to-do to one or more "Calendar Users";

      

      . Reschedule an existing to-do;

      

      . Update the details of an existing to-do, without rescheduling
        it;

      

      . Update the completion status of "Attendees" of an existing to-
        do, without rescheduling it;

      

      . Reconfirm an existing to-do, without rescheduling it;

      

      . Delegate/reassign an existing to-do to another "Calendar User".

   The assigned "Calendar Users" are identified in the "VTODO" calendar
   component by individual "ATTENDEE;ROLE=ATTENDEE" property value
   sequences.

   The originator of a "REQUEST" is the "Organizer" of the to-do. The
   recipient of a "REQUEST" is the "Calendar User" assigned the to-do,
   called the Attendee. The "Attendee" uses the "REPLY" method to convey
   their acceptance and completion status to the "Organizer" of the
   "REQUEST".

   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 to-do. If the "UID" property value is found on
   the recipient's calendar, then the "REQUEST" is for either a
   rescheduling, an update, or a reconfirm of the "VTODO" calendar
   object.

   If the "Organizer" of the "REQUEST" method is not authorized to make
   a to-do request on the "Attendee's" calendar system, then an
   exception is returned in the "REQUEST-STATUS" property of a
   subsequent "REPLY" method, but no scheduling action is performed.

Silverberg/Mansour/Dawson/Hopson  29                   Expires MAY 1998
   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "VTODO - Request" COMPONENT "VTODO" METHOD "REQUEST"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"REQUEST"})
     MUST COMPONENT = VTODO(
          MUST PROPERTY = ATTENDEE{For Owner and Organizer if different
               and each Attendee},DESCRIPTION{MAYBE NULL}, DTSTAMP,
               DTSTART, PRIORITY, SEQUENCE{IF NE 0}, UID
          MAY PROPERTY = ATTACH, CATEGORIES, CLASS, COMMENT, CONTACT,

Silverberg/Mansour/Dawson/Hopson  27                   Expires MAY 1998
               CREATED, DUE, EXDATE, EXRULE, GEO, LAST-MODIFIED,
               LOCATION, PERCENT-COMPLETE, RELATED-TO, RDATE,
               RECURRENCE-ID, RESOURCES, RRULE, SEQUENCE{IF EQ 0},
               STATUS{TENTATIVE/CONFIRMED/CANCELLED}, SUMMARY{MAYBE
               NULL}, URL
          NOT PROPERTY = COMPLETED, REQUEST-STATUS)
     MAY COMPONENT = VTIMEZONE (
          MUST PROPERTY = DTSTART, TZOFFSET
          MAY PROPERTY = COMMENT, DAYLIGHT, (RDATE / RRULE), TZNAME
          NOT PROPERTY = CREATED)
     MAY COMPONENT = VALARM (
          MUST PROPERTY = CATEGORIES, DTSTART, DSTART, DURATION, REPEAT
          MAY PROPERTY = ATTACH, DESCRIPTION, SUMMARY
          NOT PROPERTY =  COMMENT, CREATED, LAST-MODIFIED, RELATED-TO,
               URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VEVENT
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     )

3.3.2.1   REQUEST for Rescheduling a VTODO

   The "REQUEST" method MAY be used to reschedule a "VTODO" calendar
   component .

   A rescheduled "VTODO" calendar component involves a change to the
   existing "VTODO" calendar component in terms of it's start or due
   time or recurrence intervals and possibly the description. If the
   recipient "CUA"  of a "REQUEST" method finds that the "UID" property
   value already exists on the calendar, but that the "SEQUENCE"
   property value in the "REQUEST" is greater than the value for the
   existing VTODO, then the "REQUEST" method describes a rescheduling of
   the "VTODO" calendar component.

Silverberg/Mansour/Dawson/Hopson  30                   Expires MAY 1998

3.3.2.2   REQUEST for Update or Reconfirmation of a VTODO

   The "REQUEST" method MAY be used to update or reconfirm a "VTODO"
   calendar component. Reconfirmation is merely an update of "Attendee"
   completion status or overall "VTODO" calendar component status.

   An update to an existing "VTODO" calendar component does not involve
   changes to the start or due time or recurrence intervals, nor
   generally to the description for the "VTODO" calendar component. 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
   "VTODO" calendar component details, but no rescheduling of the
   "VTODO" calendar component.

   The update "REQUEST" is the appropriate response to a "REFRESH"
   method sent from an "Attendee" to the "Organizer" of a "VTODO"
   calendar component.

Silverberg/Mansour/Dawson/Hopson  28                   Expires MAY 1998

   Unsolicited "REQUEST" methods MAY also be sent by the "Organizer" of
   a "VTODO" calendar component. The unsolicited "REQUEST" methods MAY
   be used to either update the details of the VTODO, without
   rescheduling it or to update the completion status of "Attendees" or
   the "VTODO" calendar component itself (i.e., reconfirm the VTODO).

3.3.2.3   REQUEST for Delegating a VTODO

   The "REQUEST" method MAY be used to delegate or reassign ownership of
   a "VTODO" calendar component to another "Calendar User". The
   "REQUEST" method is used to delegate the "Attendee's" role (i.e. "
   "Organizer", or "Attendee") for a "VTODO" calendar component. The
   "REQUEST" method is sent by one of the "Attendees" of an existing
   "VTODO" calendar component request to some other individual. In order
   to avoid scheduling loops, the method MUST NOT be sent from an
   "Attendee" back to the "Organizer" of the "VTODO" calendar component.
   An "Attendee" of a "VTODO" calendar component MAY NOT delegate to the
   "Organizer" of the event.

   For the purposes of this description, the "Attendee" delegating the
   "VTODO" calendar component is referred to as the "delegator". The
   "Attendee" receiving the delegation request is referred to as the
   "delegatee".

   The "delegator" of a "VTODO" calendar component MUST forward the
   existing "REQUEST" method for a "VTODO" calendar component to the
   "delegatee". The "VTODO" calendar component description MUST include
   the "delegator's" up-to-date "VTODO" calendar component definition.
   The "REQUEST" method MUST also include an "ATTENDEE" property with
   the calendar address of the "delegatee". The "delegator" MUST also
   send a "REPLY" method back to the "Organizer" with the "delegator's"
   "Attendee" property "STATUS" parameter value set to DELEGATED. In

Silverberg/Mansour/Dawson/Hopson  31                   Expires MAY 1998
   addition, the "DELEGATED-TO" parameter SHOULD be included with the
   calendar address of the "delegatee". A response to the delegation
   "REQUEST" is sent from the "delegatee" to the "Organizer" and
   optionally, to the "delegator". The "REPLY" method from the
   "delegatee" SHOULD include the "ATTENDEE" property with their
   calendar address and the "DELEGATED-FROM" parameter with the value of
   the "delegator's"calendar address.

   The delegation "REQUEST" method MUST assign the values of the "RSVP"
   and "EXPECT" property parameters associated with the "delegator's"
   "Attendee" property to that of the "delegatee's" "Attendee" property.
   For example if the "delegator's" "Attendee" property specifies
   "RSVP=TRUE;EXPECT=REQUEST", then the "delegatee's" "Attendee"
   property MUST specify "RSVP=TRUE;EXPECT=REQUEST".

3.3.2.4   REQUEST Forwarded To An Uninvited Calendar User

   An "Attendee" assigned a "VTODO" calendar component MAY also assign
   the "VTODO" calendar component to another new "Calendar User", not
   previously associated with the "VTODO" calendar component. The
   current "Attendee" assigned the "VTODO" calendar component
   accomplishes this scheduling action by forwarding the original
   "REQUEST" method to the new "Calendar User".

Silverberg/Mansour/Dawson/Hopson  29                   Expires MAY 1998

   An "Organizer" of a "VTODO" calendar component MAY also request an
   updated completion status from one of the "Attendees". This is
   achieved by the "Organizer" sending a "REQUEST" method to the
   "Attendee" with the "ATTENDEE;RSVP=TRUE" property sequence. The
   "SEQUENCE" property for the "VTODO" calendar component 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 an updated status. The recipient SHOULD
   respond with a "REPLY" method indicating their current status with
   respect to the "REQUEST".

3.3.2.5   REQUEST Updated Attendee Status

   An "Organizer" of a to-do MAY also request an updated status from one
   of the "Attendees". This is achieved by the "Organizer" sending a
   "REQUEST" method to the "Attendee" with the "ATTENDEE;RSVP=TRUE"
   property sequence. The "SEQUENCE" property for the to-do 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 an updated status. The recipient SHOULD
   respond with a "REPLY" method indicating their current status with
   respect to the "REQUEST".

   This capability MAY also be achieved by the "Organizer" sending the
   "REFRESH" method to the "Attendees".

Silverberg/Mansour/Dawson/Hopson  32                   Expires MAY 1998

3.3.3     REPLY

   The "REPLY" method in a "VTODO" calendar component is used to respond
   (e.g., accept or decline) to a request or to reply to a delegation
   request. It is also used by an "Attendee" to update their completion
   status. When used to provide a delegation response, the "delegator"
   SHOULD include the calendar address of the "delegatee" in the
   "DELEGATED-TO" parameter of the "delegator's" "ATTENDEE" property.
   The "delegatee" SHOULD include the calendar address of the
   "delegator" on the "DELEGATED-FROM" parameter of the "delegatee's"
   "ATTENDEE" property.

   The "REPLY" method MAY also be used to respond to an unsuccessful
   "VTODO" calendar component "REQUEST" method. Depending on the
   "REQUEST-STATUS" value, no scheduling action MAY have been performed.

   The "Organizer" of a "VTODO" calendar component MAY receive a "REPLY"
   method from a "Calendar User" not in the original "REQUEST". For
   example, a "REPLY" method MAY be received from a "delegatee" of a
   "VTODO" calendar component. In addition, the "REPLY" method MAY be
   received from an unknown "Calendar User"; forwarded the "REQUEST"
   from an original "Attendee" assigned the "VTODO" calendar component.
   This uninvited "Attendee" MAY be accepted, or the "Organizer" MAY
   cancel the "VTODO" calendar component for the uninvited "Attendee" by
   sending them a "CANCEL" method.

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "VTODO - Reply" COMPONENT "VTODO" METHOD "REPLY"

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     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"REPLY"})
     MUST COMPONENT = VTODO(
          MUST PROPERTY = ATTENDEE{MUST be address of ATTENDEE
               replying}, DTSTAMP, SEQUENCE{IF NE 0}, UID{UID
               associated with original REQUEST}
          MAY PROPERTY = COMMENT{provides comment from ATTENDEE to
               "Organizer"}, COMPLETED, EXDATE, EXRULE, RECURRENCE-ID,
               REQUEST-STATUS, REQUEST-
               STATUS, PERCENT-COMPLETE, SEQUENCE{IF EQ 0}, SUMMARY
               {MAYBE NULL}, URL
          NOT PROPERTY = ATTACH, CATEGORIES, CLASS, CONTACT, CREATED,
               DESCRIPTION, DTSTART, DUE, GEO, LAST-MODIFIED, PRIORITY,
               RELATED-TO, RESOURCES, RDATE, RRULE, STATUS, SUMMARY,
               TRANSP)
               TRANSP, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VEVENT
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     NOT COMPONENT = VTIMEZONE
     NOT COMPONENT = VALARM
     )

Silverberg/Mansour/Dawson/Hopson  33                   Expires MAY 1998

3.3.4     CANCEL

   The "CANCEL" method in a "VTODO" calendar component is used to send a
   cancellation notice of an existing "VTODO" calendar request request
   to the "Attendees". The message is sent by the "Organizer" of a
   "VTODO" calendar component to the "Attendees" of the "VTODO" calendar
   component. For a recurring "VTODO" calendar component, either the
   whole "VTODO" calendar component or instances of a "VTODO" calendar
   component MAY be cancelled. To cancel the complete range of a
   recurring "VTODO" calendar component, the "UID" property value for
   the "VTODO" calendar component MUST be specified in the "CANCEL"
   method. In order to cancel an individual instance of a recurring
   "VTODO" calendar component, the "RECURRENCE-ID" property value for
   the "VTODO" calendar component MUST be specified in the "CANCEL"
   method. In order to cancel a sequence of instances of a recurring
   "VTODO" calendar component, either the "RECURRENCE-ID" property for
   the first instance in the sequence MUST be specified with the "RANGE"
   property parameter value of THISANDPRIOR or THISANDFUTURE; to
   indicate cancellation of the "VTODO" calendar component instances
   before and after the first instance, respectively. Lastly, individual
   recurrence instances MAY be cancelled by specifying multiple
   "RECURRENCE-ID" properties corresponding to the instances to be
   cancelled.

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "VTODO - Cancel" COMPONENT "VTODO" METHOD "CANCEL"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"CANCEL"})

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     MUST COMPONENT = VTODO(
          MUST PROPERTY = DTSTAMP, SEQUENCE{IF NE 0}, UID{UID
               associated with original REQUEST}
          MAY PROPERTY = COMMENT{provides comment from "Organizer" to
               ATTENDEE}, EXDATE, EXRULE, RECURRENCE-ID, SEQUENCE{IF EQ
               0}, STATUS{CANCELLED}
          NOT PROPERTY = ATTACH, ATTENDEE, CATEGORIES, CLASS,
               COMPLETED, CONTACT, CREATED,
               DESCRIPTION, DTSTART, DUE, GEO, LAST-MODIFIED, PRIORITY,
               RDATE, RELATED-TO, RESOURCES, REQUEST-STATUS, RRULE,
               SUMMARY, TRANSP, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VEVENT
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     NOT COMPONENT = VTIMEZONE
     NOT COMPONENT = VALARM
     )

Silverberg/Mansour/Dawson/Hopson  34                   Expires MAY 1998

3.3.5     REFRESH

   The "REFRESH" method in a "VTODO" calendar component is used by
   "Attendees" of an existing "VTODO" calendar component to request an
   updated description from the "Organizer" of the "VTODO" calendar
   component. The "Organizer" of the "VTODO" calendar component MAY also
   use this method to request an updated status from the "Attendees".
   The "REFRESH" method MUST specify the "UID" property corresponding to
   the "VTODO" calendar component needing update.

   A refresh of a recurrence instance of a "VTODO" calendar component
   MAY be requested by specifying the "RECURRENCE-ID" property
   corresponding to the associated "VTODO" calendar component. The
   "Organizer" MUST respond with the latest description and rendition of
   the "VTODO" calendar component. This method is intended to facilitate
   machine processing of requests for updates to a "VTODO" calendar
   component.

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "VTODO - Refresh" COMPONENT "VTODO" METHOD "REFRESH"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"REFRESH"})
     MUST COMPONENT = VTODO(
          MUST PROPERTY = ATTENDEE{address of requestor}, DTSTAMP,
               SEQUENCE{IF NE 0}, UID{UID associated with original
               REQUEST} MAY PROPERTY = COMMENT{provides comment from
               ATTENDEE to "Organizer"}, RECURRENCE-ID, SEQUENCE{IF EQ
               0}
          NOT PROPERTY = ATTACH, CATEGORIES, CLASS, COMPLETED, CONTACT, CREATED,
               DESCRIPTION, DTSTART, DUE, EXDATE, EXRULE, GEO,
               LAST-MODIFIED, LAST-
               MODIFIED, PRIORITY, RDATE,RELATED-TO, RESOURCES,
               REQUEST-STATUS, RRULE,SUMMARY, STATUS, TRANSP, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VEVENT

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     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     NOT COMPONENT = VTIMEZONE
     NOT COMPONENT = VALARM
     )

3.3.6     COUNTER

   The "COUNTER" method in a "VTODO" calendar component is used by an
   "Attendee" of an existing "VTODO" calendar component to submit to the
   "Organizer" a counter proposal for the "VTODO" calendar component.
   The "Attendee" MUST send the message to the "Organizer" of the
   "VTODO" calendar component.

Silverberg/Mansour/Dawson/Hopson  35                   Expires MAY 1998
   The counter proposal is an iCalendar object consisting of a "VTODO"
   calendar component describing the complete description of the
   alternate "VTODO" calendar component.

   The "Organizer" rejects the counter proposal by sending the
   "Attendee" a "DECLINECOUNTER" "DECLINE-COUNTER" method. The "Organizer" accepts the
   counter proposal by sending all of the "Attendees" of the "VTODO"
   calendar component a "REQUEST" method rescheduling the "VTODO"
   calendar component. In the later case, the "Organizer" SHOULD reset
   the individual "RSVP" property parameter values to TRUE on each
   "ATTENDEE" property; in order to force a response by the "Attendees".

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "VTODO- Request" COMPONENT "VTODO" METHOD "REQUEST"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"REQUEST"})
     MUST COMPONENT = VTODO(
          MUST PROPERTY = ATTENDEE{For Owner and Orginator if different
               and Attendees}, DESCRIPTION{MAYBE NULL}, DTSTAMP,
               DTSTART, PRIORITY, SEQUENCE{IF NE 0}, UID
          MAY PROPERTY = ATTACH, CATEGORIES, CLASS, COMMENT, COMPLETED,
               CONTACT, CREATED, COMMENT,CREATED,
               DUE, EXDATE, EXRULE, GEO, LAST-
               MODIFIED,LOCATION,RELATED-TO, LAST-MODIFIED,
               LOCATION,RELATED-TO, RDATE, RECURRENCE-ID, RESOURCES,
               RRULE, SEQUENCE{IF EQ 0},
               STATUS{TENTATIVE/CONFIRMED/CANCELLED}, STATUS{TENTATIVE/CONFIRMED
               /CANCELLED}, SUMMARY{MAYBE NULL}, URL
          NOT PROPERTY = REQUEST-STATUS)
     MAY COMPONENT = VTIMEZONE (
          MUST PROPERTY = DTSTART, TZOFFSET
          MAY PROPERTY = COMMENT, DAYLIGHT, (RDATE / RRULE), TZNAME
          NOT PROPERTY = CREATED)
     MAY COMPONENT = VALARM (
          MUST PROPERTY = CATEGORIES, DTSTART, DSTART, DURATION, REPEAT
          MAY PROPERTY = ATTACH, DESCRIPTION, SUMMARY
     NOT PROPERTY =  COMMENT, CREATED, LAST-MODIFIED, RELATED-TO, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VEVENT
     NOT COMPONENT = VJOURNAL

Silverberg/Mansour/Dawson/Hopson  33                   Expires MAY 1998
     NOT COMPONENT = VFREEBUSY
     )

3.3.7     DECLINECOUNTER

   The "DECLINECOUNTER" "DECLINE-COUNTER" method in a "VTODO" calendar component is used
   by an "Organizer" of "VTODO" calendar component to reject a counter
   proposal offered by one of the "Attendees". The "Organizer" MUST send
   the message to the "Attendee" that sent the "COUNTER" method to the
   "Organizer".

Silverberg/Mansour/Dawson/Hopson  36                   Expires MAY 1998
   The counter proposal is an iCalendar object consisting of a "VTODO"
   calendar component describing the complete description of the
   alternate "VTODO" calendar component.

   The "Organizer" rejects the counter proposal by sending the
   "Attendee" a "DECLINECOUNTER" "DECLINE-COUNTER" method. The "Organizer" accepts the
   counter proposal by sending all of the "Attendees" of the "VTODO"
   calendar component a "REQUEST" method rescheduling the "VTODO"
   calendar component. Since this is a rescheduled "VTODO", the
   "SEQUENCE" property value will be incremented. In the later case, the
   "Organizer" SHOULD reset the individual "RSVP" property parameter
   values to TRUE on all of the "ATTENDEE" properties in order to force
   a response by the "Attendees".

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "VTODO - Cancel" COMPONENT "VTODO" METHOD
     "DECLINECOUNTER"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD
               {"DECLINECOUNTER"})
     MUST COMPONENT = VTODO(
          MUST PROPERTY = DTSTAMP, SEQUENCE{IF NE 0}, UID{same UID
               specified In Original REQUEST and subsequent COUNTER}
          MAY PROPERTY = COMMENT{provides comment from "Organizer" to
               ATTENDEE}, RECURRENCE-ID, REQUEST-STATUS, SEQUENCE{IF EQ
               0}
          NOT PROPERTY = ATTACH, ATTENDEE, CATEGORIES, CLASS,
               COMPLETED, CONTACT, CREATED,
               DESCRIPTION, DTSTART, DUE, EXDATE, EXRULE, GEO, LAST-MODIFIED, LAST-
               MODIFIED, PRIORITY, RDATE, RELATED-TO, RESOURCES, RRULE,
               STATUS, SUMMARY, TRANSP, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VEVENT
     NOT COMPONENT = VJOURNAL
     NOT COMPONENT = VFREEBUSY
     NOT COMPONENT = VTIMEZONE
     NOT COMPONENT = VALARM
     )

Silverberg/Mansour/Dawson/Hopson  34                   Expires MAY 1998

3.4 Methods For VJOURNAL Component

   This section defines the property set for the methods that are
   applicable to the "VJOURNAL" calendar component. Each of the methods
   is defined using a grammar that clarifies the property constraints
   that define the particular method.

   The following summarizes the methods that are defined for the
   "VJOURNAL" calendar component.

 +================+==================================================+
 | Method         |  Description                                     |

Silverberg/Mansour/Dawson/Hopson  37                   Expires MAY 1998
 |================+==================================================|
 | PUBLISH        | Post a journal entry. Used primarily as a method |
 |                | of advertising the existence of a journal entry  |
 | CANCEL         | Cancel an existing journal entry request.        |
 | REFRESH        | A request sent to the journal "Organizer" for    |
 |                | the latest version of the journal entry to be    |
 |                | resent the requester.                            |
 +================+==================================================+

3.4.1     PUBLISH

   The "PUBLISH" method in a "VJOURNAL" calendar component has no reply
   response associated with it. Instead, it is simply a posting of an
   iCalendar object that MAY be added to a calendar by a "Calendar User"
   agent. It requires and accepts no responses to the "Organizer". The
   expected usage is for encapsulating an arbitrary journal entry as an
   iCalendar object. The "Organizer" MAY subsequently update (with
   another "PUBLISH" method) or cancel (with a "CANCEL" method) a
   previously published journal entry.

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "Journal - Publish" COMPONENT "VJOURNAL" METHOD
          "PUBLISH

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"PUBLISH"})
     MUST COMPONENT = VJOURNAL (
          MUST PROPERTY = DESCRIPTION{MAYBE NULL}, DTSTAMP,
               DTSTART{VALUE=DATE}, SEQUENCE{IF NE 0}, UID
          MAY PROPERTY = ATTACH, ATTENDEE{only ROLE=ORGANIZER and
               OWNER if different}, CATEGORIES, CLASS, COMMENT,
               CONTACT,
               CREATED, EXDATE, EXRULE, LAST-MODIFIED, RELATED-TO,
               RDATE, RECURRENCE-ID, RRULE, SEQUENCE{IF EQ 0},
               SUMMARY{MAYBE NULL}, URL
          NOT PROPERTY = REQUEST-STATUS)
     MAY COMPONENT = VTIMEZONE (
          MUST PROPERTY = DTSTART, TZOFFSET
          MAY PROPERTY = COMMENT, DAYLIGHT, (RDATE / RRULE), TZNAME
          NOT PROPERTY = CREATED)
     MAY COMPONENT = X-TOKENS (ANY)

Silverberg/Mansour/Dawson/Hopson  35                   Expires MAY 1998
     NOT COMPONENT = VEVENT
     NOT COMPONENT = VTODO
     NOT COMPONENT = VALARM
     NOT COMPONENT = VFREEBUSY
     )

Silverberg/Mansour/Dawson/Hopson  38                   Expires MAY 1998

3.4.2     CANCEL

   The "CANCEL" method in a "VJOURNAL" calendar component is used to
   send a cancellation notice of an existing journal entry request to
   the "Attendees". The message is sent by the "Organizer" of a journal
   entry to the "Attendees" of the journal entry. For a recurring
   journal entry, either the whole journal entry or instances of a
   journal entry MAY be cancelled. To cancel the complete range of a
   recurring journal entry, the "UID" property value for the journal
   entry MUST be specified in the "CANCEL" method. In order to cancel an
   individual instance of the journal entry, the "RECURRENCE-ID"
   property value for the journal entry MUST be specified in the
   "CANCEL" method. In order to cancel a sequence of instances in a
   recurring journal entry, the "RECURRENCE-ID" property for the first
   journal entry instance in the sequence MUST be specified with the
   "RANGE" property parameter value of THISANDPRIOR or THISANDFUTURE; to
   indicate cancellation of the journal entry instances before and after
   the first journal entry instance, respectively. Lastly, individual
   recurrence instances MAY be cancelled by specifying multiple
   "RECURRENCE-ID" properties corresponding to the instances to be
   cancelled.

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "Journal - Cancel" COMPONENT "VJOURNAL" METHOD
          "CANCEL"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"CANCEL"})
     MUST COMPONENT = VJOURNAL (
          MUST PROPERTY = DTSTAMP, SEQUENCE{IF NE 0}, UID{UID
               associated with original REQUEST}
          MAY PROPERTY = COMMENT{provides comment from "Organizer" to
               ATTENDEE}, EXDATE, EXRULE, RECURRENCE-ID, SEQUENCE{IF EQ
               0}, STATUS{CANCELLED}
          NOT PROPERTY = ATTACH, ATTENDEE, CATEGORIES, CLASS, CONTACT, CREATED,
               DESCRIPTION, DTSTART, LAST-MODIFIED, RDATE, RELATED-TO,
               REQUEST-STATUS, RRULE, SUMMARY, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VEVENT
     NOT COMPONENT = VTODO
     NOT COMPONENT = VFREEBUSY
     NOT COMPONENT = VTIMEZONE
     NOT COMPONENT = VALARM
     )

Silverberg/Mansour/Dawson/Hopson  36                   Expires MAY 1998

3.4.3     REFRESH

   The "REFRESH" method in a "VJOURNAL" calendar component is used by
   "Attendees" of an existing journal entry to request an updated
   description from the journal entry "Organizer". The "REFRESH" method

Silverberg/Mansour/Dawson/Hopson  39                   Expires MAY 1998
   MUST specify the "UID" property corresponding to the journal entry
   needing update. A recurrence instance of a journal entry MAY be
   requested by specifying the"RECURRENCE-ID" property corresponding to
   the associated journal entry. The "Organizer" MUST respond with the
   latest description and version of the journal entry. This method is
   intended to facilitate machine processing of the "REFRESH" response.

   This method type is an iCalendar object that conforms to the
   following property constraints:

     (DESCRIPTION "Journal - Refresh" COMPONENT "VJOURNAL" METHOD
          "REFRESH"

     MUST COMPONENT = CALPROPS (
          MUST PROPERTY = PRODID, VERSION{"2.0"}, METHOD{"REFRESH"})
     MUST COMPONENT = VJOURNAL (
          MUST PROPERTY = ATTENDEE{address of requestor}, DTSTAMP,
               SEQUENCE{IF NE 0}, UID{UID associated with original
               REQUEST}
          MAY PROPERTY = COMMENT{provides comment from ATTENDEE to
               "Organizer"}, RECURRENCE-ID, SEQUENCE{IF EQ 0}
          NOT PROPERTY = ATTACH, CATEGORIES, CLASS, CONTACT, CREATED,
               DESCRIPTION, DTSTART, EXDATE, EXRULE, LAST-MODIFIED,
               PRIORITY, RDATE, RELATED-TO, REQUEST-STATUS, RRULE,
               SUMMARY, URL)
     MAY COMPONENT = X-TOKENS (ANY)
     NOT COMPONENT = VEVENT
     NOT COMPONENT = VTODO
     NOT COMPONENT = VFREEBUSY
     NOT COMPONENT = VTIMEZONE
     NOT COMPONENT = VALARM
     )

3.5 Status Replies

   The "REQUEST-STATUS" property MAY include the following values:

|==============+============================+=========================|
| Short Return | Longer Return Status       | Offending Data          |
| Status Code  | Description                |                         |
|==============+============================+=========================|
| 2.0          | Success.                   | None.                   |
|==============+============================+=========================|
| 2.1          | Success but fallback taken | Property name and value |
|              | on one or more property    | MAY be specified.       |
|              | values.                    |                         |
|==============+============================+=========================|
| 2.2          | Success, invalid property  | Property name MAY be    |

Silverberg/Mansour/Dawson/Hopson  37                   Expires MAY 1998
|              | ignored.                   | specified.              |
|==============+============================+=========================|
| 2.3          | Success, invalid property  | Property parameter name |
|              | parameter ignored.         | and value MAY be        |

Silverberg/Mansour/Dawson/Hopson  40                   Expires MAY 1998

|              |                            | specified.              |
|==============+============================+=========================|
| 2.4          | Success, unknown non-      | Non-standard property   |
|              | standard property ignored. | name MAY be specified.  |
|==============+============================+=========================|
| 2.5          | Success, unknown non       | Property and non-       |
|              | standard property value    | standard value MAY be   |
|              | ignored.                   | specified.              |
|==============+============================+=========================|
| 2.6          | Success, invalid calendar  | Calendar component      |
|              | component ignored.         | sentinel (e.g., "BEGIN: |
|              |                            | ALARM") MAY be          |
|              |                            | specified.              |
|==============+============================+=========================|
| 2.7          | Success, request forwarded | Original and forwarded  |
|              | to Calendar User.          | caluser addresses MAY   |
|              |                            | be specified.           |
|==============+============================+=========================|
| 2.8          | Success, repeating event   | RRULE or RDATE property |
|              | ignored. Scheduled as a    | name and value MAY be   |
|              | single event.              | specified.              |
|==============+============================+=========================|
| 2.9          | Success, truncated end date| DTEND property value    |
|              | time to date boundary.     | MAY be specified.       |
|==============+============================+=========================|
| 2.10         | Success, repeating VTODO   | RRULE or RDATE property |
|              | ignored. Scheduled as a    | name and value MAY be   |
|              | single VTODO.              | specified.              |
|==============+============================+=========================|
| 3.0          | Invalid property name.     | Property name MAY be    |
|              |                            | specified.              |
|==============+============================+=========================|
| 3.1          | Invalid property value.    | Property name and value |
|              |                            | MAY be specified.       |
|==============+============================+=========================|
| 3.2          | Invalid property parameter.| Property parameter name |
|              |                            | and value MAY be        |
|              |                            | specified.              |
|==============+============================+=========================|
| 3.3          | Invalid property parameter | Property parameter name |
|              | value.                     | and value MAY be        |
|              |                            | specified.              |
|==============+============================+=========================|
| 3.4          | Invalid calendar component | Calendar component      |
|              | sequence.                  | sentinel MAY be         |
|              |                            | specified (e.g., BEGIN: |
|              |                            | VTIMEZONE).             |
|==============+============================+=========================|
| 3.5          | Invalid date or time.      | Date/time value(s) MAY  |
|              |                            | be specified.           |

Silverberg/Mansour/Dawson/Hopson  38                   Expires MAY 1998
|==============+============================+=========================|
| 3.6          | Invalid rule.              | Rule value MAY be       |
|              |                            | specified.              |
|==============+============================+=========================|

Silverberg/Mansour/Dawson/Hopson  41                   Expires MAY 1998

| 3.7          | Invalid Calendar User.     | Attendee property value |
|              |                            |MAY be specified.        |
|==============+============================+=========================|
| 3.8          | No authority.              | PROFILE and ATTENDEE    |
|              |                            | property values MAY be  |
|              |                            | specified.              |
|==============+============================+=========================|
| 3.9          | Unsupported version.       | VERSION property name   |
|              |                            | and value MAY be        |
|              |                            | specified.              |
|==============+============================+=========================|
| 3.10         | Request entity too large.  | None.                   |
|==============+============================+=========================|
| 4.0          | Event conflict. Date/time  | DTSTART and DTEND       |
|              | is busy.                   | property name and values|
|              |                            | MAY be specified.       |
|==============+============================+=========================|
| 5.0          | Request not supported.     | Method property value   |
|              |                            | MAY be specified.       |
|==============+============================+=========================|
| 5.1          | Service unavailable.       | ATTENDEE property value |
|              |                            | MAY be specified.       |
|==============+============================+=========================|
| 5.2          | Invalid calendar service.  | ATTENDEE property value |
|              |                            | MAY be specified.       |
|==============+============================+=========================|
| 5.3          | No scheduling support for  | ATTENDEE property value |
|              | user.                      | MAY be specified.       |
|==============+============================+=========================|

3.6 Implementation Considerations

3.6.1     Working With Recurrence Instances

   iCalendar includes a recurrence grammar to represent recurring
   events. The benefit of such a grammar is the ability to represent a
   number of events in a single object. However, while this simplifies
   creation of a recurring event, meeting instances MAY still need to be
   referenced. For instance, an "Attendee" MAY decline the third
   instance of a recurring Friday event. Similarly, the "Organizer" MAY
   change the time or location to a single instance of the recurring
   event.

   Since implementations MAY elect to store recurring events as either a
   single event object or a collection of discreet, related event
   objects, the protocol is designed so that each recurring instance MAY
   be both referenced and versioned. Hence, implementations that choose
   to maintain per-instance properties (such as "ATTENDEE" property
   "STATUS" parameter) MAY do so. However, the protocol does not require

Silverberg/Mansour/Dawson/Hopson  39                   Expires MAY 1998
   per-instance recognition unless the instance itself MUST be
   renegotiated.

Silverberg/Mansour/Dawson/Hopson  42                   Expires MAY 1998
   The scenarios for recurrence instance referencing are listed below.
   For purposes of simplification a change to an event refers to a
   "trigger property."  That is, a property that has a substantive
   affect on the meeting itself such as start time, location, due date
   (for "VTODO" calendar component components) and possibly description.

      

      . "Organizer" initiated actions:

      

      . "Organizer" deletes or changes a single instance of a recurring
        event

      

      . "Organizer" makes changes that affect all future instances

      

      . "Organizer" makes changes that affect all previous instances

      

      . "Organizer" deletes or modifies a previously changed instance

      

      . Attendee initiated actions:

      

      . Attendee changes status for a particular recurrence instance

      

      . Attendee sends Event-Counter for a particular recurrence
        instance

   An instance of a recurring event is assigned a unique identification,
   "RECURRENCE-ID" property, when that instance MUST be renegotiated.
   Negotiation is necessary when the start time, end time, due date or
   location are modified. If the "Organizer" wishes to identify a
   specific recurrence instance it is done using the "RECURRENCE-ID"
   property. The property value is equal to the date/time of the
   instance. If the "Organizer" wishes to change the"DTSTART", the
   original "DTSTART" value is used for"RECURRENCE-ID" property and the
   new "DTSTART" and "DTEND" values reflect the change. If the
   "Organizer" wishes to add a new instance to the recurring event then
   a "REQUEST" is issued with an "RDATE" property equal to the new
   instance date. It is recommended that the "Organizer" include the
   "RECURRENCE-ID" property[SS1]. Since the creation of a new event
   instance requires negotiation, the sequence number is also
   incremented.

3.6.2     Attendee Property Considerations

   The "ATTENDEE" property for the "Organizer" is required on published
   events, to-dos, and journal entries for two reasons. First, a
   published only the "Organizer" is allowed to update an event, to-do,
   or journal entry component. The "Organizer" "ATTENDEE" property MUST
   be present in the event, to-do, or journal entry component so that
   the "CUA" has a basis for authorizing an update. Second, it is
   prudent to provide a point of contact for anyone who receives a
   published component in case of problems.

   There are valid RFC 822 addresses that represent groups. Sending
   email to such an address results in mail being sent to multiple

Silverberg/Mansour/Dawson/Hopson  43                   Expires MAY 1998
   recipients. Such an address MAY be used as the value of an "ATTENDEE"
   property. Thus, it is possible that the recipient of a "REQUEST" does
   not appear explicitly in the list list.

Silverberg/Mansour/Dawson/Hopson  40                   Expires MAY 1998

   It is recommended that the general approach to finding a "Calendar
   User" in an attendee list be as follows:

     1.        Search for the "Calendar User" in the attendee list where
       "TYPE=INDIVIDUAL"

     2.        Failing (1) look for attendees where "TYPE=GROUP" or
       'TYPE=UNKNOWN". The "CUA" MUST then determine if the "CU" is a
       member of one of these groups. If so, the "REPLY" method sent to
       the "Organizer" MUST contain a new "ATTENDEE" property in which
       the "TYPE" property parameter is set to INDIVIDUAL and the
       "GROUP" property parameter is set to the name of the group.

     3.        Failing (2) the "CUA" MAY ignore or accept the request as the
       "Calendar User" wishes.

3.6.3     When To Refresh An Event

   An "VEVENT" or "VTODO" calendar component SHOULD be resent to all
   "Attendees" whenever the "SEQUENCE" property is incremented or any
   other substantive change is made.

3.6.4     Timezones

   If a recurring event has any instance where "DTSTART" and "DTEND"
   fall on different sides of a time zone shift, the "VTIMEZONE"
   components are required.

   The threat of duplicate time zone definitions exists. SHOULD an
   iCalendar object contain multiple conflicting time zone components,
   the one with the latest "DTSTART" property supersedes the others.

3.6.5     Alarms

   It is recommended that application software ask the user whether or
   not they want alarms included when they read the event.

3.6.6     SUMMARY Property

   The minimum support for the "SUMMARY" property in a recipient MUST be
   for a 255 byte value. Implementations MAY truncate longer length
   values.

Silverberg/Mansour/Dawson/Hopson  44                   Expires MAY 1998

3.6.7     X-Tokens

   To make iCalendar objects extensible, new property types MAY be
   inserted into components. These properties are called X-Tokens as
   they are prefixed with "X-". A client is not required to make sense
   of X-Tokens. Clients are not required to save X-Tokens or use them in
   event replies.

Silverberg/Mansour/Dawson/Hopson  41                   Expires MAY 1998

4  Examples

4.1 Published Event Examples

   In the calendaring and scheduling context, publication refers to the
   one way transfer of event information. Consumers of published events
   simply incorporate the event into a calendar. No reply is expected.
   Individual "A" publishes an event. Individual "B" reads the event and
   incorporates it into their calendar. Events MAY be published in
   several ways including: embedding the event as an object in a web
   page, e-mailing the event to a distribution list, and posting the
   event to a newsgroup.

   The table below illustrates the sequence of events between the
   publisher and the consumers of a published event.

+-------------------------------------------------------------------+
| Action                          |  "Organizer"                    |
+---------------------------------+---------------------------------+
| Publish an event                | "A" sends or posts a PUBLISH    |
|                                 | message                         |
+---------------------------------+---------------------------------+
| "B" reads a published event     |                                 |
+---------------------------------+---------------------------------+
| Publish an updated event        | "A" sends or posts a PUBLISH    |
|                                 | message                         |
+---------------------------------+---------------------------------+
| "B" reads the updated event     |                                 |
+---------------------------------+---------------------------------+
| Cancel a published event        | "A" sends or posts a CANCEL     |
|                                 | message                         |
+---------------------------------+---------------------------------+
| "B" reads the canceled event    |                                 |
|  publication                    |                                 |
+---------------------------------+---------------------------------+

4.1.1     A Minimal Published Event

   The iCalendar object below describes a single event that begins on
   July 1, 1997 at 20:00 UTC. This event contains the minimum set of
   properties for a "PUBLISH" for a "VEVENT" calendar component.

Silverberg/Mansour/Dawson/Hopson  45                   Expires MAY 1998
     BEGIN:VCALENDAR
     METHOD:PUBLISH
     PRODID:-//ACME/DesktopCalendar//EN
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER:a@host.com
     ATTENDEE;ROLE=OWNER:mailto:a@host.com
     DTSTART:19970701T200000Z
     DTSTAMP:19970611T190000Z
     SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
     UID:0981234-1234234-23@host.com
     END:VEVENT

Silverberg/Mansour/Dawson/Hopson  42                   Expires MAY 1998
     END:VCALENDAR

4.1.2     Changing A Published Event

   The iCalendar object below describes an update to the event described
   in 4.1.1, the time has been changed, an end time has been added, and
   the sequence number has been adjusted.

     BEGIN:VCALENDAR
     METHOD:PUBLISH
     VERSION:2.0
     PRODID:-//ACME/DesktopCalendar//EN
     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER:a@acme.com
     ATTENDEE;ROLE=OWNER:mailto:A@example.com
     DTSTAMP:19970612T190000Z
     DTSTART:19970701T210000Z
     DTEND:19970701T230000Z
     SEQUENCE:2
     UID:0981234-1234234-23@host.com
     SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
     END:VEVENT
     END:VCALENDAR

   The "UID" property is used by the client to identify the event. The
   "SEQUENCE" property indicates that this is the second change to the
   event. Events with sequence numbers 0 and 1 are superseded by this
   event.

   The "SEQUENCE" property provides a reliable way to distinguish
   different versions of the same event. Each time an event is
   published, its sequence number is incremented. If a client receives
   an event with a sequence number 5 and finds it has the same event
   with sequence number 2, the event SHOULD be updated. However, if the
   client received an event with sequence number 2 and finds it already
   has sequence number 5 of the same event, the event SHOULD NOT be
   updated.

Silverberg/Mansour/Dawson/Hopson  46                   Expires MAY 1998

4.1.3     Canceling A Published Event

   The iCalendar object below cancels the event described in 4.1.1. This
   cancels the event with "SEQUENCE" property of 0, 1, and 2.

     BEGIN:VCALENDAR
     METHOD:CANCEL
     VERSION:2.0
     PRODID:-//ACME/DesktopCalendar//EN
     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER:a@acme.com
     ATTENDEE;ROLE=OWNER:mailto:A@example.com
     COMMENT:DUKES forfeit the game
     SEQUENCE:2
     UID:0981234-1234234-23@host.com
     DTSTAMP:19970613T190000Z
     STATUS:CANCELLED

Silverberg/Mansour/Dawson/Hopson  43                   Expires MAY 1998
     END:VEVENT
     END:VCALENDAR

4.1.4     A Rich Published Event

   This example describes the same event as in 4.1.1, but in much
   greater detail.

     BEGIN:VCALENDAR

     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:PUBLISH
     CALSCALE:GREGORIAN
     SCALE:GREGORIAN
     SOURCE:http://www.midwaystadium.com/stadium-cal/1997-events.or4
     NAME:1997 GAME SCHEDULE
     VERSION:2.0

     BEGIN:VTIMEZONE
     DAYLIGHT:TRUE
     DTSTART:19970406T070000-0600
     RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
     TZNAME:CDT
     TZOFFSET:-0500
     END:VTIMEZONE

     BEGIN:VTIMEZONE
     DAYLIGHT:FALSE
     DTSTART:19971026T0200-0500
     RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
     TZNAME:CST
     TZOFFSET:-0600
     END:VTIMEZONE

     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER:a@acme.com
     ATTENDEE;ROLE=OWNER:mailto:A@example.com

Silverberg/Mansour/Dawson/Hopson  47                   Expires MAY 1998
     ATTACH:http://www.midwaystadium.com
     CATEGORIES:SPORTS EVENT;ENTERTAINMENT
     CLASS:PRIVATE
     CREATED:19970415T194319Z
     DESCRIPTION:MIDWAY STADIUM\n
      Big time game. MUST see.\n
      Expected duration:2 hours\n
     DTEND:19970701T180000
     DTSTART:19970702T160000
     DTSTAMP:19970614T190000Z
     STATUS:CONFIRMED
     LAST-MODIFIED:19970416T162421Z
     LOCATION;VALUE=URL:http://www.midwaystadium.com/
     PRIORITY:2
     RESOURCES:SCOREBOARD
     SEQUENCE:3
     SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
     UID:0981234-1234234-23@host.com

Silverberg/Mansour/Dawson/Hopson  44                   Expires MAY 1998
     RELATED-TO:0981234-1234234-14@host.com

     BEGIN:VALARM
     DTSTART:19970701T190000Z
     REPEAT:2
     DURATION:PT2H
     CATEGORIES:DISPLAY,AUDIO
     DESCRIPTION:Itís
     DESCRIPTION:It's almost game time
     END:VALARM

     BEGIN:VALARM
     DTSTART:19970701T153000
     CATEGORIES:DISPLAY,AUDIO
     DESCRIPTION:You SHOULD leave now. Game starts in 30 min!
     END:VALARM

     END:VEVENT
     END:VCALENDAR

   The "CLASS" property is specified, though it is not really needed
   here. Since this is a published event, a program that displays it
   need not apply any content filtering based on the "CLASS" attribute.
   If this event is copied into a userís user's calendar, the "CLASS" would be
   included as part of the copy.  The handling of the "CLASS" tag at
   that point is implementation specific.

   The "RELATED-TO" field contains the "UID" property of a related
   calendar event. The handling of this property is application
   dependent.

   The "SEQUENCE" property 3 indicates that this event supersedes
   versions 0, 1, and 2.

Silverberg/Mansour/Dawson/Hopson  48                   Expires MAY 1998

4.1.5     Anniversaries or Events attached to entire days

   This example demonstrates the use of the "value" parameter to tie a
   VEVENT to day rather than a specific time.

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:PUBLISH
     VERSION:2.0
     BEGIN:VEVENT
     DTSTAMP:19970614T190000Z
     UID:0981234-1234234-23@host.com
     DTSTART;VALUE=DATE:19970714
     RRULE:FREQ=YEARLY;INTERVAL=1
     SUMMARY: Bastille Day
     END:VEVENT
     END:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  45                   Expires MAY 1998

4.2 Group Event Examples

   Group events are distinguished from published events in that they
   have "Attendees" and that there is interaction between the
   "Attendees" with respect to the event. Individual "A" requests a
   meeting between individuals "A", "B", "C" and "D". Individual "B"
   confirms attendance to the meeting. Individual "C" declines
   attendance. Individual "D" tentatively confirms their attendance.
   This is sometimes referred to as "penciling-in" the event on a
   calendar. The following table illustrates the sequence of messages
   that would be exchanged between these individuals. The table below
   illustrates the message flow.

+--------------------------------------------------------------------+
| Action             |  "Organizer"        | Attendee                |
+--------------------------------------------------------------------+
| Initiate a meeting | "A" sends a REQUEST |                         |
| request            | message to "B", "C",|                         |
|                    | and "D"             |                         |
+--------------------------------------------------------------------+
| Accept the meeting |                     | "B" sends a REPLY       |
| request            |                     | message to "A" with its |
|                    |                     | ATTENDEE STATUS para-   |
|                    |                     | set to "ACCEPTED"       |
+--------------------------------------------------------------------+
| Decline the meeting|                     | "C" sends a REPLY       |
| request            |                     | message to "A" with its |
|                    |                     | ATTENDEE STATUS para-   |
|                    |                     | set to "DECLINED"       |
+--------------------------------------------------------------------+
| Tentatively accept |                     | "D" sends a REPLY       |
| the meeting request|                     | message to "A" with its |
|                    |                     | ATTENDEE STATUS para-   |

Silverberg/Mansour/Dawson/Hopson  49                   Expires MAY 1998

|                    |                     | set to "TENTATIVE"      |
+--------------------------------------------------------------------+
| Confirm meeting    | "A" sends a REQUEST |                         |
| status with        | message to "B" and  |                         |
| attendees          | "C" with updated    |                         |
|                    | information.        |                         |
+--------------------------------------------------------------------+

4.2.1     A Group Event Request

   A sample meeting request that "A" sends to "B", "C", and "D".

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REQUEST
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:A@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:B@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:C@acme.com

Silverberg/Mansour/Dawson/Hopson  46                   Expires MAY 1998
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:D@acme.com
     ATTENDEE;RSVP=NO;EXPECT=REQUIRE;TYPE=ROOM:CR_Big_One@acme.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:B@example.
com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:C@example.
com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:D@example.
com
     ATTENDEE;RSVP=FALSE;EXPECT=REQUIRE;TYPE=ROOM:CR_Big@example.com
     DTSTAMP:19970611T190000Z
     DTSTART:19970701T100000-0700
     DTEND:19970701T103000-0700
     SUMMARY:Phone Conference
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:0
     STATUS:CONFIRMED
     END:VEVENT
     END:VCALENDAR

4.2.2     Reply To A Group Event Request

   Attendee "B" accepts the meeting.

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;STATUS=ACCEPTED:B@acme.com
     ATTENDEE;STATUS=ACCEPTED:Mailto:B@example.com
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:0
     REQUEST-STATUS:2.0;Success
     DTSTAMP:19970612T190000Z

Silverberg/Mansour/Dawson/Hopson  50                   Expires MAY 1998
     END:VEVENT
     END:VCALENDAR

   "B" could have declined the meeting or indicated tentative acceptance
   by setting the ATTENDEE;"STATUS" parameter to DECLINED or TENTATIVE,
   respectively.

4.2.3     Update An Event

   The event is moved to a different time. The combination of the "UID"
   property(which remains the same) and the SEQUENCE (bumped to 1)
   properties indicate the update.

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REQUEST
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:A@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:B@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:C@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:D@acme.com
     ATTENDEE;RSVP=NO;EXPECT=REQUIRE;TYPE=ROOM:CR_Big_One@acme.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:B@example.
com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:C@example.
com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:D@example.
com
     ATTENDEE;RSVP=FALSE;EXPECT=REQUIRE;TYPE=ROOM:CR_Big@example.com
     DTSTART:19970701T110000-0700
     DTEND:19970701T113000-0700
     SUMMARY:Phone Conference

Silverberg/Mansour/Dawson/Hopson  47                   Expires MAY 1998
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:1
     DTSTAMP:19970613T190000Z
     STATUS:CONFIRMED
     END:VEVENT
     END:VCALENDAR

4.2.4     Countering an Event Proposal

   Attendee A sends "REQUEST" to B and C. B makes a counter proposal to
   A to change the time and location.

   Attendee A sends "REQUEST":

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REQUEST
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:A@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:B@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:C@acme.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com

Silverberg/Mansour/Dawson/Hopson  51                   Expires MAY 1998
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:B@example.
     com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:C@example.
com
     DTSTART:19970701T190000Z
     DTEND:19970701T200000Z
     SUMMARY:Discuss the Merits of the election results
     LOCATION:The Big Conference Room
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:0
     DTSTAMP:19970611T190000Z
     STATUS:CONFIRMED
     END:VEVENT
     END:VCALENDAR

   Attendee B sends "COUNTER" to A, requesting changes to time and
   place:

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:COUNTER
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:A@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:B@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:C@acme.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:B@example.
     com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:C@example.
com
     DTSTART:19970701T160000Z
     DTEND:19970701T190000Z
     DTSTAMP:19970612T190000Z
     SUMMARY:Discuss the Merits of the election results
     LOCATION:The Small Conference Room
     COMMENT:This time works much better and I think the big conference
       room is too big
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:0

Silverberg/Mansour/Dawson/Hopson  48                   Expires MAY 1998
     DTSTAMP:19970611T190000Z
     END:VEVENT
     END:VCALENDAR

   Attendee A accepts the changes from B

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REQUEST
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:A@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:B@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:C@acme.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com

Silverberg/Mansour/Dawson/Hopson  52                   Expires MAY 1998
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:B@example.
com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:C@example.
com
     DTSTAMP:19970613T190000Z
     DTSTART:19970701T160000Z
     DTEND:19970701T190000Z
     SUMMARY:Discuss the Merits of the election results - changed to
       suite B's schedule
     LOCATION:The Small Conference Room
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:1
     STATUS:CONFIRMED
     END:VEVENT
     END:VCALENDAR

   A rejects B's counter proposal

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:COUNTERDECLINE
     METHOD:DECLINECOUNTER
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:A@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:B@acme.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:B@example.
com
     COMMENT:Sorry, I cannot change this meeting time
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:1
     DTSTAMP:19970614T190000Z
     END:VEVENT

4.2.5     Delegate An Event

   When delegating an event request to another "Calendar User", the
   "delegator" MUST both update the "Organizer" with a "REPLY" and send
   a request to the "delegatee". There is currently no protocol
   limitation to delegation depth. It is possible for the original
   delegate to delegate the meeting to someone else, and so on. When a
   request is delegated from one "CUA" to another there are a number of
   responsibilities required of the "delegator". They MUST:

Silverberg/Mansour/Dawson/Hopson  49                   Expires MAY 1998
      ∑

      . Send an REPLY to the "Organizer" with their attendee/status
        property parameter set to "Delegated"

      

      . Include the delegate as an additional attendee with the
        "Delegated-From" property parameter set to the delegator

      

      . Include the original UID of the REQUEST

      

Silverberg/Mansour/Dawson/Hopson  53                   Expires MAY 1998
      . The delegator MUST also send a copy of the original REQUEST to
        the delegate. The delegator modifies the request to include:

      

      . The ATTENDEE/STATUS property parameter for the delegator
        (sender in this case) is set to "DELEGATED"

      

      . ATTENDEE/DELEGATED-TO parameter is set to the address of the
        delegatee

      

      . An ATTENDEE property is added for delegatee

   As a rule, it is not required that the "delegatee" include the
   "delegator" in their "REPLY" method. However, it is strongly advised
   since this will inform the "delegator" whether their proxy plans to
   attend the meeting. If the "delegatee" declines the meeting, the
   "delegator" MAY elect to try and delegate the "REQUEST" to another
   "CUA". The process is the same.

+---------------------------------------------------------------------+
| Action             |  "Organizer"        | Attendee                 |
+---------------------------------------------------------------------+
| Initiate a meeting | "A" sends a REQUEST |                          |
| request            | message to "B" and  |                          |
+---------------------------------------------------------------------+
| Delegate:          |                     | "C" sends a REPLY to "A" |
| "C" delegates to   |                     | with the ATTENDEE.STATUS |
| "E"                |                     | parameter set to         |
|                    |                     | "DELEGATED" and with a   |
|                    |                     | new ATTENDEE property    |
|                    |                     | for "E". "E's" ATTENDEE  |
|                    |                     | DELEGATED-FROM property  |
|                    |                     | is set to "C". "C's"     |
|                    |                     | ATTENDEE.DELEGATED-TO    |
|                    |                     | property is set to "E".  |
|                    |                     | "C" sends REQUEST message|
|                    |                     | to "E" with the original |
|                    |                     | meeting request          |
|                    |                     | information. The         |
|                    |                     | ATTENDEE/STATUS property |
|                    |                     | parameter for "C" is set |
|                    |                     | to "DELEGATED" and the   |
|                    |                     | ATTENDEE/DELEGATED-TO    |
|                    |                     | parameter is set to      |
|                    |                     | the address of "E". An   |
|                    |                     | ATTENDEE property is     |
|                    |                     | added for "E" and the    |
|                    |                     | ATTENDEE/DELEGATED-FROM  |
|                    |                     | parameter is set to      |
|                    |                     | the address of "C".      |

Silverberg/Mansour/Dawson/Hopson  50                   Expires MAY 1998
+---------------------------------------------------------------------+
| Confirm meeting    |                     | "E" sends REPLY message  |
| attendance         |                     | to "A" and optionally "C"|
|                    |                     | with its ATTENDEE/STATUS |
|                    |                     | property parameter set   |

Silverberg/Mansour/Dawson/Hopson  54                   Expires MAY 1998

|                    |                     | to "ACCEPTED"            |
+---------------------------------------------------------------------+
| Optional:          | "A" sends REQUEST   |                          |
| Redistribute       | message to "B", "C" |                          |
| meeting to         | and "E". SEQUENCE   |                          |
| attendees          | number is now 1.    |                          |
+---------------------------------------------------------------------+

   Attendee "C" responds to meeting "Organizer" "A"

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=ATTENDEE;STATUS=DELEGATED;DELEGATED-
      TO=E@acme.com:C@acme.com
      TO="Mailto:E@example.com":Mailto:C@example.com
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:0
     REQUEST-STATUS:2.0;Success
     DTSTAMP:19970611T190000Z
     END:VEVENT
     END:VCALENDAR

   Attendee "C" delegates presence at the meeting to "E".

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REQUEST
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=Organizer;STATUS=ACCEPTED:A@acme.com
     ATTENDEE;ROLE=DELEGATE;RSVP=YES;EXPECT=REQUEST;
      DELEGATED-FROM=C@acme.com:E@acme.com
     ATTENDEE;ROLE=ORGANIZER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;ROLE=DELEGATE;RSVP=TRUE;EXPECT=REQUEST;
      DELEGATED-FROM=_Mailto:C@example.com_:Mailto:E@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=DELEGATED;
      DELEGATED-TO=E@acme.com:C@acme.com
      DELEGATED-TO="Mailto:E@example.com":Mailto:C@example.com
     DTSTART:19970701T110000-0700
     DTEND:19970701T113000-0700
     SUMMARY:Phone Conference
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:0
     STATUS:CONFIRMED
     DTSTAMP:19970611T190000Z
     END:VEVENT
     END:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  51  55                   Expires MAY 1998

4.2.6     Delegate Accepts the Meeting

   To accept a delegated meeting, the delegate sends the following
   message to "A" and "C"

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=ATTENDEE;STATUS=CONFIRMED;
      DELEGATED-FROM=C@acme.com:E@acme.com
      DELEGATED-FROM="Mailto:C@example.com":Mailto:E@example.com
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:1
     REQUEST-STATUS:2.0;Success
     DTSTAMP:19970614T190000Z
     END:VEVENT
     END:VCALENDAR

4.2.7     Delegate Declines the Meeting

   In this example the delegate declines the meeting request and sets
   the "ATTENDEE" property "STATUS" parameter to DECLINED. The
   "Organizer" SHOULD resend the "REQUEST" to "C" with the status of the
   delegate set to DECLINED. This lets the "delegator" know that the
   "delegate" has declined and provides an opportunity to the
   "delegator" to either accept or delegate the request to another
   "Calendar User".

   Response from "E" to "A" and "C".

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=ATTENDEE;STATUS=DECLINED;
      DELEGATED-FROM=C@acme.com:E@acme.com
      DELEGATED-FROM="Mailto:C@example.com":Mailto:E@example.com
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:1
     REQUEST-STATUS:2.0;Success
     DTSTAMP:19970614T190000Z
     END:VEVENT
     END:VCALENDAR

   "A" resends the "REQUEST" method to "C". "A" MAY also wish to express
   the fact that the item was delegated in the "COMMENT" property.

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VEVENT

Silverberg/Mansour/Dawson/Hopson  52  56                   Expires MAY 1998
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=ATTENDEE;STATUS=DECLINED;
      DELEGATED-FROM=C@acme.com:E@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:C@acme.com
      DELEGATED-FROM="Mailto:C@example.com":Mailto:E@example.com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:C@example.
com
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:2
     REQUEST-STATUS:2.0;Success
     DTSTAMP:19970614T200000Z
     COMMENT:DELEGATE (ATTENDEE E@acme.com) Mailto:E@example.com) DECLINED YOUR
INVITATION
     END:VEVENT
     END:VCALENDAR

4.2.8     Forwarding an Event Request

   The protocol does not prevent an "Attendee" from "forwarding" an
   "VEVENT" calendar component to other "Calendar Users". Forwarding
   differs from delegation in that the forwarded "Calendar User" (often
   referred to as a "Party Crasher") does not replace the forwarding
   "Calendar User". Implementations are not required to add the "Party
   Crasher" to the "Attendee" list and hence there is no guarantee that
   a "Party Crasher" will receive additional updates to the Event. The
   forwarding "Calendar User" SHOULD NOT add the "Party Crasher" to the
   attendee list.

4.2.9     Cancel A Group Event

   Individual "A" requests a meeting between individuals "A", "B" and
   "C". Individual "B" declines attendance to the meeting. Individual
   "A" decides to cancel the meeting. The following table illustrates
   the sequence of messages that would be exchanged between these
   individuals.

   Messages related to a previously canceled event ("SEQUENCE" property
   value is less than the "SEQUENCE" property value of the "CANCEL"
   message) or "VTODO" calendar component MUST be ignored.

+--------------------------------------------------------------------+
| Action             |  "Organizer"        | Attendee                |
+--------------------------------------------------------------------+
| Initiate a meeting | "A" sends a REQUEST |                         |
| request            | message to "B" and  |                         |
|                    | and "C"             |                         |
+--------------------------------------------------------------------+
| Decline the meeting|                     | "B" sends a REPLY       |
| request            |                     | message to "A" with its |
|                    |                     | ATTENDEE STATUS para-   |
|                    |                     | set to "DECLINED".      |

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+--------------------------------------------------------------------+
| Cancel the meeting | "A" sends a CANCEL  |                         |
|                    | message to "B" and  |                         |
|                    | "C"                 |                         |
+--------------------------------------------------------------------+

   The example shows how "A" cancels the event.

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     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:CANCEL
     VERSION:2.0
     BEGIN:VEVENT
     COMMENT:Mr. B cannot attend. Iíll I'll reschedule the meeting later.
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:0
     DTSTAMP:19970613T190000Z
     STATUS:CANCELLED
     END:VEVENT
     END:VCALENDAR

   The "Organizer" of a meeting MAY "uninvite" or remove "Attendees" by
   sending a "CANCEL" method to only those "Attendees".

4.3 Busy Time Examples

   Individual "A" requests busy time from individuals "B", "C" and "D".
   Individual "B" and "C" replies with busy time data to individual "A".
   Individual "D" does not support busy time requests and does not reply
   with any data.

   The following table illustrates the sequence of messages that would
   be exchanged between these individuals.

+--------------------------------------------------------------------+
| Action             |  "Organizer"        | Attendee                |
+--------------------------------------------------------------------+
| Initiate a busy    | "A" sends a REQUEST |                         |
| time request       | message to "B" and  |                         |
|                    | and "C"             |                         |
+--------------------------------------------------------------------+
| Reply to the busy  |                     | "B" sends a REPLY       |
| request with busy  |                     | message to "A" with     |
| time data          |                     | busy time data          |
+--------------------------------------------------------------------+

4.3.1     Request Busy Time

   "A" sends a BUSY-"REQUEST" to "B" and "C" for busy time

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     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REQUEST
     VERSION:2.0
     BEGIN:VFREEBUSY
     ATTENDEE;ROLE=OWNER:A@acme.com
     ATTENDEE:B@acme.com
     ATTENDEE:C@acme.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE:Mailto:B@example.com
     ATTENDEE:Mailto:C@example.com
     DTSTAMP:19970613T190000Z
     DTSTART:19970701T080000-0700

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     DTEND:19970701T200000-0700
     UID:www.acme.com-873970198738777@host.com
     END:VFREEBUSY
     END:VCALENDAR

4.3.2     Reply To A Busy Time Request

   "B" sends a "REPLY" method type of a "VFREEBUSY" calendar component
   to "A"

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VFREEBUSY
     ATTENDEE:B@acme.com
     ATTENDEE:Mailto:B@example.com
     DTSTART:19970701T080000-0700
     DTEND:19970701T200000-0700
     UID:www.acme.com-873970198738777@host.com
     FREEBUSY:19970701T090000-0700/PT1H,19970701T140000-0700/PT30H
     DTSTAMP:19970613T190030Z
     END:VFREEBUSY
     END:VCALENDAR

   B is busy from 09:00 to 10:00 and from 14:00 to 14:30.

4.4 Recurring Event and Time Zone Examples

4.4.1     A Recurring Event Spanning Time Zones

   This event describes a weekly phone conference. The "Attendees" are
   each in a different time zone.

     BEGIN:VCALENDAR

     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REQUEST

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     VERSION:2.0

     BEGIN:VTIMEZONE
     DAYLIGHT:TRUE
     DTSTART:19970406T200000-0800
     RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
     TZNAME:PDT
     TZOFFSET:-0700
     END:VTIMEZONE

     BEGIN:VTIMEZONE
     DAYLIGHT:FALSE
     DTSTART:19971026T200000-0700
     RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
     TZNAME:PST

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     TZOFFSET:-0800
     END:VTIMEZONE

     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:sman@mcom.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:gb@mcom.fr
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:kimiko@mcom.jp
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:B@example.fr
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:c@example.jp
     DTSTAMP:19970613T190030Z
     DTSTART:19970701T140000
     DTEND:19970701T150000
     RRULE:FREQ=WEEKLY;INTERVAL=20;WKST=SU;BYDAY=TU
     RDATE:19970910T140000
     EXDATE:19970909T140000
     EXDATE:19971028T150000
     SUMMARY:Weekly Phone Conference
     UID:www.acme.com-873970198738777@host.com
     SEQUENCE:0
     STATUS:CONFIRMED
     END:VEVENT

     END:VCALENDAR

   The "VTIMEZONE" components SHOULD appear in an iCalendar object
   containing recurring events. This is especially important if a
   recurring event has "Attendees" in different time zones. There MAY be
   multiple VTIMEZONE components in an iCalendar object, however, they
   MUST be used to define the same time zone. That is, there cannot be
   VTIMEZONE components describing both PST/PDT and EST/EDT at the
   component level in the same iCalendar object.

   The first two components of this iCalendar object are the time zone
   components. The "DTSTART" date coincides with the first instance of
   the RRULE property.

   The recurring meeting is defined in a particular time zone,
   presumably that of the originator. The client for each "Attendee" has
   the responsibility of determining the recurrence time in the
   "Attendee's" time zone.

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   The repeating event starts on Tuesday, July 1, 1997 at 2:00pm. Since
   no time zone is specified in the "DTSTART" property, the time zone
   component of PDT applies to the start and end times. "Attendee"
   gb@mcom.fr
   B@example.fr is in France where the local time on this date is 7
   hours later than PDT or 21:00. "Attendee" kimiko@mcom.jp C@example.jp is in Japan
   where local time is 9 hours ahead of than UTC or Wednesday, July 2 at
   07:00. The event repeats weekly on Tuesdays (in PST/PDT). The "RRULE"
   property results in 20 instances. The last instance falls on Tuesday,
   November 11, 1997 2:00pm PST. The "RDATE" property adds another
   instance: WED, 10-SEP-1997 21:00 GMT.

   There are two exceptions to this recurring appointment. The first one
   is:

   TUE, 09-SEP-1997 21:00 GMT
   TUE, 09-SEP-1997 14:00 PDT
   WED, 10-SEP-1997 07:00 JDT

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   and the second is:

   TUE, 28-OCT-1997 22:00 GMT
   TUE, 28-OCT-1997 14:00 PST
   WED, 29-OCT-1997 07:00 JST

4.4.2     Modify A Recurring Instance

   In this example the "Organizer" issues a recurring meeting. Later the
   "Organizer" changes an instance of the event by changing the
   "DTSTART" property. Note the use of "RECURRENCE-ID" property and
   "SEQUENCE" property in the second request.

   Original Request:

     BEGIN:VCALENDAR
     METHOD:REQUEST
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VEVENT
     CREATED:19970526T083000
     UID:guid-1@host1.com
     SEQUENCE:0
     RRULE:FREQ=MONTHLY;BYMONTHDAY=1;UNTIL=19980901T210000Z
     ATTENDEE;EXPECT=REQUEST:Sman@netscape.com
     ATTENDEE;EXPECT=REQUEST:Frank_Dawson@Lotus.com
     ATTENDEE;EXPECT=REQUEST:Deriks@Microsoft.com
     ATTENDEE;EXPECT=REQUEST:Alecd@Microsoft.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:B@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:C@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:D@example.com
     DESCRIPTION:IETF-C&S Conference Call
     CLASS:PUBLIC
     SUMMARY:IETF Calendaring Working Group Meeting
     DTSTART:19970601T210000Z
     DTEND:19970601T220000Z
     LOCATION:Conference Call

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     DTSTAMP:19970526T083000
     STATUS:CONFIRMED
     END:VEVENT
     END:VCALENDAR

   The event request below is to change a time and create an exception.
   This creates an exception on July 3rd.

     BEGIN:VCALENDAR
     METHOD:REQUEST
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VEVENT
     CREATED:19970526T083000
     UID:guid-1@host1com
     RECURRENCE-ID:19970701T210000Z
     SEQUENCE:1
     RRULE:FREQ=MONTHLY;BYMONTHDAY=1;UNTIL=19980901T210000Z
     ATTENDEE;EXPECT=REQUEST:Sman@netscape.com
     ATTENDEE;EXPECT=REQUEST:Frank_Dawson@Lotus.com

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     ATTENDEE;EXPECT=REQUEST:Deriks@Microsoft.com
     ATTENDEE;EXPECT=REQUEST:Alecd@Microsoft.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:B@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:C@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:D@example.com
     DESCRIPTION:IETF-C&S Conference Call
     CLASS:PUBLIC
     SUMMARY:IETF Calendaring Working Group Meeting
     DTSTART:19970703T210000Z
     DTEND:19970703T220000Z
     LOCATION:Conference Call
     DTSTAMP:19970626T093000
     STATUS:CONFIRMED
     END:VEVENT
     END:VCALENDAR

4.4.3     Cancel A Recurring Instance

   In this example the "Organizer" of a recurring event wishes to delete
   an instance. This is referred to as an "exception" to the recurring
   event.

     BEGIN:VCALENDAR
     METHOD:CANCEL
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VEVENT
     UID:guid-1@host1.com
     RECURRENCE-ID:19970801T210000Z
     SEQUENCE:2
     DTSTAMP:19970721T093000
     STATUS:CANCELLED
     END:VEVENT

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     END:VCALENDAR

4.4.4     Cancel An Exception

   In the following example, the "Organizer" has created an exception
   (as in 4.4.3) and now wishes to cancel it. In this case a "CANCEL"
   method is sent with the specific "RECURRENCE-ID", "UID" and
   "SEQUENCE" properties of the exception. This same sequence MAY be
   used to decline a previously accepted modification to a recurring
   event (as in 4.4.2).

     BEGIN:VCALENDAR
     METHOD:CANCEL
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VEVENT
     UID:guid-1@host1.com
     RECURRENCE-ID:19970801T210000Z
     SEQUENCE:2
     DTSTAMP:19970721T103000
     STATUS:CANCELLED
     END:VEVENT

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     END:VCALENDAR

4.4.5     Cancel Recurring Event

   In this example the "Organizer" wishes to cancel the entire recurring
   event and any child exceptions.

     BEGIN:VCALENDAR
     METHOD:CANCEL
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VEVENT
     UID:guid-1@host1.com
     DTSTAMP:19970721T103000
     SEQUENCE:2
     STATUS:CANCELLED
     END:VEVENT
     END:VCALENDAR

4.4.6     Change All Future Instances

   This example changes the meeting location from a conference call to
   Seattle starting Sept 1 and extends to all future instances.

     BEGIN:VCALENDAR
     METHOD:REQUEST

Silverberg/Mansour/Dawson/Hopson  63                   Expires MAY 1998
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VEVENT
     CREATED:19970526T083000
     UID:guid-1@host1.com
     RECURRENCE-ID;THISANDFUTURE:19970901T210000Z
     SEQUENCE:3
     RRULE:FREQ=MONTHLY;BYMONTHDAY=1;UNTIL=19980901T210000Z
     ATTENDEE;EXPECT=REQUEST:Sman@netscape.com
     ATTENDEE;EXPECT=REQUEST:Frank_Dawson@Lotus.com
     ATTENDEE;EXPECT=REQUEST:Deriks@Microsoft.com
     ATTENDEE;EXPECT=REQUEST:Alecd@Microsoft.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:B@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:C@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:D@example.com
     DESCRIPTION:IETF-C&S Conference Call
     CLASS:PUBLIC
     SUMMARY:IETF Calendaring Working Group Meeting
     DTSTART:19970901T210000Z [SS2][SS3]
     DTEND:19970901T220000Z
     LOCATION:Building 32, Microsoft, Seattle, WA
     DTSTAMP:19970526T083000
     STATUS:CONFIRMED
     END:VEVENT
     END:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  59                   Expires MAY 1998

4.4.7     Add A New Instance To A Recurring Event

   This example adds a one-time additional instance to the recurring
   event. "Organizer" adds a second July meeting on the 15th.

     BEGIN:VCALENDAR
     METHOD:REQUEST
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VEVENT
     CREATED:19970526T083000
     UID:guid-1@host1.com
     RECURRENCE-ID:19970715T210000Z
     SEQUENCE:4
     RRULE:FREQ=MONTHLY;BYMONTHDAY=1;UNTIL=19980901T210000Z
     RDATE;VALUE=PERIOD:19970715T210000Z/19970715T220000Z
     ATTENDEE;EXPECT=REQUEST:Sman@netscape.com
     ATTENDEE;EXPECT=REQUEST:Frank_Dawson@Lotus.com
     ATTENDEE;EXPECT=REQUEST:Deriks@Microsoft.com
     ATTENDEE;EXPECT=REQUEST:Alecd@Microsoft.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:B@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:C@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:D@example.com
     DESCRIPTION:IETF-C&S Conference Call
     CLASS:PUBLIC
     SUMMARY:IETF Calendaring Working Group Meeting
     DTSTART:19970715T210000Z
     DTEND:19970715T220000Z
     LOCATION:Conference Call
     DTSTAMP:19970629T093000

Silverberg/Mansour/Dawson/Hopson  64                   Expires MAY 1998
     STATUS:CONFIRMED
     END:VEVENT
     END:VCALENDAR

4.4.8     Counter An Instance Of A Recurring Event

   In this example one of the "Attendees" counters the "DTSTART"
   property of the proposed second July meeting.

     BEGIN:VCALENDAR
     METHOD:COUNTER
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VEVENT
     CREATED:19970526T083000
     UID:guid-1@host1.com
     RECURRENCE-ID:19970715T210000Z
     SEQUENCE:4
     RRULE:FREQ=MONTHLY;BYMONTHDAY=1;UNTIL=19980901T210000Z
     ATTENDEE;EXPECT=REQUEST:Sman@netscape.com
     ATTENDEE;EXPECT=REQUEST:Frank_Dawson@Lotus.com
     ATTENDEE;EXPECT=REQUEST:Deriks@Microsoft.com
     ATTENDEE;EXPECT=REQUEST:Alecd@Microsoft.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:B@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:C@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:D@example.com
     DESCRIPTION:IETF-C&S Conference Call
     CLASS:PUBLIC
     SUMMARY:IETF Calendaring Working Group Meeting

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     DTSTART:19970715T220000Z
     DTEND:19970715T230000Z
     LOCATION:Conference Call
     COMMENT:May we bump this by an hour? I have a conflict
     DTSTAMP:19970629T094000
     END:VEVENT
     END:VCALENDAR

4.4.9     Error Reply To A request

   The following example illustrates a scenario where a meeting is
   proposed that contains a property that is not supported (in this
   case, the "RRULE" property).

   Original Request:

     BEGIN:VCALENDAR
     METHOD:REQUEST
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VEVENT
     CREATED:19970526T083000
     UID:guid-1@host1.com

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     SEQUENCE:0
     RRULE:FREQ=MONTHLY;BYMONTHDAY=1
     ATTENDEE;EXPECT=REQUEST:Sman@netscape.com
     ATTENDEE;EXPECT=REQUEST:Frank_Dawson@Lotus.com
     ATTENDEE;EXPECT=REQUEST:Deriks@Microsoft.com
     ATTENDEE;EXPECT=REQUEST:Alecd@Microsoft.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:B@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:C@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:D@example.com
     DESCRIPTION:IETF-C&S Conference Call
     CLASS:PUBLIC
     SUMMARY:IETF Calendaring Working Group Meeting
     DTSTART:19970601T210000Z
     DTEND:19970601T220000Z
     DTSTAMP:19970602T094000
     LOCATION:Conference Call
     STATUS:CONFIRMED
     END:VEVENT
     END:VCALENDAR

   Response to indicate that RRULE is not supported:

     BEGIN:VCALENDAR
     PRODID:-//RDU Software//NONSGML HandCal//EN
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VEVENT
     REQUEST-STATUS:2.8;Repeating event ignored. Scheduled as a single
       event;RRULE
     UID:guid-1@host1.com
     SEQUENCE:0
     DTSTAMP:19970603T094000
     END:VEVENT

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     END:VCALENDAR

4.5 Group To-do Examples

   Individual "A" creates a group task in which individuals "A", "B",
   "C" and "D" will participate. Individual "B" confirms acceptance of
   the task. Individual "C" declines the task. Individual "D"
   tentatively accepts the task. The following table illustrates the
   sequence of messages that would be exchanged between these
   individuals. Individual "A" then issues a "REFRESH" method to obtain
   the status of the to-do from each participant. The response indicates
   the individual "Attendee's" completion status. The table below
   illustrates the message flow.

+--------------------------------------------------------------------+
| Action             |  "Organizer"        | Attendee                |
+--------------------------------------------------------------------+
| Initiate a to-do   | "A" sends a REQUEST |                         |
| request            | message to "B", "C",|                         |
|                    | and "D"             |                         |

Silverberg/Mansour/Dawson/Hopson  66                   Expires MAY 1998

+--------------------------------------------------------------------+
| Accept the to-do   |                     | "B" sends a REPLY       |
| request            |                     | message to "A" with its |
|                    |                     | ATTENDEE STATUS para-   |
|                    |                     | set to "ACCEPTED".      |
+--------------------------------------------------------------------+
| Decline the to-do  |                     | "C" sends a REPLY       |
| request            |                     | message to "A" with its |
|                    |                     | ATTENDEE STATUS para-   |
|                    |                     | set to "DECLINED".      |
+--------------------------------------------------------------------+
| Tentatively accept |                     | "D" sends a REPLY       |
| the to-do request  |                     | message to "A" with its |
|                    |                     | ATTENDEE STATUS para-   |
|                    |                     | set to "TENTATIVE".     |
+--------------------------------------------------------------------+
| Check attendee     | "A" sends a REFRESH |                         |
| completion status  | message to "B" and  |                         |
|                    | "C" with current    |                         |
|                    | information.        |                         |
+--------------------------------------------------------------------+
| Attendee indicates |                     | "B" sends a REPLY       |
| percent complete   |                     | message indicating      |
|                    |                     | percent complete        |
+--------------------------------------------------------------------+
| Attendee indicates |                     | "C" sends a REPLY       |
| completion         |                     | message indicating      |
|                    |                     | completion              |
+--------------------------------------------------------------------+

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4.5.1     A VTODO Request

   A sample "REQUEST" with for a "VTODO" calendar component that "A"
   sends to "B", "C", and "D".

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REQUEST
     VERSION:2.0
     BEGIN:VTODO
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:A@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:B@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:C@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:D@acme.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:B@example.
com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:C@example.
com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:D@example.
com
     DTSTART:19970701T100000-0700
     DUE:19970722T100000-0700
     SUMMARY:Create the requirements document
     UID:www.acme.com-873970198738777-00@host.com

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     SEQUENCE:0
     DTSTAMP:19970717T200000Z
     STATUS:CONFIRMED
     END:VTODO
     END:VCALENDAR

4.5.2     A VTODO Reply

   Attendee "B" accepts the meeting.

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VTODO
     ATTENDEE;STATUS=ACCEPTED:B@acme.com
     ATTENDEE;STATUS=ACCEPTED:Mailto:B@example.com
     UID:www.acme.com-873970198738777-00@host.com
     COMMENT:I'll send you my input by e-mail
     SEQUENCE:0
     DTSTAMP:19970717T203000Z
     REQUEST-STATUS:2.0;Success
     END:VTODO
     END:VCALENDAR

   "B" could have declined the meeting or indicated tentative acceptance
   by setting the "ATTENDEE;STATUS=" property parameter sequence to
   DECLINED or TENTATIVE, respectively.

4.5.3     A VTODO Refresh

   "A" requests status from all "Attendees".

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN

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     METHOD:REFRESH
     VERSION:2.0
     BEGIN:VTODO
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:A@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:B@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:C@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:D@acme.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:B@example.
com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:C@example.
com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:D@example.
com
     UID:www.acme.com-873970198738777-00@host.com
     DTSTAMP:19970717T230000Z
     END:VTODO
     END:VCALENDAR

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4.5.4     A Refresh Reply: Percent-Complete

   A reply indicating that the task in being worked on and that "B" is
   75% complete with "B's" part of the assignment.

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VTODO
     ATTENDEE;STATUS=IN-PROCESS:B@acme.com
     ATTENDEE;STATUS=IN-PROCESS:Mailto:B@example.com
     PERCENT-COMPLETE:75
     UID:www.acme.com-873970198738777-00@host.com
     DTSTAMP:19970717T233000Z
     SEQUENCE:0
     END:VTODO
     END:VCALENDAR

4.5.5     A Refresh Reply: Completed

   A reply indicating that "C" finished with "C's" part of the
   assignment.

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VTODO
     ATTENDEE;STATUS=COMPLETED:C@acme.com
     ATTENDEE;STATUS=COMPLETED:Mailto:C@example.com
     UID:www.acme.com-873970198738777-00@host.com
     DTSTAMP:19970717T233000Z
     SEQUENCE:0
     END:VTODO
     END:VCALENDAR

4.5.6     An Updated VTODO Request

   Owner "A" resends the "VTODO" calendar component. "A" set's the
   overall completion for the to-do at 40%.

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     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REQUEST
     VERSION:2.0
     BEGIN:VTODO
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:A@acme.com
     ATTENDEE;STATUS=ACCEPTED;TYPE=INDIVIDUAL:B@acme.com
     ATTENDEE;STATUS=COMPLETED;TYPE=INDIVIDUAL:C@acme.com
     ATTENDEE;STATUS=TENTATIVE;TYPE=INDIVIDUAL:D@acme.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;STATUS=ACCEPTED;TYPE=INDIVIDUAL:Mailto:B@example.com
     ATTENDEE;STATUS=COMPLETED;TYPE=INDIVIDUAL:Mailto:C@example.com

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     ATTENDEE;STATUS=TENTATIVE;TYPE=INDIVIDUAL:Mailto:D@example.com
     DTSTART:19970701T100000-0700
     DUE:19970722T100000-0700
     SUMMARY:Create the requirements document
     UID:www.acme.com-873970198738777-00@host.com
     SEQUENCE:1
     DTSTAMP:19970718T100000Z
     STATUS:IN-PROGRESS
     PERCENT-COMPLETE:40
     END:VTODO
     END:VCALENDAR

4.5.7     A Recurring VTODOs

   The following examples relate to recurring "VTODO" calendar
   components.

4.5.7.1   Request for a Recurring VTODO

   In this example "A" sends a recurring "VTODO" calendar component to
   "B" and "C".

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REQUEST
     VERSION:2.0
     BEGIN:VTODO
     ATTENDEE;ROLE=OWNER;STATUS=ACCEPTED:A@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:B@acme.com
     ATTENDEE;RSVP=YES;EXPECT=REQUEST;TYPE=INDIVIDUAL:C@acme.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:B@example.
com
     ATTENDEE;RSVP=TRUE;EXPECT=REQUEST;TYPE=INDIVIDUAL:Mailto:C@example.
com
     RRULE:FREQ=MONTHLY;COUNT=10;BYDAY=1FR
     DTSTART:19980101T100000-0700
     DUE:19980103T100000-0700
     SUMMARY:Send Status Reports to Area Managers
     UID:www.acme.com-873970198738777-00@host.com
     SEQUENCE:0
     DTSTAMP:19970717T200000Z
     STATUS:CONFIRMED
     END:VTODO
     END:VCALENDAR

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4.5.7.2   Calculating due dates in recurring VTODOs

   The due date in a recurring "VTODO" calendar component is either a
   fixed interval specified in the "REQUEST" method or specified
   specifically using the "RECURRENCE-ID" property. The former is

Silverberg/Mansour/Dawson/Hopson  70                   Expires MAY 1998
   calculated by applying the difference between "DTSTART" and "DUE"
   properties and applying it to each of the start of each recurring
   instance. Hence, if the initial "VTODO" calendar component specifies
   a "DTSTART" property value of "19970701T190000Z" and a "DUE" property
   value of "19970801T190000Z" the interval of one day which could be
   applied to each recurring instance of the "VTODO" calendar component.

4.5.7.3   Replying to an instance of a recurring VTODO

   In this example "B" updates "A" on a single instance of the "VTODO"
   calendar component.

     BEGIN:VCALENDAR
     PRODID:-//ACME/DesktopCalendar//EN
     METHOD:REPLY
     VERSION:2.0
     BEGIN:VTODO
     ATTENDEE;STATUS=IN-PROCESS:B@acme.com
     ATTENDEE;STATUS=IN-PROCESS:Mailto:B@example.com
     PERCENT-COMPLETE:75
     UID:www.acme.com-873970198738777-00@host.com
     DTSTAMP:19970717T233000Z
     RECURRENCE-ID:19980101T100000-0700
     SEQUENCE:0
     END:VTODO
     END:VCALENDAR

4.6 Journal Examples

   The iCalendar object below describes a single journal entry for
   October 2, 1997. The "RELATED-TO" property references the phone
   conference event for which minutes were taken.

     BEGIN:VCALENDAR
     PROFILE:PUBLISH
     PRODID:-//ACME/DesktopCalendar//EN
     VERSION:2.0
     BEGIN:VJOURNAL
     DTSTART:19971002T200000Z
     SUMMARY:Phone conference minutes
     DESCRIPTION:The editors meeting was held on October 1, 1997.
       Details are in the attached document.
     UID:0981234-1234234-2410@host.com
     RELATED-TO:0981234-1234234-2402-35@host.com
     ATTACH:ftp\://ftp.example.com/pub/ed/minutes100197.txt
     END:VJOURNAL
     END:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  66  71                   Expires MAY 1998

4.7 Other Examples

4.7.1     Event Refresh

   Refresh the event with "UID" property value of "guid-1-
   12345@host1.com":

     BEGIN:VCALENDAR
     PRODID:-//RDU Software//NONSGML HandCal//EN
     METHOD:REFRESH
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;ROLE=OWNER;EXPECT=REQUEST:Sman@netscape.com
     ATTENDEE;EXPECT=REQUEST:Frank_Dawson@Lotus.com
     ATTENDEE;EXPECT=REQUEST:Deriks@Microsoft.com
     ATTENDEE;EXPECT=REQUEST:Alecd@Microsoft.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:B@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:C@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:D@example.com
     UID: guid-1-12345@host1.com
     DTSTAMP:19970603T094000
     END:VEVENT
     END:VCALENDAR

4.7.2     Bad RECURRENCE-ID

   If an "Attendee" receives a request that references a "RECURRENCE-ID"
   property that can not be found, the "Attendee" SHOULD send a
   "REFRESH" method back to the "Organizer" for the latest copy of the
   event.

+--------------------------------------------------------------------+
| Action             |  "Organizer"        | Attendee                |
+--------------------------------------------------------------------+
| Update an instance | "A" sends a REQUEST |                         |
| request            | message to "B"      |                         |
+--------------------------------------------------------------------+
| Attendee requests  |                     | "B" sends a REFRESH     |
| refresh because    |                     | message to "A"          |
| RecurrenceID was   |                     |                         |
| not found          |                     |                         |
+--------------------------------------------------------------------+
| Refresh the entire | "A" sends the       |                         |
| Event              | latest copy of the  |                         |
|                    | Event to "B"        |                         |
+--------------------------------------------------------------------+
| Attendee handles   |                     | "B" updates to the      |
| the request and    |                     | latest copy of the      |
| updates the        |                     | meeting.                |
| instance           |                     |                         |
+--------------------------------------------------------------------+

Silverberg/Mansour/Dawson/Hopson  72                   Expires MAY 1998
   Request from "A":

     BEGIN:VCALENDAR
     METHOD:REQUEST

Silverberg/Mansour/Dawson/Hopson  67                   Expires MAY 1998
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VEVENT
     UID:acme-12345@host1.com
     SEQUENCE:3
     RRULE:FREQ=WEEKLY
     RDATE;VALUE=PERIOD:19970819T210000Z/199700819T220000Z
     ATTENDEE;STATUS=ACCEPTED;ROLE=OWNER:sman@netscape.com
     ATTENDEE;EXPECT=REQUEST:stevesil@microsoft.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:B@example.com
     DESCRIPTION:IETF-C&S Conference Call
     SUMMARY:IETF Calendaring Working Group Meeting
     DTSTART:19970801T210000Z
     DTEND:19970801T220000Z
     DTSTAMP:19970726T083000
     STATUS:CONFIRMED
     END:VEVENT
     END:VCALENDAR

   "B" has the event with "UID" property"acme-12345@host1.com" but the
   "SEQUENCE" property value is "1" and the event does not have an
   instance at the specified recurrence time. This means that the
   "Owner" is either adding a new instance or that the new instance was
   added when "SEQUENCE" property value "2" of the event was generated.
   In either case, "B" needs a new copy of the event.

     BEGIN:VCALENDAR
     PRODID:-//RDU Software//NONSGML HandCal//EN
     METHOD:REFRESH
     VERSION:2.0
     BEGIN:VEVENT
     ATTENDEE;STATUS=ACCEPTED;ROLE=OWNER:sman@netscape.com
     ATTENDEE;EXPECT=REQUEST:stevesil@microsoft.com
     ATTENDEE;ROLE=OWNER:Mailto:A@example.com
     ATTENDEE;ROLE=ATTENDEE;STATUS=ACCEPTED:Mailto:A@example.com
     ATTENDEE;EXPECT=REQUEST:Mailto:B@example.com
     UID:acme-12345@host1.com
     DTSTAMP:19970603T094000
     END:VEVENT
     END:VCALENDAR

5  Application Protocol Fallbacks

5.1 Partial Implementation

   Applications that support this memo are not required to support the
   entire protocol. The following describes how methods and properties
   SHOULD "fallback" in applications that do not support the complete

Silverberg/Mansour/Dawson/Hopson  73                   Expires MAY 1998
   protocol. If a method or property is not addressed in this section,
   it MAY be ignored.

5.1.1     Event-Related Fallbacks

Method           Fallback
--------------   -----------------------------------------------------

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PUBLISH          Required.
CANCEL           Required.
REQUEST          PUBLISH
REPLY            Required.
DELEGATE         Reply with Not Supported.
REQUEST          Reply with Not Supported.
REPLY            Reply with Not Supported.
COUNTER          Reply with Not Supported
DECLINECOUNTER   Required if EVENT-COUNTER is implemented; otherwise
                 reply with Not Supported.

iCalendar
Property         Fallback
--------------   -----------------------------------------------------
CALSCALE         Ignore; assume GREGORIAN.
GEO              Ignore.
PRODID           Ignore.
METHOD           Required as described in the Method list above.
SOURCE           Ignore
NAME             Ignore.
VERSION          Ignore.

Event-Related
Components       Fallback
--------------   -----------------------------------------------------
VFREEBUSY        Reply with Not Supported.
VALARM           Reply with Not Supported.
VTIMEZONE        Required if RRULE or RDATE is implemented; otherwise
                 ignore and use local time.

Component
Property         Fallback
--------------   -----------------------------------------------------
ATTACH           Ignore.
ATTENDEE         Required if EVENT-REQUEST is not implemented;
                 otherwise reply with Not Supported.
CATEGORIES       Required if in VALARM and VALARM is implemented,
                 otherwise ignore.
CLASS            Ignore.
COMMENT          Ignore.
COMPLETED        Ignore.
CREATED          Ignore.
DAYLIGHT         Required if VTIMEZONE is implemented; otherwise
                 Ignore.
DESCRIPTION      Required.
DELEGATED-FROM   Required if EVENT-DELEGATE is implemented; otherwise

Silverberg/Mansour/Dawson/Hopson  74                   Expires MAY 1998
                 Ignore.
DELEGATED-TO     Required if EVENT-DELEGATE is implemented; otherwise
                 Ignore.
DUE              Ignore.
DURATION         Reply with Not Supported.
DTSTAMP          Required.
DTSTART          Required.
DTEND            Required.

Silverberg/Mansour/Dawson/Hopson  69                   Expires MAY 1998
EXDATE           Ignore.
EXRULE           Ignore.
FREEBUSY         Reply with Not Supported.
LAST-MODIFIED    Ignore.
LOCATION         Required.
PRIORITY         Ignore.
RELATED-TO       Ignore.
RDATE            Ignore. If implemented, VTIMEZONE MUST also be
                 implemented.
RRULE            Ignore. The first instance occurs on the DTStart
                 property.
RECURRENCE-ID    Required if RRULE is implemented; otherwise Ignore.
REQUEST-STATUS   Required.
RESOURCES        Ignore.
SEQUENCE         Required.
STATUS           Ignore.
SUMMARY          Ignore.
TRANSP           Required if FREEBUSY is implemented; otherwise Ignore.
TZNAME           Required if VTIMEZONE is implemented; otherwise
                 Ignore.
TZOFFSET         Required if VTIMEZONE is implemented; otherwise
                 Ignore.
URL              Ignore.
UID              Required.
X-               Ignore.

5.1.2     To-Do-Related Fallbacks

Method           Fallback
--------------   -----------------------------------------------------
PUBLISH          Required.
CANCEL           Required.
REQUEST          TODO-PUBLISH
REPLY            Required.

iCalendar
Property         Fallback
--------------   -----------------------------------------------------
CALSCALE         Ignore; assume GREGORIAN.
GEO              Ignore.
PRODID           Ignore.
METHOD           Required as described in the Method list above.
SOURCE           Ignore
NAME             Ignore.

Silverberg/Mansour/Dawson/Hopson  75                   Expires MAY 1998

VERSION          Ignore.

To-Do-Related
Components       Fallback
--------------   -----------------------------------------------------
VALARM           Reply with Not Supported.
VTIMEZONE        Required if RRULE or RDATE is implemented;
                 otherwise ignore and use local time.

Silverberg/Mansour/Dawson/Hopson  70                   Expires MAY 1998

Component
Property         Fallback
--------------   -----------------------------------------------------
CALSCALE         Ignore; assume GREGORIAN.
GEO              Ignore.
PRODID           Ignore.
PROFILE          Required as described in the Method list above.
SOURCE           Ignore
NAME             Ignore.
VERSION          Assume "2.0".
Property         Fallback
ATTACH           Ignore.
ATTENDEE         Required if REQUEST is not implemented; otherwise
                 ignore.
CATEGORIES       Ignore.
CLASS            Ignore.
COMMENT          Ignore.
COMPLETED        Required.
CREATED          Ignore.
DAYLIGHT         Required if VTIMEZONE is implemented; otherwise
                 ignore.
DESCRIPTION      Required.
DUE              Required.
DURATION         Ignore. Reply with Not Supported.
DTSTAMP          Required.
DTSTART          Required.
EXDATE           Ignore. Reply with Not Supported.
EXRULE           Ignore. Reply with Not Supported.
LAST-MODIFIED    Ignore.
LOCATION         Ignore.
PERCENT-COMPLETE Ignore
PRIORITY         Required.
RELATED-TO       Ignore.
RDATE            Ignore. If implemented, VTIMEZONE MUST also be
                 implemented.
RRULE            Ignore. The first instance occurs on the DTStart
                 property.
RESOURCES        Ignore.
SEQUENCE         Required.
STATUS           Required.
SUMMARY          Ignore.
TRANSP           Required if FREEBUSY is implemented; otherwise Ignore.
TZNAME           Required if VTIMEZONE is implemented; otherwise
                 Ignore.
TZOFFSET         Required if VTIMEZONE is implemented; otherwise

Silverberg/Mansour/Dawson/Hopson  76                   Expires MAY 1998
                 Ignore.
URL              Ignore.
UID              Required.
X-               Ignore.

Silverberg/Mansour/Dawson/Hopson  71                   Expires MAY 1998

5.1.3     Journal-Related Fallbacks

Method           Fallback
--------------   -----------------------------------------------------
PUBLISH          Implementations MAY ignore the profile type. The
                 REQUEST-STATUS "302;Request not supported" MUST be
                 returned.
CANCEL           Implementations MAY ignore the profile type. The
                 REQUEST-STATUS "302;Request not supported" MUST be
                 returned.
REFRESH          Implementations MAY ignore the profile type. The
                 REQUEST-STATUS "302;Request not supported" MUST be
                 returned.

iCalendar
Property         Fallback
--------------   -----------------------------------------------------
CALSCALE         Ignore; assume GREGORIAN.
GEO              Ignore.
PRODID           Ignore.
METHOD           Required as described in the Method list above.
SOURCE           Ignore
NAME             Ignore.
VERSION          Ignore.

Journal-Related
Components       Fallback
--------------   -----------------------------------------------------
VTIMEZONE        Required if RRULE or RDATE is implemented; otherwise
                 ignore and use local time.
CALSCALE         Ignore; assume GREGORIAN.
GEO              Ignore.
PRODID           Ignore.
METHOD           Required as described in the Method section above.
SOURCE           Ignore
NAME             Ignore.
VERSION          Assume "2.0".

Component
Property         Fallback
--------------   -----------------------------------------------------
ATTACH           Ignore.
ATTENDEE         Required if JOURNAL-REQUEST is implemented; otherwise
                 ignore.
CATEGORIES       Ignore.
CLASS            Ignore.
COMMENT          Ignore.

Silverberg/Mansour/Dawson/Hopson  77                   Expires MAY 1998

CREATED          Ignore.
DAYLIGHT         Required if VTIMEZONE is implemented; otherwise
                 Ignore.
DESCRIPTION      Required.
DTSTAMP          Required.
DTSTART          Required.

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DTEND            Required.
EXDATE           Ignore.
EXRULE           Ignore.
LAST-MODIFIED    Ignore.
RELATED-TO       Ignore.
RDATE            Ignore. If implemented, VTIMEZONE MUST also be
                 implemented.
RRULE            Ignore. The first instance occurs on the DTStart
                 property.
SEQUENCE         Required.
STATUS           Ignore.
TRANSP           Required if FREEBUSY is implemented; otherwise ignore.
TZNAME           Required if VTIMEZONE is implemented; otherwise
                 ignore.
TZOFFSET         Required if VTIMEZONE is implemented; otherwise
                 ignore.
URL              Ignore.
UID              Required.
X-               Ignore.

5.2 Latency Issues

   With a store-and-forward transport, it is possible for events to
   arrive out of sequence. That is, you MAY receive a "CANCEL" method
   prior to receiving the associated "REQUEST" for the calendar
   component. This section discusses a few of these scenarios.

5.2.1     Cancellation of an Unknown Calendar Component.

   When a "CANCEL" method is received before the original "REQUEST"
   method the calendar will be unable to correlate the "UID" property of
   the cancellation with an existing calendar component. It is suggested
   that messages that can not be correlated that also contain non-zero
   sequence numbers be held and not discarded. Implementations MAY age
   them out if no other messages arrive with the same "UID" property
   value and a lower sequence number.

5.2.2     Unexpected Reply from an Unknown Delegate

   When an "Attendee" delegates an item to another "Calendar User" they
   MUST send a "REPLY" method to the "Organizer" using the "ATTENDEE"
   properties to indicate the fact that the request was delegated and to
   whom the item was delegated. Hence it is possible for an "Organizer"
   to receive an "REPLY" from a "Calendar User" not listed as one of the

Silverberg/Mansour/Dawson/Hopson  78                   Expires MAY 1998
   original "Attendees". The resolution is left to the implementation
   but it is expected that the calendaring software will either accept
   the reply or hold it until the related "REPLY" method is received
   from the "delegator". If the version of the "REPLY" method is out of
   date the "Organizer" SHOULD treat the message as a "STATUS-REQUEST"
   and update the delegate with the correct version.

Silverberg/Mansour/Dawson/Hopson  73                   Expires MAY 1998

5.3 Sequence Number

   Under some conditions, a "CUA" MAY receive requests and replies with
   the same "SEQUENCE" property value. The "DTSTAMP" property is
   utilized as a tie-breaker when two items with the same "SEQUENCE"
   property value are evaluated. Furthermore, the "SEQUENCE" property is
   only incremented when one or more of the following properties
   changes:

      

      . DTSTART

      

      . DTEND

      

      . RDATE

      

      . RRULE

      

      . EXDATE

      

      . EXRULE

      

      . DUE (for VTODO components)

      

      . and possibly LOCATION

6  Security Considerations

   This memo outlines an abstract transport protocol which will be bound
   to a real-time transport, a store-and-forward transport, and perhaps
   other transports. The transport protocol will be responsible for
   providing facilities for authentication and encryption using standard
   Internet mechanisms that are mutually understood between the sender
   and receiver.

6.1 Security Threats

6.1.1     Spoofing the "Organizer"

   In this memo, the "Organizer" is the only person authorized to make
   changes to an existing "VEVENT", "VTODO", "VJOURNAL" calendar
   component and redistribute the updates to the "Attendees". An
   iCalendar object that maliciously changes or cancels an existing
   "VEVENT", "VTODO" or "VJOURNAL" calendar component MAY be constructed
   by someone other than the "Organizer" and sent to the "Attendees".

Silverberg/Mansour/Dawson/Hopson  79                   Expires MAY 1998

6.1.2     Spoofing the "Attendee"

   In this memo, an "Attendee" of a "VEVENT", "VTODO", "VJOURNAL"
   calendar component is the only person authorized to update any
   parameter associated with their "ATTENDEE" property and send it to
   the "Organizer". An iCalendar object that maliciously changes the
   "ATTENDEE" parameters MAY be constructed by someone other than the
   real "Attendee" and sent to the "Organizer".

Silverberg/Mansour/Dawson/Hopson  74                   Expires MAY 1998

6.1.3     Eavesdropping

   The iCalendar object is constructed with human-readable clear text.
   Any information contained in an iCalendar object MAY be read and/or
   changed by unauthorized persons while the object is in transit.

6.1.4     Flooding a Calendar

   Implementations MAY provide a means to automatically incorporate
   "REQUEST" methods into a calendar.  This presents the opportunity for
   a calendar to be flooded with requests, which effectively block all
   the calendar's free time.

6.1.5     Procedural Alarms

   The "REQUEST" methods for "VEVENT" and "VTODO" calendar components
   MAY contain "VALARM" calendar components. The "VALARM" calendar
   component MAY be of type PROCEDURE and MAY have an attachment
   containing some sort of executable program. Implementations that
   incorporate these types of alarms are subject to any virus or
   malicious attack that MAY occur as a result of executing the
   attachment.

6.2 Recommendations

   For an application where the information is sensitive or critical and
   the network is subject is subject to a high probability of attack,
   iTIP transactions SHOULD be secured. This MAY be accomplished using
   public key technology, specifically Security Multiparts for MIME
   [RFC1847] in the iTIP transport binding.  This helps mitigate the
   threats of spoofing, eavesdropping and malicious changes in transit.

6.2.1     Use of [RFC1847] to secure iTIP transactions

   iTIP transport bindings SHOULD provide a mechanism based on Security
   Multiparts for MIME [RFC1847] to enable authentication of the
   senderís
   sender's identity, and privacy and integrity of the data being
   transmitted. This allows the receiver of a signed iCalendar object to
   verify the identity of the sender. This sender MAY then be correlated

Silverberg/Mansour/Dawson/Hopson  80                   Expires MAY 1998
   to an "ATTENDEE" property in the iCalendar object. If the correlation
   is made and the sender is authorized to make the requested change or
   update then the operation MAY proceed. It also allows the message to
   be encrypted to prevent unauthorized reading of the message contents
   in transit. iTIP transport binding documents describe this process in
   detail.

6.2.2     Implementation Controls

   The threat of flooding a calendar SHOULD be mitigated by a calendar
   system that uses this protocol by providing controls that MAY be used
   to limit the acceptable sources for iTIP transactions, and perhaps
   the size of messages and volume of traffic, by source.

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   The threat of malicious procedural alarms SHOULD be mitigated by a
   calendar system that uses this protocol by providing controls that
   MAY be used to disallow procedural alarms in iTIP transactions and/or
   remove all alarms from the object before delivery to the recipient.

7  Acknowledgments

   A hearty thanks to the following individuals who have participated in
   the drafting, review and discussion of this memo:

   Anik Ganguly, Bruce Kahn, John Noerenberg, Leo Parker, John Rose,
   Vinod Seraphin, Richard Shusterman, Derik Stenerson, John Sun, Kevin
   Tsurutome.

8  Bibliography

   [ICAL] "Internet Calendaring and Scheduling Core Object Specification
   - iCalendar", Internet-Draft, October 1997,
   ftp://ftp.ietf.org/internet-drafts/draft-ietf-calsch-ical-03.txt.

   [ICMS] "Internet Calendaring Model Specification", Internet-Draft,
   October 1997, ftp://ftp.ietf.org/internet-drafts/draft-ietf-calsch-
   mod-01.txt.

   [ID-UTF8] "UTF-8, a transformation format of Unicode and ISO 10646",
   Internet-Draft, July 1996, ftp://ftp.ietf.org/internet-drafts/draft-
   yergeau-utf8-01.txt.

   [IMIP] "iCalendar Message-Based Interoperability Protocol - iMIP",
   Internet-Draft, October 1997, ftp://ftp.ietf.org/internet-
   drafts/draft-ietf-calsch-imip-01.txt.

   [ISO8601] "Data elements and interchange formats - information
   interchange - Representation of dates and times", ISO 8601, 1996-06-
   15, +1 (212) 642-4900 for ANSI Sales.

   [VCAL] "vCalendar - The Electronic Calendaring and Scheduling Format
   - Version 1.0", Versit Consortium, September 18, 1996,
   http://www.imc.org/pdi/vcal-10.doc.

Silverberg/Mansour/Dawson/Hopson  81                   Expires MAY 1998
   [VCARD] "vCard - The Electronic Business Card Exchange Format -
   Version 2.1", Versit Consortium, September 18, 1996,
   http://www.imc.org/pdi/vcard-21.doc.

   [RFC821] Postel, "Simple Mail Transfer Protocol", RFC 821,
   organization name, November 1996,
   http://ds.internic.net/rfc/rfc821.txt.

   [RFC1983] "Internet Users' Glossary", RFC 1983, August 1996,
   http://ds.internic.net/rfc/rfc1983.txt.

   [RFC2119] "Key words for use in RFCs to Indicate Requirement Levels",
   RFC 2119, March 1997, http://ds.internic.net/rfc/rfc2119.txt.

   [RFC2045] N. Freed and N. Borenstein, "Multipurpose Internet Mail
   Extensions - Part One - Format of Internet Message Bodies", RFC 2045,
   Innosoft, First Virtual, November 1996,
   http://ds.internic.net/rfc/rfc2045.txt.

Silverberg/Mansour/Dawson/Hopson  76                   Expires MAY 1998

   [RFC2046] N. Freed and N. Borenstein, "Multipurpose Internet Mail
   Extensions - Part Two - Media Types", RFC 2046, Innosoft, First
   Virtual, November 1996, http://ds.internic.net/rfc/rfc2046.txt.

   [UNICODE] The Unicode Consortium, "The Unicode Standard -Version
   2.0", Addison-Wesley Developers Press, July 1996. UTF-8 is described
   in section A-2.

   [US-ASCII] Coded Character Set--7-bit AmeriMAYStandard Code for
   Information Interchange, ANSI X3.4-1986.

9  Authors Addresses

   The following address information is provided in a MIME-VCARD,
   Electronic Business Card, format.

   The authors of this draft are:

     BEGIN:VCARD
     FN:Frank Dawson
     ORG:Lotus Development Corporation
     ADR;WORK;POSTAL;PARCEL:;;6544 Battleford Drive;Raleigh;NC;27613-
       3502;USA
     TEL;WORK;MSG:+1-919-676-9515
     TEL;WORK;FAX:+1-919-676-9564
     EMAIL;INTERNET:Frank_Dawson@Lotus.com
     URL:http://home.earthlink.net/~fdawson
     END:VCARD

     BEGIN:VCARD
     FN:Ross Hopson
     ORG:On Technology, Inc.
     ADR;WORK;POSTAL;PARCEL:Suite 1600;;434 Fayetteville St.
       Mall, Two Hannover Square;Raleigh;NC;27601
     TEL;WORK;MSG:+1-919-890-4036

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     TEL;WORK;FAX:+1-919-890-4100
     EMAIL;INTERNET:rhopson@on.com
     END:VCARD

     BEGIN:VCARD
     FN:Steve Mansour
     ORG:Netscape Communications Corporation
     ADR;WORK;POSTAL;PARCEL:;;501 East Middlefield Road;Mountain
       View;CA;94043;USA
     TEL;WORK;MSG:+1-415-937-2378
     TEL;WORK;FAX:+1-415-428-4059
     EMAIL;INTERNET:sman@netscape.com
     END:VCARD

     BEGIN:VCARD
     FN:Steve Silverberg
     ORG:Microsoft Corporation
     ADR;WORK;POSTAL;PARCEL:;;One Microsoft Way;
     Redmond;WA;98052-6399;USA
     TEL;WORK;MSG:+1-425-936-9277

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     TEL;WORK;FAX:+1-425-936-8019
     EMAIL;INTERNET:stevesil@Microsoft.com
     END:VCARD

   The iCalendar object is a result of the work of the Internet
   Engineering Task Force Calendaring and scheduling Working Group. The
   chairman of that working group is:

     BEGIN:VCARD
     FN:Anik Ganguly
     ORG:Campbel Services, Inc.
     ADR;WORK;POSTAL;PARCEL:10 Floor;;21700 Northwestern
       Highway;Southfield;MI;48075;USA
     TEL;WORK;MSG:+1-248-559-5955
     TEL;WORK;FAX:+1-248-559-5034
     EMAIL;INTERNET:anik@ontime.com
     END:VCARD

10 Full Copyright Statement

   "Copyright (C) The Internet Society (date).  All Rights Reserved.

   This document and translations of it MAY be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implmentation MAY be prepared, copied, published and
   distributed, in whole or in part, without restriction of any kind,
   provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself MAY NOT be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for

Silverberg/Mansour/Dawson/Hopson  83                   Expires MAY 1998
   copyrights defined in the Internet Standards process MUST be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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