Network Working Group                 Steve Silverberg, Microsoft
      INTERNET-DRAFT                            Steve Mansour, Netscape
      Calendaring and Scheduling Working Group      Frank Dawson, Lotus
<ietf-draft-calsch-itip-03.txt
      <draft-ietf-calsch-itip-04.txt       Ross Hopson, ON Technologies
      Expires in six months from                               March 13, after:                            May 11, 1998

             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
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     To learn view the current status entire list of any Internet-Draft, current Internet-Drafts, please check
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abstracts.txt "1id-abstracts.txt" listing contained in the Internet-Drafts
     Shadow Directories on ds.internic.net ftp.is.co.za (Africa), ftp.nordu.net
     (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au
     (Pacific Rim), ftp.ietf.org (US East Coast), nic.nordu.net (Europe), or ftp.isi.edu
     (US West Coast), or munnari.oz.au (Pacific Rim). Coast).

      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.

Silverberg/Mansour/Dawson/Hopson

      This document specifies an Internet protocol based on the iCalendar
      object specification that provides scheduling interoperability between
      different calendar systems. The Internet protocol is called the
      'iCalendar Transport-Independent Interoperability Protocol (iTIP)'.

      iTIP complements the iCalendar object specification by adding semantics
      for group scheduling methods commonly available in current calendar
      systems. These scheduling methods permit two or more calendar systems to
      perform transactions such as publish, schedule, reschedule, respond to

      Silverberg/Mansour/Daws/Hopson   1                Expires September November 1998

Silverberg/Mansour/Dawson/Hopson
      scheduling requests, negotiation of changes or cancel iCalendar-based
      calendar components.

      iTIP is defined independent of the particular transport used to transmit
      the scheduling information. Companion memos to iTIP provide bindings of
      the interoperability protocol to a number of Internet protocols.

      Silverberg/Mansour/Daws/Hopson   2                Expires September 1998

Silverberg/Mansour/Dawson/Hopson  3              Expires September November 1998
      Table of Contents

      1 INTRODUCTION.........................................................9 INTRODUCTION.........................................................6

       1.1 FORMATTING CONVENTIONS ...........................................9 ...........................................6
       1.2 RELATED DOCUMENTS ...............................................10 ................................................7
       1.3 ITIP ROLES AND TRANSACTIONS .....................................10 ......................................7

      2 INTEROPERABILITY MODELS.............................................11 MODELS..............................................9

       2.1 APPLICATION PROTOCOL ............................................12 .............................................9
         2.1.1 Calendar Entry State ........................................12 ........................................10
         2.1.2 Delegation ..................................................13 ..................................................10
         2.1.3 Acting on Behalf of other Calendar Users ....................13 ....................10
         2.1.4 Component Revisions .........................................10
         2.1.5 Message Sequencing ..........................................11

      3 APPLICATION PROTOCOL ELEMENTS.......................................13 ELEMENTS.......................................12

       3.1 COMMON COMPONENT RESTRICTION TABLES .............................14 .............................13
       3.2 METHODS FOR VEVENT CALENDAR COMPONENTS ..........................15 ..........................14
         3.2.1 PUBLISH .....................................................16 .....................................................15
         3.2.2 REQUEST .....................................................17 .....................................................16
           3.2.2.1 Rescheduling an Event....................................18
           3.2.2.2 Updating or Reconfirmation of an Event...................19 Event...................18
           3.2.2.3 Delegating an Event to another CU........................19 CU........................18
           3.2.2.4 Changing the Organizer...................................20 Organizer...................................19
           3.2.2.5 Sending on Behalf of the Organizer.......................20 Organizer.......................19
           3.2.2.6 Forwarding to An Uninvited CU............................20 CU............................19
           3.2.2.7 Updating Attendee Status.................................20
         3.2.3 REPLY .......................................................20
         3.2.4 ADD .........................................................22
         3.2.5 CANCEL ......................................................23
         3.2.6 REFRESH .....................................................25
         3.2.7 COUNTER .....................................................26
         3.2.8 DECLINECOUNTER ..............................................28 ..............................................27
       3.3 METHODS FOR VFREEBUSY COMPONENTS ................................29 ................................28
         3.3.1 PUBLISH .....................................................30 .....................................................29
         3.3.2 REQUEST .....................................................31 .....................................................30
         3.3.3 REPLY .......................................................32 .......................................................31
       3.4 METHODS FOR VTODO COMPONENTS ....................................34 ....................................32
         3.4.1 PUBLISH .....................................................35 .....................................................33
         3.4.2 REQUEST .....................................................36 .....................................................34
           3.4.2.1 REQUEST for Rescheduling a VTODO.........................37 VTODO.........................36
           3.4.2.2 REQUEST for Update or Reconfirmation of a VTODO..........38 VTODO..........36
           3.4.2.3 REQUEST for Delegating a VTODO...........................38 VTODO...........................37
           3.4.2.4 REQUEST Forwarded To An Uninvited Calendar User..........39 User..........37
           3.4.2.5 REQUEST Updated Attendee Status..........................39 Status..........................38
         3.4.3 REPLY .......................................................39 .......................................................38
         3.4.4 ADD .........................................................41 .........................................................39
         3.4.5 CANCEL ......................................................42 ......................................................41

      Silverberg/Mansour/Daws/Hopson   3                Expires November 1998
         3.4.6 REFRESH .....................................................43 .....................................................42
         3.4.7 COUNTER .....................................................45 .....................................................44
         3.4.8 DECLINECOUNTER ..............................................46 ..............................................45
       3.5 METHODS FOR VJOURNAL COMPONENTS .................................47

Silverberg/Mansour/Dawson/Hopson  4              Expires September 1998 .................................46
         3.5.1 PUBLISH .....................................................47
         3.5.2 ADD .........................................................49 .........................................................48
         3.5.3 CANCEL ......................................................50 ......................................................49
       3.6 STATUS REPLIES ..................................................51 ..................................................50
       3.7 IMPLEMENTATION CONSIDERATIONS ...................................53 ...................................52
         3.7.1 Working With Recurrence Instances ...........................53 ...........................52
         3.7.2 Attendee Property Considerations ............................54 ............................53
         3.7.3 X-Tokens ....................................................55 ....................................................54

      4 EXAMPLES............................................................55 EXAMPLES............................................................54

       4.1 PUBLISHED EVENT EXAMPLES ........................................55 ........................................54
         4.1.1 A Minimal Published Event ...................................56 ...................................55
         4.1.2 Changing A Published Event ..................................56 ..................................55
         4.1.3 Canceling A Published Event .................................57 .................................56
         4.1.4 A Rich Published Event ......................................57 ......................................56
         4.1.5 Anniversaries or Events attached to entire days .............58 .............57
       4.2 GROUP EVENT EXAMPLES ............................................59 ............................................58
         4.2.1 A Group Event Request .......................................60 .......................................58
         4.2.2 Reply To A Group Event Request ..............................60 ..............................59
         4.2.3 Update An Event .............................................61 .............................................60
         4.2.4 Countering an Event Proposal ................................61 ................................60
         4.2.5 Delegating an Event .........................................63 .........................................62
         4.2.6 Delegate Accepts the Meeting ................................65 ................................64
         4.2.7 Delegate Declines the Meeting ...............................66 ...............................65
         4.2.8 Forwarding an Event Request .................................67 .................................66
         4.2.9 Cancel A Group Event ........................................67 ........................................66
         4.2.10 Removing Attendees .........................................68 .........................................67
         4.2.11 Replacing the Organizer ....................................69 ....................................68
       4.3 BUSY TIME EXAMPLES ..............................................70 ..............................................69
         4.3.1 Request Busy Time ...........................................70
         4.3.2 Reply To A Busy Time Request ................................71 ................................70
       4.4 RECURRING EVENT AND TIME ZONE EXAMPLES ..........................71 ..........................70
         4.4.1 A Recurring Event Spanning Time Zones .......................71 .......................70
         4.4.2 Modify A Recurring Instance .................................73 .................................72
         4.4.3 Cancel an Instance ..........................................74 ..........................................73
         4.4.4 Cancel Recurring Event ......................................75 ......................................74
         4.4.5 Change All Future Instances .................................75 .................................74
         4.4.6 Add A New Instance To A Recurring Event .....................75
         4.4.7 Add A New Series of Instances To A Recurring Event ..........76 ..........75
         4.4.8 Counter An Instance Of A Recurring Event ....................80 ....................79
         4.4.9 Error Reply To A Request ....................................80 ....................................79
       4.5 GROUP TO-DO EXAMPLES ............................................81 ............................................80
         4.5.1 A VTODO Request .............................................82 .............................................81
         4.5.2 A VTODO Reply ...............................................83 ...............................................82
         4.5.3 A VTODO Request for Updated Status ..........................83 ..........................82
         4.5.4 A Reply: Percent-Complete ...................................84 ...................................83
         4.5.5 A Reply: Completed ..........................................84 ..........................................83
         4.5.6 An Updated VTODO Request ....................................84 ....................................83
         4.5.7 Recurring VTODOs ............................................85 ............................................84

      Silverberg/Mansour/Daws/Hopson   4                Expires November 1998
           4.5.7.1 Request for a Recurring VTODO............................85 VTODO............................84
           4.5.7.2 Calculating due dates in recurring VTODOs................85
           4.5.7.3 Replying to an instance of a recurring VTODO.............86 VTODO.............85
       4.6 JOURNAL EXAMPLES ................................................86

Silverberg/Mansour/Dawson/Hopson  5              Expires September 1998 ................................................85
       4.7 OTHER EXAMPLES ..................................................87 ..................................................86
         4.7.1 Event Refresh ...............................................87 ...............................................86
         4.7.2 Bad RECURRENCE-ID ...........................................87 ...........................................86

      5 APPLICATION PROTOCOL FALLBACKS......................................88

       5.1 PARTIAL IMPLEMENTATION ..........................................88
         5.1.1 Event-Related Fallbacks .....................................89 .....................................88
         5.1.2 Free/Busy-Related Fallbacks .................................90
         5.1.3 To-Do-Related Fallbacks .....................................90
   5.1.3
         5.1.4 Journal-Related Fallbacks ...................................92
       5.2 LATENCY ISSUES ..................................................93
         5.2.1 Cancellation of an Unknown Calendar Component. ..............93
         5.2.2 Unexpected Reply from an Unknown Delegate ...................93
       5.3 SEQUENCE NUMBER .................................................94 .................................................93

      6 SECURITY CONSIDERATIONS.............................................94

       6.1 SECURITY THREATS ................................................94
         6.1.1 Spoofing the "Organizer" ....................................94
         6.1.2 Spoofing the "Attendee" .....................................94
         6.1.3 Unauthorized Replacement of the Organizer ...................95 ...................94
         6.1.4 Eavesdropping ...............................................95 ...............................................94
         6.1.5 Flooding a Calendar .........................................95
         6.1.6 Procedural Alarms ...........................................95
         6.1.7 Unauthorized REFRESH Requests ...............................95
       6.2 RECOMMENDATIONS .................................................95
         6.2.1 Use of [RFC1847] [RFC-1847] to secure iTIP transactions ................96 ...............95
         6.2.2 Implementation Controls .....................................96

      7 ACKNOWLEDGMENTS.....................................................96

      8 BIBLIOGRAPHY........................................................97 BIBLIOGRAPHY........................................................96

      9 AUTHORS ADDRESSES...................................................98 ADDRESSES...................................................97

      10 FULL COPYRIGHT STATEMENT...........................................99

Silverberg/Mansour/Dawson/Hopson  6

      Silverberg/Mansour/Daws/Hopson   5                Expires September November 1998
      1  Introduction

      This document specifies how calendaring systems use iCalendar objects to
      interoperate with other calendar systems. In particular, it specifies
      how to schedule events, to-dos, or daily journal entries. It further
      specifies how to search for available busy time information. It does so
      in a general way so as to allow multiple methods of communication
      between systems. Subsequent documents specify transport bindings between
      systems that use this protocol.

      This protocol is based on messages sent from an originator to one or
      more recipients. For certain types of messages, a recipient may reply,
      in order to update their status and may also return transaction/request
      status information. The protocol supports the ability for the message
      originator to modify or cancel the original message. The protocol also
      supports the ability for recipients to suggest changes to the originator
      of a message. The elements of the protocol also define the user roles
      for its transactions.

      1.1 Formatting Conventions

      In order to refer to elements of the calendaring and scheduling model,
      core object or interoperability protocol defined in [ICMS], [ICAL] [iCAL] and
[ITIP]
      [iTIP] several formatting conventions have been utilized.

      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
      "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this
      document are to be interpreted as described in [RFC 2119]. [RFC-2119].

      Calendaring and scheduling roles described 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"
      (CU) within the scheduling protocol defined by [ITIP]. [iTIP]. Calendar
      components defined by [ICAL] [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] [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] [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

Silverberg/Mansour/Dawson/Hopson  7

      Silverberg/Mansour/Daws/Hopson   6                Expires September November 1998
      type for a property value. Enumerated values defined by this memo are
      referred to with capitalized text, either alone or followed by the word
      "value".

      In tables, the quoted-string text is specified without quotes in order
      to minimize the table length.

      1.2 Related Documents

      Implementers will need to be familiar with several other memos that,
      along with this one, describe the Internet calendaring and scheduling
      standards. This document, [ITIP], [iTIP], specifies an interoperability protocol
      for scheduling between different implementations. The related documents
      are:

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

     [ICAL]

           [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]

           [iMIP] specifies an Internet email binding for [ITIP]. [iTIP].

      This memo does not attempt to repeat the specification of concepts or
      definitions from these other memos. Where possible, references are made
      to the memo that provides for the specification of these concepts or
      definitions.

      1.3 ITIP Roles and Transactions

      ITIP defines seven methods for exchanging [ICAL] [iCAL] objects for the purposes of
      group calendaring and scheduling between "Calendar Users" (CUs). CUs
      take on one of two roles in iTIP. The CU who initiates an exchange takes
      on the role of "Organizer". For example, the CU who proposes a group
      meeting is the "Organizer". The CUs asked to participate in the group
      meeting by the "Organizer" take on the role of "Attendee". Note that
      "role" is also a descriptive parameter to the _ATTENDEE_ property. Its
      use is to convey descriptive context to an "Attendee" such as "chair",
      "req-participant" or "non-participant" and has nothing to do with the
      calendaring workflow.

      The ITIP methods are defined listed below and their usage and semantics are
outlined
      defined in section 3 of this document.

      +================+==================================================+
      | Method         |  Description                                     |
      |================+==================================================|
      | PUBLISH        | Used to publish a calendar entry to one or more  |

Silverberg/Mansour/Dawson/Hopson  8              Expires September 1998
      |                | Calendar Users. There is no interactivity        |
      |                | between the publisher and any other calendar     |
      |                | user. An example might include a baseball team   |

      Silverberg/Mansour/Daws/Hopson   7                Expires November 1998
      |                | publishing its schedule to the public.           |
      |                |                                                  |
      | REQUEST        | Used to schedule a calendar entry with other     |
      |                | Calendar Users. Requests are interactive in that |
      |                | they require the receiver to respond using       |
      |                | the the Reply methods. Meeting Requests, Busy    |
      |                | Time requests and the assignment of VTODOs to    |
      |                | other Calendar Users are all examples.           |
      |                | Requests are also used by the "Organizer" to     |
      |                | update the status of a calendar entry.           |
      |                |                                                  |
      | REPLY          | A Reply is used in response to a Request to      |
      |                | convey "Attendee" status to the "Organizer".     |
      |                | Replies are commonly used to respond to meeting  |
      |                | and task requests.                               |
      |                |                                                  |
      | ADD            | Add one or more instances to an existing         |
      |                | VEVENT, VTODO, or VJOURNAL.                      |
      |                |                                                  |
      | CANCEL         | Cancel one or more instances of an existing      |
      |                | VEVENT, VTODO, or VJOURNAL.                      |
      |                |                                                  |
      | REFRESH        | The Refresh method is used by an "Attendee" to   |
      |                | request the latest version of a calendar entry.  |
      |                |                                                  |
      | COUNTER        | The Counter method is used by an "Attendee" to   |
      |                | negotiate a change in the calendar entry.        |
      |                | Examples include the request to change a         |
      |                | proposed Event time or change the due date for a |
      |                | VTODO.                                           |
      |                |                                                  |
      | DECLINE-       | Used by the "Organizer" to decline the proposed  |
      | COUNTER        | counter-proprosal.                               |
      +================+==================================================+

      Group scheduling in iTIP is accomplished using the set of "request" and
      "response" methods described above. The following table shows the
      methods broken down by who can send them.

      +================+==================================================+
      | Originator     | Methods                                          |
      |================+==================================================|
      | Organizer      | PUBLISH, REQUEST, ADD, CANCEL, DECLINECOUNTER    |
      |                |                                                  |
      | Attendee       | REPLY, REFRESH, COUNTER                          |
      |                | REQUEST only when delegating                     |
      +================+==================================================+

      Note that for some calendar component types, the allowable methods are a
      subset of the above set.

      Silverberg/Mansour/Daws/Hopson   8                Expires November 1998
      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 described listed
      above. The Transport Protocol defines how the iCalendar objects are sent
      between the sender and receiver. This document focuses on the
      Application Protocol. Binding documents such as [IMIP] and [IRIP] [iMIP] focus on the
      Transport Protocol.

      The connection between Sender and Receiver in the diagram below refers
      to the Application Protocol. The iCalendar objects passed from the
      Sender to the Receiver are presented in Section 3, Application Protocol
      Elements.

Silverberg/Mansour/Dawson/Hopson  9              Expires September 1998

      +----------+                      +----------+
      |          |        iTIP          |          |
      |  Sender  |<-------------------->| Receiver |
      |          |                      |          |
      +----------+                      +----------+

      There are several variations of this diagram in which the Sender and
      Receiver take on various roles of a "Calendar User Agent" (CUA) or a
      "Calendar Service" (CS). 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.

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

      2.1 Application Protocol

The

      In the iTIP model is in which model, a calendar entry is created and managed by an
      "Organizer". The "Organizer" interacts with other CUs by sending one or
      more of the iTIP messages described listed above. "Attendees" use the "REPLY"
      method to communicate their status. "Attendees" do not make direct
      changes to the master calendar entry. They can, however, use the
      "COUNTER" method to suggest changes to the "Organizer". The In any case, the
      "Organizer" has complete control over the master calendar entry.

      Silverberg/Mansour/Daws/Hopson   9                Expires November 1998
      2.1.1     Calendar Entry State

      There are two distinct states relevant to calendar entries: the overall
      state of the entry and the state associated with an "Attendee" to that
      entry.

      The state of an entry is defined by the "STATUS" property and is
      controlled by the "Organizer." There is no default value for the
      "STATUS" property. The "Organizer" sets the "STATUS" property to the
      appropriate value for each calendar entry.

      The state of a particular "Attendee" relative to an entry is defined by
      the "attstat" "partstat" parameter in the "ATTENDEE" property for each "Attendee".
      When an "Organizer" issues the initial entry, "Attendee" status is
      unknown. The "Organizer" specifies this by setting the "attstat" "partstat"
      parameter to "needs-action". "NEEDS-ACTION". Each "Attendee" modifies their "ATTENDEE"
      property "attstat" "partstat" parameter to an appropriate value as part of a
      "REPLY" message sent back to the "Organizer".

Silverberg/Mansour/Dawson/Hopson  10             Expires September 1998

      2.1.2     Delegation

      Delegation is defined as the process by which an "Attendee" grants
      another CU (or several CUs) the right to attend on their behalf. The
      "Organizer" is made aware of this change because the delegating
      "Attendee" informs the "Organizer" of this change. "Organizer". These steps are detailed in the
      REQUEST method section.

      2.1.3     Acting on Behalf of other Calendar Users

      In many organizations one user will act on behalf of another to organize
      and/or respond to meeting requests. ITIP provides two mechanisms that
      support these activities.

      First, the "Organizer" is treated as a special entity, separate from
      "Attendees". All responses from "Attendees" flow to the "Organizer",
      making it easy to separate a calendar user organizing a meeting from
      calendar users attending the meeting. Additionally, iCalendar provides
      descriptive roles for each "Attendee". For instance, a role of "chair"
      may be ascribed to one or more "Attendees". The "chair "chair" and the
      "Organizer" may or may not be the same calendar user. This maps well to
      scenarios where an assistant may manage meeting logistics for another
      individual who chairs a one-time or recurring meeting.

      Second, a "sent-by" parameter may be specified in either the "Organizer"
      or "Attendee" properties. When specified, the "sent-by" parameter
      indicates that the responding CU acted on behalf of the specified
      "Attendee" or "Organizer".

3 Application Protocol Elements

ITIP messages are "text/calendar" MIME entities that contain calendaring
and scheduling information.

      2.1.4     Component Revisions

      The particular type of [ICAL] message is
referred to as the "method type". Each method type "SEQUENCE" property is identified used by a
"METHOD" property specified as part of the "text/calendar" content type.
The table below shows various combinations of "Organizer" to indicate revisions
      to the calendar components and component. The rules for incrementing the method types that this memo supports.

+=================================================+
|         | VEVENT | VTODO | VJOURNAL | VFREEBUSY |
|=================================================|
|Publish  |  Yes   |  Yes  |  Yes     |   Yes     |
|Request  |  Yes   |  Yes  |  No      |   Yes     |
|Refresh  |  Yes   |  Yes  |  No      |   No      |
|Cancel   |  Yes   |  Yes  |  Yes     |   No      |
|Add      |  Yes   |  Yes  |  Yes     |   No      |
|Reply    |  Yes   |  Yes  |  No      |   Yes     |
|Counter  |  Yes   |  Yes  |  No      |   No      |
|Decline- |        |       |          |           |
|Counter  |  Yes   |  Yes  |  No      |   No      |
+=================================================+

Silverberg/Mansour/Dawson/Hopson  11 "SEQUENCE"
      number are defined in [iCAL]. For clarity, these rules are paraphrased

      Silverberg/Mansour/Daws/Hopson  10                Expires September November 1998

Each method type is defined
      here in terms of its associated components and
properties. Some components and properties are required, some are
optional and others are excluded. The restrictions how they are expressed applied in this
document using [iTIP]. For a simple "restriction table". The first column indicates
the name of given "UID" in a
      calendar component:

      . For the "PUBLISH" and "REQUEST" methods, the "SEQUENCE" property
        value is incremented according to the rules defined in [iCAL].

      . The "SEQUENCE" property value MUST be incremented each time the
        "Organizer" uses the "ADD" or "CANCEL" methods.

      . The "SEQUENCE" property value MUST NOT be incremented when using
        "REPLY", "REFRESH", "COUNTER", "DECLINECOUNTER", or when sending a
        delegation "REQUEST".

      In some circumstances the "Organizer" may not have received responses to
      the final revision sent out. In this situation, the "Organizer" may wish
      to send an update "REQUEST", and set "RSVP=TRUE" for all "Attendees", so
      that current responses can be collected.

      The value of the "SEQUENCE" property contained in a response from an
      "Attendee" may not always match the "Organizer's" revision.
      Implementations may choose to have the CUA indicate to the CU that the
      response is to an entry that has been revised and allow the CU to decide
      whether or not to accept the response.

      2.1.5     Message Sequencing

      CUAs that handle the [iTIP] application protocol must often correlate a
      component in a calendar store with a component received in the [iTIP]
      message. For example, an event may be updated with a later revision of
      the same event. To accomplish this, a CUA must correlate the version of
      the event already in its calendar store with the version sent in the
      [iTIP] message. In addition to this correlation, there are several
      factors that can cause [iTIP] messages to arrive in an unexpected order.
      That is, an "Organizer" could receive a reply to an earlier revision of
      a component AFTER receiving a reply to a later revision.

      To maximize interoperability and to handle messages that arrive in an
      unexpected order, use the following rules:

      1.         The primary key for referencing a particular iCalendar component is
        the "UID" property value. To reference an instance of a recurring
        component, the primary key is composed of the "UID" and the
        "RECURRENCE-ID" properties.

      2.         The secondary key for referencing a component is the "SEQUENCE"
        property value.  For components where the "UID" is the same, the
        component with the highest numeric value for the "SEQUENCE" property
        obsoletes all other revisions of the component with lower values.

      3.         "Attendees" send "REPLY" messages to the "Organizer".  For replies
        where the "UID" property value is the same, the value of the
        "SEQUENCE" property indicates the revision of the component to which

      Silverberg/Mansour/Daws/Hopson  11                Expires November 1998
        the "Attendee" is replying.  The reply with the highest numeric value
        for the "SEQUENCE" property obsoletes all other replies with lower
        values.

      4.         In situations where the "UID" and "SEQUENCE" properties match, the
        "DTSTAMP" property is used as the tie-breaker. The component with the
        latest "DTSTAMP" overrides all others. Similarly, for "Attendee"
        responses where the "UID" property values match and the "SEQUENCE"
        property values match, the response with the latest "DTSTAMP"
        overrides all others.

      Hence, CUAs must persist the following component properties: "UID",
      "RECURRENCE-ID", "SEQUENCE", and "DTSTAMP".  Furthermore, for each
      "ATTENDEE" property of a component CUAs must persist the "SEQUENCE" and
      "DTSTAMP" property values associated with the "Attendee's" response.

      3 Application Protocol Elements

      ITIP messages are "text/calendar" MIME entities that contain calendaring
      and scheduling information. The particular type of [iCAL] message is
      referred to as the "method type". Each method type is identified by a
      "METHOD" property specified as part of the "text/calendar" content type.
      The table below shows various combinations of calendar components and
      the method types that this memo supports.

      +=================================================+
      |         | VEVENT | VTODO | VJOURNAL | VFREEBUSY |
      |=================================================|
      |Publish  |  Yes   |  Yes  |  Yes     |   Yes     |
      |Request  |  Yes   |  Yes  |  No      |   Yes     |
      |Refresh  |  Yes   |  Yes  |  No      |   No      |
      |Cancel   |  Yes   |  Yes  |  Yes     |   No      |
      |Add      |  Yes   |  Yes  |  Yes     |   No      |
      |Reply    |  Yes   |  Yes  |  No      |   Yes     |
      |Counter  |  Yes   |  Yes  |  No      |   No      |
      |Decline- |        |       |          |           |
      |Counter  |  Yes   |  Yes  |  No      |   No      |
      +=================================================+

      Each method type is defined in terms of its associated components and
      properties. Some components and properties are required, some are
      optional and others are excluded. The restrictions are expressed in this
      document using a simple "restriction table". The first column indicates
      the name of a component or property. Properties of the iCalendar object
      are not indented. Properties of a component are indented. The second
      column contains "MUST" if the component or property must be present,
      "MAY" if the component or property is optional, and "NOT" if the
      component or property must not be present. Entries in the second column
      sometimes contain comments for further clarification.

      Silverberg/Mansour/Daws/Hopson  12                Expires November 1998
      3.1 Common Component Restriction Tables

      The restriction table below applies to properties of the iCalendar
      object. That is, the properties at the outermost scope. The presence
      column uses the following values to assert whether a property is
      required, is optional and the number of times it may appear in the
      iCalendar object.

      Presence Value       Description
      --------------------------------------------------------------
      1                 One instance MUST be present
      1+                At least one instance MUST be present
      0                 Instances of this property Must NOT be present
      0+                Multiple instances MAY be present
      0 or 1            Up to 1 instance of this property MAY be present
      ---------------------------------------------------------------

      The tables also call out "X-PROPERTY" and  "X-COMPONENT" to show where
      vendor-specific properties and components can appear.  The tables do not
      lay out the restrictions of property parameters. Those restrictions are
      defined in [iCAL].

      Component/Property  Presence
      ------------------- ----------------------------------------------
      CALSCALE            0 or 1
      PRODID              1
      VERSION             1       Value MUST be "2.0"
      X-PROPERTY          0+

      DateTime values MAY refer to a "VTIMEZONE" component. The property
      restrictions in the table below apply to any "VTIMEZONE" component in an
      ITIP message.

      Component/Property  Presence
      ------------------- ----------------------------------------------
      VTIMEZONE           0+      MUST be present if any date/time refers to a
                                  timezone
    LAST-MODIFIED   MAY
    TZID
          DAYLIGHT        0+      MUST
    TZURL           MAY be one or more of either STANDARD        MUST or
                                  DAYLIGHT
             COMMENT      0 or 1
             DTSTART      1       MUST be present if RRULE is present
       TZOFFSETFROM MUST
       TZOFFSETTO   MUST
       COMMENT      MAY local time format
             RDATE        MAY be present,        0+      if present RRULE must not MUST NOT be present
             RRULE        MAY be present,        0+      if present RDATE must not MUST NOT be present
             TZNAME       MAY
    DAYLIGHT        MAY
      DTSTART       MUST       0 or 1
             TZOFFSET     1
             TZOFFSETFROM 1
             TZOFFSETTO   1
             X-PROPERTY   0+
          LAST-MODIFIED   0 or 1
          STANDARD        0+      MUST be one or more of either STANDARD or
                                  DAYLIGHT
             COMMENT       MAY
      RDATE         MAY      0 or 1

      Silverberg/Mansour/Daws/Hopson  13                Expires November 1998
             DTSTART      1       MUST be present, local time format
             RDATE        0+      if present RRULE must not MUST NOT be present
             RRULE         MAY be present,        0+      if present RDATE must not MUST NOT be present
             TZNAME        MAY       0 or 1
             TZOFFSETFROM 1
             TZOFFSETTO   1
             X-PROPERTY   0+
          TZID            1
          TZURL           0 or 1
          X-PROPERTY      0+

      The property restrictions in the table below apply to any "VALARM"
      component in an ITIP message.

      Component/Property  Presence
      ------------------- ----------------------------------------------
      VALARM              MAY
    ALARM-TYPE      MUST              0+
          ACTION          1
          ATTACH          0+
          DESCRIPTION     0 or 1
          DURATION        MUST

Silverberg/Mansour/Dawson/Hopson  12             Expires September 1998        0 or 1  if present REPEAT MUST
    TRIGGER be present
          REPEAT          0 or 1  if present DURATION MUST
    ATTACH          MAY
    DESCRIPTION     MAY be present
          SUMMARY         MAY
    COMMENT         NOT
    CREATED         NOT
    LAST-MODIFIED   NOT
    RELATED-TO      NOT
    URL             NOT         0 or 1
          TRIGGER         1
          X-PROPERTY      0+

      3.2 Methods for VEVENT Calendar Components

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

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

      +================+==================================================+
      | Method         |  Description                                     |
      |================+==================================================|
      | PUBLISH        | Post notification of an event. Used primarily as |
      |                | a method of advertising the existence of an      |
      |                | event.                                           |
      |                |                                                  |
      | REQUEST        | Make a request for an event. This is an explicit |
      |                | invitation to one or more "Attendees". Event     |
      |                | Requests are also used to update or change an    |
      |                | existing event. Clients that cannot handle       |
      |                | REQUEST may degrade the event to view it as an   |
      |                | PUBLISH.                                         |
      |                |                                                  |
      | REPLY          | Reply to an event request. Clients may set their |
      |                | status ("attstat") ("partstat") to ACCEPTED, DECLINED,        |

      Silverberg/Mansour/Daws/Hopson  14                Expires November 1998
      |                | TENTATIVE, or DELEGATED.                         |
      |                |                                                  |
      | ADD            | Add one or more instances to an existing event.  |
      |                |                                                  |
      | CANCEL         | Cancel one or more instances of an existing      |
      |                | event.                                           |
      |                |                                                  |
      | REFRESH        | A request is sent to an "Organizer" by an        |
      |                | "Attendee" asking for the latest version of an   |
      |                | event to be resent to the requester.             |
      |                |                                                  |
      | COUNTER        | Counter a REQUEST with an alternative proposal,  |
      |                | Sent by an "Attendee" to the "Organizer".        |
      |                |                                                  |
      | DECLINECOUNTER | Decline a counter proposal. Sent to an           |

Silverberg/Mansour/Dawson/Hopson  13             Expires September 1998
      |                | "Attendee" by the "Organizer".                   |
      +================+==================================================+

      3.2.1     PUBLISH

      The "PUBLISH" method in a "VEVENT" calendar component is an unsolicited
      posting of an iCalendar object. Any CU may add published components to
      their calendar. The "Organizer" MUST be present in a published iCalendar
      component. Other "Attendees" MAY MUST NOT be present. However, no replies are
expected. Its expected usage is for
      encapsulating an arbitrary event as an iCalendar object. The "Organizer"
      may subsequently update (with another "PUBLISH" method), add instances
      to (with an "ADD" method), or cancel (with a "CANCEL" method) a
      previously published "VEVENT" calendar component.

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

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID              MUST
VERSION             MUST be "2.0"
      METHOD              1       MUST be equal "PUBLISH"
      VEVENT              MUST              1+
           DTSTAMP        MUST        1
           DTSTART        MUST        1
           ORGANIZER      MUST      1
           SUMMARY        1       Can be null.
           UID            1
           RECURRENCE-ID  MUST  0 or 1  only if referring to an instance of a
                                  recurring calendar component.  Otherwise it
                        must
                                  MUST NOT be present.
           SEQUENCE       0 or 1  MUST be present if not value is greater than 0, may
                                  MAY be present if 0
     SUMMARY        MUST; may be null.
     UID            MUST

     ATTENDEE       MAY
           ATTACH         MAY         0+
           CATEGORIES     MAY     0 or 1  This property may contain a list of values
           CLASS          MAY          0 or 1
           COMMENT        MAY        0 or 1
           CONTACT        MAY        0+
           CREATED        MAY        0 or 1
           DESCRIPTION    MAY    0 or 1  Can be null

      Silverberg/Mansour/Daws/Hopson  15                Expires November 1998
           DTEND          0 or 1  if present and MAY DURATION MUST NOT be NULL present
           DURATION       0 or 1  if present DTEND          MAY MUST NOT be present
           EXDATE         MAY         0+
           EXRULE         MAY         0+
           GEO            MAY            0 or 1
           LAST-MODIFIED  MAY  0 or 1
           LOCATION       MAY       0 or 1
           PRIORITY       MAY
     RELATED-TO     MAY       0 or 1
           RDATE          MAY          0+
           RELATED-TO     0+
           RESOURCES      0 or 1 This property MAY contain a list of values
           RRULE          MAY

Silverberg/Mansour/Dawson/Hopson  14             Expires September 1998          0+
           STATUS         0 or 1 MAY be one of TENTATIVE/CONFIRMED/CANCELLED
           TRANSP         MAY         0 or 1
           URL            MAY

     DURATION       NOT

VTODO               NOT            0 or 1
           X-PROPERTY     0+

           ATTENDEE       0
           REQUEST-STATUS 0

      VALARM              0+
      VFREEBUSY           0
      VJOURNAL            NOT            0
      VTODO               0
      VTIMEZONE           0+    MUST be present if any date/time refers to a
                                 timezone
VALARM              MAY
VFREEBUSY           NOT
X-TOKENS            MAY
      X-COMPONENT         0+

      3.2.2     REQUEST

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

        .  Invite "Attendees" to an event;
        .  Reschedule an existing event;
        .  Response to a REFRESH request;
        .  Update the details of an existing event, without rescheduling it;
        .  Update the status of "Attendees" of an existing event, without
           rescheduling it;
        .  Reconfirm an existing event, without rescheduling it;
        . To forward  Forward a VEVENT "VEVENT" to another uninvited CU.
        .  For an existing "VEVENT" calendar component, delegate the role of
           "Attendee" to another CU;
        .  For an existing "VEVENT" calendar component, changing the role of
           "Organizer" to another CU.

      The "Organizer" originates the "REQUEST". The recipients of the
      "REQUEST" method are the CUs invited to the event, the "Attendees".
      "Attendees" use the "REPLY" method to convey attendance status to the
      "Organizer".

      The "UID" and "SEQUENCE" properties are used to distinguish the various
      uses of the "REQUEST" method. If the "UID" property value in the

      Silverberg/Mansour/Daws/Hopson  16                Expires November 1998
      "REQUEST" is not found on the recipient's calendar, then the "REQUEST"
      is for a new "VEVENT" calendar component. If the "UID" property value is
      found on the recipient's calendar, then the "REQUEST" is for a
      rescheduling, an update, or a reconfirm of the "VEVENT" calendar
      component.

      For the "REQUEST" method, multiple "VEVENT" components in a single
      iCalendar object are only permitted when for components with the same
      "UID" property.  That is, a series of recurring events may have
      instance-specific information.  In this case, multiple "VEVENT"
      components are needed to express the entire series.

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

      Component/Property  Presence
------------------- ----------------------------------------------
PRODID              MUST
VERSION             MUST be "2.0"
      -----------------------------------------------------------------
      METHOD              1       MUST be "REQUEST"

Silverberg/Mansour/Dawson/Hopson  15             Expires September 1998
      VEVENT              1+      All components MUST have the same UID
          ATTENDEE        MUST        1+
          DTSTAMP         MUST         1
          DTSTART         MUST         1
          ORGANIZER       MUST
    RECURRENCE-ID   MUST only if referring to an instance of a
                        recurring calendar component.  Otherwise it
                        must NOT be present.       1
          SEQUENCE        0 or 1  MUST be present if non-zero, may value is greater than 0,
                                  MAY be present if zero 0
          SUMMARY         MUST be present, may         1       Can be NULL null
          UID             MUST             1

          ATTACH          MAY          0+
          CATEGORIES      MAY      0 or 1  This property may contain a list of values
          CLASS           MAY           0 or 1
          COMMENT         MAY         0 or 1
          CONTACT         MAY         0+
          CREATED         MAY         0 or 1
          DESCRIPTION     MAY     0 or 1  Can be null
          DTEND           0 or 1  if present and may DURATION MUST NOT be NULL present
          DURATION        0 or 1  if present DTEND           MAY MUST NOT be present
          EXDATE          MAY          0+
          EXRULE          MAY          0+
          GEO             MAY             0 or 1
          LAST-MODIFIED   MAY   0 or 1
          LOCATION        MAY        0 or 1
          PRIORITY        MAY        0 or 1
          RDATE           MAY           0+
          RECURRENCE-ID   0 or 1  only if referring to an instance of a
                                  recurring calendar component.  Otherwise it
                                  MUST NOT be present.
          RELATED-TO      MAY      0+
          REQUEST-STATUS  0+
          RESOURCES       0 or 1  This property MAY contain a list of values
          RRULE           MAY           0+
          STATUS          0 or 1  MAY be one of TENTATIVE/CONFIRMED
          TRANSP          MAY          0 or 1
          URL             MAY

    DURATION        NOT
    REQUEST-STATUS  NOT

VTODO               NOT
VJOURNAL            NOT             0 or 1

      Silverberg/Mansour/Daws/Hopson  17                Expires November 1998
          X-PROPERTY      0+

      VALARM              0+
      VTIMEZONE           0+      MUST be present if any date/time refers to
                                  a timezone
VALARM              MAY
      X-COMPONENT         0+

      VFREEBUSY           NOT
X-TOKENS            MAY           0
      VJOURNAL            0
      VTODO               0

      3.2.2.1   Rescheduling an Event

      The "REQUEST" method may be used to reschedule an event. A rescheduled
      event involves a change to the existing event in terms of its time or
      recurrence intervals and possibly the location or description. If the
      recipient CUA of a "REQUEST" method finds that the "UID" property value
      already exists on the calendar, but that the "SEQUENCE" (or "DTSTAMP")
      property value in the "REQUEST" method is greater than the value for the

Silverberg/Mansour/Dawson/Hopson  16             Expires September 1998
      existing event, then the "REQUEST" method describes a rescheduling of
      the event.

      3.2.2.2   Updating or Reconfirmation of an Event

      The "REQUEST" method may be used to update or reconfirm an event. An
      update to an existing event does not involve changes to the time or
      recurrence intervals, and might not involve a change to the location or
      description for the event. If the recipient CUA of a "REQUEST" method
      finds that the "UID" property value already exists on the calendar and
      that the "SEQUENCE" property value in the "REQUEST" is the same as the
      value for the existing event, then the "REQUEST" method describes an
      update of the event details, but no rescheduling of the event.

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

      The "Organizer" of an event may also send unsolicited "REQUEST" methods.
      The unsolicited "REQUEST" methods may be used to update the details of
      the event without rescheduling it, to update the "attstat" "partstat" parameter of
      "Attendees", or to reconfirm the event.

      3.2.2.3   Delegating an Event to another CU

      Some calendar and scheduling systems allow "Attendees" to delegate their
      presence at an event to another calendar user. ITIP supports this
      concept using the following workflow. Any "Attendee" may delegate their
      right to participate in a calendar VEVENT to another CU. The implication
      is that the delegate participates in lieu of the original "Attendee";
      NOT in addition to the "Attendee". The delegator MUST notify the
      "Organizer" of this action using the steps outlined below.
      Implementations may support or restrict delegation as they see fit. For

      Silverberg/Mansour/Daws/Hopson  18                Expires November 1998
      instance, some implementations may restrict a delegate from delegating a
      "REQUEST" to another CU.

      The "Delegator" of an event forwards the existing "REQUEST" to the
      "Delegate". The "REQUEST" method MUST include an "ATTENDEE" property
      with the calendar address of the "Delegate". The "Delegator" MUST also
      send a "REPLY" method to the "Organizer" with the "Delegator's"
      "ATTENDEE" property "attstat" "partstat" parameter value set to "delegated". In
      addition, the "delegated-to" parameter MUST be included with the
      calendar address of the "Delegate".

      In response to the request, the "Delegate" MUST send a "REPLY" method to
      the "Organizer" and optionally, to the "Delegator". The "REPLY" method "
      SHOULD include the "ATTENDEE" property with the "delegated-from"
      parameter value of the "Delegator's" calendar address.

Silverberg/Mansour/Dawson/Hopson  17             Expires September 1998

      The "Delegator" may continue to receive updates to the event even though
      they will not be attending. This is accomplished by When the "Delegator"
      sends "REPLY" to the "Organizer"

      3.2.2.4   Changing the Organizer

      The situation may arise where the "Organizer" of a VEVENT is no longer
      able to perform the "Organizer" role and abdicates without passing on
      the "Organizer" role to someone else. When this occurs the "Attendees"
      of the VEVENT may use out-of-band mechanisms to communicate the
      situation and agree upon a new "Organizer".  The new "Organizer" should
      then send out a new "REQUEST" with a modified version of the VEVENT in
      which the "SEQUENCE" number has been incremented and value of the
      "ORGANIZER" property has been changed to the calendar address of the new
      "Organizer".

      3.2.2.5   Sending on Behalf of the Organizer

      There are a number of scenarios that support the need for a calendar
      user to act on behalf of the "Organizer" without explicit role changing.
      This might be the case if the CU designated as "Organizer" was sick or
      unable to perform duties associated with that function. In these cases
      iTIP supports the notion of one CU acting on behalf of another. Using
      the "sent-by" parameter, a calendar user could send an updated "VEVENT"
      REQUEST. In the case where one CU sends on behalf of another CU, the
      "Attendee" responses are still directed back towards the CU designated
      as "Organizer".

      3.2.2.6   Forwarding to An Uninvited CU

      An "Attendee" invited to an event may invite another uninvited CU to the
      event. The invited "Attendee" accomplishes this by forwarding the
      original "REQUEST" method to the uninvited CU. Whether The "Organizer" decides
      whether or not the uninvited CU is added to the attendee list, and thus informed of changes list. If the
      "Organizer" decides not to add the
"VEVENT" calendar component, uninvited CU no further action is an issue left

      Silverberg/Mansour/Daws/Hopson  19                Expires November 1998
      required, however the "Organizer" MAY send the uninvited CU a "CANCEL"
      message.  If the "Organizer" decides to individual
implementations. It is not required. It add uninvited CU, a new
      "ATTENDEE" property is important to note that when added for the uninvited CU with its property
      parameters set as the "Organizer" deems appropriate. When forwarding a
      "REQUEST" to another CU, the forwarding "Attendee" MUST NOT make changes
      to the VEVENT property set.

      3.2.2.7   Updating Attendee Status

      The "Organizer" of an event may also request updated status from one or
      more "Attendees. The "Organizer" sends a "REQUEST" method to the
      "Attendee" and sets the "ATTENDEE;RSVP=TRUE" property parameter. The
      "SEQUENCE" property for the event is not changed from its previous
      value. A recipient will determine that the only change in the "REQUEST"
      is that their "RSVP" property parameter indicates a request for updated
      status. The recipient SHOULD respond with a "REPLY" method indicating
      their current status with respect to the "REQUEST".

      3.2.3     REPLY

      The "REPLY" method in a "VEVENT" calendar component is used to respond
      (e.g., accept or decline) to a "REQUEST" or to reply to a delegation

Silverberg/Mansour/Dawson/Hopson  18             Expires September 1998
      "REQUEST". When used to provide a delegation response, the "Delegator"
      SHOULD include the calendar address of the "Delegate" on the "delegated-
      to" property parameter  of the "Delegator's" "ATTENDEE" property. The
      "Delegate" SHOULD include the calendar address of the "Delegator" on the
      "delegated-from" property parameter of the "Delegate's" "ATTENDEE"
      property.

      The "REPLY" method may also be used to respond to an unsuccessful
      "REQUEST" method. Depending on the value of the "REQUEST-STATUS"
      property no scheduling action may have been performed.

      The "Organizer" of an event may receive the "REPLY" method from a CU not
      in the original "REQUEST". For example, a "REPLY" may be received from a
      "Delegate" to an event. In addition, the "REPLY" method may be received
      from an unknown CU (a "Party Crasher"). This uninvited "Attendee" may be
      accepted, or the "Organizer" may cancel the event for the uninvited
      "Attendee" by sending a "CANCEL" method to the uninvited "Attendee".

      An "Attendee" can include a message to the "Organizer" using the
      "COMMENT" property. For example, if the user indicates tentative
      acceptance and wants to let the "Organizer" know why, the reason can be
      expressed in the "COMMENT" property value.

      The "Organizer" may also receive a "REPLY" from one CU on behalf of
      another. Like the scenario enumerated above for the "Organizer",
      "Attendees" may have another CU respond on their behalf. This is done
      using the "sent-by" parameter.

      Silverberg/Mansour/Daws/Hopson  20                Expires November 1998
      The optional properties listed in the table below (those listed as
"MAY") "0+"
      or "0 or 1") MUST NOT be changed from those of the original request.  If
      property changes are desired the COUNTER message must be used.

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

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID              MUST
VERSION             MUST be "2.0"
      METHOD              1       MUST be "REPLY"

      VEVENT              1+      All components MUST have the same UID
          ATTENDEE        1       MUST be the address of the Attendee
                                  replying.
          DTSTAMP         MUST         1
          ORGANIZER       MUST       1
          RECURRENCE-ID   MUST   0 or 1  only if referring to an instance of a
                        recurring calendar component.  Otherwise it
                        must referring to an instance of a
                                  recurring calendar component.  Otherwise it
                                  must NOT be present.
          UID             1       MUST be the UID of the original REQUEST

          SEQUENCE        0 or 1  MUST if non-zero, MUST be the sequence
                                  number of the original REQUEST. MAY be
                                  present if 0.

          ATTACH          0+
          CATEGORIES      0 or 1  This property may contain a list of values
          CLASS           0 or 1
          COMMENT         0 or 1
          CONTACT         0+
          CREATED         0 or 1
          DESCRIPTION     0 or 1
          DTEND           0 or 1  if present DURATION MUST NOT be present.
    SEQUENCE        MUST present
          DTSTART         0 or 1
          DURATION        0 or 1  if non-zero
    UID present DTEND MUST NOT be the UID of the original REQUEST

    ATTACH          MAY
    COMMENT         MAY
    CONTACT         MAY present
          EXDATE          MAY          0+
          EXRULE          MAY
    REQUEST-STATUS  MAY

    CATEGORIES      MAY

Silverberg/Mansour/Dawson/Hopson  19             Expires September 1998
    CLASS           MAY
    CREATED         MAY
    DESCRIPTION     MAY
    DTSTART         MAY
    DTEND           MAY
    DURATION        MAY          0+
          GEO             MAY             0 or 1
          LAST-MODIFIED   MAY   0 or 1
          LOCATION        0 or 1
          PRIORITY        MAY        0 or 1
          RDATE           0+
          RELATED-TO      MAY      0+
          RESOURCES       0 or 1  This property MAY
    RDATE           MAY contain a list of values
          REQUEST-STATUS  0+
          RRULE           MAY           0+
          STATUS          MAY          0 or 1
          SUMMARY         MAY         0 or 1
          TRANSP          MAY          0 or 1
          URL             MAY             0 or 1
          X-PROPERTY      0+

      VTIMEZONE           0 or 1 MUST be present if any date/time refers to a
                                 timezone
X-TOKENS            NOT
VTODO               NOT
VJOURNAL            NOT
VFREEBUSY           NOT

      Silverberg/Mansour/Daws/Hopson  21                Expires November 1998
      X-COMPONENT         0+

      VALARM              NOT              0
      VFREEBUSY           0
      VJOURNAL            0
      VTODO               0

      3.2.4     ADD

      The "ADD" method in a "VEVENT" calendar component is used to add one or
      more instances to an existing "VEVENT". Unlike the "REQUEST" method,
      when using issuing an "ADD" method, the "Organizer" does not send the
      full "VEVENT" description; only the new instance(s). The "ADD" method is
      especially useful if there are instance-specific properties to be
      preserved in a recurring "VEVENT". For instance, an "Organizer" may have
      originally scheduled a weekly Thursday meeting. At some point, several
      instances changed. Location or start time may have changed, or some
      instances may have unique "DESCRIPTION" properties. The "ADD" method
      allows the "Organizer" to add new instances to an existing event using a
      single ITIP message without redefining the entire recurring pattern.

      The "UID" must be that of the existing event. If the "UID" property
      value in the "ADD" is not found on the recipient's calendar, then the
      recipient SHOULD send a "REFRESH" to the "Organizer" in order to be
      updated with the latest version of the "VEVENT".  If an "Attendee"
      implementation does not support the "ADD" method it should respond with
      a "REQUEST-STATUS" value of 5.3 and ask for a "REFRESH".

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

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID              MUST

Silverberg/Mansour/Dawson/Hopson  20             Expires September 1998

VERSION             MUST be "2.0"
      METHOD              1      MUST be "ADD"
      VEVENT              MUST              1
          DTSTAMP         MUST         1
          DTSTART         MUST         1
          ORGANIZER       MUST       1
          SEQUENCE        1      MUST be greater than 0
          SUMMARY         MUST be present, may         1      Can be NULL null
          UID             1      MUST match that of the original event

          ATTACH          MAY          0+
          ATTENDEE        MAY        0+
          CATEGORIES      0 or 1 This property MAY contain a list of values
          CLASS           MAY           0 or 1
          COMMENT         MAY         0 or 1
          CONTACT         MAY         0+
          CREATED         MAY         0 or 1
          DESCRIPTION     MAY     0 or 1  Can be null
          DTEND           0 or 1  if present and may DURATION MUST NOT be NULL present
          DURATION        0 or 1  if present DTEND           MAY MUST NOT be present
          EXDATE          MAY          0+

      Silverberg/Mansour/Daws/Hopson  22                Expires November 1998
          EXRULE          MAY          0+
          GEO             MAY             0 or 1
          LAST-MODIFIED   MAY   0 or 1
          LOCATION        MAY        0 or 1
          PRIORITY        MAY        0 or 1
          RDATE           MAY           0+
          RELATED-TO      MAY      0+
          RESOURCES       0 or 1  This property MAY contain a list of values
          RRULE           MAY           0+
          STATUS          0 or 1  MAY be one of TENTATIVE/CONFIRMED
          TRANSP          MAY          0 or 1
          URL             MAY

    DURATION        NOT             0 or 1
          X-PROPERTY      0+

          RECURRENCE-ID   NOT   0
          REQUEST-STATUS  NOT

VTODO               NOT
VJOURNAL            NOT  0

      VALARM              0+
      VTIMEZONE           0+     MUST be present if any date/time refers to
                                 a timezone
VALARM              MAY
      X-COMPONENT         0+

      VFREEBUSY           NOT
X-TOKENS            MAY           0
      VTODO               0
      VJOURNAL            0

      3.2.5     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 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 and a "RECURRENCE-ID" MUST NOT be

Silverberg/Mansour/Dawson/Hopson  21             Expires September 1998
      specified in the "CANCEL" method. In order to cancel an individual
      instance of the event, the "RECURRENCE-ID" property value for the event
      MUST be specified in the "CANCEL" method.

      There are two options for canceling a sequence of instances of a
      recurring "VEVENT" calendar component:

      (a)          the "RECURRENCE-ID" property for an instance in the sequence MUST be
        specified with the "RANGE" property parameter value of THISANDPRIOR
        (or THISANDFUTURE)  to indicate cancellation of the specified
        "VEVENT" calendar component and all instances before (or after); or

      (b)          individual recurrence instances may be cancelled by specifying
        multiple "RECURRENCE-ID" properties corresponding to the instances to
        be cancelled.

      When a "VEVENT" is cancelled, the "SEQUENCE" property value MUST be
      incremented.

      Silverberg/Mansour/Daws/Hopson  23                Expires November 1998
      This method type is an iCalendar object that conforms to the following
      property constraints:

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID              MUST
VERSION             MUST be "2.0"
      METHOD              1      MUST be "CANCEL"

      VEVENT              1+     All must have the same UID
          ATTENDEE        0+     MUST
    DTSTAMP         MUST
    ORGANIZER       MUST
    RECURRENCE-ID include all "Attendees" being removed
                                 the event. MUST only include all "Attendees" if referring to one or more instances of
                        a recurring calendar component.  Otherwise it
                        MUST NOT be present.
                                 the entire event is cancelled.
          DTSTAMP         1
          ORGANIZER       1
          SEQUENCE        MUST        1
          UID             1       MUST be the UID of the original REQUEST

          COMMENT         MAY
    STATUS          Must be set to "Cancelled". If uninviting specific
                        "Attendees" then MUST NOT be included.         0 or 1
          ATTACH          MAY
    ATTENDEE        MAY          0+
          CATEGORIES      MAY      0 or 1  This property may contain a list of values
          CLASS           MAY           0 or 1
          CONTACT         MAY         0+
          CREATED         MAY         0 or 1
          DESCRIPTION     MAY     0 or 1
          DTEND           0 or 1 if present DURATION MUST NOT be present
          DTSTART         MAY         0 or 1
          DURATION        MAY        0 or 1 if present DTEND           MAY MUST NOT be present
          EXDATE          MAY          0+
          EXRULE          MAY          0+
          GEO             MAY             0 or 1
          LAST-MODIFIED   MAY   0 or 1
          LOCATION        0 or 1
          PRIORITY        MAY        0 or 1
          RDATE           0+
          RECURRENCE-ID   0 or 1  MUST be present if referring to one or more
                                  or more recurring instances. Otherwise it
                                  MUST NOT be present
          RELATED-TO      MAY

Silverberg/Mansour/Dawson/Hopson  22             Expires September 1998
    REQUEST-STATUS  MAY      0+
          RESOURCES       MAY
    RDATE           MAY       0 or 1
          RRULE           MAY           0+
          STATUS          MAY          0 or 1  MUST be set to CANCELLED. If uninviting
                                  specific "Attendees" then MUST NOT be
                                  included.
          SUMMARY         MAY         0 or 1
          TRANSP          MAY          0 or 1
          URL             MAY             0 or 1
          X-PROPERTY      0+
          REQUEST-STATUS  0

      VTIMEZONE           0+     MUST be present if any date/time refers to
                                 a timezone

X-TOKENS            MAY
      X-COMPONENT         0+

      VTODO               NOT               0
      VJOURNAL            NOT            0

      Silverberg/Mansour/Daws/Hopson  24                Expires November 1998
      VFREEBUSY           NOT           0
      VALARM              NOT              0

      3.2.6     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 of the event to update. A recurrence instance of an event may
      be requested by specifying the "RECURRENCE-ID" property corresponding to
      the associated event. The "Organizer" responds with the latest
      description and version of the event.

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

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID              MUST
VERSION             MUST be "2.0"
      METHOD              1      MUST be "REFRESH"

      VEVENT              MUST              1
          ATTENDEE        1      MUST be the address of requestor
          DTSTAMP         1
          ORGANIZER       1
          UID             1      MUST be the UID associated with original
                                 REQUEST
          COMMENT         0 or 1
          RECURRENCE-ID   0 or 1 MUST only if referring to an instance of a
                                 recurring calendar component.  Otherwise it
                                 must NOT be present.
    UID             MUST be the UID associated with original
                        REQUEST

    COMMENT         MAY
          X-PROPERTY      0+

          ATTACH          NOT
    ATEGORIES       NOT          0
          CATEGORIES      0
          CLASS           NOT           0
          CONTACT         MAY         0
          CREATED         NOT

Silverberg/Mansour/Dawson/Hopson  23             Expires September 1998         0
          DESCRIPTION     NOT
    DTSTART         NOT     0
          DTEND           NOT           0
          DTSTART         0
          DURATION        NOT        0
          EXDATE          NOT          0
          EXRULE          NOT          0
          GEO             NOT             0
          LAST-MODIFIED   NOT
    ORGANIZER       NOT   0
          LOCATION        0
          PRIORITY        NOT        0
          RDATE           NOT           0
          RELATED-TO      NOT
    RESOURCES       NOT      0
          REQUEST-STATUS  NOT  0
          RESOURCES       0
          RRULE           NOT           0
          SEQUENCE        NOT
    SUMMARY         NOT        0

      Silverberg/Mansour/Daws/Hopson  25                Expires November 1998
          STATUS          NOT          0
          SUMMARY         0
          TRANSP          NOT          0
          URL             NOT

VTIMEZONE           MUST be present if any date/time refers to a
                        timezone

X-TOKENS            MAY             0

      X-COMPONENT         0+

      VTODO               NOT               0
      VJOURNAL            NOT            0
      VFREEBUSY           NOT           0
      VTIMEZONE           0
      VALARM              NOT              0

      3.2.7     COUNTER

      The "COUNTER" method for 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" sends this 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 "DECLINE-COUNTER" "DECLINECOUNTER" 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 latter case, the
"Organizer" SHOULD reset the individual "RSVP" property parameter values
to TRUE on each "ATTENDEE" property event as described in order to force a response by the
"Attendees". section 3.2.2.1
           Rescheduling an Event.

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

      Component/Property  Presence

Silverberg/Mansour/Dawson/Hopson  24             Expires September 1998
      ------------------- ----------------------------------------------
PRODID              MUST
VERSION             MUST be "2.0"
      METHOD              1      MUST be "COUNTER"

      VEVENT              MUST              1
          DTSTAMP         1
          DTSTART         1
          ORGANIZER       1       MUST
    RECURRENCE-ID   MUST only if referring to an instance of a
                        recurring calendar component.  Otherwise it
                        must NOT be present. the "Organizer" of the original
                                  event
          SEQUENCE        1       MUST be present if non-zero, value is greater than 0,
                                  MAY be present if zero 0
          SUMMARY         MUST be present may         1       Can be NULL null
          UID             1       MUST be the UID associated with the REQUEST
                                  being countered

          ATTACH          MAY          0+
          ATTENDEE        MAY        0+      Can also  be used to propose other
                                  "Attendees"
          CATEGORIES      MAY      0 or 1  This property may contain a list of values
          CLASS           MAY           0 or 1
          COMMENT         MAY         0 or 1

      Silverberg/Mansour/Daws/Hopson  26                Expires November 1998
          CONTACT         MAY         0+
          CREATED         MAY         0 or 1
          DESCRIPTION     MAY be present, may     0 or 1
          DTEND           0 or 1  if present DURATION MUST NOT be NULL
    DTSTART         MAY present
          DURATION        0 or 1  if present DTEND           MAY MUST NOT be present
          EXDATE          MAY          0+
          EXRULE          MAY          0+
          GEO             MAY             0 or 1
          LAST-MODIFIED   MAY   0 or 1
          LOCATION        MAY        0 or 1
          PRIORITY        MAY        0 or 1
          RDATE           MAY           0+
          RECURRENCE-ID   0 or 1  MUST only if referring to an instance of a
                                  recurring calendar component.  Otherwise it
                                  MUST NOT be present.
          RELATED-TO      MAY      0+
          REQUEST-STATUS  0+
          RESOURCES       MAY       0 or 1  This property may contain a list of values
          RRULE           MAY           0+
          STATUS          MAY          0 or 1  Value must be one of CONFIRMED/TENATIVE/
                                  CANCELLED
          TRANSP          MAY          0 or 1
          URL             MAY

    COMPLETED       NOT
    DUE             NOT
    DURATION        NOT
    ORGANIZER       NOT
    REQUEST-STATUS  NOT             0 or 1
          X-PROPERTY      0+

      VALARM              0+
      VTIMEZONE           0+      MUST be present if any date/time refers to
                                  a timezone
VALARM              MAY

X-TOKENS            MAY
      X-COMPONENT         0+

      VTODO               NOT               0
      VJOURNAL            NOT            0
      VFREEBUSY           NOT

Silverberg/Mansour/Dawson/Hopson  25             Expires September 1998           0

      3.2.8     DECLINECOUNTER

      The "DECLINE-COUNTER" "DECLINECOUNTER" 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 "DECLINE-COUNTER" "DECLINECOUNTER" message to
      the "Attendee" that sent the "COUNTER" method to the "Organizer".

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

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID              MUST
VERSION             MUST be "2.0"
      METHOD              1      MUST be "DECLINECOUNTER"

      VEVENT              MUST              1
          DTSTAMP         MUST         1
          ORGANIZER       MUST       1
          UID             1       MUST, same UID specified in original
                                  REQUEST and subsequent COUNTER

      Silverberg/Mansour/Daws/Hopson  27                Expires November 1998
          COMMENT         0 or 1
          RECURRENCE-ID   0 or 1  MUST only if referring to an instance of a
                                  recurring calendar component.  Otherwise it
                        must
                                  MUST NOT be present.
          REQUEST-STATUS  0+
          SEQUENCE        0 OR 1  MUST be present if non-zero, value is greater than 0,
                                  MAY be present if zero
    UID             MUST, same UID specified in original
                        REQUEST and subsequent COUNTER

    COMMENT         MAY
    REQUEST-STATUS  MAY 0
          X-PROPERTY      0+

          ATTACH          NOT          0
          ATTENDEE        NOT        0
          CATEGORIES      NOT      0
          CLASS           NOT           0
          CONTACT         NOT         0
          CREATED         NOT         0
          DESCRIPTION     NOT
    DTSTART         NOT     0
          DTEND           NOT           0
          DTSTART         0
          DURATION        NOT        0
          EXDATE          NOT          0
          EXRULE          NOT          0
          GEO             NOT             0
          LAST-MODIFIED   NOT   0
          LOCATION        0
          PRIORITY        NOT        0
          RDATE           NOT           0
          RELATED-TO      NOT      0
          RESOURCES       NOT       0
          RRULE           NOT           0
          STATUS          NOT          0
          SUMMARY         NOT         0
          TRANSP          NOT          0
          URL             NOT

VTIMEZONE           MUST be present if any date/time refers to a

Silverberg/Mansour/Dawson/Hopson  26             Expires September 1998
                        timezone
X-TOKENS            MAY             0

      X-COMPONENT         0+
      VTODO               NOT               0
      VJOURNAL            NOT            0
      VFREEBUSY           NOT           0
      VTIMEZONE           0
      VALARM              NOT              0

      3.3 Methods For VFREEBUSY Components

      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 restriction table.

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

      Silverberg/Mansour/Daws/Hopson  28                Expires November 1998
      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 individual "D" returns an "unsupported
      capability" message to individual "A".

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

      |================|==================================================|

Silverberg/Mansour/Dawson/Hopson  27             Expires September 1998
      | Method         |  Description                                     |
      |================|==================================================|
      | PUBLISH        | Publish unsolicited busy time data.              |
      | REQUEST        | Request busy time data.                          |
      | REPLY          | Reply to a busy time request.                    |
      |================|==================================================|

      3.3.1     PUBLISH

      The "PUBLISH" method in a "VFREEBUSY" calendar component is used to
      publish busy time data. The method may be sent from one CU 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.

      The "ATTENDEE" property must be specified in the busy time information.
      The value is the CU address of the originator of the busy time
      information.

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

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID              MUST
VERSION             MUST be "2.0"
      METHOD              1       MUST be "PUBLISH"

      VFREEBUSY           MUST
    ATTENDEE        MUST contain the address of originator of
                        busy time data           1+
          DTSTAMP         MUST         1
          DTSTART         1       DateTime values must be in UTC
          DTEND           1       DateTime values must be in UTC
          FREEBUSY        1+      MUST be BUSYTIME. Multiple instances are
                                  allowed. Multiple instances must be sorted
                                  in ascending
                        order.
    ATTACH          MAY
    RELATED-TO      MAY
    COMMENT         MAY
    CONTACT         MAY
    CREATED         MAY specifies when order
          ORGANIZER       1       MUST contain the busy time data was
                        Created
    DTSTART         MAY be present to represent start address of the
                        interval for busy time data
    DTEND           MAY be present to represent the end originator of
                        the interval for
                                  busy time data
    GEO             MAY
    ORGANIZER       MAY data.

          COMMENT         0 or 1
          CONTACT         0+
          X-PROPERTY      0+
          URL             MAY (specifies             0 or 1  Specifies busy time URL)

    CATEGORIES      NOT
    CLASS           NOT
    DESCRIPTION     NOT

Silverberg/Mansour/Dawson/Hopson  28             Expires September 1998 URL

          ATTENDEE        0
          DURATION        NOT
    EXDATE          NOT
    EXRULE          NOT
    LAST-MODIFIED   NOT
    PRIORITY        NOT
    RDATE           NOT
    RECURRENCE-ID   NOT        0
          REQUEST-STATUS  NOT
    RESOURCES       NOT
    RRULE           NOT
    SEQUENCE        NOT
    STATUS          NOT
    SUMMARY         NOT
    TRANSP          NOT  0
          UID             NOT

VTIMEZONE           MUST be present if any date/time refers to a
                        timezone
X-TOKENS            NOT             0

      X-COMPONENT         0+

      VEVENT              NOT              0
      VTODO               NOT               0
      VJOURNAL            NOT            0
      VTIMEZONE           0
      VALARM              NOT              0

      3.3.2     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.

      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 SHOULD be 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:

      Silverberg/Mansour/Daws/Hopson  30                Expires November 1998
      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID              MUST
VERSION             MUST be "2.0"
      METHOD              1      MUST be "REQUEST"

      VFREEBUSY           MUST           1
          ATTENDEE        MUST        1+     contain the address of the calendar store
                                 for which busy time is being requested.

Silverberg/Mansour/Dawson/Hopson  29             Expires September 1998
          DTEND           MUST           1      DateTime values must be in UTC
          DTSTAMP         MUST         1
          DTSTART         MUST         1      DateTime values must be in UTC
          ORGANIZER       1      MUST be the request originator's address

    ATTACH          MAY
          UID             1
          COMMENT         MAY         0 or 1
          CONTACT         MAY
    GEO             MAY
    URL             MAY

    CATEGORIES      NOT
    CLASS           NOT
    CREATED         NOT
    DESCRIPTION     NOT
    DURATION        NOT
    EXDATE          NOT
    EXRULE          NOT         0+
          X-PROPERTY      0+

          FREEBUSY        NOT
    LAST-MODIFIED   NOT
    PRIORITY        NOT
    RDATE           NOT
    RECURRENCE-ID   NOT
    RELATED-TO      NOT        0
          DURATION        0
          REQUEST-STATUS  NOT
    RESOURCES       NOT
    RRULE           NOT
    SEQUENCE        NOT
    STATUS          NOT
    SUMMARY         NOT
    TRANSP          NOT
    UID             NOT

VTIMEZONE           MUST be present if any date/time refers to a

X-TOKENS            MAY  0
          URL             0

      X-COMPONENT         0+
      VALARM              0
      VEVENT              NOT              0
      VTODO               NOT               0
      VJOURNAL            NOT
VALARM              NOT            0
      VTIMEZONE           0

      3.3.3     REPLY

      The "REPLY" method in a "VFREEBUSY" calendar component is used to
      respond to a busy time request. The method is sent by the recipient of a
      busy time request to the originator of the request.

      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.

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

Silverberg/Mansour/Dawson/Hopson  30             Expires September 1998

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID              MUST
VERSION             MUST be "2.0"
      METHOD              1      MUST be "REPLY"

      VFREEBUSY           MUST           1
          ATTENDEE        MUST        1      (address of recipient replying)
          DTSTAMP         MUST
    DTSTART         MUST         1
          DTEND           MUST           1      DateTime values must be in UTC
          DTSTART         1      DateTime values must be in UTC
          FREEBUSY        MUST        1+      (values MUST all be of the same data

      Silverberg/Mansour/Daws/Hopson  31                Expires November 1998
                                  type. Multiple instances are allowed.
                                  Multiple instances MUST be sorted in
                                  ascending order. Values MAY NOT overlap)
          ORGANIZER       1       MUST be the request originator's address
    RECURRENCE-ID   MUST only if referring to an instance of a
                        recurring calendar component.  Otherwise it
                        must NOT be present.
          UID             MUST

    ATTACH          MAY             1

          COMMENT         MAY         0 or 1
          CONTACT         MAY
    CREATED         MAY specifies when the busy time data was
                        created)
    DTSTART         MAY (represents start of interval for busy
                        time data}, DTEND{represents end of
                        interval for busy time data)
    GEO             MAY
    RELATED-TO      MAY         0+
          REQUEST-STATUS  MAY
    SEQUENCE        MAY be present if non-zero  0+
          URL             MAY             0 or 1  (specifies busy time URL)

    CATEGORIES      NOT
    CLASS           NOT
    DESCRIPTION     NOT
          X-PROPERTY      0+
          DURATION        NOT
    EXDATE          NOT
    EXRULE          NOT
    FREEBUSY        NOT
    LAST-MODIFIED   NOT
    PRIORITY        NOT
    RDATE           NOT
    RESOURCES       NOT
    RRULE           NOT        0
          SEQUENCE        NOT
    STATUS          NOT
    SUMMARY         NOT
    TRANSP          NOT

VTIMEZONE           MUST be present if any date/time refers to a

Silverberg/Mansour/Dawson/Hopson  31             Expires September 1998
                        timezone

X-TOKENS            MAY        0

      X-COMPONENT         0+
      VALARM              0
      VEVENT              NOT              0
      VTODO               NOT               0
      VJOURNAL            NOT
VALARM              NOT            0
      VTIMEZONE           0

      3.4 Methods For VTODO Components

      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 restriction table that specifies the property
      constraints that define the particular method.

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

      +================+==================================================+
      | 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|
      |                | one or more Calendar Users. The REQUEST method   |
      |                | is also used to update or change an existing     |
      |                | VTODO. Clients that cannot handle REQUEST MAY    |
      |                | degrade the method to treat it as a PUBLISH.     |
      |                |                                                  |
      | REPLY          | Reply to a VTODO request. Attendees MAY set      |
      |                | ATTSTAT PARTSTAT to ACCEPTED, DECLINED, TENTATIVE,       |
      |                | DELEGATED, PARTIAL, and COMPLETED.               |
      |                |                                                  |
      | ADD            | Add one or more instances to an existing to-do.  |
      |                |                                                  |
      | CANCEL         | Cancel one or more instances of an existing      |
      |                | to-do.                                           |
      |                |                                                  |

      Silverberg/Mansour/Daws/Hopson  32                Expires November 1998
      | REFRESH        | A request sent to a VTODO "Organizer" Organizer asking for   |
      |                | the latest version of a VTODO.                   |
      |                |                                                  |
      | COUNTER        | Counter a REQUEST with an alternative proposal.  |
      |                |                                                  |
      | DECLINECOUNTER | Decline a counter proposal by an "Attendee." Attendee.       |
      +================+==================================================+

Silverberg/Mansour/Dawson/Hopson  32             Expires September 1998

      3.4.1     PUBLISH

      The "PUBLISH" method in a "VTODO" calendar component has no associated
      response. It is simply a posting of an iCalendar object that maybe added
      to a calendar by a "Calendar User". calendar. It MUST have an "Organizer".  It MUST NOT have
      "Attendees". Its expected usage is for encapsulating an arbitrary
      "VTODO" calendar component as an iCalendar object. The "Organizer" MAY
      subsequently update (with another "PUBLISH" method), add instances to
      (win an "ADD" 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:

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID               MUST
VERSION              MUST be "2.0"
      METHOD               1       MUST be "PUBLISH"
      VTODO                MUST                1+
          DTSTAMP          MUST          1
          DTSTART          MUST          1
          ORGANIZER        MUST
    RECURRENCE-ID    MUST only if referring to an instance of a
                         recurring calendar component.  Otherwise it
                         must NOT be present.        1
          PRIORITY         1
          SEQUENCE         0 or 1  MUST be present if not value is greater than
                                   0, may MAY be present if 0
          SUMMARY          MUST; may          1       Can be null.
          UID              MUST

    ATTENDEE         MAY              1

          ATTACH           MAY           0+
          CATEGORIES       MAY       0 or 1  This property may contain a list of values
          CLASS            MAY            0 or 1
          COMMENT          MAY          0 or 1
          CONTACT          MAY          0+
          CREATED          MAY          0 or 1
          DESCRIPTION      MAY      0 or 1  Can be null
          DUE              0 or 1  If present and MAY DURATION MUST NOT be NULL present
          DURATION         MAY
    DTEND            MAY         0 or 1  If present DUE MUST NOT be present
          EXDATE           MAY           0+
          EXRULE           MAY           0+
          GEO              MAY              0 or 1
          LAST-MODIFIED    MAY    0 or 1
          LOCATION         MAY         0 or 1
          PERCENT-COMPLETE MAY
    PRIORITY         MAY
    RELATED-TO       MAY 0 or 1
          RDATE            MAY            0+
          RECURRENCE-ID    0 or 1  MUST only if referring to an instance of a

      Silverberg/Mansour/Daws/Hopson  33                Expires November 1998
                                   recurring calendar component.  Otherwise
                                   it MUST NOT be present.

          RELATED-TO       0+
          RESOURCES        MAY        0 or 1  This property may contain a list of values
          RRULE            MAY            0+
      STATUS           0 or 1  MAY be one of COMPLETED/NEEDS ACTION/IN-PROCESS
    TRANSP           MAY ACTION/IN-
                                   PROCESS/CANCELLED
          URL              MAY

Silverberg/Mansour/Dawson/Hopson  33             Expires September 1998

VEVENT               NOT
VJOURNAL             NOT              0 or 1
          X-PROPERTY      0+

          ATTENDEE         0
          REQUEST-STATUS   0

      VTIMEZONE            0+    MUST be present if any date/time refers to
                                 a timezone
      VALARM               MAY               0+
      X-COMPONENT          0+

      VFREEBUSY            NOT
X-TOKENS             MAY            0
      VEVENT               0
      VJOURNAL             0

      3.4.2     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=REQ-PARTICIPANT" 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-the
"Attendee". to-do. The
      "Attendee" uses the "REPLY" method to convey their acceptance and
      completion status to the "Organizer" of the "REQUEST".

      The "UID", "SEQUENCE", and "DTSTAMP" 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 a rescheduling, an
      update, or a reconfirm of the "VTODO" calendar object.

      Silverberg/Mansour/Daws/Hopson  34                Expires November 1998
      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 "REQUEST-STATUS" property of a subsequent "REPLY"
      method, but no scheduling action is performed.

      For the "REQUEST" method, multiple "VTODO" components in a single
      iCalendar object are only permitted when for components with the same
      "UID" property.  That is, a subsequent "REPLY"
method, but no scheduling action is performed. series of recurring events may have
      instance-specific information.  In this case, multiple "VTODO"
      components are needed to express the entire series.

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

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID                MUST
VERSION               MUST be "2.0"
      METHOD                1       MUST be "REQUEST"

Silverberg/Mansour/Dawson/Hopson  34             Expires September 1998
      VTODO                 MUST                 1+      All components must have the same UID
          ATTENDEE          MUST          1+
          DTSTAMP           MUST           1
          DTSTART           MUST           1
          ORGANIZER         MUST
    RECURRENCE-ID     MUST only if referring to an instance of a
                          recurring calendar component.  Otherwise it
                          must NOT be present.         1
          PRIORITY          1
          SEQUENCE          0 or 1  MUST be present if not value is greater than
                                    0, may MAY be present if 0
          SUMMARY           MUST; may           1       Can be null.
          UID               MUST               1

          ATTACH            MAY            0+
          CATEGORIES        MAY        0 or 1   This property may contain a list of
                                     values
          CLASS             MAY             0 or 1
          COMMENT           MAY           0 or 1
          CONTACT           MAY           0+
          CREATED           MAY           0 or 1
          DESCRIPTION       MAY       0 or 1  Can be null
          DUE               0 or 1  If present and MAY DURATION MUST NOT be NULL present
          DURATION          MAY
    DTEND             MAY          0 or 1  If present DUE MUST NOT be present
          EXDATE            MAY            0+
          EXRULE            MAY            0+
          GEO               MAY               0 or 1
          LAST-MODIFIED     MAY     0 or 1
          LOCATION          MAY          0 or 1
          PERCENT-COMPLETE  MAY
    PRIORITY          MAY
    RELATED-TO        MAY  0 or 1
          RDATE             MAY             0+
          RECURRENCE-ID     0 or 1  present if referring to an instance of a
                                    recurring calendar component.  Otherwise
                                    it MUST NOT be present.
          RELATED-TO        0+
          RESOURCES         MAY         0 or 1  This property may contain a list of
                                    values
          RRULE             MAY             0+
          STATUS            0 or 1  MAY be one of COMPLETED/NEEDS ACTION/IN-PROCESS
    TRANSP            MAY ACTION/IN-

      Silverberg/Mansour/Daws/Hopson  35                Expires November 1998
                                    PROCESS
          URL               MAY

VEVENT                NOT
VJOURNAL              NOT               0 or 1
          X-PROPERTY        0+

          REQUEST-STATUS    0

      VALARM                0+
      VTIMEZONE             0+  MUST be present if any date/time refers
                                to a timezone
VALARM                MAY
      X-COMPONENT           0+

      VEVENT                0
      VFREEBUSY             NOT
X-TOKENS              MAY             0
      VJOURNAL              0

      3.4.2.1   REQUEST for Rescheduling a VTODO

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

      Rescheduling a "VTODO" calendar component involves a change to the
      existing "VTODO" calendar component in terms of its 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"

Silverberg/Mansour/Dawson/Hopson  35             Expires September 1998
      is greater than the value for the existing VTODO, then the "REQUEST"
      method describes a rescheduling of the "VTODO" calendar component.

      3.4.2.2   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 not a 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.

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

      Silverberg/Mansour/Daws/Hopson  36                Expires November 1998
      3.4.2.3   REQUEST for Delegating a VTODO

      The "REQUEST" method is also used to delegate or reassign ownership of a
      "VTODO" calendar component to another "Calendar User". For example, it
      may be used to delegate an "Attendee's" role (i.e. "chair", or
      "participant") for a "VTODO" calendar component. The "REQUEST" method is
      sent by one of the "Attendees" of an existing "VTODO" calendar component
      to some other individual. An "Attendee" of a "VTODO" calendar component
      MUST 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
      "Delegate".

      The "Delegator" of a "VTODO" calendar component MUST forward the
      existing "REQUEST" method for a "VTODO" calendar component to the
      "Delegate". 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 "Delegate". The "Delegator" MUST also send a
      "REPLY" method back to the "Organizer" with the "Delegator's" "Attendee"
      property "attstat" "partstat" parameter value set to "DELEGATED". In addition, the
      "delegated-to" parameter SHOULD MUST be included with the calendar address of

Silverberg/Mansour/Dawson/Hopson  36             Expires September 1998 of
      the "Delegate". A response to the delegation "REQUEST" is sent from the
      "Delegate" to the "Organizer" and optionally, to the "Delegator". The
      "REPLY" method from the "Delegate" 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 a value for the "RSVP"
      property parameter associated with the "Delegator's" "Attendee" property
      to that of the "Delegate's" "ATTENDEE" property. For example if the
      "Delegator's" "ATTENDEE" property specifies "RSVP=TRUE", then the
      "Delegate's" "ATTENDEE" property MUST specify "RSVP=TRUE".

      3.4.2.4   REQUEST Forwarded To An Uninvited Calendar User

      An "Attendee" assigned a "VTODO" calendar component may assign send the "VTODO"
      calendar component to another new "Calendar User", CU, not previously associated with the
      "VTODO" calendar component. The current "Attendee" assigned the "VTODO"
      calendar component accomplishes does this
scheduling action by forwarding the original "REQUEST" method
      to the new
"Calendar User". CU. The new CU can send a "REPLY" to the "Organizer" of the
      "VTODO" calendar component. The reply contains an "ATTENDEE" property
      for the new CU.

      The "Organizer" ultimately decides whether or not the new CU becomes
      part of the to-do and is not obligated to do anything with a "REPLY"
      from a new (uninvited) CU. If the "Organizer" does not want the new CU
      to be part of the to-do, the new "ATTENDEE" property is not added to the
      "VTODO" calendar component. The "Organizer" MAY send the CU a "CANCEL"
      message to indicate that they will not be added to the to-do. If the
      "Organizer" decides to add the new CU, the new "ATTENDEE" property is

      Silverberg/Mansour/Daws/Hopson  37                Expires November 1998
      added to the "VTODO" calendar component. Furthermore, the "Organizer" is
      free to change any "ATTENDEE" property parameter from the values
      supplied by the new CU to something the "Organizer" considers
      appropriate.

      3.4.2.5   REQUEST Updated Attendee Status

      An "Organizer" of a "VTODO" may request an updated status from one or
      more "Attendees". The "Organizer" sends a "REQUEST" method to the
      "Attendee" with the "ATTENDEE;RSVP=TRUE" property sequence. The
      "SEQUENCE" property for the "VTODO" is not changed from its previous
      value. A recipient determines 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".

      3.4.3     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 MUST
      include the calendar address of the "Delegate" in the "delegated-
to" "delegated-to"
      parameter of the "Delegator's" "ATTENDEE" property. The "Delegate"
SHOULD MUST
      include the calendar address of the "Delegator" on the "delegated-from"
      parameter of the "Delegate'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 "Delegate" of a "VTODO"
      calendar component. In addition, the "REPLY" method MAY be received from

Silverberg/Mansour/Dawson/Hopson  37             Expires September 1998
      an unknown "Calendar User", having been forwarded the "REQUEST" by an
      original "Attendee" of 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:

      Component/Property   Presence
      -------------------  ---------------------------------------------
PRODID               MUST
VERSION              MUST be "2.0"
      METHOD               1      MUST be "REPLY"
      VTODO                1+     All component MUST have the same UID
          ATTENDEE         MUST         1+
          DTSTAMP          1
          ORGANIZER        1

      Silverberg/Mansour/Daws/Hopson  38                Expires November 1998
          REQUEST-STATUS   1+
          UID              1      MUST must be the address of the replying attendee
    DTSTAMP          MUST
    ORGANIZER        MUST the replying
                                  attendee

          ATTACH           0+
          CATEGORIES       0 or 1 This property may contain a list of values
          CLASS            0 or 1
          COMMENT          0 or 1
          CONTACT          0+
          CREATED          0 or 1
          DESCRIPTION      0 or 1
          DTSTART          0 or 1
          DUE              0 or 1  If present DURATION MUST NOT be present
          DURATION         0 or 1  If present DUE MUST NOT be present
          EXDATE           0+
          EXRULE           0+
          GEO              0 or 1
          LAST-MODIFIED    0 or 1
          LOCATION         0 or 1
          PERCENT-COMPLETE 0 or 1
          PRIORITY         0 or 1
          RDATE            0+
          RELATED-TO       0+
          RESOURCES        0 or 1  This property may contain a list of values
          RRULE            0+
          RECURRENCE-ID    0 or 1  MUST only if referring to an instance of a
                                   Recurring calendar component. Otherwise it
                          Must
                                   MUST NOT be present
          SEQUENCE         0 or 1  MUST

    COMMENT          MAY
    PERCENT-COMPLETE MAY
    REQUEST-STATUS be the sequence number of
                                   the original REQUEST if greater than 0.
                                   MAY

    DTSTART          NOT
    CREATED          NOT
    DESCRIPTION      NOT
    PRIORITY         NOT
    CLASS            NOT
    CATEGORIES       NOT
    CONTACT          NOT
    CREATED          NOT
    DTEND            NOT
    GEO              NOT
    LAST-MODIFIED    NOT
    LOCATION         NOT
    RDATE            NOT
    RRULE            NOT
    RELATED-TO       NOT
    RESOURCE         NOT be present if 0.
          STATUS           NOT
    TRANSP           NOT           0 or 1
          SUMMARY          0 or 1  Can be null
          URL              NOT              0 or 1
          X-PROPERTY       0+

      VTIMEZONE            0 or 1  MUST be present if any date/time refers to
                                   a timezone
      X-COMPONENT          0+

      VALARM               NOT               0
      VEVENT               NOT               0
      VFREEBUSY            NOT
X-TOKENS             NOT

Silverberg/Mansour/Dawson/Hopson  38             Expires September 1998            0

      3.4.4     ADD

      The "ADD" method in a "VTODO" calendar component is used to add one or
      more instances to an existing to-do.

      If the "UID" property value in the "ADD" is not found on the recipient's
      calendar, then the recipient SHOULD send a "REFRESH" to the "Organizer"
      in order to be updated with the latest version of the "VTODO". If an
      "Attendee" implementation does not support the "ADD" method it should
      respond with a "REQUEST-STATUS" value of 5.3 and ask for a "REFRESH".

      Silverberg/Mansour/Daws/Hopson  39                Expires November 1998
      The "SEQUENCE" property value is incremented as the sequence of to-dos
      has changed.

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

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID                MUST
VERSION               MUST be "2.0"
      METHOD                1       MUST be "ADD"
      VTODO                 MUST                 1
          DTSTAMP           MUST
    DTSTART           MUST           1
          ORGANIZER         MUST         1
          PRIORITY          1
          SEQUENCE          1       MUST be greater than 0
          SUMMARY           MUST; may           1       Can be null.
          UID               1       MUST match that of the original to-do

    ATTENDEE          MAY

          ATTACH            MAY            0+
          ATTENDEE          0+
          CATEGORIES        MAY        0 or 1  This property may contain a list of
                                    values
          CLASS             MAY             0 or 1
          COMMENT           MAY           0 or 1
          CONTACT           MAY           0+
          CREATED           MAY           0 or 1
          DESCRIPTION       MAY       0 or 1  Can be null
          DTSTART           0 or 1
          DUE               0 or 1  If present and MAY DURATION MUST NOT be NULL
    DTEND             MAY present
          DURATION          MAY          0 or 1  If present DUE MUST NOT be present
          EXDATE            MAY            0+
          EXRULE            MAY            0+
          GEO               MAY               0 or 1
          LAST-MODIFIED     MAY     0 or 1
          LOCATION          MAY          0 or 1
          PERCENT-COMPLETE  MAY
    PRIORITY          MAY
    RELATED-TO        MAY  0 or 1
          RDATE             MAY             0+
          RELATED-TO        0+
          RESOURCES         MAY         0 or 1  This property may contain a list of
                                    values
          RRULE             MAY             0+
          STATUS            0 or 1  MAY be one of COMPLETED/NEEDS ACTION/IN-PROCESS
    TRANSP            MAY ACTION/IN-
                                    PROCESS
          URL               MAY

Silverberg/Mansour/Dawson/Hopson  39             Expires September 1998               0 or 1
          X-PROPERTY        0+

          RECURRENCE-ID     NOT     0
          REQUEST-STATUS    NOT

VEVENT                NOT
VJOURNAL              NOT    0

      VALARM                0+
      VTIMEZONE             0+      MUST be present if any date/time refers
                                    to a timezone
VALARM                MAY
      X-COMPONENT           0+

      VEVENT                0

      Silverberg/Mansour/Daws/Hopson  40                Expires November 1998
      VJOURNAL              0
      VFREEBUSY             NOT
X-TOKENS              MAY             0

      3.4.5     CANCEL

      The "CANCEL" method in a "VTODO" calendar component is used to send a
      cancellation notice of an existing "VTODO" calendar 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 and a "RECURRENCE-ID" MUST NOT 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.

      There are two options for canceling a sequence of instances of a
      recurring "VTODO" calendar component:

      (a)          the "RECURRENCE-ID" property for an instance in the sequence MUST be
        specified with the "RANGE" property parameter value of THISANDPRIOR
        (or THISANDFUTURE)  to indicate cancellation of the specified "VTODO"
        calendar component and all instances before (or after); or

      (b)          individual recurrence instances may be cancelled by specifying
        multiple "RECURRENCE-ID" properties corresponding to the instances to
        be cancelled.

      When a "VTODO" is cancelled, the "SEQUENCE" property value MUST be
      incremented.

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

      Component/Property   Presence
      -------------------  ---------------------------------------------
PRODID               MUST
VERSION              MUST be "2.0"
      METHOD               1     MUST be "CANCEL"
      VTODO                1
          ATTENDEE         0+    include all "Attendees" being removed from
                                 the todo. MUST include all "Attendees" if
                                 the entire todo is cancelled.
          UID              1     MUST must echo original UID
          DTSTAMP          MUST          1
          ORGANIZER        MUST        1
          SEQUENCE         MUST

Silverberg/Mansour/Dawson/Hopson  40         1

          ATTACH           0+
          CATEGORIES       0 or 1 This property MAY contain a list of values
          CLASS            0 or 1
          COMMENT          0 or 1

      Silverberg/Mansour/Daws/Hopson  41                Expires September November 1998
          CONTACT          0+
          CREATED          0 or 1
          DESCRIPTION      0 or 1
          DTSTART          0 or 1
          DUE              0 or 1  If present DURATION MUST NOT be present
          DURATION         0 or 1  If present DUE MUST NOT be present
          EXDATE           0+
          EXRULE           0+
          GEO              0 or 1
          LAST-MODIFIED    0 or 1
          LOCATION         0 or 1
          PERCENT-COMPLETE 0 or 1
          RDATE            0+
          RECURRENCE-ID    0 or 1 MUST only if referring to one or more
                                  instances of a recurring calendar
                                  component. Otherwise it MUST NOT be present
    COMMENT          MAY
    ATTENDEE         MAY
    DTSTART          MAY
    CREATED          MAY
    DESCRIPTION      MAY
    ORGANIZER        MAY
    PRIORITY         MAY
    CLASS            MAY
    CATEGORIES       MAY
    CONTACT          MAY
    CREATED          MAY
    DTEND            MAY
    GEO              MAY
    LAST-MODIFIED    MAY
    LOCATION         MAY
    PERCENT-COMPLETE MAY
    PRIORITY         MAY
    RDATE            MAY
    RRULE            MAY
                                  present.
          RELATED-TO       0+
          RESOURCES        0 or 1 This property MAY
    REQUEST-STATUS   MAY
    RESOURCE         MAY contain a list of values
          RRULE            0+
          PRIORITY         0 or 1
          STATUS           MAY           0 or 1  If present it must MUST be set to "CANCELLED".
                                   MUST NOT be used if purpose is to remove
                                   "ATTENDEES" rather than cancel the entire
                                   VTODO.
    TRANSP           MAY
          URL              MAY              0 or 1
          X-PROPERTY       0+

          REQUEST-STATUS   0

      VTIMEZONE            0 or 1  MUST be present if any date/time refers to
                                   a timezone
      X-COMPONENT          0+

      VALARM               MAY               0
      VEVENT               MAY               0
      VFREEBUSY            MAY
X-TOKENS             MAY            0

      3.4.6     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 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" responds with
      the latest description and rendition of the "VTODO" calendar component.

Silverberg/Mansour/Dawson/Hopson  41
      In most cases this will be a REQUEST unless the "VTODO" has been

      Silverberg/Mansour/Daws/Hopson  42                Expires September November 1998
      cancelled, in which case the ORGANIZER MUST send a "CANCEL". 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:

      Component/Property   Presence
      -------------------  ---------------------------------------------
PRODID               MUST
VERSION              MUST be "2.0"
      METHOD               1      MUST be "REFRESH"
      VTODO                MUST                1
          ATTENDEE         MUST         1
          DTSTAMP          1
          UID              1       MUST echo original UID

          RECURRENCE-ID    0 or 1  MUST only if referring to an instance of a
                                   Recurring calendar component. Otherwise it
                                   MUST NOT be present
    UID              MUST echo original UID
    COMMENT          MAY
    REQUEST-STATUS   MAY
    DTSTART          MAY
    CREATED          MAY
    DESCRIPTION      MAY
    PRIORITY         MAY
    CLASS            MAY
          X-PROPERTY       0+

          ATTACH           0
          CATEGORIES       MAY       0
          CLASS            0
          COMMENT          0
          CONTACT          MAY          0
          CREATED          MAY
    DTEND            MAY          0
          DESCRIPTION      0
          DTSTART          0
          DUE              0
          DURATION         0
          EXDATE           0
          EXRULE           0
          GEO              MAY              0
          LAST-MODIFIED    MAY
    PERCENT-COMPLETE MAY    0
          LOCATION         0
          ORGANIZER        MAY        0
          PERCENT-COMPLETE 0
          PRIORITY         MAY
    LOCATION         MAY         0
          RDATE            MAY
    RRULE            MAY            0
          RELATED-TO       MAY
    RESOURCE         MAY       0
          REQUEST-STATUS   0
          RESOURCES        0
          RRULE            0
          SEQUENCE         MAY         0
          STATUS           MAY
    TRANSP           MAY           0
          URL              MAY
VTIMEZONE            MUST be present if any date/time refers to a
                         timezone              0

      X-COMPONENT          0+

      VALARM               MAY               0
      VEVENT               MAY               0
      VFREEBUSY            MAY
X-TOKENS             MAY

Silverberg/Mansour/Dawson/Hopson  42            0
      VTIMEZONE            0

      Silverberg/Mansour/Daws/Hopson  43                Expires September November 1998
      3.4.7     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" sends the message to the "Organizer" of the "VTODO" calendar
      component.

      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
"DECLINE-COUNTER"
      "DECLINECOUNTER" 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
      latter 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:

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID               MUST
VERSION              MUST be "2.0"
      METHOD               1      MUST be "COUNTER"
      VTODO                MUST                1
          ATTENDEE         1+
          DTSTAMP          MUST
    DTSTART          MAY          1
          ORGANIZER        1
          PRIORITY         1
          SUMMARY          1      Can be null
          UID              1

          ATTACH           0+
          CATEGORIES       0 or 1 This property MAY contain a list of values
          CLASS            0 or 1
          COMMENT          0 or 1
          CONTACT          0+
          CREATED          0 or 1
          DESCRIPTION      0 or 1 Can be null
          DTSTART          0 or 1
          DUE              0 or 1  If present DURATION MUST NOT be present
          DURATION         0 or 1  If present DUE MUST NOT be present
          EXDATE           0+
          EXRULE           0+
          GEO              0 or 1
          LAST-MODIFIED    0 or 1
          LOCATION         0 or 1
          PERCENT-COMPLETE 0 or 1
          RDATE            0+

      Silverberg/Mansour/Daws/Hopson  44                Expires November 1998
          RECURRENCE-ID    0 or 1 MUST only if referring to an instance of a
                                  recurring calendar component.  Otherwise it
                                  MUST NOT be present. NOT be present.
          RELATED-TO       0+
          REQUEST-STATUS   0+
          RESOURCES        0 or 1 This property MAY contain a list of values
          RRULE            0 or 1
          SEQUENCE         0 or 1 MUST echo the original SEQUENCE number.
                                  MUST be present if NOT 0, non-zero. MAY be present
                                  if 0
    SUMMARY          MUST be present; MAY be NULL
    UID              MUST

    ATTENDEE         MAY
    ATTACH           MAY
    CATEGORIES       MAY
    CLASS            MAY
    COMMENT          MAY
    CONTACT          MAY
    CREATED          MAY
    DESCRIPTION      MAY be present; MAY be NULL
    DURATION         MAY
    DTEND            MAY
    EXDATE           MAY
    EXRULE           MAY
    GEO              MAY
    LAST-MODIFIED    MAY

Silverberg/Mansour/Dawson/Hopson  43             Expires September 1998
    LOCATION         MAY
    PERCENT-COMPLETE MAY
    PRIORITY         MAY
    RELATED-TO       MAY
    RDATE            MAY
    RESOURCES        MAY
    RRULE            MAY zero.
          STATUS           0 or 1 MAY be one of COMPLETED/NEEDS ACTION/IN-PROCESS
    TRANSP           MAY ACTION/IN-
                                  PROCESS/CANCELLED
          URL              MAY
VEVENT               MAY
VJOURNAL             MAY              0 or 1
          X-PROPERTY       0+

      VALARM               0+
      VTIMEZONE            0 or 1  MUST be present if any date/time refers to
                                   a timezone
VALARM               MAY
      X-COMPONENT          0+

      VEVENT               0
      VFREEBUSY            MAY
X-TOKENS             MAY            0

      3.4.8     DECLINECOUNTER

      The "DECLINE-COUNTER" "DECLINECOUNTER" 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" sends the
      message to the "Attendee" that sent the "COUNTER" method to the
      "Organizer".

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

      Component/Property   Presence
      -------------------  ---------------------------------------------
PRODID               MUST
VERSION              MUST be "2.0"
      METHOD               1       MUST be "DECLINECOUNTER"

      VTODO                MUST                1
          ATTENDEE         1+      MUST for all attendees
    UID
          DTSTAMP          1
          ORGANIZER        1
          SEQUENCE         1       MUST must echo the original UID
    DTSTAMP          MUST SEQUENCE number
          UID              1       MUST
    RECURRENCE-ID    MUST only if referring to an instance of echo original UID

          ATTACH           0+
          CATEGORIES       0 or 1  This property may contain a
                          recurring calendar component.  Otherwise it
                          MUST NOT be present. list of values
          CLASS            0 or 1
          COMMENT          MAY
    PERCENT-COMPLETE MAY
    REQUEST-STATUS   MAY
    DTSTART          MAY          0 or 1
          CONTACT          0+
          CREATED          MAY          0 or 1
          DESCRIPTION      MAY
    ORGANIZER        MAY
    PRIORITY         MAY

Silverberg/Mansour/Dawson/Hopson  44      0 or 1
          DTSTART          0 or 1

      Silverberg/Mansour/Daws/Hopson  45                Expires September November 1998
    CLASS            MAY
    CATEGORIES       MAY
    CONTACT          MAY
    CREATED          MAY
    DTEND            MAY
          DUE              0 or 1  If present DURATION MUST NOT be present
          DURATION         0 or 1  If present DUE MUST NOT be present
          EXDATE           0+
          EXRULE           0+
          GEO              MAY              0 or 1
          LAST-MODIFIED    MAY    0 or 1
          LOCATION         MAY         0 or 1
          PERCENT-COMPLETE 0 or 1
          PRIORITY         0 or 1
          RDATE            MAY
    RRULE            MAY            0+
          RECURRENCE-ID    0 or 1  MUST only if referring to an instance of a
                                   recurring calendar component.  Otherwise
                                   it MUST NOT be present.
          RELATED-TO       0+
          REQUEST-STATUS   0+
          RESOURCES        0 or 1  This property MAY
    RESOURCE         MAY contain a list of values
          RRULE            0+
          STATUS           0 or 1  MAY be one of COMPLETED/NEEDS ACTION/IN-PROCESS
    TRANSP           MAY ACTION/IN-
                                   PROCESS
          URL              MAY              0 or 1
          X-PROPERTY       0+

      VTIMEZONE            0+  MUST be present if any date/time refers to
                               a timezone
      X-COMPONENT          0+

      VALARM               MAY               0
      VEVENT               MAY
VTODO                MAY               0
      VFREEBUSY            MAY
X-TOKENS             MAY            0

      3.5 Methods For VJOURNAL Components

      This section defines the property set for the methods that are
      applicable to the "VJOURNAL" calendar component.

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

      +================+==================================================+
      | Method         |  Description                                     |
      |================+==================================================|
      | PUBLISH        | Post a journal entry. Used primarily as a method |
      |                | of advertising the existence of a journal entry. |
      |                |                                                  |
      | ADD            | Add one or more instances to an existing journal |
      |                | entry.                                           |
      |                |                                                  |
      | CANCEL         | Cancel one or more instances of an existing      |
      |                | journal entry.                                   |
      +================+==================================================+

      Silverberg/Mansour/Daws/Hopson  46                Expires November 1998
      3.5.1     PUBLISH

      The "PUBLISH" method in a "VJOURNAL" calendar component has no
      associated response. It is simply a posting of an iCalendar object that
      may be added to a calendar by a CUA. There is no response to the calendar. It MUST have an "Organizer". It MUST NOT
      have "Attendees". The expected usage is for encapsulating an arbitrary
      journal entry as an iCalendar object. The "Organizer" MAY subsequently

Silverberg/Mansour/Dawson/Hopson  45             Expires September 1998
      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:

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID               MUST
VERSION              MUST be "2.0"
      METHOD               1       MUST be "PUBLISH"
      VJOURNAL             MUST             1+
          DESCRIPTION      1       Can be null.
          DTSTAMP          MUST          1
          DTSTART          MUST          1
          ORGANIZER        MUST        1
          UID              1

          ATTACH           0+
          CATEGORIES       0 or 1  This property MAY contain a list of values
          CLASS            0 or 1
          COMMENT          0 or 1
          CONTACT          0+
          CREATED          0 or 1
          EXDATE           0+
          EXRULE           0+
          LAST-MODIFIED    0 or 1
          RDATE            0+
          RECURRENCE-ID    0 or 1  MUST only if referring to an instance of a
                                   recurring calendar component.  Otherwise
                                   it MUST NOT be present.
          RELATED-TO       0+
          RRULE            0+
          SEQUENCE         0 or 1  MUST echo the original SEQUENCE number.
                                   MUST be present if not 0, non-zero. MAY be
                                   present if 0
    SUMMARY          MUST be present and MAY be NULL
    UID              MUST

    ATTENDEE         MAY
    ATTACH           MAY
    CATEGORIES       MAY
    CLASS            MAY
    COMMENT          MAY
    CONTACT          MAY
    CREATED          MAY
    DESCRIPTION      MAY be present; MAY be NULL.
    DURATION         MAY
    DTEND            MAY
    EXDATE           MAY
    EXRULE           MAY
    GEO              MAY
    LAST-MODIFIED    MAY
    LOCATION         MAY
    PRIORITY         MAY
    RELATED-TO       MAY
    RDATE            MAY
    RESOURCES        MAY
    RRULE            MAY zero.
          STATUS           0 or 1  MAY be one of DRAFT/FINAL/CANCELLED
    TRANSP           MAY
          SUMMARY          0 or 1  Can be null
          URL              MAY

VEVENT               MAY
VTODO                MAY              0 or 1
          X-PROPERTY       0+

          ATTENDEE         0

      VALARM               0+
      VTIMEZONE            0+      MUST be present if any date/time refers to
                                   a timezone
VALARM               MAY
VFREEBUSY            MAY
X-TOKENS             MAY

Silverberg/Mansour/Dawson/Hopson  46
      X-COMPONENT          0+

      VEVENT               0

      Silverberg/Mansour/Daws/Hopson  47                Expires September November 1998
      VFREEBUSY            0
      VTODO                0

      3.5.2     ADD

      The "ADD" method in a "VJOURNAL" calendar component is used to add one
      or more instances to an existing "VJOURNAL" entry. There is no response
      to the "Organizer".

      If the "UID" property value in the "ADD" is not found on the recipient's
      calendar, then the recipient MAY treat the "ADD" as a "PUBLISH".

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

      Component/Property  Presence
      ------------------- ----------------------------------------------
PRODID               MUST
VERSION              MUST be "2.0"
      METHOD               1      MUST be "ADD"
      VJOURNAL             MUST             1
          DESCRIPTION      1      Can be null.
          DTSTAMP          MUST          1
          DTSTART          MUST          1
          ORGANIZER        MUST        1
          SEQUENCE         1      MUST be greater than 0
    SUMMARY          MUST be present and MAY be NULL
          UID              1      MUST match that of the original journal

          ATTACH           MAY           0+
          CATEGORIES       0 or 1 This property MAY contain a list of values
          CLASS            MAY            0 or 1
          COMMENT          MAY          0 or 1
          CONTACT          MAY          0+
          CREATED          MAY
    DESCRIPTION      MAY be present; may be null.
    DURATION         MAY
    DTEND            MAY          0 or 1
          EXDATE           MAY           0+
          EXRULE           MAY
    GEO              MAY           0+
          LAST-MODIFIED    MAY
    LOCATION         MAY
    PRIORITY         MAY
    RELATED-TO       MAY    0 or 1
          RDATE            MAY
    RESOURCES        MAY            0+
          RELATED-TO       0+
          RRULE            MAY            0+
          STATUS           0 or 1  MAY be one of DRAFT/FINAL/CANCELLED
    TRANSP           MAY
          SUMMARY          0 or 1  Can be null
          URL              MAY              0 or 1
          X-PROPERTY       0+

          ATTENDEE         NOT         0
          RECURRENCE-ID    NOT

VEVENT               MAY
VTODO                MAY    0

      VALARM               0+
      VTIMEZONE            0 or 1 MUST be present if any date/time refers to
                                  a

Silverberg/Mansour/Dawson/Hopson  47             Expires September 1998 timezone
VALARM               MAY
      X-COMPONENT          0+

      VEVENT               0
      VFREEBUSY            MAY
X-TOKENS             MAY            0

      Silverberg/Mansour/Daws/Hopson  48                Expires November 1998
      VTODO                0

      3.5.3     CANCEL

      The "CANCEL" method in a "VJOURNAL" calendar component is used to send a
      cancellation notice of an existing journal entry. The message is sent by
      the "Organizer" of a 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 and a
      "RECURRENCE-ID" property MUST NOT 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.

      There are two options for canceling a sequence of instances of a
      recurring "VJOURNAL" calendar component:

      (a)          the "RECURRENCE-ID" property for an instance in the sequence MUST be
        specified with the "RANGE" property parameter value of THISANDPRIOR
        (or THISANDFUTURE)  to indicate cancellation of the specified "VTODO"
        calendar component and all instances before (or after); or

      (b)          individual recurrence instances may be cancelled by specifying
        multiple "RECURRENCE-ID" properties corresponding to the instances to
        be cancelled.

      When a "VJOURNAL" is cancelled, the "SEQUENCE" property value MUST be
      incremented.

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

      Component/Property   Presence
      -------------------  ---------------------------------------------
PRODID              MUST
VERSION             MUST be "2.0"
      METHOD               1       MUST be "CANCEL"
      VJOURNAL             1+      All MUST have the same UID
          DTSTAMP         MUST          1
          ORGANIZER       MUST
    RECURRENCE-ID   MUST only if referring to an instance of a
                         recurring calendar component.  Otherwise it
                         MUST NOT be present.        1
          SEQUENCE        MUST         1
          UID              1       MUST be the UID of the original REQUEST

    COMMENT         MAY
    STATUS          MAY be present, must be "CANCELLED" if present

          ATTACH          MAY           0+
          ATTENDEE        MAY         0+
          CATEGORIES       0 or 1  This property MAY

Silverberg/Mansour/Dawson/Hopson  48             Expires September 1998 contain a list of values
          CLASS           MAY            0 or 1
          COMMENT          0 or 1
          CONTACT         MAY          0+
          CREATED         MAY          0 or 1
          DESCRIPTION     MAY      0 or 1
          DTSTART         MAY
    DTEND           MAY          0 or 1
          EXDATE          MAY           0+

      Silverberg/Mansour/Daws/Hopson  49                Expires November 1998
          EXRULE          MAY
    GEO             MAY           0+
          LAST-MODIFIED   MAY
    %-COMPLETE      MAY
    PRIORITY        MAY
    RELATED-TO      MAY
    REQUEST-STATUS  MAY
    RESOURCES       MAY    0 or 1
          RDATE           MAY            0+
          RECURRENCE-ID    0 or 1  only if referring to an instance of a
                                   recurring calendar component.  Otherwise
                                   it MUST NOT be present.
          RELATED-TO       0+
          RRULE           MAY            0+
          STATUS           0 or 1  MAY be present, must be "CANCELLED" if
                                   present
          SUMMARY         MAY
    TRANSP          MAY          0 or 1
          URL             MAY

VTODO               MAY
VEVENT              MAY
VFREEBUSY           MAY              0 or 1
          X-PROPERTY       0+

          REQUEST-STATUS   0

      VTIMEZONE            0+      MUST be present if any date/time refers to
                                   a timezone
      X-COMPONENT          0+
      VALARM              MAY
X-TOKENS            MAY               0
      VEVENT               0
      VFREEBUSY            0
      VTODO                0

      3.6 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    |
      |              | ignored.                   | specified.              |
      |==============+============================+=========================|
      | 2.3          | Success, invalid property  | Property parameter name |
      |              | parameter ignored.         | and value MAY be        |
      |              |                            | specified.              |
      |==============+============================+=========================|
      | 2.4          | Success, unknown non-      | Non-standard property   |

Silverberg/Mansour/Dawson/Hopson  49             Expires September 1998
      |              | standard property ignored. | name MAY be specified.  |
      |==============+============================+=========================|
      | 2.5          | Success, unknown non       | Property and non-       |
      |              | standard property value    | standard value MAY be   |
      |              | ignored.                   | specified.              |
      |==============+============================+=========================|

      Silverberg/Mansour/Daws/Hopson  50                Expires November 1998
      | 2.6          | Success, invalid calendar  | Calendar component      |
      |              | component ignored.         | sentinel (e.g., "BEGIN: BEGIN:  |
      |              |                            | ALARM") 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. component.          | 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.              |
      |==============+============================+=========================|
      | 2.11         | Success, RRULE or EXRULE   | RRULE or EXRULE property|
|              | too complex. Scheduled as  | name and value MAY be   |
|              | a single event.            | specified.              |
|==============+============================+=========================|
| 2.12         | Success, unbounded RRULE   | RRULE property name and |
      |              | clipped at some finite     | value MAY be specified. |
      |              | number of instances        | Number of instances MAY |
      |              |                            | also be 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).             |
      |==============+============================+=========================|

Silverberg/Mansour/Dawson/Hopson  50             Expires September 1998
      | 3.5          | Invalid date or time.      | Date/time value(s) MAY  |
      |              |                            | be specified.           |
      |==============+============================+=========================|
      | 3.6          | Invalid rule.              | Rule value MAY be       |
      |              |                            | specified.              |
      |==============+============================+=========================|
      | 3.7          | Invalid Calendar User.     | Attendee property value |
      |              |                            |MAY be specified.        |
      |==============+============================+=========================|
      | 3.8          | No authority.              | PROFILE METHOD and Attendee     |

      Silverberg/Mansour/Daws/Hopson  51                Expires November 1998
      |              |                            | property values MAY be  |
      |              |                            | specified.              |
      |==============+============================+=========================|
      | 3.9          | Unsupported version.       | VERSION property name   |
      |              |                            | and value MAY be        |
      |              |                            | specified.              |
      |==============+============================+=========================|
      | 3.10         | Request entity too large.  | None.                   |
      |==============+============================+=========================|
      | 3.11         | Required component or      | Component or property   |
      |              | property missing.          | name MAY be specified.  |
      |==============+============================+=========================|
      | 3.12         | Unknown component or       | Component or property   |
      |              | property found             | name MAY be specified   |
      |==============+============================+=========================|
      | 3.13         | Unsupported component or   | Component or property   |
      |              | property found             | name MAY be specified   |
      |==============+============================+=========================|
      | 3.14         | Unsupported capability     | Method or action MAY    |
      |              |                            | be specified            |
      |==============+============================+=========================|
      | 4.0          | Event conflict. Date/time  | DTSTART and DTEND       |
      |              | is busy.                   | property name and values|
      |              |                            | MAY be specified.       |
      |==============+============================+=========================|
      | 5.0          | Request MAY 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.       |
      |==============+============================+=========================|

      3.7 Implementation Considerations

      3.7.1     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 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.

Silverberg/Mansour/Dawson/Hopson  51             Expires September 1998

      Since implementations may elect to store recurring events as either a
      single event object or a collection of discreet, related event objects,

      Silverberg/Mansour/Daws/Hopson  52                Expires November 1998
      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 "attstat" "partstat"
      parameter) may do so. However, the protocol does not require per-
      instance recognition unless the instance itself must be renegotiated.

      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 effect 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 is renegotiated.
      Negotiation may be necessary when a substantive change to the event or
      to-do has be made (such as changing the start time, end time, due date
      or location). The "Organizer" can identify a specific recurrence
      instance 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.
      Note that after the change has occurred, the "RECURRENCE-ID" has changed
      to the new "DTSTART" value.

      3.7.2     Attendee Property Considerations

      The "ORGANIZER" property is required on published events, to-dos, and
      journal entries for two reasons. First, only the "Organizer" is allowed
      to update and redistribute an event or to-do component. It follows that
      the "ORGANIZER" 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 [RFC-822] addresses that represent groups. Sending email
      to such an address results in mail being sent to multiple recipients.
      Such an address may be used as the value of an "ATTENDEE" property.

Silverberg/Mansour/Dawson/Hopson  52

      Silverberg/Mansour/Daws/Hopson  53                Expires September November 1998
      Thus, it is possible that the recipient of a "REQUEST" does not appear
      explicitly in the list.

      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 then determines if the "Calendar User" 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 which:
        .  the "TYPE" "type" property parameter is set to INDIVIDUAL and
        .  the "group" "member" property parameter is set to the name of the group. group

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

      3.7.3     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 replies.

      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 are 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                         |

Silverberg/Mansour/Dawson/Hopson  53

      Silverberg/Mansour/Daws/Hopson  54                Expires September November 1998
      +---------------------------------+---------------------------------+
      | "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.

      BEGIN:VCALENDAR
      METHOD:PUBLISH
      PRODID:-//ACME/DesktopCalendar//EN
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:mailto:a@example.com
      DTSTART:19970701T200000Z
      DTSTAMP:19970611T190000Z
      SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
      UID:0981234-1234234-23@example.com
      END:VEVENT
      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
      ORGANIZER:mailto:a@example.com
      DTSTAMP:19970612T190000Z
      DTSTART:19970701T210000Z
      DTEND:19970701T230000Z
SEQUENCE:2
      SEQUENCE:1
      UID:0981234-1234234-23@example.com
      SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
      END:VEVENT
      END:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  54

      Silverberg/Mansour/Daws/Hopson  55                Expires September November 1998
      The "UID" property is used by the client to identify the event. The
      "SEQUENCE" property indicates that this is the second a change to the event. Events The
      event with a matching UID and sequence numbers number 0 and 1 are is 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 MUST NOT be updated.

      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
      ORGANIZER:mailto:a@example.com
      COMMENT:DUKES forfeit the game
      SEQUENCE:2
      UID:0981234-1234234-23@example.com
      DTSTAMP:19970613T190000Z
      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
      SCALE:GREGORIAN
SOURCE:http://www.midwaystadium.com/stadium-cal/1997-events.or4
      VERSION:2.0
      BEGIN:VTIMEZONE
      TZID:America-Chicago
      TZURL:http://zones.stds_r_us.net/tz/America-Chicago
LAST-MODIFIED:19870101T000000Z
      BEGIN:STANDARD
      DTSTART:19671029T020000
      RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
      TZOFFSETFROM:-0500
      TZOFFSETTO:-0600
      TZNAME:CST

Silverberg/Mansour/Dawson/Hopson  55             Expires September 1998
      END:STANDARD
      BEGIN:DAYLIGHT

      Silverberg/Mansour/Daws/Hopson  56                Expires November 1998
      DTSTART:19870405T020000
      RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
      TZOFFSETFROM:-0600
      TZOFFSETTO:-0500
      TZNAME:CDT
      END:DAYLIGHT
      END:VTIMEZONE
      BEGIN:VEVENT
      ORGANIZER:mailto:a@example.com
ATTACH:http://www.midwaystadium.com
      ATTACH:http://www.dukes.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;TZID=America-Chicago:19970701T180000
      DTSTART;TZID=America-Chicago: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@example.com
      RELATED-TO:0981234-1234234-14@example.com
      BEGIN:VALARM
TRIGGER:PT2H
ALARM-TYPE:DISPLAY
DESCRIPTION:It's almost
      TRIGGER:-PT2H
      ACTION:DISPLAY
      DESCRIPTION:You should be leaving for the game time now.
      END:VALARM
      BEGIN:VALARM
TRIGGER:PT30M
ALARM-TYPE:AUDIO
DESCRIPTION:You SHOULD leave now. Game starts in 30 minutes!
      TRIGGER:-PT30M
      ACTION:AUDIO
      END:VALARM
      END:VEVENT
      END:VCALENDAR

      The "RELATED-TO" field contains the "UID" property of a related calendar
      event. The "SEQUENCE" property 3 indicates that this event supersedes
      versions 0, 1, and 2.

      4.1.5     Anniversaries or Events attached to entire days

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

Silverberg/Mansour/Dawson/Hopson  56             Expires September 1998

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:PUBLISH
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:mailto:a@example.com

      Silverberg/Mansour/Daws/Hopson  57                Expires November 1998
      DTSTAMP:19970614T190000Z
      UID:0981234-1234234-23@example.com
      DTSTART;VALUE=DATE:19970714
      RRULE:FREQ=YEARLY;INTERVAL=1
      SUMMARY: Bastille Day
      END:VEVENT
      END:VCALENDAR

      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" and
      the "Organizer" 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 attendance. The following table
      illustrates the the message flow between these individuals. A, the CU
      scheduling the meeting, is referenced as the "Organizer".

      +--------------------------------------------------------------------+
      | 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 "attstat" "partstat" para-|
      |                    |                     | set to "accepted"       |
      +--------------------------------------------------------------------+
      | Decline the meeting|                     | "C" sends a REPLY       |
      | request            |                     | message to "A" with its |
      |                    |                     | ATTENDEE "attstat" "partstat" para-|
      |                    |                     | set to "declined"       |
      +--------------------------------------------------------------------+
      | Tentatively accept |                     | "D" sends a REPLY       |
      | the meeting request|                     | message to "A" with its |
      |                    |                     | ATTENDEE "attstat" "partstat" para-|
      |                    |                     | set to "tentative"      |
      +--------------------------------------------------------------------+
      | Confirm meeting    | "A" sends a REQUEST |                         |
      | status with        | message to "B" and  |                         |
      | attendees          | "C" "D" with updated    |                         |
      |                    | information.        |                         |
      +--------------------------------------------------------------------+

Silverberg/Mansour/Dawson/Hopson  57             Expires September 1998

      4.2.1     A Group Event Request

      A sample meeting request is sent from "A" to "B", "C", and "D". _E_ is
      also sent a copy of the request but is not expected to attend and need
      not reply. "E" illustrates how CUAs might implement a "CC" an "FYI" type

      Silverberg/Mansour/Daws/Hopson  58                Expires November 1998
      feature. Note the use of the "role" parameter. The default value for the
      "role" parameter is "req-participant" and it need not be enumerated. In
      this case we are using the value "non-participant" to indicate "E" is a non-
attending
      non-attending CU. The parameter is not needed on other "Attendees" since
      "participant" is the default value.

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED;CN=BIG
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED;CN=BIG A:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL;CN=B:Mailto:B@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL;CN=C:Mailto:C@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL;CN=Hal:Mailto:D@example.com
      ATTENDEE;RSVP=FALSE;TYPE=ROOM:conf_Big@example.com
      ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE:Mailto:E@example.com
      DTSTAMP:19970611T190000Z
      DTSTART:19970701T200000Z
DTEND:19970701T203000Z
SUMMARY:Phone Conference
UID:www.acme.com-873970198738777@example.com
      DTEND:19970701T2000000Z
      SUMMARY:Conference
      UID:calsrv.example.com-873970198738777@example.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;ATTSTAT=ACCEPTED:Mailto:B@example.com
      ATTENDEE;PARTSTAT=ACCEPTED:Mailto:B@example.com
      ORGANIZER:MAILTO:A@example.com
UID:www.acme.com-873970198738777@example.com
      UID:calsrv.example.com-873970198738777@example.com
      SEQUENCE:0
      REQUEST-STATUS:2.0;Success
      DTSTAMP:19970612T190000Z
      END:VEVENT
      END:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  58             Expires September 1998

      "B" could have declined the meeting or indicated tentative acceptance by
      setting the ATTENDEE "attstat" "ATTENDEE" "partstat" parameter to "declined" or
      "tentative", respectively. Also, "REQUEST-STATUS" is not required on a in
      successful transactions.

      Silverberg/Mansour/Daws/Hopson  59                Expires November 1998
      4.2.3     Update An Event

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

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:C@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:D@example.com
ATTENDEE;RSVP=FALSE;TYPE=ROOM:Mailto:Conf@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL;CN=Hal:Mailto:D@example.com
      ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE;
       CUTYPE=ROOM:Mailto:Conf@example.com
      ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE:Mailto:E@example.com
      DTSTART:19970701T180000Z
DTEND:19970701T1200000Z
      DTEND:19970701T190000Z
      SUMMARY:Phone Conference
UID:www.acme.com-873970198738777@example.com
      UID:calsrv.example.com-873970198738777@example.com
      SEQUENCE:1
      DTSTAMP:19970613T190000Z
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      4.2.4     Countering an Event Proposal

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

      "A" sends the following "REQUEST":

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:C@example.com

Silverberg/Mansour/Dawson/Hopson  59             Expires September 1998
      DTSTART:19970701T190000Z
      DTEND:19970701T200000Z
      SUMMARY:Discuss the Merits of the election results
LOCATION:The Big
      LOCATION:Green Conference Room
UID:www.acme.com-873970198738777@example.com
      UID:calsrv.example.com-873970198738777a@example.com
      SEQUENCE:0

      Silverberg/Mansour/Daws/Hopson  60                Expires November 1998
      DTSTAMP:19970611T190000Z
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      "B" sends "COUNTER" to "A", requesting changes to time and place. "B"
      uses the "COMMENT" property to communicate a rationale for the change: change.
      Note that the "SEQUENCE" property is NOT incremented on a "COUNTER".

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:COUNTER
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:C@example.com
      DTSTART:19970701T160000Z
      DTEND:19970701T190000Z
      DTSTAMP:19970612T190000Z
      SUMMARY:Discuss the Merits of the election results
LOCATION:The Small
      LOCATION:Green Conference Room
      COMMENT:This time works much better and I think the big conference
        room is too big
UID:www.acme.com-873970198738777@example.com
      UID:calsrv.example.com-873970198738777a@example.com
      SEQUENCE:0
      DTSTAMP:19970611T190000Z
      END:VEVENT
      END:VCALENDAR

      "A" accepts the changes from "B". To accept a counter-proposal, the
      "Organizer" sends a new Event REQUEST event "REQUEST" with an incremented sequence
      number.

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:C@example.com
      DTSTAMP:19970613T190000Z
      DTSTART:19970701T160000Z
      DTEND:19970701T190000Z

Silverberg/Mansour/Dawson/Hopson  60             Expires September 1998
      SUMMARY:Discuss the Merits of the election results - changed to
        meet B's schedule
LOCATION:The Small
      LOCATION:Green Conference Room
UID:www.acme.com-873970198738777@example.com
      UID:calsrv.example.com-873970198738777@example.com
      SEQUENCE:1

      Silverberg/Mansour/Daws/Hopson  61                Expires November 1998
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      Instead, "A" rejects "B's" counter proposal

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:DECLINECOUNTER
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
      COMMENT:Sorry, I cannot change this meeting time
UID:www.acme.com-873970198738777@example.com
SEQUENCE:1
      UID:calsrv.example.com-873970198738777@example.com
      SEQUENCE:0
      DTSTAMP:19970614T190000Z
      END:VEVENT
      END:VCALENDAR

      4.2.5     Delegating 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 "Delegate". 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 The "Delegator" MUST:

        .  Send an REPLY a "REPLY" to the "Organizer" with their the following updates:
        .  The "Delegator's" "ATTENDEE" property
  "attstat" "partstat" parameter set to
           "delegated"
. Include and the delegate as "delegated-to" parameter is set to the address
           of the "Delegate"
        .  Add an additional "Attendee" "ATTENDEE" property for the "Delegate" with the "delegated-
  from"
           "delegated-from" property parameter set to the value of the delegator "Delegator"
        . Include  Indicate whether they want to continue to receive updates when the original UID
           "Organizer" sends out updated versions of the "REQUEST" method event.  Setting the
           "rsvp" property parameter to "TRUE" will cause the updates to be
           sent, setting it to "FALSE" causes no further updates to be sent.
           Note that in either case, if the "Delegate" declines the invitation
           the "Delegator" will be notified.
        .  The "Delegator" MUST also send a copy of the original "REQUEST"
           method to the "Delegate". The delegator modifies the request as
  follows:
. The "ATTENDEE" property "attstat" parameter for the delegator (sender
  in this case) is set to "delegated"
. "ATTENDEE" "delegated-to" parameter is set to the address of the
  "Delegate"
. An "ATTENDEE" property is added for the "Delegate"

      It is not required that the "Delegate" include the "Delegator" in their
      "REPLY" method. However, it is strongly advised since this will inform
      the "Delegator" whether the "Delegate" plans to attend the meeting.
      [Editors note:  How so?] If

Silverberg/Mansour/Dawson/Hopson  61             Expires September 1998 the "Delegate" declines the meeting, the
      "Delegator" may elect to delegate the "REQUEST" to another CUA. The
      process is the same.

      Silverberg/Mansour/Daws/Hopson  62                Expires November 1998
      +---------------------------------------------------------------------+
      | Action             |  "Organizer"        | Attendee                 |
      +---------------------------------------------------------------------+
      | Initiate a meeting | "A" sends a REQUEST |                          |
      | request            | message to "B" and  |                          |
      |                    | "C"                 |                          |
      +---------------------------------------------------------------------+
      | Delegate:          |                     | "C" sends a REPLY to "A" |
      | "C" delegates to   |                     | with the ATTENDEE.       |
      | "E"                |                     | "attstat"parameter "partstat" parameter set to|  |
      |                    |                     | to "delegated" and with a   | a|
      |                    |                     | new "ATTENDEE" property  |
      |                    |                     | for "E". "E's" ATTENDEE  |
      |                    |                     | "delegated-from" param   |
      |                    |                     | is set to "C". "C's"     |
      |                    |                     | ATTENDEE "delegated-to"  |
      |                    |                     | param is set to "E".     |
      |                    |                     | "C" sends REQUEST message|
      |                    |                     | to "E" with the original |
      |                    |                     | meeting request          |
      |                    |                     | information. The         |
      |                    |                     |  "attstat"  "partstat" property      |
      |                    |                     | parameter for "C" is set |
      |                    |                     | to "delegated" and the   |
      |                    |                     |  "delegated-to"          |
      |                    |                     | parameter is set to      |
      |                    |                     | the address of "E". An   |
      |                    |                     | "ATTENDEE" property is   |
      |                    |                     | added for "E" and the    |
      |                    |                     | "delegated-from"         |
      |                    |                     | parameter is set to      |
      |                    |                     | the address of "C".      |
      +---------------------------------------------------------------------+
      | Confirm meeting    |                     | "E" sends REPLY message  |
      | attendance         |                     | to "A" and optionally "C"|
      |                    |                     | with its "attstat" "partstat"       |
      |                    |                     | property parameter set   |
      |                    |                     | to "accepted" "ACCEPTED"            |
      +---------------------------------------------------------------------+
      | Optional:          | "A" sends REQUEST   |                          |
      | Redistribute       | message to "B", "C" |                          |
      | meeting to         | and "E". SEQUENCE            |                          |
      | attendees          | number is now 1.                     |                          |
      +---------------------------------------------------------------------+

      "C" responds to the "Organizer".

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

Silverberg/Mansour/Dawson/Hopson  62             Expires September 1998
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:MAILTO:A@Example.com
ATTENDEE;ATTSTAT=DELEGATED;DELEGATED-
TO=Mailto:E@example.com:Mailto:C@example.com
UID:www.acme.com-873970198738777@example.com

      Silverberg/Mansour/Daws/Hopson  63                Expires November 1998
      ATTENDEE;PARTSTAT=DELEGATED;DELEGATED-
       TO="Mailto:E@example.com":Mailto:C@example.com
      UID:calsrv.example.com-873970198738777@example.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
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ATTSTAT=DELEGATED;DELEGATED-
TO=Mailto:E@example.com:Mailto:C@example.com
ATTENDEE;ROLE=DELEGATE;RSVP=TRUE;
 DELEGATED-FROM=Mailto:C@example.com:Mailto:E@example.com
      ATTENDEE;PARTSTAT=DELEGATED;DELEGATED-
       TO="Mailto:E@example.com":Mailto:C@example.com
      ATTENDEE;RSVP=TRUE;
       DELEGATED-FROM="Mailto:C@example.com":Mailto:E@example.com
      DTSTART:19970701T180000Z
DTEND:19970701T120000Z
      DTEND:19970701T200000Z
      SUMMARY:Phone Conference
UID:www.acme.com-873970198738777@example.com
      UID:calsrv.example.com-873970198738777@example.com
      SEQUENCE:0
      STATUS:CONFIRMED
      DTSTAMP:19970611T190000Z
      END:VEVENT
      END:VCALENDAR

      4.2.6     Delegate Accepts the Meeting

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

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REPLY
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:MAILTO:A@Example.com
ATTENDEE;ATTSTAT=CONFIRMED;DELEGATED-
FROM=Mailto:C@example.com:Mailto:E@example.com
ATTENDEE;ATTSTAT=DELEGATED;DELEGATED-
TO=Mailto:E@example.com:Mailto:C@example.com
UID:www.acme.com-873970198738777@example.com
SEQUENCE:1
      ATTENDEE;PARTSTAT=ACCEPTED;DELEGATED-
       FROM="Mailto:C@example.com":Mailto:E@example.com
      ATTENDEE;PARTSTAT=DELEGATED;
       DELEGATED-TO="Mailto:E@example.com":Mailto:C@example.com
      UID:calsrv.example.com-873970198738777@example.com
      SEQUENCE:0
      REQUEST-STATUS:2.0;Success

Silverberg/Mansour/Dawson/Hopson  63             Expires September 1998
      DTSTAMP:19970614T190000Z
      END:VEVENT
      END:VCALENDAR

      Silverberg/Mansour/Daws/Hopson  64                Expires November 1998
      4.2.7     Delegate Declines the Meeting

      In this example the "Delegate" declines the meeting request and sets the
      "ATTENDEE" property "attstat" "partstat" parameter to DECLINED. "DECLINED". The "Organizer"
      SHOULD resend the "REQUEST" to "C" with the "attstat" "partstat" parameter 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 the request or delegate it to another CU.

      Response from "E" to "A" and "C". Note the use of the "COMMENT" property
      "E" uses to indicate why the delegation was declined.

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REPLY
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:MAILTO:A@Example.com
ATTENDEE;ATTSTAT=DECLINED;DELEGATED-
FROM=Mailto:C@example.com:Mailto:E@example.com
UID:www.acme.com-873970198738777@example.com
ATTENDEE;ATTSTAT=DELEGATED;DELEGATED-
TO=Mailto:E@example.com:Mailto:C@example.com
SEQUENCE:1
      ATTENDEE;PARTSTAT=DELEGATED;
       DELEGATED-TO="Mailto:E@example.com":Mailto:C@example.com
      ATTENDEE;PARTSTAT=DECLINED;
       DELEGATED-FROM="Mailto:C@example.com":Mailto:E@example.com
      COMMENT:Sorry, I will be out of town at that time.
      UID:calsrv.example.com-873970198738777@example.com
      SEQUENCE:0
      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
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:MAILTO:A@Example.com
ATTENDEE;ATTSTAT=DECLINED;DELEGATED-
FROM=Mailto:C@example.com:Mailto:E@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:C@example.com
UID:www.acme.com-873970198738777@example.com
SEQUENCE:2
REQUEST-STATUS:2.0;Success
      ATTENDEE;PARTSTAT=DECLINED;
       DELEGATED-FROM="Mailto:C@example.com":Mailto:E@example.com
      ATTENDEE;RSVP=TRUE:Mailto:C@example.com
      UID:calsrv.example.com-873970198738777@example.com
      SEQUENCE:0
      SUMMARY:Phone Conference
      DTSTART:19970701T180000Z
      DTEND:19970701T200000Z
      DTSTAMP:19970614T200000Z
      COMMENT:DELEGATE (ATTENDEE Mailto:E@example.com) DECLINED YOUR
       INVITATION
      END:VEVENT

Silverberg/Mansour/Dawson/Hopson  64
      END:VCALENDAR

      Silverberg/Mansour/Daws/Hopson  65                Expires September November 1998

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. The "Organizer" MAY add the forwarded "Calendar User" to
      the attendee list.

      4.2.9     Cancel A Group Event

      Individual "A" requests a meeting between individuals "A", "B", "C", and
      "D". 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) MUST be ignored.

      +--------------------------------------------------------------------+
      | Action             |  "Organizer"        | "Attendee"              |
      +--------------------------------------------------------------------+
      | Initiate a meeting | "A" sends a REQUEST |                         |
      | request            | message to "B", "C",|                         |
      |                    | and "D"             |                         |
      +--------------------------------------------------------------------+
      | Decline the meeting|                     | "B" sends a "REPLY"     |
      | request            |                     | message to "A" with its |
      |                    |                     | "attstat" "partstat" para-         |
      |                    |                     | set to "declined".      |
      +--------------------------------------------------------------------+
      | Cancel the meeting | "A" sends a CANCEL  |                         |
      |                    | message to "B", "C" |                         |
      |                    | and "D"             |                         |
      +--------------------------------------------------------------------+

      The example shows how "A" cancels the event.

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:CANCEL
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com

Silverberg/Mansour/Dawson/Hopson  65
      ATTENDEE;TYPE=INDIVIDUAL;Mailto:A@example.com

      Silverberg/Mansour/Daws/Hopson  66                Expires September November 1998

ATTENDEE;TYPE=INDIVIDUAL;Mailto:A@example.com
      ATTENDEE;TYPE=INDIVIDUAL:Mailto:B@example.com
      ATTENDEE;TYPE=INDIVIDUAL:Mailto:C@example.com
      ATTENDEE;TYPE=INDIVIDUAL:Mailto:D@example.com
      COMMENT:Mr. B cannot attend. It's raining. Lets cancel.
UID:www.acme.com-873970198738777@example.com
SEQUENCE:0
      UID:calsrv.example.com-873970198738777@example.com
      SEQUENCE:1
      STATUS:CANCELLED
      DTSTAMP:19970613T190000Z
      END:VEVENT
      END:VCALENDAR

      4.2.10    Removing Attendees

      "A" wants to remove "B" from a meeting. This is done by sending a
      "CANCEL" to "B" and removing "B" from the attendee list in the master
      copy of the event.

      +--------------------------------------------------------------------+
      | Action             |  "Organizer"        | "Attendee"              |
      +--------------------------------------------------------------------+
      | Remove an "B"      | "A" sends a CANCEL  |                         |
      | as an "Attendee"   | message to "B"      |                         |
      +--------------------------------------------------------------------+
      | Update the master  | "A" sends the       |                         |
      | copy of the event  | updated event to    |                         |
      |                    | the remaining       |                         |
      |                    | "Attendees"         |                         |
      +--------------------------------------------------------------------+

      The original meeting includes "A", "B", "C", and "D". The example below
      shows the "CANCEL" that "A" sends to "B". Note that in the example below
      the "STATUS" property is omitted. This is used when the meeting itself
      is cancelled and not when the intent is to remove an "Attendee" from the
      Event.

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:CANCEL
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com
      ATTENDEE:mailto:B@example.com
      COMMENT:You're off the hook for this meeting
UID:www.acme.com-873970198738777@example.com
      UID:calsrv.example.com-873970198738777@example.com
      DTSTAMP:19970613T193000Z
      SEQUENCE:1
      END:VEVENT
      END:VCALENDAR

      The updated master copy of the event is shown below. The "Organizer" MAY
      resend the updated event to the remaining "Attendees". Note that "B" has
      been removed.

BEGIN:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  66

      Silverberg/Mansour/Daws/Hopson  67                Expires September November 1998
      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;TYPE=INDIVIDUAL:Mailto:C@example.com
      ATTENDEE;TYPE=INDIVIDUAL:Mailto:D@example.com
      ATTENDEE;TYPE=ROOM:CR_Big@example.com
      ATTENDEE;ROLE=NON-PARTICIPANT;
       RSVP=FALSE:Mailto:E@example.com
      DTSTAMP:19970611T190000Z
      DTSTART:19970701T200000Z
      DTEND:19970701T203000Z
      SUMMARY:Phone Conference
UID:www.acme.com-873970198738777@example.com
SEQUENCE:0
      UID:calsrv.example.com-873970198738777@example.com
      SEQUENCE:2
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      4.2.11    Replacing the Organizer

      The scenario for this example begins with "A" as the "Organizer" for a
      recurring meeting with "B", "C", and "D". "A" receives a new job offer
      in another country and leaves without changing the "Organizer" to this
meeting. drops out of touch.  "A" left no forwarding
      address or way to be reached.  Using out-of-band communication, the
      other "Attendees" eventually learn what has happened and reach an
      agreement that "B" should become the new "Organizer" for the meeting. To
      do this, "B" sends out a new version of the event and the other
      "Attendees" agree to accept "B" as the new "Organizer". "B" also removes
      "A" from the event event.

      When the "Organizer" is replaced, the "SEQUENCE" property value MUST be
      incremented.

      This is the message "B" sends to "C" and "D"

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:B@example.com
      ATTENDEE;ROLE=CHAIR;STATUS=ACCEPTED:Mailto:B@example.com
      ATTENDEE;TYPE=INDIVIDUAL:Mailto:C@example.com
      ATTENDEE;TYPE=INDIVIDUAL:Mailto:D@example.com
      DTSTAMP:19970611T190000Z
      DTSTART:19970701T200000Z
      DTEND:19970701T203000Z
      RRULE:FREQ=WEEKLY
      SUMMARY:Phone Conference
      UID:123456@example.com

      Silverberg/Mansour/Daws/Hopson  68                Expires November 1998
      SEQUENCE:1
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  67             Expires September 1998

      4.3 Busy Time Examples

      Busy time objects can be used in several ways. First, a CU may Request request
      busy time from another CU for a specific range of time. That request can
      be answered with a busy time Reply. Additionally, a CU may simply
      publish busy their busy time for a given interval and point other CUs to
      the published location. The following examples outline both scenarios.

      Individual "A" publishes Busy busy time for one week.

      BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//ENVERSION:2.0
      PRODID:-//ACME/DesktopCalendar//EN
      VERSION:2.0
      METHOD:PUBLISH
      BEGIN:VFREEBUSY
      DTSTAMP:19980101T124100Z
ATTENDEE:MAILTO:A@Example.com
      ORGANIZER:MAILTO:A@Example.com
      DTSTART:19980101T124200Z
      DTEND:19980107T124200Z
      FREEBUSY:19980101T180000Z/19980101T190000Z
      FREEBUSY:19980103T020000Z/19980103T050000Z
      FREEBUSY:19980107T020000Z/19980107T050000Z
      FREEBUSY:19980113T000000Z/19980113T010000Z
      FREEBUSY:19980115T190000Z/19980115T200000Z
      FREEBUSY:19980115T220000Z/19980115T230000Z
      FREEBUSY:19980116T013000Z/19980116T043000Z
      END:VFREEBUSY
      END:VCALENDAR

      Individual "A" requests busy time from individuals "B", "C". Individual
      "B" and "C" replies with busy time data to individual "A". The following
      table illustrates the sequence of messages that would be exchanged
      between these individuals.

      +--------------------------------------------------------------------+
      | Action             |  "Organizer"        | Attendee                |
      +--------------------------------------------------------------------+
      | Initiate a busy    | "A" sends "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          |
      +--------------------------------------------------------------------+

      Silverberg/Mansour/Daws/Hopson  69                Expires November 1998
      4.3.1     Request Busy Time

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

Silverberg/Mansour/Dawson/Hopson  68             Expires September 1998

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VFREEBUSY
      ORGANIZER:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR:Mailto:A@example.com
      ATTENDEE:Mailto:B@example.com
      ATTENDEE:Mailto:C@example.com
      DTSTAMP:19970613T190000Z
      DTSTART:19970701T080000Z
      DTEND:19970701T200000
UID:www.acme.com-873970198738777@example.com
      UID:calsrv.example.com-873970198738777@example.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
      ORGANIZER:MAILTO:A@example.com
      ATTENDEE:Mailto:B@example.com
      DTSTART:19970701T080000Z
      DTEND:19970701T200000Z
UID:www.acme.com-873970198738777@example.com
FREEBUSY:19970701T090000Z/PT1H,19970701T140000Z/PT30H
      UID:calsrv.example.com-873970198738777@example.com
      FREEBUSY:19970701T090000Z/PT1H,19970701T140000Z/PT30M
      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

Silverberg/Mansour/Dawson/Hopson  69

      Silverberg/Mansour/Daws/Hopson  70                Expires September November 1998
      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VTIMEZONE
      TZID:America-SanJose
      TZURL:http://zones.stds_r_us.net/tz/America-SanJose
LAST-MODIFIED:19870101T000000Z
      BEGIN:STANDARD
      DTSTART:19671029T020000
      RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
      TZOFFSETFROM:-0700
      TZOFFSETTO:-0800
      TZNAME:PST
      END:STANDARD
      BEGIN:DAYLIGHT
      DTSTART:19870405T020000
      RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
      TZOFFSETFROM:-0800
      TZOFFSETTO:-0700
      TZNAME:PDT
      END:DAYLIGHT
      END:VTIMEZONE
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED;TYPE=INDIVIDUAL:A@example.COM
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED;TYPE=INDIVIDUAL:A@example.COM
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:B@example.fr
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:c@example.jp
      DTSTAMP:19970613T190030Z
      DTSTART;TZID=America-SanJose:19970701T140000
      DTEND;TZID=America-SanJose:19970701T150000
      RRULE:FREQ=WEEKLY;INTERVAL=20;WKST=SU;BYDAY=TU
      RDATE;TZID=America-SanJose:19970910T140000
      EXDATE;TZID=America-SanJose:19970909T140000
      EXDATE;TZID=America-SanJose:19971028T140000
      SUMMARY:Weekly Phone Conference
UID:www.acme.com-873970198738777@example.com
      UID:calsrv.example.com-873970198738777@example.com
      SEQUENCE:0
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      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.

      The repeating event starts on Tuesday, July 1, 1997 at 2:00pm PDT.
      "Attendee" B@example.fr is in France where the local time on this date

Silverberg/Mansour/Dawson/Hopson  70             Expires September 1998
      is 7 9 hours later than ahead of PDT or 21:00. 23:00. "Attendee" C@example.jp is in Japan

      Silverberg/Mansour/Daws/Hopson  71                Expires November 1998
      where local time is 9 8 hours ahead of than UTC or Wednesday, July 2 at
07:00. 06:00.
      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. PDT. The "RDATE" property adds another instance: WED,
      10-SEP-1997 2:00 PM PST.

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

      TUE, 09-SEP-1997 21:00 23:00 GMT
      TUE, 09-SEP-1997 14:00 PDT
      WED, 10-SEP-1997 07:00 JDT 06:00 JST

      and the second is:

      TUE, 28-OCT-1997 22:00 23:00 GMT
      TUE, 28-OCT-1997 14:00 PST
      WED, 29-OCT-1997 07:00 06:00 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:19970526T083000Z
      UID:guid-1@host1.com
      SEQUENCE:0
      RRULE:FREQ=MONTHLY;BYMONTHDAY=1;UNTIL=19980901T210000Z
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE:Mailto:B@example.com
      ATTENDEE:Mailto:C@example.com
      ATTENDEE: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
      DTSTAMP:19970526T083000Z
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  71

      Silverberg/Mansour/Daws/Hopson  72                Expires September November 1998
      The event request below is to change the time of a specific instance.
      This changes the July 1st instance to July 3rd.

      BEGIN:VCALENDAR
      METHOD:REQUEST
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
CREATED:19970526T083000Z
      UID:guid-1@host1com
      RECURRENCE-ID:19970701T210000Z
      SEQUENCE:1
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE:Mailto:B@example.com
      ATTENDEE:Mailto:C@example.com
      ATTENDEE: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:19970626T093000Z
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      4.4.3     Cancel an Instance

      In this example the "Organizer" of a recurring event deletes the August
      1st instance.

      BEGIN:VCALENDAR
      METHOD:CANCEL
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
      UID:guid-1@host1.com
      ORGANIZER:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE:Mailto:B@example.com
      ATTENDEE:Mailto:C@example.com
      ATTENDEE:Mailto:D@example.com
      RECURRENCE-ID:19970801T210000Z
      SEQUENCE:2
      STATUS:CANCELLED
      DTSTAMP:19970721T093000Z
      END:VEVENT
      END:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  72

      Silverberg/Mansour/Daws/Hopson  73                Expires September November 1998
      4.4.4     Cancel Recurring Event

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

      BEGIN:VCALENDAR
      METHOD:CANCEL
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
      UID:guid-1@host1.com
      ORGANIZER:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE:Mailto:B@example.com
      ATTENDEE:Mailto:C@example.com
      ATTENDEE:Mailto:D@example.com
      DTSTAMP:19970721T103000Z
SEQUENCE:2
      STATUS:CANCELLED
      SEQUENCE:3
      END:VEVENT
      END:VCALENDAR

      4.4.5     Change All Future Instances

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

      BEGIN:VCALENDAR
      METHOD:REQUEST
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
CREATED:19970526T083000Z
      UID:guid-1@host1.com
      RECURRENCE-ID;THISANDFUTURE:19970901T210000Z
      SEQUENCE:3
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:Mailto:B@example.com
      ATTENDEE;RSVP=TRUE:Mailto:C@example.com
      ATTENDEE;RSVP=TRUE:Mailto:D@example.com
      DESCRIPTION:IETF-C&S Discussion
      CLASS:PUBLIC
      SUMMARY:IETF Calendaring Working Group Meeting
      DTSTART:19970901T210000Z
      DTEND:19970901T220000Z
      LOCATION:Building 32, Microsoft, Seattle, WA
      DTSTAMP:19970526T083000Z
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      Silverberg/Mansour/Daws/Hopson  74                Expires November 1998
      4.4.6     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.

Silverberg/Mansour/Dawson/Hopson  73             Expires September 1998

      BEGIN:VCALENDAR
      METHOD:ADD
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
CREATED:19970526T083000Z
      UID:123456789@host1.com
      SEQUENCE:4
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:Mailto:B@example.com
      ATTENDEE;RSVP=TRUE:Mailto:C@example.com
      ATTENDEE;RSVP=TRUE: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:19970629T093000Z
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      4.4.7     Add A New Series of Instances To A Recurring Event

      The scenario for this example involves an ongoing meeting, originally
      set up to occur every Tuesday.  The "Organizer" later decides that the
      meetings need to be on Tuesdays and Thursdays, but does not want to
      reschedule the entire meeting or lose any of the per-instance
      information already collected.

      The original event:

      BEGIN:VCALENDAR
      METHOD:REQUEST
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
      UID:123456789@host1.com
      SEQUENCE:0
      RRULE:WKST=SU;BYDAY=TU;FREQ=WEEKLY
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:Mailto:B@example.com
      SUMMARY:Review Accounts
      DTSTART:19980303T210000Z
      DTEND:19980303T220000Z
      LOCATION:The White Room
      DTSTAMP:19980301T093000Z

      Silverberg/Mansour/Daws/Hopson  75                Expires November 1998
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  74             Expires September 1998

      Assume that many other updates happen to this event and that a lot of
      instance-specific information exists in the recurring series. The
      "SEQUENCE" property value is 7 for the next update. Now the "Organizer" adds
      wants to add Thursdays to the event:

      BEGIN:VCALENDAR
      METHOD:ADD
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
      UID:123456789@host1.com
      SEQUENCE:7
      RRULE:WKST=SU;BYDAY=TH;FREQ=WEEKLY
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:Mailto:B@example.com
      SUMMARY:Review Accounts
      DTSTART:19980303T210000Z
      DTEND:19980303T220000Z
      DTSTAMP:19980303T193000Z
      LOCATION:The Usual conference room
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      Alternatively, if the "Organizer" is not concerned with per-instance
      updates, the entire event can be rescheduled using a "REQUEST". This is
      done by using the "UID" of the event to reschedule and including the
      modified RRULE. "RRULE". Note, that since this is an entire rescheduling of the
      event, any instance-specific information will be lost.

      BEGIN:VCALENDAR
METHOD:ADD
      METHOD:REQUEST
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
      UID:123456789@host1.com
      SEQUENCE:7
      RRULE:WKST=SU;BYDAY=TU,TH;FREQ=WEEKLY
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:Mailto:B@example.com
      SUMMARY:Review Accounts
      DTSTART:19980303T210000Z
      DTEND:19980303T220000Z
      DTSTAMP:19980303T193000Z
      LOCATION:The White Room
      STATUS:CONFIRMED

      Silverberg/Mansour/Daws/Hopson  76                Expires November 1998
      END:VEVENT
      END:VCALENDAR

      The next series of examples illustrate how an "Organizer" would respond
      to a "REFRESH" submitted by an "Attendee" after a series of instance-
      specific modifications. To convey all instance-specific changes, the
      "Organizer" must provide the latest event description and the relevant
      instances. The first three examples show the history including the

Silverberg/Mansour/Dawson/Hopson  75             Expires September 1998
      initial "VEVENT" request and subsequent instance changes and finally the
      "REFRESH".

      Original Request:

      BEGIN:VCALENDAR
      METHOD:REQUEST
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
      UID:123456789@host1.com
      SEQUENCE:0
      RDATE:19980304T180000Z
      RDATE:19980311T180000Z
      RDATE:19980318T180000Z
RDATE:19980325T180000Z
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:Mailto:B@example.com
      SUMMARY:Review Accounts
      DTSTART:19980304T180000Z
      DTEND:19980304T200000Z
      DTSTAMP:19980303T193000Z
      LOCATION:Conference Room A
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      Organizer changes 2nd instance Location and Time:

      BEGIN:VCALENDAR
      METHOD:REQUEST
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
      UID:123456789@host1.com
      SEQUENCE:1
      RECURRENCE-ID:19980311T180000Z
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:Mailto:B@example.com
      SUMMARY:Review Accounts
      DTSTART:19980311T160000Z
DTEND:19980304T180000Z
      DTEND:19980311T180000Z
      DTSTAMP:19980306T193000Z
      LOCATION:The Small conference room
      STATUS:CONFIRMED

      Silverberg/Mansour/Daws/Hopson  77                Expires November 1998
      END:VEVENT
      END:VCALENDAR

      Organizer adds a 4th instance of the meeting using the "ADD" method

      BEGIN:VCALENDAR
      METHOD:ADD

Silverberg/Mansour/Dawson/Hopson  76             Expires September 1998
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
      UID:123456789@host1.com
      SEQUENCE:2
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:Mailto:B@example.com
      SUMMARY:Review Accounts
      DTSTART:19980315T180000Z
      DTEND:19980315T200000Z
      DTSTAMP:19980307T193000Z
      LOCATION:Conference Room A
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      If "B" requests a "REFRESH", "A" responds with the following to capture
      all instance-specific data. In this case both the initial request and an
      additional "VEVENT" that specifies the instance-specific data are
      included. Because these are both of the same type (they are both
      "VEVENTS"), they can be conveyed in the same iCalendar object.

      BEGIN:VCALENDAR
      METHOD:REQUEST
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
      UID:123456789@host1.com
SEQUENCE:3
      SEQUENCE:2
      RDATE:19980304T180000Z
RDATE:19980318T180000Z
      RDATE:19980311T160000Z
      RDATE:19980315T180000Z
      Error! Bookmark not defined.
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:Mailto:B@example.com
      SUMMARY:Review Accounts
      DTSTART:19980304T180000Z
      DTEND:19980304T200000Z
      DTSTAMP:19980303T193000Z
      LOCATION:Conference Room A
      STATUS:CONFIRMED
      END:VEVENT

      BEGIN:VEVENT
      Error! Bookmark not defined.
SEQUENCE:3

      Silverberg/Mansour/Daws/Hopson  78                Expires November 1998
      SEQUENCE:2
      RECURRENCE-ID:19980311T160000Z
      Error! Bookmark not defined.
      ATTENDEE;ROLE=CHAIR;Error! Bookmark not defined.
      ATTENDEE;Error! Bookmark not defined.
      SUMMARY:Review Accounts
      DTSTART:19980311T160000Z

Silverberg/Mansour/Dawson/Hopson  77             Expires September 1998
      DTEND:19980304T180000Z
      DTSTAMP:19980306T193000Z
      LOCATION:The Small conference room
      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:19970526T083000Z
      UID:guid-1@host1.com
      RECURRENCE-ID:19970715T210000Z
      SEQUENCE:4
      ORGANIZER:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;RSVP=TRUE:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:Mailto:B@example.com
      ATTENDEE;RSVP=TRUE:Mailto:C@example.com
      ATTENDEE;RSVP=TRUE:Mailto:D@example.com
      DESCRIPTION:IETF-C&S Conference Call
      CLASS:PUBLIC
      SUMMARY:IETF Calendaring Working Group Meeting
      DTSTART:19970715T220000Z
      DTEND:19970715T230000Z
      LOCATION:Conference Call
      COMMENT:May we bump this by an hour? I have a conflict
      DTSTAMP:19970629T094000Z
      END:VEVENT
      END:VCALENDAR

      4.4.9     Error Reply To A Request

      The following example illustrates a scenario where a meeting is proposed
      containing an unsupported property and a bad property.

      Original Request

      Silverberg/Mansour/Daws/Hopson  79                Expires November 1998
      BEGIN:VCALENDAR
      METHOD:REQUEST
      PRODID:-//RDU Software//NONSGML HandCal//EN
      VERSION:2.0
      BEGIN:VEVENT
CREATED:19970526T083000Z

Silverberg/Mansour/Dawson/Hopson  78             Expires September 1998
      UID:guid-1@host1.com
      SEQUENCE:0
      RRULE:FREQ=MONTHLY;BYMONTHDAY=1
      ORGANIZER:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:Mailto:B@example.com
      ATTENDEE;RSVP=TRUE:Mailto:C@example.com
      ATTENDEE;RSVP=TRUE:Mailto:D@example.com
      DESCRIPTION:IETF-C&S Conference Call
      CLASS:PUBLIC
      SUMMARY:IETF Calendaring Working Group Meeting
      DTSTART:19970601T210000Z
      DTEND:19970601T220000Z
      DTSTAMP:19970602T094000Z
      LOCATION:Conference Call
      STATUS:CONFIRMED
      FOO:BAR
      END:VEVENT
      END:VCALENDAR

      Response from "B" to indicate that RRULE is not supported and an
      unrecognized property was encountered

      BEGIN:VCALENDAR
      PRODID:-//RDU Software//NONSGML HandCal//EN
      METHOD:REPLY
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com
      ATTENDEE:Mailto:B@example.com
      REQUEST-STATUS:2.8;Repeating event ignored. Scheduled as a single
        event;RRULE
      REQUEST-STATUS:3.0;Invalid Property Name;FOO
      UID:guid-1@host1.com
      SEQUENCE:0
      DTSTAMP:19970603T094000Z
      END:VEVENT
      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 "REQUEST" method to obtain the status of the to-do

      Silverberg/Mansour/Daws/Hopson  80                Expires November 1998
      from each participant. The response indicates the individual
      "Attendee's" completion status. The table below illustrates the message
      flow.

Silverberg/Mansour/Dawson/Hopson  79             Expires September 1998

      +--------------------------------------------------------------------+
      | Action             |  "Organizer"        | Attendee                |
      +--------------------------------------------------------------------+
      | Initiate a to-do   | "A" sends a REQUEST |                         |
      | request            | message to "B", "C",|                         |
      |                    | and "D"             |                         |
      +--------------------------------------------------------------------+
      | Accept the to-do   |                     | "B" sends a "REPLY"     |
      | request            |                     | message to "A" with its |
      |                    |                     | "attstat" "partstat" paramater     |
      |                    |                     | set to "accepted".      |
      +--------------------------------------------------------------------+
      | Decline the to-do  |                     | "C" sends a REPLY       |
      | request            |                     | message to "A" with its |
      |                    |                     | "attstat" "partstat" parameter     |
      |                    |                     | set to "declined".      |
      +--------------------------------------------------------------------+
      | Tentatively accept |                     | "D" sends a REPLY       |
      | the to-do request  |                     | message to "A" with its |
      |                    |                     | "attstat" "partstat" parameter     |
      |                    |                     | set to "tentative".     |
      +--------------------------------------------------------------------+
      | Check attendee     | "A" sends a REQUEST |                         |
      | completion status  | message to "B" and  |                         |
      |                    | "C" "D" with current    |                         |
      |                    | information.        |                         |
      +--------------------------------------------------------------------+
      | Attendee indicates |                     | "B" sends a "REPLY"     |
      | percent complete   |                     | message indicating      |
      |                    |                     | percent complete        |
      +--------------------------------------------------------------------+
      | Attendee indicates |                     | "C" "D" sends a "REPLY"     |
      | completion         |                     | message indicating      |
      |                    |                     | completion              |
      +--------------------------------------------------------------------+

      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
      ORGANIZER:Mailto:A@example.com

      Silverberg/Mansour/Daws/Hopson  81                Expires November 1998
      ATTENDEE;ROLE=CHAIR:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE:B@example.com
      ATTENDEE;RSVP=TRUE:Mailto:C@example.com
      ATTENDEE;RSVP=TRUE:Mailto:D@example.com
      DTSTART:19970701T170000Z

Silverberg/Mansour/Dawson/Hopson  80             Expires September 1998
      DUE:19970722T170000Z
      PRIORITY:1
      SUMMARY:Create the requirements document
UID:www.acme.com-873970198738777-00@example.com
      UID:calsrv.example.com-873970198738777-00@example.com
      SEQUENCE:0
      DTSTAMP:19970717T200000Z
      STATUS:Needs Action
      END:VTODO
      END:VCALENDAR

      4.5.2     A VTODO Reply

Attendee

      "B" accepts the meeting. to-do.

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REPLY
      VERSION:2.0
      BEGIN:VTODO
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ATTSTAT=ACCEPTED:Mailto:B@example.com
UID:www.acme.com-873970198738777-00@example.com
      ATTENDEE;PARTSTAT=ACCEPTED:Mailto:B@example.com
      UID:calsrv.example.com-873970198738777-00@example.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 TODO or indicated tentative acceptance by
      setting the "attstat" "partstat" property parameter sequence to "declined" or
      "tentative", respectively.

      4.5.3     A VTODO Request for Updated Status

      "A" requests status from all "Attendees".

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VTODO
      ORGANIZER:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:C@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:D@example.com
UID:www.acme.com-873970198738777-00@example.com

      Silverberg/Mansour/Daws/Hopson  82                Expires November 1998
      UID:calsrv.example.com-873970198738777-00@example.com
      SUMMARY:Create the requirements document
      PRIORITY:1
      SEQUENCE:0
      STATUS:IN-PROCESS
      DTSTART:19970701T170000Z
      DTSTAMP:19970717T230000Z
      END:VTODO

Silverberg/Mansour/Dawson/Hopson  81             Expires September 1998
      END:VCALENDAR

      4.5.4     A Reply: Percent-Complete

      A reply indicating the task 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
      ORGANIZER:MAILTO:A@example.com
ATTENDEE;ATTSTAT=IN-PROCESS:Mailto:B@example.com
      ATTENDEE;PARTSTAT=IN-PROCESS:Mailto:B@example.com
      PERCENT-COMPLETE:75
UID:www.acme.com-873970198738777-00@example.com
      UID:calsrv.example.com-873970198738777-00@example.com
      DTSTAMP:19970717T233000Z
      SEQUENCE:0
      END:VTODO
      END:VCALENDAR

      4.5.5     A Reply: Completed

      A reply indicating that "C" "D" completed "C's" "D's" part of the assignment.

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REPLY
      VERSION:2.0
      BEGIN:VTODO
      ORGANIZER:MAILTO:A@example.com
ATTENDEE;ATTSTAT=COMPLETED:Mailto:C@example.com
UID:www.acme.com-873970198738777-00@example.com
      ATTENDEE;PARTSTAT=COMPLETED:Mailto:D@example.com
      UID:calsrv.example.com-873970198738777-00@example.com
      DTSTAMP:19970717T233000Z
      SEQUENCE:0
      END:VTODO
      END:VCALENDAR

      4.5.6     An Updated VTODO Request

      Organizer "A" resends the "VTODO" calendar component. "A" sets the
      overall completion for the to-do at 40%.

      Silverberg/Mansour/Daws/Hopson  83                Expires November 1998
      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VTODO
      ORGANIZER:Mailto:A@example.com

Silverberg/Mansour/Dawson/Hopson  82             Expires September 1998

ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;ATTSTAT=ACCEPTED;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;ATTSTAT=COMPLETED;TYPE=INDIVIDUAL:Mailto:C@example.com
ATTENDEE;ATTSTAT=IN-PROCESS;TYPE=INDIVIDUAL:Mailto:D@example.com
DTSTART:19970701T100000-0700
DUE:19970722T100000-0700
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;PARTSTAT=ACCEPTED;TYPE=INDIVIDUAL:Mailto:B@example.com
      ATTENDEE;PARTSTAT=IN-PROCESS;TYPE=INDIVIDUAL:Mailto:D@example.com
      DTSTART:19970701T170000Z
      DUE:19970722T170000Z
      PRIORITY:1
      SUMMARY:Create the requirements document
UID:www.acme.com-873970198738777-00@example.com
      UID:calsrv.example.com-873970198738777-00@example.com
      SEQUENCE:1
      DTSTAMP:19970718T100000Z
      STATUS:IN-PROGRESS
      PERCENT-COMPLETE:40
      END:VTODO
      END:VCALENDAR

      4.5.7     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". "D".

      BEGIN:VCALENDAR
      PRODID:-//ACME/DesktopCalendar//EN
      METHOD:REQUEST
      VERSION:2.0
      BEGIN:VTODO
      ORGANIZER:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR:Mailto:A@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:C@example.com
      ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:D@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@example.com
      UID:calsrv.example.com-873970198738777-00@example.com
      SEQUENCE:0
      DTSTAMP:19970717T200000Z
      STATUS:NEEDS ACTION
      PRIORITY:1
      END:VTODO
      END:VCALENDAR

      Silverberg/Mansour/Daws/Hopson  84                Expires November 1998
      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 using the
      "RECURRENCE-ID" property. The former is calculated by applying the
      difference between "DTSTART" and "DUE" properties and applying it to

Silverberg/Mansour/Dawson/Hopson  83             Expires September 1998
      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 is applied to each recurring instance of the
      "VTODO" calendar component to determine the "DUE" date of the instance.

      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;ATTSTAT=IN-PROCESS:Mailto:B@example.com
      ATTENDEE;PARTSTAT=IN-PROCESS:Mailto:B@example.com
      PERCENT-COMPLETE:75
UID:www.acme.com-873970198738777-00@example.com
      UID:calsrv.example.com-873970198738777-00@example.com
      DTSTAMP:19970717T233000Z
      RECURRENCE-ID:19980101T170000Z
      SEQUENCE:1
      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
      METHOD:PUBLISH
      PRODID:-//ACME/DesktopCalendar//EN
      VERSION:2.0
      BEGIN:VJOURNAL
      DTSTART:19971002T200000Z
      ORGANIZER:MAILTO:A@Example.com
      SUMMARY:Phone conference minutes
      DESCRIPTION:The editors meeting was held on October 1, 1997.
        Details are in the attached document.
      UID:0981234-1234234-2410@example.com

      Silverberg/Mansour/Daws/Hopson  85                Expires November 1998
      RELATED-TO:0981234-1234234-2402-35@example.com
ATTACH:ftp\://ftp.example.com/pub/ed/minutes100197.txt
      ATTACH:ftp://ftp.example.com/pub/ed/minutes100197.txt
      END:VJOURNAL
      END:VCALENDAR

Silverberg/Mansour/Dawson/Hopson  84             Expires September 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
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE:Mailto:B@example.com
      ATTENDEE:Mailto:C@example.com
      ATTENDEE:Mailto:D@example.com
      UID: guid-1-12345@host1.com
      DTSTAMP:19970603T094000
      END:VEVENT
      END:VCALENDAR

      4.7.2     Bad RECURRENCE-ID

If

      Component instances are identified by the combination of "UID",
      "RECURRENCE-ID", and "SEQUENCE". When an "Attendee" receives "Organizer" sends a request that references a to
      an "Attendee", there are three cases in which an instance cannot be
      found.  They are:

      1.         The component with the referenced "UID" and "RECURRENCE-ID"
property has been
        found but the "SEQUENCE" number in the calendar store does not match
        that of the ITIP message.

      2.         The component with the referenced "UID" has been found, the
        "SEQUENCE" numbers match, but the "RECURRENCE-ID" cannot be found, found.

      3.         The "UID" and "SEQUENCE" numbers are found but the CUA does not
        support recurrences.

      In case (1), two things can happen. If the "SEQUENCE" number of the
      "Attendee's" instance is larger than that in the "Organizer's" message
      then the "Attendee" is receiving an out-of-sequence message and MUST
      ignore it.  If the "SEQUENCE" number of the "Attendee's" instance is
      smaller, then the "Organizer" is sending out a newer version of the
      component and the "Attendee's" version needs to be updated. Since one or

      Silverberg/Mansour/Daws/Hopson  86                Expires November 1998
      more updates have been missed, the "Attendee" SHOULD send a "REFRESH"
      message to the "Organizer" to get an updated version of the event.

      In case (2), something has gone wrong.  Both the "Organizer" and the
      "Attendee" should have the same instances, but the "Attendee" does not
      have the referenced instance.  In this case the "Attendee" SHOULD send a
      "REFRESH"
method back to the "Organizer" for the latest copy of "Organizer" to get an updated version of the event.

      In case (3), the limitations of the "Attendee's" CUA makes it impossible
      to match an instance other than the single instance scheduled. In this
      case, the "Attendee" need not send a "REFRESH" to the "Organizer".

      The example below shows a sequence in which an "Attendee" sends a
      "REFRESH" to the event. "Organizer".

      +--------------------------------------------------------------------+
      | Action             |  "Organizer"        | Attendee                |
      +--------------------------------------------------------------------+
      | Update an instance | "A" sends  "REQUEST"|                         |
      | request            | message to "B"      |                         |
      +--------------------------------------------------------------------+
      | Attendee requests  |                     | "B" sends a "REFRESH"   |
      | refresh because    |                     | message to "A"          |
      | "RECURRENCE-ID" 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           |                     |                         |
      +--------------------------------------------------------------------+

      Request from "A":

Silverberg/Mansour/Dawson/Hopson  85             Expires September 1998

      BEGIN:VCALENDAR
      METHOD:REQUEST
      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
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;ATTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
      ATTENDEE:Mailto:B@example.com
      DESCRIPTION:IETF-C&S Conference Call
      SUMMARY:IETF Calendaring Working Group Meeting
      DTSTART:19970801T210000Z

      Silverberg/Mansour/Daws/Hopson  87                Expires November 1998
      DTEND:19970801T220000Z
      RECURRENCE-ID:19970809T210000Z
      DTSTAMP:19970726T083000
      STATUS:CONFIRMED
      END:VEVENT
      END:VCALENDAR

      "B" has the event with "UID" property "acme-12345@host1.com" but the "B's"
      "SEQUENCE" property value is "1" and the event does not have an instance
      at the specified recurrence time. This means that "B" has missed at
      least one update and needs a new copy of the event.  "B" requests the
      latest copy of the event with the following refresh message:

      BEGIN:VCALENDAR
      PRODID:-//RDU Software//NONSGML HandCal//EN
      METHOD:REFRESH
      VERSION:2.0
      BEGIN:VEVENT
      ORGANIZER:Mailto:A@example.com
ATTENDEE;ATTSTAT=ACCEPTED:Mailto:B@example.com
      ATTENDEE: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
      protocol. If a method or property is not addressed in this section, it
      may be ignored.

Silverberg/Mansour/Dawson/Hopson  86             Expires September 1998

      5.1.1     Event-Related Fallbacks

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

      Silverberg/Mansour/Daws/Hopson  88                Expires November 1998
      iCalendar
      Property         Fallback
      --------------   -----------------------------------------------------
      CALSCALE         Ignore; assume GREGORIAN.
GEO              Ignore. GREGORIAN
      PRODID           Ignore.           Ignore
      METHOD           Required as described in the Method list above.
SOURCE           Ignore
NAME             Ignore. above
      VERSION          Ignore.          Ignore

      Event-Related
      Components       Fallback
      --------------   -----------------------------------------------------
VFREEBUSY        Reply with Not Supported.
      VALARM           Reply with Not Supported. Supported
      VTIMEZONE        Required if RRULE or RDATE is implemented; otherwise
                 ignore and use local time. any DateTime value refers to a time zone.

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

Silverberg/Mansour/Dawson/Hopson  87             Expires September 1998

DUE              Ignore.
      DURATION         Reply with Not Supported. Supported
      DTSTAMP          Required.          Required
      DTSTART          Required.          Required
      DTEND            Required.            Required
      EXDATE           Ignore.           Ignore
      EXRULE           Ignore.
FREEBUSY           Ignore Reply with Not Supported.
LAST-MODIFIED    Ignore.
LOCATION         Required.
PRIORITY         Ignore.
RELATED-TO       Ignore.
RDATE            Ignore. If implemented,
                       VTIMEZONE MUST also be implemented.
      GEO              Ignore
      LAST-MODIFIED    Ignore
      LOCATION         Required
      ORGANIZER        Ignore
      PRIORITY         Ignore
      RELATED-TO       Ignore
      RDATE            Ignore
      RRULE            Ignore. The first instance occurs on the DTStart
                       property. If implemented, VTIMEZONE MUST also be
                       implemented.
      RECURRENCE-ID    Required if RRULE is implemented; otherwise Ignore. Ignore
      REQUEST-STATUS   Required.   Required
      RESOURCES        Ignore.        Ignore
      SEQUENCE         Required.         Required
      STATUS           Ignore.           Ignore
      SUMMARY          Ignore.          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. Ignore
      URL              Ignore.              Ignore
      UID              Required.              Required
      X-               Ignore.               Ignore

      Silverberg/Mansour/Daws/Hopson  89                Expires November 1998
      5.1.2     To-Do-Related     Free/Busy-Related Fallbacks

      Method           Fallback
      --------------   -----------------------------------------------------
      PUBLISH          Required.
CANCEL           Required.
ADD              Required.          Implementations MAY ignore the METHOD type. The
                       REQUEST-STATUS "3.14;Unsupported capability" MUST be
                       returned.
      REQUEST          TODO-PUBLISH.          Implementations MAY ignore the METHOD type. The
                       REQUEST-STATUS "3.14;Unsupported capability" MUST be
                       returned.
      REPLY            Required.            Implementations MAY ignore the METHOD type. The
                       REQUEST-STATUS "3.14;Unsupported capability" MUST be
                       returned.

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

Silverberg/Mansour/Dawson/Hopson  88             Expires September 1998          Ignore

      Component
      Property         Fallback
      --------------   -----------------------------------------------------
      COMMENT          Ignore
      CONTACT          Ignore
      DTEND            Required
      DTSTAMP          Required
      DTSTART          Required
      DURATION         Required
      FREEBUSY         Required
      ORGANIZER        Ignore
      REQUEST-STATUS   Ignore
      UID              Required
      URL              Ignore
      X-               Ignore

      5.1.3     To-Do-Related
Components Fallbacks

      Method           Fallback
      --------------   -----------------------------------------------------
VALARM
      PUBLISH          Required
      REQUEST          PUBLISH
      REPLY            Required
      ADD              Required
      CANCEL           Required

      Silverberg/Mansour/Daws/Hopson  90                Expires November 1998
      REFRESH          Required
      COUNTER          Reply with Not Supported.
VTIMEZONE Supported
      DECLINECOUNTER   Required if RRULE or RDATE VTODO - COUNTER is implemented; otherwise ignore and use local time.

Component
                       reply with Not Supported

      iCalendar
      Property         Fallback
      --------------   -----------------------------------------------------
      CALSCALE         Ignore; assume GREGORIAN.
GEO              Ignore.
      PRODID           Ignore.
PROFILE           Ignore
      METHOD           Required as described in the Method list above.
SOURCE           Ignore.
NAME             Ignore.
      VERSION          Assume "2.0".          Ignore

      To-Do-Related
      Components       Fallback
      --------------   -----------------------------------------------------
      VALARM           Reply with Not Supported
      VTIMEZONE        Required if any DateTime value refers to a time zone.

      Component
      Property         Fallback
      --------------   -----------------------------------------------------
      ATTACH           Ignore.           Ignore
      ATTENDEE         Required if REQUEST is not implemented; otherwise
                 ignore.
                       ignore
      CATEGORIES       Ignore.       Ignore
      CLASS            Ignore.            Ignore
      COMMENT          Ignore.          Ignore
      COMPLETED        Required.
CREATED          Ignore.
DAYLIGHT        Required if VTIMEZONE is implemented; otherwise
                 ignore.
      CONTACT          Ignore
      CREATED          Ignore
      DESCRIPTION      Required.      Required
      DUE              Required.              Required
      DURATION         Ignore.         Ignore Reply with Not Supported. Supported
      DTSTAMP          Required.          Required
      DTSTART          Required.          Required
      EXDATE           Ignore.           Ignore Reply with Not Supported. Supported
      EXRULE           Ignore.           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.
      LAST-MODIFIED    Ignore
      LOCATION         Ignore
      ORGANIZER        Ignore
      PERCENT-COMPLETE Ignore
      PRIORITY         Required
      RECURRENCE-ID    Ignore
      RELATED-TO       Ignore
      REQUEST-STATUS   Ignore
      RDATE            Ignore
      RRULE            Ignore.  The first instance occurs on the DTSTART
                       property. If implemented, VTIMEZONE MUST also be
                       implemented.
      RESOURCES        Ignore.        Ignore

      Silverberg/Mansour/Daws/Hopson  91                Expires November 1998
      SEQUENCE         Required.
STATUS           Required.
SUMMARY          Ignore.
TRANSP           Required if FREEBUSY is implemented; otherwise ignore.
TZNAME         Required if VTIMEZONE is implemented; otherwise
                 ignore.
TZOFFSET
      STATUS           Required if VTIMEZONE is implemented; otherwise
                 ignore.
      SUMMARY          Ignore
      URL              Ignore.

Silverberg/Mansour/Dawson/Hopson  89             Expires September 1998              Ignore
      UID              Required.              Required
      X-               Ignore.

5.1.3               Ignore

      5.1.4     Journal-Related Fallbacks

      Method           Fallback
      --------------   -----------------------------------------------------
      PUBLISH          Implementations MAY ignore the profile METHOD type. The
                       REQUEST-STATUS "302;Request Not supported" "3.14;Unsupported capability" MUST be
                       returned.
CANCEL
      ADD              Implementations MAY ignore the profile METHOD type. The
                       REQUEST-STATUS "302;Request Not supported" "3.14;Unsupported capability" MUST be
                       returned.
ADD
      CANCEL           Implementations MAY ignore the profile METHOD type. The
                       REQUEST-STATUS "302;Request Not supported" "3.14;Unsupported capability" MUST be
                       returned.

      iCalendar
      Property         Fallback
      --------------   -----------------------------------------------------
      CALSCALE         Ignore; assume GREGORIAN.
GEO              Ignore.
      PRODID           Ignore.           Ignore
      METHOD           Required as described in the Method list above.
SOURCE           Ignore
NAME             Ignore.
      VERSION          Ignore.          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". any DateTime value refers to a time zone.

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

Silverberg/Mansour/Dawson/Hopson  90             Expires September 1998
                 ignore.          Ignore
      DESCRIPTION      Required.      Required
      DTSTAMP          Required.          Required
      DTSTART          Required.
DTEND            Required.          Required
      EXDATE           Ignore.           Ignore

      Silverberg/Mansour/Daws/Hopson  92                Expires November 1998
      EXRULE           Ignore.
LAST-MODIFIED    Ignore.
RELATED-TO       Ignore.
RDATE            Ignore.           Ignore Reply with Not Supported. If implemented,
                       VTIMEZONE MUST also be implemented.
      LAST-MODIFIED    Ignore
      ORGANIZER        Ignore
      RECURRENCE-ID    Ignore
      RELATED-TO       Ignore
      RDATE            Ignore.
      RRULE            Ignore. The first instance occurs on the DTSTART
                       property. If implemented, VTIMEZONE MUST also be
                       implemented.
      SEQUENCE         Required.
STATUS           Ignore.
TRANSP           Required if FREEBUSY is implemented; otherwise ignore.
TZNAME         Required if VTIMEZONE is implemented; otherwise
                 ignore.
TZOFFSET
      STATUS           Ignore
      SUMMARY          Required if VTIMEZONE is implemented; otherwise
                 ignore.
      URL              Ignore.              Ignore
      UID              Required.              Required
      X-               Ignore.               Ignore

      5.2 Latency Issues

      With a store-and-forward transport, it is possible for events to arrive
      out of sequence. That is, a "CANCEL" method may be received 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 CU they MUST send a
      "REPLY" method to the "Organizer" using the "ATTENDEE" properties to
      indicate that the request was delegated and to whom. Hence, it is
      possible for an "Organizer" to receive an "REPLY" from a CU not listed
      as one of the 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

Silverberg/Mansour/Dawson/Hopson  91             Expires September 1998
      out of date the "Organizer" SHOULD treat the message as a "STATUS-
REQUEST" "REFRESH"
      message and update the delegate with the correct version.

      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

      Silverberg/Mansour/Daws/Hopson  93                Expires November 1998
      tie-breaker when two items with the same "SEQUENCE" property value are
      evaluated. Furthermore, the "SEQUENCE" property SHOULD only incremented
when one or more of the following properties changes:

DTSTART
DTEND
RDATE
RRULE
EXDATE
EXRULE
DUE (for VTODO components)
and possibly LOCATION  (at the user's discretion)

      6  Security Considerations

      ITIP is 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 iTIP, the "Organizer" (or someone working on the "Organizer's"
      behalf) is the only person authorized to make changes to an existing
      "VEVENT", "VTODO", "VJOURNAL" calendar component and republish it or
      redistribute 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 republished or sent to the "Attendees".

      6.1.2     Spoofing the "Attendee"

      In iTIP, an "Attendee" of a "VEVENT" or "VTODO" calendar component (or
      someone working on the "Attendee's" behalf) 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".

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      6.1.3     Unauthorized Replacement of the Organizer

      There will be circumstances when "Attendees" of an event or to-do
      decide, using out-of-band mechanisms, that the "Organizer" must be
      replaced. When the new "Organizer" sends out the updated "VEVENT" or
      "VTODO" the "Attendee's" CUA will detect that the "Organizer" has been
      changed, but it has no way of knowing whether or not the change was
      mutually agreed upon.

      6.1.4     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.

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      6.1.5     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.

      6.1.6     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 "PROCEDURE" and MAY have an attachment containing an
      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.

      6.1.7     Unauthorized REFRESH Requests

      It is possible for an "Organizer" to receive a "REFRESH" request from
      someone who is not an "Attendee" of an event or to-do. Only "Attendee's"
      of an event or to-do are authorized to receive replies to "REFRESH"
      requests. Replying to such requests to anyone who is not an "Attendee"
      may be a security problem.

      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. encrypted. This may be accomplished using public
      key technology, specifically Security Multiparts for MIME [RFC1847] [RFC-1847] in
      the iTIP transport binding. This helps mitigate the threats of spoofing,
      eavesdropping and malicious changes in transit.

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      6.2.1     Use of [RFC1847] [RFC-1847] to secure iTIP transactions

      iTIP transport bindings SHOULD MUST provide a mechanism based on Security
      Multiparts for MIME [RFC1847] [RFC-1847] to enable authentication of the 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 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.

      Implementations MAY provide controls for users to disable this
      capability.

      Silverberg/Mansour/Daws/Hopson  95                Expires November 1998
      6.2.2     Implementation Controls

      The threat of unauthorized replacement of the "Organizer" SHOULD be
      mitigated by a calendar system that uses this protocol by providing
      controls or alerts that make "Calendar Users" aware of such "Organizer"
      changes and allowing them to decide whether or not the request should be
      honored.

      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.

      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.

      The threat of unauthorized "REFRESH" requests SHOULD be mitigated by a
      calendar system that uses this protocol by providing controls or alerts
      that allow "Calendar User" to decide whether or not the request should
      be honored.  An implementation MAY decide to maintain, for audit or
      historical purposes,  "Calendar Users" who were part of an attendee list
      and who were subsequently uninvited.  Similar controls or alerts should
      be provided when a "REFRESH" request is received from these "Calendar
      Users" as well.

      7  Acknowledgments

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

      Anik Ganguly, Dan Hickman, Paul Hill, Daryl Huff, Bruce Kahn, Antoine
      Leca, Bob Mahoney, John Noerenberg, Leo Parker, John Rose, Doug Royer,
      Vinod Seraphin, Richard Shusterman, Derik Stenerson, John Sun, Kevin
      Tsurutome.

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      8  Bibliography

[ICAL]

      [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.
      drafts/draft-ietf-calsch-ical-07.txt.

      [ICMS] "Internet Calendaring Model Specification", Internet-Draft,
      October 1997, ftp://ftp.ietf.org/internet-drafts/draft-ietf-calsch-mod-
01.txt.
      03.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]

      Silverberg/Mansour/Daws/Hopson  96                Expires November 1998
      [iMIP] "iCalendar Message-Based Interoperability Protocol - iMIP",
      Internet-Draft, October 1997, ftp://ftp.ietf.org/internet-drafts/draft-
ietf-calsch-imip-01.txt.
      ietf-calsch-imip-05.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.

      [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]

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

[RFC1983]

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

[RFC2119]

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

[RFC2045]

      [RFC-2045] 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.

[RFC2046]

      [RFC-2046] 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 American Standard Code for
      Information Interchange, ANSI X3.4-1986.

Silverberg/Mansour/Dawson/Hopson  95             Expires September 1998

      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
      VERSION:2.1
      FN:Frank Dawson
      ORG:Lotus Development Corporation

      Silverberg/Mansour/Daws/Hopson  97                Expires November 1998
      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
      VERSION:2.1
      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
      TEL;WORK;FAX:+1-919-890-4100
      EMAIL;INTERNET:rhopson@on.com
      END:VCARD

      BEGIN:VCARD
      VERSION:2.1
      FN:Steve Mansour
      ORG:Netscape Communications Corporation
      ADR;WORK;POSTAL;PARCEL:;;501 East Middlefield Road;Mountain
        View;CA;94043;USA
      TEL;WORK;MSG:+1-650-937-2378
      TEL;WORK;FAX:+1-650-937-2103
      EMAIL;INTERNET:sman@netscape.com
      END:VCARD

      BEGIN:VCARD
      VERSION:2.1
      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
      TEL;WORK;FAX:+1-425-936-8019
      EMAIL;INTERNET:stevesil@Microsoft.com
      END:VCARD

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      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

      Silverberg/Mansour/Daws/Hopson  98                Expires November 1998
      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 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 may be
      revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an

      THIS DOCUMENT AND THE INFORMATION CONTAINED HEREIN IS PROVIDED ON AN "AS
      IS" basis and BASIS AND THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
      FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
      LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT
      INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR
      FITNESS FOR A PARTICULAR PURPOSE.

Silverberg/Mansour/Dawson/Hopson  97

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