tech-invite   World Map     

IETF     RFCs     Groups     SIP     ABNFs    |    3GPP     Specs     Glossaries     Architecture     IMS     UICC    |    search

RFC 2446

 
 
 

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

Part 4 of 4, p. 78 to 109
Prev RFC Part

 


prevText      Top      Up      ToC       Page 78 
4.4 Recurring Event and Time Zone Examples

4.4.1 A Recurring Event Spanning Time Zones

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

   BEGIN:VCALENDAR
   PRODID:-//ACME/DesktopCalendar//EN
   METHOD:REQUEST
   VERSION:2.0
   BEGIN:VTIMEZONE
   TZID:America-SanJose
   TZURL:http://zones.stds_r_us.net/tz/America-SanJose
   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;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

Top      Up      ToC       Page 79 
   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 is 9 hours ahead of PDT or 23:00. "Attendee" C@example.jp is in
   Japan where local time is 8 hours ahead of UTC or Wednesday, July 2
   at 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 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 23:00 GMT
   TUE, 09-SEP-1997 14:00 PDT
   WED, 10-SEP-1997 06:00 JST

   and the second is:

   TUE, 28-OCT-1997 23:00 GMT
   TUE, 28-OCT-1997 14:00 PST
   WED, 29-OCT-1997 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

Top      Up      ToC       Page 80 
   PRODID:-//RDU Software//NONSGML HandCal//EN
   VERSION:2.0
   BEGIN:VEVENT
   UID:guid-1@host1.com
   SEQUENCE:0
   RRULE:FREQ=MONTHLY;BYMONTHDAY=1;UNTIL=19980901T210000Z
   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
   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

   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
   UID:guid-1@host1com
   RECURRENCE-ID:19970701T210000Z
   SEQUENCE:1
   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
   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

Top      Up      ToC       Page 81 
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

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
   STATUS:CANCELLED
   SEQUENCE:3
   END:VEVENT
   END:VCALENDAR

Top      Up      ToC       Page 82 
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
   UID:guid-1@host1.com
   RECURRENCE-ID;THISANDFUTURE:19970901T210000Z
   SEQUENCE:3
   ORGANIZER: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

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.

   BEGIN:VCALENDAR
   METHOD:ADD
   PRODID:-//RDU Software//NONSGML HandCal//EN
   VERSION:2.0
   BEGIN:VEVENT
   UID:123456789@host1.com
   SEQUENCE:4
   ORGANIZER: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

Top      Up      ToC       Page 83 
   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;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
   STATUS:CONFIRMED
   END:VEVENT
   END:VCALENDAR

   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" wants to add Thursdays to the event:

   BEGIN:VCALENDAR
   METHOD:ADD
   PRODID:-//RDU Software//NONSGML HandCal//EN
   VERSION:2.0

Top      Up      ToC       Page 84 
   BEGIN:VEVENT
   UID:123456789@host1.com
   SEQUENCE:7
   RRULE:WKST=SU;BYDAY=TH;FREQ=WEEKLY
   ORGANIZER: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". Note, that since this is an entire rescheduling
   of the event, any instance-specific information will be lost.

   BEGIN:VCALENDAR
   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;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
   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 initial "VEVENT" request and subsequent instance

Top      Up      ToC       Page 85 
   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
   ORGANIZER: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;PARTSTAT=ACCEPTED:Mailto:A@example.com
   ATTENDEE;RSVP=TRUE:Mailto:B@example.com
   SUMMARY:Review Accounts
   DTSTART:19980311T160000Z
   DTEND:19980311T180000Z
   DTSTAMP:19980306T193000Z
   LOCATION:The Small conference room
   STATUS:CONFIRMED
   END:VEVENT
   END:VCALENDAR

Top      Up      ToC       Page 86 
   Organizer adds a 4th instance of the meeting using the "ADD" method

   BEGIN:VCALENDAR
   METHOD:ADD
   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;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:2
   RDATE:19980304T180000Z
   RDATE:19980311T160000Z
   RDATE:19980315T180000Z
   Error! Bookmark not defined.
   ORGANIZER: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

Top      Up      ToC       Page 87 
   END:VEVENT

   BEGIN:VEVENT
   Error! Bookmark not defined.
   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
   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
   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

Top      Up      ToC       Page 88 
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

   BEGIN:VCALENDAR
   METHOD:REQUEST
   PRODID:-//RDU Software//NONSGML HandCal//EN
   VERSION:2.0
   BEGIN:VEVENT
   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

Top      Up      ToC       Page 89 
   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 from each participant. The response indicates
   the individual "Attendee's" completion status. The table below
   illustrates the message flow.

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

Top      Up      ToC       Page 90 
+--------------------------------------------------------------------+
| Attendee indicates |                     | "D" sends a "REPLY"     |
| completion         |                     | message indicating      |
|                    |                     | completion              |
+--------------------------------------------------------------------+

4.5.1 A VTODO Request

   A sample "REQUEST" 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
   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
   DTSTART:19970701T170000Z
   DUE:19970722T170000Z
   PRIORITY:1
   SUMMARY:Create the requirements document
   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

   "B" accepts the to-do.

   BEGIN:VCALENDAR
   PRODID:-//ACME/DesktopCalendar//EN
   METHOD:REPLY
   VERSION:2.0
   BEGIN:VTODO
   ORGANIZER:Mailto:A@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

Top      Up      ToC       Page 91 
   END:VTODO
   END:VCALENDAR

   "B" could have declined the TODO or indicated tentative acceptance by
   setting the "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:D@example.com
   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
   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;PARTSTAT=IN-PROCESS:Mailto:B@example.com
   PERCENT-COMPLETE:75
   UID:calsrv.example.com-873970198738777-00@example.com
   DTSTAMP:19970717T233000Z
   SEQUENCE:0
   END:VTODO
   END:VCALENDAR

Top      Up      ToC       Page 92 
4.5.5 A Reply: Completed

   A reply indicating that "D" completed "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;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%.

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

Top      Up      ToC       Page 93 
4.5.7.1 Request for a Recurring VTODO

   In this example "A" sends a recurring "VTODO" calendar component to
   "B" and "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:D@example.com
   RRULE:FREQ=MONTHLY;COUNT=10;BYDAY=1FR
   DTSTART:19980101T100000-0700
   DUE:19980103T100000-0700
   SUMMARY:Send Status Reports to Area Managers
   UID:calsrv.example.com-873970198738777-00@example.com
   SEQUENCE:0
   DTSTAMP:19970717T200000Z
   STATUS:NEEDS ACTION
   PRIORITY:1
   END:VTODO
   END:VCALENDAR

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 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

Top      Up      ToC       Page 94 
   BEGIN:VTODO
   ATTENDEE;PARTSTAT=IN-PROCESS:Mailto:B@example.com
   PERCENT-COMPLETE:75
   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
   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
   RELATED-TO:0981234-1234234-2402-35@example.com
   ATTACH:ftp://ftp.example.com/pub/ed/minutes100197.txt
   END:VJOURNAL
   END:VCALENDAR

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;PARTSTAT=ACCEPTED:Mailto:A@example.com
   ATTENDEE:Mailto:B@example.com
   ATTENDEE:Mailto:C@example.com

Top      Up      ToC       Page 95 
   ATTENDEE:Mailto:D@example.com
   UID: guid-1-12345@host1.com
   DTSTAMP:19970603T094000
   END:VEVENT
   END:VCALENDAR

4.7.2 Bad RECURRENCE-ID

   Component instances are identified by the combination of "UID",
   "RECURRENCE-ID", and "SEQUENCE". When an "Organizer" sends a request
   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" 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.

   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 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" to the "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 "Organizer".

Top      Up      ToC       Page 96 
+--------------------------------------------------------------------+
| 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":

   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;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
   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
   "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

Top      Up      ToC       Page 97 
   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: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.

5.1.1 Event-Related Fallbacks

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

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

Top      Up      ToC       Page 98 
Event-Related
Components       Fallback
--------------   -----------------------------------------------------
VALARM           Reply with Not Supported
VTIMEZONE        Required if any DateTime value refers to a time zone.

Component
Property         Fallback
--------------   -----------------------------------------------------
ATTACH           Ignore
ATTENDEE         Required if EVENT-REQUEST is not implemented;
                 otherwise reply with Not Supported
CATEGORIES       Ignore
CLASS            Ignore
COMMENT          Ignore
COMPLETED        Ignore
nCONTACT          Ignore
CREATED          Ignore
DESCRIPTION      Required
DURATION         Reply with Not Supported
DTSTAMP          Required
DTSTART          Required
DTEND            Required
EXDATE           Ignore
EXRULE           Ignore Reply with Not Supported. 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
REQUEST-STATUS   Required
RESOURCES        Ignore
SEQUENCE         Required
STATUS           Ignore
SUMMARY          Ignore
TRANSP           Required if FREEBUSY is implemented; otherwise Ignore
URL              Ignore
UID              Required
X-               Ignore

Top      Up      ToC       Page 99 
5.1.2 Free/Busy-Related Fallbacks

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


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

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

Top      Up      ToC       Page 100 
CANCEL           Required
REFRESH          Required
COUNTER          Reply with Not Supported
DECLINECOUNTER   Required if VTODO - COUNTER is implemented; otherwise
                 reply with Not Supported

iCalendar
Property         Fallback
--------------   -----------------------------------------------------
CALSCALE         Ignore; assume GREGORIAN.
PRODID           Ignore
METHOD           Required as described in the Method list above.
VERSION          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
ATTENDEE         Required if REQUEST is not implemented; otherwise
                 ignore
CATEGORIES       Ignore
CLASS            Ignore
COMMENT          Ignore
COMPLETED        Required
CONTACT          Ignore
CREATED          Ignore
DESCRIPTION      Required
DUE              Required
DURATION         Ignore Reply with Not Supported
DTSTAMP          Required
DTSTART          Required
EXDATE           Ignore Reply with Not Supported
EXRULE           Ignore Reply with Not Supported. If implemented,
                 VTIMEZONE MUST also be implemented.
LAST-MODIFIED    Ignore
LOCATION         Ignore
ORGANIZER        Ignore
PERCENT-COMPLETE Ignore
PRIORITY         Required
RECURRENCE-ID    Ignore

Top      Up      ToC       Page 101 
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
SEQUENCE         Required
STATUS           Required
SUMMARY          Ignore
URL              Ignore
UID              Required
X-               Ignore

5.1.4 Journal-Related Fallbacks


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


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


Journal-Related
Components       Fallback
--------------   -----------------------------------------------------
VTIMEZONE        Required if any DateTime value refers to a time zone.

Top      Up      ToC       Page 102 
Component
Property         Fallback
--------------   -----------------------------------------------------
ATTACH           Ignore
ATTENDEE         Required if JOURNAL-REQUEST is implemented; otherwise
                 ignore
CATEGORIES       Ignore
CLASS            Ignore
COMMENT          Ignore
CONTACT          Ignore
CREATED          Ignore
DESCRIPTION      Required
DTSTAMP          Required
DTSTART          Required
EXDATE           Ignore
EXRULE           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
SUMMARY          Required
URL              Ignore
UID              Required
X-               Ignore

5.2 Latency Issues

   With a store-and-forward transport, it is possible for events to
   arrive out of sequence. That is, 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.

Top      Up      ToC       Page 103 
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 out of date the "Organizer" SHOULD treat the
   message as a "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 tie-breaker when two items with the same "SEQUENCE"
   property value are evaluated.

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

Top      Up      ToC       Page 104 
   maliciously changes the "ATTENDEE" parameters may be constructed by
   someone other than the real "Attendee" and sent to the "Organizer".

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.

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" 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 encrypted. This may be accomplished using
   public key technology, specifically Security Multiparts for MIME

Top      Up      ToC       Page 105 
   [RFC-1847] in the iTIP transport binding. This helps mitigate the
   threats of spoofing, eavesdropping and malicious changes in transit.

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

   iTIP transport bindings MUST provide a mechanism based on Security
   Multiparts for MIME [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.

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.

Top      Up      ToC       Page 106 
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,
   Alexander Taler, Kevin Tsurutome.

8 Bibliography

   [iCAL]     Dawson, F. and D. Stenerson, "Internet Calendaring and
              Scheduling Core Object Specification - iCalendar", RFC
              2445, November 1998.

   [iMIP]     Dawson, F., Mansour, S. and S. Silverberg, "iCalendar
              Message-Based Interoperability Protocol - iMIP", RFC 2447,
              November 1998.

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

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

Top      Up      ToC       Page 107 
9 Authors' Addresses

   The following address information is provided in a vCard v3.0,
   Electronic Business Card, format.

   The authors of this memo are:

   BEGIN:VCARD
   VERSION:3.0
   N:Dawson;Frank
   FN:Frank Dawson
   ORG:Lotus Development Corporation
   ADR;WORK;POSTAL;PARCEL:;;6544 Battleford Drive;Raleigh;NC;27613-
    3502;USA
   TEL;TYPE=WORK,MSG:+1-919-676-9515
   TEL;TYPE=WORK,FAX:+1-919-676-9564
   EMAIL;TYPE=PREF,INTERNET:Frank_Dawson@Lotus.com
   EMAIL;TYPE=INTERNET:fdawson@earthlink.net
   URL:http://home.earthlink.net/~fdawson
   END:VCARD

   BEGIN:VCARD
   VERSION:3.0
   N:Hopson;Ross
   FN:Ross Hopson
   ORG:On Technology, Inc.
   ADR;TYPE=WORK,POSTAL,PARCEL:;Suite 1600;434 Fayetteville St.
     Mall\, Two Hannover Square;Raleigh;NC;27601
   TEL;TYPE=WORK,MSG:+1-919-890-4036
   TEL;TYPE=WORK,FAX:+1-919-890-4100
   EMAIL;TYPE=INTERNET:rhopson@on.com
   END:VCARD

   BEGIN:VCARD
   VERSION:3.0
   N:Mansour;Steve
   FN:Steve Mansour
   ORG:Netscape Communications Corporation
   ADR;TYPE=WORK,POSTAL,PARCEL:;;501 East Middlefield Road;Mountain
     View;CA;94043;USA
   TEL;TYPE=WORK,MSG:+1-650-937-2378
   TEL;TYPE=WORK,FAX:+1-650-937-2103
   EMAIL;TYPE=INTERNET:sman@netscape.com
   END:VCARD

Top      Up      ToC       Page 108 
   BEGIN:VCARD
   VERSION:3.0
   N:Silverberg;Steve
   FN:Steve Silverberg
   ORG:Microsoft Corporation
   ADR;TYPE=WORK,POSTAL,PARCEL:;;One Microsoft Way;
   Redmond;WA;98052-6399;USA
   TEL;TYPE=WORK,MSG:+1-425-936-9277
   TEL;TYPE=WORK,FAX:+1-425-936-8019
   EMAIL;INTERNET:stevesil@Microsoft.com
   END:VCARD

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

   BEGIN:VCARD
   VERSION:3.0
   N:Ganguly;Anik
   FN:Anik Ganguly
   ORG:Open Text Inc.
   ADR;TYPE=WORK,POSTAL,PARCEL:;Suite 101;38777 West Six Mile Road;
    Livonia;MI;48152;USA
   TEL;TYPE=WORK,MSG:+1-734-542-5955
   EMAIL;TYPE=INTERNET:ganguly@acm.org
   END:VCARD

   The co-chairman of that working group is:

   BEGIN:VCARD
   VERSION:3.0
   N:Moskowitz;Robert
   FN:Robert Moskowitz
   NICKNAME:Bob
   EMAIL; TYPE=INTERNET:rgm-ietf@htt-consult.com
   END:VCARD

Top      Up      ToC       Page 109 
10.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  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 implementation 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 not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   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.