iTip using PARTICIPANT only

Internet-Draft	iTip participants	December 2024
Douglass	Expires 4 June 2025	[Page]

Abstract

This specification defines updates to RFC5546 iTip which allow scheduling using the "PARTICIPANT" calendar components specified in RFC9073.¶

New properties are also defined for use within the "PARTICIPANT" calendar component.¶

Status of This Memo

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

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶

This Internet-Draft will expire on 4 June 2025.¶

Copyright Notice

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

1. Introduction

This specification details how the "PARTICIPANT" calendar component introduced in [RFC9073] may be used for scheduling in place of [RFC5545] "ATTENDEE" and "ORGANIZER" properties. Additionally, some properties are defined in this specification to be used within the "PARTICIPANT" calendar component.¶

For "VEVENT", "VTODO", "VFREEBUSY", and "VAVAILABILITY" calendar components; the "ORGANIZER" and "ATTENDEE" properties MUST be supplied as specified in [RFC5546]. For new components such as the "VPOLL" calendar component, defined elsewhere, only "PARTICIPANT" calendar components MUST be used. A participant object that takes part in group scheduling MUST have the following characteristics:¶

It MUST have a calendar address as defined in Section 6.4 of [RFC9073].¶
It must have one or more scheduling roles defined in PARTICIPANT-TYPE¶
Exactly 1 PARTICIPANT MUST have the OWNER role¶

Scheduling with "PARTICIPANT" calendar components behaves exactly as with "ATTENDEE" and "ORGANIZER" properties. When iTip specifies the setting of "ATTENDEE" or "ORGANIZER" property parameters then the appropriate properties will be set within the "PARTICIPANT" calendar component.¶

2. Terms and definitions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].¶

The notation used in this memo to (re-)define iCalendar elements is the ABNF notation of [RFC5234] as used by [RFC5545]. Any syntax elements shown below that are not explicitly defined in this specification come from iCalendar [RFC5545].¶

Additionally, the following terms are used:¶

2.1. participant

Represents an agent that takes part in scheduling or publishing. A participant may be a human, for example an attendee, or a resource, for example a conference room.¶

2.2. publishable

A component which takes part in [RFC5546] publishing operations.¶

2.3. schedulable

A component which takes part in [RFC5546] scheduling operations.¶

2.4. owner

The "Owner" of a "Schedulable" component is equivalent to the "Organizer" in [RFC5546]. As such, there may be only one "Owner" though future specifications may relax or extend that constraint. The "Owner" is indicated by a role of "OWNER".¶

3. iCalendar Extensions

3.1. New Property Parameters

3.1.1. Required

Parameter name: REQUIRED¶
Purpose: To specify whether the associated property is required in the current context.¶
Format Definition: This parameter is defined by the following notation:¶

requiredparam = "REQUIRED"  "=" ("TRUE" / "FALSE")
  ; Default is FALSE

Description: This parameter MAY be specified on "REPLY-URL" property and, if the value is TRUE, indicates the "Owner" requires all replies to be made via the specified service rather than iTip replies.¶

3.2. New Properties

3.2.1. Reply-URL

Property name: REPLY-URL¶
Purpose: This property may be used in scheduling messages to indicate additional reply methods, for example a web-service.¶
Value type: URI¶
Property Parameters: Non-standard, required or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified once in any schedulable component.¶
Description: When used in a scheduling message this property indicates an additional or required service that can be used to reply. Typically, this would be a web service of some form.¶

When the "REQUIRED" property parameter is absent then this property provides an alternative to standard iTip based scheduling.¶

When the "REQUIRED" property parameter is present then this property provides the only mechanism by which participants can reply. This allows the implementation of a web-based service without the ability to accept incoming mail for example.¶
Format Definition: This property is defined by the following notation:¶

reply-url = "REPLY-URL" reply-urlparams ":" uri CRLF

reply-urlparams = *(
                  (";" requiredparam) /
                  (";" other-param)
                  )

3.3. Redefined participation type

This specification redefines the "PARTICIPANT-TYPE" property allowing it to take multiple values and extending those values to align with [RFC8984] roles. There are also changes to the description to clarify its use defining the roles that participant takes.¶

Property name: PARTICIPANT-TYPE¶
Purpose: This property is equivalent to the [RFC5545] "ROLE" property parameter but includes more values to align with [RFC8984].¶
Value Type: The value type for this property is TEXT. The allowable values are defined below.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MUST be specified once within a "PARTICIPANT" calendar component.¶
Description: This property defines the type of participation, that is the roles the participant takes.
¶

It includes the values defined in [RFC8984].¶

Note that the kind of participant, for example individual or group, is defined in the "KIND" property specified here.¶

Some of the roles are required for the participant to be a "schedulable" object. These are the roles that are shown below.¶
Format Definition: This property is defined by the following notation:¶

participanttype   = "PARTICIPANT-TYPE" partvalueparam ":"
                     partvalue
                     *("," partvalue) CRLF

partvalue    = ("OWNER"
               / "ATTENDEE"
               / "OPTIONAL"
               / "INFORMATIONAL"
               / "CHAIR"
               / "ACTIVE"
               / "INACTIVE"
               / "SPONSOR"
               / "CONTACT"
               / "BOOKING-CONTACT"
               / "EMERGENCY-CONTACT"
               / "PUBLICITY-CONTACT"
               / "PLANNER-CONTACT"
               / "PERFORMER"
               / "SPEAKER"
               / iana-token)     ; Other IANA-registered
                                 ; values

partvalueparam   = *(";" other-param)

The values have the same meaning as defined in [RFC8984] and [RFC9073].¶

Other roles defined here have no direct equivalent in [RFC5545]¶

To map [RFC5545] "ROLE" property parameter values to "PARTICIPANT-TYPE" property values use the following.¶

Table 1
RFC5545 ROLE	PARTICIPANT-TYPE
CHAIR¶	CHAIR¶
REQ-PARTICIPANT¶	ATTENDEE¶
OPT-PARTICIPANT¶	OPTIONAL¶
NON-PARTICIPANT¶	INFORMATIONAL¶

The following table shows those roles that MUST appear in the "PARTICIPANT-TYPE" property for group-scheduling. Additionally, the mapping for "PARTICIPANT-TYPE" property values to [RFC5545] values are shown.¶

Table 2
PARTICIPANT-TYPE	RFC5545 ROLE
OWNER¶	Create ORGANIZER¶
ATTENDEE¶	REQ-PARTICIPANT¶
OPTIONAL¶	OPT-PARTICIPANT¶
INFORMATIONAL¶	NON-PARTICIPANT¶
CHAIR¶	CHAIR¶
Subsequent values have no [RFC5545] equivalent¶
CONTACT¶
VOTER¶
ACTIVE¶
INACTIVE¶
SPONSOR¶
BOOKING-CONTACT¶
EMERGENCY-CONTACT¶
PUBLICITY-CONTACT¶
PLANNER-CONTACT¶
PERFORMER¶
SPEAKER¶

Examples

PARTICIPANT-TYPE=OWNER,... equivalent to the "ORGANIZER" property¶
PARTICIPANT-TYPE=ATTENDEE,... equivalent to the "ATTENDEE" property¶

4. New Participant Properties for iTip

The following properties are defined to be used within the "PARTICIPANT" calendar component during scheduling and take the place of "ATTENDEE" and "ORGANIZER" properties and parameters.¶

4.1. Kind

Property name: KIND¶
Purpose: This is what kind of entity this participant is, if known.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified in a "PARTICIPANT" calendar component.¶
Description: When used in a "PARTICIPANT" calendar component this property indicates the kind of entity, individual, group etc.
¶

It takes the values shown below which are a redefinition of the "CUTYPE" property parameter values defined in [RFC5545] and aligned with [RFC8984] .¶
Format Definition: This property is defined by the following notation:¶

kind = "KIND" kindparams ":"
                "INDIVIDUAL"   ; An individual
              / "GROUP"        ; A group of individuals
              / "RESOURCE"     ; A physical resource
              / "LOCATION"     ; A location resource e.g a room
              / iana-token CRLF

kindparams = *(";" other-param)

4.2. Participation-status

Property name: PARTICIPATION-STATUS¶
Purpose: This property is used in the "PARTICIPANT" calendar component to indicate the participation status - if any.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified in a "PARTICIPANT" calendar component.¶
Description: When used in a "PARTICIPANT" calendar component this property indicates what status, if any, the participant has.
¶

It takes the same values as the "PARTSTAT" property parameter defined in [RFC5545].¶
Format Definition: This property is defined by the following notation:¶

participation-status = "PARTICIPATION-STATUS"
                       participation-statusparams ":"
              NEEDS-ACTION / ; No status
                       ; has yet been set by the participant.
              ACCEPTED / ; The invited
                       ; participant will participate.
              DECLINED / ; The invited
                       ; participant will not participate.
              TENTATIVE / ; The invited participant
                       ; may participate.
              DELEGATED / ; The invited participant
                       ; has delegated their attendance to
                       ; another participant, as specified
                       ; in the PARTICIPATION-DELEGATED-TO property.
              COMPLETED / ; The assigned task is
                       ; completed.
              IN-PROCESS / ; The assigned task is
                       ; being worked on.
              iana-token ("," iana-token) CRLF

participation-statusparams = *(";" other-param)

4.3. Participation delegated from

Property name: PARTICIPATION-DELEGATED-FROM¶
Purpose: This property is used in the "PARTICIPANT" calendar component to indicate who has delegated their participation to this participant.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified in a "PARTICIPANT" calendar component 0 or more times.¶
Description: This property specifies a calendar user that has delegated their participation in a group-scheduled component to the calendar user specified by the component.¶
Format Definition: This property is defined by the following notation:¶

participation-delfrom = "PARTICIPATION-DELEGATED-FROM"
                        participation-delfromparams ":"
              CAL-ADDRESS
              iana-token ("," iana-token) CRLF

participation-delfromparams = *(";" other-param)

4.4. Participation delegated to

Property name: PARTICIPATION-DELEGATED-TO¶
Purpose: To specify the calendar user to whom the calendar user specified by the component has delegated participation.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified in a "PARTICIPANT" calendar component 0 or more times.¶
Description: This property specifies the calendar user that has been delegated participation in a group-scheduled component by the calendar user specified by the component.¶
Format Definition: This property is defined by the following notation:¶

participation-delto = "PARTICIPATION-DELEGATED-TO"
                      participation-deltoparams ":"
              CAL-ADDRESS
              iana-token ("," iana-token) CRLF

participation-deltoparams = *(";" other-param)

4.5. Member of

Property name: MEMBER-OF¶
Purpose: To specify the group or list membership of the calendar user specified by the component.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified in a "PARTICIPANT" calendar component 0 or more times.¶
Description: This property identifies the group or list membership for the calendar user specified by the component.¶
Format Definition: This property is defined by the following notation:¶

member-of = "MEMBER-OF" member-ogparams ":"
              CAL-ADDRESS
              iana-token ("," iana-token) CRLF

memberofparams = *(";" other-param)

4.6. Lang

Property name: LANG¶
Purpose: This is the language tag, as defined in [RFC5646], that best describes the participant's preferred language, if known.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified in any appropriate component.¶
Format Definition: This property is defined by the following notation:¶

lang = "LANG" langparams ":" TEXT CRLF

langparams = *(";" other-param)

4.7. Expect reply

Property name: EXPECT-REPLY¶
Purpose: If true, the organizer is expecting the participant to notify them of their participation status.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified once in the "PARTICIPANT" calendar component.¶
Format Definition: This property is defined by the following notation:¶

expect-reply = "EXPECT-REPLY"
              expect-replyparams ":"
              ( "TRUE" / "FALSE") CRLF

expect-replyparams = *(";" other-param)

4.8. Scheduling-agent

Property name: SCHEDULING-AGENT¶
Purpose: This is who is responsible for sending scheduling messages with this calendar object to the participant.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified once in the "PARTICIPANT" calendar component.¶
Format Definition: This property is defined by the following notation:¶

scheduling-agent = "SCHEDULING-AGENT"
              scheduling-agentparams ":"
              ( "SERVER" /
                "CLIENT" /
                "NONE") CRLF

scheduling-agentparams = *(";" other-param)

The value MUST be one of the following values from the registry defined in Section 12.4.1 of [RFC6638], or a vendor-specific value.¶

SERVER: The calendar server will send the scheduling messages.¶
CLIENT: The calendar client will send the scheduling messages.¶
NONE: No scheduling messages are to be sent to this participant.¶

4.9. Scheduling-force-send

Property name: SCHEDULING-FORCE-SEND¶
Purpose: A client may set the property on a participant to true to request that the server send a scheduling message to the participant when it would not normally do so (e.g., if no significant change is made the object or the scheduleAgent is set to client). The property MUST NOT be stored in the object on the server or appear in a scheduling message.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified once in the "PARTICIPANT" calendar component.¶
Format Definition: This property is defined by the following notation:¶

scheduling-force-send = "SCHEDULING-FORCE-SEND"
              scheduling-force-sendparams ":"
              ( "TRUE" / "FALSE") CRLF

scheduling-force-sendparams = *(";" other-param)

Description: This property MAY be specified in "PARTICIPANT" calendar components for which the "SCHEDULE-AGENT" property is set to the value "SERVER" or is absent. This property is used to force a server to send a scheduling message to a specific calendar user in situations where the server would not send a scheduling message otherwise (e.g., when no change that warrants the delivery of a new scheduling message was performed on the scheduling object resource). An "Owner" MAY specify this property for a PARTICIPANT with the value "REQUEST" to force a "REQUEST" scheduling message to be sent to the user.¶

Participants who are not the "Owner" MAY specify this property in the "Owner" PARTICIPANT with the value "REPLY" to force a "REPLY" scheduling message to be sent to the "Owner".¶

Servers MUST NOT preserve this property in scheduling object resources, nor include it in any scheduling messages sent as the result of a scheduling operation.¶

Clients MUST NOT include this property in any scheduling messages that they themselves send.¶

Servers MUST set the "SCHEDULING-STATUS" property of the participant to 2.5 (i.e., "Success; unknown, non-standard property value ignored."; see Section 3.6.6 of [RFC5546]) when the "SCHEDULE-FORCE-SEND" property is set to an iana-token value they do not recognize.¶

4.10. Scheduling-status

Property name: SCHEDULING-STATUS¶
Purpose: This is a list of status codes, returned from the processing of the most recent scheduling message sent to this participant. The status codes MUST be valid statcode values as defined in the ABNF in Section 3.8.8.3 of [RFC5545].¶

Servers MUST only add or change this property when they send a scheduling message to the participant. Clients SHOULD NOT change or remove this property if it was provided by the server. Clients MAY add, change, or remove the property for participants where the client is handling the scheduling.This property MUST NOT be included in scheduling messages.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified in any appropriate component.¶
Format Definition: This property is defined by the following notation:¶

scheduling-status = "SCHEDULING-STATUS"
            scheduling-statusparams ":" TEXT CRLF

scheduling-statusparams = *(";" other-param)

4.11. Scheduling-dtstamp

Property name: SCHEDULING-DTSTAMP¶
Purpose: This is the timestamp for the most recent response from this participant.¶

This is the updated property of the last response when using iTIP. It can be compared to the updated property in future responses to detect and discard older responses delivered out of order.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified in any appropriate component.¶
Format Definition: This property is defined by the following notation:¶

scheduling-dtstamp = "SCHEDULING-DTSTAMP"
            scheduling-dtstampparams ":" DATE-TIME CRLF

scheduling-dtstampparams = *(";" other-param)

4.12. Invited-by

Property name: INVITED-BY¶
Purpose: This is the calendar address of the participant who added this participant to the entity, if known.¶
Property Parameters: Non-standard or iana parameters can be specified on this property.¶
Conformance: This property MAY be specified in any appropriate component.¶
Format Definition: This property is defined by the following notation:¶

invited-by = "INVITED-BY"
            invited-byparams ":" CAL-ADDRESS CRLF

invited-byparams = *(";" other-param)

5. Attendee parameters mapping

Table 3
Parameter	iCalendar PARTICIPANT
CN¶	NAME (defined in [RFC7986])¶
CUTYPE¶	KIND (defined here)¶
DELEGATED-FROM¶	PARTICIPATION-DELEGATED-FROM Section 4.3 ¶
DELEGATED-TO¶	PARTICIPATION-DELEGATED-TO (defined here)¶
DIR¶	LINK [RFC9253]¶
LANGUAGE¶	LANG (defined here)¶
MEMBER¶	MEMBER-OF (defined here)¶
PARTSTAT¶	PARTICIPATION-STATUS (defined here)¶
ROLE¶	PARTICIPATION-TYPE (updated here)¶
RSVP¶	EXPECT-REPLY (defined here)¶
SENT-BY¶

6. Security Considerations

There should be no new security risks additional to those noted in [RFC5546].¶

7. IANA Considerations

7.1. Parameter Registrations

This document defines the following new iCalendar property parameters to be added to the registry defined in Section 8.2.4 of [RFC5545]:¶

Table 4
Property Parameter	Status	Reference
REQUIRED¶	Current¶	Section 3.1.1 ¶

7.2. Property Registrations

This document defines the following new iCalendar properties to be added to the registry defined in Section 8.2.3 of [RFC5545]:¶

Table 5
Property	Status	Reference
EXPECT-REPLY¶	Current¶	Section 4.7 ¶
INVITED-BY¶	Current¶	Section 4.12 ¶
KIND¶	Current¶	Section 4.1 ¶
LANG¶	Current¶	Section 4.6 ¶
MEMBER-OF¶	Current¶	Section 4.5 ¶
PARTICIPATION-DELEGATED-FROM¶	Current¶	Section 4.3 ¶
PARTICIPATION-DELEGATED-TO¶	Current¶	Section 4.4 ¶
PARTICIPATION-STATUS¶	Current¶	Section 4.2 ¶
REPLY-URL¶	Current¶	Section 3.2.1 ¶
SCHEDULING-AGENT¶	Current¶	Section 4.8 ¶
SCHEDULING-DTSTAMP¶	Current¶	Section 4.11 ¶
SCHEDULING-FORCE-SEND¶	Current¶	Section 4.9 ¶
SCHEDULING-STATUS¶	Current¶	Section 4.10 ¶

7.3. Updated Participant Type Registrations

This updates the participant types registry defined in Section 11.2.1 of [RFC9073]¶

Table 6
Participant Type	Status	Reference
OWNER¶	Current¶	RFC8984 Section 4.4.6 of [RFC8984]¶
ATTENDEE¶	Current¶	RFC8984 Section 4.4.6 of [RFC8984]¶
OPTIONAL¶	Current¶	RFC8984 Section 4.4.6 of [RFC8984]¶
INFORMATIONAL¶	Current¶	RFC8984 Section 4.4.6 of [RFC8984]¶
CHAIR¶	Current¶	RFC8984 Section 4.4.6 of [RFC8984]¶

8. Acknowledgements

The authors would like to thank the members of the Calendaring and Scheduling Consortium (CalConnect) for contributing their ideas and support.¶

9. Normative References

[RFC2119]: Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", IETF, DOI 10.17487/RFC2119, BCP 14, RFC 2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>.
[RFC5234]: Overell, P. and D. Crocker, "Augmented BNF for Syntax Specifications: ABNF", IETF, STD 68, DOI 10.17487/RFC5234, BCP 68, RFC 5234, January 2008, <https://www.rfc-editor.org/info/rfc5234>.
[RFC5545]: Desruisseaux, B., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", IETF, DOI 10.17487/RFC5545, RFC 5545, September 2009, <https://www.rfc-editor.org/info/rfc5545>.
[RFC5546]: Daboo, C., "iCalendar Transport-Independent Interoperability Protocol (iTIP)", IETF, DOI 10.17487/RFC5546, RFC 5546, December 2009, <https://www.rfc-editor.org/info/rfc5546>.
[RFC5646]: Phillips, A. and M. Davis, "Tags for Identifying Languages", IETF, DOI 10.17487/RFC5646, BCP 47, RFC 5646, September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[RFC6638]: Daboo, C. and B. Desruisseaux, "Scheduling Extensions to CalDAV", IETF, DOI 10.17487/RFC6638, RFC 6638, June 2012, <https://www.rfc-editor.org/info/rfc6638>.
[RFC7986]: Daboo, C., "New Properties for iCalendar", IETF, DOI 10.17487/RFC7986, RFC 7986, October 2016, <https://www.rfc-editor.org/info/rfc7986>.
[RFC8984]: Jenkins, N. and R. Stepanek, "JSCalendar: A JSON Representation of Calendar Data", IETF, DOI 10.17487/RFC8984, RFC 8984, July 2021, <https://www.rfc-editor.org/info/rfc8984>.
[RFC9073]: Douglass, M., "Event Publishing Extensions to iCalendar", IETF, DOI 10.17487/RFC9073, RFC 9073, August 2021, <https://www.rfc-editor.org/info/rfc9073>.
[RFC9253]: Douglass, M., "Support for iCalendar Relationships", IETF, DOI 10.17487/RFC9253, RFC 9253, August 2022, <https://www.rfc-editor.org/info/rfc9253>.

Author's Address

Michael Douglass

Email: mdouglass@bedework.com