CalDAV Scheduling (RFC 6638)

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This document specifies extensions to the CalDAV "calendar-access" [RFC4791] feature to enable scheduling of iCalendar-based [RFC5545] calendar components between calendar users.

This extension leverages the scheduling methods defined in the iCalendar Transport-independent Interoperability Protocol (iTIP) [RFC5546] to permit calendar users to perform scheduling operations such as schedule, reschedule, respond to scheduling request, or cancel calendar components, as well as search for busy time information. However, the following iTIP [RFC5546] features are not covered: publishing, countering, delegating, refreshing, and forwarding calendar components, as well as replacing the "Organizer" of a calendar component. It is expected that future extensions will be developed to address these.

This specification defines a client/server scheduling protocol, where the server is made responsible for sending scheduling messages and processing incoming scheduling messages. The client operations of creating, modifying, or deleting a calendar component in a calendar are enough to trigger the server to deliver the necessary scheduling messages to the appropriate calendar users. This approach is sometimes referred to as "implicit scheduling".

This specification only addresses how scheduling occurs with users on a single system (i.e., scheduling between CalDAV servers, or some other calendaring and scheduling system, is not defined). However, this specification is compatible with servers being able to send or receive scheduling messages with "external" users (e.g., using the iCalendar Message-Based Interoperability Protocol (iMIP) [RFC6047]).

Section 3 defines the automated "Scheduling Operations" that allow a client to store iCalendar data on a CalDAV server, with the server taking specific actions in response. One of three scheduling operations can take place -- "create", "modify", or "remove", based on the HTTP method used for the request -- in addition to a comparison between any existing and any new iCalendar data.

Section 4 defines how the server processes scheduling messages sent as the result of a scheduling operation.

Section 5 defines how freebusy requests with an immediate response are accomplished.

Section 6 defines access control privileges for the scheduling operations defined in this specification.

For the majority of the following discussion, scheduling of events will be discussed. However, scheduling of to-dos is also fully supported by this specification.

This specification has been under development for a number of years, and most current implementations of CalDAV support it. With the publication of this document, it is expected that all new CalDAV implementations will support it by default. Interoperability tests have been performed regularly. Significant issues with incompatible CalDAV implementations are not anticipated.