📄 rfc3283.txt
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[RFC-2445] format, and have semantics that identify the message as
being an invitation to a meeting, an acceptance of an invitation,
or the assignment of a task.
iTIP [RFC-2446] messages are used in the scheduling workflow,
where users exchange messages in order to organize things such as
events and to-dos. CUAs generate and interpret iTIP [RFC-2446]
messages at the direction of the calendar user. With iTIP [RFC-
2446] users can create, modify, delete, reply to, counter, and
decline counters to the various iCalendar [RFC-2445] components.
Furthermore, users can also request the free/busy time of other
people.
iTIP [RFC-2446] is transport-independent, and has one specified
transport binding: iMIP [RFC-2447] binds iTIP to e-mail. In
addition [CAP] will provide a real-time binding of iTIP [RFC-
2446], allowing CUAs to perform calendar management and scheduling
over a single connection.
- Calendar management protocol: [CAP]
[CAP] describes the messages used to manage calendars on a
calendar store. These messages use iCalendar [RFC-2445] to
describe various components such as events and to-dos. These
messages make it possible to perform iTIP [RFC-2446] operations,
as well as other operations relating to a calendar store such as
searching, creating calendars, specifying calendar properties, and
specifying calendar access rights.
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3. Solutions
3.1 Examples
Returning to the scenarios presented in section 2.1, the calendaring
protocols can be used in the following ways:
a] The doctor can use a proprietary CUA with a local store, and
perhaps use iCalendar [RFC-2445] as a storage mechanism. This
would allow her to easily import her data store into another
application that supports iCalendar [RFC-2445].
b] The musician who wishes to access her agenda from anywhere can
use a [CAP]-enabled calendar service accessible over the Internet.
She can then use any available [CAP] clients to access the data.
A proprietary system that provides access through a Web-based
interface could also be employed, but the use of [CAP] would be
superior in that it would allow the use of third party
applications, such as PDA synchronization tools.
c] The development team can use a calendar service which supports
[CAP], and each member can use a [CAP]-enabled CUA of their
choice.
Alternatively, each member could use an iMIP [RFC-2447]-enabled
CUA, and they could book meetings over e-mail. This solution has
the drawback that it is difficult to examine other users' agendas,
making the organization of meetings more difficult.
Proprietary solutions are also available, but they require that
all members use clients by the same vendor, and disallow the use
of third party applications.
d] The teacher can set up a calendar service, and have students
book time through any of the iTIP [RFC-2446] bindings. [CAP]
provides real-time access, but could require additional
configuration. iMIP [RFC-2447] would be the easiest to configure,
but may require more e-mail processing.
If [CAP] access is provided then determining the state of the
teacher's schedule is straightforward. If not, this can be
determined through iTIP [RFC-2446] free/busy requests. Non-
standard methods could also be employed, such as serving up
iCalendar [RFC-2445], HTML, or XML over HTTP.
A proprietary system could also be used, but would require that
all students be able to use software from a specific vendor.
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e] [CAP] would be preferred for publishing a movie theater's
schedule, since it provides advanced access and search
capabilities. It also allows easy integration with customers'
calendar systems.
Non-standard methods such as serving data over HTTP could also be
employed, but would be harder to integrate with customers'
systems.
Using a completely proprietary solution would be very difficult,
if not impossible, since it would require every user to install
and use the proprietary software.
f] The social club could distribute meeting information in the
form of iTIP [RFC-2446] messages, sent via e-mail using iMIP
[RFC-2447]. The club could distribute meeting invitations, as
well as a full published agenda.
Alternatively, the club could provide access to a [CAP]-enabled
calendar service. However, this solution would be more expensive
since it requires the maintenance of a server.
3.2 Systems
The following diagrams illustrate possible systems and their usage of
the various protocols.
3.2.1 Standalone Single-user System
A single user system that does not communicate with other systems
need not employ any of the protocols. However, it may use iCalendar
[RFC-2445] as a data format in some places.
----------- O
| CUA w/ | -+- user
|local store| A
----------- / \
3.2.2 Single-user Systems Communicating
Users with single-user systems may schedule meetings with each others
using iTIP [RFC-2446]. The easiest binding of iTIP [RFC-2446] to use
would be iMIP [RFC-2447], since messages can be held in the users'
mail queues, which we assume to already exist. [CAP] could also be
used.
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O ----------- ----------- O
-+- | CUA w/ | -----[iMIP]----- | CUA w/ | -+- user
A |local store| Internet |local store| A
/ \ ----------- ----------- / \
3.2.3 Single-user with Multiple CUAs
A single user may use more than one CUA to access his or her
calendar. The user may use a PDA, a Web client, a PC, or some other
device, depending on accessibility. Some of these clients may have
local stores and others may not. Those with local stores need to
synchronize the data on the CUA with the data on the CS.
-----------
| CUA w | -----[CAP]----------+
|local store| |
O ----------- ----------
-+- | CS |
A | |
/ \ ----------
----------- |
| CUA w/o | -----[CAP]----------+
|local store|
-----------
3.2.4 Single-user with Multiple Calendars
A single user may have many independent calendars; for example, one
may contain work-related information and another personal
information. The CUA may or may not have a local store. If it does,
then it needs to synchronize the data of the CUA with the data on
both of the CS.
----------
+------------[CAP]------ | CS |
| | |
O ----------- ----------
-+- | CUA |
A | |
/ \ -----------
| ----------
+------------[CAP]------ | CS |
| |
----------
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3.2.5 Users Communicating on a Multi-user System
Users on a multi-user system may schedule meetings with each other
using [CAP]-enabled CUAs and services. The CUAs may or may not have
local stores. Those with local stores need to synchronize the data
on the CUAs with the data on the CS.
O -----------
-+- | CUA w | -----[CAP]----------+
A |local store| |
/ \ ----------- ----------
| CS |
| |
----------
O ----------- |
-+- | CUA w/o | -----[CAP]----------+
A |local store|
/ \ -----------
3.2.6 Users Communicating through Different Multi-user Systems
Users on a multi-user system may need to schedule meetings with users
on a different multi-user system. The services can communicate using
[CAP] or iMIP [RFC-2447].
O ----------- ----------
-+- | CUA w | -----[CAP]-------| CS |
A |local store| | |
/ \ ----------- ----------
|
[CAP] or [iMIP]
|
O ----------- ----------
-+- | CUA w/o | -----[CAP]-------| CS |
A |local store| | |
/ \ ----------- ----------
4. Important Aspects
There are a number of important aspects of these calendaring
standards of which people, especially implementers, should be aware.
4.1 Timezones
The dates and times in components can refer to a specific time zone.
Time zones can be defined in a central store, or they may be defined
by a user to fit his or her needs. All users and applications should
be aware of time zones and time zone differences. New time zones may
Mahoney, et. al. Informational [Page 10]
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need to be added, and others removed. Two different vendors may
describe the same time zone differently (such as by using a different
name).
4.2 Choice of Transport
There are issues to be aware of in choosing between a network
protocol such as [CAP], or a store and forward protocol, such as iMIP
[RFC-2447].
The use of a network ("on-the-wire") mechanism may require some
organizations to make provisions to allow calendaring traffic to
traverse a corporate firewall on the required ports. Depending on
the organizational culture, this may be a challenging social
exercise.
The use of an email-based mechanism exposes time-sensitive data to
unbounded latency. Large or heavily utilized mail systems may
experience an unacceptable delay in message receipt.
4.3 Security
See the "Security Considerations" (Section 6) section below.
4.4 Amount of data
In some cases, a component may be very large, for instance, a
component with a very large attachment. Some applications may be
low-bandwidth or may be limited in the amount of data they can store.
Maximum component size may be set in [CAP]. It can also be
controlled in iMIP [RFC-2447] by restricting the maximum size of the
e-mail that the application can download.
4.5 Recurring Components
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