One document matched: draft-ietf-calsch-imp-guide-00.txt
Guide to Implementors
Network Working Group Bob Mahoney/MIT
Internet-Draft Alexander Taler/CS&T
<draft-ietf-calsch-imp-guide-00.txt>
4-Oct-99
Expires: <date + 6 months>
Implementors' Guide to Internet Calendaring
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
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 documents as
Internet-Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document describes the relationship between the various internet
calendaring and scheduling protocols defined by RFC 2445 (iCalendar),
RFC 2446 (iTIP), and RFC 2447 (iMIP), as well as the works in
progress,"iCalendar Real-time Interoperability Protocol" (iRIP),
and "Calendar Access Protocol" (CAP). It's intention is to provide
a context for these protocols, assist in their understanding, and
ultimately help implementors in the design of their internet
calendaring and scheduling systems.
This document also describes issues and problems which are not solved
by these protocols, and could be targets for future work.
Status of this Memo
1. Introduction
Terminology
2. Requirements
Fundamental Need
Protocol Requirements
3. Standards Solution
Examples
Systems
Standalone single-user system
Single-user systems communicating
4. Open Issues
Scheduling People, not calendars
Administration
Notification
5. Security Considerations
Access Control
Authentication
Using Email
Other issues
6. Acknowldegements
7. Bibliography
8. Author's Addresses
9. Full Copyright Statement
1. Introduction
The calendaring and scheduling protocols are intended to provide for
the needs of individuals attempting to obtain information and
schedule meetings across the internet, organizations attempting to
provide information on the internet, as well as organizations looking
for a calendaring and scheduling solution to deploy internally.
It is the intent of this document to provide guidance for
implementors of calendaring and scheduling products in determining
which of the various existing protocol documents are applicable to
their work, as well as providing some background information and
pointers to the less obvious implications of the available choices.
Problems not solved by these protocols, as well as security issues
to be kept in mind, are discussed at the end of the document.
1.1 Terminology
This memo uses much of the same terminology as [ICAL], [ITIP],
[IMIP], [IRIP] and [CAP]. The following definitions are provided as
introductory, the definitions in the protocol specifications are the
canonical ones.
Calendar
A collection of events, todos, journal entries, etc. A calendar
could be the content of a person's or a resource's agenda; it
could also be a collection of data serving a more specialized
need. Calendars are the basic storage containers for calendaring
information.
Calendar Access Rights
A set of rules for a calendar describing who may perform which
operations on that calendar, such as reading and writing
information.
Calendar Service
A running server application which provides access to a
collection of calendars.
Calendar Store
A data store of a calendar service. A calendar service may have
several calendar stores, and each store may contain several
calendars, as well as properties and components outside of the
calendars.
Calendar User
An entity (often a human) which accesses calendar information.
Calendar User Agent (CUA)
Software used by the calendar user which communicates with
calendar services to provide the user access to calendar
information.
Component
A piece of calendar data such as an event, a todo or an alarm.
Information about components is stored as properties of those
components.
Property
A property of a component, such as a description or a start time.
2. Requirements
2.1 Fundamental Needs
The following examples illustrate people's basic calendaring and
scheduling needs:
a] A busy musician wants to maintain her schedule on an
internet-based agenda which she can access from anywhere.
Need: Read and manipulate one's own calendar.
b] A software development team wishes to share agenda information
by using a group scheduling product in order to more effectively
schedule their time.
Need: Share calendar information with users using the same
calendar service.
c] A teacher wants his students to be able to book time slots
during his office hours.
Need: Schedule calendar events and todos with users using the
same calendar service.
d] A movie theatre wants to publish its schedule so that
prospective customers can easily access it.
Need: Share calendar information with users using other calendar
services, possibly from different vendors.
e] A social club wants to be able to organise events more
effectively by booking time with its members.
Need: Schedule calendar events and todos with users using other
calendar services, possibly from different vendors.
2.2 Protocol requirements
The first three needs can be satisfied through proprietary solutions,
but the last two cannot. From these needs we can establish that
protocols are required for accessing information in a calendar store,
and for scheduling events and todos. In addition these protocols
require a data format for representing calendar information.
These roles are filled by the following protocol requirements.
- [ICAL] is the data format
[ICAL] provides data format for representing calendar information
which the other protocols can use. [ICAL] can also be used in
other contexts such as a drag and drop format or an export/import
format.
All the other protocols depend on [ICAL], so all elements of a
standards-based calendaring and scheduling systems will have to
interpret [ICAL].
- [ITIP] is the scheduling protocol
[ITIP] describes the messages used to schedule calendar events.
These messages are represented in [ICAL], and have semantics that
include such things as being an invitation to a meeting, an
acceptance of an invitation or the assignation of a task.
[ITIP] messages are used in the scheduling work flow, where users
exchange messages in order to organize things such as events and
todos. CUAs generate and interpret [ITIP] messages at the
direction of the calendar user.
[ITIP] is transport-independent, but has two specified transport
bindings, [IMIP] is a binding to email and [IRIP] is a real-time
binding. In addition [CAP] will provide a second real-time
binding of [ITIP], allowing CUAs to perform calendar management
as well as scheduling over a single connection.
Both CUAs and calendar services may have [ITIP] interpreters.
- [CAP] is the calendar management protocol
[CAP] describes the messages used to manage calendars. These
messages are represented in [ICAL], and have semantics such as
being a search for data, being data in response to a search or
the being the creation of a meeting.
[CAP] also provides a real-time binding for the calendar
management messages. Although other bindings, such as an email
binding, could be defined, this is not done because it is
inappropriate for this protocol.
The following diagram describes the implementation dependencies
between the protocols. A calendar system using these standards
will implement at least one of the leaves of the tree. The
calendar management message and transport protocol parts of CAP are
separated in the diagram to highlight its relationship to ITIP.
------------------
| iCalendar |
------------------
|
|
|
-------------------------------------
| |
------------------ |
| iTIP | |
------------------ |
| |
| ----------|-------
| | CAP | |
| | message |
---------------------------------------- format |
| | | | | |
---------- ----------- | | | |
| Session | | E-mail | | transport |
| iRIP | | iMIP | | protocol |
---------- ----------- ------------------
3. Solutions
3.1 Examples
Returning to the examples of section 2.1, they can be solved using
the protocols in the following ways:
a] The musician who wishes to access her agenda from anywhere can
use a [CAP] enabled calendar service accessible through the
internet. She can then use whichever [CAP] clients are
available to access the data.
A proprietary system could also be employed which provides
access through a web-based interface, but the use of [CAP] would
be superior in that it would allow the use of third party tools,
such as PDA synchronization tools.
b] The development team can use a calendar service which supports
[CAP] and then each member can use a [CAP]-enabled CUA of their
choice.
Alternatively, each member could use an [IMIP]-enabled CUA, and
they could book meetings over email. This solution has the
drawback that it is difficult to examine the other agendas,
making organizing meetings more difficult.
Proprietary solutions are also available, but they require that
all people use clients by the same vendor, and disallow the use
of third party applications.
c] The teacher can set up a calendar service, and have students
book time through any of the [ITIP] bindings. [CAP] or [IRIP]
provide real-time access, but could require additional
configuration. [IMIP] would be the easiest to configure, but
may require more email 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] free-busy requests. Non-standard
methods could also be employed, such as serving up ICAL, HTML,
XML through HTTP.
A proprietary system could also be used, but would require that
all students be able to use software from a specific vendor.
d] For publishing a movie theatre's schedule [CAP] provides the
most advanced access and search capabilities. It also allows
easy integration with its customer's calendar systems.
Non-standard methods such as serving data over HTTP could also
be employed, but would be harder to integrate with customer's
systems.
Using a completely proprietary solutions would be very difficult
since it would require every user to install and use proprietary
software.
e] The social club could distribute meeting information in the form
of [ITIP] messages. This could be done over email using [IMIP],
or [IRIP] depending on the recipient. Meeting invitations, as
well as a full published agenda could be distributed.
Alternatively, the social 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 example systems and usage
of the protocols. [ed. More coming]
3.2.1 Standalone single-user system
A single user system which does not communicate with other systems
need not employ any of the protocols. However, it may use [ICAL] 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 other
using [ITIP]. The easiest binding of [ITIP] to use is [IMIP], since
it messages can be held in their mail queue, which we assume to
already exist. [IRIP] or [CAP] would require at least one user to run
a listening server.
O ----------- ----------- O
-+- | CUA w/ | -----[IMIP]----- | CUA w/ | -+- user
A |local store| Internet |local store| A
/ \ ----------- ----------- / \
4. Open Issues
Many issues are not currently resolved by these protocols, and many
desirable features are not yet provided. Some of the more prominent
ones follow.
4.1 Scheduling people, not calendars
Meetings are scheduled with people, however people may have many
calendars, and may store these calendars in many places. There may
also be many routes to contact them. These protocols do not attempt
to provide unique access for contacting a single person. Instead,
'calendar addresses' are booked, which may be email addresses or
individual calendars. It is up to the users themselves to
orchestrate mechanisms to ensure that the bookings go to the right
place.
4.2 Administration
These protocols do not address the issues of administering users and
calendars on a calendar service. This must be handled by proprietary
mechanisms for each implementation.
4.3 Notification
People often wish to be notified of upcoming events, new events, or
changes to events. These protocols do not attempt to address these
needs in a real-time fashion. Instead, the ability to store alarm
information on events is provided, which can be used to provide
client-side notification of upcoming events. To organize
notification of new or changed events clients will have to poll the
data store.
5. Security considerations
5.1 Access Control
There has to be reasonable granularity in the configuration options
for access to data through [CAP], so that what should be released to
requestors is, and what shouldn't isn't. Details of handling this
are described in [CAP].
5.2 Authentication
Access control must be coupled with a good authentication system, so
that the right people get the right information. For [CAP] this
means requiring authentication before any data base access can be
performed, and checking access rights and authentication credentials
before releasing information. In [IMIP], this may present some
challenges, as authentication is often not a consideration in
store-and-forward protocols.
Authentication is also important for scheduling, in that receivers of
scheduling messages should be able to validate the apparent sender.
Since scheduling messages are wrapped in MIME, signing and encryption
is available for free. For messages transmitted over mail this is
the only available alternative. It is suggested that developers take
care in implementing the security features in [IMIP], bearing in
mind that the concept and need may be foreign or non-obvious to users,
yet essential for the system to function as they might expect.
The real-time protocols provide for the authentication of users, and
the preservation of that authentication information, allowing for
validation by the receiving end-user or server.
5.3 Using email
Because scheduling information can be transmitted over mail without
any authentication information, email spoofing is extremely easy if
the receiver is not checking for authentication. It is suggested
that implementors consider requiring authentication as a default,
using mechanisms such as are described in Section 2 of [IMIP].
The use of email, and the potential for anonymous connections, means
that 'calendar spam' is possible. Developers should consider this
threat when designing systems, particularly those that allow for
automated request processing.
5.4 Other issues
The current security context should be obvious to users. Because the
underlying mechanisms may not be clear to users, efforts to make
clear the current state in the UI should be made. One example is the
'lock' icon used in some web browsers during secure connections.
6. Acknowledgements
Thanks to the following who have participated in the development of
this document:
Eric Busboom, Pat Egen, David Madeo, Shawn Packwood.
7. Bibliography
[ICAL] [RFC-2445] Calendaring and Scheduling Core Object Specification
[ITIP] [RFC-2446] iCalendar Transport-Independent Interoperability
Protocol
[IMIP] [RFC-2447] iCalendar Message-Based Interoperability Protocol
[IRIP] draft-ietf-calsch-irip iCalendar Real-time Interoperability
Protocol
[CAP] draft-ietf-calsch-cap Calendar Access Protocol
[RFC-1847] Security Multiparts for MIME
[RFC-2045] MIME Part 1: Format of Internet Message Bodies
[RFC-2046] MIME Part 2: Media Types
[RFC 2047] MIME Part 3: Message Header Extensions for Non-ASCII Text
[RFC-2048] MIME Part 4: Registration Procedures
[RFC-2049] MIME Part 5: Conformance Criteria and Examples
8. Author's Addresses
Alexander Taler
CS&T
3333 Graham Boulevard, 5th Floor
Montreal, QC H3R 3L5
Tel: (514) 733-8500
Email: alext@cst.ca
Bob Mahoney
MIT
E40-327
77 Massachusetts Avenue
Cambridge, MA 02139
Tel: (617) 253-0774
Email: bobmah@mit.edu
9. Full Copyright Statement
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