One document matched: draft-ietf-calsch-imp-guide-01.txt
Differences from draft-ietf-calsch-imp-guide-00.txt
Network Working Group
Guide to Implementors Bob Mahoney/MIT
Internet-Draft Alexander Taler/CS&T
<draft-ietf-calsch-imp-guide-01.txt> George Babics/CS&T
July 14, 2000
Expires: January 14, 2001
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.
Copyright (C) The Internet Society 2000. All Rights Reserved.
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.
[Note: in the past there has been some discussion as to whether iRIP
was a live effort, given that interest has waned and some functionality
has been moved to CAP. What's the status?]
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
Expires January 2001 [Page 2]
Draft Implementors' Guide to Internet Calendaring July 2000
Protocol Requirements
3. Standards Solution
Examples
Systems
Standalone single-user system
Single-user systems communicating
4. Open Issues
Choice of Transport
Scheduling People, not calendars
Administration
Notification
5. Security Considerations
Access Control
Authentication
Using Email
Other issues
6. Acknowledgements
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.
Expires January 2001 [Page 3]
Draft Implementors' Guide to Internet Calendaring July 2000
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.
1.2 Concepts and Relationships
[A rough outline, based on some comments from Bruce. We have some
basic problems throughout this doc with exactly where our real-time
efforts are concentrated, iRIP or CAP. We do not currently have an
unexpired iRIP document. There has been some discussion in the past
noting that the iRIP intent has largely been rolled into CAP. We need
to settle on an approach. iRIP has been left in this draft for the
moment, but overlap is apparent]
iCalendar is the Language to be used in calendar events.
iTIP is how you use the language.
iMIP is further definition for use over email.
CAP/iRIP is the Language used over a real-time transport.
Another way to put it is as follows:
iCalendar are the words
iTIP is the grammar book or the "Rosetta Stone".
iMIP is "expressing it in email terminology" an EMAIL dictionary
CAP/iRIP is "expressing it for use in a Real Time transport"
Expires January 2001 [Page 4]
Draft Implementors' Guide to Internet Calendaring July 2000
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 organize 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.
f] A doctor wishes to keep track of all his appointments.
Need: Read and manipulate one's own calendar with only one CUA.
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
Expires January 2001 [Page 5]
Draft Implementors' Guide to Internet Calendaring July 2000
[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.
Expires January 2001 [Page 6]
Draft Implementors' Guide to Internet Calendaring July 2000
------------------
| 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.
Expires January 2001 [Page 7]
Draft Implementors' Guide to Internet Calendaring July 2000
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.
f] The doctor can use a proprietary CUA with a local store,
and perhaps use [ICAL] as a storage mechanism.
3.2 Systems
The following diagrams illustrate possible example systems and usage
of the protocols.
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.
Expires January 2001 [Page 8]
Draft Implementors' Guide to Internet Calendaring July 2000
----------- 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
/ \ ----------- ----------- / \
3.2.3 Single-user with multiple CUA
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 an accessibility. Some of these clients may have
local stores and others may not. If they do, then they need to
ensure that the data on the CUA is synchronized 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. One may be work
related, another for personal use. The CUA may or may not have a
local store. If it does, then it needs to ensure that the data on
the CUA is synchronized with the data on both of the CS.
Expires January 2001 [Page 9]
Draft Implementors' Guide to Internet Calendaring July 2000
----------
+------------[CAP]------ | CS |
| | |
O ----------- ----------
-+- | CUA |
A | |
/ \ -----------
| ----------
+------------[CAP]------ | CS |
| |
----------
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 CUA and service. The CUA may or may not have
a local store. If they do, then they need to ensure that the
data on the CUA is synchronized 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
user on a different multi user system. The services can
communicate using [CAP]
O ----------- ----------
-+- | CUA w | -----[CAP]-------| CS |
A |local store| | |
/ \ ----------- ----------
|
[CAP]
|
O ----------- ----------
-+- | CUA w/o | -----[CAP]-------| CS |
A |local store| | |
/ \ ----------- ----------
Expires January 2001 [Page 10]
Draft Implementors' Guide to Internet Calendaring July 2000
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 Choice of Transport
There are issues to be aware of in choosing a transport mechanism.
The choices are a network protocol, such as CAP, or a store and forward
(email) solution.
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 innately time-sensitive
data to unbounded latency. Large or heavily utilized mail systems may
experience an unacceptable delay in message receipt.
4.2 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.
4.3 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.
4.4 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
Expires January 2001 [Page 11]
Draft Implementors' Guide to Internet Calendaring July 2000
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. [CAP] uses SASL for this authentication.
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.
Expires January 2001 [Page 12]
Draft Implementors' Guide to Internet Calendaring July 2000
With both [iMIP] and [CAP], the possibilities of Denial of Service
attacks must be considered. The ability to flood a calendar system
with bogus requests is likely to be exploited once these systems
become widely deployed, and detection and recovery methods will need
to be considered.
6. Acknowledgements
Thanks to the following who have participated in the development of
this document:
Eric Busboom, Pat Egen, David Madeo, Shawn Packwood, Bruce Kahn.
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: alex@elea.dhs.org
Bob Mahoney
MIT
E40-327
77 Massachusetts Avenue
Cambridge, MA 02139
Tel: (617) 253-0774
Email: bobmah@mit.edu
Expires January 2001 [Page 13]
Draft Implementors' Guide to Internet Calendaring July 2000
George Babics
Research & Development
Corporate Software & Technologies
3333 Graham Boulevard, 5th floor
MontrÄal, QuÄbec, Canada
H3R 3L5
Tel: (514) 733-8500 x303
Fax: (514) 733-8878
E-mail: georgeb@cst.ca
9. Full Copyright Statement
"Copyright (C) The Internet Society 2000. 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
| PAFTECH AB 2003-2026 | 2026-04-24 12:48:41 |