draft-ietf-calsch-inetcal-guide-02.txt   rfc3283.txt 
Network Working Group B. Mahoney Network Working Group B. Mahoney
Internet-Draft MIT Request for Comments: 3283 MIT
Expires: January 16, 2002 G. Babics Category: Informational G. Babics
Steltor Steltor
A. Taler A. Taler
July 18, 2001 June 2002
Guide to Internet Calendaring Guide to Internet Calendaring
draft-ietf-calsch-inetcal-guide-02
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This memo provides information for the Internet community. It does
all provisions of Section 10 of RFC2026. not specify an Internet standard of any kind. Distribution of this
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved. Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract Abstract
This document describes the various Internet calendaring and This document describes the various Internet calendaring and
scheduling standards and works in progress, and the relationships scheduling standards and works in progress, and the relationships
between them. Its intent is to provide a context for these between them. Its intent is to provide a context for these
documents, assist in their understanding, and potentially help in the documents, assist in their understanding, and potentially aid in the
design of standards-based calendaring and scheduling systems. The design of standards-based calendaring and scheduling systems. The
standards addressed are RFC 2445 (iCalendar), RFC 2446 (iTIP), and standards addressed are RFC 2445 (iCalendar), RFC 2446 (iTIP), and
RFC 2447 (iMIP). The work in progress addressed is "Calendar Access RFC 2447 (iMIP). The work in progress addressed is "Calendar Access
Protocol" (CAP). This document also describes issues and problems Protocol" (CAP). This document also describes issues and problems
that are not solved by these protocols, and that could be targets for that are not solved by these protocols, and that could be targets for
future work. future work.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Concepts and Relationships . . . . . . . . . . . . . . . . . 5 1.2 Concepts and Relationships . . . . . . . . . . . . . . . . . 4
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Fundamental Needs . . . . . . . . . . . . . . . . . . . . . 6 2.1 Fundamental Needs . . . . . . . . . . . . . . . . . . . . . 4
2.2 Protocol Requirements . . . . . . . . . . . . . . . . . . . 6 2.2 Protocol Requirements . . . . . . . . . . . . . . . . . . . 5
3. Solutions . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. Solutions . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2 Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2.1 Standalone Single-user System . . . . . . . . . . . . . . . 9 3.2.1 Standalone Single-user System . . . . . . . . . . . . . . . 8
3.2.2 Single-user Systems Communicating . . . . . . . . . . . . . 9 3.2.2 Single-user Systems Communicating . . . . . . . . . . . . . 8
3.2.3 Single-user with Multiple CUAs . . . . . . . . . . . . . . . 10 3.2.3 Single-user with Multiple CUAs . . . . . . . . . . . . . . . 9
3.2.4 Single-user with Multiple Calendars . . . . . . . . . . . . 10 3.2.4 Single-user with Multiple Calendars . . . . . . . . . . . . 9
3.2.5 Users Communicating on a Multi-user System . . . . . . . . . 11 3.2.5 Users Communicating on a Multi-user System . . . . . . . . . 10
3.2.6 Users Communicating through Different Multi-user Systems . . 11 3.2.6 Users Communicating through Different Multi-user Systems . . 10
4. Important Aspects . . . . . . . . . . . . . . . . . . . . . 12 4. Important Aspects . . . . . . . . . . . . . . . . . . . . . 10
4.1 Timezones . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1 Timezones . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2 Choice of Transport . . . . . . . . . . . . . . . . . . . . 12 4.2 Choice of Transport . . . . . . . . . . . . . . . . . . . . 11
4.3 Security . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.3 Security . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.4 Amount of data . . . . . . . . . . . . . . . . . . . . . . . 12 4.4 Amount of data . . . . . . . . . . . . . . . . . . . . . . . 11
4.5 Recurring Components . . . . . . . . . . . . . . . . . . . . 12 4.5 Recurring Components . . . . . . . . . . . . . . . . . . . . 11
5. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . 14 5. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1 Scheduling People, not Calendars . . . . . . . . . . . . . . 14 5.1 Scheduling People, not Calendars . . . . . . . . . . . . . . 12
5.2 Administration . . . . . . . . . . . . . . . . . . . . . . . 14 5.2 Administration . . . . . . . . . . . . . . . . . . . . . . . 12
5.3 Notification . . . . . . . . . . . . . . . . . . . . . . . . 14 5.3 Notification . . . . . . . . . . . . . . . . . . . . . . . . 12
6. Security considerations . . . . . . . . . . . . . . . . . . 15 6. Security Considerations . . . . . . . . . . . . . . . . . . 12
6.1 Access Control . . . . . . . . . . . . . . . . . . . . . . . 15 6.1 Access Control . . . . . . . . . . . . . . . . . . . . . . . 12
6.2 Authentication . . . . . . . . . . . . . . . . . . . . . . . 15 6.2 Authentication . . . . . . . . . . . . . . . . . . . . . . . 12
6.3 Using E-mail . . . . . . . . . . . . . . . . . . . . . . . . 15 6.3 Using E-mail . . . . . . . . . . . . . . . . . . . . . . . . 13
6.4 Other Issues . . . . . . . . . . . . . . . . . . . . . . . . 16 6.4 Other Issues . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 16 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 13
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 17 References . . . . . . . . . . . . . . . . . . . . . . . . . 14
B. Bibliography . . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 15
Full Copyright Statement . . . . . . . . . . . . . . . . . . 19 Full Copyright Statement . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
Calendaring and scheduling protocols are intended to aid individuals Calendaring and scheduling protocols are intended to aid individuals
in obtaining calendaring information and scheduling meetings across in obtaining calendaring information and scheduling meetings across
the Internet, to aid organizations in providing calendaring the Internet, to aid organizations in providing calendaring
information on the Internet, and to provide for organizations looking information on the Internet, and to provide for organizations looking
for a calendaring and scheduling solution to deploy internally. for a calendaring and scheduling solution to deploy internally.
It is the intent of this document to provide a context for these It is the intent of this document to provide a context for these
documents, assist in their understanding, and potentially help in the documents, assist in their understanding, and potentially help in the
design of standards-based calendaring and scheduling systems. design of standards-based calendaring and scheduling systems.
Problems not solved by these protocols, as well as security issues to Problems not solved by these protocols, as well as security issues to
be kept in mind, are discussed at the end of the document. be kept in mind, are discussed at the end of the document.
1.1 Terminology 1.1 Terminology
This memo uses much of the same terminology as iCalendar [RFC-2445], This memo uses much of the same terminology as iCalendar [RFC-2445],
iTIP [RFC-2446], iMIP [RFC-2447], and [CAP]. The following iTIP [RFC-2446], iMIP [RFC-2447], and [CAP]. The following
definitions are provided as an introducttion; the definitions in the definitions are provided as an introduction; the definitions in the
protocol specifications themselves should be considered canonical. protocol specifications themselves should be considered canonical.
Calendar Calendar
A collection of events, to-dos, journal entries, etc. A calendar A collection of events, to-dos, journal entries, etc. A calendar
could be the content of a person or resource's agenda; it could could be the content of a person or resource's agenda; it could
also be a collection of data serving a more specialized need. also be a collection of data serving a more specialized need.
Calendars are the basic storage containers for calendaring Calendars are the basic storage containers for calendaring
information. information.
Calendar Access Rights Calendar Access Rights
A set of rules defining who may perform what operations, such as A set of rules defining who may perform what operations, such as
reading or writing information, on a given calendar. reading or writing information, on a given calendar.
Calendar Service Calendar Service
A running server application that provides access to a number of A running server application that provides access to a number of
calendars. calendar stores.
Calendar Store (CS) Calendar Store (CS)
A data store of a calendar service. A calendar service may have A data store of a calendar service. A calendar service may have
several calendar stores, and each store may contain several several calendar stores, and each store may contain several
calendars, as well as properties and components outside of those calendars, as well as properties and components outside of those
calendars. calendars.
Calendar User (CU) Calendar User (CU)
An entity (often a human) that accesses calendar information. An entity (often a human) that accesses calendar information.
Calendar User Agent (CUA) Calendar User Agent (CUA)
Software with which the calendar user communicates with a calendar Software with which the calendar user communicates with a calendar
service or local calendar store to access calendar information. service or local calendar store to access calendar information.
Component Component
A piece of calendar data such as an event, a to-do or an alarm. A piece of calendar data such as an event, a to-do or an alarm.
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service or local calendar store to access calendar information. service or local calendar store to access calendar information.
Component Component
A piece of calendar data such as an event, a to-do or an alarm. A piece of calendar data such as an event, a to-do or an alarm.
Information about components is stored as properties of those Information about components is stored as properties of those
components. components.
Delegator Delegator
A calendar user (sometimes called the delegatee) who has assigned A calendar user who has assigned his or her participation in a
his or her participation in a scheduled calendar component (e.g. scheduled calendar component (e.g. a VEVENT) to another calendar
a VEVENT) to another calendar user (sometimes called the delegate user (sometimes called the delegate or delegatee). An example of
or delegatee). An example of a delegator is a busy executive a delegator is a busy executive sending an employee to a meeting
sending an employee to a meeting in his or her place. in his or her place.
Delegate Delegate
A calendar user (sometimes called the delegatee) who has been A calendar user (sometimes called the delegatee) who has been
assigned to participate in a scheduled calendar component (e.g. a assigned to participate in a scheduled calendar component (e.g. a
VEVENT) by one of the attendees in that component (sometimes VEVENT) in place of one of the attendees in that component
called the delegator). An example of a delegate is a team member (sometimes called the delegator). An example of a delegate is a
sent to a particular meeting. team member sent to a particular meeting.
Designate Designate
A calendar user authorized to act on behalf of another calendar A calendar user authorized to act on behalf of another calendar
user. An example of a designate is an assistant scheduling user. An example of a designate is an assistant scheduling
meetings for his or her superior. meetings for his or her superior.
Local Store Local Store
A CS that is on the same device as the CUA. A CS that is on the same device as the CUA.
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1.2 Concepts and Relationships 1.2 Concepts and Relationships
iCalendar is the language used to describe calendar objects. iTIP iCalendar is the language used to describe calendar objects. iTIP
describes a way to use the iCalendar language to do scheduling. iMIP describes a way to use the iCalendar language to do scheduling. iMIP
describes how to do iTIP scheduling via e-mail. CAP describes a way describes how to do iTIP scheduling via e-mail. CAP describes a way
to use the iCalendar language to access a calendar store in real- to use the iCalendar language to access a calendar store in real-
time. time.
The relationship between calendaring protocols is similar to that The relationship between calendaring protocols is similar to that
between e-mail protocols. In those terms, iCalendar is analogous to between e-mail protocols. In those terms, iCalendar is analogous to
RFC 822, iTIP and iMIP are analogous to the Simple Mail Transfer RFC 2822, iTIP and iMIP are analogous to the Simple Mail Transfer
Protocol (SMTP), and CAP is analogous to the Post Office Protocol Protocol (SMTP), and CAP is analogous to the Post Office Protocol
(POP) or Internet Message Access Protocol (IMAP). (POP) or Internet Message Access Protocol (IMAP).
2. Requirements 2. Requirements
2.1 Fundamental Needs 2.1 Fundamental Needs
The following scenarios illustrate people and organizations' basic The following scenarios illustrate people and organizations' basic
calendaring and scheduling needs: calendaring and scheduling needs:
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d] A teacher wants his students to schedule appointments during d] A teacher wants his students to schedule appointments during
his office hours. his office hours.
Need: To schedule calendar events, to-dos and journals with other Need: To schedule calendar events, to-dos and journals with other
users of the same calendar service. users of the same calendar service.
e] A movie theater wants to publish its schedule for prospective e] A movie theater wants to publish its schedule for prospective
customers. customers.
Need: To share calendar information with users of other calendar Need: To share calendar information with users of other calendar
services, possibly from multiple different vendors. services, possibly from a number of different vendors.
f] A social club wants to schedule calendar entries effectively f] A social club wants to schedule calendar entries effectively
with its members. with its members.
Need: To schedule calendar events and to-dos with users of other Need: To schedule calendar events and to-dos with users of other
calendar services, possibly from multiple different vendors. calendar services, possibly from a number of different vendors.
2.2 Protocol Requirements 2.2 Protocol Requirements
Some of these needs can be met by proprietary solutions (a, c, d), Some of these needs can be met by proprietary solutions (a, c, d),
but others can not (b, e, f). These latter scenarios show that but others can not (b, e, f). These latter scenarios show that
standard protocols are required for accessing information in a standard protocols are required for accessing information in a
calendar store and scheduling calendar entries. In addition, these calendar store and scheduling calendar entries. In addition, these
protocols require a common data format for representing calendar protocols require a common data format for representing calendar
information. information.
These requirements are met by the following protocol specifications. These requirements are met by the following protocol specifications.
- Data format: iCalendar [RFC-2445] - Data format: iCalendar [RFC-2445]
iCalendar [RFC-2445] provides a data format for representing iCalendar [RFC-2445] provides a data format for representing
calendar information, to be used and exchanged by other protocols. calendar information, to be used and exchanged by other protocols.
iCalendar [RFC-2445] can also be used in other contexts, such as a iCalendar [RFC-2445] can also be used in other contexts, such as a
drag-and-drop interface, or an export/import feature. All the drag-and-drop interface, or an export/import feature. All the
other calendaring protocols depend on iCalendar [RFC-2445], so all other calendaring protocols depend on iCalendar [RFC-2445], so all
elements of a standards-based calendaring and scheduling systems elements of a standards-based calendaring and scheduling systems
will have to be able interpret iCalendar [RFC-2445]. will have to be able to interpret iCalendar [RFC-2445].
- Scheduling protocol: iTIP [RFC-2446] - Scheduling protocol: iTIP [RFC-2446]
iTIP [RFC-2446] describes the messages used to schedule calendar iTIP [RFC-2446] describes the messages used to schedule calendar
events. Within iTIP messages, events are represented in iCalendar events. Within iTIP messages, events are represented in iCalendar
[RFC-2445] format, and have semantics that identify the message as [RFC-2445] format, and have semantics that identify the message as
being an invitation to a meeting, an acceptance of an invitation, being an invitation to a meeting, an acceptance of an invitation,
or the assignment of a task. or the assignment of a task.
iTIP [RFC-2446] messages are used in the scheduling workflow, iTIP [RFC-2446] messages are used in the scheduling workflow,
skipping to change at page 8, line 24 skipping to change at page 7, line 24
would allow her to easily import her data store into another would allow her to easily import her data store into another
application that supports iCalendar [RFC-2445]. application that supports iCalendar [RFC-2445].
b] The musician who wishes to access her agenda from anywhere can b] The musician who wishes to access her agenda from anywhere can
use a [CAP]-enabled calendar service accessible over the Internet. use a [CAP]-enabled calendar service accessible over the Internet.
She can then use any available [CAP] clients to access the data. She can then use any available [CAP] clients to access the data.
A proprietary system that provides access through a Web-based A proprietary system that provides access through a Web-based
interface could also be employed, but the use of [CAP] would be interface could also be employed, but the use of [CAP] would be
superior in that it would allow the use of third party superior in that it would allow the use of third party
applications such as PDA synchronization tools. applications, such as PDA synchronization tools.
c] The development team can use a calendar service which supports c] The development team can use a calendar service which supports
[CAP], and each member can use a [CAP]-enabled CUA of their [CAP], and each member can use a [CAP]-enabled CUA of their
choice. choice.
Alternatively, each member could use an iMIP [RFC-2447]-enabled Alternatively, each member could use an iMIP [RFC-2447]-enabled
CUA, and they could book meetings over e-mail. This solution has CUA, and they could book meetings over e-mail. This solution has
the drawback that it is difficult to examine other users' agendas, the drawback that it is difficult to examine other users' agendas,
making organizing meetings more difficult. making the organization of meetings more difficult.
Proprietary solutions are also available, but they require that Proprietary solutions are also available, but they require that
all members use clients by the same vendor, and disallow the use all members use clients by the same vendor, and disallow the use
of third party applications. of third party applications.
d] The teacher can set up a calendar service, and have students d] The teacher can set up a calendar service, and have students
book time through any of the iTIP [RFC-2446] bindings. [CAP] book time through any of the iTIP [RFC-2446] bindings. [CAP]
provides real-time access, but could require additional provides real-time access, but could require additional
configuration. iMIP [RFC-2447] would be the easiest to configure, configuration. iMIP [RFC-2447] would be the easiest to configure,
but may require more e-mail processing. but may require more e-mail processing.
If [CAP] access is provided then determining the state of the If [CAP] access is provided then determining the state of the
teacher's schedule is straightforward. If not, this can be teacher's schedule is straightforward. If not, this can be
determined through iTIP [RFC-2446] free/busy requests. Non- determined through iTIP [RFC-2446] free/busy requests. Non-
standard methods could also be employed, such as serving up iCAL, standard methods could also be employed, such as serving up
HTML, and XML over HTTP. iCalendar [RFC-2445], HTML, or XML over HTTP.
A proprietary system could also be used, but would require that A proprietary system could also be used, but would require that
all students be able to use software from a specific vendor. all students be able to use software from a specific vendor.
e] [CAP] would be preferred for publishing a movie theater's e] [CAP] would be preferred for publishing a movie theater's
schedule, since it provides advanced access and search schedule, since it provides advanced access and search
capabilities. It also allows easy integration with customers' capabilities. It also allows easy integration with customers'
calendar systems. calendar systems.
Non-standard methods such as serving data over HTTP could also be Non-standard methods such as serving data over HTTP could also be
employed, but would be harder to integrate with customers' employed, but would be harder to integrate with customers'
systems. systems.
Using a completely proprietary solution would be very difficult, Using a completely proprietary solution would be very difficult,
if not impossible, since it would require every user to install if not impossible, since it would require every user to install
and use the proprietary software. and use the proprietary software.
f] The social club could distribute meeting information in the f] The social club could distribute meeting information in the
form of iTIP [RFC-2446] messages, sent via e-mail using iMIP [RFC- form of iTIP [RFC-2446] messages, sent via e-mail using iMIP
2447]. The club could distribute meeting invitations, as well as [RFC-2447]. The club could distribute meeting invitations, as
a full published agenda. well as a full published agenda.
Alternatively, the club could provide access to a [CAP]-enabled Alternatively, the club could provide access to a [CAP]-enabled
calendar service. However, this solution would be more expensive calendar service. However, this solution would be more expensive
since it requires the maintenance of a server. since it requires the maintenance of a server.
3.2 Systems 3.2 Systems
The following diagrams illustrate possible systems and their usage of The following diagrams illustrate possible systems and their usage of
the various protocols. the various protocols.
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need not employ any of the protocols. However, it may use iCalendar need not employ any of the protocols. However, it may use iCalendar
[RFC-2445] as a data format in some places. [RFC-2445] as a data format in some places.
----------- O ----------- O
| CUA w/ | -+- user | CUA w/ | -+- user
|local store| A |local store| A
----------- / \ ----------- / \
3.2.2 Single-user Systems Communicating 3.2.2 Single-user Systems Communicating
Users with single-user systems may schedule meetings with each other Users with single-user systems may schedule meetings with each others
using iTIP [RFC-2446]. The easiest binding of iTIP [RFC-2446] to use 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' 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 mail queues, which we assume to already exist. [CAP] could also be
used. used.
O ----------- ----------- O O ----------- ----------- O
-+- | CUA w/ | -----[iMIP]----- | CUA w/ | -+- user -+- | CUA w/ | -----[iMIP]----- | CUA w/ | -+- user
A |local store| Internet |local store| A A |local store| Internet |local store| A
/ \ ----------- ----------- / \ / \ ----------- ----------- / \
3.2.3 Single-user with Multiple CUAs 3.2.3 Single-user with Multiple CUAs
A single user may use more than one CUA to access his or her 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 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 device, depending on accessibility. Some of these clients may have
local stores and others may not. Those with local stores need to local stores and others may not. Those with local stores need to
synchronize the data on the CUA with the data on the CS. synchronize the data on the CUA with the data on the CS.
----------- -----------
| CUA w | -----[CAP]----------+ | CUA w | -----[CAP]----------+
|local store| | |local store| |
O ----------- ---------- O ----------- ----------
-+- | CS | -+- | CS |
A | | A | |
/ \ ---------- / \ ----------
----------- | ----------- |
| CUA w/o | -----[CAP]----------+ | CUA w/o | -----[CAP]----------+
|local store| |local store|
----------- -----------
3.2.4 Single-user with Multiple Calendars 3.2.4 Single-user with Multiple Calendars
A single user may have many independent calendars; for example, one A single user may have many independent calendars; for example, one
may contain work-related information and another personal may contain work-related information and another personal
information. The CUA may or may not have a local store. If it does, 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 then it needs to synchronize the data of the CUA with the data on
both of the CS. both of the CS.
---------- ----------
+------------[CAP]------ | CS | +------------[CAP]------ | CS |
| | | | | |
O ----------- ---------- O ----------- ----------
-+- | CUA | -+- | CUA |
A | | A | |
/ \ ----------- / \ -----------
| ---------- | ----------
+------------[CAP]------ | CS | +------------[CAP]------ | CS |
| | | |
---------- ----------
3.2.5 Users Communicating on a Multi-user System 3.2.5 Users Communicating on a Multi-user System
Users on a multi-user system may schedule meetings with each other 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 using [CAP]-enabled CUAs and services. The CUAs may or may not have
local stores. Those with local stores need to synchronize the data local stores. Those with local stores need to synchronize the data
on the CUAs with the data on the CS. on the CUAs with the data on the CS.
O ----------- O -----------
-+- | CUA w | -----[CAP]----------+ -+- | CUA w | -----[CAP]----------+
A |local store| | A |local store| |
/ \ ----------- ---------- / \ ----------- ----------
| CS | | CS |
| | | |
---------- ----------
O ----------- | O ----------- |
-+- | CUA w/o | -----[CAP]----------+ -+- | CUA w/o | -----[CAP]----------+
A |local store| A |local store|
/ \ ----------- / \ -----------
3.2.6 Users Communicating through Different Multi-user Systems 3.2.6 Users Communicating through Different Multi-user Systems
Users on a multi-user system may need to schedule meetings with users Users on a multi-user system may need to schedule meetings with users
on a different multi-user system. The services can communicate using on a different multi-user system. The services can communicate using
[CAP] or iMIP [RFC-2447]. [CAP] or iMIP [RFC-2447].
O ----------- ---------- O ----------- ----------
-+- | CUA w | -----[CAP]-------| CS | -+- | CUA w | -----[CAP]-------| CS |
A |local store| | | A |local store| | |
/ \ ----------- ---------- / \ ----------- ----------
| |
[CAP] or [iMIP] [CAP] or [iMIP]
| |
O ----------- ---------- O ----------- ----------
-+- | CUA w/o | -----[CAP]-------| CS | -+- | CUA w/o | -----[CAP]-------| CS |
A |local store| | | A |local store| | |
/ \ ----------- ---------- / \ ----------- ----------
4. Important Aspects 4. Important Aspects
There are a number of important aspects of these calendaring There are a number of important aspects of these calendaring
standards of which people, especially implementers, should be aware. standards of which people, especially implementers, should be aware.
4.1 Timezones 4.1 Timezones
The dates and times in components can refer to a specific time zone. 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 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 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 be aware of time zones and time zone differences. New time zones may
need to be added, and others removed. Two different vendors may need to be added, and others removed. Two different vendors may
describe the same time zone differently (such as by using a different describe the same time zone differently (such as by using a different
name). name).
4.2 Choice of Transport 4.2 Choice of Transport
There are issues to be aware of in choosing between a network There are issues to be aware of in choosing between a network
protocol such as [CAP], or a store and forward (e-mail) solution. 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 The use of a network ("on-the-wire") mechanism may require some
organizations to make provisions to allow calendaring traffic to organizations to make provisions to allow calendaring traffic to
traverse a corporate firewall on the required ports. Depending on traverse a corporate firewall on the required ports. Depending on
the organizational culture, this may be a challenging social the organizational culture, this may be a challenging social
exercise. exercise.
The use of an email-based mechanism exposes time-sensitive data to The use of an email-based mechanism exposes time-sensitive data to
unbounded latency. Large or heavily utilized mail systems may unbounded latency. Large or heavily utilized mail systems may
experience an unacceptable delay in message receipt. experience an unacceptable delay in message receipt.
4.3 Security 4.3 Security
See the "Security Considerations" (Section 6) section below. See the "Security Considerations" (Section 6) section below.
4.4 Amount of data 4.4 Amount of data
In some cases, a component may be very large, for instance, a In some cases, a component may be very large, for instance, a
component with a very large attachment. Some applications may be component with a very large attachment. Some applications may be
low- bandwidth or may be limited in the amount of data they can low-bandwidth or may be limited in the amount of data they can store.
store. Maximum component size may be set in [CAP]. It can also be Maximum component size may be set in [CAP]. It can also be
controlled in iMIP [RFC-2447] by restricting the maximum size of the controlled in iMIP [RFC-2447] by restricting the maximum size of the
e-mail that the application can download. e-mail that the application can download.
4.5 Recurring Components 4.5 Recurring Components
In iCAL [RFC-2445] one can specify complex recurrence rules for In iCAL [RFC-2445], one can specify complex recurrence rules for
VEVENTs, VTODOs, and VJOURNALs. One must be careful to correctly VEVENTs, VTODOs, and VJOURNALs. One must be careful to correctly
interpret these recurrence rules and pay extra attention to being interpret these recurrence rules and pay extra attention to being
able to interoperate using them. able to interoperate using them.
5. Open Issues 5. Open Issues
Many issues are not currently resolved by these protocols, and many Many issues are not currently resolved by these protocols, and many
desirable features are not yet provided. Some of the more prominent desirable features are not yet provided. Some of the more prominent
ones are outlined below. ones are outlined below.
skipping to change at page 15, line 5 skipping to change at page 12, line 32
5.3 Notification 5.3 Notification
People often wish to be notified of upcoming events, new events, or People often wish to be notified of upcoming events, new events, or
changes to existing events. The calendaring protocols do not attempt changes to existing events. The calendaring protocols do not attempt
to address these needs in a real-time system. Instead, the ability to address these needs in a real-time system. Instead, the ability
to store alarm information on events is provided, which can be used to store alarm information on events is provided, which can be used
to provide client-side notification of upcoming events. To organize to provide client-side notification of upcoming events. To organize
notification of new or changed events, clients have to poll the data notification of new or changed events, clients have to poll the data
store. store.
6. Security considerations 6. Security Considerations
6.1 Access Control 6.1 Access Control
There has to be reasonable granularity in the configuration options There has to be reasonable granularity in the configuration options
for access to data through [CAP], so that what should be released to for access to data through [CAP], so that what should be released to
requesters is released, and what shouldn't is not. Details of requesters is released, and what shouldn't is not. Details of
handling this are described in [CAP]. handling this are described in [CAP].
6.2 Authentication 6.2 Authentication
Access control must be coupled with a good authentication system, so Access control must be coupled with a good authentication system, so
that the right people get the right information. For [CAP] this that the right people get the right information. For [CAP], this
means requiring authentication before any database access can be means requiring authentication before any database access can be
performed, and checking access rights and authentication credentials performed, and checking access rights and authentication credentials
before releasing information. [CAP] uses the Simple Authentication before releasing information. [CAP] uses the Simple Authentication
Security Layer (SASL) for this authentication. In iMIP [RFC-2447], Security Layer (SASL) for this authentication. In iMIP [RFC-2447],
this may present some challenges, as authentication is often not a this may present some challenges, as authentication is often not a
consideration in store-and-forward protocols. consideration in store-and-forward protocols.
Authentication is also important for scheduling, in that receivers of Authentication is also important for scheduling, in that receivers of
scheduling messages should be able to validate the apparent sender. scheduling messages should be able to validate the apparent sender.
Since scheduling messages are wrapped in MIME [RFC-2045], signing and Since scheduling messages are wrapped in MIME [RFC-2045], signing and
encryption are freely available. For messages transmitted over mail encryption are freely available. For messages transmitted over mail,
this is the only available alternative. It is suggested that this is the only available alternative. It is suggested that
developers take care in implementing the security features in iMIP developers take care in implementing the security features in iMIP
[RFC-2447], bearing in mind that the concept and need may be foreign [RFC-2447], bearing in mind that the concept and need may be foreign
or non-obvious to users, yet essential for the system to function as or non-obvious to users, yet essential for the system to function as
they might expect. they might expect.
The real-time protocols provide for the authentication of users, and The real-time protocols provide for the authentication of users, and
the preservation of that authentication information, allowing for the preservation of that authentication information, allowing for
validation by the receiving end-user or server. validation by the receiving end-user or server.
skipping to change at page 16, line 11 skipping to change at page 13, line 37
connections, means that 'calendar spam' is possible. Developers connections, means that 'calendar spam' is possible. Developers
should consider this threat when designing systems, particularly should consider this threat when designing systems, particularly
those that allow for automated request processing. those that allow for automated request processing.
6.4 Other Issues 6.4 Other Issues
The current security context should be obvious to users. Because the The current security context should be obvious to users. Because the
underlying mechanisms may not be clear to users, efforts to make underlying mechanisms may not be clear to users, efforts to make
clear the current state in the UI should be made. One example of clear the current state in the UI should be made. One example of
this is the 'lock' icon used in some Web browsers during secure this is the 'lock' icon used in some Web browsers during secure
connections. With both iMIP [RFC-2447] and [CAP], the possibilities connections.
of Denial of Service attacks must be considered. The ability to
flood a calendar system with bogus requests is likely to be exploited With both iMIP [RFC-2447] and [CAP], the possibilities of Denial of
once these systems become widely deployed, and detection and recovery Service attacks must be considered. The ability to flood a calendar
methods will need to be considered. 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.
Acknowledgments
Thanks to the following, who have participated in the development of
this document:
Eric Busboom, Pat Egen, David Madeo, Shawn Packwood, Bruce Kahn,
Alan Davies, Robb Surridge.
References
[RFC-2445] Dawson, F. and D. Stenerson, "Internet Calendaring and
Scheduling Core Object Specification - iCalendar", RFC
2445, November 1998.
[RFC-2446] Silverberg, S., Mansour, S., Dawson, F. and R. Hopson,
"iCalendar Transport-Independent Interoperability Protocol
(iTIP): Scheduling Events, Busy Time, To-dos and Journal
Entries", RFC 2446, November 1998.
[RFC-2447] Dawson, F., Mansour, S. and S. Silverberg, "iCalendar
Message-Based Interoperability Protocol - iMIP", RFC 2447,
November 1998.
[RFC-2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) - Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[CAP] Mansour, S., Royer, D., Babics, G., and Hill, P.,
"Calendar Access Protocol (CAP)", Work in Progress.
Authors' Addresses Authors' Addresses
Bob Mahoney Bob Mahoney
MIT MIT
E40-327 E40-327
77 Massachusetts Avenue 77 Massachusetts Avenue
Cambridge, MA 02139 Cambridge, MA 02139
US US
skipping to change at page 16, line 38 skipping to change at page 15, line 26
George Babics George Babics
Steltor Steltor
2000 Peel Street 2000 Peel Street
Montreal, Quebec H3A 2W5 Montreal, Quebec H3A 2W5
CA CA
Phone: (514) 733-8500 x4201 Phone: (514) 733-8500 x4201
EMail: georgeb@steltor.com EMail: georgeb@steltor.com
Alex Taler Alexander Taler
EMail: dissent@elea.dhs.org
Appendix A. Acknowledgments
Thanks to the following, who have participated in the development of
this document:
Eric Busboom, Pat Egen, David Madeo, Shawn Packwood, Bruce Kahn,
Alan Davies, Robb Surridge.
Appendix B. Bibliography
[RFC-2445] Dawson, F. and D. Stenerson, "Internet Calendaring
and Scheduling Core Object Specification - iCalendar", RFC 2445,
November 1998.
[RFC-2446] Silverberg, S., Mansour, S., Dawson, F. and R.
Hopson, "iCalendar Transport-Independent Interoperability Protocol
(iTIP): Scheduling Events, Busy Time, To-dos and Journal Entries",
RFC 2446, November 1998.
[RFC-2447] Dawson, F., Mansour, S. and S. Silverberg, "iCalendar
Message-Based Interoperability Protocol - iMIP", RFC 2447,
November 1998.
[RFC-2045] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) - Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[CAP] Mansour, S., Royer, D., Babics, G., and Hill, P. "Calendar EMail: alex@0--0.org
Access Protocol (CAP)" draft-ietf-calsch-cap-04.txt
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved. Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of Internet organizations, except as needed for the purpose of
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