IMPP WG D. Crocker
Internet-Draft Brandenburg
Expires: April 27, 2003 A. Diacakis
F. Mazzoldi
Net Proj
C. Huitema
Microsoft
G. Klyne
Baltimore
J. Rosenberg
R. Sparks
dynamicsoft
H. Sugano
Fujitsu
J. Peterson
NeuStar
October 27, 2002
Common Profile: Presence
draft-ietf-impp-pres-00
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
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This Internet-Draft will expire on April 27, 2003.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
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Abstract
Presence is defined in RFC2778 [12]. Today, numerous presence
protocols are in use (largely as components of commercial instant
messaging services), and little interoperability between services
based on these protocols has been achieved. This specification
defines common semantics and data formats for presence to facilitate
the creation of gateways between presence services.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Abstract Presence Service . . . . . . . . . . . . . . . . . 5
3.1 Overview of the Presence Service . . . . . . . . . . . . . . 5
3.2 Identification of PRESENTITIES and WATCHERS . . . . . . . . 7
3.3 Format of Presence Information . . . . . . . . . . . . . . . 7
3.4 The Presence Service . . . . . . . . . . . . . . . . . . . . 7
3.4.1 The Subscribe Operation . . . . . . . . . . . . . . . . . . 7
3.4.2 The Notify Operation . . . . . . . . . . . . . . . . . . . . 8
3.4.3 Subscribe Operation (with Zero Duration) . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . 11
5.1 The PRES URI Scheme . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 13
A. PRES URL IANA Registration Template . . . . . . . . . . . . 16
A.1 URL scheme name . . . . . . . . . . . . . . . . . . . . . . 16
A.2 URL scheme syntax . . . . . . . . . . . . . . . . . . . . . 16
A.3 Character encoding considerations . . . . . . . . . . . . . 16
A.4 Intended usage . . . . . . . . . . . . . . . . . . . . . . . 16
A.5 Applications and/or protocols which use this URL scheme
name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
A.6 Interoperability considerations . . . . . . . . . . . . . . 16
A.7 Security considerations . . . . . . . . . . . . . . . . . . 17
A.8 Relevant publications . . . . . . . . . . . . . . . . . . . 17
A.9 Person & email address to contact for further information . 17
A.10 Author/Change controller . . . . . . . . . . . . . . . . . . 17
A.11 Applications and/or protocols which use this URL scheme
name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
B. Issues of Interest . . . . . . . . . . . . . . . . . . . . . 18
B.1 Address Mapping . . . . . . . . . . . . . . . . . . . . . . 18
B.2 Source-Route Mapping . . . . . . . . . . . . . . . . . . . . 18
References . . . . . . . . . . . . . . . . . . . . . . . . . 12
C. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 19
Full Copyright Statement . . . . . . . . . . . . . . . . . . 20
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1. Introduction
Presence is defined in RFC2778 [12]. Today, numerous presence
protocols are in use (largely as components of commercial instant
messaging services, and little interoperability between services
based on these protocols has been achieved. This specification
defines semantics and data formats for common services of presence to
facilitate the creation of gateways between presence services.
Service behavior is described abstractly in terms of operations
invoked between the consumer and provider of a service. Accordingly,
each presence service must specify how this behavior is mapped onto
its own protocol interactions. The choice of strategy is a local
matter, providing that there is a clear relation between the abstract
behaviors of the service (as specified in this memo) and how it is
faithfully realized by a particular presence service.
The parameters for each operation are defined using an abstract
syntax. Although the syntax specifies the range of possible data
values, each Presence and IM service must specify how well-formed
instances of the abstract representation are encoded as a concrete
series of bits.
For example, one strategy might transmit presence information as key/
value pairs, another might use a compact binary representation, and a
third might use nested containers. The choice of strategy is a local
matter, providing that there is a clear relation between the abstract
syntax (as specified in this memo) and how it is faithfully encoded
by an particular presence service.
In order to provide a means for the preservation of end-to-end
features (especially security) to pass through presence
interoperability gateways, this specification also provides
recommendations for presence document formats that could be employed
by presence protocols.
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2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in RFC2119 [1] and indicate requirement levels for
compliant implementations.
This memos makes use of the vocabulary defined in RFC 2778[9]. Terms
such as CLOSED, INSTANT INBOX, PRESENCE, and OPEN are used in the
same meaning as defined therein.
This document defines operations and attributes of a presence
service. In order for a protocol to interface with a presence
gateway, it must support all of the operations described in this
document (i.e. the presence protocol must have some message or
capability that provides the function described by this operation).
Similarly, the attributes defined for these operations must
correspond to information available in the presence protocol in order
for the protocol to interface with gateways defined by this
specification. Note that these attributes provide only the minimum
possible information that needs to be specified for interoperability
- the functions in a presence protocol that correspond to the
operations described in this document can contain additional
information that will not be mapped by CPIM.
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3. Abstract Presence Service
3.1 Overview of the Presence Service
When an application wants to (periodically) receive the presence
information associated with a PRESENTITY, it invokes the subscribe
operation, e.g.,
+-------+ +-------+
| | | |
| appl. | -- subscribe ----> | pres. |
| | | svc. |
+-------+ +-------+
The subscribe operation has the following attributes: watcher,
target, duration, SubscriptID and TransID. The 'watcher' and
'target' identify the WATCHER and PRESENTITY, respectively, using the
identifiers described in Section 3.2. The duration specifies the
maximum number of seconds that the SUBSCRIPTION should be active
(which may be zero, in which case this is a one-time request for
presence information). The SubscriptID creates a reference to the
SUBSCRIPTION that is used when unsubscribing. The TransID is a
unique identifier used to correlate the subscribe operation with a
response operation.
Upon receiving a subscribe operation, the service immediately
responds by invoking the response operation containing the same
transaction- identifier, e.g.,
+-------+ +-------+
| | | |
| appl. | <----- response -- | pres. |
| | | svc. |
+-------+ +-------+
The response operation has the following attributes: status, TransID,
and duration. 'status' indicates whether the subscribe operation has
succeeded or failed. The TransID of the response operation
corresponds to the TransID of the subscription operation to which it
is responding. The 'duration' attribute specifies the number of
seconds for which the subscription will be active (which may differ
from the value requested in the subscribe operation).
If the response operation indicates success, the service immediate
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invokes the notify operation to communicate the presence information
to the WATCHER, e.g.,
+-------+ +-------+
| | | |
| appl. | <------- notify -- | pres. |
| | | svc. |
+-------+ +-------+
The notify operation has the following attributes: watcher, target,
and TransID. The values of 'watcher' and 'target' are identical to
those given in the subscribe operation that triggered this notify
operation. The TransID is a unique identifier for this notification.
The notify operation also has content, namely PRESENCE INFORMATION.
Some further information on notify content is given in Section 3.3.
If the duration parameter is non-zero, then for up to the specified
duration, the service invokes the notify operation whenever there are
any changes to the PRESENTITY's presence information. Otherwise,
exactly one notify operation is invoked, achieving a one-time poll of
the presence information. Regardless, there is no application
response to the notify operation (i.e., the application does not
invoke a response operation when a notify operation occurs) defined
in CPP.
The application may prematurely cancel a subscription by re-invoking
the subscribe operation (as described above) with a duration of 0,
e.g.,
+-------+ +-------+
| | | |
| appl. | -- subscribe 0 --> | pres. |
| | | svc. |
+-------+ +-------+
The service immediately responds by invoking the response operation
containing the same transaction- identifier, e.g.,
+-------+ +-------+
| | | |
| appl. | <----- response -- | pres. |
| | | svc. |
+-------+ +-------+
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3.2 Identification of PRESENTITIES and WATCHERS
A PRESENTITY is specified using the PRES URI scheme, which is further
described in Appendix A. An example would be:
"pres:fred@example.com"
To resolve identifiers associated with the Presence A client
determines the address of an appropriate system running a server by
resolving the destination domain name that is part of the identifier
to either an intermediate relay system or a final target system.
Compliant implementations SHOULD follow the guidelines for
dereferencing URIs given in [2].
3.3 Format of Presence Information
This specification defines an abstract interoperability mechanism for
presence protocols; the message content definition given here
pertains to semantics rather than syntax. However, some important
properties for interoperability can only be provided if a common end-
to-end format for presence is employed by the interoperating presence
protocols. Implementations therefore SHOULD support the format
defined in PIDF [10].
3.4 The Presence Service
An implementation of the service must maintain information about both
presence information and in- progress operations in persistent
storage.
Note that the transaction-identifier parameter used by the service is
potentially long-lived. Accordingly, the values generated for this
parameter should be unique across a significant duration of time.
3.4.1 The Subscribe Operation
When an application wants to (periodically) receive the presence
information associated with a PRESENTITY, it invokes the subscribe
operation.
When the service is informed of the subscribe operation, it performs
these steps:
1. If the watcher or target parameter does not refer to a valid
PRESENTITY, a response operation having status "failure" is
invoked.
2. If access control does not permit the application to request this
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operation, a response operation having status "failure" is
invoked.
3. If the duration parameter is non-zero, and if the watcher and
target parameters refer to an in-progress subscribe operation for
the application, a response operation having status "failure" is
invoked.
4. Otherwise, if the service is able to successfully deliver the
message:
A response operation having status "success" is immediately
invoked. (If the service chooses a different duration for the
subscription then it conveys this information in the response
operation.)
A notify operation, corresponding to the target's presence
information, is immediately invoked for the watcher.
For up to the amount of time indicated by the duration
parameter, if the target's presence information changes, and
if access control allows, a notify operation is invoked for
the watcher.
Note that if the duration parameter is zero-valued, then the
subscribe operation is making a one-time poll of the presence
information. Accordingly, the final step above (continued
notifications for the duration of the subscription) does not occur.
When the service invokes a response operation as a result of this
processing, the transID parameter is identical to the value found in
the subscribe operation invoked by the application.
3.4.2 The Notify Operation
The service invokes the notify operation whenever the presence
information associated with a PRESENTITY changes and there are
subscribers to that information.
There is no application response to the notify operation.
3.4.3 Subscribe Operation (with Zero Duration)
When an application wants to terminate a subscription, it issues a
SUBSCRIBE 0 with the transID of an existing subscription.
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There is no explicit UNSUBSCRIBE command.
When an application wants to directly request presence information to
be supplied immediately without initiating any persistent
subscription, it issues a SUBSCRIBE 0 with a new transID.
There is no explicit FETCH command.
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4. Security Considerations
Detailed security considerations for presence protocols given in
RFC2779 (in particular, requirements are given in sections 5.1
through 5.3 and some motivating discussion in 8.2).
CPP defines an interoperability function that is employed by gateways
between presence protocols. CPP gateways MUST be compliant with the
minimum security requirements of the presence protocols with which
they interface.
Note that end-to-end security properties (especially confidentiality
and integrity) between presentities and watchers that interface
through a CPIM gateway can only be provided if a common presence
format (such as the format described in [10]) is supported by the
protocols interfacing with the CPIM gateway.
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5. IANA Considerations
The IANA assigns the "pres" URL scheme.
5.1 The PRES URI Scheme
The Presence (PRES) URI scheme designates an Internet resource,
namely a PRESENTITY or WATCHER.
The syntax of a PRES URL is given in Appendix A.
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References
[1] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", RFC 2119, March 1997.
[2] Crocker, D., Diacakis, A., Mazzoldi, F., Huitema, C., Klyne,
G., Rosenberg, J., Sparks, R., Sugano, H. and J. Peterson,
"Address resolution for Instant Messaging and Presence", draft-
ietf-impp-srv-00 (work in progress), October 2002.
[3] Crocker, D., "Standard for the format of ARPA Internet text
Messages", RFC 822, STD 11, August 1982.
[4] Resnick, P., "Internet Message Format", RFC 2822, STD 11, April
2001.
[5] Mockapetris, P., "Domain Names - Concepts and Facilities", RFC
1034, STD 13, November 1987.
[6] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
[7] Callas, J., Donnerhacke, L., Finney, H. and R. Thayer, "OpenPGP
Message Format", RFC 2440, November 1998.
[8] Klyne, G., "XML Coding of RFC822 Messages", draft-klyne-
message-rfc822-xml-00 (work in progress), November 2001.
[9] Atkins, D. and G. Klyne, "Common Presence and Instant
Messaging: Message Format", draft-ietf-impp-cpim-msgfmt-05
(work in progress), December 2001.
[10] Sugano, H., "CPIM Presence Information Data Format", draft-
ietf-impp-cpim-pidf-00 (work in progress), August 2001.
[11] Ramsdell, B., "S/MIME Version 3 Certificate Handlng", RFC 2632,
June 1999.
[12] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[13] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
Presence Protocol Requirements", RFC 2779, February 2000.
[14] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for
Specifying the Location of Services (SRV)", RFC 2782, February
2000.
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[15] Allocchio, C., "GSTN Address Element Extensions in Email
Services", RFC 2846, June 2000.
Authors' Addresses
Dave Crocker
Brandenburg InternetWorking
675 Spruce Drive
Sunnyvale, CA 94086
US
Phone: +1 408/246-8253
EMail: dcrocker@brandenburg.com
Athanassios Diacakis
Network Projects Inc.
4516 Henry Street
Suite 113
Pittsburgh, PA 15213
US
Phone: +1 412/681-6950 x202
EMail: thanos@networkprojects.com
Florencio Mazzoldi
Network Projects Inc.
4516 Henry Street
Suite 113
Pittsburgh, PA 15213
US
Phone: +1 412/681-6950
EMail: flo@networkprojects.com
Christian Huitema
Microsoft Corporation
One Microsoft Way
Redmund, WA 98052-6399
US
EMail: huitema@microsoft.com
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Graham Klyne
Baltimore Technologies
1310 Waterside
Arlington Business Park
Theale, Reading RG7 4SA
UK
Phone: +44 118 903 8000
EMail: gk@acm.org
Jonathan Rosenberg
dynamicsoft
200 Executive Drive
Suite 120
West Orange, NJ 07052
US
EMail: jdrosen@dynamicsoft.com
Robert Sparks
dynamicsoft
200 Executive Drive
Suite 120
West Orange, NJ 07052
US
EMail: rsparks@dynamicsoft.com
Hiroyasu Sugano
Fujitsu Laboratories Ltd.
200 Executive Drive
64 Nishiwaki, Ohkubo-cho
Akashi 674-8555
JP
EMail: suga@flab.fujitsu.co.jp
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Jon Peterson
NeuStar, Inc.
1800 Sutter St
Suite 570
Concord, CA 94520
US
Phone: +1 925/363-8720
EMail: jon.peterson@neustar.biz
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Appendix A. PRES URL IANA Registration Template
This section provides the information to register the pres: presence
URL .
A.1 URL scheme name
pres
A.2 URL scheme syntax
The syntax follows the existing mailto: URL syntax specified in
RFC2368. The ABNF is:
PRES-URL = "pres:" [ to ] [ headers ]
to = #mailbox
headers = "?" header *( "&" header )
header = hname "=" hvalue
hname = *urlc
hvalue = *urlc
A.3 Character encoding considerations
Representation of non-ASCII character sets in local-part strings is
limited to the standard methods provided as extensions to RFC 2822[1]
A.4 Intended usage
Use of the pres: URL follows closely usage of the mailto: URL. That
is, invocation of an PRES URL will cause the user's instant messaging
application to start, with destination address and message headers
fill-in according to the information supplied in the URL.
A.5 Applications and/or protocols which use this URL scheme name
It is anticipated that protocols compliant with RFC2779, and meeting
the interoperability requirements specified here, will make use of
this URL scheme name.
A.6 Interoperability considerations
The underlying exchange protocol used to send an instant message may
vary from service to service. Therefore complete, Internet-scale
interoperability cannot be guaranteed. However, a service conforming
to this specification permits gateways to achieve interoperability
sufficient to the requirements of RFC2779.
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A.7 Security considerations
When PRES URLs are placed in presence protocols, they convey the
identity of the sender and/or the recipient. In some cases,
anonymous messaging may be desired. Such a capability is beyond the
scope of this specification.
A.8 Relevant publications
RFC2779, RFC2778
A.9 Person & email address to contact for further information
Jon Peterson [mailto:jon.peterson@neustar.biz]
A.10 Author/Change controller
This scheme is registered under the IETF tree. As such, IETF
maintains change control.
A.11 Applications and/or protocols which use this URL scheme name
Instant messaging service; presence service
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Appendix B. Issues of Interest
This appendix briefly discusses issues that may be of interest when
designing an interoperation gateway.
B.1 Address Mapping
When mapping the service described in this memo, mappings that place
special information into the im: address local-part MUST use the
meta-syntax defined in RFC 2846[12].
B.2 Source-Route Mapping
The easiest mapping technique is a form of source- routing and
usually is the least friendly to humans having to type the string.
Source-routing also has a history of operational problems.
Use of source-routing for exchanges between different services is by
a transformation that places the entire, original address string into
the im: address local part and names the gateway in the domain part.
For example, if the destination INSTANT INBOX is "pepp://example.com/
fred", then, after performing the necessary character conversions,
the resulting mapping is:
im:pepp=example.com/fred@relay-domain
where "relay-domain" is derived from local configuration information.
Experience shows that it is vastly preferable to hide this mapping
from end-users - if possible, the underlying software should perform
the mapping automatically.
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Appendix C. Acknowledgments
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Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
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The limited permissions granted above are perpetual and will not be
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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