IMPP WG D. Crocker
Internet-Draft Brandenburg
Expires: June 6, 2003 J. Peterson
NeuStar
December 6, 2002
Common Profile: Presence
draft-ietf-impp-pres-01
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Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
Presence is defined in RFC2778 [5]. 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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Abstract Presence Service . . . . . . . . . . . . . . . . . 4
3.1 Overview of the Presence Service . . . . . . . . . . . . . . 4
3.2 Identification of PRESENTITIES and WATCHERS . . . . . . . . 6
3.3 Format of Presence Information . . . . . . . . . . . . . . . 6
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 . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . 9
5.1 The PRES URI Scheme . . . . . . . . . . . . . . . . . . . . 9
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 10
A. PRES URI IANA Registration Template . . . . . . . . . . . . 10
A.1 URI scheme name . . . . . . . . . . . . . . . . . . . . . . 10
A.2 URI scheme syntax . . . . . . . . . . . . . . . . . . . . . 10
A.3 Character encoding considerations . . . . . . . . . . . . . 11
A.4 Intended usage . . . . . . . . . . . . . . . . . . . . . . . 11
A.5 Applications and/or protocols which use this URI scheme
name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
A.6 Interoperability considerations . . . . . . . . . . . . . . 11
A.7 Security considerations . . . . . . . . . . . . . . . . . . 11
A.8 Relevant publications . . . . . . . . . . . . . . . . . . . 11
A.9 Person & email address to contact for further information . 12
A.10 Author/Change controller . . . . . . . . . . . . . . . . . . 12
A.11 Applications and/or protocols which use this URI scheme
name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
B. Issues of Interest . . . . . . . . . . . . . . . . . . . . . 12
B.1 Address Mapping . . . . . . . . . . . . . . . . . . . . . . 12
B.2 Source-Route Mapping . . . . . . . . . . . . . . . . . . . . 12
Normative References . . . . . . . . . . . . . . . . . . . . 9
C. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 13
Full Copyright Statement . . . . . . . . . . . . . . . . . . 14
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1. Introduction
Presence is defined in RFC2778 [5]. 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.
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 RFC2778 [5]. Terms
such as CLOSED, INSTANT INBOX, PRESENCE, and OPEN are used in the
same meaning as defined therein.
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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 CPP.
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.,
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+-------+ +-------+
| | | |
| 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 immediately
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 and
the same SubscriptID as the original subscribe operation , e.g.,
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+-------+ +-------+
| | | |
| appl. | -- subscribe 0 --> | pres. |
| | | svc. |
+-------+ +-------+
Note that a notify operation will be invoke when a subscription is
prematurely canceled in this fashion; this notification may be
discarded by the watcher.
The service immediately responds by invoking the response operation
containing the same transaction- identifier, e.g.,
+-------+ +-------+
| | | |
| appl. | <----- response -- | pres. |
| | | svc. |
+-------+ +-------+
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 presence URIs, 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 [4].
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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
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
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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 SubscriptID of an existing subscription. Note
that an notify operation will be invoked by the presentity when a
subscription is canceled in this fashion; this notification can be
discarded by the watcher. There is no independent UNSUBSCRIBE
operation.
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 SubscriptID. There
is no independent FETCH operation.
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 CPP gateway can only be provided if a common presence
format (such as the format described in [4]) is supported by the
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protocols interfacing with the CPP gateway.
5. IANA Considerations
The IANA assigns the "pres" URI 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 URI is given in Appendix A.
6. Contributors
The following individuals made substantial textual contributions to
this document:
Athanassios Diacakis (thanos.diacakis@openwave.com)
Florencio Mazzoldi (flo@networkprojects.com)
Christian Huitema (huitema@microsoft.com)
Graham Klyne (gk@ninebynine.org)
Jonathan Rosenberg (jdrosen@dynamicsoft.com)
Robert Sparks (rsparks@dynamicsoft.com)
Hiroyasu Sugano (suga@flab.fujitsu.co.jp)
Normative References
[1] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", RFC 2119, March 1997.
[2] Crocker, D. and J. Peterson, "Address resolution for Instant
Messaging and Presence", draft-ietf-impp-srv-00 (work in
progress), October 2002.
[3] Resnick, P., "Internet Message Format", RFC 2822, STD 11, April
2001.
[4] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and
J. Peterson, "CPIM Presence Information Data Format", draft-
ietf-impp-cpim-pidf-00 (work in progress), August 2001.
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[5] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[6] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
Presence Protocol Requirements", RFC 2779, February 2000.
[7] 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
Jon Peterson
NeuStar, Inc.
1800 Sutter St
Suite 570
Concord, CA 94520
US
Phone: +1 925/363-8720
EMail: jon.peterson@neustar.biz
Appendix A. PRES URI IANA Registration Template
This section provides the information to register the pres: presence
URI .
A.1 URI scheme name
pres
A.2 URI scheme syntax
The syntax follows the existing mailto: URI syntax specified in
RFC2368. The ABNF is:
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PRES-URI = "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 RFC2822"
[3].
A.4 Intended usage
Use of the pres: URI follows closely usage of the mailto: URI. That
is, invocation of an PRES URI 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 URI.
A.5 Applications and/or protocols which use this URI scheme name
It is anticipated that protocols compliant with RFC2779, and meeting
the interoperability requirements specified here, will make use of
this URI 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.
A.7 Security considerations
When PRES URIs 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
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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 URI scheme name
Instant messaging service; presence service
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 RFC2846 [7].
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
The authors would like to acknowledge John Ramsdell for his comments,
suggestions and enthusiasm. Thanks to Derek Atkins for editorial
fixes.
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Full Copyright Statement
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