IMPP WG D. Crocker
Internet-Draft Brandenburg
Expires: June 6, 2003 J. Peterson
NeuStar
December 6, 2002
Common Profile: Instant Messaging
draft-ietf-impp-im-01
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
Instant messaging is defined in RFC2778 [5]. Today, numerous instant
messaging protocols are in use, and little interoperability between
services based on these protocols has been achieved. This
specification defines common semantics and data formats for instant
messaging to facilitate the creation of gateways between instant
messaging services.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Abstract Instant Messaging Service . . . . . . . . . . . . . 4
3.1 Overview of Instant Messaging Service . . . . . . . . . . . 4
3.2 Identification of INSTANT INBOXes . . . . . . . . . . . . . 5
3.2.1 Address Resolution . . . . . . . . . . . . . . . . . . . . . 5
3.3 Format of Instant Messages . . . . . . . . . . . . . . . . . 5
3.4 The Messaging Service . . . . . . . . . . . . . . . . . . . 5
3.4.1 The Message Operation . . . . . . . . . . . . . . . . . . . 5
3.4.2 Looping . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7
5.1 The IM URI Scheme . . . . . . . . . . . . . . . . . . . . . 7
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 8
A. IM URI IANA Registration Template . . . . . . . . . . . . . 9
A.1 URI scheme name . . . . . . . . . . . . . . . . . . . . . . 9
A.2 URI scheme syntax . . . . . . . . . . . . . . . . . . . . . 9
A.3 Character encoding considerations . . . . . . . . . . . . . 9
A.4 Intended usage . . . . . . . . . . . . . . . . . . . . . . . 9
A.5 Applications and/or protocols which use this URI scheme
name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
A.6 Interoperability considerations . . . . . . . . . . . . . . 10
A.7 Security considerations . . . . . . . . . . . . . . . . . . 10
A.8 Relevant publications . . . . . . . . . . . . . . . . . . . 10
A.9 Person & email address to contact for further information . 10
A.10 Author/Change controller . . . . . . . . . . . . . . . . . . 10
A.11 Applications and/or protocols which use this URI scheme
name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
B. Issues of Interest . . . . . . . . . . . . . . . . . . . . . 10
B.1 Address Mapping . . . . . . . . . . . . . . . . . . . . . . 10
B.2 Source-Route Mapping . . . . . . . . . . . . . . . . . . . . 11
Normative References . . . . . . . . . . . . . . . . . . . . 8
C. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 11
Full Copyright Statement . . . . . . . . . . . . . . . . . . 12
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1. Introduction
Instant messaging is defined in RFC2778 [5]. Today, numerous instant
messaging protocols are in use, and little interoperability between
services based on these protocols has been achieved. This
specification defines semantics and data formats for common services
of Instant Messaging to facilitate the creation of gateways between
instant messaging services.
Service behavior is described abstractly in terms of operations
invoked between the consumer and provider of a service. Accordingly,
each IM 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 instant messaging service.
The attributes for each operation are defined using an abstract
syntax. Although the syntax specifies the range of possible data
values, each 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 an instant message as
textual 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 instant messaging
service.
In order to provide a means for the preservation of end-to-end
features (especially security) to pass through instant messaging
interoperability gateways, this specification also provides
recommendations for instant messaging document formats that could be
employed by instant messaging 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, INSTANT MESSAGE, and OPEN are used in
the same meaning as defined therein.
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This document defines operations and attributes of an instant
messaging service. In order for a protocol to interface with an
instant messaging gateway, it must support all of the operations
described in this document (i.e. the instant messaging 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 instant
messaging 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 an instant
messaging protocol that correspond to the operations described in
this document can contain additional information that will not be
mapped by CPIM.
3. Abstract Instant Messaging Service
3.1 Overview of Instant Messaging Service
When an application wants to send a message to an INSTANT INBOX, it
invokes the message operation, e.g.,
+-------+ +-------+
| | | |
| appl. | -- message ------> | IM |
| | | svc. |
+-------+ +-------+
The message operation has the following attributes: source,
destination, MaxForwards and TransID. 'source' and 'destination'
identity the originator and destination of an instant message,
respectively, and consist of an INSTANT INBOX identifier (as
described in Section 3.2). The MaxForwards is a hop counter used in
order to avoid loops through gateways. The TransID is a unique
identifier used to correlate message operations to response
operations.
The message operation also has some content, the instant message
itself, which may be textual, or which may consist of other data.
Some further information on content is provided in Section 3.3.
Upon receiving a message operation, the service immediately responds
by invoking the response operation containing the same transaction-
identifier, e.g.,
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+-------+ +-------+
| | | |
| appl. | <----- response -- | IM |
| | | svc. |
+-------+ +-------+
The response operation contains the following attributes: TransID and
status. The TransID is used to correlate the response to a
particular instant message. Status indicates whether the delivery of
the message succeeded or failed.
3.2 Identification of INSTANT INBOXes
An INSTANT INBOX is specified using an instant messaging URI with the
'im:' URI scheme. The full syntax of the IM URI scheme is given in
Appendix A. An example would be: "im:fred@example.com"
3.2.1 Address Resolution
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 Instant Messages
This specification defines an abstract interoperability mechanism for
instant messaging 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 instant messaging is employed by the
interoperating instant messaging protocols. Implementations
therefore SHOULD support the format defined in MSGFMT [4].
3.4 The Messaging Service
Note that the transaction-identifier parameters used with the instant
messaging service are potentially long-lived. Accordingly, the
values generated for this parameter should be unique across a
significant duration of time.
3.4.1 The Message Operation
When an application wants to send an INSTANT MESSAGE, it invokes the
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message operation.
When the service is informed of the message operation, it performs
these steps:
1. If the source or destination does not refer to a valid INSTANT
INBOX, 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. Otherwise:
If the service is able to successfully deliver the message, a
response operation having status "success" is invoked.
If the service is unable to successfully deliver the message,
a response operation having status "failure" is invoked.
If the service must delegate responsibility for delivery, and
if the delegation will not result in a future authoritative
indication to the service, a response operation having status
"indeterminant" is invoked.
If the service must delegate responsibility for delivery, and
if the delegation will result in a future authoritative
indication to the service, then a response operation is
invoked immediately after the indication is received.
When the service invokes the response operation, the transID
parameter is identical to the value found in the message operation
invoked by the application.
3.4.2 Looping
The dynamic routing of instant messages can result in looping of a
message through a relay. Detection of loops is not always obvious,
since aliasing and group list expansions can legitimately cause a
message to pass through a relay more than one time.
This document assumes that instant messaging protocols that can be
gatewayed by CPIM support some semantic equivalent to an integer
value that indicates the maximum number of hops through which a
message can pass. When that number of hops has been reached, the
message is assumed to have looped.
When a CPIM gateway relays an instant message, it decrements the
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value of the MaxForwards attribute. This document does not mandate
any particular initial setting for the MaxForwards element in instant
messaging protocols, but it is recommended that the value be
reasonably large (over one hundred).
If a CPIM gateway handles an instant message operation that has a
MaxForwards attribute of 0, it discards the message and invokes a
failure operation.
4. Security Considerations
Detailed security considerations for instant messaging protocols are
given in RFC2779 (in particular, requirements are given in section
5.4 and some motivating discussion in 8.1).
CPIM defines an interoperability function that is employed by
gateways between instant messaging protocols. CPIM gateways MUST be
compliant with the minimum security requirements of the instant
messaging protocols with which they interface.
Note that end-to-end security properties (especially confidentiality
and integrity) between instant messaging user agents that interface
through a CPIM gateway can only be provided if a common instant
message format (such as the format described in MSGFMT [4]) is
supported by the protocols interfacing with the CPIM gateway.
5. IANA Considerations
The IANA assigns the "im" scheme.
5.1 The IM URI Scheme
The Instant Messaging (IM) URI scheme designates an Internet
resource, namely an INSTANT INBOX.
The syntax of an IM 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)
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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] Atkins, D. and G. Klyne, "Common Presence and Instant Messaging:
Message Format", draft-ietf-impp-cpim-msgfmt-05 (work in
progress), December 2001.
[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
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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
Appendix A. IM URI IANA Registration Template
This section provides the information to register the im: instant
messaging URI.
A.1 URI scheme name
im
A.2 URI scheme syntax
The syntax follows the existing mailto: URI syntax specified in
RFC2368. The ABNF is:
IM-URI = "im:" [ 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 im: URI follows closely usage of the mailto: URI. That
is, invocation of an IM 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
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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 IM URIs are placed in instant messaging 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 URI scheme name
Instant messaging 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].
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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.
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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