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

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   This Internet-Draft will expire on June 6, 2003.

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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Full Copyright Statement

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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