Subject: Re: IM and Presence history

From: Dave Crocker <[email-masked]>
Date: Wed, 29 Nov 2006 16:34:12 -0800

Dave Crocker wrote:
> SIP obtained this design from previous work on IM and Presence:

Sorry.  The reference I gave was to the later specification that split the DNS 
SRV usage.

The original design seems to have been in:

    A Common Profile for Instant Messaging (CPIM)
    draft-ietf-impp-common-01
    November 2000

I've attached a copy, since I can't find one through a Google search and the 
historical reference is worth recording.

d/
-- 

   Dave Crocker
   Brandenburg InternetWorking
   bbiw.net

Network Working Group                                         D. Crocker
Internet-Draft                                    Brandenburg Consulting
Expires: April 1, 2001                                       A. Diacakis
                                                             F. Mazzoldi
                                                   Network Projects Inc.
                                                              C. Huitema
                                                   Microsoft Corporation
                                                                G. Klyne
                                                    Content Technologies
                                                                 M. Rose
                                                        Invisible Worlds
                                                            J. Rosenberg
                                                               R. Sparks
                                                             dynamicsoft
                                                               H. Sugano
                                               Fujitsu Laboratories Ltd.
                                                           November 2000

             A Common Profile for Instant Messaging (CPIM)
                       draft-ietf-impp-common-01

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
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 1, 2001.

Copyright Notice

   Copyright (C) The Internet Society (2000). All Rights Reserved.

Abstract

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   Semantics and data formats for common services of Instant Messaging
   and online Presence, independent of underlying transport
   infrastructure, are described. The CPIM profile meets the
   requirements specified in RFC 2779 using a minimalist approach
   allowing interoperation of a wide range of IM and Presence systems.

Table of Contents

   1.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  3
   1.1     Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   1.2     A Note on The Examples . . . . . . . . . . . . . . . . . .  3
   2.      Abstract Messaging Service . . . . . . . . . . . . . . . .  4
   2.1     Overview of the Messaging Service  . . . . . . . . . . . .  4
   2.2     Identification of INSTANT INBOXes  . . . . . . . . . . . .  5
   2.2.1   Address Resolution . . . . . . . . . . . . . . . . . . . .  5
   2.2.1.1 Domain Name Lookup . . . . . . . . . . . . . . . . . . . .  5
   2.2.1.2 Processing SRV RRs . . . . . . . . . . . . . . . . . . . .  6
   2.2.1.3 Processing Multiple Addresses  . . . . . . . . . . . . . .  6
   2.3     Format of Instant Messages . . . . . . . . . . . . . . . .  7
   2.4     The Messaging Service  . . . . . . . . . . . . . . . . . .  8
   2.4.1   The Message Operation  . . . . . . . . . . . . . . . . . .  8
   2.4.2   Looping  . . . . . . . . . . . . . . . . . . . . . . . . .  9
   3.      Abstract Presence Service  . . . . . . . . . . . . . . . . 10
   3.1     Overview of the Presence Service . . . . . . . . . . . . . 10
   3.2     Identification of PRESENTITIES . . . . . . . . . . . . . . 11
   3.3     Format of Presence Information . . . . . . . . . . . . . . 12
   3.4     The Presence Service . . . . . . . . . . . . . . . . . . . 13
   3.4.1   The Subscribe Operation  . . . . . . . . . . . . . . . . . 13
   3.4.2   The Notify Operation . . . . . . . . . . . . . . . . . . . 15
   3.4.3   The Unsubscribe Operation  . . . . . . . . . . . . . . . . 16
   4.      Security Considerations  . . . . . . . . . . . . . . . . . 17
   4.1     Hop-by-hop security  . . . . . . . . . . . . . . . . . . . 17
   4.2     End-to-end security  . . . . . . . . . . . . . . . . . . . 18
   4.2.1   Instant messages . . . . . . . . . . . . . . . . . . . . . 18
   4.2.2   Presence service . . . . . . . . . . . . . . . . . . . . . 18
   5.      IANA Considerations  . . . . . . . . . . . . . . . . . . . 19
   5.1     The IM URI Scheme  . . . . . . . . . . . . . . . . . . . . 19
   5.2     The PRES URI Scheme  . . . . . . . . . . . . . . . . . . . 19
   6.      The Common Service DTD . . . . . . . . . . . . . . . . . . 20
   7.      The Messaging Service DTD  . . . . . . . . . . . . . . . . 21
   8.      The Presence Service DTD . . . . . . . . . . . . . . . . . 22
   9.      The Presence Information DTD . . . . . . . . . . . . . . . 23
           References . . . . . . . . . . . . . . . . . . . . . . . . 24
           Authors' Addresses . . . . . . . . . . . . . . . . . . . . 24
   A.      Issues of Interest . . . . . . . . . . . . . . . . . . . . 27
   A.1     Address Mapping  . . . . . . . . . . . . . . . . . . . . . 27
   A.1.1   Source-Route Mapping . . . . . . . . . . . . . . . . . . . 27
           Full Copyright Statement . . . . . . . . . . . . . . . . . 28

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1. Introduction

   To achieve interoperation of IM systems that are compliant with RFC 
   2779[8], there must be a common agreement on both Instant Messaging
   and Presence services. This memo defines such an agreement according
   to the philosophy that there must be no loss of information between
   IM systems that are minimally conformant to RFC2779.

   This memo focuses on interoperation. Accordingly only those aspects
   of IM that require interoperation are discussed. For example, the
   "open instant inbox" operation is not applicable as this operation
   occurs within a single IM system and not across systems.

   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
   behavior of the service (as specified in this memo) and how it is
   faithfully realized by a particular IM service.

   The parameters 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 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 IM service.

1.1 Terminology

   This memos makes use of the vocabulary defined in RFC  2778[7].
   Terms such as as CLOSED, INSTANT INBOX, INSTANT MESSAGE, OPEN,
   PRESENCE SERVICE, PRESENTITY, SUBSCRIPTION, and WATCHER are used in
   the same meaning as defined therein.

1.2 A Note on The Examples

   In the examples which follow, this memo uses time-sequence diagrams
   annotated with XML fragments to illustrate operations and their
   parameters. The use of XML is an artifact of this memo's
   presentation style and does not imply any requirement for the use of
   XML in an IM system.

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2. Abstract Messaging Service

2.1 Overview of the 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. | +-------+ +-------+ <message source='im:[email-masked]'
   destination=IM:[email-masked]' transID='1' /> ... Content-Type: text/plain;
   charset="us-ascii" Yabba, dabba, doo!

   The service immediately responds by invoking the response operation
   containing the same transaction-identifier, e.g.,

   +-------+ +-------+ | | | | | appl. | <----- response -- | IM | | | | svc. | +-------+
   +-------+ <response status='success' transID='1' />

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2.2 Identification of INSTANT INBOXes

   An INSTANT INBOX is specified using the IM URI (Section 5.1)f RFC
   822[1] (i.e., "local@domain") is used, where the local-part MUST be
   interpreted and assigned semantics only by the host specified in the
   domain part of the identifier. Representation of non-ASCII character
   sets in local-part strings is limited to the standard methods
   provided as extensions to RFC 822[1]

2.2.1 Address Resolution

   A client determines the address of an appropriate host running a
   server by resolving the destination domain name that is part of the
   identifier to either an intermediate relay host or a final target
   host.

   Only resolvable, fully-qualified, domain names (FQDNs) are permitted
   when domain names are used in the messaging service (i.e., domain
   names that can be resolved to SRV[9] or A RRs).

2.2.1.1 Domain Name Lookup

   A client lexically identifies a domain to which instant messages
   will be delivered for processing, a DNS lookup MUST be performed to
   resolve the domain[2]. The names MUST be fully-qualified domain
   names (FQDNs) -- mechanisms for inferring FQDNs from partial names
   or local aliases are a local matter.

   The lookup first attempts to locate SRV RRs associated with the
   domain. If a CNAME RR is found instead, the resulting domain is
   processed as if it were the initial domain.

   If one or more SRV RRs are found for a given domain, a sender MUST
   NOT utilize any A RRs associated with that domain unless they are
   located using the SRV RRs; otherwise, if no SRV RRs are found, but
   an A RR is found, then the A RR is treated as if it was associated
   with an implicit SRV RR, with a preference of 0, pointing to that
   host.

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2.2.1.2 Processing SRV RRs

   To process an IM URI, a lookup is performed for SRVs for the target
   domain and a desired IM transport protocol.

   For example, if the destination INSTANT INBOX is
   "IM:[email-masked]", and the sender wishes to use an IM transport
   protocol called "SIP", then a SRV lookup is performed for:
    _IM_sip.example.com.
   The returned RRs, if any, specify the next-hop server.

   The choice of IM transport protocol is a local configuration option
   for each system.

   Using this mechanism, seamless routing of IM traffic is possible,
   regardless of whether a gateway is necessary for interoperation. To
   achieve this transparency, a separate RR for a gateway must be
   present for each transport protocol and domain pair that it serves.

2.2.1.3 Processing Multiple Addresses

   When the lookup succeeds, the mapping can result in a list of
   alternative delivery addresses rather than a single address, because
   of multiple SRV records, multihoming, or both. For reliable
   operations, the client MUST be able to try each of the relevant
   addresses in this list in order, until a delivery attempt succeeds.
   However, there MAY also be a configurable limit on the number of
   alternate addresses that can be tried. In any case, the client
   SHOULD try at least two addresses. Two types of information are used
   to rank the host addresses: multiple SRV records, and multihomed
   hosts.

   Multiple SRV records contain a preference indication that MUST be
   used in sorting. Lower numbers are preferable to higher ones. If
   there are multiple destinations with the same preference, and there
   is no clear reason to favor one (e.g., by recognition of an
   easily-reached address), then the sender MUST randomize them to
   spread the load across multiple servers for a specific destination.

   The destination host (perhaps taken from the preferred SRV record)
   may be multihomed, in which case the resolver will return a list of
   alternative IP addresses. It is the responsibility of the resolver
   to have ordered this list by decreasing preference if necessary, and
   the sender MUST try them in the order presented.

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2.3 Format of Instant Messages

   An INSTANT MESSAGE comprises a MIME Multipart/Related,
   Type=message/RFC822+XML object, as defined in XML/MIME[5].
   Representation of non-ASCII character sets in MIME is a standard
   feature of MIME.

   Note that the IETF provides numerous technologies that allow
   end-users to exchange authenticated and private messages formatted
   as MIME objects, c.f., PGP-MIME[4] and S/MIME[6].

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2.4 The Messaging Service

   Section 6 and Section 7 define the abstract syntax of the operations
   invoked with the service.

   Note that the transaction-identifier parameters used with the
   service are potentially long-lived. Accordingly, the values of
   transaction-identifiers should appear to be unpredictable.

2.4.1 The Message Operation

   When an application wants to send an INSTANT MESSAGE, it invokes the
   message operation.

   The message operation has these parameters: 

   o  the source parameter specifies the INSTANT INBOX on whose behalf
      this message is sent (using an IM URI);

   o  the destination parameter specifies the INSTANT INBOX that the
      message should be delivered to (using an IM URI);

   o  the transID parameter specifies the transaction-identifier
      associated with this operation; and,

   o  the message to be sent.

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   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: 

       1.  If the service is able to successfully deliver the message,
           a response operation having status "success" is invoked.

       2.  If the service is unable to successfully deliver the
           message, a response operation having status "failure" is
           invoked.

       3.  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.

       4.  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.

2.4.2 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.

   [[[ In Internet Mail, counting the number of Received headers is the
   accepted technique for guessing that looping is occurring. Use of
   this technique will require Instant Messaging to support Received
   headers. /editor ]]]

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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.
   | +-------+ +-------+ <subscribe watcher='pres:[email-masked]' target='pres:[email-masked]'
   duration='86400' transID='2' />

   The service immediately responds by invoking the response operation
   containing the same transaction-identifier, e.g.,
    +-------+ +-------+
   | | | | | appl. | <----- response -- | pres. | | | | svc. | +-------+ +-------+
   <response status='success' transID='2' duration='3600' />
   A WATCHER may have at most one subscription for a PRESENTITY.

   If the response operation indicates success, the service immediate
   invokes the notify operation to communicate the presence information
   to the WATCHER, e.g.,
    +-------+ +-------+ | | |
   | | appl. | <------- notify -- | pres. | | | | svc. | +-------+ +-------+ <notify
   watcher='pres:[email-masked]' target='pres:[email-masked]' transID='1234'>
   <presence entityInfo='http://www.example.com/Fred/'> <tuple destination=IM:[email-masked]'
   status='open' /> </presence> </notify>
   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).

   The application may prematurely cancel a subscription by invoking
   the unsubscribe operation, e.g.,
    +-------+ +-------+ | | | | |
   appl. | -- unsubscribe --> | pres. | | | | svc. | +-------+ +-------+ <unsubscribe
   watcher='pres:[email-masked]' target='pres:[email-masked]' transID='3' />

   The service immediately responds by invoking the response operation
   containing the same transaction-identifier, e.g.,
    +-------+ +-------+ | | | | | appl. | <-----
   response -- | pres. | | | | svc. | +-------+ +-------+ <response status='success'
   transID='3' />

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3.2 Identification of PRESENTITIES

   A PRESENTITY is specified using the PRES URI (Section 5.2) scheme.
   Briefly, the "addr-spec" syntax of RFC 822[1] (i.e., "local@domain")
   is used, where the local-part MUST be interpreted and assigned
   semantics only by the host specified in the domain part of the
   identifier. Representation of non-ASCII character sets in local-part
   strings is limited to the standard methods provided as extensions to
   RFC 822[1]

   To resolve identifiers associated with the Presence service, the
   mechanism defined in Section 2.2.1 is used, except that the
   processing of a PRES URI is performed by looking up SRV RRs for a
   desired presence transport protocol.

   For example, if the destination PRESENTITY is
   "pres:[email-masked]", and the sender wishes to use a presence
   transport protocol called "PEPP", then a SRV lookup is performed for:
    _pres._pepp.example.com.

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3.3 Format of Presence Information

   Section 9 defines the syntax for presence information using an XML
   DTD.

   Each PRESENTITY's presence information contains an "entityInfo"
   attribute, and contains one or more "tuple" elements: 

   o  the "entityInfo" attribute specifies arbitrary information about
      the PRESENTITY (using a URI); and,

   o  each "tuple" element specifies information associated with the
      PRESENTITY.

   Each "tuple" element has a "destination" attribute, a "status"
   attribute, and contains arbitrary content: 

   o  the "destination" attribute specifies a URI;

   o  the "status" attribute is either OPEN or CLOSED; and,

   o  the content of the "tuple" element contains arbitrary information
      about the tuple.

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3.4 The Presence Service

   Section 6 and Section 8 define the abstract syntax of the operations
   invoked with the 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 with the service
   is potentially long-lived. Accordingly, the values generated for
   this parameter should appear to be unpredictable.

3.4.1 The Subscribe Operation

   When an application wants to (periodically) receive the presence
   information associated with an PRESENTITY, it invokes the subscribe
   operation.

   The subscribe operation has these parameters: 

   o  the watcher parameter specifies the WATCHER associated with the
      subscription;

   o  the target parameter specifies the PRESENTITY associated with the
      presence information;

   o  the duration parameter specifies the maximum number of seconds
      that the SUBSCRIPTION should be active; and,

   o  the transID parameter specifies the transaction-identifier
      associated with this operation.

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   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: 

       1.  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.)

       2.  A notify operation, corresponding to the target's presence
           information, is immediately invoked for the watcher.

       3.  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, Step 4.3 above 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.

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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.

   The notify operation has these parameters: 

   o  the watcher parameter specifies the WATCHER associated with the
      subscription;

   o  the target parameter specifies the PRESENTITY associated with the
      presence information;

   o  the transID parameter specifies the transaction-identifier
      associated with this operation; and,

   o  the presence information for the PRESENTITY.

   There is no application response to the notify operation.

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3.4.3 The Unsubscribe Operation

   When an application wants to terminate a subscription, it invokes
   the unsubscribe operation.

   The unsubscribe operations has these parameters: 

   o  the watcher parameter specifies the WATCHER associated with the
      subscription;

   o  the target parameter specifies the PRESENTITY associated with the
      presence information; and,

   o  the transID parameter specifies the transaction-identifier
      associated with this operation.

   When the service is informed of the unsubscribe operation, it
   performs these steps: 

   1.  If the watcher and target parameters do not refer to an
       in-progress subscribe operation for the application, a response
       operation having status "failure" is invoked.

   2.  Otherwise, the in-progress subscribe operation for the
       application is terminated, and a response operation having
       status "success" is invoked by the service.

   Note that following a successful unsubscribe operation, the WATCHER
   may receive further notifications. Although the service will no
   longer invoke the notify operation after successfully processing a
   unsubscribe operation, earlier notify operations may still be in
   progress.

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4. Security Considerations

   This memo makes no specific requirements on security procedures for
   interoperation between IM systems. Accordingly, trust between
   interconnected IM systems is determined in a bilateral matter.

   However, this memo does require that each IM system control access
   to its Instant Messaging and Presence services. Consult both RFC
   2778 and RFC2779 for a discussion of security considerations for for
   IM systems.

   [[[ THREAT ANALYSIS GOES HERE -- No WG discussion or consensus
   provides a basis for candidate text, yet. /Editor ]]]

   Instant messaging and presence systems can provide security at two
   levels: hop-by-hop and/or end-to-end.

4.1 Hop-by-hop security

   A useful but imperfect level of security can be provided on a
   hop-by-hop basis using transport level security between servers. The
   main drawback of this approach is that it requires that each server
   that handles message or presence information must be trusted. But it
   is relatively easy to deploy, because it depends only on bilateral
   arrangements between directly communicating servers, with all
   aspects of the communication, including message content and
   originator verification.

   The underlying principles for using hop-by-hop security are:

   (a) each server and/or domain must keep their own house in order,
   ensuring that operations and information accesses are allowed only
   to appropriately authorized parties, and

   (b) each server and/or domain must make its own choices about the
   levels of trust to be established to any other server and/or domain
   with which they directly communicate. [[[Some debate about the
   degree of trust necessary between servers. /dc]]]

   When passing IM and presence information between services using
   different protocols, a gateway system MUST be capable of using
   security mechanisms appropriate to each of the protocols concerned,
   and must have access to keys needed to authenticate any other system
   with which it needs to directly communicate in a secure fashion.

   [[[SUGGESTION: to allow the use of common keys across different
   protocols, we might say that hop-by-hop security should be based on
   SASL, and specify specific profiles that should be used. This
   doesn't buy anything at the protocol level, but it might make it

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   easier to leverage some common key-distribution infrastructure, and
   avoid having to distribute different keys for communicating with a
   gateway using different protocols.]]]

4.2 End-to-end security

   End-to-end security is widely regarded as being more satisfactory
   than hop-by-hop security, as the need to trust intermediate parties
   is reduced. However, some aspects of end-to-end security are
   difficult to achieve because they need bilateral arrangement between
   any pair of communicating parties about acceptable security
   standards to use, and key exchange. Reliance on bilateral agreements
   does not scale well. A moderating alternative is a third-party
   certification service and this approach, so far, has not found
   large-scale use.

   The two IETF standards for end-to-end MIME object security are
   OpenPGP[7] and S/MIME[8]. They require a public key operation for
   each message. For repeated, short transactions, this overhead can be
   onerous. A version of these specifications which permitted reuse of
   the public key across multiple messages would greatly reduce instant
   messaging overhead.

4.2.1  Instant messages

   End to end security for instant messages can be provided using any
   of the MIME-based security mechanisms (S/MIME [8], OpenPGP [7]), as
   instant message payload content is not interpreted or reformatted in
   transit.

   [[[NOTE: may need to say something about allowable MIME C-T-Es?]]]

   This specification allows any pair of communicating parties to use
   any MIME-based security framework for instant messages (c.f. section
   2.3), but mechanisms for establishing the required bilateral
   arrangements and key exchange are not specified here.

4.2.2 Presence service

   The situation regarding end-to-end security for presence services is
   unclear, as there is no common encapsulation framework specified for
   presence, and the presence data itself is not invariant across
   different IM services.

   [[[NOTE: this raises a case for fixing the presence information to a
   specific format if end-to-end security capability is to be a
   requirement.]]]

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5. IANA Considerations

   The IANA assigns the "IM" and "pres" URL schemes.

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 URL has the form:
    "IM:" addr-spec
   where "addr-spec" is defined in RFC 822.

5.2 The PRES URI Scheme

   The Presence (PRES) URI scheme designates an Internet resource,
   namely a PRESENTITY or WATCHER.

   The syntax of a PRES URL has the form:
    "pres:" addr-spec
   where "addr-spec" is defined in RFC 822.

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6. The Common Service DTD
    <!-- DTD for the IM common profile, as of 2000-08-16
   Refer to this DTD as: <!ENTITY % IMCOMMON PUBLIC "-//Blocks//DTD IM COMMON//EN"
   "http://xml.resource.org/syntaxes/IM/im-common.dtd"> %IMCOMMON; --> <!-- DTD data
   types: entity syntax/reference example ====== ================ ======= a language
   tag LANG c.f., [RFC-1766] "en", "en-US", etc. seconds SECONDS 0..2147483647 600
   unique-identifier UNIQID 1..2147483647 42 authoritative identity URI c.f., [RFC-2396]
   http://invisible.net/ --> <!ENTITY % LANG "NMTOKEN"> <!ENTITY % SECONDS "CDATA">
   <!ENTITY % UNIQID "CDATA"> <!ENTITY % URI "CDATA"> <!-- Abstract syntax for the
   response operation --> <!ELEMENT response (#PCDATA)> <!ATTLIST response status
   (success | failure | indeterminant) #REQUIRED transID %UNIQID; #REQUIRED duration
   %SECONDS; #IMPLIED xml:lang %LANG; #IMPLIED >

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7. The Messaging Service DTD

   <!-- DTD for the abstract IM messaging service, as of 2000-08-16 Refer to this
   DTD as: <!ENTITY % IMMESSAGING PUBLIC "-//Blocks//DTD IM MESSAGING//EN" "http://xml.resource.org/syntaxes/IM/im-messaging.dtd">
   %IMMESSAGING; --> <!ENTITY % IMCOMMON PUBLIC "-//Blocks//DTD IM COMMON//EN" "http://xml.resource.org/syntaxes/IM/im-common.dtd">
   %IMCOMMON; <!-- DTD data types: entity syntax/reference example ====== ================
   ======= INBOX c.f., Section 5.1 IM:[email-masked] --> <!ENTITY % INBOX "CDATA">
   <!-- Abstract syntax for the message operation --> <!ELEMENT message (#PCDATA)>
   <!ATTLIST message source %INBOX; #REQUIRED destination %INBOX; #REQUIRED transID
   %UNIQID; #REQUIRED >

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8. The Presence Service DTD
    <!-- DTD for the abstract IM presence service, as
   of 2000-08-16 Refer to this DTD as: <!ENTITY % IMPRESENCE PUBLIC "-//Blocks//DTD
   IM PRESENCE//EN" "http://xml.resource.org/syntaxes/IM/im-presence.dtd"> %IMPRESENCE;
   --> <!ENTITY % IMCOMMON PUBLIC "-//Blocks//DTD IM COMMON//EN" "http://xml.resource.org/syntaxes/IM/im-common.dtd">
   %IMCOMMON; <!-- DTD data types: entity syntax/reference example ====== ================
   ======= PRESENTITY c.f., Section 5.2 pres:[email-masked] --> <!ENTITY % PRESENTITY
   "CDATA"> <!-- Abstract syntax for presence information --> <!ELEMENT presence
   (tuple+)> <!ATTLIST presence entityInfo %URI; "" > <!ELEMENT tuple (#PCDATA)>
   <!ATTLIST tuple destination %URI; #REQUIRED status (open | closed) #REQUIRED >
   <!-- Abstract syntax for the subscribe operation --> <!ELEMENT subscribe EMPTY>
   <!ATTLIST subscribe watcher %PRESENTITY; #REQUIRED target %PRESENTITY; #REQUIRED
   duration %SECONDS; #REQUIRED transID %UNIQID; #REQUIRED > <!-- Abstract syntax
   for the notify operation --> <!ELEMENT notify (presence)> <!ATTLIST notify watcher
   %PRESENTITY; #REQUIRED target %PRESENTITY; #REQUIRED transID %UNIQID; #REQUIRED
   > <!-- Abstract syntax for the unsubscribe operation --> <!ELEMENT unsubscribe
   EMPTY> <!ATTLIST unsubscribe watcher %PRESENTITY; #REQUIRED target %PRESENTITY;
   #REQUIRED transID %UNIQID; #REQUIRED >

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9. The Presence Information DTD
    <!-- DTD the IM presence information of 2000-11-6 Refer to
   this DTD as: <!ENTITY % IMPRESENCEINFO PUBLIC "-//Blocks//DTD IM PRESENCE//EN"
   "http://xml.resource.org/syntaxes/IM/im-presence-info.dtd"> %IMPRESENCEINFO; -->
   <!ENTITY % IMCOMMON PUBLIC "-//Blocks//DTD IM COMMON//EN" "http://xml.resource.org/syntaxes/IM/im-common.dtd">
   %IMCOMMON; <!-- DTD data types: entity syntax/reference example ====== ================
   ======= PRESENTITY c.f., Section 5.2 pres:[email-masked] --> <!ENTITY % PRESENTITY
   "CDATA"> <!-- Abstract syntax for presence information --> <!ELEMENT presence
   (tuple+)> <!ATTLIST presence entityInfo %URI; "" > <!ELEMENT tuple (#PCDATA)>
   <!ATTLIST tuple destination %URI; #REQUIRED status (open | closed) #REQUIRED >

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References

   [1]   Crocker, D., "Standard for the format of ARPA Internet text
         messages", RFC 822, STD 11, Aug 1982.

   [2]   Mockapetris, P.V., "Domain names - concepts and facilities",
         RFC 1034, STD 13, Nov 1987.

   [3]   Freed, N. and N. Borenstein, "Multipurpose Internet Mail
         Extensions (MIME) Part One: Format of Internet Message
         Bodies", RFC 2045, November 1996.

   [4]   Callas, J., Donnerhacke, L., Finney, H. and R. Thayer,
         "OpenPGP Message Format", RFC 2440, November 1998.

   [5]   Klyne, G., "XML coding of RFC822 messages", I-D
         draft-klyne-message-rfc822-xml-00.txt,November 2000.

   [6]   Ramsdell, B., "S/MIME Version 3 Certificate Handling", RFC
         2632, June 1999.

   [7]   Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence
         and Instant Messaging", RFC 2778, February 2000.

   [8]   Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
         Presence Protocol Requirements", RFC 2779, February 2000.

   [9]   Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for
         specifying the location of services (DNS SRV)", RFC 2782,
         February 2000.

   [10]  Allocchio, C., "GSTN Address Element Extensions in E-mail
         Services", RFC 2846, June 2000.

Authors' Addresses

   Dave Crocker
   Brandenburg Consulting
   4516 Henry Street
   Suite 113
   Pittsburgh, PA  15213
   US

   Phone: +1 408 246 8253
   EMail: [email-masked]

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   Athanassios Diacakis
   Network Projects Inc.
   4516 Henry Street
   Suite 113
   Pittsburgh, PA  15213
   US

   Phone: +1 412 681 6950 x202
   EMail: [email-masked]

   Florencio Mazzoldi
   Network Projects Inc.
   4516 Henry Street
   Suite 113
   Pittsburgh, PA  15213
   US

   Phone: +1 412 681 6950
   EMail: [email-masked]

   Christian Huitema
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052-6399
   US

   EMail: [email-masked]

   Graham Klyne
   Content Technologies

   Phone: 
   EMail: 

   Marshall Rose
   Invisible Worlds

   Phone: 
   EMail: 

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   Jonathan Rosenberg
   dynamicsoft
   200 Executive Drive
   Suite 120
   West Orange, NJ  07052
   US

   EMail: [email-masked]

   Robert Sparks
   dynamicsoft
   200 Executive Drive
   Suite 120
   West Orange, NJ  07052
   US

   EMail: [email-masked]

   Hiroyasu Sugano
   Fujitsu Laboratories Ltd.
   64 Nishiwaki, Ohkubo-cho
   Akashi  674-8555
   JP

   EMail: [email-masked]

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Appendix A. Issues of Interest

   This appendix briefly discusses issues that may be of interest when
   designing an interoperation gateway.

A.1 Address Mapping

   When mapping the service described in this memo, mappings which
   place special information into the IM address local part SHOULD use
   the meta-syntax defined in RFC 2486[10].

A.1.1 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.

   The transformation 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 mapping should be performed
   automatically by the underlying software.

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Full Copyright Statement

   Copyright (C) The Internet Society (2000). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
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Acknowledgement

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

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