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rfc:rfc3340

Network Working Group M. Rose Request for Comments: 3340 Dover Beach Consulting, Inc. Category: Standards Track G. Klyne

                                                Clearswift Corporation
                                                            D. Crocker
                                           Brandenburg InternetWorking
                                                             July 2002
                   The Application Exchange Core

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

 This memo describes Application Exchange (APEX) Core, an extensible,
 asynchronous message relaying service for application layer programs.

Table of Contents

 1.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  2
 1.1     Overview . . . . . . . . . . . . . . . . . . . . . . . . .  3
 1.2     Architecture at a Glance . . . . . . . . . . . . . . . . .  4
 2.      Service Principles . . . . . . . . . . . . . . . . . . . .  5
 2.1     Modes of Operation . . . . . . . . . . . . . . . . . . . .  5
 2.2     Naming of Entities . . . . . . . . . . . . . . . . . . . .  6
 2.2.1   Comparing Endpoints  . . . . . . . . . . . . . . . . . . .  7
 3.      Service Provisioning . . . . . . . . . . . . . . . . . . .  7
 3.1     Connection Establishment . . . . . . . . . . . . . . . . .  7
 3.2     Authentication . . . . . . . . . . . . . . . . . . . . . .  8
 3.3     Authorization  . . . . . . . . . . . . . . . . . . . . . .  8
 3.4     Confidentiality  . . . . . . . . . . . . . . . . . . . . .  8
 3.5     Relaying Integrity . . . . . . . . . . . . . . . . . . . .  8
 3.6     Traffic Analysis . . . . . . . . . . . . . . . . . . . . .  9
 4.      The APEX . . . . . . . . . . . . . . . . . . . . . . . . .  9
 4.1     Use of XML and MIME  . . . . . . . . . . . . . . . . . . .  9
 4.2     Profile Identification and Initialization  . . . . . . . . 10
 4.3     Message Syntax . . . . . . . . . . . . . . . . . . . . . . 11

Rose, et. al. Standards Track [Page 1] RFC 3340 The Application Exchange Core July 2002

 4.4     Message Semantics  . . . . . . . . . . . . . . . . . . . . 11
 4.4.1   The Attach Operation . . . . . . . . . . . . . . . . . . . 11
 4.4.2   The Bind Operation . . . . . . . . . . . . . . . . . . . . 13
 4.4.3   The Terminate Operation  . . . . . . . . . . . . . . . . . 14
 4.4.4   The Data Operation . . . . . . . . . . . . . . . . . . . . 15
 4.4.4.1 Relay Processing of Data . . . . . . . . . . . . . . . . . 17
 4.4.4.2 Application Processing of Data . . . . . . . . . . . . . . 18
 4.5     APEX Access Policies . . . . . . . . . . . . . . . . . . . 19
 4.5.1   Access Policies in the Endpoint-Relay Mode . . . . . . . . 19
 4.5.2   Access Policies in the Relay-Relay Mode  . . . . . . . . . 20
 5.      APEX Options . . . . . . . . . . . . . . . . . . . . . . . 20
 5.1     The statusRequest Option . . . . . . . . . . . . . . . . . 22
 6.      APEX Services  . . . . . . . . . . . . . . . . . . . . . . 26
 6.1     Use of the APEX Core DTD . . . . . . . . . . . . . . . . . 27
 6.1.1   Transaction-Identifiers  . . . . . . . . . . . . . . . . . 27
 6.1.2   The Reply Element  . . . . . . . . . . . . . . . . . . . . 28
 6.2     The Report Service . . . . . . . . . . . . . . . . . . . . 28
 7.      Registration Templates . . . . . . . . . . . . . . . . . . 29
 7.1     APEX Option Registration Template  . . . . . . . . . . . . 29
 7.2     APEX Service Registration Template . . . . . . . . . . . . 29
 7.3     APEX Endpoint Application Registration Template  . . . . . 30
 8.      Initial Registrations  . . . . . . . . . . . . . . . . . . 30
 8.1     Registration: The APEX Profile . . . . . . . . . . . . . . 30
 8.2     Registration: The System (Well-Known) TCP port number for
         apex-mesh  . . . . . . . . . . . . . . . . . . . . . . . . 31
 8.3     Registration: The System (Well-Known) TCP port number for
         apex-edge  . . . . . . . . . . . . . . . . . . . . . . . . 31
 8.4     Registration: The statusRequest Option . . . . . . . . . . 31
 8.5     Registration: The Report Service . . . . . . . . . . . . . 32
 9.      DTDs . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
 9.1     The APEX Core DTD  . . . . . . . . . . . . . . . . . . . . 32
 9.2     The Report Service DTD . . . . . . . . . . . . . . . . . . 34
 10.     Reply Codes  . . . . . . . . . . . . . . . . . . . . . . . 35
 11.     Security Considerations  . . . . . . . . . . . . . . . . . 36
         References . . . . . . . . . . . . . . . . . . . . . . . . 36
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . 38
 A.      Acknowledgements . . . . . . . . . . . . . . . . . . . . . 39
 B.      IANA Considerations  . . . . . . . . . . . . . . . . . . . 39
         Full Copyright Statement . . . . . . . . . . . . . . . . . 40

1. Introduction

 Network applications can be broadly distinguished by five operational
 characteristics:
 o  server push or client pull;
 o  synchronous (interactive) or asynchronous (batch);

Rose, et. al. Standards Track [Page 2] RFC 3340 The Application Exchange Core July 2002

 o  time-assured or time-insensitive;
 o  best-effort or reliable; and,
 o  stateful or stateless.
 For example:
 o  the world-wide web is a pull, synchronous, time-insensitive,
    reliable, stateless service; whilst
 o  Internet mail is a push, asynchronous, time-insensitive, best-
    effort (without DSN), stateless service.
 Messaging applications vary considerably in their operational
 requirements.  For example, some messaging applications require
 assurance of timeliness and reliability, whilst others do not.
 These features come at a cost, in terms of both infrastructural and
 configuration complexity.  Accordingly, the underlying service must
 be extensible to support different requirements in a consistent
 manner.
 This memo defines a core messaging service that supports a range of
 operational characteristics.  The core service supports a variety of
 tailored services for both user-based and programmatic exchanges.

1.1 Overview

 APEX provides an extensible, asynchronous message relaying service
 for application layer programs.
 APEX, at its core, provides a best-effort datagram service.  Each
 datagram, simply termed "data", is originated and received by APEX
 "endpoints" -- applications that dynamically attach to the APEX
 "relaying mesh".
 The data transmitted specifies:
 o  an originating endpoint;
 o  an opaque content (via a URI-reference);
 o  one or more recipient endpoints; and,
 o  zero or more options.

Rose, et. al. Standards Track [Page 3] RFC 3340 The Application Exchange Core July 2002

 Options are used to alter the semantics of the service, which may
 occur on a per-recipient or per-data basis, and may be processed by
 either a single or multiple relays.
 Additional APEX services are provided on top of the relaying mesh;
 e.g., access control and presence information.
 APEX is specified, in part, as a BEEP [1] "profile".  Accordingly,
 many aspects of APEX (e.g., authentication) are provided within the
 BEEP core.  Throughout this memo, the terms "peer", "initiator",
 "listener", "client", and "server" are used in the context of BEEP.
 In particular, Section 2.1 of the BEEP core memo discusses the roles
 that a BEEP peer may perform.
 When reading this memo, note that the terms "endpoint" and "relay"
 are specific to APEX, they do not exist in the context of BEEP.

1.2 Architecture at a Glance

 The APEX stack:
    +-------------+
    | APEX        |        an APEX process is either:
    |     process |
    +-------------+            - an application attached as an APEX
    |             |              endpoint; or,
    |    APEX     |
    |             |            - an APEX relay
    +-------------+
    |             |        APEX services are realized as applications
    |    BEEP     |        having a special relationship with the APEX
    |             |        relays in their administrative domain
    +-------------+
    |     TCP     |
    +-------------+
    |     ...     |
    +-------------+

Rose, et. al. Standards Track [Page 4] RFC 3340 The Application Exchange Core July 2002

 The APEX entities:
        administrative domain #1          administrative domain #2
     +----------------------------+    +----------------------------+
     |   +------+                 |    |                 +------+   |
     |   |      |                 |    |                 |      |   |
     |   | appl |                 |    |                 | appl |   |
     |   |      |                 |    |                 |      |   |
     |   +......+       +------+  |    |  +------+       +......+   |
     |   |      |       |      |  |    |  |      |       |      |   |
     |   |end-  |       |relay |  |    |  |relay |       |end-  |   |
     |   | point|       |      |  |    |  |      |       | point|   |
     |   +------+       +------+  |    |  +------+       +------+   |
     |   |      |       |      |  |    |  |      |       |      |   |
     |   | APEX |       | APEX |  |    |  | APEX |       | APEX |   |
     |   |      |       |      |  |    |  |      |       |      |   |
     |   +------+       +------+  |    |  +------+       +------+   |
     |        ||         ||  ||   |    |   ||  ||         ||        |
     |        =============  ================  =============        |
     +----------------------------+    +----------------------------+
                    | <---- APEX relaying mesh ----> |
         Note: relaying between administrative domains is configured
               using SRV RRs.  Accordingly, the actual number of
               relays between two endpoints is not fixed.

2. Service Principles

2.1 Modes of Operation

 APEX is used in two modes:
 endpoint-relay: in which the endpoint is always the BEEP initiator of
    the service, whilst relays are always the BEEP listeners.  In this
    context, applications attach as endpoints, and then the
    transmission of data occurs.
 relay-relay: in which relays typically, though not necessarily,
    reside in different administrative domains.  In this context,
    applications bind as relays, and then the transmission of data
    occurs.
 In the endpoint-relay mode, an endpoint (BEEP initiator) may:
 o  attach as one or more endpoints;
 o  send data to other endpoints;

Rose, et. al. Standards Track [Page 5] RFC 3340 The Application Exchange Core July 2002

 o  receive data from other endpoints; and,
 o  terminate any of its attachments.
 A relay (BEEP listener), in addition to servicing requests from a
 BEEP initiator, may:
 o  terminate any of the endpoint's attachments;
 o  deliver data from other endpoints; and,
 o  indicate the delivery status of data sent earlier by the endpoint.
 In the relay-relay mode, a relay (BEEP listener or initiator) may:
 o  bind as one or more administrative domains;
 o  send data;
 o  receive data; and,
 o  terminate any bindings.

2.2 Naming of Entities

 Endpoints are named using the following ABNF [2] syntax:
    ;; Domain is defined in [3], either a FQDN or a literal
    entity      = local "@" Domain
    local       = address [ "/" subaddress ]
    address     = token
    subaddress  = token
    ;; all non-control characters, excluding "/" and "@" delimiters
    token       = 1*(%x20-2E / %x30-3F / %x41-7E / UTF-8) ;; [4]
 Two further conventions are applied when using this syntax:
 the "apex=" convention: All endpoint identities having a local-part
    starting with "apex=" are reserved for use by APEX services
    registered with the IANA; and,

Rose, et. al. Standards Track [Page 6] RFC 3340 The Application Exchange Core July 2002

 the "subaddress" convention: If the solidus character ("/", decimal
    code 47) occurs in the local-part, this identifies a subaddress of
    an endpoint identity (e.g., "fred/appl=wb@example.com" is a
    subaddress of the APEX endpoint "fred@example.com").
    All subaddresses starting with "appl=" are reserved for use by
    APEX endpoint applications registered with the IANA.
 Relays, although not named, serve of behalf of administrative
 domains, as identified by a FQDN or a domain-literal, e.g.,
 "example.com" or "[10.0.0.1]".
 In APEX, "endpoints" and "relays" are the fundamental entities.  APEX
 is carried over BEEP, which has the "peer" as its fundamental entity.
 The relationship between BEEP peer entities and APEX endpoint and
 relay entities are defined by APEX's Access Policies (Section 4.5).

2.2.1 Comparing Endpoints

 Note that since the "local" part of an entity is a string of UTF-8
 [4] octets, comparison operations on the "local" part use exact
 matching (i.e., are case-sensitive).
 Accordingly, "fred@example.com" and "Fred@example.com" refer to
 different endpoints.  Of course, relays serving the "example.com"
 administrative domain may choose to treat the two endpoints
 identically for the purposes of routing and delivery.
 Finally, note that if an APEX endpoint is represented using a
 transmission encoding, then, prior to comparison, the encoding is
 reversed.  For example, if the URL encoding is used, then
 "apex:fred@example.com" is identical to "apex:f%72ed@example.com".

3. Service Provisioning

3.1 Connection Establishment

 The SRV algorithm [5] is used to determine the IP/TCP addressing
 information assigned to the relays for an administrative domain
 identified by a FQDN:
 service: "apex-edge" (for the endpoint-relay mode), or "apex-mesh"
    (for the relay-relay mode);
 protocol: "tcp"; and,
 domain: the administrative domain.

Rose, et. al. Standards Track [Page 7] RFC 3340 The Application Exchange Core July 2002

 If the administrative domain is identified by a domain-literal, then
 the IP address information is taken directly from the literal and the
 TCP port number used is assigned by the IANA for the registration in
 Section 8.2.

3.2 Authentication

 Authentication is a matter of provisioning for each BEEP peer (c.f.,
 Section 4.5).
 An APEX relay might be provisioned to allow a BEEP peer identity to
 coincide with a given endpoint identity.  For example, a relay in the
 "example.com" administrative domain may be configured to allow a BEEP
 peer identified as "fred@example.com" to be authorized to attach as
 the APEX endpoint "fred@example.com".

3.3 Authorization

 Authorization is a matter of provisioning for each BEEP peer (c.f.,
 Section 4.5).
 Typically, a relay requires that its BEEP peer authenticate as a
 prelude to authorization, but an endpoint usually does not require
 the same of its BEEP peer.

3.4 Confidentiality

 Confidentiality is a matter of provisioning for each BEEP peer.
 Typically, any data considered sensitive by an originating endpoint
 will have its content encrypted for the intended recipient
 endpoint(s), rather than relying on hop-by-hop encryption.
 Similarly, an originating endpoint will sign the content if end-to-
 end authentication is desired.

3.5 Relaying Integrity

 Data are relayed according to SRV entries in the DNS.  Accordingly,
 relaying integrity is a function of the DNS and the applications
 making use of the DNS.  Additional assurance is provided if the BEEP
 initiator requires that the BEEP listener authenticate itself.

Rose, et. al. Standards Track [Page 8] RFC 3340 The Application Exchange Core July 2002

3.6 Traffic Analysis

 Hop-by-hop protection of data transmitted through the relaying mesh
 (endpoint identities and content) is afforded at the BEEP level
 through the use of a transport security profile.  Other traffic
 characteristics, e.g., volume and timing of transmissions, are not
 protected from third-party analysis.

4. The APEX

 Section 8.1 contains the BEEP profile registration for APEX.

4.1 Use of XML and MIME

 Each BEEP payload exchanged via APEX consists of an XML document and
 possibly an arbitrary MIME content.
 If only an XML document is sent in the BEEP payload, then the mapping
 to a BEEP payload is straight-forward, e.g.,
    C: MSG 1 2 . 111 39
    C: Content-Type: application/beep+xml
    C:
    C: <terminate transID='1' />
    C: END
 Otherwise, if an arbitrary MIME content is present, it is indicated
 by a URI-reference [6] in the XML control document.  The URI-
 reference may contain an absolute-URI (and possibly a fragment-
 identifier), or it may be a relative-URI consisting only of a
 fragment-identifier.  Arbitrary MIME content is included in the BEEP
 payload by using a "multipart/related" [7], identified using a "cid"
 URL [8], and the XML control document occurs as the start of the
 "multipart/related", e.g.,
    C: MSG 1 1 . 42 1234
    C: Content-Type: multipart/related; boundary="boundary";
    C:               start="<1@example.com>";
    C:               type="application/beep+xml"
    C:
    C: --boundary
    C: Content-Type: application/beep+xml
    C: Content-ID: <1@example.com>
    C:
    C: <data content='cid:2@example.com'>
    C:     <originator identity='fred@example.com' />
    C:     <recipient identity='barney@example.com' />
    C: </data>

Rose, et. al. Standards Track [Page 9] RFC 3340 The Application Exchange Core July 2002

    C: --boundary
    C: Content-Type: image/gif
    C: Content-Transfer-Encoding: binary
    C: Content-ID: <2@example.com>
    C:
    C: ...
    C: --boundary--
    C: END
 Because BEEP provides an 8bit-wide path, a "transformative" Content-
 Transfer-Encoding (e.g., "base64" or "quoted-printable") should not
 be used.  Further, note that MIME [9] requires that the value of the
 "Content-ID" header be globally unique.
 If the arbitrary MIME content is itself an XML document, it may be
 contained within the control document directly as a "data-content"
 element, and identified using a URI-reference consisting of only a
 fragment-identifier, e.g.,
    C: MSG 1 1 . 42 295
    C: Content-Type: application/beep+xml
    C:
    C: <data content='#Content'>
    C:     <originator identity='fred@example.com' />
    C:     <recipient identity='barney@example.com' />
    C:     <data-content Name='Content'>
    C:         <statusResponse transID='86'>
    C:             <destination identity='barney@example.com'>
    C:                 <reply code='250' />
    C:             </destination>
    C:         </statusResponse>
    C:     </data-content>
    C: </data>
    C: END

4.2 Profile Identification and Initialization

 The APEX is identified as
    http://iana.org/beep/APEX
 in the BEEP "profile" element during channel creation.
 No elements are required to be exchanged during channel creation;
 however, in the endpoint-relay mode, the BEEP initiator will
 typically include an "attach" element during channel creation, e.g.,

Rose, et. al. Standards Track [Page 10] RFC 3340 The Application Exchange Core July 2002

    <start number='1'>
        <profile uri='http://iana.org/beep/APEX'>
            <![CDATA[<attach endpoint='fred@example.com'
                             transID='1' />]]>
        </profile>
    </start>
 Similarly, in the relay-relay mode, the BEEP initiator will typically
 include an "bind" element during channel creation, e.g.,
    <start number='1'>
        <profile uri='http://iana.org/beep/APEX'>
            <![CDATA[<bind relay='example.com'
                           transID='1' />]]>
        </profile>
    </start>

4.3 Message Syntax

 Section 9.1 defines the BEEP payloads that are used in the APEX.

4.4 Message Semantics

4.4.1 The Attach Operation

 When an application wants to attach to the relaying mesh as a given
 endpoint, it sends an "attach" element to a relay, e.g.,
        +-------+                  +-------+
        |       | -- attach -----> |       |
        | appl. |                  | relay |
        |       | <--------- ok -- |       |
        +-------+                  +-------+
      C: <attach endpoint='fred@example.com' transID='1' />
      S: <ok />
 or
        +-------+                  +-------+
        |       | -- attach -----> |       |
        |       |                  |       |
        |       | <--------- ok -- |       |
        | appl. |                  | relay |
        |       | -- attach -----> |       |
        |       |                  |       |
        |       | <--------- ok -- |       |
        +-------+                  +-------+

Rose, et. al. Standards Track [Page 11] RFC 3340 The Application Exchange Core July 2002

      C: <attach endpoint='fred@example.com' transID='1' />
      S: <ok />
      C: <attach endpoint='wilma@example.com' transID='2' />
      S: <ok />
 or
        +-------+                  +-------+
        |       | -- attach -----> |       |
        | appl. |                  | relay |
        |       | <------ error -- |       |
        +-------+                  +-------+
      C: <attach endpoint='fred@example.com' transID='1' />
      S: <error code='537'>access denied</error>
 The "attach" element has an "endpoint" attribute, a "transID"
 attribute, and contains zero or more "option" elements:
 o  the "endpoint" attribute specifies the endpoint that the
    application wants to attach as;
 o  the "transID" attribute specifies the transaction-identifier
    associated with this operation; and,
 o  the "option" elements, if any, specify additional processing
    options (Section 5).
 When a relay receives an "attach" element, it performs these steps:
 1. If the transaction-identifier refers to a previous, non-terminated
    operation on this BEEP channel, an "error" element having code 555
    is returned.
 2. If the relay is in a different administrative domain than this
    endpoint, an "error" element having code 553 is returned.
 3. If the application is not authorized to attach as this endpoint
    (c.f., Section 4.5.1), an "error" element having code 537 is
    returned.
 4. If any options are present, they are processed.
 5. If another application has already attached as this endpoint, an
    "error" element having code 554 is returned.
 6. Otherwise, the application is bound as this endpoint, and an "ok"
    element is returned.

Rose, et. al. Standards Track [Page 12] RFC 3340 The Application Exchange Core July 2002

4.4.2 The Bind Operation

 When an application wants to identify itself as a relay, it sends a
 "bind" element to another relay, e.g.,
        +-------+                  +-------+
        |       | -- bind -------> |       |
        | relay |                  | relay |
        |   #1  | <--------- ok -- |   #2  |
        +-------+                  +-------+
      C: <bind relay='example.com' transID='1' />
      S: <ok />
 or
        +-------+                  +-------+
        |       | -- bind -------> |       |
        |       |                  |       |
        |       | <--------- ok -- |       |
        | relay |                  | relay |
        |   #1  | -- bind -------> |   #2  |
        |       |                  |       |
        |       | <--------- ok -- |       |
        +-------+                  +-------+
      C: <bind relay='example.com' transID='1' />
      S: <ok />
      C: <bind relay='rubble.com' transID='2' />
      S: <ok />
 or
        +-------+                  +-------+
        |       | -- bind -------> |       |
        | relay |                  | relay |
        |   #1  | <------ error -- |   #2  |
        +-------+                  +-------+
      C: <bind relay='example.com' transID='1' />
      S: <error code='537'>access denied</error>
 The "bind" element has a "relay" attribute, a "transID" attribute,
 and contains zero or more "option" elements:
 o  the "relay" attribute specifies the administrative domain on whose
    behalf the application wants to serve;

Rose, et. al. Standards Track [Page 13] RFC 3340 The Application Exchange Core July 2002

 o  the "transID" attribute specifies the transaction-identifier
    associated with this operation; and,
 o  the "option" elements, if any, specify additional processing
    options (Section 5).
 When a relay receives an "bind" element, it performs these steps:
 1. If the transaction-identifier refers to a previous, non-terminated
    operation on this BEEP channel, an "error" element having code 555
    is returned.
 2. If the application is not authorized to bind on behalf of this
    administrative domain (c.f., Section 4.5.2), an "error" element
    having code 537 is returned.
 3. If any options are present, they are processed.
 4. Otherwise, the application is accepted as serving this
    administrative domain, and an "ok" element is returned.

4.4.3 The Terminate Operation

 When an application or relay wants to release an attachment or
 binding, it sends a "terminate" element, e.g.,
        +-------+                  +-------+
        |       | -- terminate --> |       |
        | appl. |                  | relay |
        |       | <--------- ok -- |       |
        +-------+                  +-------+
      C: <terminate transID='1' />
      S: <ok />
 or
        +-------+                  +-------+
        |       | -- terminate --> |       |
        | appl. |                  | relay |
        |       | <------ error -- |       |
        +-------+                  +-------+
      C: <terminate transID='13' />
      S: <error code='550'>unknown transaction-identifier</error>
 or

Rose, et. al. Standards Track [Page 14] RFC 3340 The Application Exchange Core July 2002

        +-------+                  +-------+
        |       | <-- terminate -- |       |
        | appl. |                  | relay |
        |       | -- ok ---------> |       |
        +-------+                  +-------+
      C: <terminate transID='1' />
      S: <ok />
 The "terminate" element has a "transID" attribute, an optional "code"
 attribute, an optional "xml:lang" attribute, and may contain
 arbitrary textual content:
 o  the "transID" attribute specifies the transaction-identifier
    associated with this operation;
 o  the "code" attribute, if present, is a three-digit reply code
    meaningful to programs (c.f., Section 10);
 o  the "xml:lang" attribute, if present, specifies the language that
    the element's content is written in; and,
 o  the textual content is a diagnostic (possibly multiline) which is
    meaningful to implementers, perhaps administrators, and possibly
    even users.
 When an application or relay receives a "terminate" element, it
 performs these steps:
 1. If the value of the transaction-identifier is zero, then all
    associations established by this application over this BEEP
    session, either as an endpoint attachment or a relay binding, are
    terminated, and an "ok" element is returned.
 2. Otherwise, if the transaction-identifier does not refer to a
    previous unterminated operation on this BEEP channel, an "error"
    element having code 550 is returned.
 3. Otherwise, the application is no longer bound as an endpoint or a
    relay, and an "ok" element is returned.

4.4.4 The Data Operation

 When an application or relay wants to transmit data over the relaying
 mesh, it sends a "data" element, e.g.,

Rose, et. al. Standards Track [Page 15] RFC 3340 The Application Exchange Core July 2002

        +-------+                  +-------+
        |       | -- data -------> |       |
        | appl. |                  | relay |
        |   #1  | <--------- ok -- |       |
        +-------+                  +-------+
      C: <data content='cid:1@example.com'>
             <originator identity='fred@example.com' />
             <recipient identity='barney@example.com' />
         </data>
      S: <ok />
 or
        +-------+                  +-------+
        |       | -- data -------> |       |
        | appl. |                  | relay |
        |   #1  | <------ error -- |       |
        +-------+                  +-------+
      C: <data content='cid:1@example.com'>
             <originator identity='fred@example.com' />
             <recipient identity='barney@example.com' />
         </data>
      S: <error code='537'>access denied</error>
 or
                    +-------+                  +-------+
                    |       | -- data -------> |       |
                    | relay |                  | appl. |
                    |       | <--------- ok -- |   #2  |
                    +-------+                  +-------+
      C: <data content='cid:1@example.com'>
             <originator identity='fred@example.com' />
             <recipient identity='barney@example.com' />
         </data>
      S: <ok />
 The "data" element has a "content" attribute, and contains an
 "originator" element, one or more "recipient" elements, zero or more
 "option" elements, and, optionally, a "data-content" element:
 o  the "content" attribute is a URI-reference that specifies the
    contents of the data (c.f., Section 4.1);
 o  the "originator" element refers to the endpoint sending the data;

Rose, et. al. Standards Track [Page 16] RFC 3340 The Application Exchange Core July 2002

 o  each "recipient" element refers to an endpoint destination for the
    data;
 o  the "option" elements, if any, specify additional processing
    options (Section 5), termed per-data options; and,
 o  the "data-content" element, if present, specifies a nested XML
    entity that is referenced using a URI fragment-identifier as the
    value of the "content" attribute.
 The "originator" element has an "identity" attribute, and contains
 zero or more option elements:
 o  the "identity" attribute specifies the sending endpoint; and
 o  the "option" elements, if any, specify additional processing
    options for the originator, termed per-originator options.
 Each "recipient" element has an "identity" attribute, and contains
 zero or more option elements:
 o  the "identity" attribute specifies the destination endpoint; and
 o  the "option" elements, if any, specify additional processing
    options for this recipient, termed per-recipient options.

4.4.4.1 Relay Processing of Data

 When a relay receives a "data" element, it performs these steps:
 1. If the BEEP client is not authorized to originate or relay data on
    behalf of the "originator" endpoint (c.f., Section 4.5), an
    "error" element having code 537 is returned.
 2. If any per-data options are present, they are processed.
 3. An "ok" element is returned.
 4. If any per-originator options are present, they are processed.
 5. For each recipient:
    1. If any per-recipient options are present, they are processed.

Rose, et. al. Standards Track [Page 17] RFC 3340 The Application Exchange Core July 2002

    2. If the recipient endpoint is not in the administrative domain
       associated with the relay, then an APEX session is established
       to a relay that accepts data for the recipient's administrative
       domain, and a new "data" element, containing that "recipient"
       element and all applicable options, is sent to that relay.
       If an APEX session is established, the new "data" is sent, and
       the recipient's relay returns an "ok" element, then the
       recipient is considered to be successfully processed.
    3. Otherwise, if the recipient endpoint is in the same
       administrative domain as the relay, the APEX access service
       must check that the originator endpoint is allowed to
       communicate with the recipient endpoint (the access entries
       [10] whose "owner" is the recipient must contain a "core:data"
       token for the originator), and the recipient endpoint must be
       currently attached.
       If so, a new "data" element, containing only that "recipient"
       element, is sent to the corresponding application.  If the
       recipient's endpoint returns an "ok" element, then the
       recipient is considered to be successfully processed.
 Providing that these semantics are preserved, a relay may choose to
 optimize its behavior by grouping multiple recipients in a single
 "data" element that is subsequently transmitted.
 Finally, note that a relay receiving a "data" element from an
 application may be configured to add administrative-specific options.
 Regardless, all relays are expressly forbidden from modifying the
 content of the "data" element at any time.

4.4.4.2 Application Processing of Data

 When an application receives a "data" element, it performs these
 steps:
 1. If any per-data or per-originator options are present, they are
    not processed (but may be noted).
 2. For each recipient:
    1. If any per-recipient options are present, they are not
       processed (but may be noted).
    2. If the application is not attached as the recipient endpoint,
       then an error in processing has occurred.

Rose, et. al. Standards Track [Page 18] RFC 3340 The Application Exchange Core July 2002

    3. Otherwise, the "data" element is further processed in an
       application-specific manner, and the recipient is considered to
       be successfully processed.
 3. If no recipients could be successfully processed, an "error"
    element is returned; otherwise, an "ok" element is returned.

4.5 APEX Access Policies

 Access to APEX is provided by the juxtaposition of:
 o  authenticating as a BEEP peer;
 o  attaching as an APEX endpoint or binding as an APEX relay; and,
 o  being listed as an actor by the APEX access service (c.f., [10]).
 Each of these activities occurs according to the policies of the
 relevant administrative domain:
 o  each administrative domain is responsible for keeping its own
    house in order through "local provisioning"; and,
 o  each administrative domain decides the level of trust to associate
    with other administrative domains.

4.5.1 Access Policies in the Endpoint-Relay Mode

 o  When an application wants to attach to the relaying mesh, local
    provisioning maps BEEP peer identities to allowed APEX endpoints
    (c.f., Step 3 of Section 4.4.1).
    Typically, the identity function is used, e.g., if an application
    authenticates itself as the BEEP peer named as "fred@example.com",
    it is allowed to attach as the APEX endpoint named as
    "fred@example.com".
    However, using the "subaddress" convention of Section 2.2, an
    application authorized to attach as a given APEX endpoint is also
    authorized to attach as any subaddress of that APEX endpoint,
    e.g., an application authorized to attach as the APEX endpoint
    "fred@example.com" is also authorized to attach as the APEX
    endpoint "fred/appl=wb@example.com".
 o  When an application wants to send data, local provisioning maps
    attached endpoints to allowed originators (c.f., Step 1 of Section
    4.4.4.1).

Rose, et. al. Standards Track [Page 19] RFC 3340 The Application Exchange Core July 2002

    Typically, the identity function is used, e.g., if an application
    attaches as the APEX endpoint named as "fred@example.com", it is
    allowed to send data originating from the same APEX endpoint.
    However, other policies are permissible, for example, the
    administrative domain may allow the application attached as the
    APEX endpoint named as "wilma@example.com" to send data
    originating as either "wilma@example.com" or "fred@example.com".
 o  Finally, when a relay is delivering to an endpoint within its own
    administrative domain, it consults the recipient's access entry
    looking for an entry having the originator as an actor (c.f., Step
    5.3 of Section 4.4.4.1).

4.5.2 Access Policies in the Relay-Relay Mode

 o  When an application wants to bind as a relay on behalf of an
    administrative domain, local provisioning may map BEEP peer
    identities to allowed APEX relays (c.f., Step 3).
    If so, then typically the identity function is used.  e.g., if an
    application authenticates itself as the BEEP peer named as
    "example.com", it is allowed to bind as a relay on behalf of the
    administrative domain "example.com".
 o  When a relay is sending data, no access policies, per se, are
    applied.
 o  When a relay is receiving data, local provisioning maps BEEP peer
    identities to allowed originators (c.f., Step 1 of Section
    4.4.4.1).
    Typically, the identity function is used, e.g., if a relay
    authenticates itself as being from the same administrative domain
    as the originator of the data, then the data is accepted.
    In addition, some relays may also be configured as "trusted"
    intermediaries, so that if a BEEP peer authenticates itself as
    being from such a relay, then the data is accepted.

5. APEX Options

 APEX, at its core, provides a best-effort datagram service.  Options
 are used to alter the semantics of the core service.
 The semantics of the APEX "option" element are context-specific.
 Accordingly, the specification of an APEX option must define:
 o  the identity of the option;

Rose, et. al. Standards Track [Page 20] RFC 3340 The Application Exchange Core July 2002

 o  the context in which the option may appear;
 o  what content, if any, is contained within the option; and,
 o  the processing rules for the option.
 An option registration template (Section 7.1) organizes this
 information.
 An "option" element is contained within either a "data",
 "originator", "recipient", or an "attach" element, all of which are
 termed the "containing" element.  The "option" element has several
 attributes and contains arbitrary content:
 o  the "internal" and the "external" attributes, exactly one of which
    is present, uniquely identify the option;
 o  the "targetHop" attribute specifies which relays should process
    the option;
 o  the "mustUnderstand" attribute specifies whether the option, if
    unrecognized, must cause an error in processing to occur;
 o  the "transID" attribute specifies a transaction-identifier for the
    option; and,
 o  the "localize" attribute, if present, specifies one or more
    language tokens, each identifying a desirable language tag to be
    used if textual diagnostics are returned to the originator.
 Note that if the containing element is an "attach", then the values
 of the "targetHop" and "transID" attributes are ignored.
 The value of the "internal" attribute is the IANA-registered name for
 the option.  If the "internal" attribute is not present, then the
 value of the "external" attribute is a URI or URI with a fragment-
 identifier.  Note that a relative-URI value is not allowed.
 The "targetHop" attribute specifies which relay(s) should process the
 option:
    this: the option applies to this relay, and must be removed prior
    to transmitting the containing element.
    final: the option applies to this relay, only if the relay will
    transmit the containing element directly to the recipient.

Rose, et. al. Standards Track [Page 21] RFC 3340 The Application Exchange Core July 2002

    all: the option applies to this relay and is retained for the
    next.
 Note that a final relay does not remove any options as it transmits
 the containing element directly to the recipient.
 The "mustUnderstand" attribute specifies whether the relay may ignore
 the option if it is unrecognized, and is consulted only if the
 "targetHop" attribute indicates that the option applies to that
 relay.  If the option applies, and if the value of the
 "mustUnderstand" attribute is "true", and if the relay does not
 "understand" the option, then an error in processing has occurred.

5.1 The statusRequest Option

 Section 8.4 contains the APEX option registration for the
 "statusRequest" option.
 If this option is present, then each applicable relay sends a
 "statusResponse" message to the originator.  This is done by issuing
 a data operation whose originator is the report service associated
 with the issuing relay, whose recipient is the endpoint address of
 the "statusRequest" originator, and whose content is a
 "statusResponse" element.
 A "statusRequest" option MUST NOT be present in any data operation
 containing a "statusResponse" element.  In general, applications
 should be careful to avoid potential looping behaviors if an option
 is received in error.
 Consider these examples:
     +-------+                  +-------+
     |       | -- data -------> |       |
     | appl. |                  | relay |
     |   #1  | <--------- ok -- |       |
     +-------+                  +-------+
   C: <data content='cid:1@example.com'>
          <originator identity='fred@example.com' />
          <recipient identity='barney@example.com' />
          <option internal='statusRequest' targetHop='final'
                  mustUnderstand='true' transID='86' />
      </data>
   S: <ok />

Rose, et. al. Standards Track [Page 22] RFC 3340 The Application Exchange Core July 2002

                                +-------+                  +-------+
                                |       | -- data -------> |       |
                                | relay |                  | appl. |
                                |       | <--------- ok -- |   #2  |
                                +-------+                  +-------+
   C: <data content='cid:1@example.com'>
          <originator identity='fred@example.com' />
          <recipient identity='barney@example.com' />
          <option internal='statusRequest' targetHop='final'
                  mustUnderstand='true' transID='86' />
      </data>
   S: <ok />
     +-------+                  +-------+
     |       | <------- data -- |       |
     | appl. |                  | relay |
     |   #1  | -- ok ---------> |       |
     +-------+                  +-------+
   C: <data content='#Content'>
          <originator identity='apex=report@example.com' />
          <recipient identity='fred@example.com' />
          <data-content Name='Content'>
              <statusResponse transID='86'>
                  <destination identity='barney@example.com'>
                      <reply code='250' />
                  </destination>
              </statusResponse>
          </data-content>
      </data>
   S: <ok />
 or
     +-------+                  +-------+
     |       | -- data -------> |       |
     | appl. |                  | relay |
     |   #1  | <--------- ok -- |       |
     +-------+                  +-------+
   C: <data content='cid:1@example.com'>
          <originator identity='fred@example.com' />
          <recipient identity='barney@example.com' />
          <option internal='statusRequest' targetHop='final'
                  mustUnderstand='true' transID='86' />
      </data>
   S: <ok />

Rose, et. al. Standards Track [Page 23] RFC 3340 The Application Exchange Core July 2002

     +-------+                  +-------+
     |       | <------- data -- |       |
     | appl. |                  | relay |
     |   #1  | -- ok ---------> |       |
     +-------+                  +-------+
   C: <data content='#Content'>
          <originator identity='apex=report@example.com' />
          <recipient identity='fred@example.com' />
          <data-content Name='Content'>
              <statusResponse transID='86'>
                  <destination identity='barney@example.com'>
                      <reply code='550'>unknown endpoint
                                        identity</reply>
                  </destination>
              </statusResponse>
          </data-content>
      </data>
   S: <ok />
 or
     +-------+                  +-------+
     |       | -- data -------> |       |
     | appl. |                  | relay |
     |   #1  | <--------- ok -- |   #1  |
     +-------+                  +-------+
   C: <data content='cid:1@example.com'>
          <originator identity='fred@example.com' />
          <recipient identity='barney@rubble.com' />
          <option internal='statusRequest' targetHop='final'
                  mustUnderstand='true' transID='86' />
      </data>
   S: <ok />
                                +-------+                  +-------+
                                |       | -- data -------> |       |
                                | relay |                  | relay |
                                |   #1  | <--------- ok -- |   #2  |
                                +-------+                  +-------+
   C: <data content='cid:1@example.com'>
          <originator identity='fred@example.com' />
          <recipient identity='barney@rubble.com' />
          <option internal='statusRequest' targetHop='final'
                  mustUnderstand='true' transID='86' />
      </data>
   S: <ok />

Rose, et. al. Standards Track [Page 24] RFC 3340 The Application Exchange Core July 2002

                                +-------+                  +-------+
                                |       | -- data -------> |       |
                                | relay |                  | appl. |
                                |   #2  | <--------- ok -- |   #2  |
                                +-------+                  +-------+
   C: <data content='cid:1@example.com'>
          <originator identity='fred@example.com' />
          <recipient identity='barney@example.com' />
          <option internal='statusRequest' targetHop='final'
                  mustUnderstand='true' transID='86' />
      </data>
   S: <ok />
                                +-------+                  +-------+
                                |       | <------- data -- |       |
                                | relay |                  | relay |
                                |   #1  | -- ok ---------> |   #2  |
                                +-------+                  +-------+
   C: <data content='#Content'>
          <originator identity='apex=report@rubble.com' />
           <recipient identity='fred@example.com' />
           <data-content Name='Content'>
               <statusResponse transID='86'>
                   <destination identity='barney@rubble.com'>
                       <reply code='250' />
                   </destination>
               </statusResponse>
           </data-content>
       </data>
   S: <ok />
     +-------+                  +-------+
     |       | <------- data -- |       |
     | appl. |                  | relay |
     |   #1  | -- ok ---------> |   #1  |
     +-------+                  +-------+
   C: <data content='#Content'>
          <originator identity='apex=report@rubble.com' />
          <recipient identity='fred@example.com' />
          <data-content Name='Content'>
              <statusResponse transID='86'>
                  <destination identity='barney@rubble.com'>
                      <reply code='250' />
                  </destination>
              </statusResponse>

Rose, et. al. Standards Track [Page 25] RFC 3340 The Application Exchange Core July 2002

          </data-content>
      </data>
   S: <ok />
 Note that a trace of a data's passage through the relaying mesh can
 be achieved by setting the "targetHop" attribute to "all".

6. APEX Services

 APEX, at its core, provides a best-effort datagram service.  Within
 an administrative domain, all relays must be able to handle messages
 for any endpoint within that administrative domain.  APEX services
 are logically defined as endpoints but, given their ubiquitous
 semantics, they do not necessarily need to be associated with a
 single physical endpoint.  As such, they may be provisioned co-
 resident with each relay within an administrative domain, even though
 they are logically provided on top of the relaying mesh, i.e.,
    +----------+     +----------+    +----------+    +---------+
    |   APEX   |     |   APEX   |    |   APEX   |    |         |
    |  access  |     | presence |    |  report  |    |   ...   |
    | service  |     |  service |    | service  |    |         |
    +----------+     +----------+    +----------+    +---------+
         |                |               |               |
         |                |               |               |
 +----------------------------------------------------------------+
 |                                                                |
 |                            APEX core                           |
 |                                                                |
 +----------------------------------------------------------------+
 That is, applications communicate with an APEX service by exchanging
 data with a "well-known endpoint" (WKE).
 For example, APEX applications communicate with the report service by
 exchanging data with the well-known endpoint "apex=report" in the
 corresponding administrative domain, e.g., "apex=report@example.com"
 is the endpoint associated with the report service in the
 "example.com" administrative domain.
 The specification of an APEX service must define:
 o  the WKE of the service;
 o  the syntax and sequence of messages exchanged with the service;
 o  what access control tokens are consulted by the service.

Rose, et. al. Standards Track [Page 26] RFC 3340 The Application Exchange Core July 2002

 A service registration template (Section 7.2) organizes this
 information.
 Finally, note that within a single administrative domain, the
 relaying mesh makes use of the APEX access service in order to
 determine if an originator is allowed to transmit data to a recipient
 (c.f., Step 5.3 of Section 4.4.4.1).

6.1 Use of the APEX Core DTD

 The specification of an APEX service may use definitions found in the
 APEX core DTD (Section 9.1).  For example, the reply operation
 (Section 6.1.2) is defined to provide a common format for responses.

6.1.1 Transaction-Identifiers

 In using APEX's transaction-identifiers, note the following:
 o  In the endpoint-relay and relay-relay modes, transaction-
    identifiers are meaningful only during the lifetime of a BEEP
    channel.
    For example, when an application issues the attach operation, the
    associated transaction-identifier has meaning only within the
    context of the BEEP channel used for the attach operation.  When
    the BEEP connection is released, the channel no longer exists and
    the application is no longer attached to the relaying mesh.
 o  In contrast, when an application communicates with an APEX
    service, transaction-identifiers are often embedded in the data
    that is sent.  This means that transaction-identifiers are
    potentially long-lived.
    For example, an application may attach as an endpoint, send data
    (containing an embedded transaction-identifier) to a service, and,
    some time later, detach from the relaying mesh.  Later on, a
    second application may attach as the same endpoint, and send data
    of its own (also containing embedded transaction-identifiers).
    Subsequently, the second application may receive data from the
    service responding to the first application's request and
    containing the transaction-identifier used by the first
    application.
 To minimize the likelihood of ambiguities with long-lived
 transaction-identifiers, the values of transaction-identifiers
 generated by applications should appear to be unpredictable.

Rose, et. al. Standards Track [Page 27] RFC 3340 The Application Exchange Core July 2002

6.1.2 The Reply Element

 Many APEX services make use of a reply operation.  Although each
 service defines the circumstances in which a "reply" element is sent,
 the syntax of the "reply" element is defined in Section 9.1.
 The "reply" element has a "code" attribute, a "transID" attribute, an
 optional "xml:lang" attribute, and may contain arbitrary textual
 content:
 o  the "code" element specifies a three-digit reply code (c.f.,
    Section 10);
 o  the "transID" attribute specifies the transaction-identifier
    corresponding to this reply;
 o  the "xml:lang" attribute, if present, specifies the language that
    the element's content is written in; and,
 o  the textual content is a diagnostic (possibly multiline) which is
    meaningful to implementers, perhaps administrators, and possibly
    even users.

6.2 The Report Service

 Section 8.5 contains the APEX service registration for the report
 service:
 o  Within an administrative domain, the service is addressed using
    the well-known endpoint of "apex=report".
 o  Section 9.2 defines the syntax of the operations exchanged with
    the service.
 o  A consumer of the service does not initiate communications with
    the service.
 o  The service initiates communications by sending data containing
    the "statusResponse" operation.
 If a relay processes a "statusRequest" option (Section 5.1), then it
 sends data to the originator containing a "statusResponse" element
 (Section 9.2).
 The "statusResponse" element has a "transID" attribute and contains
 one or more "destination" elements:

Rose, et. al. Standards Track [Page 28] RFC 3340 The Application Exchange Core July 2002

 o  the "transID" attribute specifies the value contained in the
    "statusRequest" option; and,
 o  each "destination" element has an "identity" attribute and
    contains a "reply" element:
  • the "identity" attribute specifies the recipient endpoint that

is being reported on; and,

  • the "reply" element (Section 6.1.2) specifies the delivery

status of that recipient.

7. Registration Templates

7.1 APEX Option Registration Template

 When an APEX option is registered, the following information is
 supplied:
 Option Identification: specify the NMTOKEN or the URI that
    authoritatively identifies this option.
 Present in: specify the APEX elements in which the option may appear.
 Contains: specify the XML content that is contained within the
    "option" element.
 Processing Rules: specify the processing rules associated with the
    option.
 Contact Information: specify the postal and electronic contact
    information for the author of the profile.

7.2 APEX Service Registration Template

 When an APEX service is registered, the following information is
 supplied:
 Well-Known Endpoint: specify the local-part of an endpoint identity,
    starting with "apex=".
 Syntax of Messages Exchanged: specify the elements exchanged with the
    service.
 Sequence of Messages Exchanged: specify the order in which data is
    exchanged with the service.

Rose, et. al. Standards Track [Page 29] RFC 3340 The Application Exchange Core July 2002

 Access Control Tokens: specify the token(s) used to control access to
    the service (c.f., [10]).
 Contact Information: specify the postal and electronic contact
    information for the author of the profile.
 Note that the endpoints "apex=all" and "apex=core" may not be
 assigned.

7.3 APEX Endpoint Application Registration Template

 When an APEX endpoint application is registered, the following
 information is supplied:
 Endpoint Application: specify the subaddress used for an endpoint
    application, starting with "appl=".
 Application Definition: specify the syntax and semantics of the
    endpoint application identified by this registration.
 Contact Information: specify the postal and electronic contact
    information for the author of the profile.

8. Initial Registrations

8.1 Registration: The APEX Profile

 Profile Identification: http://iana.org/beep/APEX
 Messages exchanged during Channel Creation: "attach", "bind"
 Messages starting one-to-one exchanges: "attach", "bind",
    "terminate", or "data"
 Messages in positive replies: "ok"
 Messages in negative replies: "error"
 Messages in one-to-many exchanges: none
 Message Syntax: c.f., Section 9.1
 Message Semantics: c.f., Section 4.4
 Contact Information: c.f., the "Authors' Addresses" section of this
    memo

Rose, et. al. Standards Track [Page 30] RFC 3340 The Application Exchange Core July 2002

8.2 Registration: The System (Well-Known) TCP port number for apex-mesh

 Protocol Number: TCP
 Message Formats, Types, Opcodes, and Sequences: c.f., Section 9.1
 Functions: c.f., Section 4.4
 Use of Broadcast/Multicast: none
 Proposed Name: APEX relay-relay service
 Short name: apex-mesh
 Contact Information: c.f., the "Authors' Addresses" section of this
    memo

8.3 Registration: The System (Well-Known) TCP port number for apex-edge

 Protocol Number: TCP
 Message Formats, Types, Opcodes, and Sequences: c.f., Section 9.1
 Functions: c.f., Section 4.4
 Use of Broadcast/Multicast: none
 Proposed Name: APEX endpoint-relay service
 Short name: apex-edge
 Contact Information: c.f., the "Authors' Addresses" section of this
    memo

8.4 Registration: The statusRequest Option

 Option Identification: statusRequest
 Present in: APEX's "data" and "recipient" elements
 Contains: nothing
 Processing Rules: c.f., Section 5.1
 Contact Information: c.f., the "Authors' Addresses" section of this
    memo

Rose, et. al. Standards Track [Page 31] RFC 3340 The Application Exchange Core July 2002

8.5 Registration: The Report Service

 Well-Known Endpoint: apex=report
 Syntax of Messages Exchanged: c.f., Section 9.2
 Sequence of Messages Exchanged: c.f., Section 6.2
 Access Control Tokens: none
 Contact Information: c.f., the "Authors' Addresses" section of this
    memo

9. DTDs

9.1 The APEX Core DTD

 <!--
   DTD for the APEX core, as of 2001-07-09
   Refer to this DTD as:
     <!ENTITY % APEXCORE PUBLIC "-//IETF//DTD APEX CORE//EN" "">
     %APEXCORE;
   -->
 <!ENTITY % BEEP PUBLIC "-//IETF//DTD BEEP//EN" "">
 %BEEP;
 <!--
   DTD data types:
        entity        syntax/reference     example
        ======        ================     =======
     APEX endpoint
        ENDPOINT      entity,              fred@example.com
                      c.f., Section 2.2
     domain, either a FQDN or a literal
         DOMAIN       c.f., [RFC-2821]     example.com or [10.0.0.1]
     seconds
         SECONDS      0..2147483647        600
     timestamp
         TIMESTAMP    c.f., [12]           2000-05-15T13:02:00-08:00
     unique-identifier

Rose, et. al. Standards Track [Page 32] RFC 3340 The Application Exchange Core July 2002

         UNIQID       1..2147483647        42
     unique-identifier OR zero
         UNIZID       0..2147483647        0
   -->
 <!ENTITY  % ENDPOINT  "CDATA">
 <!ENTITY  % DOMAIN    "CDATA">
 <!ENTITY  % SECONDS   "CDATA">
 <!ENTITY  % TIMESTAMP "CDATA">
 <!ENTITY  % UNIQID    "CDATA">
 <!ENTITY  % UNIZID    "CDATA">
 <!--
   APEX messages, exchanged as application/beep+xml
      role       MSG         RPY         ERR
     ======      ===         ===         ===
       I         attach      ok          error
     I or L      bind        ok          error
     I or L      terminate   ok          error
     I or L      data        ok          error
   -->
 <!ELEMENT attach      (option*)>
 <!ATTLIST attach
           endpoint    %ENDPOINT;        #REQUIRED
           transID     %UNIQID;          #REQUIRED>
 <!ELEMENT bind        (option*)>
 <!ATTLIST bind
           relay       %DOMAIN;          #REQUIRED
           transID     %UNIQID;          #REQUIRED>
 <!ELEMENT terminate   (#PCDATA)>
 <!ATTLIST terminate
           code        %XYZ;             "250"
           xml:lang    %LANG;            #IMPLIED
           transID     %UNIZID;          "0">
 <!ELEMENT data        (originator,recipient+,option*,data-content?)>
 <!ATTLIST data
           content     %URI;             #REQUIRED>
 <!ELEMENT originator  (option*)>

Rose, et. al. Standards Track [Page 33] RFC 3340 The Application Exchange Core July 2002

 <!ATTLIST originator
           identity    %ENDPOINT;        #REQUIRED>
 <!ELEMENT recipient   (option*)>
 <!ATTLIST recipient
           identity    %ENDPOINT;        #REQUIRED>
 <!ELEMENT data-content
                       ANY>
 <!ATTLIST Name        ID                #REQUIRED>
 <!ELEMENT ok          EMPTY>
 <!ELEMENT reply       (#PCDATA)>
 <!ATTLIST reply
           code        %XYZ;             #REQUIRED
           transID     %UNIQID;          #REQUIRED
           xml:lang    %LANG;            #IMPLIED>
 <!-- either the "internal" or the "external" attribute is present in
      an option -->
 <!ELEMENT option      ANY>
 <!ATTLIST option
           internal    NMTOKEN           ""
           external    %URI;             ""
           targetHop   (this|final|all)  "final"
           mustUnderstand
                       (true|false)      "false"
           transID     %UNIQID;          #REQUIRED
           localize    %LOCS;            "i-default">

9.2 The Report Service DTD

 <!--
   DTD for the APEX report service, as of 2000-12-12
   Refer to this DTD as:
     <!ENTITY % APEXREPORT PUBLIC "-//Blocks//DTD APEX REPORT//EN" "">
     %APEXREPORT;
   -->
 <!ENTITY % APEXCORE PUBLIC "-//Blocks//DTD APEX CORE//EN" "">
 %APEXCORE;
 <!--
   Synopsis of the APEX report service

Rose, et. al. Standards Track [Page 34] RFC 3340 The Application Exchange Core July 2002

     service WKE: apex=report
     message exchanges:
         service initiates    consumer replies
         =================    ================
         statusResponse       (nothing)
     access control tokens: none
   -->
 <!ELEMENT statusResponse
                       (destination+)>
 <!ATTLIST statusResponse
           transID     %UNIQID;          #REQUIRED>
 <!ELEMENT destination (reply)>
 <!ATTLIST destination
           identity    %ENDPOINT;        #REQUIRED>

10. Reply Codes

    code    meaning
    ====    =======
    250     transaction successful
    421     service not available
    450     requested action not taken
    451     requested action aborted
    454     temporary authentication failure
    500     general syntax error (e.g., poorly-formed XML)
    501     syntax error in parameters (e.g., non-valid XML)
    504     parameter not implemented
    530     authentication required
    534     authentication mechanism insufficient
    535     authentication failure
    537     action not authorized for user

Rose, et. al. Standards Track [Page 35] RFC 3340 The Application Exchange Core July 2002

    538     authentication mechanism requires encryption
    550     requested action not taken
    553     parameter invalid
    554     transaction failed (e.g., policy violation)
    555     transaction already in progress

11. Security Considerations

 Consult Section 3 and Section 4.5 for a discussion of security
 issues, e.g., relaying integrity.
 Although service provisioning is a policy matter, at a minimum, all
 APEX implementations must provide the following tuning profiles:
 for authentication: http://iana.org/beep/SASL/DIGEST-MD5
 for confidentiality: http://iana.org/beep/TLS (using the
    TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher)
 for both: http://iana.org/beep/TLS (using the
    TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher supporting client-side
    certificates)
 Further, APEX endpoint implementations may choose to offer MIME-based
 security services providing message integrity and confidentiality,
 such as OpenPGP [13] or S/MIME [14].
 Regardless, since APEX is a profile of the BEEP, consult [1]'s
 Section 9 for a discussion of BEEP-specific security issues.
 Finally, the statusRequest option (Section 5.1) may be used to expose
 private network topology.  Accordingly, an administrator may wish to
 choose to disable this option except at the ingress/egress points for
 its administrative domain.

References

 [1]   Rose, M., "The Blocks Extensible Exchange Protocol Core", RFC
       3080, March 2001.
 [2]   Crocker, D. and P. Overell, "Augmented BNF for Syntax
       Specifications: ABNF", RFC 2234, November 1997.

Rose, et. al. Standards Track [Page 36] RFC 3340 The Application Exchange Core July 2002

 [3]   Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April
       2001.
 [4]   Yergeau, F., "UTF-8, a transformation format of Unicode and ISO
       10646", RFC 2044, October 1996.
 [5]   Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for
       specifying the location of services (DNS SRV)", RFC 2782,
       February 2000.
 [6]   Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
       Resource Identifiers (URI): Generic Syntax", RFC 2396, August
       1998.
 [7]   Levinson, E., "The MIME Multipart/Related Content-type", RFC
       2387, August 1998.
 [8]   Levinson, E., "Content-ID and Message-ID Uniform Resource
       Locators", RFC 2392, August 1998.
 [9]   Freed, N. and N. Borenstein, "Multipurpose Internet Mail
       Extensions (MIME) Part One: Format of Internet Message Bodies",
       RFC 2045, November 1996.
 [10]  Rose, M., Klyne, G. and D. Crocker, "The Application Exchange
       (APEX) Access Service", RFC 3341, July 2002.
 [11]  Rose, M., Klyne, G. and D. Crocker, "The Application Exchange
       (APEX) Presence Service", Work in Progress.
 [12]  Newman, C. and G. Klyne, "Date and Time on the Internet:
       Timestamps", RFC 3339, July 2002.
 [13]  Elkins, M., Del Torto, D., Levien, R. and T. Roessler, "MIME
       Security with OpenPGP", RFC 3156, August 2001.
 [14]  Ramsdell, B., "S/MIME Version 3 Message Specification", RFC
       2633, June 1999.

Rose, et. al. Standards Track [Page 37] RFC 3340 The Application Exchange Core July 2002

Appendix A. Acknowledgements

 The authors gratefully acknowledge the contributions of: Jeffrey
 Altman, Harald Alvestrand, Eric Dixon, Ronan Klyne, Darren New, Chris
 Newman, Scott Pead, and Bob Wyman.

Appendix B. IANA Considerations

 The IANA has registered "APEX" as a standards-track BEEP profile, as
 specified in Section 8.1.
 The IANA has registered "apex-mesh" as a TCP port number, as
 specified in Section 8.2.
 The IANA has registered "apex-edge" as a TCP port number, as
 specified in Section 8.3.
 The IANA maintains a list of:
 o  APEX options, c.f., Section 7.1;
 o  APEX services, c.f., Section 7.2; and,
 o  APEX endpoint applications, c.f., Section 7.3.
 For each list, the IESG is responsible for assigning a designated
 expert to review the specification prior to the IANA making the
 assignment.  As a courtesy to developers of non-standards track APEX
 options and services, the mailing list apexwg@invisible.net may be
 used to solicit commentary.
 The IANA makes the registrations specified in Section 8.4 and Section
 8.5.

Rose, et. al. Standards Track [Page 38] RFC 3340 The Application Exchange Core July 2002

Authors' Addresses

 Marshall T. Rose
 Dover Beach Consulting, Inc.
 POB 255268
 Sacramento, CA  95865-5268
 US
 Phone: +1 916 483 8878
 EMail: mrose@dbc.mtview.ca.us
 Graham Klyne
 Clearswift Corporation
 1310 Waterside
 Arlington Business Park
 Theale, Reading  RG7 4SA
 UK
 Phone: +44 11 8903 8903
 EMail: Graham.Klyne@MIMEsweeper.com
 David H. Crocker
 Brandenburg InternetWorking
 675 Spruce Drive
 Sunnyvale, CA  94086
 US
 Phone: +1 408 246 8253
 EMail: dcrocker@brandenburg.com
 URI:   http://www.brandenburg.com/

Rose, et. al. Standards Track [Page 39] RFC 3340 The Application Exchange Core July 2002

Full Copyright Statement

 Copyright (C) The Internet Society (2002).  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
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 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
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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Acknowledgement

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 Internet Society.

Rose, et. al. Standards Track [Page 40]

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