RFC 
 3340 
 TOC 
Network Working GroupM. Rose
Request for Comments: 3340Dover Beach Consulting, Inc.
Category: Standards TrackG. 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 © 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.


 RFC 
 3340 
 TOC 

Table of Contents

1.  Introduction
    1.1.  Overview
    1.2.  Architecture at a Glance
2.  Service Principles
    2.1.  Modes of Operation
    2.2.  Naming of Entities
        2.2.1.  Comparing Endpoints
3.  Service Provisioning
    3.1.  Connection Establishment
    3.2.  Authentication
    3.3.  Authorization
    3.4.  Confidentiality
    3.5.  Relaying Integrity
    3.6.  Traffic Analysis
4.  The APEX
    4.1.  Use of XML and MIME
    4.2.  Profile Identification and Initialization
    4.3.  Message Syntax
    4.4.  Message Semantics
        4.4.1.  The Attach Operation
        4.4.2.  The Bind Operation
        4.4.3.  The Terminate Operation
        4.4.4.  The Data Operation
    4.5.  APEX Access Policies
        4.5.1.  Access Policies in the Endpoint-Relay Mode
        4.5.2.  Access Policies in the Relay-Relay Mode
5.  APEX Options
    5.1.  The statusRequest Option
6.  APEX Services
    6.1.  Use of the APEX Core DTD
        6.1.1.  Transaction-Identifiers
        6.1.2.  The Reply Element
    6.2.  The Report Service
7.  Registration Templates
    7.1.  APEX Option Registration Template
    7.2.  APEX Service Registration Template
    7.3.  APEX Endpoint Application Registration Template
8.  Initial Registrations
    8.1.  Registration: The APEX Profile
    8.2.  Registration: The System (Well-Known) TCP port number for apex-mesh
    8.3.  Registration: The System (Well-Known) TCP port number for apex-edge
    8.4.  Registration: The statusRequest Option
    8.5.  Registration: The Report Service
9.  DTDs
    9.1.  The APEX Core DTD
    9.2.  The Report Service DTD
10.  Reply Codes
11.  Security Considerations
12.  References
Appendix A.  Acknowledgements
Appendix B.  IANA Considerations
§  Authors' Addresses
§  Intellectual Property and Copyright Statements




 TOC 

1.  Introduction

Network applications can be broadly distinguished by five operational characteristics:

For example:

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.



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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:

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 (Rose, M., “The Blocks Extensible Exchange Protocol Core,” March 2001.) [RFC3080] "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.



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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     |
   +-------------+
   |     ...     |
   +-------------+

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.


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2.  Service Principles



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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:

A relay (BEEP listener), in addition to servicing requests from a BEEP initiator, may:

In the relay-relay mode, a relay (BEEP listener or initiator) may:



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2.2.  Naming of Entities

Endpoints are named using the following ABNF (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” November 1997.) [RFC2234] 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,
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 (APEX Access Policies).



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2.2.1.  Comparing Endpoints

Note that since the "local" part of an entity is a string of UTF-8 (Yergeau, F., “UTF-8, a transformation format of Unicode and ISO 10646,” October 1996.) [RFC2044] 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".



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3.  Service Provisioning



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3.1.  Connection Establishment

The SRV algorithm (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.) [RFC2782] 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.

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



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3.2.  Authentication

Authentication is a matter of provisioning for each BEEP peer (c.f., Section 4.5 (APEX Access Policies)).

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".



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3.3.  Authorization

Authorization is a matter of provisioning for each BEEP peer (c.f., Section 4.5 (APEX Access Policies)).

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.



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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.



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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.



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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.



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4.  The APEX

Section 8.1 (Registration: The APEX Profile) contains the BEEP profile registration for APEX.



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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 (Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifiers (URI): Generic Syntax,” August 1998.) [RFC2396] 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" (Levinson, E., “The MIME Multipart/Related Content-type,” August 1998.) [RFC2387], identified using a "cid" URL (Levinson, E., “Content-ID and Message-ID Uniform Resource Locators,” August 1998.) [RFC2392], 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>
    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 (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,” November 1996.) [RFC2045] 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


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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.,

    <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>


 TOC 

4.3.  Message Syntax

Section 9.1 (The APEX Core DTD) defines the BEEP payloads that are used in the APEX.



 TOC 

4.4.  Message Semantics



 TOC 

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 -- |       |
    +-------+                  +-------+

  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:

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 (Access Policies in the Endpoint-Relay Mode)), 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.


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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:

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 (Access Policies in the Relay-Relay Mode)), 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.


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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

    +-------+                  +-------+
    |       | <-- 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:

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.


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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.,

    +-------+                  +-------+
    |       | -- 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:

The "originator" element has an "identity" attribute, and contains zero or more option elements:

Each "recipient" element has an "identity" attribute, and contains zero or more option elements:



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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 (APEX Access Policies)), 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.
    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 (Rose, M., Klyne, G., and D. Crocker, “The Application Exchange (APEX) Access Service,” July 2002.) [RFC3341] 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.



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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.
    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.


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4.5.  APEX Access Policies

Access to APEX is provided by the juxtaposition of:

Each of these activities occurs according to the policies of the relevant administrative domain:



 TOC 

4.5.1.  Access Policies in the Endpoint-Relay Mode



 TOC 

4.5.2.  Access Policies in the Relay-Relay Mode



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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:

An option registration template (APEX Option Registration Template) 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:

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.
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.



 TOC 

5.1.  The statusRequest Option

Section 8.4 (Registration: The statusRequest Option) 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 />

                               +-------+                  +-------+
                               |       | -- 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 />

    +-------+                  +-------+
    |       | <------- 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 />

                               +-------+                  +-------+
                               |       | -- 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>
         </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".



 TOC 

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:

A service registration template (APEX Service Registration Template) 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 (Relay Processing of Data)).



 TOC 

6.1.  Use of the APEX Core DTD

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



 TOC 

6.1.1.  Transaction-Identifiers

In using APEX's transaction-identifiers, note the following:

To minimize the likelihood of ambiguities with long-lived transaction-identifiers, the values of transaction-identifiers generated by applications should appear to be unpredictable.



 TOC 

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 APEX Core DTD).

The "reply" element has a "code" attribute, a "transID" attribute, an optional "xml:lang" attribute, and may contain arbitrary textual content:



 TOC 

6.2.  The Report Service

Section 8.5 (Registration: The Report Service) contains the APEX service registration for the report service:

If a relay processes a "statusRequest" option (The statusRequest Option), then it sends data to the originator containing a "statusResponse" element (The Report Service DTD).

The "statusResponse" element has a "transID" attribute and contains one or more "destination" elements:



 TOC 

7.  Registration Templates



 TOC 

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.


 TOC 

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.
Access Control Tokens:
specify the token(s) used to control access to the service (c.f., [RFC3341] (Rose, M., Klyne, G., and D. Crocker, “The Application Exchange (APEX) Access Service,” July 2002.)).
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.



 TOC 

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.


 TOC 

8.  Initial Registrations



 TOC 

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 (The APEX Core DTD)
Message Semantics:
c.f., Section 4.4 (Message Semantics)
Contact Information:
c.f., the "Authors' Addresses" section of this memo


 TOC 

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 (The APEX Core DTD)
Functions:
c.f., Section 4.4 (Message Semantics)
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


 TOC 

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 (The APEX Core DTD)
Functions:
c.f., Section 4.4 (Message Semantics)
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


 TOC 

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 (The statusRequest Option)
Contact Information:
c.f., the "Authors' Addresses" section of this memo


 TOC 

8.5.  Registration: The Report Service

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


 TOC 

9.  DTDs



 TOC 

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
        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*)>
<!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">


 TOC 

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

    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>


 TOC 

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

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


 TOC 

11.  Security Considerations

Consult Section 3 (Service Provisioning) and Section 4.5 (APEX Access Policies) 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 (Elkins, M., Del Torto, D., Levien, R., and T. Roessler, “MIME Security with OpenPGP,” August 2001.) [RFC3156] or S/MIME (Ramsdell, B., “S/MIME Version 3 Message Specification,” June 1999.) [RFC2633].

Regardless, since APEX is a profile of the BEEP, consult [RFC3080] (Rose, M., “The Blocks Extensible Exchange Protocol Core,” March 2001.)'s Section 9 for a discussion of BEEP-specific security issues.

Finally, the statusRequest option (The statusRequest Option) 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.



 TOC 

12. References

[RFC3080] Rose, M., “The Blocks Extensible Exchange Protocol Core,” RFC 3080, March 2001 (TXT, HTML, XML).
[RFC2234] Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” RFC 2234, November 1997 (TXT).
[RFC2821] Klensin, J., “Simple Mail Transfer Protocol,” RFC 2821, April 2001 (TXT).
[RFC2044] Yergeau, F., “UTF-8, a transformation format of Unicode and ISO 10646,” RFC 2044, October 1996 (TXT).
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” RFC 2782, February 2000 (TXT).
[RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifiers (URI): Generic Syntax,” RFC 2396, August 1998 (TXT, HTML, XML).
[RFC2387] Levinson, E., “The MIME Multipart/Related Content-type,” RFC 2387, August 1998 (TXT, HTML, XML).
[RFC2392] Levinson, E., “Content-ID and Message-ID Uniform Resource Locators,” RFC 2392, August 1998 (TXT, HTML, XML).
[RFC2045] Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,” RFC 2045, November 1996 (TXT).
[RFC3341] Rose, M., Klyne, G., and D. Crocker, “The Application Exchange (APEX) Access Service,” RFC 3341, July 2002.
[RFC3343] Rose, M., Klyne, G., and D. Crocker, “The Application Exchange (APEX) Presence Service,” RFC 3343, July 2002.
[RFC3339] Newman, C. and G. Klyne, “Date and Time on the Internet: Timestamps,” RFC 3339, July 2002.
[RFC3156] Elkins, M., Del Torto, D., Levien, R., and T. Roessler, “MIME Security with OpenPGP,” RFC 3156, August 2001 (TXT).
[RFC2633] Ramsdell, B., “S/MIME Version 3 Message Specification,” RFC 2633, June 1999 (TXT).


 TOC 

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.



 TOC 

Appendix B.  IANA Considerations

The IANA has registered "APEX" as a standards-track BEEP profile, as specified in Section 8.1 (Registration: The APEX Profile).

The IANA has registered "apex-mesh" as a TCP port number, as specified in Section 8.2 (Registration: The System (Well-Known) TCP port number for apex-mesh).

The IANA has registered "apex-edge" as a TCP port number, as specified in Section 8.3 (Registration: The System (Well-Known) TCP port number for apex-edge).

The IANA maintains a list of:

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@lists.beepcore.org may be used to solicit commentary.

The IANA makes the registrations specified in Section 8.4 (Registration: The statusRequest Option) and Section 8.5 (Registration: The Report Service).



 TOC 

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/


 TOC 

Full Copyright Statement

Intellectual Property

Acknowledgment