Network Working Group M.T. Rose Internet-Draft Invisible Worlds, Inc. Expires: December 10, 2000 G. Klyne Content Technologies Limited D.H. Crocker Brandenburg Consulting June 11, 2000 The IMXP draft-mrose-imxp-core-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 10, 2000. Copyright Notice Copyright (C) The Internet Society (2000). All Rights Reserved. Abstract This memo describes IMXP, an extensible, asynchronous message relaying service for application layer programs. Rose, et. al. Expires December 10, 2000 [Page 1] Internet-Draft The IMXP June 2000 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Architecture at a Glance . . . . . . . . . . . . . . . . . 5 2. Service Principles . . . . . . . . . . . . . . . . . . . . 7 2.1 Modes of Operation . . . . . . . . . . . . . . . . . . . . 7 2.2 Naming of Entities . . . . . . . . . . . . . . . . . . . . 8 3. Service Provisioning . . . . . . . . . . . . . . . . . . . 9 3.1 Connection Establishment . . . . . . . . . . . . . . . . . 9 3.2 Authentication . . . . . . . . . . . . . . . . . . . . . . 9 3.3 Authorization . . . . . . . . . . . . . . . . . . . . . . 9 3.4 Confidentiality . . . . . . . . . . . . . . . . . . . . . 9 3.5 Routing Integrity . . . . . . . . . . . . . . . . . . . . 10 3.6 Traffic Analysis . . . . . . . . . . . . . . . . . . . . . 10 4. The IMXP . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.1 Use of XML and MIME . . . . . . . . . . . . . . . . . . . 11 4.2 Profile Identification and Initialization . . . . . . . . 13 4.3 Request and Response Messages . . . . . . . . . . . . . . 13 4.4 Message Semantics . . . . . . . . . . . . . . . . . . . . 14 4.4.1 The Attach Operation . . . . . . . . . . . . . . . . . . . 14 4.4.2 The Terminate Operation . . . . . . . . . . . . . . . . . 16 4.4.3 The Data Operation . . . . . . . . . . . . . . . . . . . . 17 4.4.3.1 Relay Processing of Data . . . . . . . . . . . . . . . . . 19 4.4.3.2 Application Processing of Data . . . . . . . . . . . . . . 20 4.5 IMXP Access Policies . . . . . . . . . . . . . . . . . . . 21 5. IMXP Options . . . . . . . . . . . . . . . . . . . . . . . 23 5.1 The statusRequest Option . . . . . . . . . . . . . . . . . 25 6. IMXP Services . . . . . . . . . . . . . . . . . . . . . . 30 6.1 Use of the IMXP Core DTD . . . . . . . . . . . . . . . . . 31 6.1.1 Transaction-Identifiers . . . . . . . . . . . . . . . . . 31 6.1.2 The Reply Operation . . . . . . . . . . . . . . . . . . . 32 6.2 The Report Service . . . . . . . . . . . . . . . . . . . . 33 7. IMXP Reply Codes . . . . . . . . . . . . . . . . . . . . . 34 8. IMXP Option Registration Template . . . . . . . . . . . . 35 9. IMXP Service Registration Template . . . . . . . . . . . . 36 10. Registration: The IMXP Profile . . . . . . . . . . . . . . 37 11. Registration: The statusRequest Option . . . . . . . . . . 38 12. Registration: The Report Service . . . . . . . . . . . . . 39 13. The IMXP Core DTD . . . . . . . . . . . . . . . . . . . . 40 14. The Report Service DTD . . . . . . . . . . . . . . . . . . 43 15. Security Considerations . . . . . . . . . . . . . . . . . 44 16. IANA Considerations . . . . . . . . . . . . . . . . . . . 45 References . . . . . . . . . . . . . . . . . . . . . . . . 46 Authors' Addresses . . . . . . . . . . . . . . . . . . . . 46 A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 48 Full Copyright Statement . . . . . . . . . . . . . . . . . 49 Rose, et. al. Expires December 10, 2000 [Page 2] Internet-Draft The IMXP June 2000 1. Introduction Network applications can be broadly distinguished by five operational characteristics: o server push or client pull; o synchronous (interactive) or asynchronous (batch); 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. Rose, et. al. Expires December 10, 2000 [Page 3] Internet-Draft The IMXP June 2000 1.1 Overview IMXP provides an extensible, asynchronous message relaying service for application layer programs. IMXP, at its core, provides a best-effort datagram service. Each datagram, simply termed "data", is originated and received by IMXP "endpoints" -- applications that dynamically attach to the IMXP "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. Options are used to alter the semantics of the the service, may occur on a per-recipient or per-data basis, and may be processed by either a single or multiple relays. Additional IMXP services are provided on top of the relaying mesh; e.g., access control and presence information. Typically these services are provided by servers that are co-resident with one or more relays within an administrative domain. IMXP is specified as a BXXP[1] "profile". Accordingly, many aspects of IMXP (e.g., authentication) are provided within the BXXP framework. Throughout this memo, the terms "peer", "initiator", "listener", "client" (or "requestor"), and "server" (or "responder") are used in the context of BXXP. In particular, Section 2.1 of the BXXP framework memo discusses the roles that a BXXP peer may perform. When reading this memo, note that the terms "endpoint" and "relay" are specific to IMXP, they do not exist in the context of BXXP. Rose, et. al. Expires December 10, 2000 [Page 4] Internet-Draft The IMXP June 2000 1.2 Architecture at a Glance The IMXP stack: +-------------+ | IMXP | an IMXP process is either: | process | +-------------+ - an application attached as an IMXP | | endpoint; or, | IMXP | | | - an IMXP relay +-------------+ | | IMXP services are realized as applications | BXXP | having a special relationship with the IMXP | | relays in their administrative domain +-------------+ | TCP/IP | +-------------+ | ... | +-------------+ Rose, et. al. Expires December 10, 2000 [Page 5] Internet-Draft The IMXP June 2000 The IMXP entities: administrative domain #1 administrative domain #2 +----------------------------+ +----------------------------+ | +------+ | | +------+ | | | | | | | | | | | appl | | | | appl | | | | | | | | | | | +......+ +------+ | | +------+ +......+ | | | | | | | | | | | | | | |end- | |relay | | | |relay | |end- | | | | point| | | | | | | | point| | | +------+ +------+ | | +------+ +------+ | | | | | | | | | | | | | | | IMXP | | IMXP | | | | IMXP | | IMXP | | | | | | | | | | | | | | | +------+ +------+ | | +------+ +------+ | | | | | | | | | | | | | | | BXXP | | BXXP | | | | BXXP | | BXXP | | | | | | | | | | | | | | | +------+ +------+ | | +------+ +------+ | | || || || | | || || || | | ============= ================ ============= | +----------------------------+ +----------------------------+ | <---- IMXP relaying mesh ----> | Note: routing between administrative domains is configured using SRV RRs. Accordingly, the actual number of relays between two endpoints is not fixed. Rose, et. al. Expires December 10, 2000 [Page 6] Internet-Draft The IMXP June 2000 2. Service Principles 2.1 Modes of Operation IMXP is used in two modes: endpoint-relay: in which the endpoint is always the BXXP initiator of the service, whilst relays are always the BXXP 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, only the transmission of data occurs. In the endpoint-relay mode, an endpoint (BXXP initiator) may: o attach as one or more endpoints; o send data to other endpoints; o receive data from other endpoints; and, o terminate any of its attachments. A relay (BXXP listener), in addition to servicing requests from a BXXP 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, the BXXP initiators and listeners transmit data on behalf of endpoints. Rose, et. al. Expires December 10, 2000 [Page 7] Internet-Draft The IMXP June 2000 2.2 Naming of Entities Endpoints are named using the "addr-spec" syntax of RFC 822[2], i.e., "local@domain". Using the conventions of RFC 2303[3], all endpoint identities having a local-part starting with "imxp=" are reserved for use by IMXP services registered with the IANA. The URL scheme "im" is used to identify endpoints when written as URIs, e.g., "im:fred@example.com". Relays, although not named, belong to an administrative domain, as identified by a FQDN, e.g., "example.com". In IMXP, the "endpoint" is the fundamental entity. IMXP is carried over BXXP, which has the "peer" as its fundamental entity. The relationship between BXXP peer entities and IMXP endpoint entities are defined by IMXP's Access Policies (Section 4.5). Rose, et. al. Expires December 10, 2000 [Page 8] Internet-Draft The IMXP June 2000 3. Service Provisioning 3.1 Connection Establishment The SRV algorithm[4] is used to determine the IP address and TCP port number assigned to a relay for an administrative domain: service: "imxp-edge" (for the endpoint-relay mode), or "imxp-mesh" (for the relay-relay mode); protocol: "tcp"; and, domain: the administrative domain. 3.2 Authentication Authentication is a matter of provisioning for each BXXP peer (c.f., Section 4.5). An IMXP relay might be provisioned to allow a BXXP 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 BXXP peer identified as "fred@example.com" to be authorized to attach as the IMXP endpoint "fred@example.com". 3.3 Authorization Authorization is a matter of provisioning for each BXXP peer (c.f., Section 4.5). Typically, a relay requires that its BXXP peer authenticate as a prelude to authorization, but an endpoint usually does not require the same of its BXXP peer. 3.4 Confidentiality Confidentiality is a matter of provisioning for each BXXP 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. Rose, et. al. Expires December 10, 2000 [Page 9] Internet-Draft The IMXP June 2000 3.5 Routing Integrity Data are routed according to SRV entries in the DNS. Accordingly, routing integrity is a function of the DNS and the applications making use of the DNS. Additional assurance is provided if the BXXP initiator requires that the BXXP listener authenticate itself. 3.6 Traffic Analysis Hop-by-hop protection of data transmitted through the relaying mesh (endpoint identities and content) is afforded at the BXXP level through the use of a transport security profile. Other traffic characteristics, e.g., volume and timing of transmissions, is not protected from third-party analysis. Rose, et. al. Expires December 10, 2000 [Page 10] Internet-Draft The IMXP June 2000 4. The IMXP Section 10 contains the BXXP profile registration for IMXP. 4.1 Use of XML and MIME Each BXXP payload exchanged via IMXP consists of an XML document and possibly an arbitrary MIME content. If only an XML document is sent, then the BXXP payload defaults ("Content-Type: text/xml" and "Content-Transfer-Encoding: binary") are used, e.g., C: REQ . 1 0 27 1 C: C: C: END Otherwise, if an arbitrary MIME content is present, it is indicated by a URI-reference[5] 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 BXXP payload by using a "multipart/related"[6], identified using a "cid" URL[7], and the XML control document occurs as the start of the "multipart/related", e.g., C: REQ . 1 0 1234 1 C: Content-Type: multipart/related; boundary="boundary"; C: start="<1@example.com>"; C: type="text/xml" C: C: --boundary C: Content-Type: text/xml C: Content-ID: <1@example.com> C: C: C: C: C: --boundary C: Content-Type: image/gif C: Content-Transfer-Encoding: binary C: Content-ID: <2@example.com> C: C: ... C: --boundary-- C: END Rose, et. al. Expires December 10, 2000 [Page 11] Internet-Draft The IMXP June 2000 Because BXXP provides an 8bit-wide path, a "transformative" Content-Transfer-Encoding (e.g., "base64" or "quoted-printable") should not be used. Further, note that MIME[8] 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 with the control document directly, and identified using a URI-reference consisting of only a fragment-identifier, e.g., C: REQ . 1 0 259 1 C: C: C: C: C: C: C: C: C: C: C: Rose, et. al. Expires December 10, 2000 [Page 12] Internet-Draft The IMXP June 2000 4.2 Profile Identification and Initialization The IMXP is identified as http://xml.resource.org/profiles/IMXP in the BXXP "profile" element during channel creation. No elements are required to be exchanged during channel creation; however, in the endpoint-relay mode, the BXXP initiator will typically include an "attach" element during channel creation, e.g., 4.3 Request and Response Messages Section 13 defines the BXXP payloads that are used in the IMXP: o "REQ" messages carry either the "attach", "terminate", or "data" element as BXXP payload; o positive "RSP" messages carry the "ok" element as BXXP payload; and, o negative "RSP" messages carry the "error" element as BXXP payload. Rose, et. al. Expires December 10, 2000 [Page 13] Internet-Draft The IMXP June 2000 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: C: C: S: or +-------+ +-------+ | | -- attach -----> | | | | | | | | <--------- ok -- | | | appl. | | relay | | | -- attach -----> | | | | | | | | <--------- ok -- | | +-------+ +-------+ C: C: C: S: C: C: C: S: Rose, et. al. Expires December 10, 2000 [Page 14] Internet-Draft The IMXP June 2000 or +-------+ +-------+ | | -- attach -----> | | | appl. | | relay | | | <------ error -- | | +-------+ +-------+ C: C: C: S: access denied The "attach" element has a "transID" attribute, and contains a "recipient" element, which, in turn, has an "identity" attribute and contains zero or more "option" elements: o the "transID" attribute specifies the transaction-identifier associated with this operation; o the "identity" attribute specifies the desired endpoint; 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 attach operation on this BXXP channel (that has not yet been terminated), 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, an "error" element having code 537 is returned. 4. If any options are present, they are examined. 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. Expires December 10, 2000 [Page 15] Internet-Draft The IMXP June 2000 4.4.2 The Terminate Operation When an application or relay wants to detach an endpoint, it sends a "terminate" element, e.g., +-------+ +-------+ | | -- terminate --> | | | appl. | | relay | | | <--------- ok -- | | +-------+ +-------+ C: S: or +-------+ +-------+ | | -- terminate --> | | | appl. | | relay | | | <------ error -- | | +-------+ +-------+ C: S: unknown transaction-identifier or +-------+ +-------+ | | <-- terminate -- | | | appl. | | relay | | | -- ok ---------> | | +-------+ +-------+ C: S: The "terminate" element has a "transID" attribute that specifies the transaction-identifier associated a previous attach operation, and has no content. When an application or relay receives a "terminate" element, it performs these steps: 1. If the transaction-identifier does not refer to a previous attach operation on this BXXP channel (that has not yet been terminated), an "error" element having code 550 is returned. 2. Otherwise, the application is no longer bound as the corresponding endpoint, and an "ok" element is returned. Rose, et. al. Expires December 10, 2000 [Page 16] Internet-Draft The IMXP June 2000 4.4.3 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: S: or +-------+ +-------+ | | -- data -------> | | | appl. | | relay | | #1 | <------ error -- | | +-------+ +-------+ C: S: barney@example.com not attached or +-------+ +-------+ | | -- data -------> | | | relay | | appl. | | | <--------- ok -- | #2 | +-------+ +-------+ C: S: Rose, et. al. Expires December 10, 2000 [Page 17] Internet-Draft The IMXP June 2000 The "data" element has an "originator" and a "content" attribute, and contains one or more "recipient" elements, zero or more "option" elements, and, optionally, a "data-content" element: o the "originator" attribute specifies the endpoint sending the data; o the "content" attribute is a URI-reference that specifies the contents of the data (c.f., Section 4.1); 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 using a URI fragment-identifier as the value of the "content" attribute. 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. Rose, et. al. Expires December 10, 2000 [Page 18] Internet-Draft The IMXP June 2000 4.4.3.1 Relay Processing of Data When a relay receives a "data" element, it performs these steps: 1. If the BXXP client is not authorized to originate or relay data on behalf of the "originator" endpoint, an "error" element having code 537 is returned. 2. If any per-data options are present, they are examined. 3. For each recipient: 1. If any per-recipient options are present, they are examined. 2. If the recipient endpoint is not in the administrative domain associated with the relay, then an IMXP session is established to a relay that accepts data for the recipient's administrative domain, and a new "data" element, containing only that "recipient" element (and all applicable options), is sent to that relay. If no errors (e.g., an IMXP session can not be established) occur during processing, and if the recipient's relay returns an "ok" element, then the recipient is considered to be successfully processed. 3. Otherwise, the IMXP access service must allow the originator endpoint to communicate with the recipient endpoint (the recipient's access entry[9] 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 (and no options), is sent to the corresponding application, and the recipient is considered to be successfully processed. 4. If no recipients could be successfully processed, an "error" element is returned; otherwise, an "ok" element is returned. Note that an implementation may choose to optimize its behavior by grouping multiple recipients in a single "data" element that is subsequently transmitted. It may do so providing that the optimization retains these semantics and any other semantics related to per-data and per-recipient options. Finally, note that a relay receiving a "data" element from an application may be configured to add domain-specific options. Rose, et. al. Expires December 10, 2000 [Page 19] Internet-Draft The IMXP June 2000 4.4.3.2 Application Processing of Data When an application receives a "data" element, it performs these steps: 1. For each recipient: 1. If the application is not attached as the recipient endpoint, then an error in processing has occurred. 2. Otherwise, the "data" element is further processed in an application-specific manner, and the recipient is considered to be successfully processed. 2. If no recipients could be successfully processed, an "error" element is returned; otherwise, an "ok" element is returned. Rose, et. al. Expires December 10, 2000 [Page 20] Internet-Draft The IMXP June 2000 4.5 IMXP Access Policies Access to IMXP is provided by the juxtaposition of: o authenticating as a BXXP peer; o attaching as an IMXP endpoint; and, o being listed as an actor by the IMXP access service (c.f., [9]). 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. Rose, et. al. Expires December 10, 2000 [Page 21] Internet-Draft The IMXP June 2000 IMXP access policies are used in these contexts: o In the endpoint-relay mode, when an application wishes to attach to the relaying mesh, local provisioning maps BXXP peer identities to allowed IMXP 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 BXXP peer named as "fred@example.com", it is allowed to attach as the IMXP endpoint named as "fred@example.com". o In the endpoint-relay mode, when an application wishes to send data, local provisioning maps attached endpoints to allowed originators (c.f., Step 1 of Section 4.4.3.1). Typically, the identity function is used, e.g., if an application attaches as the IMXP endpoint named as "fred@example.com", it is allowed to send data originating from the same IMXP endpoint. However, other policies are permissible, for example, the administrative domain may allow the application attached as the IMXP endpoint named as "wilma@example.com" to send data originating as either "wilma@example.com" or "fred@example.com". o In the relay-relay mode, when a relay is sending data, no access policies, per se, are applied. o In the relay-relay mode, when a relay is receiving data, local provisioning maps BXXP peer identities to allowed originators (c.f., Step 1 of Section 4.4.3.1). Typically, if a BXXP peer authenticates itself as being from the same administrative domain as the originator of the data, or if the BXXP peer authenticates itself as being from a "trusted" intermediate relay, then the data is accepted. 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 3.3 of Section 4.4.3.1). Rose, et. al. Expires December 10, 2000 [Page 22] Internet-Draft The IMXP June 2000 5. IMXP Options IMXP, at its core, provides a best-effort datagram service. Options are used to alter the semantics of the core service. The semantics of the IMXP "option" element are context-specific. Accordingly, the specification of an IMXP option must define: o the identity of the option; 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 8) organizes this information. An "option" element is contained within either a "data" element or a "recipient" element, either of which is 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 "seeNoEvil" attribute specifies whether the option, if unrecognized, may be safely ignored; 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. 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. Rose, et. al. Expires December 10, 2000 [Page 23] Internet-Draft The IMXP June 2000 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 not transmit the containing element to another relay. all: the option applies to this relay and is retained for the next. Note that in all cases, prior to transmitting the containing element to an endpoint, all options are removed. The "seeNoEvil" 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 "seeNoEvil" attribute is "false", and if the relay does not "understand" the option, then this is considered a processing error. Rose, et. al. Expires December 10, 2000 [Page 24] Internet-Draft The IMXP June 2000 5.1 The statusRequest Option Section 11 contains the IMXP 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. Rose, et. al. Expires December 10, 2000 [Page 25] Internet-Draft The IMXP June 2000 Consider these examples: +-------+ +-------+ | | -- data -------> | | | appl. | | relay | | #1 | <--------- ok -- | | +-------+ +-------+ C: S: +-------+ +-------+ | | -- data -------> | | | relay | | appl. | | | <--------- ok -- | #2 | +-------+ +-------+ C: S: +-------+ +-------+ | | <------- data -- | | | appl. | | relay | | #1 | -- ok ---------> | | +-------+ +-------+ C: S: Rose, et. al. Expires December 10, 2000 [Page 26] Internet-Draft The IMXP June 2000 or +-------+ +-------+ | | -- data -------> | | | appl. | | relay | | | <--------- ok -- | #1 | +-------+ +-------+ C: S: +-------+ +-------+ | | -- data -------> | | | relay | | relay | | #1 | <------ error -- | #2 | +-------+ +-------+ C: S: unknown endpoint identity +-------+ +-------+ | | <------- data -- | | | appl. | | relay | | | -- ok ---------> | #1 | +-------+ +-------+ C: unknown endpoint identity S: Rose, et. al. Expires December 10, 2000 [Page 27] Internet-Draft The IMXP June 2000 or +-------+ +-------+ | | -- data -------> | | | appl. | | relay | | | <--------- ok -- | #1 | +-------+ +-------+ C: S: +-------+ +-------+ | | -- data -------> | | | relay | | relay | | #1 | <--------- ok -- | #2 | +-------+ +-------+ C: S: +-------+ +-------+ | | <------- data -- | | | relay | | relay | | #1 | -- ok ---------> | #2 | +-------+ +-------+ C: S: Rose, et. al. Expires December 10, 2000 [Page 28] Internet-Draft The IMXP June 2000 +-------+ +-------+ | | -- data -------> | | | appl. | | relay | | | <--------- ok -- | #1 | +-------+ +-------+ C: S: Note that a trace of a data's passage through the relaying mesh can be achieved by setting the "targetHop" attribute to "all". Rose, et. al. Expires December 10, 2000 [Page 29] Internet-Draft The IMXP June 2000 6. IMXP Services IMXP, at its core, provides a best-effort datagram service. Errors are reported through the use of a co-resident IMXP report service. All other IMXP services are provided on top of the relaying mesh, e.g., +----------+ +----------+ +----------+ | IMXP | | IMXP | | | | access | | presence | | ... | | service | | service | | | +----------+ +----------+ +----------+ | | | | | | +------------------------------------------------+---------+ | | IMXP | | IMXP core | report | | | service | +------------------------------------------------+---------+ Applications communicate with IMXP services by sending data to a "well-known endpoint" (WKE). The specification of an IMXP service must define: o the WKE of the service; o the syntax of messages exchanged with the service; o the sequence of messages exchanged with the service; and, o what access control tokens are consulted by the service. A service registration template (Section 9) organizes this information. Note that both the IMXP access[9] and presence[10] services are logically layered above the IMXP core; however, implementers may choose to physically co-reside these services with IMXP relay software. Finally, note that within a single administrative domain, the relaying mesh makes use of the IMXP access service in order to determine if an originator is allowed to transmit data to a recipient (c.f., Step 3.3 of Section 4.4.3.1) Rose, et. al. Expires December 10, 2000 [Page 30] Internet-Draft The IMXP June 2000 6.1 Use of the IMXP Core DTD The specification of an IMXP service may use definitions found in the IMXP core DTD (Section 13). 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 IMXP's transaction-identifiers, note the following: o In the endpoint-relay mode, transaction-identifiers are meaningful only during the lifetime of a BXXP channel. For example, when an application issues the attach operation, the associated transaction-identifier has meaning only within the context of the BXXP channel used for the attach operation. When the BXXP 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 IMXP 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. Expires December 10, 2000 [Page 31] Internet-Draft The IMXP June 2000 6.1.2 The Reply Operation Many IMXP services make use of a reply operation. Accordingly, Section 13 contains a definition of a "reply" element that can be used for this purpose. 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 7); 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. Rose, et. al. Expires December 10, 2000 [Page 32] Internet-Draft The IMXP June 2000 6.2 The Report Service Section 12 contains the IMXP service registration for the report service: o Within an administrative domain, the service is addressed using the well-known endpoint of "imxp=report". o Section 14 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. Unlike other IMXP services, the report service is co-resident with the IMXP core -- the report service is provided by each and every relay. If a relay processes a "statusRequest" option (Section 5.1), then it sends data to the originator containing a "statusResponse" element (Section 14). The "statusResponse" element has a "transID" attribute and contains one or more "destination" elements: 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. Rose, et. al. Expires December 10, 2000 [Page 33] Internet-Draft The IMXP June 2000 7. IMXP 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 Rose, et. al. Expires December 10, 2000 [Page 34] Internet-Draft The IMXP June 2000 8. IMXP Option Registration Template When an IMXP 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 IMXP 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. Rose, et. al. Expires December 10, 2000 [Page 35] Internet-Draft The IMXP June 2000 9. IMXP Service Registration Template When an IMXP service is registered, the following information is supplied: Well-Known Endpoint: specify the local-part of an endpoint identity, starting with "imxp=". 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., [9]). Rose, et. al. Expires December 10, 2000 [Page 36] Internet-Draft The IMXP June 2000 10. Registration: The IMXP Profile Profile Identification: http://xml.resource.org/profiles/IMXP Elements Exchanged during Channel Creation: none required Messages in "REQ" frames: "attach", "terminate", "data" Messages in positive "RSP" frames: "ok" Messages in negative "RSP" frames: "error" Message Syntax: c.f., Section 13 Message Semantics: c.f., Section 4.4 Rose, et. al. Expires December 10, 2000 [Page 37] Internet-Draft The IMXP June 2000 11. Registration: The statusRequest Option Option Identification: statusRequest Present in: IMXP's "data" and "recipient" elements Contains: nothing Processing Rules: c.f., Section 5.1 Rose, et. al. Expires December 10, 2000 [Page 38] Internet-Draft The IMXP June 2000 12. Registration: The Report Service Well-Known Endpoint: imxp=report Syntax of Messages Exchanged: c.f., Section 14 Sequence of Messages Exchanged: c.f., Section 6.2 Access Control Tokens: none Rose, et. al. Expires December 10, 2000 [Page 39] Internet-Draft The IMXP June 2000 13. The IMXP Core DTD %BXXP; Rose, et. al. Expires December 10, 2000 [Page 40] Internet-Draft The IMXP June 2000 Rose, et. al. Expires December 10, 2000 [Page 41] Internet-Draft The IMXP June 2000 Rose, et. al. Expires December 10, 2000 [Page 42] Internet-Draft The IMXP June 2000 14. The Report Service DTD %IMXPCORE; Rose, et. al. Expires December 10, 2000 [Page 43] Internet-Draft The IMXP June 2000 15. Security Considerations Consult Section 3 and Section 4.5 for a discussion of security issues, e.g., routing integrity. In addition, since IMXP is a profile of the BXXP, consult [1]'s Section 8 for a discussion of BXXP-specific security issues. In addition, the statusRequest option (Section 5.1) may be used to expose private network topology. Accordingly, administrators may wish to choose to disable this option except at the ingress/egress points for their domain. Rose, et. al. Expires December 10, 2000 [Page 44] Internet-Draft The IMXP June 2000 16. IANA Considerations The IANA assigns the "im" URL scheme to identify IMXP endpoints. The IANA maintains a list of: o IMXP options, c.f., Section 5 and Section 8; and, o IMXP services, c.f., Section 6 and Section 9. Rose, et. al. Expires December 10, 2000 [Page 45] Internet-Draft The IMXP June 2000 References [1] Rose, M.T., "The Blocks eXtensible eXchange Protocol Framework", draft-mrose-blocks-protocol-03 (work in progress), May 2000. [2] Crocker, D., "Standard for the format of ARPA Internet text messages", RFC 822, STD 11, Aug 1982. [3] Allocchio, C., "Minimal PSTN address format in Internet Mail", RFC 2303, March 1998. [4] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000. [5] Berners-Lee, T., Fielding, R.T. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. [6] Levinson, E., "The MIME Multipart/Related Content-type", RFC 2387, August 1998. [7] Levinson, E., "Content-ID and Message-ID Uniform Resource Locators", RFC 2392, August 1998. [8] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [9] Rose, M.T., Klyne, G. and D.H. Crocker, "The IMXP Access Service", draft-mrose-imxp-access-00 (work in progress), June 2000. [10] Rose, M.T., Klyne, G. and D.H. Crocker, "The IMXP Presence Service", draft-mrose-imxp-presence-00 (work in progress), June 2000. [11] mailto:dnew@san.rr.com [12] mailto:spead@novell.com Rose, et. al. Expires December 10, 2000 [Page 46] Internet-Draft The IMXP June 2000 Authors' Addresses Marshall T. Rose Invisible Worlds, Inc. 1179 North McDowell Boulevard Petaluma, CA 94954-6559 US Phone: +1 707 789 3700 EMail: mrose@invisible.net URI: http://invisible.net/ Graham Klyne Content Technologies Limited 1220 Parkview Arlington Business Park Theale, Reading RG7 4SA UK Phone: +44 118 930 1300 EMail: gk@acm.org David H. Crocker Brandenburg Consulting 675 Spruce Drive Sunnyvale, CA 94086 US Phone: +1 408 246 8253 EMail: dcrocker@brandenburg.com URI: http://www.brandenburg.com/ Rose, et. al. Expires December 10, 2000 [Page 47] Internet-Draft The IMXP June 2000 Appendix A. Acknowledgements The authors gratefully acknowledge the contributions of: Darren New[11] and Scott Pead[12]. Rose, et. al. Expires December 10, 2000 [Page 48] Internet-Draft The IMXP June 2000 Full Copyright Statement Copyright (C) The Internet Society (2000). All Rights Reserved. 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