RFC 3835

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Network Working Group                                          A. Barbir
Request for Comments: 3835                                      R. Penno
Category: Informational                                  Nortel Networks
                                                                 R. Chen
                                                               AT&T Labs
                                                              M. Hofmann
                                           Bell Labs/Lucent Technologies
                                                                H. Orman
                                               Purple Streak Development
                                                             August 2004

        An Architecture for Open Pluggable Edge Services (OPES)

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).


   This memo defines an architecture that enables the creation of an
   application service in which a data provider, a data consumer, and
   zero or more application entities cooperatively implement a data
   stream service.

Table of Contents

   1.  Introduction 
   2 . The Architecture 
       2.1.  OPES Entities
             2.1.1.  Data Dispatcher
       2.2.  OPES Flows 
       2.3.  OPES Rules 
       2.4.  Callout Servers
       2.5.  Tracing Facility
   3.  Security and Privacy Considerations  
       3.1.  Trust Domains
       3.2.  Establishing Trust and Service Authorization 
       3.3.  Callout Protocol 
       3.4.  Privacy
       3.5.  End-to-end Integrity 
   4.  IAB Architectural and Policy Considerations for OPES 
       4.1.  IAB consideration (2.1) One-party Consent
       4.2.  IAB consideration (2.2) IP-Layer Communications
       4.3.  IAB consideration (3.1 and 3.2) Notification 
       4.4.  IAB consideration (3.3) Non-Blocking
       4.5.  IAB consideration (4.1) URI Resolution 
       4.6.  IAB consideration (4.2) Reference Validity 
       4.7.  IAB consideration (4.3) Application Addressing
       4.8.  IAB consideration (5.1) Privacy
   5.  Security Considerations  
   6.  IANA Considerations 
   7.  Summary  
   8.  References 
       8.1.  Normative References
       8.2.  Informative References
   9.  Acknowledgements 
   10. Authors' Addresses
   11. Full Copyright Statement

1.  Introduction

   When supplying a data stream service between a provider and a
   consumer, the need to provision the use of other application
   entities, in addition to the provider and consumer, may arise.  For
   example, some party may wish to customize a data stream as a service
   to a consumer.  The customization step might be based on the
   customer's resource availability (e.g., display capabilities).

   In some cases it may be beneficial to provide a customization service
   at a network location between the provider and consumer host rather
   than at one of these endpoints.  For certain services performed on

   behalf of the end-user, this may be the only option of service
   deployment.  In this case, zero or more additional application
   entities may participate in the data stream service.  There are many
   possible provisioning scenarios which make a data stream service
   attractive.  The OPES Use Cases and Deployment Scenarios [1] document
   provides examples of OPES services.  The document discusses services
   that modify requests, services that modify responses, and services
   that create responses.  It is recommended that the document on OPES
   Use Cases and Deployment Scenarios [1] be read before reading this

   This document presents the architectural components of Open Pluggable
   Edge Services (OPES) that are needed in order to perform a data
   stream service.  The architecture addresses the IAB considerations
   described in [2].  These considerations are covered in various parts
   of the document.  Section 2.5 addresses tracing; section 3 addresses
   security considerations.  Section 4 provides a summary of IAB
   considerations and how the architecture addresses them.

   The document is organized as follows: Section 2 introduces the OPES
   architecture.  Section 3 discusses OPES security and privacy
   considerations.  Section 4 addresses IAB considerations for OPES.
   Section 5 discusses security considerations.  Section 6 addresses
   IANA considerations.  Section 7 provides a summary of the
   architecture and the requirements for interoperability.

2.  The Architecture

   The architecture of Open Pluggable Edge Services (OPES) can be
   described in terms of three interrelated concepts, mainly:

   o  OPES entities: processes operating in the network;

   o  OPES flows:  data flows that are cooperatively realized by the
      OPES entities; and,

   o  OPES rules: these specify when and how to execute OPES services.

2.1.  OPES Entities

   An OPES entity is an application that operates on a data flow between
   a data provider application and a data consumer application.  OPES
   entities can be:

   o  an OPES service application, which analyzes and possibly
      transforms messages exchanged between the data provider
      application and the data consumer application;

   o  a data dispatcher, which invokes an OPES service application based
      on an OPES ruleset and application-specific knowledge.

   The cooperative behavior of OPES entities introduces additional
   functionality for each data flow provided that it matches the OPES
   rules.  In the network, OPES entities reside inside OPES processors.
   In the current work, an OPES processor MUST include a data
   dispatcher.  Furthermore, the data provider and data consumer
   applications are not considered as OPES entities.

   To provide verifiable system integrity (see section 3.1 on trust
   domains below) and to facilitate deployment of end-to-end encryption
   and data integrity control, OPES processors MUST be:

   o  explicitly addressable at the IP layer by the end user (data
      consumer application).  This requirement does not preclude a chain
      of OPES processors with the first one in the chain explicitly
      addressed at the IP layer by the end user (data consumer

   o  consented to by either the data consumer or data provider
      application.  The details of this process are beyond the scope of
      the current work.

   The OPES architecture is largely independent of the protocol that is
   used by the data provider application and the data consumer
   application to exchange data.  However, this document selects HTTP
   [3] as the example for the underlying protocol in OPES flows.

2.1.1.   Data Dispatcher

   Data dispatchers include a ruleset that can be compiled from several
   sources and MUST resolve into an unambiguous result.  The combined
   ruleset enables an OPES processor to determine which service
   applications to invoke for which data flow.  Accordingly, the data
   dispatcher constitutes an enhanced policy enforcement point, where
   policy rules are evaluated and service-specific data handlers and
   state information are maintained, as depicted in Figure 1.

                                        |  callout |
                                        |  server  |
                         | +-----------+     ||     |
                         | |   OPES    |     ||     |
                         | |  service  |     ||     |
                         | |application|     ||     |
                         | +-----------+     ||     |
                         | +----------------------+ |
         OPES flow <---->| | data dispatcher and  | |<----> OPES flow
                         | | policy enforcement   | |
                         | +----------------------+ |
                         |           OPES           |
                         |         processor        |

                          Figure 1: Data Dispatchers

   The architecture allows for more than one policy enforcement point to
   be present on an OPES flow.

2.2.  OPES Flows

   An OPES flow is a cooperative undertaking between a data provider
   application, a data consumer application, zero or more OPES service
   applications, and one or more data dispatchers.

   Since policies are enforced by data dispatchers, the presence of at
   least one data dispatcher is required in the OPES flow.

    data          OPES               OPES             data
      consumer        processor A        processor N      provider

    +-----------+    +-----------+  .  +-----------+    +-----------+
    |   data    |    |  OPES     |  .  |  OPES     |    |   data    |
    | consumer  |    | service   |  .  | service   |    | provider  |
    |application|    |application|  .  |application|    |application|
    +-----------+    +-----------+  .  +-----------+    +-----------+
    |           |    |           |  .  |           |    |           |
    |   HTTP    |    |    HTTP   |  .  |    HTTP   |    |   HTTP    |
    |           |    |           |  .  |           |    |           |
    +-----------+    +-----------+  .  +-----------+    +-----------+
    |  TCP/IP   |    |   TCP/IP  |  .  |   TCP/IP  |    |  TCP/IP   |
    +-----------+    +-----------+  .  +-----------+    +-----------+
         ||             ||    ||    .       ||    ||         ||
         ================      =====.========      ===========

         | <----------------- OPES flow -------------------> |

                       Figure 2: An OPES flow

   Figure 2 depicts two data dispatchers that are present in the OPES
   flow.  The architecture allows for one or more data dispatchers to be
   present in any flow.

2.3.  OPES Rules

   OPES' policy regarding services and the data provided to them is
   determined by a ruleset consisting of OPES rules.  The rules consist
   of a set of conditions and related actions.  The ruleset is the
   superset of all OPES rules on the processor.  The OPES ruleset
   determines which service applications will operate on a data stream.
   In this model, all data dispatchers are invoked for all flows.

   In order to ensure predictable behavior, the OPES architecture
   requires the use of a standardized schema for the purpose of defining
   and interpreting the ruleset.  The OPES architecture does not require
   a mechanism for configuring a ruleset into a data dispatcher.  This

   is treated as a local matter for each implementation (e.g., through
   the use of a text editor or a secure upload protocol), as long as
   such a mechanism complies with the requirements set forth in section

2.4.  Callout Servers

   The evaluation of the OPES ruleset determines which service
   applications will operate on a data stream.  How the ruleset is
   evaluated is not the subject of the architecture, except to note that
   it MUST result in the same unambiguous result in all implementations.

   In some cases it may be useful for the OPES processor to distribute
   the responsibility of service execution by communicating with one or
   more callout servers.  A data dispatcher invokes the services of a
   callout server by using the OPES callout protocol (OCP).  The
   requirements for the OCP are given in [5].  The OCP is application-
   agnostic, being unaware of the semantics of the encapsulated
   application protocol (e.g., HTTP).  However, the data dispatcher MUST
   incorporate a service aware vectoring capability that parses the data
   flow according to the ruleset and delivers the data to either the
   local or remote OPES service application.

   The general interaction situation is depicted in Figure 3, which
   illustrates the positions and interaction of different components of
   OPES architecture.

   | +-----------+            |
   | |   OPES    |            |
   | |  service  |            |      +---------------+     +-----------+
   | |application|            |      | Callout       |     | Callout   |
   | +-----------+            |      | Server A      |     | Server X  |
   |     ||                   |      | +--------+    |     |           |
   | +----------------------+ |      | | OPES   |    |     |           |
   | |     data dispatcher  | |      | | Service|    |     | +--------+|
   | +----------------------+ |      | | Appl A |    |     | | OPES   ||
   |      ||           ||     |      | +--------+    |     | |Service ||
   |  +---------+  +-------+  |      |     ||        |     | | Appl X ||
   |  |  HTTP   |  |       |  |      | +--------+    | ... | +--------||
   |  |         |  |  OCP  |=========| | OCP    |    |     |    ||     |
   |  +---------+  +-------+  |      | +--------+    |     | +------+  |
   |  |         |     ||      |      +---------------+     | | OCP  |  |
   |  | TCP/IP  |     =======================================|      |  |
   |  |         |             |                            | +------+  |
   |  +---------+             |                            +-----------+
            || ||
 +--------+ || ||                                       +--------+
 |data    |==  =========================================|data    |
 |producer|                                             |consumer|
 +--------+                                             +--------+

              Figure 3: Interaction of OPES Entities

2.5.  Tracing Facility

   The OPES architecture requires that each data dispatcher provides
   tracing facilities that allow the appropriate verification of its
   operation.  The OPES architecture requires that tracing be feasible
   on the OPES flow, per OPES processor, using in-band annotation.  One
   of those annotations could be a URI with more detailed information on
   the OPES services being executed in the OPES flow.

   Providing the ability for in-band annotation MAY require header
   extensions on the application protocol that is used (e.g., HTTP).
   However, the presence of an OPES processor in the data request/
   response flow SHALL NOT interfere with the operations of non-OPES
   aware clients and servers.  Non-OPES clients and servers need not
   support these extensions to the base protocol.

   OPES processors MUST obey tracing, reporting, and notification
   requirements set by the center of authority in the trust domain to
   which an OPES processor belongs.  As part of these requirements, the
   OPES processor may be instructed to reject or ignore such
   requirements that originate from other trust domains.

3. Security and Privacy Considerations

   Each data flow MUST be secured in accordance with several policies.
   The primary stakeholders are the data consumer and the data provider.
   The secondary stakeholders are the entities to which they may have
   delegated their trust.  The other stakeholders are the owners of the
   callout servers.  Any of these parties may be participants in the
   OPES flow.

   These parties MUST have a model, explicit or implicit, describing
   their trust policy, which of the other parties are trusted to operate
   on data, and what security enhancements are required for
   communication.  The trust might be delegated for all data, or it
   might be restricted to granularity as small as an application data

   All parties that are involved in enforcing policies MUST communicate
   the policies to the parties that are involved.  These parties are
   trusted to adhere to the communicated policies.

   In order to delegate fine-grained trust, the parties MUST convey
   policy information by implicit contract, by a setup protocol, by a
   dynamic negotiation protocol, or in-line with application data

3.1.  Trust Domains

   The delegation of authority starts at either a data consumer or data
   provider and moves to more distant entities in a "stepwise" fashion.
   Stepwise means A delegates to B, and B delegates to C, and so forth.
   The entities thus "colored" by the delegation are said to form a
   trust domain with respect to the original delegating party.  Here,
   "Colored" means that if the first step in the chain is the data
   provider, then the stepwise delegation "colors" the chain with that
   data "provider" color.  The only colors defined are the data
   "provider" and the data "consumer".  Delegation of authority
   (coloring) propagates from the content producer start of authority or
   from the content consumer start of authority, which may be different
   from the end points in the data flow.

   Figure 4 illustrates administrative domains, out-of-band rules, and
   policy distribution.

 provider administrative domain         consumer administrative domain
 +------------------------------+      +-------------------------------+
 | +--------------+             |      |            +--------------+   |
 | |Provider      |      <- out-of-band rules, ->   |Consumer      |   |
 | |Administrative|~~>~~~:  policies and         ~<~|Administrative|   |
 | |Authority     |      : service authorization :  |Authority     |   |
 | +--------------+      :        |     |        :  +--------------+   |
 |         :             :        |     |        :           :         |
 |         :             :        |     |        :           :         |
 |   +----------+        :        |     |        :        +----------+ |
 |   |  callout |    +---------+  |     |  +---------+    |  callout | |
 |   |  server  |====|         |  |     |  |         |====|  server  | |
 |   +----------+    |         |  |     |  |         |    +----------+ |
 |                   | OPES    |  |     |  | OPES    |                 |
 |   +----------+    |processor|  |     |  |processor|   +----------+  |
 |   |          |    |         |  |     |  |         |   |          |  |
 |   | data     |    |         |  |     |  |         |   | data     |  |
 |   | provider |    |         |  |     |  |         |   | consumer |  |
 |   |          |    +---------+  |     |  +---------+   +----------+  |
 |   +----------+     ||     ||   |     |   ||    ||     +----------+  |
 |        ||          ||     ||   |     |   ||    ||         ||        |
 |        =============     =================      ===========         |
 |                               |     |                               |
 +-------------------------------+     +-------------------------------+
          | <----------------- OPES flow -----------------> |

    Figure 4: OPES administrative domains and policy distribution

   In order to understand the trust relationships between OPES entities,
   each is labeled as residing in an administrative domain.  Entities
   associated with a given OPES flow may reside in one or more
   administrative domains.

   An OPES processor may be in several trust domains at any time.  There
   is no restriction on whether the OPES processors are authorized by
   data consumers and/or data providers.  The original party has the
   option of forbidding or limiting redelegation.

   An OPES processor MUST have a representation of its trust domain
   memberships that it can report in whole or in part for tracing
   purposes.  It MUST include the name of the party that delegated each
   privilege to it.

3.2.  Establishing Trust and Service Authorization

   The OPES processor will have a configuration policy specifying what
   privileges the callout servers have and how they are to be
   identified.  OPES uses standard protocols for authentication and
   other security communication with callout servers.

   An OPES processor will have a trusted method for receiving
   configuration information, such as rules for the data dispatcher,
   trusted callout servers, primary parties that opt-in or opt-out of
   individual services, etc.

   Protocol(s) for policy/rule distribution are out of scope for this
   document, but the OPES architecture assumes the existence of such a

   Requirements for the authorization mechanism are set in a separate
   document [4].

   Service requests may be done in-band.  For example, a request to
   bypass OPES services could be signalled by a user agent using an HTTP
   header string "Bypass-OPES".  Such requests MUST be authenticated.
   The way OPES entities will honor such requests is subordinate to the
   authorization policies effective at that moment.

3.3.  Callout Protocol

   The determination of whether or not OPES processors will use the
   measures that are described in the previous section during their
   communication with callout servers depends on the details of how the
   primary parties delegated trust to the OPES processors and the trust
   relationship between the OPES processors and the callout server.
   Strong authentication, message authentication codes, and encryption
   SHOULD be used.  If the OPES processors are in a single
   administrative domain with strong confidentiality and integrity
   guarantees, then cryptographic protection is recommended but

   If the delegation mechanism names the trusted parties and their
   privileges in some way that permits authentication, then the OPES
   processors will be responsible for enforcing the policy and for using
   authentication as part of that enforcement.

   The callout servers MUST be aware of the policy governing the
   communication path.  They MUST not, for example, communicate
   confidential information to auxiliary servers outside the trust

   A separate security association MUST be used for each channel
   established between an OPES processor and a callout server.  The
   channels MUST be separate for different primary parties.

3.4.  Privacy

   Some data from OPES flow endpoints is considered "private" or
   "sensitive", and OPES processors MUST advise the primary parties of
   their privacy policy and respect the policies of the primary parties.
   The privacy information MUST be conveyed on a per-flow basis.  This
   can be accomplished by using current available privacy techniques
   such as P3P [7] and HTTP privacy capabilities.

   The callout servers MUST also participate in the handling of private
   data, they MUST be prepared to announce their own capabilities, and
   enforce the policy required by the primary parties.

3.5.  End-to-End Integrity

   Digital signature techniques can be used to mark data changes in such
   a way that a third-party can verify that the changes are or are not
   consistent with the originating party's policy.  This requires an
   inline method to specify policy and its binding to data, a trace of
   changes and the identity of the party making the changes, and strong
   identification and authentication methods.

   Strong end-to-end integrity can fulfill some of the functions
   required by "tracing".

4.  IAB Architectural and Policy Considerations for OPES

   This section addresses the IAB considerations for OPES [2] and
   summarizes how the architecture addresses them.

4.1.  IAB Consideration (2.1) One-Party Consent

   The IAB recommends that all OPES services be explicitly authorized by
   one of the application-layer end-hosts (that is, either the data
   consumer application or the data provider application).

   The current work requires that either the data consumer application
   or the data provider application consent to OPES services.  These
   requirements have been addressed in sections 2 (section 2.1) and 3.

4.2.  IAB Consideration (2.2) IP-Layer Communications

   The IAB recommends that OPES processors must be explicitly addressed
   at the IP layer by the end user (data consumer application).

   This requirement has been addressed in section 2.1, by the
   requirement that OPES processors be addressable at the IP layer by
   the data consumer application.

4.3.  IAB Consideration (3.1 and 3.2) Notification

   The IAB recommends that the OPES architecture incorporate tracing
   facilities.  Tracing enables data consumer and data provider
   applications to detect and respond to actions performed by OPES
   processors that are deemed inappropriate to the data consumer or data
   provider applications.

   Section 3.2 of this document discusses the tracing and notification
   facilities that must be supported by OPES services.

4.4.  IAB Consideration (3.3) Non-Blocking

   The OPES architecture requires the specification of extensions to
   HTTP.  These extensions will allow the data consumer application to
   request a non-OPES version of the content from the data provider
   application.  These requirements are covered in Section 3.2.

4.5.  IAB Consideration (4.1) URI Resolution

   This consideration recommends that OPES documentation must be clear
   in describing OPES services as being applied to the result of URI
   resolution, not as URI resolution itself.

   This requirement has been addressed in sections 2.5 and 3.2, by
   requiring OPES entities to document all the transformations that have
   been performed.

4.6.  IAB Consideration (4.2) Reference Validity

   This consideration recommends that all proposed services must define
   their impact on inter- and intra-document reference validity.

   This requirement has been addressed in section 2.5 and throughout the
   document whereby OPES entities are required to document the performed

4.7.  IAB Consideration (4.3) Application Addressing Extensions

   This consideration recommends that any OPES services that cannot be
   achieved while respecting the above two considerations may be
   reviewed as potential requirements for Internet application
   addressing architecture extensions, but must not be undertaken as ad
   hoc fixes.

   The current work does not require extensions of the Internet
   application addressing architecture.

4.8.  IAB Consideration (5.1) Privacy

   This consideration recommends that the overall OPES framework must
   provide for mechanisms for end users to determine the privacy
   policies of OPES intermediaries.

   This consideration has been addressed in section 3.

5.  Security Considerations

   The proposed work has to deal with security from various
   perspectives.  There are security and privacy issues that relate to
   data consumer application, callout protocol, and the OPES flow.  In
   [6], there is an analysis of the threats against OPES entities.

6.  IANA Considerations

   The proposed work will evaluate current protocols for OCP.  If the
   work determines that a new protocol needs to be developed, then there
   may be a need to request new numbers from IANA.

7.  Summary

   Although the architecture supports a wide range of cooperative
   transformation services, it has few requirements for

   The necessary and sufficient elements are specified in the following

   o  the OPES ruleset schema, which defines the syntax and semantics of
      the rules interpreted by a data dispatcher; and,

   o  the OPES callout protocol (OCP) [5], which defines the
      requirements for the protocol between a data dispatcher and a
      callout server.

8.  References

8.1.  Normative References

   [1]  Barbir, A., Burger, E., Chen, R., McHenry, S., Orman, H., and R.
        Penno, "Open Pluggable Edge Services (OPES) Use Cases and
        Deployment Scenarios", RFC 3752, April 2004.

   [2]  Floyd, S. and L. Daigle, "IAB Architectural and Policy
        Considerations for Open Pluggable Edge Services", RFC 3238,
        January 2002.

   [3]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
        Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
        HTTP/1.1", RFC 2616, June 1999.

   [4]  Barbir, A., Batuner, O., Beck, A., Chan, T., and H. Orman,
        "Policy, Authorization, and Enforcement Requirements of the Open
        Pluggable Edge Services (OPES)", RFC 3838, August 2004.

   [5]  Beck, A., Hofmann, M., Orman, H., Penno, R., and A. Terzis,
        "Requirements for Open Pluggable Edge Services (OPES) Callout
        Protocols", RFC 3836, August 2004.

   [6]  Barbir, A., Batuner, O., Srinivas, B., Hofmann, M., and H.
        Orman, "Security Threats and Risks for Open Pluggable Edge
        Services (OPES)", RFC 3837, August 2004.

8.2.  Informative References

   [7]  Cranor, L. et. al, "The Platform for Privacy Preferences 1.0
        (P3P1.0) Specification", W3C Recommendation 16
        http://www.w3.org/TR/2002/REC-P3P-20020416/, April 2002.

9.  Acknowledgements

   This document is the product of OPES WG.  Oskar Batuner (Independent
   consultant) and Andre Beck (Lucent) are additional authors that have
   contributed to this document.

   Earlier versions of this work were done by Gary Tomlinson (The
   Tomlinson Group) and Michael Condry (Intel).

   The authors gratefully acknowledge the contributions of: John Morris,
   Mark Baker, Ian Cooper and Marshall T. Rose.

10.  Authors' Addresses

   Abbie Barbir
   Nortel Networks
   3500 Carling Avenue
   Nepean, Ontario  K2H 8E9

   Phone: +1 613 763 5229
   EMail: abbieb@nortelnetworks.com

   Yih-Farn Robin Chen
   AT&T Labs - Research
   180 Park Avenue
   Florham Park, NJ  07932

   Phone: +1 973 360 8653
   EMail: chen@research.att.com

   Markus Hofmann
   Bell Labs/Lucent Technologies
   Room 4F-513
   101 Crawfords Corner Road
   Holmdel, NJ  07733

   Phone: +1 732 332 5983
   EMail: hofmann@bell-labs.com

   Hilarie Orman
   Purple Streak Development

   EMail: ho@alum.mit.edu

   Reinaldo Penno
   Nortel Networks
   600 Technology Park Drive
   Billerica, MA 01821

   EMail: rpenno@nortelnetworks.com

11.  Full Copyright Statement

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