1. RFC 3752
Network Working Group                                          A. Barbir
Request for Comments: 3752                               Nortel Networks
Category: Informational                                        E. Burger
                                             Brooktrout Technology, Inc.
                                                                 R. Chen
                                                               AT&T Labs
                                                              S. McHenry
                                                  Individual Contributor
                                                                H. Orman
                                               Purple Streak Development
                                                                R. Penno
                                                         Nortel Networks
                                                              April 2004

                  Open Pluggable Edge Services (OPES)
                   Use Cases and Deployment Scenarios

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).  All Rights Reserved.


   This memo provides a discussion of use cases and deployment scenarios
   for Open Pluggable Edge Services (OPES).  The work examines services
   that could be performed to requests and/or responses.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Types of OPES services . . . . . . . . . . . . . . . . . . . .  3
       2.1.  Services performed on requests . . . . . . . . . . . . .  3
             2.1.1.  Services intending to modify requests  . . . . .  3
             2.1.2.  Services *not* intending to modify requests  . .  4
       2.2.  Services performed on responses. . . . . . . . . . . . .  4
             2.2.1.  Services intending to modify responses . . . . .  4
             2.2.2.  Services *not* intending to modify responses . .  5
       2.3.  Services creating responses. . . . . . . . . . . . . . .  5
   3.  OPES deployment scenarios  . . . . . . . . . . . . . . . . . .  5
       3.1.  Surrogate Overlays . . . . . . . . . . . . . . . . . . .  6
       3.2.  Delegate Overlays  . . . . . . . . . . . . . . . . . . .  7

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       3.3.  Enterprise environment . . . . . . . . . . . . . . . . .  8
       3.4.  Callout Servers  . . . . . . . . . . . . . . . . . . . .  9
       3.5.  Chaining of OPES data filters and callout servers  . . .  9
             3.5.1.  Chaining along the content path. . . . . . . . .  9
             3.5.2.  Chaining along the callout path. . . . . . . . .  9
   4.  Failure cases and service notification . . . . . . . . . . . . 10
   5.  Security Considerations. . . . . . . . . . . . . . . . . . . . 11
   6.  Informative References . . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   8.  Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12
   9.  Full Copyright Statement . . . . . . . . . . . . . . . . . . . 14

1.  Introduction

   The Open Pluggable Edge Services (OPES) [1] architecture enables
   cooperative application services (OPES services) between a data
   provider, a data consumer, and zero or more OPES processors.  The
   application services under consideration analyze and possibly
   transform application-level messages exchanged between the data
   provider and the data consumer.  The execution of such services is
   governed by a set of filtering rules installed on the OPES processor.

   The rules enforcement can trigger the execution of service
   applications local to the OPES processor.  Alternatively, the OPES
   processor can distribute the responsibility of service execution by
   communicating and collaborating with one or more remote callout [6]

   The document presents examples of services in which Open Pluggable
   Edge Services (OPES) would be useful.  There are different types of
   OPES services: services that modify requests, services that modify
   responses, and a special case of the latter, services that create

   The work also examines various deployment scenarios of OPES services.
   The two main deployment scenarios, as described by the OPES
   architecture [1], are surrogate overlays and delegate overlays.
   Surrogate overlays act on behalf of data provider applications, while
   delegate overlays act on behalf of data consumer applications.  The
   document also describes combined surrogate and delegate overlays, as
   one might find within an enterprise deployment.

   The document is organized as follows: Section 2 discusses the various
   types of OPES services.  Section 3 introduces OPES deployment
   scenarios.  Section 4 discusses failure cases and service
   notification.  Section 5 discusses security considerations.

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   The IAB has expressed architectural and policy concerns [2] about
   OPES.  Other OPES documents that may be relevant are, "OPES Service
   Authorization and Enforcement Requirements" [5].  See references [3,
   4] for recommended background reading.

2.  Types of OPES services

   OPES scenarios involve services that can be performed on requests for
   data and/or responses.  OPES services can be classified into three
   categories: services performed on requests, services performed on
   responses, and services creating responses.  In Figure 1, the four
   service activation points for an OPES processor are depicted.  The
   data dispatcher examines OPES rules, enforces policies, and invokes
   service applications (if applicable) at each service activation

              |         +-------------+-------------+          |
              |         |   Service Application     |          |
              |         +---------------------------+          |
         Responses      |       Data Dispatcher     |     Responses
       <============4== +---------------------------+ <=3===========
         Requests       |           HTTP            |      Requests
       =============1=> +---------------------------+ ==2==========>
              |                  OPES Processor                |

                  Figure 1: Service Activation Points

2.1.  Services performed on requests

   An OPES service performed on HTTP requests may occur when a request
   arrives at an OPES processor (point 1) or when it is about to leave
   the OPES processor (point 2).

   The services performed on requests can further be divided into two
   cases: those that intend to modify requests and those that do not.

2.1.1.  Services intending to modify requests

   An OPES processor may modify a service request on behalf of the data
   consumer for various reasons, such as:

   o  Owner of a Web access device might need control over what kind of
      Web content can be accessed with the device, parental control for

   o  Organization may restrict or redirect access to certain web

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      services based on various criteria such as time of the day or the
      employee access privileges.

   o  Hiding the data consumer's identity, user agent, or referrer.

   o  Adding user preferences or device profile to the service request
      to get personalized or adapted services.

   o  Blocking or redirecting a service request due to a corporate

   An OPES processor may also modify a service request on behalf of the
   data provider in several ways, such as:

   o  Redirecting the request to a different server to reduce the server
      work load.

   o  Redirecting image requests to improve access time.

2.1.2.  Services *not* intending to modify requests

   An OPES processor may invoke useful service applications that do not
   modify the user requests.  Examples include:

   o  Administrative functions for the data provider, such as service
      monitoring or usage tracking for billing purposes.

   o  Useful services for the data consumer, such as user profiling
      (with the user's consent) for service adaptation later on.

2.2.  Services performed on responses

   An OPES service performed on HTTP responses may occur when a response
   arrives at an OPES processor (point 3) or when it is about to leave
   the OPES processor (point 4).   In the case of a caching proxy, the
   former service may be an encoding operation before the content is
   stored in the cache, while the latter may be a decoding operation
   before the content is returned to the data consumer.

   The services performed on responses can further be divided into two
   cases: those that intend to modify responses and those that do not.

2.2.1.  Services intending to modify responses

   There are several reasons why responses from the data providers might
   be modified before delivery to the data consumer:

   o  Content adaptation:  the data provider may not have all the device

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      profiles and templates necessary to transcode the original content
      into a format appropriate for mobile devices of limited screen
      size and display capabilities.

   o  Language translation:  the data provider may not have all the
      translation capabilities needed to deliver the same content in
      multiple languages to various areas around the world.  An OPES
      processor may perform the language translation or it may invoke
      different callout servers to perform different language
      translation tasks.

2.2.2.  Services *not* intending to modify responses

   An OPES service may be performed on the responses without modifying
   them.  Examples include:

   o  Logging/Monitoring: Each response may be examined and recorded for
      monitoring or debugging purposes.

   o  Accounting: An OPES processor may record the usage data (time and
      space) of each service request for billing purposes.

2.3.  Services creating responses

   Services creating responses may include OPES services that
   dynamically assemble web pages based on the context of the data
   consumer application.

   Consider a content provider offering web pages that include a local
   weather forecast based on the requestor's preferences.  The OPES
   service could analyze received requests, identify associated user
   preferences, select appropriate templates, insert the corresponding
   local weather forecasts, and would then deliver the content to the
   requestor.  Note that the OPES processor may perform the tasks with
   or without direct access to the weather data.  For example, the
   service could use locally cached weather data or it could simply
   embed a URL pointing to another server that holds the latest local
   weather forecast information.

3.  OPES deployment scenarios

   OPES entities can be deployed over an overlay network that supports
   the provisioning of data services in a distributed manner.  Overlay
   networks are an abstraction that creates a virtual network of
   connected devices layered on an existing underlying IP networks in
   order to perform application level services.

   The use of overlay networks creates virtual networks that via OPES

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   entities enables the necessary network infrastructure to provide
   better services for data consumer and provider applications.  At the
   application level, the resulting overlay networks are termed OPES
   Services Networks.

   There are two parties that are interested in the services that are
   offered by OPES entities, the delegate and the surrogate.  Delegates
   are authorized agents that act on behalf of data consumers.
   Surrogates are authorized agents that act on behalf of 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.  Surrogate Overlays

   A surrogate overlay is a specific type of OPES service network, which
   is delegated the authority to provide data services on behalf of one
   or more origin servers.  Such services include, but are not limited
   to, dynamic assembling of web pages, watermarking, and content

   The elements of surrogate overlays act on behalf of origin severs and
   logically belong to the authoritative domain of the respective origin
   servers.  The scenario is depicted in Figure 2.

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              *                                           *
              *    +--------+             Authoritative   *
              *    | Origin |                    Domain   *
              *    | Server |                             *
              *    +--------+       +------------+        *
              *         |           | OPES Admin |        *
              *         |           |   Server   |        *
              *         |           +------------+        *
              *         |         /                       *
              *         |       /                         *
              * +--------------+      +-----------------+ *
              * |     OPES     |----- | Remote Call-out | *
              * |   Processor  |      |     Server      | *
              * +--------------+      +-----------------+ *
              *         |                                 *
                   | Data consumer application |

         Figure 2: Authoritative Domains for Surrogate Overlays

3.2.  Delegate Overlays

   A delegate overlay is a specific type of OPES service network, which
   is delegated the authority to provide data services on behalf of one
   or more data consumer applications.

   Delegate overlays provide services that would otherwise be performed
   by the data consumer applications.  Such services include, but are
   not limited to, virus scanning and content filtering.

   The elements of delegate overlays logically belong to the
   authoritative domain of the respective data consumer application.
   The situation is illustrated in Figure 3.

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                   | Origin |
                   | Server |
              *         |                                 *
              * +--------------+      +-----------------+ *
              * |     OPES     |----- | Remote Call-out | *
              * |    Processor |      |     Server      | *
              * +--------------+      +-----------------+ *
              *         |       \                         *
              *         |         +------------+          *
              *         |         | OPES Admin |          *
              *         |         |   Server   |          *
              *         |         +------------+          *
              *    +---------------------+                *
              *    | Data consumer Appl. | Authoritative  *
              *    +---------------------+        Domain  *
              *                                           *

         Figure 3: Authoritative Domains for Delegate Overlays

3.3.  Enterprise environment

   Deployment of OPES services in an enterprise environment is unique in
   several ways:

   o  Both data providers and data consumers are in the same
      administrative domain and trust domain.  This implies that the
      logical OPES administrator has the authority to enforce corporate
      policies on all data providers, data consumers, and OPES entities.

   o  In the case when a callout server outside the corporate firewall
      is invoked for services (such as language translation) that cannot
      be performed inside the corporation, care must be taken to
      guarantee a secure communication channel between the callout
      server and corporate OPES entities.  The callout server must also
      adhere to all corporate security policies for the services

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3.4.  Callout Servers

   In some cases the deployment of OPES services can benefit from the
   use of callout servers that could distribute the workload of OPES
   processors or to contract specialized services from other OPES

   In general, operations such as virus scanning that operate on large
   objects are better handled through the use of a dedicated callout
   server that is better designed to perform the memory intensive task
   than what an OPES processor could handle.

3.5.  Chaining of OPES data filters and callout servers

   OPES data processors can be "chained" in two dimensions: along the
   content path or along the callout path.  In the latter case, the
   callout servers can themselves be organized in series for handling
   requests.  Any content that is touched by more than one data
   processor or more than one callout server has been handled by a

   NOTE: Chaining of callout servers is deferred from version 1 of the
   Protocol.  The discussion of chaining is included here for

3.5.1.  Chaining along the content path

   An OPES provider may have assigned OPES services to a set of
   processors arranged in series.  All content might move through the
   series, and if the content matches the rules for a processor, it is
   subjected to the service.  In this way, the content can be enhanced
   by several services.  This kind of chaining can be successful if the
   services are relatively independent.  For example, the content might
   be assembled by a service early in the chain and then further
   decorated by a later service.

3.5.2.  Chaining along the callout path

   Alternatively, an OPES data processor might act as a content-level
   switch in a cluster of other data processors and callout servers.

   The first stage might develop a processing schedule for the content
   and direct it to other OPES data processors and/or callout servers.
   For example, OPES processor A might handle all services assembling
   content, OPES processor B might handle all services involving URL
   translation, and OPES processor C might handle all content security
   services.  The first processor would determine that processors A and

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   C were needed for a particular content object, and it would direct
   the content to those processors.  In turn, the processors might use
   several callout servers to accomplish the task.

4.  Failure cases and service notification

   These are illustrative cases where information about OPES processing
   can help endpoint users determine where and why content modifications
   are being performed.

   o  Content provider uses an OPES data processor to enhance content
      based only on context local to the provider.  The local context
      might be time of day, local URL, or available advertising, for
      example.  The content provider might find OPES logging to be
      sufficient for debugging any problems in this case.  However, the
      content provider might also try direct probing by issuing a
      request for the content and examining headers related to tracing.
      If unexpected parameters show up in the trace headers, the content
      provider's administrator can use these to correct the OPES rules
      or detect the presence of an unexpected OPES processor in the
      content path.

   o  Content provider uses an OPES data processor to enhance content
      based on context related to the requestor.  The requestor may
      notice that his requests do not elicit the same response as
      another requestor.  He may, for example, get an error message.  If
      he believes there is a configuration error on the OPES data
      processor, he will need to provide information to the
      administrator of it.  If the information includes "OPES service
      access control, action: blocked", for example, he can inquire
      about the circumstances that will allow him to be added to the
      access control list.  In another example, if he sees a picture
      unrelated to the surrounding text, and if the tracing shows "OPES
      service choose picture, action: insert 640x480 weather.gif", he
      might complain that the OPES service does not properly recognize
      his geographic location and inserts the wrong weather map.  In any
      case, if the information is forwarded to the content provider, the
      problem may be fixed.

   o  End user has OPES processor available as part of his network
      access environment.  The end user may have selected "translate
      English to Spanish" as an OPES service.  If he sees "OPES service
      language translation, action: destination language not supported,
      no action", then he may inquire of the OPES service provider about
      what languages are supported by the package.  If the end user
      feels that the source language is not properly represented by the

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      provider, resulting in inability for the service to operate, he
      (or the language service provider) can contact the content

   o  If the content provider gets complaints from users about the
      translation service and feels that the problem is not in the
      content but in the service, he may recommend that the service not
      be applied to his pages.  He can do that through content headers,
      for example, with the notation "No OPES service #8D3298EB" or "No
      OPES class language translation".

   o  End user's ISP or enterprise uses OPES to control user access
      based on user profiles.  The end user can see that the OPES
      services are being applied by his ISP, but he cannot control them.
      If he feels that the transformations bowdlerize the content he can
      complain to the provider organization.

   o  The content provider or end user relies on a content distribution
      network and OPES is used within that network.  OPES may be
      authorized by either the content provider, end user, or both.  The
      content provider may suspect that his access control rules are not
      being applied properly, for example.  He may ask for notification
      on all accesses to his content through a log.  This request and
      the logfile are outside the OPES architecture; there are security
      implications for the request, the response, and the resources used
      by the logfile.

5.  Security Considerations

   The document presents usage scenarios and deployment cases.  Issues
   related to the overall security of OPES entities are given in [1].

6.  Informative References

   [1]  A. Barbir et al., "An Architecture for Open Pluggable Edge
        Services (OPES)", Work in Progress, July 2002.

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

   [3]  Westerinen, A., Schnizlein, J., Strassner, J., Scherling, M.,
        Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry, J. and S.
        Waldbusser, "Terminology for Policy-Based Management", RFC 3198,
        November 2001.

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

   [5]  OPES Working Group, "OPES Service Authorization and Enforcement
        Requirements", Work in Progress, May 2002.

   [6]  Beck, A., et al., "Requirements for OPES Callout Protocols",
        Work in Progress, July 2002.

7.  Acknowledgements

   The authors would like to thank the participants of the OPES WG for
   their comments on this document.

8.  Authors' Addresses

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

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

   Eric W. Burger
   Brooktrout Technology, Inc.
   18 Keewaydin Dr.
   Salem, NH  03079

   EMail: e.burger@ieee.org

   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

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   Stephen McHenry
   305 Vineyard Town Center, #251
   Morgan Hill, CA  95037

   Phone: +1 408 683 2700
   EMail: stephen@mchenry.net

   Hilarie Orman
   Purple Streak Development

   EMail: ho@alum.mit.edu

   Reinaldo Penno
   Nortel Networks
   600 Technology Park Drive
   Billerica, MA  01803

   EMail: rpenno@nortelnetworks.com

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9.  Full Copyright Statement

   Copyright (C) The Internet Society (2004).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78 and
   except as set forth therein, the authors retain all their rights.

   This document and the information contained herein are provided on an

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  1. RFC 3752