Open Pluggable Edge Services (OPES) Treatment of IAB Considerations
draft-ietf-opes-iab-05

Open Pluggable Edge Services                                   A. Barbir
Internet-Draft                                           Nortel Networks
Expires: October 11, 2004                                    A. Rousskov
                                                 The Measurement Factory
                                                          April 12, 2004

                  OPES Treatment of IAB Considerations
                         draft-ietf-opes-iab-05

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
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Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

   IETF Internet Architecture Board (IAB) expressed nine
   architecture-level considerations for the Open Pluggable Edge
   Services (OPES) framework.  This document describes how OPES
   addresses those considerations.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Consideration (2.1) 'One-party consent'  . . . . . . . . . . .  5
   4.  Consideration (2.2) 'IP-layer communications'  . . . . . . . .  6
   5.  Notification Considerations  . . . . . . . . . . . . . . . . .  8
   5.1 Notification versus trace  . . . . . . . . . . . . . . . . . .  8
   5.2 An example of an OPES trace for HTTP . . . . . . . . . . . . . 10
   5.3 Consideration (3.1) 'Notification' . . . . . . . . . . . . . . 11
   5.4 Consideration (3.2) 'Notification' . . . . . . . . . . . . . . 12
   6.  Consideration (3.3) 'Non-blocking' . . . . . . . . . . . . . . 13
   7.  Consideration (4.1) 'URI resolution' . . . . . . . . . . . . . 14
   8.  Consideration (4.2) 'Reference validity' . . . . . . . . . . . 15
   9.  Consideration (4.3) 'Addressing extensions'  . . . . . . . . . 16
   10. Consideration (5.1) 'Privacy'  . . . . . . . . . . . . . . . . 17
   11. Consideration 'Encryption' . . . . . . . . . . . . . . . . . . 18
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   13. Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . 20
   A.  Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 21
       Normative References . . . . . . . . . . . . . . . . . . . . . 24
       Informative References . . . . . . . . . . . . . . . . . . . . 25
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 25
       Intellectual Property and Copyright Statements . . . . . . . . 26

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1. Introduction

   The Open Pluggable Edge Services (OPES) architecture
   [I-D.ietf-opes-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.

   In the process of chartering OPES, the IAB made recommendations on
   issues that OPES solutions should be required to address. These
   recommendations were formulated in the form of a specific IAB
   considerations document [RFC3238].  In that document, IAB emphasized
   that its considerations did not recommend specific solutions and did
   not mandate specific functional requirements. Addressing an IAB
   consideration may involve showing appropriate protocol mechanisms or
   demonstrating that the issue does not apply. Addressing a
   consideration does not necessarily mean supporting technology implied
   by the consideration wording.

   The primary goal of this document is to show that all formal IAB
   recommendations are addressed by OPES, to the extent that those
   considerations can be addressed by an IETF working group. The
   limitations of OPES working group to address certain aspects of IAB
   considerations are also explicitly documented.

   IAB considerations document [RFC3238] contains many informal
   recommendations. For example, while the IAB informally requires OPES
   architecture to "protect end-to-end data integrity by supporting
   end-host detection and response to inappropriate behavior by OPES
   intermediaries", the IAB has chosen to formalize these requirements
   via a set of more specific recommendations, such as Notification
   considerations addressed in Section 5.3 and Section 5.4 below. OPES
   framework addresses informal IAB recommendations by addressing
   corresponding formal considerations.

   There are nine formal IAB considerations [RFC3238] that OPES has to
   address. In the core of this document are the corresponding nine
   "Consideration" sections. For each IAB consideration, its section
   contains general discussion as well as references to specific OPES
   mechanisms relevant to the consideration.

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2. Terminology

   This document does not introduce any new terminology but uses
   terminology from other OPES documents it quotes.

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3. Consideration (2.1) 'One-party consent'

   "An OPES framework standardized in the IETF must require that the use
   of any OPES service be explicitly authorized by one of the
   application-layer end-hosts (that is, either the content provider or
   the client)."[RFC3238]

   OPES architecture requires that "OPES processors MUST be consented to
   by either the data consumer or data provider application"
   [I-D.ietf-opes-architecture]. While this requirement directly
   satisfies IAB concern, no requirement alone can prevent consent-less
   introduction of OPES processors. In other words, OPES framework
   requires one-party consent but cannot guarantee it in the presence of
   incompliant OPES entities.

   In [I-D.ietf-opes-end-comm], the OPES architecture enables concerned
   parties to detect unwanted OPES processors by examining OPES traces.
   While the use of traces in OPES is mandatory, a tracing mechanism on
   its own cannot detect processors that are in violation of OPES
   specifications.  Examples include OPES processors operating in
   stealth mode.  However, the OPES architecture allows the use of
   content signature to verify the authenticity of performed
   adaptations.  Content signatures is a strong but expensive mechanism
   that can detect any modifications of signed content provided that the
   content provider is willing to sign the data and that the client is
   willing to either check the signature or relay received content to
   the content provider for signature verification.

   OPES entities may copy or otherwise access content without modifying
   it. Such access cannot be detected using content signatures.  Thus,
   "passive" OPES entities can operate on signed content without the
   data consumer or provider consent.  If content privacy is a concern,
   then content encryption can be used. A passive processor is no
   different from any intermediary operating outside of OPES framework.
   No OPES mechanism (existing or foreseeable) can prevent non-modifying
   access to content.

   In summary, the one-party consent is satisfied by including the
   corresponding requirement in the IAB architecture document. That
   requirement alone cannot stop incompliant OPES entities to perform
   consent-less adaptations, but OPES framework allows for various means
   of detecting and/or preventing such adaptations. These means
   typically introduce overheads and require some level of
   producer-consumer cooperation.

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4. Consideration (2.2) 'IP-layer communications'

   "For an OPES framework standardized in the IETF, the OPES
   intermediary must be explicitly addressed at the IP layer by the end
   user."[RFC3238]

   The OPES architecture requires that "OPES processors MUST be
   addressable at the IP layer by the end user (data consumer
   application)" [I-D.ietf-opes-architecture]. The IAB and the
   architecture documents mention an important exception: addressing the
   first OPES processor in a chain of processors is sufficient. That is,
   a chain of OPES processors is viewed as a single OPES "system" at the
   address of the first chain element.

   The notion of a chain is not strictly defined by IAB. For the purpose
   of addressing this consideration, a group of OPES processors working
   on a given application transaction is considered. Such a group would
   necessarily form a single processing chain, with a single "exit" OPES
   processor (i.e., the processor that adapted the given message last).
   The OPES architecture essentially requires that last OPES processor
   to be explicitly addressable at the IP layer by the data consumer
   application. The chain formation, including its exit point may depend
   on an application message and other dynamic factors such as time of
   the day or system load.

   Furthermore, if OPES processing is an internal processing step at a
   data consumer or a data provider application side, then the last OPES
   processor may reside in a private address space and may not be
   explicitly addressable from the outside. In such situations, the
   processing side must designate an addressable point on the same
   processing chain. That designated point may not be, strictly
   speaking, an OPES processor, but it will suffice as such as far as
   IAB considerations are concerned -- the data consumer application
   will be able to address it explicitly at the IP layer and it will
   represent the OPES processing chain to the outside world.

   Designating an addressable processing point avoids the conflict
   between narrow interpretation of the IAB consideration and real
   system designs. It is irrational to expect a content provider to
   provide access to internal hosts participating in content generation,
   whether OPES processors are involved or not. Moreover, providing such
   access would serve little practical purpose because internal OPES
   processors are not likely to be able to answer any data consumer
   queries, being completely out of content generation context. For
   example, an OPES processor adding customer-specific information to
   XML pages may not understand or be aware of any final HTML content
   that the data consumer application receives and may not be able to
   map end user request to any internal user identification. Since OPES

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   requires the end of the message processing chain to be addressable,
   the conflict does not exist. OPES places no requirements on the
   internal architecture of data producer systems while requiring the
   entire OPES-related content production "system" to be addressable at
   the IP layer.

   Private Domain    | Public Domain     | Private Domain
                     |                   |
   +--------------+  |             +-------------+      +--------+
   | Data         |  |             | OPES System |      |Data    |
   | Consumer     |<--- network -->| with public |<---->|Provider|
   | Application  |  |             | IP address  |      |App     |
   +--------------+  |             +-------------+      +--------+
                     |                   |
                     |                   |

                                Figure 1

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5. Notification Considerations

   This section discusses how OPES framework addresses IAB Notification
   considerations 3.1 and 3.2.

5.1 Notification versus trace

   Before specific considerations are discussed, the relationship
   between IAB notifications and OPES tracing has to be explained. OPES
   framework concentrates on tracing rather than notification. The OPES
   Communications specification [I-D.ietf-opes-end-comm] defines "OPES
   trace" as information about OPES adaptations that is embedded in an
   application message. Thus, OPES trace follows the application message
   it traces. The trace is for the recipient of the application message.
   Traces are implemented as extensions of application protocols being
   adapted and traced.

   As opposed to an OPES trace, provider notification (as implied by
   IAB) notifies the sender of the application message rather than the
   recipient. Thus, notifications propagate in the opposite direction of
   traces. Supporting notifications directly would require a new
   protocol. Figure 2 illustrates the differences between a trace and
   notification from a single application message point of view.

   sender --[message A]--> OPES --[message A']--> recipient
      ^                       V                             [with trace]
      |                       |
      +-<-- [notification] ---+

                                Figure 2

   Since notifications cannot be piggy-backed to application messages,
   they create new messages and may double the number of messages the
   sender has to process. The number of messages that need to be proceed
   is larger if several intermediaries on the message path generate
   notifications. Associating notifications with application messages
   may require duplicating application message information in
   notifications and may require maintaining a sender state until
   notification is received. These actions increase the performance
   overhead of notifications.

   The level of available details in notifications versus provider
   interest in supporting notification is another concern.  Experience
   shows that content providers often require very detailed information
   about user actions to be interested in notifications at all. For
   example, Hit Metering protocol [RFC2227] has been designed to supply
   content providers with proxy cache hit counts, in an effort to reduce
   cache busting behavior which was caused by content providers desire

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   to get accurate site "access counts". However, the Hit Metering
   protocol is currently not widely deployed because the protocol does
   not supply content providers with information such as client IP
   addresses, browser versions, or cookies.

   Hit Metering experience is relevant because Hit Metering protocol was
   designed to do for HTTP caching intermediaries what OPES
   notifications are meant to do for OPES intermediaries. Performance
   requirements call for state reduction via aggregation of
   notifications while provider preferences call for state preservation
   or duplication. Achieving the right balance when two sides belong to
   different organizations and have different optimization priorities
   may be impossible.

   Thus, instead of explicitly supporting notifications at the protocol
   level, OPES concentrates on tracing facilities. In essence, OPES
   supports notifications indirectly, using tracing facilities. In other
   words, the IAB choice of "Notification" label is interpreted as
   "Notification assistance" (i.e.  making notifications meaningful) and
   is not interpreted as a "Notification protocol".

   The above concerns call for making notification optional. The OPES
   architecture allows for an efficient and meaningful notification
   protocol to be implemented in certain OPES environments.  For
   example, an OPES callout server attached to a gateway or firewall may
   scan outgoing traffic for signs of worm or virus activity and notify
   a local Intrusion Detection System (IDS) of potentially compromised
   hosts (e.g., servers or client PCs) inside the network. Such
   notifications may use OPES tracing information to pinpoint the
   infected host (which could be another OPES entity). In this example,
   notifications are essentially sent back to the content producer (the
   local network) and use OPES tracing to supply details.

   Another environment where efficient and meaningful notification using
   OPES tracing is possible are Content Delivery Networks (CDNs).  A CDN
   node may use multiple content adaptation services to customize
   generic content supplied by the content producer (a web site). For
   example, a callout service may insert advertisements for client-local
   events.  The CDN node itself may not understand specifics of the ad
   insertion algorithm implemented at callout servers.  However, the
   node may use information in the OPES trace (e.g., coming from the
   callout service) to notify the content producer. Such notifications
   may be about the number of certain advertisements inserted (i.e., the
   number of "impressions" delivered to the customer) or even the number
   of ad "clicks" the customer made (e.g., if the node hosts content
   linked from the ads).  Callout services doing ad insertion may lack
   details (e.g., a customer ID/address or a web server authentication
   token) to contact the content producer directly in this case. Thus,

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   OPES trace produced by an OPES service becomes essential in enabling
   meaningful notifications that the CDN node sends to the content
   producer.

5.2 An example of an OPES trace for HTTP

   The example below illustrates adaptations done to HTTP request at an
   OPES processor operated by the client ISP. Both original (as sent by
   an end user) and adapted (as received by the origin web server)
   requests are shown. The primary adaptation is the modification of
   HTTP "Accept" header. The secondary adaptation is the addition of an
   OPES-System HTTP extension header [I-D.ietf-opes-http].

   GET /pub/WWW/ HTTP/1.1
   Host: www.w3.org
   Accept: text/plain

                                Figure 3

   ... may be adapted by an ISP OPES system to become:

   GET /pub/WWW/ HTTP/1.1
   Host: www.w3.org
   Accept: text/plain; q=0.5, text/html, text/x-dvi; q=0.8
   OPES-System: http://www.isp-example.com/opes/?client-hash=1234567

                                Figure 4

   The example below illustrates adaptations done to HTTP response at an
   OPES intermediary operated by a Content Distribution Network (CDN).
   Both original (as sent by the origin web server) and adapted (as
   received by the end user) responses are shown. The primary adaptation
   is the conversion from HTML markup to plain text. The secondary
   adaptation is the addition of an OPES-System HTTP extension header.

   HTTP/1.1 200 OK
   Content-Length: 12345
   Content-Encoding: text/html

   <html><head><h1>Available Documenta...

                                Figure 5

   ... may be adapted by a CDN OPES system to become:

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   HTTP/1.1 200 OK
   Content-Length: 2345
   Content-Encoding: text/plain
   OPES-System: http://www.cdn-example.com/opes/?site=7654&svc=h2t

   AVAILABLE DOCUMENTA...

                                Figure 6

   In the above examples, OPES-System header values contain URIs that
   may point to OPES-specific documents such as description of the OPES
   operator and its privacy policy.  Those documents may be
   parameterized to allow for customizations specific to the transaction
   being traced (e.g., client or even transaction identifier may be used
   to provide more information about performed adaptations). An OPES-Via
   header may be used to provide a more detailed trace of specific OPES
   entities within an OPES System that adapted the message. Traced OPES
   URIs may be later used to request OPES bypass
   [I-D.ietf-opes-end-comm].

5.3 Consideration (3.1) 'Notification'

   "The overall OPES framework needs to assist content providers in
   detecting and responding to client-centric actions by OPES
   intermediaries that are deemed inappropriate by the content
   provider."[RFC3238]

   OPES tracing mechanisms assist content providers in detecting
   client-centric actions by OPES intermediaries. Specifically, a
   compliant OPES intermediary or system notifies a content provider of
   its presence by including its tracing information in the application
   protocol requests. An OPES system MUST leave its trace
   [I-D.ietf-opes-end-comm].  Detection assistance has its limitations.
   Some OPES intermediaries may work exclusively on responses and may
   not have a chance to trace the request. Moreover, some application
   protocols may not have explicit requests (e.g., a content push
   service).

   OPES tracing mechanisms assist content providers in responding to
   client-centric actions by OPES intermediaries. Specifically, OPES
   traces MUST include identification of OPES systems and SHOULD include
   a list of adaptation actions performed on provider's content. This
   tracing information may be included in the application request.
   Usually, however, this information will be included in the
   application response, an adapted version of which does not reach the
   content provider. If OPES end points cooperate, then notification can
   be assisted with traces. Content providers that suspect or experience
   difficulties can do any of the following:

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   o  Check whether requests they receive pass through OPES
      intermediaries. Presence of OPES tracing info will determine that.
      This check is only possible for request/response protocols. For
      other protocols (e.g., broadcast or push), the provider would have
      to assume that OPES intermediaries are involved until proven
      otherwise.

   o  If OPES intermediaries are suspected, request OPES traces from
      potentially affected user(s). The trace will be a part of the
      application message received by the user software. If involved
      parties cooperate, the provider(s) may have access to all the
      needed information.  Certainly, lack of cooperation may hinder
      access to tracing information. To encourage cooperation, data
      providers might be able to deny service to uncooperative users.

   o  Some traces may indicate that more information is available by
      accessing certain resources on the specified OPES intermediary or
      elsewhere. Content providers may query for more information in
      this case.

   o  If everything else fails, providers can enforce no-adaptation
      policy using appropriate OPES bypass mechanisms and/or end-to-end
      encryption mechanisms.

   OPES detection and response assistance is limited to application
   protocols with support for tracing extensions. For example, HTTP
   [RFC2616] has such support while DNS over UDP does not.

5.4 Consideration (3.2) 'Notification'

   "The overall OPES framework should assist end users in detecting the
   behavior of OPES intermediaries, potentially allowing them to
   identify imperfect or compromised intermediaries."[RFC3238]

   OPES tracing mechanisms assist end users in detecting OPES
   intermediaries. Specifically, a compliant OPES intermediary or system
   notifies an end user of its presence by including its tracing
   information in the application protocol messages sent to the client.
   An OPES system MUST leave its trace [I-D.ietf-opes-end-comm].
   However, detection assistance has its limitations. Some OPES systems
   may work exclusively on requests and may not have a chance to trace
   the response.  Moreover, some application protocols may not have
   explicit responses (e.g., event logging service).

   OPES detection assistance is limited to application protocols with
   support for tracing extensions. For example, HTTP [RFC2616] has such
   support while DNS over UDP does not.

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6. Consideration (3.3) 'Non-blocking'

   "If there exists a "non-OPES" version of content available from the
   content provider, the OPES architecture must not prevent users from
   retrieving this "non-OPES" version from the content
   provider."[RFC3238]

   "OPES entities MUST support a bypass feature"
   [I-D.ietf-opes-end-comm]. If an application message includes bypass
   instructions and an OPES intermediary is not configured to ignore
   them, the matching OPES intermediary will not process the message. An
   OPES intermediary may be configured to ignore bypass instructions
   only if no non-OPES version of content is available.  Bypass may
   generate content errors since some OPES services may be essential but
   may not be configured as such.

   Bypass support has limitations similar to the two
   notification-related considerations above.

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7. Consideration (4.1) 'URI resolution'

   "OPES documentation must be clear in describing these services as
   being applied to the result of URI resolution, not as URI resolution
   itself."[RFC3238]

   "OPES Scenarios and Use Cases" specification
   [I-D.ietf-opes-scenarios] documents content adaptations that are in
   scope of the OPES framework.  Scenarios include content adaptation of
   requests and responses. These documented adaptations do not include
   URI resolution. In some environments, it is technically possible to
   use documented OPES mechanisms to resolve URIs (and other kinds of
   identifiers or addresses).  The OPES framework cannot effectively
   prevent any specific kind of adaptation.

   For example, a CDN node may substitute domain names in URLs with
   CDN-chosen IP addresses, essentially performing a URI resolution on
   behalf of the content producer (i.e., the web site owner). An OPES
   callout service running on a user PC may rewrite all HTML-embedded
   advertisement URLs to point to a user-specified local image,
   essentially performing a URI redirection on behalf of the content
   consumer (i.e., the end user). Such URI manipulations are outside of
   the OPES framework scope, but cannot be effectively eliminated from
   the real world.

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8. Consideration (4.2) 'Reference validity'

   "All proposed services must define their impact on inter- and
   intra-document reference validity."[RFC3238]

   The OPES framework does not propose adaptation services. However,
   OPES tracing requirements include identification of OPES
   intermediaries and services (for details, see "Notification"
   consideration sections in this document). It is required that
   provided identification can be used to locate information about the
   OPES intermediaries, including the description of impact on reference
   validity [I-D.ietf-opes-end-comm].

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9. Consideration (4.3) 'Addressing extensions'

   "Any 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."[RFC3238]

   OPES framework does not contain ad hoc fixes. This document in
   combination with and other OPES documents should be sufficient to
   inform service creators of IAB considerations. If a service does URI
   resolution or silently affects document reference validity, the
   authors are requested to review service impact on Internet
   application addressing architecture and work within IETF on potential
   extension requirements. Such actions would be outside of the current
   OPES framework.

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10. Consideration (5.1) 'Privacy'

   "The overall OPES framework must provide for mechanisms for end users
   to determine the privacy policies of OPES intermediaries."[RFC3238]

   OPES tracing mechanisms allow end users to identify OPES
   intermediaries (for details, see "Notification" consideration
   sections in this document). It is required that provided
   identification can be used to locate information about the OPES
   intermediaries, including their privacy policies.

   The term "privacy policy" is not defined in this context (by IAB or
   OPES working group). OPES tracing mechanisms allow end users and
   content providers to identify an OPES system and/or intermediaries.
   It is believed that once an OPES system is identified, it would be
   possible to locate relevant information about that system, including
   information relevant to requesters perception of privacy policy or
   reference validity.

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11. Consideration 'Encryption'

   "If OPES is chartered, the OPES working group will also have to
   explicitly decide and document whether the OPES architecture must be
   compatible with the use of end-to-end encryption by one or more ends
   of an OPES-involved session. If OPES was compatible with end-to-end
   encryption, this would effectively ensure that OPES boxes would be
   restricted to ones that are known, trusted, explicitly addressed at
   the IP layer, and authorized (by the provision of decryption keys) by
   at least one of the ends."[RFC3238]

   The above quoted requirement was not explicitly listed as on of the
   IAB considerations, but still needs to be addressed. The context of
   the quote implies that the phrase "end-to-end encryption" refers to
   encryption along all links of the end-to-end path, with the OPES
   intermediaries as encrypting/decrypting participants or hops (e.g.,
   encryption between the provider and the OPES intermediaries, and
   between the OPES intermediaries and the client).

   Since OPES processors are regular hops on the application protocol
   path, OPES architecture allows for such encryption, provided the
   application protocol being adapted supports it. Hop-by-hop encryption
   would do little good for the overall application message path
   protection if callout services have to receive unencrypted content.
   To allow for complete link encryption coverage, OPES callout protocol
   (OCP) supports encryption of OCP connections between an OPES
   processor and a callout server via optional (negotiated) transport
   encryption mechanisms [I-D.ietf-opes-ocp-core].

   For example, TLS encryption [RFC2817] can be used among HTTP hops
   (some of which could be OPES processors) and between each OPES
   processor and a callout server.

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12. Security Considerations

   This document does not define any mechanisms that may be subject to
   security considerations. This document scope is to address specific
   IAB considerations. Security of OPES mechanisms are discussed in
   Security Considerations sections of the corresponding OPES framework
   documents.

   For example, OPES tracing mechanisms assist content providers and
   consumers in protecting content integrity and confidentiality by
   requiring OPES intermediaries to disclose their presence. Security of
   the tracing mechanism is discussed in the Security Considerations
   section of [I-D.ietf-opes-end-comm].

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13. Compliance

   This document may be perceived as a proof of OPES compliance with IAB
   implied recommendations. However, this document does not introduce
   any compliance subjects. Compliance of OPES implementations is
   defined in other OPES documents discussed above.

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Appendix A. Change Log

   RFC Editor Note: This section is to be removed during the final
   publication of the document.

   Internal WG revision control ID: $Id: iab-cons.xml,v 1.36 2004/04/12
   16:06:52 rousskov Exp $

   2004/04/08

      *  Replaced "Cable Company ISP" Notification example with two new
         examples to address IESG uncertainty about the meaning of the
         old convoluted example.

      *  Polished text addressing "One-party consent" concern to better
         show why the concern is addressed. It is not clear whether the
         changes will address IESG review comment that "the WG does not
         seem to get it" [because?] the text does not "name situations
         where one-party consent does make sense". It is currently not
         clear how naming such situations can address IAB concern, and
         why naming such situations is in this document scope.

      *  Polished text discussing URI resolution consideration to talk
         more specifically about the resolution of URIs rather than
         (more general) adaptation of URIs and added examples. This
         change is meant to address IESG concern that URI resolution is
         not addressed or the corresponding description is confusing.

      *  Clarified in the Introduction that the purpose of this document
         is to address nine formal IAB considerations, and that we hope
         that addressing formal consideration is sufficient to address
         any informal ones that are scattered through the IAB
         Considerations document. This is meant to address IESG concern
         that some [informal] words from the IAB Consideration document
         do not explicitly appear in this document.

      *  Be more specific about where security of OPES mechanisms is
         discussed. Added an example of where security of OPES tracing
         mechanisms is discussed. This document is about addressing
         specific IAB considerations and is not a map/index to OPES
         mechanisms or their security. However, polished text and
         example may provide the reader with more direct clues on where
         to find security-related information that goes beyond the scope
         of this document.

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   2003/11/18

      *  Added an example where an efficient and meaningful notification
         protocol can be implemented in OPES.

      *  Assume Communications draft will contain wording about
         documenting impact on reference validity.

      *  Use OPES-System HTTP header for examples and mention OPES-Via.
         We still need to get HTTP Adaptations draft in sync with this
         change, but the text now assumes that has been done.

   2003/10/24

      *  Addressed hop-by-hop encryption concerns mentioned in the IAB
         draft.

      *  Polished IP addressing figure.

      *  Removed resolved XXXs.

   2003/10/01

      *  Polishing (Abbie Barbir).

   2003/09/23

      *  Added a reference to Optional Notification section of the
         ietf-opes-end-comm draft.

      *  Fixed "Consideration (3.3) Non-blocking" section position.

   head-sid15

      *  Added a figure showing a chain of internal OPES intermediaries
         behind a public IP address. Needs more work. More cases?

   head-sid14

      *  Rewrote the Introduction to the IP addressing consideration.
         Do NOT explain how IAB considerations, if interpreted literary,
         do not satisfy important real-world constraints. Instead, use
         the "chain of OPES intermediaries" exception introduced by IAB
         itself to show that OPES architecture addresses IAB concerns as
         long as the "chain" is defined/formed for a given application
         message rather than being a statically configured application
         routing table of sorts. IAB had to add the "chain" exception to
         cover one of the most obvious real-world usage scenario. We use

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         the very same exception to cover all usage scenarios we care
         about.

      *  Polished text explaining the differences between tracing and
         notification mechanisms.

      *  Added examples of OPES/HTTP traces.

      *  Be careful not to imply that all OPES intermediaries must obey
         bypass instructions. Bypass should be ignored when no non-OPES
         version of the content exists. Ideally, this may need to be
         polished further -- if there is no non-OPES version of the
         content, most IAB considerations probably do not apply because
         there is really no adaptation, only creation of content (and we
         should not restrict content creation).

      *  Added references to OPES "Communications" draft
         [I-D.ietf-opes-end-comm].

   head-sid9

      *  Polished to meet new xml2rfc strict requirements.

   head-sid8

      *  Added unpolished meat for all nine considerations.

      *  Added Abbie Barbir as an author.

   head-sid7

      *  Initial revision

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Normative References

   [I-D.ietf-opes-end-comm]
              Barbir, A., "OPES entities and end points communication",
              draft-ietf-opes-end-comm-06 (work in progress), December
              2003.

   [I-D.ietf-opes-architecture]
              Barbir, A., "An Architecture for Open Pluggable Edge
              Services (OPES)", draft-ietf-opes-architecture-04 (work in
              progress), December 2002.

   [I-D.ietf-opes-scenarios]
              Barbir, A., "OPES Use Cases and Deployment Scenarios",
              draft-ietf-opes-scenarios-01 (work in progress), August
              2002.

   [RFC3238]  Floyd, S. and L. Daigle, "IAB Architectural and Policy
              Considerations for Open Pluggable Edge Services", RFC
              3238, January 2002.

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Informative References

   [RFC2227]  Mogul, J. and P. Leach, "Simple Hit-Metering and
              Usage-Limiting for HTTP", RFC 2227, October 1997.

   [RFC2616]  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.

   [RFC2817]  Khare, R. and S. Lawrence, "Upgrading to TLS Within HTTP/
              1.1", RFC 2817, May 2000.

   [I-D.ietf-opes-http]
              Rousskov, A. and M. Stecher, "HTTP adaptation with OPES",
              draft-ietf-opes-http-01 (work in progress), October 2003.

   [I-D.ietf-opes-ocp-core]
              Rousskov, A., "OPES Callout Protocol Core",
              draft-ietf-opes-ocp-core-03 (work in progress), November
              2003.

Authors' Addresses

   Abbie Barbir
   Nortel Networks
   3500 Carling Avenue
   Nepean, Ontario
   CA

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

   Alex Rousskov
   The Measurement Factory

   EMail: rousskov@measurement-factory.com
   URI:   http://www.measurement-factory.com/

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