Open Pluggable Edge Services                                   A. Barbir
Internet-Draft                                           Nortel Networks
Expires: February 25, March 23, 2004                                      A. Rousskov
                                                 The Measurement Factory
                                                         August 27,
                                                      September 23, 2003

                  OPES Treatment of IAB Considerations

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.


   IETF Internet Architecture Board (IAB) expressed nine
   architecture-level considerations when Open Pluggable Edge Services
   (OPES) working group was being chartered at the IETF.  The working
   group was chartered under the condition that IAB considerations were
   addressed by the group. This document describes how OPES addresses
   those considerations.

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 . . . . . . . . . . . . .  9
   5.3 Consideration (3.1) Notification . . . . . . . . . . . . . . . 10
   5.4 Consideration (3.2) Notification . . . . . . . . . . . . . . . 12
   6.  Consideration (3.3) Non-blocking . . . . . . . . . . . . . . . 12
   6. 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. Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   12. Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . 19
   13. To-do  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
   A.  Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 21
       Normative References . . . . . . . . . . . . . . . . . . . . . 23
       Informative References . . . . . . . . . . . . . . . . . . . . 24
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 24
       Intellectual Property and Copyright Statements . . . . . . . . 25

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 specific IAB
   considerations [RFC3238].  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 IAB
   considerations are addressed by OPES, to the extent those
   considerations can be addressed by an IETF working group. Limitations
   of OPES working group ability to address certain aspects of IAB
   considerations are explicitly documented.

   There are nine 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.

2. Terminology

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

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]. This requirement alone cannot prevent
   consent-less introduction of OPES processors. In
   [I-D.ietf-opes-end-comm], the OPES architecture enables concerned
   parties to detect unwanted OPES processors by examining OPES traces.
   The use of traces in OPES is mandatory.

   Tracing mechanism on its own is unable to 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 the
   content provider is willing to sign the data and the client is
   willing to either check the signature or relay received content to
   content provider for signature verification.

   OPES adaptations may include copying and other forms of non-modifying
   access to content. These kinds of adaptations cannot be detected by
   the above mentioned mechanisms. Thus, "passive" OPES processors can
   operate without consent. If presence of such processors is a concern,
   content encryption can be used. A passive processor is no different
   from a proxy or intermediary operating outside of OPES framework. No
   OPES mechanism can prevent non-modifying access to content.

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

   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]. IAB and the architecture draft 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, we consider a group of OPES
   processors working on a given application transaction. Such a group
   would necessarily form a single processing chain, with a single
   "exit" OPES processor (the processor that adapted the given message
   last). OPES architecture essentially requires that last OPES
   processor to be explicitly addressable at the IP layer by the end
   user. Note that chain formation, including its exit point may depend
   on an application message and other dynamic factors such as time of
   day or system load.

   Furthermore, if OPES processing is an internal processing step at
   data consumer or provider side, then the last OPES processor may
   reside in a private address space of the side's network and may not
   be explicitly addressable. 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 other side 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 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 end user 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 end user
   receives and may not be able to map end user request to any internal
   user identification. Since OPES 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.

   Public/Private Domain                              |   Private Domain
   +--------------+                                   |   +------+
   | Data         |     *-------*     +----------+    |   | OPES |
   | Consumer     |<-->/ Network \<-->| Public IP|    |   +------+
   | Application  |    \(Public) /    | Address  |<-->|      .
   +--------------+     *-------*     | OPES     |    |      .
                                      +----------+    |      .
                                                      |    +------+
                                                      |    | OPES |
                                                      |    +------+

                                Figure 1

   (XXX: should we add a picture showing internal and external OPES
   intermediaries? more pictures showing other OPES layouts? Move to
   architecture draft?)

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
   tracing specification [I-D.ietf-opes-end-comm] defines "OPES trace"
   as "application message information about OPES entities that adapted
   that message" and "OPES tracing" as "the process of including,
   manipulating, and interpreting an OPES trace" (XXX: keep these in
   sync). 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

   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 XXX illustrates the differences between a trace and
   notification from a single application message point of view.

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

                                Figure 2

   Since notifications cannot be piggy-backed to application messages,
   they create new messages and may at least double the number of
   messages the sender has to process (more if several intermediaries on
   the message path emit notifications). Moreover, associating
   notifications with application messages may require duplicating
   application message information in notifications and/or maintaining a
   sender state until notification is received, increasing performance
   overhead of notifications. These concerns call for optional
   notification, with a special protocol to enable notifications when

   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 [XXX] 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
   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 on a protocol
   level, OPES concentrates on tracing facilities and supports
   notifications indirectly, using those 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".

   Nevertheless, OPES architecture allows for an efficient and
   meaningful notification protocol to be implemented in certain OPES
   environments.  For specific examples, see the "Optional Notification"
   section in [I-D.ietf-opes-end-comm].

5.2 An example of an OPES trace for HTTP

   The example below illustrates adaptations done to HTTP request at an
   OPES intermediary 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-Via" HTTP extension header.

   GET /pub/WWW/ HTTP/1.1
   Accept: text/plain

                                Figure 3

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

   GET /pub/WWW/ HTTP/1.1
   Accept: text/plain; q=0.5, text/html, text/x-dvi; q=0.8

                                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-Via" 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:

   HTTP/1.1 200 OK
   Content-Length: 2345
   Content-Encoding: text/plain


                                Figure 6

   In the above examples, "OPES-Via" header values contain URLs 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). Traced OPES
   URLs may be later used to request OPES bypass. (XXX: OPES specs will
   need to define OPES-Via format and semantics)

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

   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 (XXX quote
   tracing draft) [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:

      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

      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 users
      cooperate, the provider(s) have all the information they need. If
      users do not cooperate, the provider(s) cannot do much about it
      (they might be able to deny service to uncooperative users in some

      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
      that case.

      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.

   (XXX: should we prohibit adaptation of application protocols that do
   not allow for tracing?)

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 intermediary MUST leave its trace (XXX quote tracing draft)
   [I-D.ietf-opes-end-comm].  Detection assistance has its limitations.
   Some OPES intermediaries 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

   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.

   (XXX: should we prohibit adaptation of application protocols that do
   not allow for tracing?)


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

   OPES intermediaries MUST support a bypass feature (XXX quote bypass
   draft) [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 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. (XXX: but it is possible
   to instruct all OPES intermediaries to bypass an application message
   without knowing all OPES intermediaries IDs).

   (XXX: Ideally, this section 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.)


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

   "OPES Scenarios and Use Cases" specification
   [I-D.ietf-opes-scenarios] documents content adaptations that are in
   scope of the OPES framework (XXX provide a quote). These adaptations
   do not include URI resolution (XXX check). In some environments, it
   is technically possible to adapt URIs (and other kinds of identifiers
   or addresses) using documented OPES mechanisms.


8. Consideration (4.2) Reference validity

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

   OPES working group 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 (XXX quote tracing draft) [I-D.ietf-opes-end-comm].


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 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.


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 terms "privacy" and "privacy policy" are not defined in this
   context (by IAB or OPES working group). OPES tracing mechanisms allow
   end users and content providers to identify OPES intermediaries. It
   is believed that once an intermediary is identified, it would be
   possible to locate relevant information about that intermediary,
   including information relevant to requesters perception of privacy
   policy or reference validity. (XXX: should we move this paragraph
   into a separate section and expand it? one the other hand, it is
   probably the job of the architecture draft to define these things so
   that we can refer to them from here.)


11. Security Considerations



12. 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.


13. To-do

   security section: Does this document have any original security
      matters worth documenting?

   normative IDs: To be normative, OPES Internet-Drafts must be replaced
      with corresponding RFCs when the latter are published.

   architecture draft: Should architecture draft talk about external/
      internal OPES intermediaries, OPES systems, and privacy policies?
      Should this document be limited to a compilation of references
      from other OPES drafts, or should we introduce/discuss new
      concepts here?

Appendix A. Change Log

   Internal WG revision control ID: $Id: iab-cons.xml,v 1.19 2003/08/28
   03:48:32 1.20 2003/09/24
   05:20:21 rousskov Exp $


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

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


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


      *  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
         the very same exception to cover all usage scenarios we care

      *  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


      *  Polished to meet new xml2rfc strict requirements.


      *  Added unpolished meat for all nine considerations.

      *  Added Abbie Barbir as an author.


      *  Initial revision

Normative References

              Barbir, A., "OPES processor and end points
              communications", draft-ietf-opes-end-comm-00 draft-ietf-opes-end-comm-02 (work in
              progress), June September 2003.

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

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

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

Informative References

   [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.

Authors' Addresses

   Abbie Barbir
   Nortel Networks
   3500 Carling Avenue
   Nepean, Ontario

   Phone: +1 613 763 5229

   Alex Rousskov
   The Measurement Factory


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