Open Pluggable Edge Services                                     A. Beck
Internet-Draft                                                M. Hofmann
Expires: November 22, December 17, 2002                           Lucent Technologies
                                                                H. Orman
                                               Purple Streak Development
                                                                R. Penno
                                                         Nortel Networks
                                                               A. Terzis
                                                   Individual Consultant
                                                            May 24,
                                                           June 18, 2002

                Requirements for OPES Callout Protocols
                    draft-ietf-opes-protocol-reqs-00
                    draft-ietf-opes-protocol-reqs-01

Status of this Memo

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

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Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document specifies the requirements that the OPES (Open
   Pluggable Edge Services) callout protocol must satisfy in order to
   support the remote execution of OPES services [1].  The requirements
   are intended to help evaluating possible protocol candidates and to
   guide the development of such protocols.

Table of Contents

   1.   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.   Functional Requirements  . . . . . . . . . . . . . . . . . .   5
   3.1  Callout Transactions . . . . . . . . . . . . . . . . . . . .   5
   3.2  Callout Channels . . . . . . . . . . . . . . . . . . . . . .   5
   3.3  Reliability  . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.4  Congestion and Flow Control  . . . . . . . . . . . . . . . .   6
   3.5  Support for Keep-Alive Mechanism . . . . . . . . . . . . . .   6
   3.6  Operation in NAT Environments  . . . . . . . . . . . . . . .   7
   3.7  Multiple Callout Servers . . . . . . . . . . . . . . . . . .   7
   3.8  Multiple Data OPES Processors . . . . . . . . . . . . . . . . . .   7
   3.9  Support for Different Application Protocols  . . . . . . . .   7
   3.10 Capability and Parameter Negotiations  . . . . . . . . . . .   7
   3.11 Meta Data and Instructions . . . . . . . . . . . . . . . . .   8
   3.12 Asynchronous Message Exchange  . . . . . . . . . . . . . . .   9
   3.13 Message Segmentation . . . . . . . . . . . . . . . . . . . .   9
   4.   Performance Requirements . . . . . . . . . . . . . . . . . .  11
   4.1  Protocol Efficiency  . . . . . . . . . . . . . . . . . . . .  11
   5.   Security Requirements  . . . . . . . . . . . . . . . . . . .  12
   5.1  Authentication, Confidentiality, and Integrity . . . . . . .  12
   5.2  Hop-by-Hop Confidentiality . . . . . . . . . . . . . . . . .  12
   5.3  Operation Across Un-trusted Domains  . . . . . . . . . . . .  12
   5.4  Privacy  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
   6.   Security Considerations  . . . . . . . . . . . . . . . . . .  14
   7.   Acknowledgments
        References . . . . . . . . . . . . . . . . . . . . . . . . .  15
        References
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  15
   A.   Acknowledgments  . . . . . . . . . . . . . . . . . . .  16
        Authors' Addresses . . .  17
   B.   Change Log . . . . . . . . . . . . . . . . . .  16 . . . . . . .  18
        Full Copyright Statement . . . . . . . . . . . . . . . . . .  18  19

1. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [2].

2. Introduction

   The Open Pluggable Edge Services (OPES) architecture [1] enables
   cooperative application services (OPES services) between a data
   provider, a data consumer, and zero or more data 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 data OPES processor.  The rules enforcement can
   trigger the execution of service applications local to the data OPES
   processor.  Alternatively, the data OPES processor can distribute the
   responsibility of service execution by communicating and
   collaborating with one or more remote callout servers.  As described
   in [1], a data an OPES processor communicates with and invokes services on a
   callout server by using a callout protocol.  This document presents
   the requirements for such a protocol.

   The requirements in this document are divided into three categories -
   functional requirements, performance requirements, and security
   requirements.  Each requirement is presented as one or more
   statements, followed by brief explanatory material as appropriate.

3. Functional Requirements

3.1 Callout Transactions

   The OPES callout protocol MUST enable an OPES data processor and a callout
   server to perform callout transactions with the purpose of exchanging
   partial or complete application-level protocol messages (or
   modifications thereof).  More specifically, the callout protocol MUST
   enable an OPES data processor to forward a complete or partial application
   message to a callout server so that one or more OPES services can
   process the forwarded application message (or parts thereof).  The
   result of the service operation may be a modified application
   message.  The callout protocol MUST therefore enable the callout
   server to return a modified application message or the modified parts
   of an application message to the OPES data processor.

   A callout transaction is defined as a message exchange between an
   OPES data processor and a callout server consisting of a callout request
   and a callout response.  Both, the callout request as well as the
   callout response, MAY each consist of one or more protocol messages,
   i.e.  a series of protocol messages.

   Callout transactions are always initiated by a callout request from
   an OPES data processor and typically terminated by a callout response from
   a callout server.  The OPES callout protocol MUST, however, also
   allow either endpoint of a callout transaction to terminate a callout
   transaction prematurely, i.e.  before a callout request or response
   has been completely received by the corresponding endpoint.  The
   callout protocol MAY provide an explicit (e.g.  through a termination
   message) or implicit (e.g.  through a connection tear-down) mechanism
   to terminate a callout transaction prematurely.  Such a mechanism
   MUST ensure, however, that a premature termination of a callout
   transaction does not result in the loss of application message data.

   A premature termination of a callout transaction is required to
   support OPES services which may terminate even before they have
   processed the entire application message.  Content analysis services,
   for example, may be able to classify a Web object after having
   processed just the first few bytes of a Web object.

   The callout protocol MUST further enable a callout server to report
   back to the OPES data processor the result of a callout transaction, e.g.
   in the form of a status code.

3.2 Callout Channels

   The OPES callout protocol MUST enable an OPES data processor and a callout
   server to perform multiple callout transactions over a callout
   channel.  A callout channel is defined as a logical connection at the
   application-layer between an OPES data processor and a callout server.

   Callout channels MUST always be established by an OPES data processor.  A
   callout channel MAY be closed by either endpoint of the callout
   channel provided that all callout transactions associated with the
   channel have terminated.

   A callout channel MAY have certain parameters associated with it, for
   example parameters that control the fail-over behavior of channel
   endpoints.  Callout channel parameters MAY be negotiated between OPES
   data
   processors and callout servers (see Section 3.10).

3.3 Reliability

   The OPES callout protocol MUST be able to provide ordered reliability
   for the communication between OPES data processor and callout server.
   Additionally, the callout protocol SHOULD be able to provide
   unordered reliability.

   In order to satisfy the reliability requirements, the callout
   protocol MAY specify that it must be used with a lower-level
   transport protocol which provides ordered reliability at the
   transport-layer.

3.4 Congestion and Flow Control

   The OPES callout protocol MUST ensure that congestion and flow
   control mechanisms are applied on all callout transactions.  For this
   purpose, the callout protocol MAY specify callout protocol-specific
   mechanisms or refer to a lower-level transport protocol and discuss
   how its mechanisms provide for congestion and flow control.

3.5 Support for Keep-Alive Mechanism

   The OPES callout protocol MUST provide an optional keep-alive
   mechanism which, if used, would allow both endpoints of a callout
   channel to detect a failure of the other endpoint even in the absence
   of callout transactions.  The callout protocol MAY specify that keep-
   alive messages be exchanged over existing callout channel connections
   or a separate connection between OPES data processor and callout server.

   The detection of a callout server failure may enable an OPES data
   processor to establish a channel connection with a stand-by callout
   server so that future callout transactions do not result in the loss
   of application message data.  The detection of the failure of an OPES
   data
   processor may enable a callout server to release resources which
   would otherwise not be available for callout transactions with other
   OPES data processors.

3.6 Operation in NAT Environments

   The OPES protocol SHOULD be NAT-friendly, i.e.  its operation should
   not be compromised by the presence of one or more NAT devices in the
   path between an OPES data processor and a callout server.

3.7 Multiple Callout Servers

   The OPES callout protocol MUST allow an OPES data processor to
   simultaneously communicate with more than one callout server.

   In larger networks, OPES services are likely to be hosted by
   different callout servers.  Therefore, an OPES data processor will likely
   have to communicate with multiple callout servers.  The protocol
   design MUST enable an OPES data processor to do so.

3.8 Multiple Data OPES Processors

   The OPES callout protocol MUST allow a callout server to
   simultaneously communicate with more than one OPES data processor.

   The protocol design MUST support a scenario in which multiple OPES
   data
   processors use the services of a single callout server.

3.9 Support for Different Application Protocols

   The OPES callout protocol MUST be application protocol-agnostic, i.e.
   it MUST not make any assumptions about the characteristics of the
   application-layer protocol used on the data path between data
   provider and data consumer.

   The OPES entities on the data path may use different application-
   layer protocols, including, but not limited to, HTTP [3] and RTP [4].
   It would be desirable to be able to use the same OPES callout
   protocol for any such application-layer protocol.

3.10 Capability and Parameter Negotiations

   The OPES callout protocol MUST support the negotiation of
   capabilities and callout channel parameters between an OPES data processor
   and a callout server.  This implies that the OPES data processor and the
   callout server MUST be able to exchange their capabilities and
   preferences and engage into a deterministic negotiation process at
   the end of which the two endpoints have either agreed on the
   capabilities and parameters to be used for future callout channel
   transactions or determined that their capabilities are incompatible.

   Capabilities and parameters that could be negotiated between an OPES
   data
   processor and a callout server include (but are not limited to):
   callout protocol version, transport-layer protocol, fail-over
   behavior, heartbeat rate for keep-alive messages, security-related
   parameters etc.

   Channel parameters may also pertain to the characteristics of OPES
   callout services if, for example, callout channels are associated
   with one or more specific OPES services.  An OPES service-specific
   parameter may, for example, specify which parts of an application
   message an OPES service requires for its operation.

   The parties to a callout protocol MAY use callout channels to
   negotiate all or some of their capabilities and parameters.  They MAY
   also use a separate control connection for this purpose.  If there is
   a need for callout channel parameters, then they MUST be negotiated
   on a per-callout channel basis and before any callout transactions
   are performed over the corresponding channel.  Other parameters and
   capabilities, such as the fail-over behavior, MAY be negotiated
   between the two endpoints independently of callout channels.

3.11 Meta Data and Instructions

   The OPES callout protocol MUST provide a mechanism for the endpoints
   of a particular callout transaction to include in callout requests
   and responses meta data and instructions for the OPES data processor or
   callout server.

   Specifically, the callout protocol MUST enable an OPES data processor to
   include information about the forwarded application message in a
   callout request, e.g.  in order to specify the type of the forwarded
   application message or to specify what part(s) of the application
   message are forwarded to the callout server.  Likewise, the callout
   server MUST be able to include information about the returned
   application message.

   The OPES data processor MUST further be able to uniquely specify include an ordered list of
   one or more uniquely specified OPES services which are to be
   performed on the forwarded application message.  The message in the specified
   order.  However, as the callout protocol MAY also choose to associate
   callout channels with specific OPES services so that services, there
   is no may not be a need
   to identify OPES service on a per-callout transaction basis.

   Additionally, the OPES callout protocol MUST allow the callout server
   to indicate to the OPES data processor the cacheability of callout
   responses.  This implies that callout responses may have to carry
   cache-control instructions for the OPES data processor.

   The OPES callout protocol MUST further enable the OPES data processor to
   indicate to the callout server if it has kept a local copy of the
   forwarded application message (or parts thereof).  This information
   enables the callout server to determine whether the forwarded
   application message must be returned to the OPES data processor even it
   has not been modified by an OPES service.

   The OPES callout protocol MUST also allow OPES data processors to comply
   with the tracing requirements of the OPES architecture as laid out in
   [1] and [5].  This implies that the callout protocol MUST enable a
   callout server to convey to the OPES data processor information about the
   OPES service operations performed on the forwarded application
   message.

3.12 Asynchronous Message Exchange

   The OPES callout protocol MUST support an asynchronous message
   exchange between an OPES data processor and a callout server.

   In order to allow asynchronous processing on the OPES data processor and
   callout server, it MUST be possible to separate request issuance from
   response processing.  The protocol MUST therefore allow multiple
   outstanding requests and provide a method to correlate responses to
   requests.

   Additionally, the callout protocol MUST enable a callout server to
   respond to a callout request before it has received the entire
   request.

3.13 Message Segmentation

   The OPES callout protocol MUST allow an OPES data processor to forward an
   application message to a callout server in a series of smaller
   message fragments.  The callout protocol MUST further enable the
   receiving callout server to assemble the fragmented application
   message.

   Likewise, the callout protocol MUST enable a callout server to return
   an application message to a data an OPES processor in a series of smaller
   message fragments.  The callout protocol MUST enable the receiving
   data
   OPES processor to assemble the fragmented application message.

   Depending on the application-layer protocol used on the data path,
   application messages may be very large in size (for example in the
   case of audio/video streams) or of unknown size.  In both cases, the
   OPES data processor has to initiate a callout transaction before it has
   received the entire application message to avoid long delays for the
   data consumer.  The OPES data processor MUST therefore be able to forward
   fragments or chunks of an application message to a callout server as
   it receives them from the data provider or consumer.  Likewise, the
   callout server MUST be able to process and return application message
   fragments as it receives them from the data OPES processor.

4. Performance Requirements

4.1 Protocol Efficiency

   The OPES callout protocol SHOULD be efficient in that it minimizes
   the additionally introduced latency, for example by minimizing the
   protocol overhead.  At a minimum, the callout protocol SHOULD satisfy
   the performance requirements of the application-layer protocol whose
   messages are forwarded from the OPES data processor to the callout
   server.

   As OPES callout transactions introduce additional latency to
   application protocol transactions on the data path, calllout protocol
   efficiency is crucial.

5. Security Requirements

   In the absence of any security mechanisms, sensitive information
   might be communicated between the OPES data processor and the callout
   server in violation of either endpoint's security and privacy policy
   through misconfiguration or a deliberate insider attack.  By using
   strong authentication, message encryption, and integrity checks, this
   threat can be minimized to a smaller set of insiders and/or operator
   configuration errors.

   The OPES data processor and the callout servers SHOULD have enforceable
   policies that limit the parties they communicate with, that determine
   the protections to use based on identities of the endpoints and other
   data (such as enduser policies).  In order to enforce the policies,
   they MUST be able to authenticate the callout protocol endpoints
   using cryptographic methods.

5.1 Authentication, Confidentiality, and Integrity

   The parties to the callout protocol MUST have a sound basis for
   binding authenticated identities to the protocol endpoints, and they
   MUST verify that these identities are consistent with their security
   policies.

   The OPES callout protocol MUST provide message authentication,
   confidentiality, and integrity between the OPES data processor and the
   callout server.  It MUST provide mutual authentication.  The callout
   protocol SHOULD use existing security mechanisms for this purpose.
   The callout protocol specification is not required to specify the
   security mechanisms, but it MAY instead refer to a lower-
   level lower-level
   security protocol and discuss how its mechanisms are to be used with
   the callout protocol.

5.2 Hop-by-Hop Confidentiality

   If encryption is a requirement for the content path, then this
   confidentiality MUST be extended to the communication between the
   callout servers and the OPES data processor.  In order to minimize data
   exposure, the callout protocol MUST use a different encryption key
   for each encrypted content stream.

5.3 Operation Across Un-trusted Domains

   The OPES callout protocol MUST operate securely across un-trusted
   domains between the OPES data  processor and the callout server.

   If the communication channels between the OPES data processor and callout
   server cross outside of the organization taking responsibility for
   the OPES services, then endpoint authentication and message
   protection (confidentiality and integrity) MUST be used.

5.4 Privacy

   Any communication carrying information relevant to privacy policies
   MUST protect the data using encryption.

6. Security Considerations

   The security requirements for the OPES callout protocol are discussed
   in Section 5.

7. Acknowledgments

   This document is based in parts on previous work by Anca Dracinschi
   Sailer, Volker Hilt, and Rama R.  Menon.

References

   [1]  Barbir, A., "An Architecture for Open Pluggable Edge Services
        (OPES)", draft-ietf-opes-architecture-00 draft-ietf-opes-architecture-01 (work in progress), May
        2002.

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119, March 1997.

   [3]  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.

   [4]  Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
        "RTP: A Transport Protocol for Real-Time Applications", RFC
        1889, January 1996.

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

Authors' Addresses

   Andre Beck
   Lucent Technologies
   101 Crawfords Corner Road
   Holmdel, NJ  07733
   US

   EMail: abeck@bell-labs.com

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

   Phone: +1 732 332 5983
   EMail: hofmann@bell-labs.com
   Hilarie Orman
   Purple Streak Development

   EMail: ho@alum.mit.edu
   URI:   http://www.purplestreak.com

   Reinaldo Penno
   Nortel Networks
   2305 Mission College Boulevard
   San Jose, CA  95134
   US

   EMail: rpenno@nortelnetworks.com

   Andreas Terzis
   Individual Consultant
   150 Golf Course Dr.
   Rohnert Park, CA  94928
   US

   Phone: +1 707 586 8864
   EMail: aterzis@sbcglobal.net

Appendix A. Acknowledgments

   This document is based in parts on previous work by Anca Dracinschi
   Sailer, Volker Hilt, and Rama R.  Menon.

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

Appendix B. Change Log

   Changes from draft-ietf-opes-protocol-reqs-00.txt

   o  Aligned terminology with [1]

   o  Clarified in Section 3.11 that OCP requests not only have to
      identify one or more OPES services, but also the order in which
      the services are to be executed

   o  Removed requirement from Section 4.1 that OCP must satisfy
      performance requirements of the application-layer protocol used
      between data consumer and provider

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