Network Working Group Abbie. Barbir
Internet-Draft Nortel Networks
Expires: November 1, 2002 R. Chen
AT&T Labs
M. Hofmann
Bell Labs/Lucent Technologies
H. Orman
The Purple Streak Development
R. Penno
Nortel Networks
G. Tomlinson
Cacheflow
May 3, 2002
An Architecture for Open Pluggable Edge Services (OPES)
draft-ietf-opes-architecture-00
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 (2002). All Rights Reserved.
Abstract
This memo defines an architecture for a cooperative application
service in which a data provider, a data consumer, and zero or more
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application entities cooperatively realize a data stream service.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Architecture . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 OPES Entities . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 OPES Flows . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 OPES Rules . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Callout Servers . . . . . . . . . . . . . . . . . . . . . . . 7
2.5 Policy Enforcement . . . . . . . . . . . . . . . . . . . . . . 8
2.6 Tracing Facility . . . . . . . . . . . . . . . . . . . . . . . 8
3. Security and Privacy Considerations . . . . . . . . . . . . . 10
3.1 Trust Domains . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Primary data flow . . . . . . . . . . . . . . . . . . . . . . 11
3.3 Callout protocol . . . . . . . . . . . . . . . . . . . . . . . 11
3.4 Privacy . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5 Establishing trust . . . . . . . . . . . . . . . . . . . . . . 12
3.6 End-to-end Integrity . . . . . . . . . . . . . . . . . . . . . 12
4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
When realizing a data stream service between a provider and a
consumer, the need may arise to provision the use of other
application entities, in addition to the provider and consumer. For
example, some party may wish to customize a data stream as a service
to a consumer, e.g., a service might customize the data based on the
customer's geographical locality (e.g., language) or resource
availability (e.g., display capabilities).
In some cases it may be impossible to offer the customization service
at either the provider or the consumer applications. In this case,
one or more additional application entities may participate in the
data stream service. There are many possible provisioning scenarios
which make a data stream service attractive. The reader is referred
to [1] for a description of several scenarios.
The document presents the architectural components of Open Pluggable
Edge Services (OPES) that are needed in order to perform a data
stream service. The architecture addresses the IAB considerations
described in [2]. These considerations are covered in the various
parts of the document, specifically with respect to tracing (Section
2.6) and security considerations (Section 3).
The document is organized as follows: Section 2 introduces the OPES
architecture. Section 3 discusses security considerations. Section
4 provides a summary of the architecture and the requirements for
interoperability.
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2. The Architecture
The architecture of Open Pluggable Edge Services (OPES) can be
described in terms of three interrelated concepts, mainly:
o OPES entities: processes operating in the network;
o OPES flows: data flows that are cooperatively realized by the
OPES entities; and,
o OPES rules: these determine how a given data flow is modified by
an OPES entity.
2.1 OPES Entities
An OPES entity is an application that operates on a data flow between
a data provider application and a data consumer application. OPES
entities can be one of the following:
o an OPES service application, which analyzes and possibly
transforms messages exchanged between the data provider
application and the data consumer application; or,
o a data dispatcher, which invokes an OPES service application based
on filtering rules and application-specific knowledge.
In the network, OPES entities reside inside OPES processors. The
cooperative behavior of OPES entities introduces additional
functionality for each data flow provided that it matches the OPES
rules.
The OPES architecture is largely independent of the protocol that is
used by the OPES entities to exchange data. However, this document
selects HTTP [4] as the example protocol to be used for realizing a
data flow. In this regard, the "protocol" stack of an OPES entity is
summarized in Figure 1.
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---------------------------------------------------------------------
OPES entity
+-------------+
| |
| HTTP |
| |
+-------------+
| TCP/IP |
+-------------+
| ... |
+-------------+
Figure 1: An OPES protocol stack
---------------------------------------------------------------------
Figure 1 depicts a "minimal" stack for OPES. However, other
protocols may be present, depending on the functions that are
performed by the application.
2.2 OPES Flows
An OPES flow is a cooperative undertaking between a data provider
application, a data consumer application, one or more OPES service
applications, and one or more data dispatchers.
In order to understand the trust relationships between OPES entities,
each is labeled as residing in an administrative domain. However,
depending on provisioning decisions, the entities associated with a
given OPES flow may reside in one or more administrative domains.
For example, Figure 2 depicts a data flow (also known as an "OPES
flow"), that spans two administrative domains.
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---------------------------------------------------------------------
consumer administrative domain provider administrative domain
+------------------------------+ +------------------------------+
| | | |
| data OPES | | OPES data |
| consumer processor | | processor provider |
| | | |
| +----------+ +--------+ | | +--------+ +----------+ |
| | data | | OPES | | | | OPES | | data | |
| | consumer | |service | | | |service | | provider | |
| | appl | | appl | | | | appl | | appl | |
| +----------+ +--------+ | | +--------+ +----------+ |
| | | | | | | | | | | |
| | HTTP | | HTTP | | | | HTTP | | HTTP | |
| | | | | | | | | | | |
| +----------+ +--------+ | | +--------+ +----------+ |
| | TCP/IP | | TCP/IP | | | | TCP/IP | | TCP/IP | |
| +----------+ +--------+ | | +--------+ +----------+ |
| || || || | | || || || |
| ============= ================= ============= |
| | | |
+------------------------------+ +------------------------------+
| <----------------- OPES flow -----------------> |
Figure 2: An OPES flow
---------------------------------------------------------------------
Figure 2 depicts two data dispatchers that are present in the OPES
flow. However, the architecture allows for zero or more data
dispatchers to be present in any flow.
2.3 OPES Rules
The behavior of data dispatchers is governed by a set of filtering
rules, consisting of a set of conditions and related actions. The
ruleset is the superset of all OPES rules on the processor. Data
dispatchers invoke OPES service applications that may perform
modifications on an OPES flow. In this model, all data filters are
invoked for all data.
In order to ensure predictable behavior the OPES architecture
requires the use of a standardized schema for the purpose of defining
and interpreting the ruleset. The OPES architecture does not require
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a mechanism for configuring a ruleset into a data dispatcher. This
is treated as a local matter for each implementation (e.g., through
the use of a text editor, secure upload protocol, and so on). Future
revisions of the architecture may introduce such a requirement.
2.4 Callout Servers
The OPES ruleset is executed within a data dispatcher, which triggers
the execution of local OPES service applications. How the ruleset is
executed is not the subject of the architecture. However, in some
cases it may be useful for the OPES processor to distribute the
responsibility of service execution by communicating with one or more
callout servers (cf., [7]). The situation is illustrated in Figure
3, which shows a data dispatcher communicating with multiple callout
servers as it processes an OPES flow.
---------------------------------------------------------------------
+----------+ +---------+ +---------+ +---------+
| data | | callout | | callout | | callout |
|dispatcher| | server | | server | | server |
+----------+ +---------+ +---------+ +---------+
| | | | | | | |
| OCP | | OCP | | OCP | ... | OCP |
| | | | | | | |
+----------+ +---------+ +---------+ +---------+
| TCP/IP | | TCP/IP | | TCP/IP | | TCP/IP |
+----------+ +---------+ +---------+ +---------+
|| || || ||
||================ || ... ||
|| || ||
||============================== ||
|| ||
================================================
Figure 3: An OPES flow with Callout servers
---------------------------------------------------------------------
In Figure 3, a data dispatcher invokes the services of a callout
server by using the OPES callout protocol (OCP). The requirements
for the OCP are given in [7]. The OCP is application-agnostic, being
unaware of the semantics of the encapsulated application protocol
(e.g., HTTP). However, the OCP must incorporate a service aware
vectoring capability that parses the data flow according to the
ruleset and delivers the data to the OPES service application that
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can be local or remote.
2.5 Policy Enforcement
Data dispatchers include a ruleset that can be compiled from several
sources and must resolve into an unambiguous result. The compiled
ruleset enables an OPES processor to detremine which service
applications to invoke for which data flow. Accordingly, the data
dispatcher consitutes an enhanced Policy Enforcement Point (PEP),
where policy rules are executed, data vectoring and connection
management is performed, and service-specific data handlers and state
information are maintained, as depicted in Figure 4.
---------------------------------------------------------------------
+----------+
| callout |
| server |
+----------+
||
||
||
||
+---------------------------+
| +----------+ || |
| | OPES | || |
| | service | || |
| | appl | || |
| +----------+ || |
| +----------------------+ |
OPES flow <---->| | data dispatcher/PEP | | <----> OPES flow
| +----------------------+ |
| OPES |
| processor |
+--------------------------+
Figure 4: Data Dispatchers and Policy Enforcement Point
---------------------------------------------------------------------
The architecture allows more than one PEP to be present on an OPES
flow.
2.6 Tracing Facility
The architecture makes no requirements as to how an OPES flow is
negotiated, provided that it is consistent with the security policy
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(Section 3) of each administrative domain that hosts the OPES
entities that are associated with the flow.
The OPES architecture requires that each data dispatcher provides
tracing facilities that allow the appropriate verification of its
operation. The OPES architecture requires that tracing be feasible
on the OPES flow per OPES processor using in-band annotation through
header extensions on the application protocol that is used (e.g.,
HTTP). One of those annotations could be a URL with more detailed
information on the transformation that occurred to the data on the
OPES flow. Future revisions of the architecture may provide for a
tracing facility to be used for subsequent out-of-band analysis.
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3. Security and Privacy Considerations
Each data flow must be secured in accordance with several policies.
The primary stakeholders are the data consumer and the data provider.
The secondary stakeholders are the entities to which they may have
delegated their trust. The other stakeholders are the owners of the
callout servers. Any of these parties may be participants in the
OPES architecture.
These parties must have a model, explicit or implicit, describing
their trust policy; which of the other parties are trusted to operate
on data, and what security enhancements are required for
communication. The trust might be delegated for all data, or it
might be restricted to granularity as small as an application data
unit.
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
headers.
3.1 Trust Domains
The delegation of authority starts at either a data consumer or data
provider and moves to more distant entities in a "stepwise" fashion.
Stepwise means A delegates to B and B delegates to C and so force.
The entities thus "colored" by the delegation are said to form a
trust domain with respect to the original delegating party. Here,
"Colored" means that if the first step in the chain is the data
provider, then the stepwise delegation "colors" the chain with that
data "provider" color. The only colors that are defined are data the
"provider" and the data "consumer". An OPES processor may be in
several trust domains at any time. There is no restriction on
whether the OPES processors are authorized by data consumers and/or
data providers. The original party has the option of forbidding or
limiting redelegation.
An OPES processor must have a representation of its trust domain
memberships that it can report in whole or in part for tracing
purposes. It must include the name of the party which delegated each
privilege to it.
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3.2 Primary data flow
The primary data flow occurs between the data provider and the data
consumer. OPES must not interfere with the capability of these
parties to use end-to-end authentication and confidentiality.
If the primary parties want the assurance that their data does not
appear in plaintext on network links, but they will permit use of
plaintext on OPES processors and/or callout servers, then the OPES
processors must use authentication and encryption between "hops".
A separate security association must be used for each channel
established between two OPES processors.
3.3 Callout protocol
The determination of whether or not OPES processors will use the
measures that are described in the previous section during their
communication with callout servers depends on the details of how the
primary parties delegated trust to the OPES processors and the trust
relationship between the OPES processors and the callout server. If
the OPES processors are in a single administrative domain with strong
confidentiality guarantees, then encryption may be optional. In
other cases, encryption and strong authentication would be at least
strongly recommended.
If the delegation mechanism names the trusted parties and their
privileges in some way that permits authentication, then the OPES
processors will be responsible for enforcing the policy and for using
authentication as part of that enforcement.
The callout servers must be aware of the policy governing the
communication path. They must not, for example, communicate
confidential information to auxiliary servers outside the trust
domain.
A separate security association must be used for each channel
established between an OPES processor and a callout server. The
channels must be separate for different primary parties.
3.4 Privacy
Some data from data consumers is considered "private" or "sensitive",
and OPES processors must both advise the primary parties of the their
privacy policy and respect the policies of the primary parties. The
privacy information must be conveyed on a per-flow basis.
The callout servers must also participate in handling of private
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data, and they must be prepared to announce their own capabilities
and to enforce the policy required by the primary parties.
3.5 Establishing trust
The OPES processor will have configuration policy specifying what
privileges the callout servers have and how they are to be
identified. This is especially critical for third-party (fourth-
party, etc.) callout servers. OPES uses standard protocols for
authenticating and otherwise security communication with callout
servers.
An OPES processor will have a trusted method for receiving
configuration information such as rules for the data dispatcher,
trusted callout servers, primary parties that opt-in or opt-out of
individual services, etc.
3.6 End-to-end Integrity
Digital signature techniques can be used to mark data changes in such
a way that a third-party can verify that the changes are or are not
consistent with the originating party's policy. This requires an
inline manner of specifying policy and its binding to data, a trace
of changes and the party making the changes, and strong identities
and authentication methods.
Strong end-to-end integrity can fulfill some of the functions
required by "tracing".
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4. Summary
Although the architecture supports a wide range of cooperative
transformation services, it has few requirements for
interoperability.
The necessary and sufficient elements are specified in the following
documents:
o the OPES ruleset schema [6] which defines the syntax and semantics
of the rules interpreted by a data dispatcher; and,
o the OPES callout protocol (OCP) [7] which defines the protocol
between a data dispatcher and a callout server.
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References
[1] McHenry, S., et. al, "OPES Scenarios and Use Cases", Internet-
Draft TBD, May 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.
[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", Internet-Draft TBD, May 2002.
[6] OPES working group, "OPES Ruleset Schema", Internet-Draft TBD,
May 2002.
[7] OPES working group, "OPES Callout Protocol and Tracing Protocol
Requirements", Internet-Draft TBD, May 2002.
Authors' Addresses
Abbie Barbir
Nortel Networks
3500 Carling Avenue
Nepean, Ontario K2H 8E9
Canada
Phone: +1 613 763 5229
EMail: abbieb@nortelnetworks.com
Robin Chen
AT&T Labs
Room E219, 180 Park Avenue
Florham Park, NJ 07932
US
Phone: +1 973 360 8653
EMail: chen@research.att.com
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Markus Hofmann
Bell Labs/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
The Purple Streak Development
EMail: ho@alum.mit.edu
Reinaldo Penno
Nortel Networks
2305 Mission College Boulevard
San Jose, CA 95134
US
EMail: rpenno@nortelnetworks.com
Gary Tomlinson
Cacheflow
EMail: gary@tomlinsongroup.net
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Appendix A. Acknowledgements
The authors gratefully acknowledge the contributions of: Marshall T.
Rose. (more to come, soon...)
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