Open Pluggable Edge Services A. Beck
Internet-Draft M. Hofmann
Expires: November 22, 2002 Lucent Technologies
H. Orman
Purple Streak Development
R. Penno
Nortel Networks
A. Terzis
Individual Consultant
May 24, 2002
Requirements for OPES Callout Protocols
draft-ietf-opes-protocol-reqs-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 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.
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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 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 . . . . . . . . . . . . . . . . . . . . . . 15
References . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 16
Full Copyright Statement . . . . . . . . . . . . . . . . . . 18
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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].
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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 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 processor. The rules enforcement can
trigger the execution of service applications local to the data
processor. Alternatively, the data 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 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.
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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
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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
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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 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
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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 one
or more OPES services which are to be performed on the forwarded
application message. The callout protocol MAY also choose to
associate callout channels with specific OPES services so that there
is no need to identify OPES service on a per-callout transaction
basis.
Additionally, the OPES callout protocol MUST allow the callout server
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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 processor in a series of smaller
message fragments. The callout protocol MUST enable the receiving
data 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
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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
processor.
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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.
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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 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
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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.
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6. Security Considerations
The security requirements for the OPES callout protocol are discussed
in Section 5.
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7. Acknowledgments
This document is based in parts on previous work by Anca Dracinschi
Sailer, Volker Hilt, and Rama R. Menon.
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References
[1] Barbir, A., "An Architecture for Open Pluggable Edge Services
(OPES)", draft-ietf-opes-architecture-00 (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
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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
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