Open Pluggable Edge Services A. Beck
Internet-Draft M. Hofmann
Expires: June 12, 2003 Lucent Technologies
H. Orman
Purple Streak Development
R. Penno
Nortel Networks
A. Terzis
Individual Consultant
December 12, 2002
Requirements for OPES Callout Protocols
draft-ietf-opes-protocol-reqs-03
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. The requirements are
intended to help evaluating possible protocol candidates as well as
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 Reliability . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2 Congestion Avoidance . . . . . . . . . . . . . . . . . . . . 5
3.3 Callout Transactions . . . . . . . . . . . . . . . . . . . . 5
3.4 Callout Connections . . . . . . . . . . . . . . . . . . . . 6
3.5 Asynchronous Message Exchange . . . . . . . . . . . . . . . 6
3.6 Message Segmentation . . . . . . . . . . . . . . . . . . . . 7
3.7 Support for Keep-Alive Mechanism . . . . . . . . . . . . . . 7
3.8 Operation in NAT Environments . . . . . . . . . . . . . . . 8
3.9 Multiple Callout Servers . . . . . . . . . . . . . . . . . . 8
3.10 Multiple OPES Processors . . . . . . . . . . . . . . . . . . 8
3.11 Support for Different Application Protocols . . . . . . . . 8
3.12 Capability and Parameter Negotiations . . . . . . . . . . . 8
3.13 Meta Data and Instructions . . . . . . . . . . . . . . . . . 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
Normative References . . . . . . . . . . . . . . . . . . . . 15
Informative References . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 16
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 18
B. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . 21
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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 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 rules
installed on the OPES processor. The rules enforcement can trigger
the execution of service applications local to the OPES processor.
Alternatively, the OPES processor can distribute the responsibility
of service execution by communicating and collaborating with one or
more remote callout servers. As described in [1], 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.
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3. Functional Requirements
3.1 Reliability
The OPES callout protocol MUST be able to provide ordered reliability
for the communication between OPES 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 SHOULD specify that it must be used with a transport
protocol which provides ordered/unordered reliability at the
transport-layer, for example TCP [6] or SCTP [7].
3.2 Congestion Avoidance
The OPES callout protocol MUST ensure that congestion avoidance that
matches the standard of RFC 2914 [4] is applied on all communication
between OPES processor and callout server. For this purpose, the
callout protocol SHOULD use a congestion-controlled transport-layer
protocol, presumably either TCP [6] or SCTP [7].
3.3 Callout Transactions
The OPES callout protocol MUST enable an OPES 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 processor to forward a partial or complete 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 processor. Additionally, the
callout protocol MUST enable a callout server to report back to the
OPES processor the result of a callout transaction, e.g. in the form
of a status code.
A callout transaction is defined as a message exchange between an
OPES 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 callout protocol
messages, i.e. a series of protocol messages. A callout request
MUST always contain a partial or complete application message. A
callout response MUST always indicate the result of the callout
transaction. A callout response MAY contain a modified application
message.
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Callout transactions are always initiated by a callout request from
an OPES processor and typically terminated by a callout response from
a callout server. The OPES callout protocol MUST, however, also
provide a mechanism that allows either endpoint of a callout
transaction to terminate a callout transaction before a callout
request or response has been completely received by the corresponding
callout endpoint. Such a mechanism MUST ensure 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.
3.4 Callout Connections
The OPES callout protocol MUST enable an OPES processor and a callout
server to perform multiple callout transactions over a callout
connection. Additionally, the callout protocol MUST provide a method
to associate callout transactions with callout connections. A
callout connection is defined as a logical connection at the
application-layer between an OPES processor and a callout server. A
callout connection MAY have certain parameters associated with it,
for example parameters that control the fail-over behavior of
connection endpoints. Callout connection-specific parameters MAY be
negotiated between OPES processors and callout servers (see Section
3.12).
The OPES callout protocol MAY choose to multiplex multiple callout
connections over a single transport-layer connection so long as a
flow control mechanism is applied which guarantees fairness among
multiplexed callout connections.
Callout connections MUST always be initiated by an OPES processor. A
callout connection MAY be closed by either endpoint of the connection
provided that doing so does not affect the normal operation of
on-going callout transactions associated with the callout connection.
3.5 Asynchronous Message Exchange
The OPES callout protocol MUST support an asynchronous message
exchange over callout connections.
In order to allow asynchronous processing on the OPES processor and
callout server, it MUST be possible to separate request issuance from
response processing. The protocol MUST therefore allow multiple
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outstanding callout requests and provide a method to correlate
callout responses to callout requests.
Additionally, the callout protocol MUST enable a callout server to
respond to a callout request before it has received the entire
request.
3.6 Message Segmentation
The OPES callout protocol MUST allow an OPES 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 re-assemble the fragmented application
message.
Likewise, the callout protocol MUST enable a callout server to return
an application message to an OPES processor in a series of smaller
message fragments. The callout protocol MUST enable the receiving
OPES processor to re-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 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 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 OPES processor.
Application message segmentation is also required if the OPES callout
protocol provides a flow control mechanism in order to multiplex
multiple callout connections over a single transport-layer connection
(see Section 3.4).
3.7 Support for Keep-Alive Mechanism
The OPES callout protocol MUST provide a keep-alive mechanism which,
if used, would allow both endpoints of a callout connection 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 connections or a separate
connection between OPES processor and callout server. The callout
protocol MAY also specify that the use of the keep-alive mechanism is
optional.
The detection of a callout server failure may enable an OPES
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processor to establish a callout 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
processor may enable a callout server to release resources which
would otherwise not be available for callout transactions with other
OPES processors.
3.8 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 processor and a callout server.
3.9 Multiple Callout Servers
The OPES callout protocol MUST allow an OPES 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 processor will likely
have to communicate with multiple callout servers. The protocol
design MUST enable an OPES processor to do so.
3.10 Multiple OPES Processors
The OPES callout protocol MUST allow a callout server to
simultaneously communicate with more than one OPES processor.
The protocol design MUST support a scenario in which multiple OPES
processors use the services of a single callout server.
3.11 Support for Different Application Protocols
The OPES callout protocol SHOULD be application protocol-agnostic,
i.e. it SHOULD not make any assumptions about the characteristics of
the application-layer protocol used on the data path between data
provider and data consumer. At a minimum, the callout protocol MUST
be compatible with HTTP [5].
The OPES entities on the data path may use different
application-layer protocols, including, but not limited to, HTTP [5]
and RTP [8]. It would be desirable to be able to use the same OPES
callout protocol for any such application-layer protocol.
3.12 Capability and Parameter Negotiations
The OPES callout protocol MUST support the negotiation of
capabilities and callout connection parameters between an OPES
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processor and a callout server. This implies that the OPES 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
connections/transactions or determined that their capabilities are
incompatible.
Capabilities and parameters that could be negotiated between an OPES
processor and a callout server include (but are not limited to):
callout protocol version, fail-over behavior, heartbeat rate for
keep-alive messages, security-related parameters etc.
The callout protocol MUST NOT negotiate the transport protocol to be
used for callout connections. The callout protocol MAY, however,
specify that a certain application message protocol (e.g. HTTP [5],
RTP [8]) requires the use of a certain transport protocol (e.g. TCP
[6], SCTP [7]).
Callout connection parameters may also pertain to the characteristics
of OPES callout services if, for example, callout connections 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.
Callout connection parameters MUST be negotiated on a per-callout
connection basis and before any callout transactions are performed
over the corresponding callout connection. Other parameters and
capabilities, such as the fail-over behavior, MAY be negotiated
between the two endpoints independently of callout connections.
The parties to a callout protocol MAY use callout connections to
negotiate all or some of their capabilities and parameters.
Alternatively, a separate control connection MAY be used for this
purpose.
3.13 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 processor or
callout server.
Specifically, the callout protocol MUST enable an OPES 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
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server MUST be able to include information about the returned
application message.
The OPES processor MUST further be able to include an ordered list of
one or more uniquely specified OPES services which are to be
performed on the forwarded application message in the specified
order. However, as the callout protocol MAY also choose to associate
callout connections with specific OPES services, there may not be a
need to identify OPES services on a per-callout transaction basis.
Additionally, the OPES callout protocol MUST allow the callout server
to indicate to the OPES processor the cacheability of callout
responses. This implies that callout responses may have to carry
cache-control instructions for the OPES processor.
The OPES callout protocol MUST further enable the OPES 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 processor even it
has not been modified by an OPES service.
The OPES callout protocol MUST also allow OPES processors to comply
with the tracing requirements of the OPES architecture as laid out in
[1] and [3]. This implies that the callout protocol MUST enable a
callout server to convey to the OPES processor information about the
OPES service operations performed on the forwarded application
message.
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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.
As OPES callout transactions introduce additional latency to
application protocol transactions on the data path, callout 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 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 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 for message authentication,
confidentiality, and integrity between the OPES processor and the
callout server. It MUST provide mutual authentication. For this
purpose, the callout protocol SHOULD use existing security
mechanisms. 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 end-to-end encryption is a requirement for the content path, then
this confidentiality MUST be extended to the communication between
the OPES processor and the callout server. While it is recommended
that the communication between OPES processor and callout server
always be encrypted, encryption MAY be optional if both the OPES
processor and the callout server are co-located with each other in a
single administrative domain with strong confidentiality guarantees.
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
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The OPES callout protocol MUST operate securely across un-trusted
domains between the OPES processor and the callout server.
If the communication channels between the OPES 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.
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6. Security Considerations
The security requirements for the OPES callout protocol are discussed
in Section 5.
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Normative References
[1] Barbir, A., "An Architecture for Open Pluggable Edge Services
(OPES)", draft-ietf-opes-architecture-04 (work in progress),
December 2002.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[3] Floyd, S. and L. Daigle, "IAB Architectural and Policy
Considerations for Open Pluggable Edge Services", RFC 3238,
January 2002.
[4] Floyd, S., "Congestion Control Principles", BCP 41, RFC 2914,
September 2000.
[5] 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.
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Informative References
[6] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
September 1981.
[7] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and V. Paxson,
"Stream Control Transmission Protocol", RFC 2960, October 2000.
[8] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", RFC
1889, January 1996.
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
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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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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.
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Appendix B. Change Log
Changes from draft-ietf-opes-protocol-reqs-02.txt
o Re-ordered some sections in the functional requirements part of
the draft
o Clarified in Section 3.3 what callout requests and responses must/
may contain
o Removed reference to explicit and implicit mechanism of
terminating a callout transaction prematurely in Section 3.3
o Added reference to RFC 2914 in congestion avoidance requirement in
Section 3.2
o Added language that states that existing solutions should be used
to achieve congestion avoidance and ordered/unordered reliability
in Section 3.2 and Section 3.1
o Clarified concept of callout connections (previously referred to
as "callout channels") in Section 3.4
o Added statement about the possibility of multiplexing multiple
callout connections over a transport connection to Section 3.4
o Clarified in Section 3.7 that use of a keep-alive mechanism is
optional
o Replaced "MUST" with "SHOULD" in OCP requirement to be application
protocol-agnostic in Section 3.11, added explicit requirement to
support HTTP
o Removed "transport protocol" from list of callout parameters which
may be negotiated, added suggestion to pick transport protocol
depending on the application protocol in Section 3.12.
o Explained that application message segementation is also necessary
for multiplexing callout connections over transport connections in
Section 3.6
o Added statement to Section 5.2 that encryption between OPES
processor and callout server may be optional if they are
co-located with each other in a single administrative domain
Changes from draft-ietf-opes-protocol-reqs-01.txt
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o Reworded and clarified several statements of the draft
Changes from draft-ietf-opes-protocol-reqs-00.txt
o Aligned terminology with [1]
o Clarified in Section 3.13 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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