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Versions: (draft-srinivas-opes-threats) 00 01 02 03 RFC 3837

Network Working Group                                         A. Barbir
Internet-Draft                                           Nortel Networks
Expires: April 20, 2003                                       O. Batuner
                                                  Independent consultant
                                                                 T. Chan
                                                             B. Srinivas
                                                                   Nokia
                                                                H. Orman
                                               Purple Streak Development
                                                        October 20, 2002


      Security Threats and Risks for Open Pluggable Edge Services
                       draft-ietf-opes-threats-00

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
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at http://
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 20, 2003.

Copyright Notice

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

Abstract

   The document investigates the security threats associated with OPES.
   The effects of security threats on the underlying architecture are
   discussed.  The document does not specify or recommend any solutions.
   Proposed solutions are viewed as illustrations of the nature of
   threats.



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Table of Contents

   1.     Introduction . . . . . . . . . . . . . . . . . . . . . . .   3
   2.     OPES Data Flow Threats . . . . . . . . . . . . . . . . . .   5
   2.1    OPES Flow Network Level Threats  . . . . . . . . . . . . .   6
   2.1.1  OPES device spoofing . . . . . . . . . . . . . . . . . . .   6
   2.1.2  Remote callout server spoofing . . . . . . . . . . . . . .   7
   2.1.3  Session Hijacking  . . . . . . . . . . . . . . . . . . . .   7
   2.1.4  Threats to data confidentiality (eavesdropping)  . . . . .   7
   2.1.5  Denial-of-Service (DoS)  . . . . . . . . . . . . . . . . .   7
   2.1.6  Threats to network robustness  . . . . . . . . . . . . . .   8
   2.2    OPES Flow Application Level Threats  . . . . . . . . . . .   8
   2.2.1  Unauthorized OPES entities . . . . . . . . . . . . . . . .   8
   2.2.2  Unauthorized actions of legitimate OPES entities . . . . .   8
   2.2.3  Unwanted content transformations . . . . . . . . . . . . .   9
   2.2.4  Corrupted content  . . . . . . . . . . . . . . . . . . . .   9
   2.2.5  Threats to message structure integrity . . . . . . . . . .   9
   2.2.6  Granularity of protection  . . . . . . . . . . . . . . . .   9
   2.2.7  Risks of hop-by-hop protection . . . . . . . . . . . . . .  10
   2.2.8  Threats to integrity of complex data . . . . . . . . . . .  10
   2.2.9  Denial of Service (DoS)  . . . . . . . . . . . . . . . . .  11
   2.2.10 Tracing and notification information . . . . . . . . . . .  11
   3.     Threats to out-of-band data  . . . . . . . . . . . . . . .  12
   3.1    Threats that endanger OPES data flow . . . . . . . . . . .  12
   3.2    Inaccurate Accounting Information  . . . . . . . . . . . .  12
   3.3    OPES service request repudiation . . . . . . . . . . . . .  13
   3.4    Exposure of private information  . . . . . . . . . . . . .  13
   3.5    Inconsistent privacy policy  . . . . . . . . . . . . . . .  13
   3.6    Exposure of privacy preferences  . . . . . . . . . . . . .  13
   3.7    Exposure of security settings  . . . . . . . . . . . . . .  13
   3.8    Improper enforcement of privacy and security policy  . . .  14
   4.     Security Considerations  . . . . . . . . . . . . . . . . .  15
          References . . . . . . . . . . . . . . . . . . . . . . . .  16
          Authors' Addresses . . . . . . . . . . . . . . . . . . . .  16
   A.     Acknowledgements . . . . . . . . . . . . . . . . . . . . .  18
          Full Copyright Statement . . . . . . . . . . . . . . . . .  19















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1. Introduction

   The Open Pluggable Edge Services (OPES) [1]  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.  The OPES processor can distribute
   the responsibility of service execution by communicating and
   collaborating with one or more remote callout servers.  The details
   of the OPES architecture can be found in  [1].

   Security threats with respect to OPES can be viewed from different
   angles.  There are security risks that affect content consumer
   applications, and those that affect the data provider applications.
   These threats affect the quality and integrity of data that the
   applications either produce or consume.  On the other hand, the
   security risks can also be categorized into trust within the system
   (i.e.  OPES service providers) and protection of the system from
   threats imposed by outsiders such as hackers and attackers.  Insiders
   are those parties that are part of the OPES system.  Outsiders are
   those entities that are not participating in the OPES system.

   It is up to OPES service providers to verify the trust relationship
   between them, whereby intentional false information is tracked.
   Insiders can intentionally or unintentionally inflect harm and damage
   on the data consumer and data provider applications.  This can be
   through bad system configuration, execution of bad software or, if
   their networks are compromised, by hackers.

   Depending on the deployment scenario, the trust within the OPES
   system is based on a transitive trust between the data provider
   application, the OPES entities and the data consumer application.
   Threats to OPES entities can be at the OPES flow level and/or at the
   network level.

   In considering threats to the OPES system, the document will follow a
   threat analysis model that identifies the threats from the
   prospective of how it will affect the data consumer and the data
   provider applications.

   The main goal of this document is threat discovery and analysis.  The
   document does not specify or recommend any solutions.  Proposed
   solutions are viewed as illustrations of the nature of threats.

   It is important to mention that the OPES architecture has many
   similarities with other so called overlay networks, specifically web
   caches and content delivery networks (CDN) (see [2] , [4] ).  This



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   document focuses on threats that are introduced by the existence of
   the OPES processor and callout servers.  Security threats specific to
   content services that do not use the OPES architecture are considered
   out-of-scope of this document.  However, this document can be used as
   input when considering security implications for web caches and CDNs.

   The document is organized as follows: Section 2 discusses threats to
   OPES data flow on network and application level, section 3 discusses
   threats to other parts of the system and section 4 discusses problems
   related to the cryptographic data protection paying special attention
   to the hop-by-hop versus end-to-end protection.








































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2. OPES Data Flow Threats

   Threats to OPES data flow can affect the data consumer and data
   provider applications.  At the OPES flow level, threats can occur at
   Policy Enforcement Points and Policy Decision Points [3]  and along
   the OPES flow path where networks elements are used to process the
   data.

   A serious problem is posed by the very fact that the OPES
   architecture is based on widely adopted protocols (HTTP is used as an
   example).  The architecture document specifically requires that "the
   presence of an OPES processor in the data request/response flow SHALL
   NOT interfere with the operations of non-OPES aware clients and
   servers".  This greatly facilitates OPES deployment but on the other
   hand a vast majority of clients (browsers) will not be able to
   exploit any safeguards added as a base protocol extensions.

   In reality active investigative actions are not feasible for the
   regular end user (Where this content comes from? Can I get it another
   way? What is the difference? Is it legitimate?).  Even if there are
   facilities and technical expertise present to pursue these questions
   such thorough examination of each result is prohibitively expensive
   in terms of time and effort.  OPES-aware content providers may try to
   protect themselves by adding verification scripts and special page
   structures.  OPES-aware end users may use special tools.  In all
   other cases (non-OPES aware clients and servers) protection will rely
   on monitoring services and investigation of occasionally discovered
   accidents.

   OPES system poses a special danger as a possible base for classical
   man-in-the-middle attack.  One of the reasons why such attacks are
   relatively rare is difficulty in finding an appropriate base: a
   combination of a traffic interception point controlling consistent
   flow of data and an application codebase with sufficient performance
   to analyze and possible modify all passing data.  OPES processor
   perfectly meets this definition.  This calls for a special attention
   to protection measures at all levels of the system.

   Any break into an OPES processor or remote callout server can have a
   ripple effect on the integrity of the affected OPES services across
   all service providers that use the service.  To mitigate this threat
   appropriate security procedures and tools (e.g., a firewall) should
   be applied.

   Specific threats can be at the network level and at OPES data flow
   level.





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2.1 OPES Flow Network Level Threats

   OPES processor and callout servers are susceptible to network level
   attacks from outsiders or from the networks of other OPES service
   providers (i.e.  if the network of a contracted OPES service is
   compromised).

   OPES architecture is based on common application protocols that do
   not provide strong guarantees of privacy, authentication, or
   integrity.  The IAB considerations [4]  require that the IP address
   of an OPES processor be accessible to data consumer applications at
   the IP level.  This exposes the OPES processor including remote
   callout servers to network level attacks.  Use of TCP/IP as network
   level protocol makes OPES processors subject to many known attacks,
   like IP spoofing and session stealing.

   The OPES system is also susceptible to a number of security threats
   that are commonly associated with network infrastructure.  These
   threats include snooping, denial of service, sabotage, vandalism,
   industrial espionage, theft of service and inadequate system
   configuration that leaves unneeded ports and services open to the
   public.

   There are best practice solutions to mitigate network level threats.
   It is recommended that the security of the OPES entities at the
   network level be enhanced using known techniques and methods that
   minimize the risks of IP spoofing, snooping, denial of service and
   session stealing.

   In the following subsections we take a more detailed look at these
   threats and potential resulting harm.

2.1.1 OPES device spoofing

   A malicious node could send false information about itself
   masquerading as an OPES device.  Alternatively, despite the presence
   of a genuine OPES device which has been authenticated, the actual
   data transformation could be performed in a malicious colocated
   callout server which is resident in the same administrative domain as
   the OPES device.  Furthermore, the malicious node could force the
   consumer or producer to use the services of a malicious OPES
   processor, which might render undesired or very expensive
   transformation services.

   As a consequence, the malicious device would be able to eavesdrop on
   all traffic between the end-systems.  In addition, unexpected and
   undesirable data transformation by the malicious processor or callout
   server would result.  Finally, the malicious entity, that



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   successfully spoofs an OPES processor (or callout server), may refuse
   to forward the legitimate traffic to the content consumers, resulting
   in a Denial-of-Service attack.

2.1.2 Remote callout server spoofing

   Similar to the threat described in 2.1.1, a malicious node could
   masquerade as a remote callout server.  Despite the presence of an
   authenticated OPES device, the malicious data transformation could be
   performed in a remote callout server.

   The effect of having such a malicious remote callout server is very
   similar to those produced by having a malicious OPES device or
   colocated callout server (see 2.1.1).

2.1.3 Session Hijacking

   If a TCP/IP session is hijacked by an attacker, it would be possible
   for the hijacker to compromise the integrity of content on an OPES
   processor.

2.1.4 Threats to data confidentiality (eavesdropping)

   An eavesdropper is typically capable of snooping on fields within
   messages in transit.  Using various eavesdropping techniques, he may
   be able to garner various kinds of information including topology/
   location/IP addresses etc.  that may not be desirable to divulge.  He
   also may be able to eavesdrop on the content messages being delivered
   to the consumer.  Furthermore, to ensure secure data traversal from
   the provider to the consumer, authentication information must be
   exchanged between the provider and the consumer.  When such security
   related information has to traverse through an OPES system, it is
   also subject to the threat of being eavesdropped on by the malicious
   entity.

2.1.5 Denial-of-Service (DoS)

   The processor or the callout server can be overloaded by spurious
   service requests issued by a malicious node, which denies the legal
   data traffic the necessary resources to render service.  The
   resources include CPU cycles, memory, network interfaces, etc.  A
   Denial-of-Service attack can be selective, generic or random in terms
   of which communication streams are affected.

   Distributed DoS is also possible when an attacker successfully
   directs multiple nodes over the network to initiate spurious service
   requests to an OPES processor  (or call-out server) simultaneously.




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2.1.6 Threats to network robustness

   if OPES implementation does violate end-to-end addressing principles,
   it could endangers the Internet infrastructure by complicating
   routing and connection management.  If it does not use flow-control
   principles for managing connections, or if it interferes with end-to-
   end flow control of connections that it did not originate, then it
   could causing Internet congestion.

   An implementation that violates IAB requirement of explicit IP level
   addressing (for example by adding OPES functional capabilities to an
   interception proxy) may defeat many protective mechanisms and
   safeguards built into the OPES architecture.

2.2 OPES Flow Application Level Threats

   At the content level threats to the OPES system can come from
   outsiders or insiders.  The threat from outsiders is always
   intentional.  Threats from insiders can be intentional or due to
   inappropriate implementations such as programming and configuration
   errors that result in bad system behavior.

   Application level problems and threats to the OPES systems are
   discussed below:

2.2.1 Unauthorized OPES entities

   Although one party authorization is mandated by the OPES architecture
   such authorization  occurs out-of-band.  Discovering the presence of
   an OPES entity and verifying authorization requires special actions
   and may present a problem.

   Adding notification and authorization information to the data
   messages (by using base protocol extensions) may help, especially if
   the UserAgent software is aware of such extensions.

2.2.2 Unauthorized actions of legitimate OPES entities

   According to the OPES architecture the authorization is not tightly
   coupled with specific rules and procedures triggered by the rules.
   Even if a requirement to approve each particular rule and procedure
   was set it looks at least impractical if not impossible to request
   such a permission from the end user.  The authorization is given
   essentially for the class of transformations.  The actual rules and
   triggered procedures may (maliciously or due to a programming error)
   perform actions that they are not authorized for.





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2.2.3 Unwanted content transformations

   An authorized OPES service may perform actions that do not adhere to
   the expectations of the party that gave the authorization for the
   service.  Examples may include ad flooding by a local ad insertion
   service or use of inappropriate policy by a content filtering
   service.

   On the other hand an OPES entity acting on behalf of one party may
   perform transformations that another party deems inappropriate.
   Examples may include replacing ads initially inserted by the content
   provider or applying filtering transformations that change the
   meaning of the text.

2.2.4 Corrupted content

   The OPES system may deliver outdated or otherwise distorted
   information due to programming problems or as a result of malicious
   attacks.  For example, a compromised server, instead of performing
   OPES service, may inject a bogus content.  Such actions may be an act
   of cyber-vandalism (including virus injection) or intentional
   distribution of misleading information (such as manipulations with
   financial data).

   A compromised OPES server or malicious entity in the data flow may
   introduce changes specifically intended to cause improper actions in
   the OPES server or callout server.  These changes may be in the
   message body, headers or both.  This type of threat is discussed in
   more detail below.

2.2.5 Threats to message structure integrity

   An OPES server may add, remove or delete certain headers in a request
   and/or response message (for example to implement additional privacy
   protection or assist in content filtering).  Such changes may violate
   end-to-end integrity requirements or defeat services that use
   information provided in such headers (for example some local
   filtering services or reference-based services).


2.2.6 Granularity of protection

   OPES services have implicit permission to modify content.  However,
   the permissions generally apply only to portions of the content, for
   example, URL's between particular HTML tags, or text in headlines, or
   URL's matching particular patterns.  In order to express such
   policies, one must be able to refer to portions of messages and to
   detect modifications to message parts.



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   Because there is currently very little support for policies that are
   expressed in terms of message parts, it will be difficult to
   attribute any particular modification to a particular OPES processor,
   or to automatically detect policy violations.

   A fine-grained policy language should be devised, and it could be
   enforced using digital signatures.  This would avoid the problems
   inherent in hop-by-hop data integrity measures.

2.2.7 Risks of hop-by-hop protection

   OPES services cannot be applied to data protected with end-to-end
   encryption methods because, by definition, the decryption key cannot
   be shared with opes processors.  This means that if the endpoint
   policies permit OPES services, the data must either be transmitted
   without confidentiality protections or else with an alternative to
   end-to-end encryption: hop-by-hop encryption.  In the latter case,
   all the parties in the OPES processing path must understand the
   encryption requirement and negotiate encrypted connections with their
   OPES partners.

   Hop-by-hop protection is less effective than end-to-end protection,
   because any processor in the path can violate the confidentiality or
   integrity of the data without detection.

   If a pair of processors in the delivery path use weak cryptography or
   manage keys poorly, there is a danger of data leakage.  For this
   reason, different cryptographic keys should be used for each leg of
   the data stream.

   Even if the data is not confidential, one might desire some checks on
   data integrity, to avoid modifications by unauthorized parties.  The
   comments above apply to the use of end-to-end integrity, if it is
   based on shared-key cryptography.  Again, it should be possible to
   use hop-by-hop data integrity to protect data as it moves between
   protection domains.

   Currently there is no method to signal hop-by-hop encryption
   requirements.  Either this must be added to the application protocol,
   or OPES must define its own signaling protocol, or all OPES traffic
   MUST ALWAYS be encrypted.

2.2.8 Threats to integrity of complex data

   The OPES system may violate data integrity by applying inconsistent
   transformations to interrelated data objects or references within the
   data object.  Problems may range from a broken reference structure
   (modified/missing targets, references to wrong locations or missing



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   documents) to deliberate replacement/deletion/insertion of links that
   violate intentions of the content provider.


2.2.9 Denial of Service (DoS)

   The data consumer application may not be able to access data if the
   OPES system fails for any reason.

   A malicious or malfunctioning node may be able to block all traffic.
   The data traffic destined for the OPES processor  (or callout server)
   may not be able to use the services of the OPES device.  The DoS may
   be achieved by preventing the data traffic from reaching the
   processor  or the callout server.

2.2.10 Tracing and notification information

   Inadequate or vulnerable implementation of the tracing and
   notification mechanisms may defeat safeguards built into the OPES
   architecture.

   Tracing and notification facilities may become a target of malicious
   attack.  Such an attack may  create problems in discovering and
   stopping other attacks.

   The absence of a standard for tracing and notification information
   may present an additional problem.  This information is produced and
   consumed by the independent entities (OPES servers/user agents/
   content provider facilities).  This calls for a set of standards
   related to each base protocol in use.





















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3. Threats to out-of-band data

   The OPES architecture separates a data flow from a control
   information flow (loading rulesets, trust establishment, tracing,
   policy propagation, etc.).  There are certain requirements set but no
   specific mechanism is prescribed.  This gives more flexibility for
   implementations but creates more burden for implementors and
   potential customers to ensure that specific implementation meets all
   requirements for data security, entity authentication and action
   authorization.

   In addition to performing correct actions on the OPES data flow any
   OPES implementation has to provide an adequate mechanism to satisfy
   requirements for out-of-band data and signaling information
   integrity.

   Whatever the specific mechanism may be, it inevitably becomes subject
   to multiple security threats and possible attacks.  The way the
   threats and attacks may be realized depends on implementation
   specifics but the resulting harm generally falls into two categories:
   threats to OPES data flow and threats to data integrity.

   The specific threats are:

3.1 Threats that endanger OPES data flow

   Any weakness in security, authentication and authorization mechanism
   implementation may open a possibility to threats and attacks
   described in section 2.

   An OPES system implementation should address all these threats and
   prove its robustness and ability to withstand malicious attacks or
   networking and programming problems.

3.2 Inaccurate Accounting Information

   Collecting and reporting accurate accounting data may be vital when
   OPES servers are used to extend a business model of content provider,
   service provider or as a basis  for third party service.  Ability to
   collect and process accounting data is an important part of OPES
   system functionality.  This functionality may be challenged by
   distortion or destruction of base accounting data (usually logs),
   processed accounting data, accounting parameters and reporting
   configuration.

   As a result a data consumer may be inappropriately charged for
   viewing content that was not successfully delivered, or a content
   provider or independent OPES services provider may not be compensated



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   for the services performed.

   OPES system may use accounting information to distribute resources
   between different consumers or limit resource usage by a specific
   consumer.  In this case an attack on accounting system (by distortion
   of data or issuing false configuration commands) may result in
   incorrect resource management and DoS by artificial resource
   starvation.

3.3 OPES service request repudiation

   An entity (producer or consumer) that is authorized to make a certain
   request to the OPES processor  claims, later, that it did not make
   that request.  As a result an OPES entity may be held liable for
   unauthorized changes to the data flow.


3.4 Exposure of private information

   The OPES system may inadvertently or maliciously expose private
   information such as (passwords, buying patterns, page views, and
   credit card numbers) of the data consumer.  Logs and accounting data
   may also contain sensitive private information.


3.5 Inconsistent privacy policy

   The OPES entities may have privacy policy not consistent with end
   user or content provider expectations.

   Privacy related problems may be further complicated if OPES entities,
   content providers and end users belong to different jurisdictions
   with different requirements and different levels of legal protection.
   As a result the end user may not be aware that he/she does not have
   the expected  legal protection.  The content provider may be exposed
   to legal risks due to a failure to comply with regulation which he is
   not even aware of.

3.6 Exposure of privacy preferences

   The OPES system may inadvertently or maliciously expose end user
   privacy settings and requirements.

3.7 Exposure of security settings

   There are risks that the OPES system may expose end user security
   settings when handling the request and responses.




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3.8 Improper enforcement of privacy and security policy

   OPES entities are part of the content distribution system and as such
   take on certain obligations to support security and privacy policies
   mandated by content producer and/or end user.  However there is a
   danger that these policies are not properly implemented and enforced.
   The data consumer application may not be aware that its protections
   are no longer in effect.

   Privacy and security related parts of the systems are most often
   targeted by malicious attacks and ability to withstand such attacks
   is of paramount importance.







































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4. Security Considerations

   This document discusses multiple security and privacy issues related
   to the OPES services.















































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References

   [1]  A. Barbir et. al, "An Architecture for Open Pluggable Edge
        Services (OPES)", Internet-Draft: http://www.ietf.org/internet-
        drafts/draft-ietf-opes-architecture-03.txt, Aug 2002.

   [2]  A. Barbir et. al, "OPES Use Cases and Deployment Scenarios",
        Internet-Draft: http://www.ietf.org/internet-drafts/draft-ietf-
        opes-architecture-02.txt, July 2002.

   [3]  A. Barbir et. al, "Requirements for Policy, Authorization  and
        Enforcement of OPES Services", Internet-Draft: http://
        www.ietf.org/internet-  drafts/draft-ietf-opes-authorization-
        00.txt , October  2002.

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

   [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.

   [6]  Cooper, I., "Internet Web Replication and Caching Taxonomy", RFC
        3040, January 2001.


Authors' Addresses

   Abbie Barbir
   Nortel Networks
   3500 Carling Avenue
   Nepean, Ontario  K2H 8E9
   Canada

   Phone: +1 613 763 5229
   EMail: abbieb@nortelnetworks.com


   Oskar Batuner
   Independent consultant



   EMail: batuner@attbi.com






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   Tat Chan
   Nokia
   5 Wayside Road
   Burlington, MA  01803
   USA

   EMail: Tat.Chan@nokia.com


   Bindignavile Srinivas
   Nokia
   5 Wayside Road
   Burlington, MA  01803
   USA

   EMail: bindignavile.srinivas@nokia.com


   Hilarie Orman
   Purple Streak Development



   Phone:
   EMail: ho@alum.mit.edu


























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Appendix A. Acknowledgements

   The authors gratefully acknowledge the contributions of: Markus
   Hofmann

   TBD













































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Full Copyright Statement

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