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In: Edit-wait
Internet Engineering Task Force                              B. Campbell
Internet-Draft                                           S. Donovan, Ed.
Intended status: Informational                                    Oracle
Expires: January 7, 2016                                     JJ. Trottin
                                                          Alcatel-Lucent
                                                            July 6, 2015


                  Diameter Load Information Conveyance
                        draft-ietf-dime-load-00

Abstract

   This document defines a mechanism for sharing of Diameter load
   information.  RFC 7068 describes requirements for Overload Control in
   Diameter.  This includes a requirement to allow Diameter nodes to
   send "load" information, even when the node is not overloaded.  The
   Diameter Overload Information Conveyance (DOIC) solution describes a
   mechanism meeting most of the requirements, but does not currently
   include the ability to send load information.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on January 7, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and Abbreviations . . . . . . . . . . . . . . . .   3
   3.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   4.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Differences between Load and Overload information . . . .   4
     4.2.  How is Load Information Used? . . . . . . . . . . . . . .   5
   5.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Theory of Operation . . . . . . . . . . . . . . . . . . .   7
   6.  Solution Procedures . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Reporting Node Behavior . . . . . . . . . . . . . . . . .   8
       6.1.1.  Endpoint Reporting Node Behavior  . . . . . . . . . .   8
       6.1.2.  Agent Reporting Node Behavior . . . . . . . . . . . .   9
     6.2.  Receiving Node Behavior . . . . . . . . . . . . . . . . .   9
       6.2.1.  Endpoint Receiving Node Behavior  . . . . . . . . . .   9
       6.2.2.  Agent Receiving Node Behavior . . . . . . . . . . . .   9
     6.3.  Extensibility . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Attribute Value Pairs . . . . . . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Appendix A.  Topology Scenarios . . . . . . . . . . . . . . . . .  10
     A.1.  No Agent  . . . . . . . . . . . . . . . . . . . . . . . .  10
     A.2.  Single Agent  . . . . . . . . . . . . . . . . . . . . . .  10
     A.3.  Multiple Agents . . . . . . . . . . . . . . . . . . . . .  11
     A.4.  Linked Agents . . . . . . . . . . . . . . . . . . . . . .  12
     A.5.  Shared Server Pools . . . . . . . . . . . . . . . . . . .  13
     A.6.  Agent Chains  . . . . . . . . . . . . . . . . . . . . . .  13
     A.7.  Fully Meshed Layers . . . . . . . . . . . . . . . . . . .  14
     A.8.  Partitions  . . . . . . . . . . . . . . . . . . . . . . .  14
     A.9.  Active-Standby Nodes  . . . . . . . . . . . . . . . . . .  14
     A.10. Addition and removal of Nodes . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   [RFC7068] describes requirements for Overload Control in Diameter
   [RFC6733].  At the time of this writing, the DIME working group is
   working on the Diameter Overload Information Conveyance (DOIC)




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   mechanism [I-D.ietf-dime-ovli] .  As currently specified, DOIC
   fulfills some, but not all, of the requirements.

   In particular, DOIC does not fulfill Req 24, which requires a
   mechanism where Diameter nodes can indicate their current load, even
   if they are not currently overloaded.  DOIC also does not fulfill Req
   23, which requires that nodes that divert traffic away from
   overloaded nodes be provided with sufficient information to select
   targets that are most likely to have sufficient capacity.

   There are several other requirements in RFC 7068 that mention both
   overload and load information that are only partially fulfilled by
   DOIC.

   The DIME working group explicitly chose not to fulfill these
   requirements in DOIC due to several reasons.  A principal reason was
   that the working group did not agree on a general approach for
   conveying load information.  It chose to progress the rest of DOIC,
   and defer load information conveyance to a DOIC extension or a
   separate mechanism.

   This document defines a mechanism that addresses the load-related
   requirements from RFC 7068.

2.  Terminology and Abbreviations

   DOIC

      Diameter Overload Information Conveyance

   Load

      The relative capacity of a Diameter node.  A low value indicates
      that the Diameter node is under utilized.  A high value indicated
      that the node is closer to being fully utilized.

   Offered Load

      The actual traffic sent to the reporting node after overload
      abatement and routing decisions are made.

3.  Conventions Used in This Document

   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 [RFC2119].





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   RFC 2119 [RFC2119] interpretation does not apply for the above listed
   words when they are not used in all-caps format.

4.  Background

4.1.  Differences between Load and Overload information

   Previous discussions of how to solve the load-related requirements in
   [RFC7068] have shown that people have not had an agreed-upon concept
   of how "load" information differs from "overload" information.  While
   the two concepts are highly interrelated, in the opinion of the
   authors, there are two primary differences.  First, a Diameter node
   always has a load.  At any given time that load maybe effectively
   zero, effectively fully loaded, or somewhere in between.  In
   contrast, overload is an exceptional condition.  A node only has
   overload information when it is in an overloaded state.  Furthermore,
   the relationship between a node's load level and overload state at
   any given time may be vague.  For example, a node may normally
   operate at a "fully loaded" level, but still not be considered
   overloaded.  Another node may declare itself to be "overloaded" even
   though it might not be fully "loaded".

   Second, Overload information, in the form of a DOIC Overload Report
   (OLR) [I-D.ietf-dime-ovli] indicates an explicit request for action
   on the part of the reacting node.  That is, the OLR requests that the
   reacting node reduce the offered load -- the actual traffic sent to
   the reporting node after overload abatement and routing decisions are
   made -- by an indicated amount or to an indicated level.
   Effectively, DOIC provides a contract between the reporting node and
   the reacting node.

   In contrast, load is informational.  That is, load information can be
   considered a hint to the recipient node.  That node may use the load
   information for load balancing purposes, as an input to certain
   overload abatement techniques, to make inferences about the
   likelihood that the sending node becomes overloaded in the immediate
   future, or for other purposes.

   None of this prevents a Diameter node from deciding to reduce the
   offered load based on load information.  The fundamental difference
   is that an overload report requires that reduction.  It is also
   reasonable for a Diameter node to decide to increase the offered load
   based on load information.








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4.2.  How is Load Information Used?

   [RFC7068] contemplates two primary uses for load information.  Req 23
   discusses how load information might be used when performing
   diversion as an overload abatement technique, as described in
   [I-D.ietf-dime-ovli].  When a reacting node diverts traffic away from
   an overloaded node, it needs load information for the other
   candidates for that traffic in order to effectively load balance the
   diverted load between potential candidates.  Otherwise, diversion has
   a greater potential to drive other nodes into overload.

   Req 24 discusses how Diameter load information might be used when no
   overload condition currently exists.  Diameter nodes can use the load
   information to make decisions to try to avoid overload conditions in
   the first place.  Normal load-balancing falls into this category.  A
   node might also take other proactive steps to reduce offered load
   based on load information, so that the loaded node never goes into
   overload in the first place.

   If the loaded nodes are Diameter servers (or clients in the case of
   server-to-client transactions), both of these uses are most
   effectively accomplished by a Diameter node that performs server
   selection.  Typically, server selection is performed by a node (a
   client or an agent) that is an immediate peer of the server.
   However, there are scenarios (see Appendix A) where a client or proxy
   that is not the immediate peer to the selected servers performs
   server selection.  In this case, the client or proxy enforces the
   server selection by inserting a Destination-Host AVP.

      For example, a Diameter node (e.g. client) can use a redirect
      agent to get candidate destination host addresses.  The redirect
      agent might return several destination host addresses, from which
      the Diameter node selects one.  The Diameter node can use load
      information received from these hosts to make the selection.

   Just as load information can be used as part of server selection, it
   can also be used as input to the selection of the next-hop peer to
   which a request is to be routed.

      Editor's Note: One area that requires thought is how load
      information is used, if at all, in the presence of an overload
      report from the same Diameter node.  It might be that the load
      information from that Diameter node is ignored for the duration of
      the time that the overload report is in effect.  It might also be
      possible that the load information can aid in the diverting of
      non-abated requests targeted for the overloaded Diameter node.





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5.  Solution Overview

   The mechanism defined here for the conveyance of load information is
   similar in some says to the mechanism defined for DOIC and is
   different in other ways.

   As with DOIC, load information is conveyed by piggy-backing the load
   AVPs on existing Diameter applications.

   There are two primary differences.  First, there is no capability
   negotiation process for load.  The sender of the load information is
   sending it with the expectation that any supporting nodes will use it
   when making routing decisions.  If there are no nodes that support
   the load extension then the load information is ignored.

   The second big difference between DOIC and Load is that DOIC
   information is sent end-to-end.  The DOIC overload reports much
   remain in the message all the way from the reporting node to the node
   that is the target for the answer message.  For the Load mechanism,
   the load information is targeted for the peer of the sender of the
   Load AVPs.

      Editor's note: It is still being discussed whether a second type
      of Load report can be included that is the load of the end-point
      and is carried end-to-end.

   The Load report applies to an individual node.  The Diameter identity
   of the node to which it applies is included in the Load report.

      Note, this is necessary so that supporting nodes can determine if
      the load report came from a peer node.  If the identity is for a
      non peer node than the peer load report can be ignored.

   In addition to the identity of the node to which the report applies,
   the load report includes the relative load of the sending node.  This
   relative load is specified in a manner consistent with that defined
   for DNS SRV [RFC2782].

   The method for calculating the load value included in the load report
   is left as an implementation decision.

   The frequency for sending of load reports is also left as an
   implementation decision.  The sending node might choose to send load
   reports in all messages or it might choose to only send load reports
   when the load value has changed by some implementation specific
   value.  The important consideration is that all nodes needing the
   load information have a sufficiently accurate view of the nodes load.




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5.1.  Theory of Operation

   This section outlines how the Diameter load mechanism is expected to
   work.

   For this discussion, assume the following Diameter network
   configuration:

           ---A1---A3----S[1], S[2]...S[p]
          /   | \ /
         C    |  x
          \   | / \
           ---A2---A4----S[p+1], S[p+2] ...S[n]


                    Figure 1: Example Diameter Network

   Also assume that the request for a Diameter transaction takes the
   following path:

         C     A1     A4     S[n]
         |      |      |      |
         |----->|----->|----->|
         xxR     xxR    xxR



                      Figure 2: Request Message Path

   When sending the answer message, a sending node that supports the
   Diameter Load mechanism includes it's own load information in the
   answer message:

         C     A1     A4     S[n]
         |      |      |      |
         |      |      |<-----|
                        xxA(Load S[n])


                    Figure 3: Answer Message from S[n]

   If Agent A4 supports the Load mechanism then it will verify that the
   load information received was from its peer.  This is achieved by
   matching the identity included in the load information with the
   identity of the peer node from which the answer message was received.

   If the load information does not match then the agent will strip the
   load AVPs from the message.



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   If the identity included in the load information AVPs matches the
   identity of the peer from which the load information is received then
   Agent A4 stores the load information for S[n] in its routing tables.

   In all cases, A4 strips the load AVPs from the message.

   A4 then calculates its own load information and inserts load
   information AVPs in the message before sending the message to A1:

         C     A1     A4     S[n]
         |      |      |      |
         |      |<-----|      |
                 xxA(Load A4)


                     Figure 4: Answer Message from A4

   A1 follows the same procedures as A4, resulting in the following
   message sent to C:

         C     A1     A4     S[n]
         |      |      |      |
         |<-----|      |      |
          xxA(Load A1)


                     Figure 5: Answer Message from A1

   C follows the same procedure for determining if the Load report was
   received from the peer from which the report was sent and, when
   finding it does, stores the load information for use when making
   future routing decisions.

   The Load information received by all nodes is then used for routing
   of subsequent request messages.

      Editor's note: The above needs to be updated if there is agreement
      to support end-point Load reports.

6.  Solution Procedures

6.1.  Reporting Node Behavior

6.1.1.  Endpoint Reporting Node Behavior







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6.1.2.  Agent Reporting Node Behavior

6.2.  Receiving Node Behavior

6.2.1.  Endpoint Receiving Node Behavior

6.2.2.  Agent Receiving Node Behavior

6.3.  Extensibility

7.  Attribute Value Pairs

8.  Security Considerations

   Load information may be sensitive information in some cases.
   Depending on the mechanism, an unauthorized recipient might be able
   to infer the topology of a Diameter network from load information.
   Load information might be useful in identifying targets for Denial of
   Service (DoS) attacks, where a node known to be already heavily
   loaded might be a tempting target.  Load information might also be
   useful as feedback about the success of an ongoing DoS attack.

   Any load information conveyance mechanism will need to allow
   operators to avoid sending load information to nodes that are not
   authorized to receive it.  Since Diameter currently only offers
   authentication of nodes at the transport level, any solution that
   sends load information to non-peer nodes might require a transitive-
   trust model.

9.  IANA Considerations

   This document makes no requests of IANA.

10.  References

10.1.  Normative References

   [I-D.ietf-dime-ovli]
              Korhonen, J., Donovan, S., Campbell, B., and L. Morand,
              "Diameter Overload Indication Conveyance", draft-ietf-
              dime-ovli-03 (work in progress), July 2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6733]  Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
              "Diameter Base Protocol", RFC 6733, October 2012.




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   [RFC7068]  McMurry, E. and B. Campbell, "Diameter Overload Control
              Requirements", RFC 7068, November 2013.

10.2.  Informative References

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

Appendix A.  Topology Scenarios

   This section presents a number of Diameter topology scenarios, and
   discusses how load information might be used in each scenario.
   Nothing in this section should be construed to mean that a given
   scenario is in scope for this effort, or even a good idea.  Some
   scenarios might be considered as not relevant in practice and
   subsequently discarded.

A.1.  No Agent

   Figure 6 shows a simple client-server scenario, where a client picks
   from a set of candidate servers available for a particular realm and
   application.  The client selects the server for a given transaction
   using the load information received from each server.

       ------S1
      /
     C
      \
       ------S2


                  Figure 6: Basic Client Server Scenario

      Open Issue: Will a Diameter node include potential peers that it
      is not currently connected to as part of the candidate set?  It is
      unlikely the client would have load information from peers that it
      is not currently connected to.

      Note: The use of dynamic connections needs to be considered.

A.2.  Single Agent

   Figure 7 shows a client that sends requests to an agent.  The agent
   selects the request destination from a set of candidate servers,
   using load information received from each server.  The client does
   not need to receive load information, since it does not select
   between multiple agents.



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            ------S1
           /
     C----A
           \
            ------S2


                      Figure 7: Simple Agent Scenario

A.3.  Multiple Agents

   Figure 8 shows a client selecting between multiple agents, and each
   agent selecting from multiple servers.  The client selects an agent
   based on the load information received from each agent.  Each agent
   selects a server based on the load information received from its
   servers.

   This scenario adds a complication that one set of servers may be more
   loaded than the other set.  If, for example, S4 was the least loaded
   server, C would need to know to select agent A2 to reach S4.  This
   might require C to receive load information from the servers as well
   as the agents.  Alternatively, each agent might use the load of its
   servers as an input into calculating its own load, in effect
   aggregating upstream load.

   Similarly, if C sends a host-routed request [I-D.ietf-dime-ovli], it
   needs to know which agent can deliver requests to the selected
   server.  Without some special, potentially proprietary, knowledge of
   the topology upstream of A1 and A2, C would select the agent based on
   the normal peer selection procedures for the realm and application,
   and perhaps consider the load information from A1 and A2.  If C sends
   a request to A1 that contains a Destination-Host AVP with a value of
   S4, A1 will not be able to deliver the request.

             -----S3
            /
       ---A1------S1
      /
     C
      \
       ---A2------S2
            \
             ---- S4


                   Figure 8: Multiple Agents and Servers





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A.4.  Linked Agents

   Figure 9 shows a scenario similar to that of Figure 8, except that
   the agents are linked, so that A1 can forward a request to A2, and
   vice-versa.  Each agent could receive load information from the
   linked agent, as well as its connected servers.

   This somewhat simplifies the complication from Figure 8, due to the
   fact that C does not necessarily need to choose a particular agent to
   reach a particular server.  But it creates a similar question of how,
   for example, A1 might know that S4 was less loaded than S1 or S3.
   Additionally, it creates the opportunity for sub-optimal request
   paths.  For example [C,A1,A2,S4] vs. [C,A2,S4].

   A likely application for linked agents is when each agent prefers to
   route only to directly connected servers and only forwards requests
   to another agent under exceptional circumstances.  For example, A1
   might not forward requests to A2 unless both S1 and S3 are
   overloaded.  In this case, A1 might use the load information from S1
   and S3 to select between those, and only consider the load
   information from A2 (and other connected agents) if it needs to
   divert requests to different agents.

              -----S3
             /
        ---A1------S1
      /    |
     C     |
      \    |
        ---A2------S2
             \
              ---- S4


                          Figure 9: Linked Agents

   Figure 10 is a variant of Figure 9.  In this case, C1 sends all
   traffic through A1 and C2 sends all traffic through A2.  By default,
   A1 will load balance traffic between S1 and S3 and A2 will load
   balance traffic between S2 and S4.

   Now, if S1 S3 are significantly more loaded than S2 S4, A1 may route
   some C1 traffic to A2.  This is non optimal path but allows a better
   load balancing between the servers.  To achieve this, A1 needs to
   receive some load info from A2 about S2/S4 load.






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              -----S3
             /
     C1----A1------S1
           |
           |
           |
     C2----A2------S2
             \
              ---- S4


                         Figure 10: Linked Agents

A.5.  Shared Server Pools

   Figure 11 is similar to Figure 9, except that instead of a link
   between agents, each agent is linked to all servers.  (The links to
   each set of servers should be interpreted as a link to each server.
   The links are not shown separately due to the limitations of ASCII
   art.)

   In this scenario, each agent can select among all of the servers,
   based on the load information from the servers.  The client need only
   be concerned with the load information of the agents.


       ---A1---S[1], S[2]...S[p]
      /     \ /
     C       x
      \     / \
       ---A2---S[p+1], S[p+2] ...S[n]


                      Figure 11: Shared Server Pools

A.6.  Agent Chains

   The scenario in Figure 12 is similar to that of Figure 8, except
   that, instead of the client possibly needing to select an agent that
   can route requests to the least loaded server, in this case A1 and A2
   need to make similar decisions when selecting between A3 or A4.  As
   the former scenario, this could be mitigated if A3 and A4 aggregate
   upstream loads into the load information they report downstream.








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       ---A1---A3----S[1], S[2]...S[p]
      /   | \ /
     C    |  x
      \   | / \
       ---A2---A4----S[p+1], S[p+2] ...S[n]


                          Figure 12: Agent Chains

A.7.  Fully Meshed Layers

   Figure 13 extends the scenario in Figure 11 by adding an extra layer
   of agents.  But since each layer of nodes can reach any node in the
   next layer, each node only needs to consider the load of its next-hop
   peer.

       ---A1---A3---S[1], S[2]...S[p]
      /   | \ / |\ /
     C    |  x  | x
      \   | / \ |/ \
       ---A2---A4---S[p+1], S[p+2] ...S[n]


                           Figure 13: Full Mesh

A.8.  Partitions

   A Diameter network with multiple is said to be "partitioned" when
   only a subset of available servers can server a particular realm-
   routed request.  For example, one group of servers may handle users
   whose names start with "A" through "M", and another group may handle
   "N" through "Z".

   In such a partitioned network, nodes cannot load-balance requests
   across partitions, since not all servers can handle the request.  A
   client, or an intermediate agent, may still be able to load-balance
   between servers inside a partition.

A.9.  Active-Standby Nodes

   The previous scenarios assume that traffic can be load balanced among
   all peers that are eligible to handle a request.  That is, the peers
   operate in an "active-active" configuration.  In an "active-standby"
   configuration, traffic would be load-balanced among active peers.
   Requests would only be sent to peers in a "standby" state if the
   active peers became unavailable.  For example, requests might be
   diverted to a stand-by peer if one or more active peers becomes
   overloaded.



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Internet-Draft              Abbreviated Title                  July 2015


A.10.  Addition and removal of Nodes

   When a Diameter node is added, the new node will start by advertising
   its load.  Downstream nodes will need to factor the new load
   information into load balancing decisions.  The downstream nodes
   should attempt to ensure a smooth increase of the traffic to the new
   node, avoiding an immediate spike of traffic to the new node.  It
   should be determined if this use case is in the scope of the load
   control mechanism.

   When removing a node in a controlled way (e.g. for maintenance
   purpose, so outside a failure case), it might be appropriate to
   progressively reduce the traffic to this node by routing traffic to
   other nodes.  Simple load information (load percentage) would be not
   sufficient.  It should be determined if this use case is in the scope
   of the load control mechanism.

Authors' Addresses

   Ben Campbell
   Oracle
   7460 Warren Parkway # 300
   Frisco, Texas  75034
   USA

   Email: ben@nostrum.com


   Steve Donovan (editor)
   Oracle
   7460 Warren Parkway # 300
   Frisco, Texas  75034
   United States

   Email: srdonovan@usdonovans.com


   Jean-Jacques Trottin
   Alcatel-Lucent
   Route de Villejust
   91620 Nozay
   France

   Email: jean-jacques.trottin@alcatel-lucent.com







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