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Architecture for Chaining Legacy Layer 4-7 Service Functions
draft-dunbar-sfc-legacy-l4-l7-chain-architecture-02

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Linda Dunbar , Ron Parker , Ning So , Donald E. Eastlake 3rd
Last updated 2014-02-08
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draft-dunbar-sfc-legacy-l4-l7-chain-architecture-02
Network working group                                         L. Dunbar
Internet Draft                                                   Huawei
Intended status: Informational                               Ron Parker
Expires: August 2014                                  Affirmed Networks
                                                     I. Smith; S. Majee
                                                            F5 Networks
                                                                  N. So
                                                    Tata Communications
                                                        Donald Eastlake
                                                                 Huawei
                                                       February 7, 2014

       Architecture for Chaining Legacy Layer 4-7 Service Functions
          draft-dunbar-sfc-legacy-l4-l7-chain-architecture-02.txt

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Copyright Notice

   Copyright (c) 2014 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
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   warranty as described in the Simplified BSD License.

Abstract

   This draft analyzes the issues associated with chaining existing
   Layer 4-7 service functions that are not aware of service
   encapsulation layers. This draft also examines the network
   architecture for chaining existing L4-L7 service functions. The
   intent is to identify optimal architecture for flexibly chaining
   existing Layer 4-7 functions to meet various service needs.

Table of Contents

   1. Introduction...................................................3
   2. Conventions used in this document..............................3
   3. Legacy Layer 4-7 Service Functions and Chaining................4
      3.1. Layer 4-7 Service Functions...............................4
      3.2. Service Functions Chaining for Wireless network...........4
   4. Architecture for Chaining Legacy Layer 4-7 Service Functions...6
      4.1. Service Function Forwarder for Layer 4-7 Service Functions6
      4.2. L4-L7 nodes connection to SFF Nodes.......................7
      4.3. Traffic Steering at SFF Nodes.............................7
   5. Challenges of Chaining L4-L7 Service Function..................9
      5.1. Challenge of Multiple Instances of a Service Function.....9
      5.2. Challenges of Layer 4-7 traffic Steering.................10
      5.3. Challenges of Service Chain Classification...............11
   6. Challenge of Service Chain from the Layer 7 Perspective.......12
   7. Conclusion and Recommendation.................................13
   8. Manageability Considerations..................................13
   9. Security Considerations.......................................13
   10. IANA Considerations..........................................13
   11. References...................................................14
      11.1. Normative References....................................14

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      11.2. Informative References..................................14
   12. Acknowledgments..............................................14

1. Introduction

   This draft analyzes the issues associated with chaining existing
   Layer 4-7 service functions that are not aware of service
   encapsulation layers. This draft also examines the network
   architecture for chaining existing L4-L7 service functions. The
   intent is to identify optimal architecture for flexibly chaining
   existing Layer 4-7 functions to meet various service needs.

2. 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].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.

   Chain Classifier: A component that performs traffic classification
   and potentially encodes a unique identifier or the SF MAP Index
   introduced by [SFC-Framework] to the packets. The unique identifier
   in the packets can be used by other nodes to associate the packets
   to a specific service chain and/or steer the packets to the
   designated service functions.

   DPI:              Deep Packet Inspection

   FW:               Firewall

   Layer 4-7 Service Function: Same as the Service Functions defined in
   [SFC-Problem] except that they don't have the Layer 2/3 forwarding
   capability and are not aware of the new service function header
   encapsulations. Many of existing Layer 4-7 service functions fall
   into this category. Exemplary functional modules include Firewall,
   Deep Packet Inspection (DPI), Encryption, Packet De-duplication,
   Compression, TCP Acceleration, NAT, and etc

   Layer 4-7 service functions can be instantiated on a standalone
   physical or virtual device, which is called "Service Node" by [SFC-
   Problem]. Layer 4-7 functions can also be embedded in another
   device, such as router/switch or other devices.

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3. Legacy Layer 4-7 Service Functions and Chaining

   Legacy Layer 4-7 service functions are the existing service
   functions that don't have Layer 2/3 forwarding capability and may
   not be aware of any new service encapsulation layers or overlay
   encapsulation layer being discussed in SFC WG.

3.1. Layer 4-7 Service Functions

   A Layer 4-7 service function performs certain action to the packets
   belonging to an end-to end flow.  The implementation of such service
   function can be either Proxy based or Packet Based, or a hybrid of
   both when more than one function is performed to the same packet
   flow.  Multiple service functions can be instantiated on a single
   service node as defined by [SFC-ARCH], or embedded in a L2/L3
   network node.

   o  Proxy based service functions: these service functions terminate
      original packets, may reassemble multiple packets, reopen a new
      connection, or formulate new packets based on the received
      packets.

   o  Packet based service functions: these service functions maintain
      original packets, i.e. they don't make changes to packets
      traversed through except possibly making changes to metadata
      attached to the packet or the packet's outer header fields.

   Some Layer 4-7 service functions might have intelligence to choose
   different subsequent service functions and pass data packets
   directly to the selected service functions. However, most existing
   Layer 4-7 service functions don't have this capability.

3.2. Service Functions Chaining for Wireless network

   [SFC-MobileNetwork] and [SFC-use-cases] have provided examples of
   service chain in mobile network. In particular, the P-GW/PCEF (per
   3GPP terminology) determines the desired service treatment, i.e.
   desired sequence of service functions, to specific flows based on
   the policies from PCRF.

   The P-GW in the figure acts as the Service Chain Classification
   Node. P-GW separates the traffic into different categories (or
   flows) based on the policies from PCRF. The traffic in each category
   (or flow) is mapped to a unique interface (a physical or virtual

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   port) or a tunnel that is connected to the needed sequence of
   service functions.

                       |       Mobile backhaul Network
           +-----+     |          +---+---+
           |PCRF |     |          |Network|
           |     |  < ---- >      |Ctrller|
           +-----+     |          +----+--+
              |        |
              |        |
       +---------+  |  +--------+   +----+      +---------+
   -- >| P-GW    | --> |LB      |---| FW |-->   | Web     | ------>
       |         |  |  |        |   |    |      | Proxy   |
   --->|         |  |  +--------+   +----+      +---------+
   --->|         |  |  +---------+   +----+
   -- >|         | --> |Video    |---| FW |-->  ----------- ------>
       |   [PCEF]|  |  |Optimizer|   |    |
       |         |  |  +---------+   +----+
   --->|         |  |  +--------+   +-----+
   -- >|         | --> |SBC     |---| ACL |-->  ----------- ------>
       |         |  |  |        |   |     |
       +---------+  |  +--------+   +-----+

                 Figure 1 Service Chain for Mobile Network

   Here are some of the issues of service chain in wireless network:

   o  large number of permutations of service functions to be chained
      together

   o  The sequence of services functions applied to selective flows can
      change. Sometimes, the change may be triggered by some service
      functions on the chain, e.g. DPI. New service functions may need
      to be inserted; existing service functions may need to be removed
      or changed.

   o  The criteria for applying service functions can take combination
      of application classification, packet headers, and/or other
      factors. For example, the factors that have direct association
      with the packet flow include packet source address, destination
      address, TCP ports. The factors that do not have association with
      the packet flow include user/source location, account status,
      time of day, network condition, and etc.

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4. Architecture for Chaining Legacy Layer 4-7 Service Functions

4.1. Service Function Forwarder for Layer 4-7 Service Functions

   For chaining together legacy Layer 4-7 service functions, the
   Service Function Forwarder (SFF) defined by [SFC-Arch] has be a
   separate entity. The SFF can terminate service layer encapsulation
   on behalf of service functions/nodes that are not aware service
   layer encapsulation. There can be multiple SFF nodes in the Service
   Chain domains [SFC-Framework].

   Even though Layer 4-7 Service functions can be instantiated
   anywhere, it is not uncommon to have multiple service functions
   instantiated on nodes in close vicinity to a Service Function
   Forwarder node. The following figure depicts the architecture for
   chaining those Layer 4-7 service nodes that are not aware of service
   layer encapsulation. Each SFF is responsible for forwarding the
   traffic to their designated local service functions and for
   forwarding the traffic to the next hop SFF after the local service
   functions treatment.

                        |1  -----   |n        |21   ---- |2m
                    +---+---+   +---+---+   +-+---+   +--+-----+
                    | Ad    |   |Content|   |Video|   |Security|
                    |Insert |   | Opt   |   | Opt |   | App    |
                    +---+---+   +---+---+   +--+--+   +--+--+--+
                        :           :          :         :  :
                        :           :          :         :  :
                         \         /            \       /
       +--------------+   +--------+             +---------+
   -- >| Chain        | ->| SFF    |--------->   | SFF     | ---->
       |classifier    |   |Node-1  |             | Node-i  |
       +--------------+   +----+---+             +----+--+-+
                                 |--                  |  |
                                 V                    +--->
                            +--------+
                            | SN     |
                            |   -j   |----->
                            +--------+

            Figure 2 Chaining existing Layer 4-7 service nodes

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   The "Chain Classifier" node in the figure is to classify the
   traffic, encode a unique SF MAP Index [SFC-Framework] to packets or
   encapsulate the packets with the SFC header.

   The forwarding policies for data packets received by the SFF Nodes
   can be carried by the SFC header in the data packets or separate
   out-of-band messages from Chain Classier or external controllers.

   The SFF nodes can be standalone devices, or can be embedded within
   network forwarding nodes. Overlay tunnels are expected to connect
   the "SFF nodes" together.

4.2. L4-L7 nodes connection to SFF Nodes

   L4-L7 Service nodes can be connected to SFF nodes in various ways.
   The topology could be bump in a wire or one armed topology.

   o  A service function can be embedded in a SFF node (i.e. embedded
      in a router or a switch). In this case, the combined entity forms
      the SF node described in the [SFC-ARCH].

   o  A service node can be one hop away from a SFF node

      The one hop between the SFF node and the service node can be a
      physical link (e.g. Ethernet link). Under this scenario, there
      would be a Link Header, i.e. an outer MAC header, added to the
      data packets that meet the steering criteria.

      The one hop link can be a transparent link, i.e. no link address
      is added to the data packets on the link between the SFF node and
      Service node. I.e. the service nodes can apply treatment to data
      frames arrived at the ingress port regardless of the Link
      Destination address.

   o  A service node can be multiple hops away, such as when a service
      function is deployed in an on-net or private *aaS offering. Under
      this scenario, a tunnel is needed between the service node and
      the SFF node.

4.3. Traffic Steering at SFF Nodes

   The forwarding (or steering) policies for data packets received by
   the SFF Nodes can be carried by the SFC header in the data packets
   or via separate out-of-band messages from external controller(s) or
   the Chain Classifier. When using the out-of-band messages to carry

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   the steering policies to SFF nodes, the SF MAP Index in the data
   packets is used to correlate the steering policies for the data
   packets.

   The policies to steer traffic to their corresponding service
   functions or service function instances can change. Those steering
   policies can be dynamically updated by SFC Header or the out-of-band
   messages.

   Some service chains may require steering traffic to their
   corresponding Layer 4-7 functions based on Layer 1 (e.g. ingress
   port), Layer 2 or 3 fields of the data packets. Some service chains
   may require steering traffic to their Layer 4-7 service functions
   based on some higher layer fields in the data packets, i.e. Layer 4
   to Layer 7 fields.

   There are multiple types of traffic steering:

   o  Fixed header based forwarding: traffic steering based on header
      fields that have fixed position in the data packets:

       o  Forwarding based on Layer 2-3 header fields, such as MAC or
          IP Destination Address, Source Addresses, MPLS label, VLAN
          ID, or combination of multiple Layer 2-3 header fields.

       o  Forwarding based on Layer 4 header (TCP or UDP).

       o  QoS header based forwarding.

   o  Layer 7 based forwarding: traffic steering (or forwarding) based
      on the payload (L7) of data packets.

      Multiple data packets may carry some meaningful data, like one
      HTTP message. Under this scenario, multiple data packets have to
      be examined before meaningful data can be extracted for making
      Layer 7 based forwarding decision.

   o  Metadata based steering:  traffic steering (or forwarding) based
      on the identity of the initiating user, the UE model or type, the
      site name or FQDN, or network conditions (congestion,
      utilization, etc.).

      However those metadata might not necessarily be carried by each
      data packet due to extended bits required that can cause high
      probability of packet fragmentation. Those metadata can be
      dynamically passed down to steering nodes in some forms of
      steering policies from network controller(s).

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5. Challenges of Chaining L4-L7 Service Function

5.1. Challenge of Multiple Instances of a Service Function

   Each service function could have multiple instances, with some in
   close proximity and others far apart being attached to different
   Service Function Forwarder (SFF) nodes. In Network Function
   Virtualization (NFV) environment, there could be very large number
   of service function instances for each service function. NFV imposes
   higher chance of state or attachment change for service function
   instances due to virtual instances' creation/deletion/migration.

   From user's perspective, the order of service functions, e.g.
   Chain#1 {s1, s4, s6}, Chain#2{s4, s7}, is important, but very often
   which instance of the Service Function "s1" is selected for the
   Chain #1 is not. It is also possible that multiple instances of one
   service function can be reached by different network nodes. The
   actual instances selected for a service chain is called "Service
   Chain Instance Path".

   There are various policies that could be employed to select
   instances for service chain instance path.   The SFC WG should stay
   away from (or open to all possible ways of) specifying the way
   policy decisions are performed.

   Some Service Chain Classifier can specify exact service chain
   instance path. Under other scenarios where there is large number of
   instances per function, it should be acceptable for Service Chain
   classifier to only identify the chaining at function level and have
   another entity managing the detailed service instance path.

   When there is change to instances selected for a service chain,
   either in-band or out-of-band messages can be sent to the SFF nodes
   to update the steering policies dynamically.

   The downside with out-of-band messages is synchronization and race
   conditions. For a newly recognized flow, it is not scalable to
   expect the classifier node to queue the packets until the out-of-
   band notification is acknowledged by every Service Function
   Forwarder node. On the other hand, it is reasonable to use out-of-
   band messages to inform forwarding policies on SFF nodes if the
   forwarding policies can be pre-established before traffic arrives at
   the Classifier nodes, e.g. subscriber profile basis service chain
   instance path.

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                          |
                 +---+------+                +---+---+   +--+-----+
                 |controller|                |Service|   |Service |
                 |          |                |Func-1 |   |Func- m |
                 +---+------+                +----+--+   +--+--+--+
                    /    \   \                    :         /
                   /      \   +---------------+   :        /
                  /        \                   \  :       /
           +-----------+     +--------+         +---------+
       -- >|Classifier | --> |SFF     |------>  | SFF     | ------>
           |   node    |     |Node-1  |         | Node-2  |
           +-----------+     +--------+         +---------+

        Figure 3 Service Chain from Traffic Steering Point of View

   Some service functions make changes to data packets, such as NAT
   changing the address fields. If any of those fields are used in
   traffic steering along the service chain, the criteria can be
   different before and after those the service functions.

5.2. Challenges of Layer 4-7 traffic Steering

   Very often the criteria for steering flows to service functions are
   based on higher layer headers, such as TCP header, HTTP header, etc.

   Most of deployed switches/routers are very efficient in forwarding
   packets based on Layer 2 or Layer 3 headers, such as MAC/IP
   destination addresses, or VLAN/MPLS labels but have limited capacity
   for forwarding data packets based on higher layer header. As of
   today, differentiating data packets based on higher layer headers
   depends on ACLs (Access Control List field matching) or DPI, both of
   which are relatively expensive and extensive use of such facilities
   may limit the bandwidth of switches/routers.

   The Service Chain classification node introduced by [Boucadair-
   framework] and [SFC-ARCH] can alleviate the workload on large number
   of nodes in the network, including SFF nodes, from steering traffic
   based on higher layer fields.

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                         |1  -----   |n        |21   ---- |2m
                   +---+---+   +---+---+   +-+---+   +--+-----+
                   | Ad    |   |Content|   |Video|   |Security|
                   |Insert |   | Opt   |   | Opt |   | App    |
                   +---+---+   +---+---+   +--+--+   +--+--+--+
                       :           :          :         :  :
                       :           :          :         :  :
                        \         /            \       /
      +--------------+   +--------+             +---------+
   - >| Chain        | ->| SFF    |-------->    | SFF     | --->
      |classification|   |Node-1  |             | Node-2  |
      +--------------+   +--------+             +---------+

                 Figure 4 Service Chain Marking At Ingress

   A Service Chain Classification node can associate a unique Service
   Chain Label (e.g. Layer 2 or 3 Label) or SF MAP Index to the packets
   in the flow. Such a Layer 2 or 3 Label makes it easier for
   subsequent nodes along the flow path to steer the flow to the
   service functions specified by the flow's service chain.

   The network elements that have the Service Chain Classification
   Function are most likely network ingress edge nodes, such as
   Wireless Packet Gateway, Broadband Network Gateways, Cell Site
   Gateways, etc.

   In some situations, like service chain for wireless subscribers,
   many flows (i.e. subscribers) have common service chain
   requirements. Under those situations, the Service Chain
   classification Functional can mark multiple flows with the same
   service chain requirement using the same Layer 2 or 3 Label, which
   effectively aggregates those flows into one service chain.

   For service chains that are shared by a great number of flows, they
   can be pre-provisioned. For example, if VLAN ID=10 is the service
   chain that need to traverse "Service-1" at SFF Node #1 and "Service-
   3" at SFF Node #2, the steering policy for VLAN ID=10 can be
   dynamically changed by controllers.

5.3. Challenges of Service Chain Classification

   The policy for associating flows with their service chains can be
   complicated and could be dynamic due to different behavior
   associated with chains, balancing load among multiple instances for
   one service function, and instance failure.

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   For a chain of {FW, Header_enrichment, smart_node, Video_opt,
   Parental Control}, the video optimizer really needs to work on the
   response path. It may also use completely different encapsulation
   e.g. ICAP for example. There could be Smart-Node to further classify
   a particular part of the flow and bypass something, say the
   video_opt. Therefore, the classification done by the service chain
   classification nodes at the network entrance can't completely
   dictate the exact sequence of service functions.

   The Service Chain Classification node can encounter flows that don't
   match with any policies. There is a default policy that applies all
   statutorily required policies to the unknown flows.

   Multiple flows can share one service chain. The criteria to select
   flows to be associated with their service chain could be different.
   For example, for one service chain "A" shared by Flow X, Y, Z:

   o  Criteria for Flow X to the Service Chain "A" are TCP port

   o  Criteria for Flow Y to the Service Chain "A" are Destination
      Address

   o  Criteria for Flow Z to the Service Chain "A" are MPLS label.

6. Challenge of Service Chain from the Layer 7 Perspective

   From the Layer 7 perspective, the service chain can be much more
   complex. As shown in the figure below, the service functions to be
   chained can depend on the HTTP message request and reply. The
   service chain classification nodes may have to examine the whole
   HTTP message to determine the specific sequence of service functions
   for the flows. The HTTP message might have to be extracted from
   multiple data packets. Sometimes, the logic to steer traffic to
   chain of service functions might depend on the data retrieved from a
   database based on messages constructed from packets. The decision
   may depend on the HTTP response rather than the request, or it may
   depend on a particular sequence of request-response messages. The
   message handler may also alter the Layer 7 service chain based on
   hints or modification done by previous service function. HTTP based
   service function may insert HTTP header to add further criterion for
   service selection in the next round of classification.

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                        +----------+
       Client --------->(  Layer 7 )--------->  Internet
              <---------(  Message )<---------
                        (  Handler )
                --------(          )--------________
               /        +----------+        \
              /           /       \          \
             |1          |2        |3         |4
         +---+---+   +---+---+   +-+---+   +--+-----+
         | Ad    |   |Content|   |Video|   |Security|
         |Insert |   | Opt   |   | Opt |   | App    |
         +---+---+   +---+---+   +--+--+   +--+--+--+
             :           :          :         :  :
             :           :          :         :  :

                 Figure 5 Layer 7 Service Chain Complexity

7. Conclusion and Recommendation

   There are many service functions being deployed already in the
   network. Many of them are not capable to adapt to new service chain
   encapsulation layer.

   This document provides architecture framework for chaining those
   Layer 4-7 service functions that are not aware of new service layer
   encapsulation.

8. Manageability Considerations

   There currently exists no single management methodology to control
   the L2-4 packet-based forwarding device, the L4-7 service delivery
   device, and the L7+ application server.  Such unified management of
   configuration state is required for service function chaining to be
   a practical solution.

9. Security Considerations

   TBD

10. IANA Considerations

   This document requires no IANA actions. RFC Editor: Please remove
   this section before publication.

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11. References

11.1. Normative References

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

11.2. Informative References

   [Boucadair-framework] M. Boucadair, et al, "Differentiated Service
             Function Chaining Framework", < draft-boucadair-service-
             chaining-framework-00>; Aug 2013

   [SFC-Problem]  P. Quinn, et al, "Service Function Chaining Problem
             statement", <draft-quinn-sfc-problem-statement-02>, Dec 9,
             2013

   [SFC-Framework] M. Boucadair, et al, "Service Function Chaining:
             Framework & Architecture", < draft-boucadair-sfc-
             framework-00>; Oct 2013

   [SFC-Arch]  P. Quinn, et al, "Service Function Chaining (SFC)
             Architecture", < draft-quinn-nsc-arch-04>, Jan 2014.

    [NSH-Header]  P. Quinn, et al, "Network Service Header", < draft-
             quinn-nsh-01>, July 12, 2013

   [SC-MobileNetwork] W. Haeffner, N. Leymann, "Network Based Services
             in Mobile Network", IETF87 Berlin, July 29 2013

   [Application-SDN] J. Giacomonni, "Application Layer SDN", Layer 123
             ONF Presentation, Singapore, June 2013

   [SC-Use-Case]  Liu, et, al., "Service Chaining Use Cases", < draft-
             liu-service-chaining-use-cases-00>, Sept, 2013

12. Acknowledgments

   This draft has merged some sections from
   http://datatracker.ietf.org/doc/draft-parker-sfc-chain-to-path/.

   This draft has taken input from "Application Layer SDN" presentation
   given by John Giacomoni of F5 at Layer 123 conference. Thanks to
   Huang Shi Bi and Li Hong Yu for the valuable comments and
   suggestions.

   This document was prepared using 2-Word-v2.0.template.dot.

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Authors' Addresses

   Linda Dunbar
   Huawei Technologies
   1700 Alma Drive, Suite 500
   Plano, TX 75075, USA
   Phone: (469) 277 5840
   Email: ldunbar@huawei.com

   Ron Parker
   Affirmed Networks
   Acton, MA 01720
   USA
   Email: ron_parker@affirmednetworks.com

   Ian Smith
   F5 Networks
   Email: I.Smith@F5.com

   Sumandra Majee
   F5 Networks
   Email: S.Majee@F5.com

   Ning So
   Tata Communications
   Email: Ning.So@tatacommunications.com

   Donald Eastlake
   Huawei Technologies
   155 Beaver Street
   Milford, MA 01757 USA
   Phone: 1-508-333-2270
   Email: d3e3e3@gmail.com

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