BIER                                                     P. Thubert, Ed.
Internet-Draft                                                     Cisco
Intended status: Standards Track                               T. Eckert
Expires: September 4, 2018                                        Huawei
                                                              Z. Brodard
                                                     Ecole Polytechnique
                                                                H. Jiang
                                                        Telecom Bretagne
                                                           March 3, 2018

   BIER-TE extensions for Packet Replication and Elimination Function
                             (PREF) and OAM


   This specification extends Bit Index Explicit Replication - Traffic
   Engineering (BIER-TE) forwarding to support in the data plane the
   DetNet Packet Replication and Elimination Functions (PREF).  It also
   provides traceability of links/adjacencies where replication and loss
   happen, in a manner that is agnostic to the forwarding 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 September 4, 2018.

Copyright Notice

   Copyright (c) 2018 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

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   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   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 . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  On BIER - Traffic Engineering . . . . . . . . . . . . . . . .   3
   4.  BIER-TE-based Replication and Elimination Control . . . . . .   4
   5.  Elimination Function (Normative)  . . . . . . . . . . . . . .   9
   6.  Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .  12
   8.  Security considerations . . . . . . . . . . . . . . . . . . .  12
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     11.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Deterministic Networking (DetNet) [I-D.ietf-detnet-problem-statement]
   provides a capability to carry unicast or multicast data flows for
   real-time applications with extremely low data loss rates and known
   upper bound maximum latency [I-D.ietf-detnet-architecture].

   DetNet applies to multiple environments where there is a desire to
   replace a point to point serial cable or a multidrop bus by a
   switched or routed infrastucture, in order to scale, lower costs, and
   simplify management.  One classical use case is found in particular
   in the context of the convergence of IT with Operational Technology
   (OT), also referred to as the Industrial Internet.  But there are
   many others use cases [I-D.ietf-detnet-use-cases], for instance in in
   professional audio and video, automotive, radio fronthauls, etc..

   The DetNet data plane alternatives [I-D.dt-detnet-dp-alt] studies the
   applicability of existing and emerging dataplane techniques that can
   be leveraged to enable DetNet properties in IP networks.  One
   critical feature in the dataplane is traceability, the capability to
   control the activity of intermediate nodes on a packet.  For
   instance, if Replication and Elimination is applied to a packet, then
   it is desirable to determine which node performed a certain copy of

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   that packet that is circulating in the network.  Likewise, engineered
   paths are required to support redundant transmission across disjoint
   paths in support of DetNets PREF functios.

   Traceability belongs to Operations, Administration, and Maintenance
   (OAM) which is the toolset for fault detection and isolation, and for
   performance measurement.  More can be found on OAM Tools in "An
   Overview of Operations, Administration and Maintenance (OAM) Tools"

   This document proposes a new set to mechanisms based on [RFC8279]
   (BIER) and more specifically BIER Traffic Engineering
   [I-D.ietf-bier-te-arch] (BIER-TE) to control the process or Packet
   Replication and Elimination Functions (PREF), and provide
   traceability of these operations, in the DetNet dataplane.  An
   adjacency, which is represented by a bit in the BIER header, can
   correspond in the dataplane to an Ethernet hop, a Label Switched
   Path, or it can correspond to an IPv6 loose or strict source routed

   BIER-TE was primarily designed to carry multicast traffic, but there
   is nothing prohibiting for it to be used with unicast traffic, and
   the authors of this document think that for networks whose size
   requirement match the supportable bitstring length (BSL) in BIER, it
   can be a good choice as the forwarding plane specifically for DetNet
   type traffic for both multicast and unicast traffic because it would
   be a common solution for unicast and multicast (limiting the number
   of different technologies a DetNet solution requires) and likely
   provides the most flexible support for path engineering, replication
   and elimination (PREF) and the novel OAM method described in this

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  On BIER - Traffic Engineering

   [RFC8279] (BIER) is a network plane replication technique that was
   initially intended as a new method for multicast distribution.  In a
   nutshell, a BIER header includes a bitmap that explicitly signals the
   listeners that are intended for a particular packet, which means that
   1) the sender is aware of the individual listeners and 2) the BIER
   control plane is a simple extension of the unicast routing as opposed
   to a dedicated multicast data plane, which represents a considerable

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   reduction in OPEX.  For this reason, the technology faces a lot of
   traction from Service Providers.

   The simplicity of the BIER technology makes it very versatile as a
   network plane signaling protocol.  Already, a new Traffic Engineering
   variation is emerging that uses bits to signal segments along a TE

   While BIER-TE was like BIER primarily developed for multicast
   traffic, the authors think that it can equally be attractive for
   unicast traffic requiring the DetNet resilience of multiple
   transitions.  If the topology of the network can well be represented
   by standard BIER-TE bitstring sizes of e.g.: up to 256 bits, then
   this would allow for a single technology for both unicast and

   BIER-TE supports a Traffic Engineered forwarding plane by explicit
   hop-by-hop forwarding and loose hop forwarding of packets.

   From the BIER-TE architecture, the key differences over BIER are:

   o  BIER-TE replaces in-network autonomous path calculation by
      explicit paths calculated off path for example by a BIER-TE
      controller host.
   o  In BIER-TE every BitPosition of the BitString of a BIER-TE packet
      indicates one or more adjacencies - instead of a BFER as in BIER.
      processing packets as a destination (BFER) is one of the possible
      adjacency types.
   o  BIER-TE in each BFR has no routing table but only a BIER-TE
      Forwarding Table (BIFT) indexed by SI:BitPosition and populated
      with only those adjacencies to which the BFR should replicate
      packets to.

   The generic view of an adjacency can be over a link, a tunnel or
   along a path segment.

4.  BIER-TE-based Replication and Elimination Control

   This document only needs to introduce new functionality to support
   the Elimination Function and OAM.  Creation of appropriate BIER-TE
   packets is subject to to existing work.

   In the solution described below, the encapsulation/insertion of flow-
   identification and sequence number into packets is performed by a
   function on the BFIR outside the scope of this document.  A companion
   document draft-huang-bier-te-encapsulation defines an encapsulation
   for BIER-TE and BIER that can support flow-id and sequence-number ID.
   Other encapsulations can be used as well, as long as they provide

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   these signaling elements and are supported by the Elimination
   Function described in this document (e.g.: that the EF can read these
   fields and therefore remove duplicates).  In the remainder of this
   document we will call this the extended BIER encapsulation and assume
   that it is used when describing examples.  Unless otherwise noted, we
   assume that the BFIR performs encapsulation of some data flow packets
   with an extended BIER header, indicates BIER-TE forwarding in it and
   fills in flow-id and sequence number.  It then fills in the bitstring
   with two (or more) alternative paths/DAGs and sends off the packets
   into the BIER-TE domain, replicating it itself if so indicated by the

   In a nutshell, BIER-TE is used as follows:

   o  A controller computes a complex path, sometimes called a track,
      which takes the general form of a ladder.  The steps and the side
      rails between them are the adjacencies that can be activated on
      demand on a per-packet basis using bits in the BIER header.

                            ===> (A) ====> (C) ====
                          //     ^ |       ^ |     \\
              ingress (I)        | |       | |       (E) egress
                          \\     | v       | v     //
                            ===> (B) ====> (D) ====

      Figure 1: Ladder Shape with Replication and Elimination Points

   o  The controller assigns a BIER domain, and inside that domain,
      assigns bits to the adjacencies.  The controller assigns each bit
      to a replication node that sends towards the adjacency, for
      instance the ingress router into a segment that will insert a
      routing header in the packet.  A single bit may be used for a step
      in the ladder, indicating the other end of the step in both

                            ===> (A) ====> (C) ====
                          // 1   ^ |  4    ^ |   7 \\
              ingress (I)        |2|       |6|       (E) egress
                          \\ 3   | v  5    | v   8 //
                            ===> (B) ====> (D) ====

                         Figure 2: Assigning Bits

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   o  The controller activates the replication by deciding the setting
      of the bits associated with the adjacencies.  This decision can be
      modified at any time, but takes the latency of a controller round
      trip to effectively take place.  Below is an example that uses
      Replication and Elimination to protect the A->C adjacency.  The
      "(EF)" in the following pictures Owner column indicates the fact
      that that BFR will perform the "Elimination Function" for received
      BIER-TE packets before further processing/copying them.  In this
      example, only C performs EF.  A (1) in the Example Bitstring
      indicates that the bit is set, but that the actual adjacency is
      not used by packets because this bit is shared with another
      adjacency and the overall bitstring will make the packet only use
      that other adjacency.  This applies to bits 2 and 6.

            | Bit # | Adjacency | Owner  | Example Bitstring |
            |   1   |    I->A   |   I    |         1         |
            |   2   |    A->B   |   A    |         1         |
            |       |    B->A   |   B    |        (1)        |
            |   3   |    I->B   |   I    |         0         |
            |   4   |    A->C   |   A    |         1         |
            |   5   |    B->D   |   B    |         1         |
            |   6   |    C->D   | C (EF) |        (1)        |
            |       |    D->C   |   D    |                   |
            |   7   |    C->E   | C (EF) |         1         |
            |   8   |    D->E   |   D    |         0         |

                Replication and Elimination Protecting A->C

                     Table 1: Controlling Replication

   o  The BIER header with the controlling BitString , flow-id and
      sequence number is injected in the packet by the ingress node I
      (BFIR).  That node may act as a replication point, in which case
      it may issue multiple copies of the packet, but for the purpose of
      this example it will not do it, so that the two paths used in this
      example only go from A to C, and therefore require explicit path
      engineering.  For example, bandwidth I-A and I-B may be more
      limited and those paths being non long-haul may not warrant the
      dual transmission.

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                          ====>  Repl ===> Elim ====
                       //         |         ^        \\
               ingress            |         |           egress
                                  v         |
                                 Fwd ====> Fwd

                       Figure 3: Enabled Adjacencies

   o  For each of its bits that is set in the BIER header, the owner
      replication point resets the bit used for a copy and transmits
      towards the associated adjacency; to achieve this, the replication
      point copies the packet and inserts the relevant data plane
      information, such as next-hop label, MAC-address or source route
      header (for a BIER-TE routed adjacency), towards the adjacency
      that corresponds to the bit

                      | Adjacency | BIER BitString |
                      |    I->A   |    01011110    |
                      |    A->B   |    00011110    |
                      |    B->D   |    00010110    |
                      |    D->C   |    00010010    |
                      |    A->C   |    01001110    |

               BitString in BIER Header as Packet Progresses

                        Table 2: BIER-TE in Action

   o  Adversely, an elimination node on the path performs the
      Elimination Function which will remove duplicate packets (same
      flow-id, same sequence number) and performs a bitwise AND on the
      BitStrings from the various copies of the packet that it has
      received, before it forwards the packet with the resulting
      BitString.  Details of the Elimination Function are described

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                      | Operation | BIER BitString |
                      |    D->C   |    00010010    |
                      |    A->C   |    01001110    |
                      |           |    --------    |
                      |  AND in C |    00000010    |
                      |           |                |
                      |    C->E   |    00000000    |

                BitString Processing at Elimination Point C

                    Table 3: BIER-TE in Action (cont.)

   o  In this example, all the transmissions succeeded and the BitString
      at arrival has all the bits reset - note that the egress may be an
      Elimination Point in which case this is evaluated after this node
      has performed its AND operation on the received BitStrings).

               | Failing Adjacency | Egress BIER BitString |
               |        I->A       |       Frame Lost      |
               |        I->B       |       Not Tried       |
               |        A->C       |        00010000       |
               |        A->B       |        01001100       |
               |        B->D       |        01001100       |
               |        D->C       |        01001100       |
               |        C->E       |       Frame Lost      |
               |        D->E       |       Not Tried       |

                       BitString indicating failures

                    Table 4: BIER-TE in Action (cont.)

   o  But if a transmission failed along the way, one (or more) bit is
      never cleared.  Table 4 provides the possible outcomes of a
      transmission.  If the frame is lost, then it is probably due to a
      failure in either I->A or C->E, and the controller should enable
      I->B and D->E to find out.  A BitString of 00010000 indicates
      unequivocally a transmission error on the A->C adjacency, and a
      BitString of 01001100 indicates a loss in either A->B, B->D or
      D->C; enabling D->E on the next packets may provide more
      information to sort things out.

   In more details:

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   The BIER header is of variable size, and a DetNet network of a
   limited size can use a model with 64 bits if 64 adjacencies are
   enough, whereas a larger deployment may be able to signal up to 256
   adjacencies for use in very complex paths.  The format of this header
   is common to BIER and BIER-TE.

   For the DetNet data plane, a replication point is an ingress point
   for more than one adjacency, and an elimination point is an egress
   point for more than one adjacency.

   A pre-populated state in a replication node indicates which bits are
   served by this node and to which adjacency each of these bits
   corresponds.  With DetNet, the state is typically installed by a
   controller entity such as a PCE.  The way the adjacency is signaled
   in the packet is fully abstracted in the bit representation and must
   be provisioned to the replication nodes and maintained as a local
   state, together with the timing or shaping information for the
   associated flow.

   The DetNet data plane uses BIER-TE to control which adjacencies are
   used for a given packet.  This is signaled from the path ingress,
   which sets the appropriate bits in the BIER BitString to indicate
   which replication must happen.

   The replication point clears the bit associated to the adjacency
   where the replica is placed, and the elimination points perform a
   logical AND of the BitStrings of the copies that it gets before

   As is apparent in the examples above, clearing the bits enables to
   trace a packet to the replication points that made any particular
   copy.  BIER-TE also enables to detect the failing adjacencies or
   sequences of adjacencies along a path and to activate additional
   replications to counter balance the failures.

   Finally, using the same BIER-TE bit for both directions of the steps
   of the ladder enables to avoid replication in both directions along
   the crossing adjacencies.  At the time of sending along the step of
   the ladder, the bit may have been already reset by performing the AND
   operation with the copy from the other side, in which case the
   transmission is not needed and does not occur (since the control bit
   is now off).

5.  Elimination Function (Normative)

   This section defines the normative behavior of the Elimination
   Function with optional OAM sub-function.

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   The Elimination Function is performed logically on reception of BIER-
   TE packets.  It is therefore not part of the adjacencies or otherwise
   assigned to a specific bit.  "Logically" means that this
   specification does not constrain implementations, especially on
   multi-linecard/multi-chassis systems to perform EF on a physcial
   egres module.  It just implies that it has to happen before
   replication to the bits in the bitstring.

   TBD: In addition to being an ingres, EF could as well be modelled as
   a new adjacency asigned to bits.  The full adjacency of a bit could
   then be a sequence of EF followed by one (or more) of existing
   adjacencies.  This is currently not considered by this document due
   to the lack of identified need to support this option - e.g.:
   problems that can not be equally/better be solved with EF logically
   on ingres.

   The Elimination Function is more formally written as EF(OAM, BIFT,
   {flows}/*), and is configured like BIFTs from the BIER-TE controller
   host and/or other future mechanisms.

   OAM is boolean and indicates whether OAM function of bitwise AND of
   received packet copies is performed.  This OAM function requires
   additional memory/processing over EF without OAM.  Note that the OAM
   function does not change the effect of the Elimination Function for
   BFR/receivers - they will continue to just receive the first copy of
   a packet.  Instead, it will continue to track further copies solely
   for the purpose of providing OAM information.  This also requires
   some timout or sequence number advancement to decide when to
   terminate waiting for further copies of packets before considering
   the OAM analysis of this packet to be complete.  BFR supporting this
   document SHOULD support the OAM sub-function.

   BIFT indicates the <SD,SI,BSL> for which to perform EF.  Devices
   SHOULD support enabling per EF. {flows}/* indicates the set of flows
   for which EF operates (using the specified BIFT).  Duplicate
   elimination has to create per-flow state to remember which sequence
   number packets for this flow where already received.  In the case of
   OAM also what bits where set in that received prior copy of the

   When a device supports "*", then it will automatically allocate such
   a flow-state for every new recognized flow and expire such flow state
   after an operator determined timeout of activity - for example with a
   default of 10 seconds.  Dynamic allocation of flow-state may cause
   some inital duplicates before this state is working and it makes the
   BFR more vulnerable to state DOS attacks, but it will allows BIER
   applications to send flows with the benefit of EF without the help of
   the controller having to know and program every flow.

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   In the {flows} option, control procedures (e.g.: BIER-TE controller
   host) indicate to the BFR explicitly the set of flows for which it
   should install/operate the EF function.  Note that the flow-id in the
   extended BIER encapsulation is the combination of BFIR-ID and entropy
   field of the BIER header.

   BFR supporting this document MUST support the {flows} option and MAY
   support the "*" option.

   The following picture explains the results of EF being performed on
   ingres in a typical example:

                            /---------- B1 ------------\
                            |                          |
                            \-- B3 -- B4 -- B5 -- B6 --/
                                 |     |    |     |
                                 |     |    |     |
                                O1    O2    O3    O4

                          Figure 4: EF with Rings

   Consider a simple ring where BFIR I1 generates BIER-TE packets.  The
   bitstring indicates that the packet is sent hop-by-hop
   counterclockwise B1->B3->B4->B6 and counterclockwise
   B1->B6->B5->B4->B3.  Bits for BFER O1, O2, O3 and O4 are also set.
   B3,B4,B5,B6,B7 perform EF.  The result of this setup is that B2
   creates two copies of the packets received from I1, one going to B6,
   the other to B3.  Assume B4 first received the counter-clockwise copy
   from B3 and B5 the clockwise copy from B6.  They will both forward
   these packets to each other because those where the first copies they
   saw, but the would block these second copies.  Therefore only the
   link B4<->B5 will have carried the packet copy twice (once in each
   direction).  All the other ring links will only carry one copy of the

   This is notably different from schemes where EF is not performed
   before replication, but afterwards.  In those schemes, both copies of
   the packets would flow counterclockwise around (most of) the ring,
   ocupying more bandwidth.

6.  Summary

   With the addition of the functions of this document, BIER-TE becomes
   a potential option for the DetNet dataplane specifically beneficial
   when PREF (replication and elimination) is required for resilience

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   (to reduce packet loss).  For DetNet multicast but also DetNet
   unicast.  The unique capabilities of this approach areare:

   o  Explicit per-packet path selection for packet.  Multicast and
   o  Control which replication take place on a per packet basis, so
      that replication points can be configured but not actually
   o  Trace the replication activity and determine which node replicated
      a particular packet
   o  Measure the quality of transmission of the actual data packet
      along the replication segments and use that in a control loop to
      adapt the setting of the bits and maintain the reliability.

7.  Implementation Status

   A research-stage implementation of the forwarding plane fir a 6TiSCH
   IOT use case was developed at Cisco's Paris Innovation Lab (PIRL) by
   Zacharie Brodard.  It was implemented on OpenWSN Open-source firmware
   and tested on the OpenMote-CC2538 hardware.  It implements the header
   types 15,16, 17, 18 and 19 (bit-by-bit encoding without group ID) in
   order to allow a BIER-TE protocol over IEE802.15.4e.

   This work was complemented with a Controller-based control loop by
   Hao Jiang.  The controller builds the complex paths (called Tracks in
   6TiSCH) and decides the setting oif the BitStrings in real time in
   order to optimize the delivery ratio within a minimal energy budget.


      OpenWSN firmware:
      OpenMote hardware:

8.  Security considerations


9.  IANA Considerations

   This document has no IANA considerations.

10.  Acknowledgements

   The method presented in this document was discussed and worked out
   together with the DetNet Data Plane Design Team:

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      Jouni Korhonen
      Janos Farkas
      Norman Finn
      Olivier Marce
      Gregory Mirsky
      Pascal Thubert
      Zhuangyan Zhuang

   The authors also like to thank the DetNet chairs Lou Berger and Pat
   Thaler, as well as Thomas Watteyne, 6TiSCH co-chair, for their
   contributions and support to this work.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

11.2.  Informative References

              Korhonen, J., Farkas, J., Mirsky, G., Thubert, P.,
              Zhuangyan, Z., and L. Berger, "DetNet Data Plane Protocol
              and Solution Alternatives", draft-dt-detnet-dp-alt-04
              (work in progress), September 2016.

              Eckert, T., Cauchie, G., Braun, W., and M. Menth, "Traffic
              Engineering for Bit Index Explicit Replication (BIER-TE)",
              draft-ietf-bier-te-arch-00 (work in progress), January

              Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", draft-ietf-
              detnet-architecture-04 (work in progress), October 2017.

              Finn, N. and P. Thubert, "Deterministic Networking Problem
              Statement", draft-ietf-detnet-problem-statement-02 (work
              in progress), September 2017.

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              Grossman, E., "Deterministic Networking Use Cases", draft-
              ietf-detnet-use-cases-14 (work in progress), February

              Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
              Weingarten, "An Overview of Operations, Administration,
              and Maintenance (OAM) Tools", draft-ietf-opsawg-oam-
              overview-16 (work in progress), March 2014.

              Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing
              Architecture", draft-ietf-spring-segment-routing-15 (work
              in progress), January 2018.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,

Authors' Addresses

   Pascal Thubert (editor)
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis  06410

   Phone: +33 4 97 23 26 34

   Toerless Eckert
   Huawei USA - Futurewei Technologies Inc.
   2330 Central Expy
   Santa Clara  95050


Thubert, et al.         Expires September 4, 2018              [Page 14]

Internet-Draft              BIER-TE PREF/OAM                  March 2018

   Zacharie Brodard
   Ecole Polytechnique
   Route de Saclay
   Palaiseau  91128

   Phone: +33 6 73 73 35 09

   Hao Jiang
   Telecom Bretagne
   2, rue de la Chataigneraie
   Cesson-Sevigne  35510

   Phone: +33 7 53 70 97 34

Thubert, et al.         Expires September 4, 2018              [Page 15]