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Versions: 00

Network Working Group                                         Y. Jiang
Internet-Draft                                                 N. Finn
Intended status: Informational                                  Huawei
                                                               J. Ryoo
                                                                  ETRI
                                                              B. Varga
                                                              Ericsson
                                                               L. Geng
                                                          China Mobile
Expires: July 2018                                    January 24, 2018


          Deterministic Networking Application in Ring Topologies
                        draft-jiang-detnet-ring-00


Abstract

   Deterministic Networking (DetNet) provides a capability to carry
   data flows for real-time applications with extremely low data loss
   rates and bounded latency. This document describes how DetNet can
   be used in ring topologies to support Point-to-Point (P2P) and
   Point-to-Multipoint (P2MP) real-time services.



Status of this Memo

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

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   This Internet-Draft will expire on July 24, 2018.




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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
   (http://trustee.ietf.org/license-info) in effect on the date of
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   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 ............................................... 3
      1.1. Conventions used in this document ....................... 4
      1.2. Terminology ............................................. 4
   2.   P2P DetNet Ring ............................................ 4
      2.1. DetNet applications on a single ring for P2P traffic .... 4
      2.2. Implementation implications of a DetNet ring for P2P
      traffic ...................................................... 5
   3.   P2MP DetNet Ring ........................................... 5
      3.1. DetNet applications on a single ring for P2MP traffic ... 5
      3.2. Section LSPs as underlay (Service layer replication) .... 6
      3.3. P2MP LSP tunnels as underlay (LSP layer replication) .... 7
   4.   DetNet Ring Interconnections ............................... 8
      4.1. Single node interconnection ............................. 8
      4.1.1.  DetNet relay node as interconnection node ............ 9
      4.1.2.  Elimination first approach ........................... 9
      4.2. Dual node interconnection .............................. 10
      4.2.1.  Dual node interconnection for P2P traffic ........... 10
      4.2.2.  Elimination first approach in dual node interconnection
      for P2P traffic ............................................. 11
      4.2.3.  Dual node interconnection for P2MP traffic using
      section LSP ................................................. 11
      4.2.4.  Elimination first approach in dual node interconnection
      for P2MP traffic using section LSP .......................... 12
      4.2.5.  Dual node interconnection for P2MP traffic using P2MP
      LSP     13
   5.   Resource reservation ...................................... 13
   6.   Security Considerations ................................... 13
   7.   IANA Considerations ....................................... 13


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   8.   References ............................................... 13
      1.1. Informative References ................................ 13
   9.   Acknowledgments .......................................... 15



1. Introduction

   An overview of Deterministic Networking (DetNet) architecture is
   given in [I-D.ietf-detnet-architecture], and DetNet data plane
   encapsulations are specified in [I-D.ietf-detnet-dp-sol]. But there
   is not any discussion on a ring topology in [I-D.ietf-detnet-
   architecture] yet. Furthermore, [I-D.ietf-detnet-use-cases]
   outlines several Detnet use cases where multicast capability is
   needed. If a multicast service replicates all of its packets from
   the source (as a traditional Virtual Private LAN Service (VPLS)
   does), the requirements of deterministic delay and high
   availability for all these replicated packets will pose a great
   challenge to the Detnet network.

   In fact, ring topologies have been very popular and widely deployed
   in network arrangements for various transport networks, such as
   Synchronous Digital Hierarchy, Synchronous Optical Network, Optical
   Transport Network, and Ethernet. The IETF has done some work on
   ring protection in Multi-Protocol Label Switching - Transport
   Profile (MPLS-TP), such as [RFC6974] and [RFC8227]. All these works,
   except Ethernet ring protection, typically use swapping or steering
   as the protection mechanism. As ring topologies are widely deployed
   for transport networks, it is also necessary for DetNet to support
   ring topologies (currently, there is not any discussion on a ring
   topology in [I-D.ietf-detnet-architecture] yet).

   This draft demonstrates how DetNet can be used in a ring topology.
   Specifically, DetNet ring supports for Point-to-Point (P2P) and
   Point-to-Multipoint (P2MP, for multicast services) are discussed in
   details. This document assumes that MPLS encapsulation for DetNet
   is supported as specified in [I-D.ietf-detnet-dp-sol] and all nodes
   in a ring network can support the Multi-Protocol Label Switching
   (MPLS) functionalities. It should be noted that it is more
   convenient for DetNet to support a ring topology with the intrinsic
   duplication and elimination mechanism, as there is no need of
   swapping or steering operations (consequently, Operations,
   Administration and Maintenance is not needed either for its working)
   for any service protection.





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1.1. 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 [RFC2119].

1.2. Terminology

   DetNet  Deterministic Networking

   LSP    Label Switched Path

   MPLS    Multi-Protocol Label Switching

   MPLS-TP Multi-Protocol Label Switching - Transport Profile

   P2MP   Point-to-Point

   P2P    Point-to-Multipoint

   PW      Pseudowire

2. P2P DetNet Ring

2.1. DetNet applications on a single ring for P2P traffic

   Figure 1 depicts an example of the DetNet ring for P2P real time
   traffic. Nodes A and C are DetNet aware devices, and P2P DetNet
   traffic is transported from node A to node C.

   A clockwise and a counter clockwise Pseudowire (PW) and Label
   Switched Path (LSP) tunnel are configured from node A to node C
   respectively. The DetNet traffic is replicated on node A,
   encapsulated with the specific PW and LSP labels, and transported
   on both LSP paths towards node C. Upon reception of the traffic,
   node C terminates the LSP and is aware of the DetNet traffic by
   inspection of the PW label carried in each packet. An elimination
   function in node C guarantees that only one copy of the DetNet
   service exits on egress with the help of the DetNet sequence number.










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                          +---+#############+---+
                          | B |-------------| C | +-- DetNet
                          +---+             +---+     egress
                          #/                    *\
                         #/                      *\
                        #/                        *\
                      +---+                     +---+
            DetNet--+ | A |                     | D |
           ingress    +---+                     +---+
                         \*                      */
                          \*                    */
                           \*                  */
                          +---+*************+---+
                          | F |-------------| E |
                          +---+             +---+

                            ----- Physical Links
                            ##### Clockwise_
                            ***** Counter Clockwise


                      Figure 1: DetNet Ring for P2P traffic



2.2. Implementation implications of a DetNet ring for P2P traffic

   In a DetNet ring for P2P traffic, one path may be far longer than
   the other path for the DetNet (this is a DetNet issue more general
   than a ring).

   The buffer need to be large enough to accommodate for the sequence
   number difference between these two paths. Otherwise, some packets
   may get lost when a link fault causes traffic switching from a path
   to another path.



3. P2MP DetNet Ring

3.1. DetNet applications on a single ring for P2MP traffic

   Figure 2 further depicts an example of the DetNet ring for P2MP
   real time traffic. Nodes A, B, C, E and F are DetNet aware devices,
   and P2MP DetNet traffic is transported from head-end node A to
   multiple tail-end nodes C, E and F.



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   Two approaches are described in Section 3.2 and 3.3 for P2MP
   traffic.

                          +---+#############+---+
                          | B |-------------| C | +-- DetNet
                          +---+*************+---+     egress
                          #/                    *\#
                         #/                      *\#
                        #/                        *\#
                      +---+                     +---+
            DetNet--+ | A |                     | D |
           ingress    +---+                     +---+
                         \*                      */#
                          \*                    */#
                           \*                  */#
                          +---+*************+---+
                DetNet--+ | F |-------------| E |+-- DetNet
                egress    +---+#############+---+    egress

                            ----- Physical Links
                            ##### Clockwise traffic
                            ***** Counter Clockwise traffic


                       Figure 2: DetNet Ring for P2MP traffic

3.2. Section LSPs as underlay (Service layer replication)

   If section LSPs are used as an underlay for DetNet services, a
   bidirectional section LSP tunnel is set up between each pair of
   neighboring nodes in the ring (e.g., node A and node B, ..., node F
   and node A). In this case, DetNet PW layer replicates the DetNet
   packets from one tail-end to another neighboring tail-end.

   The DetNet head-end (i.e., node A) in the ring needs to support
   DetNet replication function. Upon reception on node A, the DetNet
   traffic is replicated in node A, encapsulated with the specific PW
   and section LSP labels, and then transported on both section LSPs
   (i.e., A-B and A-F) originated from the head-end.

   All intermediate nodes (non tail-ends) on the ring SHOULD
   transparently forward the DetNet traffic with a specific PW to the
   next hop on the ring in the same direction.

   All DetNet tail-ends except the penultimate node (egress nodes such
   as nodes C and E in the clockwise, and node F, E and C in the
   counter clockwise) on the ring MUST support both DetNet


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   replication and elimination functions. For example, upon reception
   of the clockwise traffic, node C terminates the section LSP and is
   aware of the DetNet traffic by inspection of the PW label in the
   packet. Firstly, node C needs to transparently forward the DetNet
   traffic with a specific PW to the next hop on the ring in the same
   direction. Secondly, DetNet traffic is directed to a DetNet
   elimination function associated with a specific PW, only one copy
   of the DetNet service exits on egress by inspection of the DetNet
   sequence number.

   If multiple endpoints are attached to a tail-end node, a multicast
   module can be used to forward the filtered DetNet traffic to all
   these endpoints.

   To avoid a loop of DetNet service, the penultimate node in the ring
   (such as node B on the counter clock-wise LSP) needs to terminate
   the DetNet flow. For example, upon reception of the clockwise
   DetNet traffic, node F terminates the DetNet traffic by inspection
   of the PW label in the packet. As an alternative, the last DetNet
   tail-end (such as node C on the counter clock-wise LSP) may
   terminate the DetNet flow, so that the bandwidth from this node to
   the penultimate node can be saved.



3.3.  P2MP LSP tunnels as underlay (LSP layer replication)

   If P2MP LSPs are used as an underlay for the DetNet service, a P2MP
   unidirectional LSP tunnel in clockwise is set up from head-end
   (ingress node A) to all the tail-ends (egress nodes C, E and F) for
   the ring, and another P2MP unidirectional LSP tunnel in counter
   clockwise is set up from head-end (ingress node A) to all the tail-
   ends (egress nodes F, E and C) for the ring. Thus, LSP layer
   replicates the DetNet packets from one tail-end to another
   neighboring tail-end.

   The DetNet head-end (i.e., node A) in the ring needs to support
   DetNet replication function. Upon reception on node A, the DetNet
   traffic is replicated, encapsulated with the specific PW and P2MP
   LSP labels, and transported on both P2MP LSP tunnels in the ring.

   All DetNet tail-ends (egress nodes such as node C, E and F in
   Figure 2) on the ring need to support the DetNet elimination
   function. For example, upon reception of the traffic, node C pops
   the P2MP LSP label and is aware of the DetNet traffic by inspection
   of the PW label in the label stack. Traffic from both directions
   with the same PW is directed to the same DetNet elimination


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   function so that only one copy of the DetNet service exits on
   egress by inspection of the DetNet sequence number.

   If multiple endpoints are attached to a tail-end node, a multicast
   module can be used to forward the filtered DetNet traffic to all
   these endpoints.

4. DetNet Ring Interconnections

   Two DetNet rings can be connected via one or more interconnection
   nodes. Figures 3a and 3b show ring interconnection scenarios with a
   single node and dual nodes, respectively. In the interconnected
   rings, each ring operates in the same way as described in Sections
   2 and 3 except the nodes that are used to interconnect two rings.

   In this section, we describe the behavior of interconnection nodes
   with the traffic going from Ring L to Ring R. Symmetrical
   description is assumed for the traffic in the other direction.


                                            S   T
         B   C     S   T                    O---O
         O---O     O---O                   /     \
        /     \   /     \            B  I1/       \
       /       \ /       \           O---O  Ring R O U
    A O Ring L  O Ring R  O U       /     \       /
       \       /I\       /         /       \     /
        \     /   \     /       A O Ring L  O---O
         O---O     O---O           \       /I2  V
         F   E     W   V            \     /
                                     O---O
                                     F   E
            (a) (b)




   Figure 3: DetNet ring interconnection with: a) single node (node I),
   and b) dual nodes (nodes I1 and I2).

4.1. Single node interconnection

   In the case of the single node interconnection, as shown in Figure
   3(a), both P2P and P2MP DetNet traffic that needs to be transported
   between Ring L and Ring R uses the single interconnection node
   between two rings. Two approaches are described in the following
   subsections.


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4.1.1. DetNet relay node as interconnection node

   In this approach, the interconnection node acts as a DetNet relay
   node, which provides packet replication and elimination.

   For P2P DetNet traffic going from Ring L to Ring R, interconnection
   node I performs packet replication on input and sends the packet to
   the outputs connected to the links on Ring R clockwise and counter-
   clockwise. Then, after each output of interconnection node I
   eliminates any duplicates, the packet is transported over Ring R.
   In Figure 3(a), when interconnection node I receives traffic on
   input from node C, node I replicates the traffic and send it to
   both outputs to nodes S and W. For the traffic from input from node
   E, node I also replicates the traffic and send it to both outputs
   to nodes S and W. Then, the output to node S eliminates any
   duplicates, and sends only one copy to node S. Similarly, the
   output to node W eliminates any duplicates, and sends only one copy
   to node W.

   For P2MP DetNet traffic going from Ring L to Ring R, the input of
   interconnection node I performs the same packet replication as
   described for P2P DetNet traffic going from Ring L to Ring R. In
   addition, the third copy is sent to the other ring port on Ring L,
   in order to deliver the P2MP DetNet traffic to the remaining tail-
   end nodes that reside in the other side of Ring L over the
   interconnected node. The outputs to nodes S and W perform the same
   duplicate elimination as described for P2P DetNet traffic going
   from Ring L to Ring R.

4.1.2. Elimination first approach

   This approach uses two "logical" DetNet relay nodes (or, DA-*-PE as
   described in [I-D.ietf-detnet-dp-sol]) coupled back-to-back, such
   that interconnection node I performs the duplicate elimination
   function first.

   For the Detnet traffic arrived from both node C and node E, the
   interconnection node I performs duplicate elimination first, and
   then replicates the traffic in both clockwise and counter-clockwise
   directions of Ring R, i.e., one copy to node S and the other copy
   to node W. Therefore, this approach reduces the bandwidth used
   inside the interconnection node when there is a central unit that
   eliminates any duplicate among the packets arrived from two ring
   ports before replication.





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4.2. Dual node interconnection

   In order to prevent a single point of failure, two interconnection
   nodes can be used as shown in Figure 3(b). To provide high
   availability for DetNet services, dual node interconnection is
   recommended. Two interconnection nodes act as DetNet relay nodes,
   which provide packet replication and elimination.

4.2.1. Dual node interconnection for P2P traffic

   For the P2P DetNet traffic that flows from Ring L to Ring R, the
   operation of interconnection nodes I1 and I2 follows the
   description on relay nodes shown in Figure 1 of Section 3.2.4 in
   [I-D.ietf-detnet-architecture]. In the following, the operation is
   explained with Figure 3(a).

   When interconnection node I1 receives clockwise traffic from node B,
   it replicates the traffic and sends one copy to interconnection
   node I2 and the other copy to output towards node S.

   When interconnection node I1 receives counter-clockwise traffic
   from interconnection node I2, it forwards the traffic to the output
   that is connected to node S.

   At the output of interconnection node I1 facing to node S,
   duplicate elimination is performed for the clockwise traffic from
   node B and the counter-clockwise traffic from interconnection node
   I2, and only one copy is sent to the clockwise direction of Ring R
   (i.e., sent towards node S).

   When interconnection node I2 receives counter-clockwise traffic
   from node E, it replicates the traffic and sends one copy to
   interconnection node I1 and the other copy to the output that is
   connected to node V.

   When interconnection node I2 receives clockwise traffic from
   interconnection node I1, it forwards the traffic to the output that
   is connected to node V.

   At the output of interconnection node I2 facing to node V,
   duplicate elimination is performed for the counter-clockwise
   traffic from node E and the clockwise traffic from interconnection
   node I1, and only one copy is sent to the counter-clockwise
   direction of Ring R (i.e., sent towards node V).





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4.2.2. Elimination first approach in dual node interconnection for P2P
     traffic

   The elimination first approach described in Section 4.1.2 can also
   be used for dual node interconnection, so that each interconnection
   node performs the duplicate elimination function first.

   For the traffic arrived from both node B and interconnection node
   I2, the interconnection node I1 performs duplicate elimination
   first, and replicates the traffic in both clockwise and counter-
   clockwise directions of Ring R, i.e., one copy to node S and the
   other copy to interconnection node I2.

   For the traffic arrived from both node E and interconnection node
   I1, the interconnection node I2 performs duplicate elimination
   first, and replicates the traffic in both clockwise and counter-
   clockwise directions of Ring R, i.e., one copy to interconnection
   node I1 and the other copy to node V.

4.2.3.Dual node interconnection for P2MP traffic using section LSP

   For the P2MP traffic that flows from Ring L to Ring R, each ring is
   configured and operated as described in Section 3.2 except the
   interconnection nodes, whose operations are described below.

   When interconnection node I1 receives clockwise traffic from node B,
   it replicates the traffic and sends one copy to interconnection
   node I2 and the other copy to the output that is connected to node
   S.

   When interconnection node I1 receives the counter-clockwise traffic
   from interconnection node I2, it replicates the traffic and sends
   one copy to node B and the other copy to the output that is
   connected to node S unless interconnection node I1 is the
   penultimate node for the counter-clockwise traffic on Ring L. In
   the case that interconnection node I1 is the penultimate node for
   the counter-clockwise traffic on Ring L, the counter-clockwise
   traffic from interconnection node I2 is forwarded to the output
   that is connected to node S.

   At the output interface of I1 facing to node S, duplicate
   elimination is performed for the clockwise traffic from node B and
   the counter-clockwise traffic from interconnection node I2, and
   only one copy is sent to the clockwise direction of Ring R (i.e.,
   sent towards node S).




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   When interconnection node I2 receives the counter-clockwise traffic
   from node E, it replicates the traffic and sends one copy to
   interconnection node I1 and the other copy to the output that is
   connected to node V.

   When interconnection node I2 receives the clockwise traffic from
   interconnection node I1, it replicates the traffic and sends one
   copy to node E and the other copy to the output that is connected
   to node V unless interconnection node I2 is the penultimate node
   for the clockwise traffic in Ring L. In the case that
   interconnection node I2 is the penultimate node for the clockwise
   traffic in Ring L, the clockwise traffic from interconnection node
   I1 is forwarded to the output that is connected to node V.

   At the output interface of I2 facing to node V, duplicate
   elimination is performed for the counter-clockwise traffic from
   node E and the clockwise traffic from interconnection node I1, and
   only one copy is sent to the counter-clockwise direction of Ring R
   (i.e., sent towards node V).

4.2.4. Elimination first approach in dual node interconnection for
     P2MP traffic using section LSP

   The elimination first approach described in Section 4.2.2 is
   applied without modification for dual node interconnection for P2MP
   traffic using section LSP only if interconnection nodes I1 and I2
   are the penultimate nodes for the counter-clockwise traffic and the
   clockwise traffic on Ring L, respectively.

   When an interconnection node is not the penultimate node for either
   clockwise or counter-clockwise traffic, the interconnection node
   replicates the traffic in three ways; one for the remaining tail-
   ends on Ring L and two for the tail-ends in both clockwise and
   counter-clockwise directions on Ring R.

   For example, assume that interconnection node I2 is not the
   penultimate node for the clock-wise traffic on Ring L. For the
   traffic arrived from both node E and interconnection node I1,
   interconnection node I2 performs duplicate elimination first, and
   replicates the traffic for the following three outputs; one copy to
   the output towards node E, another copy to the output towards
   interconnection node I1, and the other copy to the output towards
   node V.






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4.2.5.Dual node interconnection for P2MP traffic using P2MP LSP

   If P2MP LSPs are used in the interconnected rings, two P2MP
   unidirectional LSP tunnels are used on each ring for the clockwise
   and counter-clockwise directions.

   When the P2MP traffic is forwarded from one ring to another ring,
   for example from Ring L to Ring R in Figure 3(b), each P2MP LSP in
   Ring L MUST include interconnection nodes I1 and I2 as tail-ends.
   For Ring R, one P2MP LSP is set up from interconnection node I1 to
   all the tail-ends in the clockwise direction on Ring R, and the
   other P2MP LSP is set up from interconnection node I2 to all the
   tail-ends in the counter-clockwise direction on Ring R. Therefore,
   an interconnection node acts as a tail-end for one ring and a head-
   end for another ring in one direction, and performs the same
   operation of tail-end and head-end as specified in Section 3.3.

5. Resource reservation

   In order to guarantee that DetNet flows don't suffer from network
   congestion, resource reservation considerations as outlined in
   Section 4.3.2 of [I-D.ietf-detnet-architecture] apply here.



6. Security Considerations

   This document describes the application of DetNet on general ring
   topologies. Thus the security considerations as described in [I-
   D.ietf-detnet-dp-sol] also apply to this document.

7. IANA Considerations

   There are no IANA actions required by this document.



8. References


1.1. Informative References

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



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   [I-D.ietf-detnet-dp-sol] Korhonen, J., Andersson, L., Jiang, Y.,
             and etc., "DetNet Data Plane Encapsulation", draft-ietf-
             detnet-dp-sol (work in progress), October, 2017

   [I-D.ietf-detnet-use-cases] Grossman, E., and etc., "Deterministic
             Networking Use Cases", draft-ietf-detnet-use-cases (work
             in progress), October, 2017

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

   [RFC6974] Weingarten, Y., Bryant, S., and etc., "Applicability of
             MPLS Transport Profile for Ring Topologies", RFC 6974,
             July 2013

   [RFC8227] Cheng, W., Wang, L., and etc., "MPLS-TP Shared-Ring
             Protection (MSRP) Mechanism for Ring Topology", RFC 8227,
             August 2017






























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9. Acknowledgments

   TBD



Authors' Addresses

   Yuanlong Jiang
   Huawei Technologies Co., Ltd.
   Bantian, Longgang district
   Shenzhen 518129, China
   Phone: +86-18926415311
   Email: jiangyuanlong@huawei.com

   Norman Finn
   Huawei Technologies Co. Ltd
   3755 Avocado Blvd,
   California  91941, USA
   Phone: +1 925 980 6430
   Email: norman.finn@mail01.huawei.com

   Jeong-dong Ryoo
   ETRI
   218 Gajeongno
   Yuseong-gu, Daejeon 305-700, South Korea
   Phone: +82-42-860-5384
   Email: ryoo@etri.re.kr

   Balazs Varga
   Ericsson
   Konyves Kalman krt. 11/B
   Budapest 1097
   Hungary
   Email: balazs.a.varga@ericsson.com

   Liang Geng
   China Mobile
   Beijing, China
   Email: gengliang@chinamobile.com









Jiang and et al         Expires July 24, 2018                [Page 15]


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