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Internet Engineering Task Force                             Q. Wang, Ed.
Internet-Draft                                                       ZTE
Intended status: Informational                          R. Valiveti, Ed.
Expires: January 3, 2018                                   Infinera Corp
                                                           H. Zheng, Ed.
                                                                  Huawei
                                                             H. Helvoort
                                                         Hai Gaoming B.V
                                                              S. Belotti
                                                                   Nokia
                                                            July 2, 2017


            GMPLS Routing and Signaling Framework for B100G
                   draft-merge-ccamp-otn-b100g-fwk-01

Abstract

   The 2016 revision of G.709 introduces support for OTU links with
   rates larger than 100G.  This document provides a framework to
   address the GMPLS routing and signalling extensions that enable GMPLS
   to setup paths through network that contain these newly introduced
   OTUCn links.

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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   This Internet-Draft will expire on January 3, 2018.

Copyright Notice

   Copyright (c) 2017 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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   (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
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  OTN terminology used in this document . . . . . . . . . .   3
   3.  Overview of B100G in G.709  . . . . . . . . . . . . . . . . .   4
     3.1.  OTUCn . . . . . . . . . . . . . . . . . . . . . . . . . .   4
       3.1.1.  Carrying OTUCn between 3R points  . . . . . . . . . .   5
     3.2.  ODUCn . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.3.  OTUCn-M . . . . . . . . . . . . . . . . . . . . . . . . .   9
     3.4.  OPUCn Time Slot Granularity . . . . . . . . . . . . . . .   9
     3.5.  Structure of OPUCn MSI with Payload type 0x22 . . . . . .  10
     3.6.  Client Signal Mappings  . . . . . . . . . . . . . . . . .  10
   4.  Usecases  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     4.1.  100GE Client Service with a homogeneous chain of OTUC1
           links . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     4.2.  100GE Client Service with a mix of OTU4, and OTUC1 links   14
     4.3.  400GE Client Service with a mix of OTUCn links  . . . . .  14
     4.4.  FlexE aware transport over OTUCn links  . . . . . . . . .  15
     4.5.  FlexE Client transport over OTUCn links . . . . . . . . .  16
     4.6.  Multihop ODUCn link . . . . . . . . . . . . . . . . . . .  17
     4.7.  Use of OTUCn-M links  . . . . . . . . . . . . . . . . . .  18
     4.8.  Intermediate State of ODU mux . . . . . . . . . . . . . .  19
   5.  GMPLS Implications  . . . . . . . . . . . . . . . . . . . . .  19
     5.1.  OTN ODUCn/OTUCn hierarchy . . . . . . . . . . . . . . . .  19
     5.2.  Implications for GMPLS Signaling  . . . . . . . . . . . .  20
     5.3.  Implications for GMPLS Routing  . . . . . . . . . . . . .  21
   6.  Open Issues . . . . . . . . . . . . . . . . . . . . . . . . .  22
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   8.  Authors (Full List) . . . . . . . . . . . . . . . . . . . . .  22
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  23
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  24
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     12.2.  Informative References . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25




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1.  Introduction

   The current GMPLS routing [RFC7138] and signaling extensions
   [RFC7139] includes coverage for all the OTN capabilities that were
   defined in the 2012 version of G.709 [ITU-T_G709_2012].

   The 2016 version of G.709 [ITU-T_G709_2012] introduces support for
   higher rate OTU signals, termed OTUCn (which have a nominal rate of n
   x 100 Gbps).  The newly introduced OTUCn represent a very powerful
   extension to the OTN capabilities, and one which naturally scales to
   transport any newer clients with bit rates in excess of 100G, as they
   are introduced.

   This document presents an overview of the changes introduced in
   [ITU-T_G709_2016] and analyzes them to identify the extensions that
   would be required in GMPLS routing and signaling to enable the new
   OTN capabilities.

1.1.  Scope

   For the purposes of the B100G control plane discussion, the OTN
   should be considered as a combination of ODU and OTSi layers.  Note
   that [ITU-T_G709_2016] is deprecating the use of the term "Och" for
   B100G entities, and leaving it intact only for maintaining continuity
   in the description of the signals with bandwidth upto 100G.  This
   document focuses on only the control of the ODU layer.  The control
   of the OTSi layer will be addressed in a separate document.

2.  Terminology

2.1.  Requirements Language

   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].

2.2.  OTN terminology used in this document

   a.  OPUCn: Optical Payload Unit -Cn.

   b.  ODUCn: Optical Data Unit - Cn.

   c.  OTUCn: Fully standardized Optical Transport Unit - Cn.

   d.  OTUCn-M: This signal is an extension of the OTUCn signal
       introduced above.  This signal contains the same amount of
       overhead as the OTUCn signal, but contains a reduced amount of




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       payload area.  Specifically the payload area consists of M 5G
       tributary slots (where M is strictly less than 20*n).

   e.  PSI: OPU Payload structure Indicator.  This is a multi-frame
       message and describes the composition of the OPU signal.  This
       field is a concatenation of the Payload type (PT) and the
       Multiplex Structrure Indicator (MSI) defined below.

   f.  MSI: Multiplex Structure Indicator.  This structure indicates the
       grouping of the tributary slots in an OPU payload area to realize
       a client signal that is multiplexed into an OPU.  The individual
       clients multiplexed into the OPU payload area are distinguished
       by the Tributary Port number (TPN).

   g.  GMP: Generic Mapping Procedure.

   Detailed description of these terms can be found in
   [ITU-T_G709_2016].

3.  Overview of B100G in G.709

   This section provides an overview of new features in
   [ITU-T_G709_2016].

3.1.  OTUCn

   In G.709 [ITU-T_G709_2012], the standard mechanism for transporting a
   client signal is to first map it into an ODU signal (of the
   appropriate rate), and then switch the resulting ODU signal through
   the OTN network.  In the course of its traversal through the OTN
   network, the ODU signal generated by the mapper is either (a)
   multiplexed into higher-order ODU, and then encapsulated to form an
   OTU or (b) directly encapsulated into an OTU signal that defines the
   section layer.  The option (b), i.e. direct encapsulation into an OTU
   was possible only for ODU1/ODU2/ODU3/ODU4; ODU signals with other
   rates (e.g.  ODUflex) would first have to be processed per option (a)
   above.  The term "client signal" is generic in the sense that it
   encompasses both Constant Bit rate (CBR) clients (e.g. 10GBASE-R,
   SONET OC-768), or packet traffic -- where the goal is to transfer the
   payload from end-to-end (without regard for bit transparency at the
   PCS layer).  Given that OTU4 was the highest rate section layer
   signal supported in [ITU-T_G709_2012], the client signal rates were
   limited to be less than 100G (if ODU-VCAT was not used).

   In order to carry client signals with rates greater than 100Gbps,
   [ITU-T_G709_2016] takes a general and scalable approach that
   decouples the rates of OTU signals from the client rate evolution.
   The new OTU signal is called OTUCn; this signal is defined to have a



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   rate of (approximately) n*100G.  The following are the key
   characteristics of the OTUCn signal:

   a.  The OTUCn signal contains one ODUCn, which in turn contains one
       OPUCn signal.  The OTUCn and ODUCn signals perform digital
       section roles only (see [ITU-T_G709_2016]:Section 6.1.1).  The
       OTUCn and ODUCn can be seen as being analogous to the regenerator
       section, and multiplex section in SDH respectively.

   b.  The OTUCn signals can be viewed as being formed by interleaving n
       OTUC signals (where are labeled 1, 2, ..., n), each of which has
       the format of a standard OTUk signal without the FEC columns (per
       [ITU-T_G709_2016]:Figure 7-1).  The ODUCn, and OPUCn have a
       similar structure, i.e. they can be seen as being formed by
       interleaving n instances of ODUC, OPUC signals (respectively) The
       OTUC signal contains the ODUC, and OPUC signals, just as in the
       case of fixed rate OTUs defined in G.709 [ITU-T_G709_2016].

   c.  Each of the OTUC "slices" have the same overhead (OH) as the
       standard OTUk signal in G.709 [ITU-T_G709_2016].  The combined
       signal OTUCn has n instances of OTUC OH, ODUC OH, and OPUC OH.

   d.  The OTUC signal has a slightly higher rate compared to the OTU4
       signal (without FEC); this is to ensure that the OPUC payload
       area can carry an ODU4 signal.

3.1.1.  Carrying OTUCn between 3R points

   As explained above, within G.709 [ITU-T_G709_2016], the OTUCn, ODUCn
   and OPUCn signal structures are presented in a (physical) interface
   independent manner, by means of n OTUC, ODUC and OPUC instances that
   are marked #1 to #n.  Specifically, the definition of the OTUCn
   signal does not cover aspects such as FEC, modulation formats, etc.
   These details are defined as part of the adaptation of the OTUCn
   layer to the optical layer(s).  The specific interleaving of
   OTUC/ODUC/OPUC signals onto the optical signals is interface specific
   and specified for OTN interfaces with standardized application codes
   in the interface specific recommendations (G.709.x).

   The following scenarios of OTUCn transport need to be considered (see
   Figure 1):

   a.  inter-domain interfaces: These types of interfaces are used for
       connecting OTN edge nodes to (a) client equipment (e.g. routers)
       or (b) hand-off points from other OTN networks.  ITU-T has
       standardized the Flexible OTN (FlexO) interfaces to support these
       functions.  Recommendation [ITU-T_G709.1] specifies a flexible
       interoperable short-reach OTN interface over which an OTUCn (n



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       >=1) is transferred, using bonded FlexO interfaces which belong
       to a FlexO group.  The FlexO group supports physical interface
       bonding, management of the group members, overhead for
       communication between FlexO peers etc. (these overheads are
       separate from the GCC0 channel defined over OTUCn).  In its
       current form, Recommendation [ITU-T_G709.1] is limited to the
       case of transporting OTUCn signals using n 100G Ethernet PHY(s).
       The mechanisms for transporting the OTUCn signals over 100G
       optical interfaces are specified in [ITU-T_G709.1] and are not
       repeated here.  When the PHY(s) for the emerging set of Ethernet
       signals, e.g. 200GbE and 400GbE, become available, new
       recommendations can define the required adaptations.

   b.  intra-domain interfaces: In these cases, the OTUCn is transported
       using a proprietary (vendor specific) encapsulation, FEC etc.  In
       future, it may be possible to transport OTUCn for intra-domain
       links using future variants of FlexO.

    ==================================================================


          +--------------------------------------------------------+
          |                 OTUCn signal                           |
          +--------------------------------------------------------+
          |  Inter+Domain    |  Intra+Domain    |  Intra+Domain    |
          |  Interface (IrDI)|  Interface (IaDI)|  Interface       |
          |  FlexO (G.709.1) |  FlexO (G.709.x) |  Proprietary     |
          |                  |  (Future)        |  Encap, FEC etc. |
          +--------------------------------------------------------+


    ==================================================================

                  Figure 1: OTUCn transport possibilities

   It is possible for an OTUCn signal to be transported via multiple
   hops of lower-layer adaptation (see Figure 2).  In this scenario, the
   OTUCn spans multiple optical paths joined by a FlexO segment.  An
   end-to-end OTUCn LSP needs to be setup after the optical circuits are
   established.  The information about the FlexO interfaces (and group)
   are configured at the FlexO endpoints, and there is no dynamic setup.










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    ==================================================================


              Optical Segment                   Optical Segment
          <-------------->                   <-------------->

     +------+         +------+           +------+        +------+
     |      |         |      +-----------+      |        |      |
     |  A   +---------+  B   |-----------|  C   +--------+  D   |
     |      |         |      +-----------+      |        |      |
     +------+         +------+     ^     +------+        +------+
                                   |
                                   +
                                  FlexO Group
          <-------------------------------------------------->  OTUCn

             +-------+         +-------+            +-------+
             | OTUCn |         | OTUCn |            | OTUCn |
             +-------+         +-------+            +-------+
             | OTSiG |         | FlexO |            | OTSiG |
             +-------+         +-------+            +-------+


    ==================================================================

                   Figure 2: OTUCn transport - Multihop

   This document views FlexO (even if there are some digital sub-layers
   involved in the adaptation) and other OTUCn transport mechanisms as
   "lower layers", and are therefore considered out-of-scope.  The OTUCn
   layer operates independent of the method used to transport the
   signal.

3.2.  ODUCn

   The ODUCn signal [ITU-T_G709_2016] can be viewed as being formed by
   the appropriate interleaving of content from n ODUC signal instances.
   The ODUC frames have the same structure as a standard ODU -- in the
   sense that it has the same Overhead (OH) area, and the payload area
   -- but has a higher rate since its payload area can embed an ODU4
   signal.  The ODUCn signal can be formed in one of the following ways:

      By multiplexing lower-rate (i.e. both low-order and high-order)
      ODUk signals.

      Each of the n instances of ODUC can carry the NULL signal (as
      specified in [ITU-T_G709_2016]: Section 17.5.1)




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      Each of the n instances of ODUC can carry the PN-11 PRBS test
      sequence (as specified in [ITU-T_G709_2016]: Section 17.5.2)

      It is concievable that vendors might implement proprietary
      mappings (Payload Type values of 0x80-x8F)of non-OTN client
      signals.  An interoperable control plane cannot make use of these
      proprietary ODUCn signals, and hence this case isn't considered in
      this document.

   The ODUCn signals have a rate that is captured in Table 1.

   +----------+--------------------------------------------------------+
   | ODU Type |                      ODU Bit Rate                      |
   +----------+--------------------------------------------------------+
   |  ODUCn   | n x 239/226 x 99,532,800 kbit/s = n x 105,258,138.053  |
   |          |                         kbit/s                         |
   +----------+--------------------------------------------------------+

                           Table 1: ODUCn rates

   The ODUCn is a multiplex section ODU signal, and is mapped into an
   OTUCn signal which provides the regenerator section layer.  In some
   scenarios, the ODUCn, and OTUCn signals will be co-terminous, i.e.
   they will have identical source/sink locations.  [ITU-T_G709_2016]
   and [ITU-T_G872] allow for the ODUCn signal to pass through a digital
   regenerator node which will terminate the OTUCn layer, but will pass
   the regenerated (but otherwise untouched) ODUCn towards a different
   OTUCn interface where a fresh OTUCn layer will be initiated (see
   Figure 3).  In this case, an ODUCn LSP needs to be set up to traverse
   the 3 OTUCn segments.

   Specifically, the OPUCn signal flows through these regenerators
   unchanged.  That is, the set of client signals, their TPNs, trib-slot
   allocation remains unchanged.  Note however that the ODUCn Overhead
   (OH) might be modified if TCM sub-layers are instantiated in order to
   monitor the performance of the repeater hops.  In this sense, the
   ODUCn should not be seen as a general ODU which can be switched via
   an ODUk cross-connect.













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   ==================================================================


                ^ FlexO group                                  ^ FlexO group
               |                                              |
+--------+     |     +--------+                +--------+     |    +--------+
|        +-----------+        |                |        +----------+        |
| OTN    |-----------| OTN    |                | OTN    |----------| OTN    |
| DXC    +-----------+ WXC    +----------------+ WXC    +----------+ DXC    |
|        |           | 3R     |                | 3R     |          |        |
+--------+           +--------+                +--------+          +--------+

     <------------------>  <----------------------> <------------------>
           OTUCn/FlexO            OTUCn/OTSiG            OTUCn/FlexO

     <-----------------------------------------------------------------> ODUCn


   ==================================================================

                     Figure 3: Multi-hop ODUCn signal

3.3.  OTUCn-M

   The standard OTUCn signal has the same rate as that of the ODUCn
   signal as captured in Table 1.  This implies that the OTUCn signal
   can only be transported over wavelength groups which have a total
   capacity of multiples of (approximately) 100G.  Modern DSPs support a
   variety of bit rates per wavelength, depending on the reach
   requirements for the optical link.  With this in mind, ITU-T supports
   the notion of a reduced rate OTUCn signal, termed the OTUCn-M.  The
   OTUCn-M signal is derived from the OTUCn signal by retaining all the
   n instances of overhead (one per OTUC slice) and crunching the OPUC
   tributary slots marked as "unavailable".

3.4.  OPUCn Time Slot Granularity

   [ITU-T_G709_2012] introduced the support for 1.25G granular tributary
   slots in OPU2, OPU3, and OPU4 signals.  With the introduction of
   higher rate signals such as the OPUCn, it is no longer practical for
   the optical networks (and the datapath hardware) to support a very
   large number of flows at such a fine granularity.  ITU-T has defined
   the OPUC with a tributary slot granularity of 5G.  This means that
   the ODUCn signal has 20*n tributary slots (of 5Gbps capacity).







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3.5.  Structure of OPUCn MSI with Payload type 0x22

   As mentioned above, the OPUCn signal has 20*n 5G tributary slots.
   The OPUCn contains n PSI structures, one per OPUC instance.  The PSI
   structure consists of the Payload Type (of 0x22), followed by a
   Reserved Field (1 byte), followed by the MSI.  The OPUCn MSI field
   has a fixed length of 40*n bytes and indicates the ODTU content of
   each TS of an OPUCn.  Two bytes are used for each of the 20*n
   tributary slots, and each such information structure has the
   following format ([ITU-T_G709_2016] G.709:Section 20.4.1):

   a.  The TS availability bit 1 indicates if the tributary slot is
       available or unavailable

   b.  The TS occupation bit 9 indicates if the tributary slot is
       allocated or unallocated

   c.  The tributary port number in bits 2-8, 10-16 indicates the
       identity of the OTN client signal (i.e.  LO-ODU) that is being
       transported in this TS; a flexible assignment of tributary port
       to tributary slots is possible.  Note that 1 <= TPN <= 10*n.  The
       value is set to all-0s when the occupation bit has the value 0
       (tributary slot is unallocated).  The same TPN value is used in
       all the TS(s) assigned to a given OTN client client signal.

3.6.  Client Signal Mappings

   Note that [ITU-T_G709_2016] introduces support for OTUCn signals with
   rates of n*100G and also introduces support for client signals with
   rates larger than 100G (e.g. the future 400GBASE-R client being
   standardized by IEEE, higher packet streams from NPUs).  The approach
   taken by the ITU-T to map non-OTN client signals to the appropriate
   ODU containers is as follows:

   a.  All client signals with rates less than 100G are mapped as
       specified in [ITU-T_G709_2016]:Clause 17.  These mappings are
       identical to those specified in the earlier revision of G.709
       [ITU-T_G709_2012].  Thus, for example, the 1000BASE-X/10GBASE-R
       signals are mapped to ODU0/ODU2e respectively (see Table 2 --
       based on Table 7-2 in [ITU-T_G709_2016])

   b.  Always map the new and emerging client signals to ODUflex signals
       of the appropriate rates (see Table 2 -- based on Table 7-2 in
       [ITU-T_G709_2016])

   c.  Drop support for ODU Virtual Concatenation.  This simplifies the
       network, and the supporting hardware since multiple different
       mappings for the same client are no longer necessary.  Note that



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       legacy implementations that transported sub-100G clients using
       ODU VCAT shall continue to be supported.

   d.  ODUflex signals are low-order signals only.  If the ODUflex
       entities have rates of 100G or less, they can be transported
       using either an ODUk (k=1..4) or an ODUCn server layer.  On the
       other hand, ODUflex connections with rates greater than 100G will
       require the server layer to be ODUCn.  The ODUCn signals must be
       adapted to an OTUCn signal.  Figure 4 illstrates the hierarchy of
       the digital signals defined in [ITU-T_G709_2016].

   +----------------+--------------------------------------------------+
   |    ODU Type    |                   ODU Bit Rate                   |
   +----------------+--------------------------------------------------+
   |      ODU0      |                  1,244,160 Kbps                  |
   |      ODU1      |             239/238 x 2,488,320 Kbps             |
   |      ODU2      |             239/237 x 9,953,280 Kbps             |
   |     ODU2e      |            239/237 x 10,312,500 Kbps             |
   |      ODU3      |            239/236 x 39,813,120 Kbps             |
   |      ODU4      |            239/227 x 99,532,800 Kbps             |
   |  ODUflex for   |         239/238 x Client signal Bit rate         |
   |   CBR client   |                                                  |
   |    signals     |                                                  |
   |  ODUflex for   |               Configured bit rate                |
   |  GFP-F mapped  |                                                  |
   | packet traffic |                                                  |
   |  ODUflex for   | s x 239/238 x 5 156 250 kbit/s: s=2,8,5*n, n >=  |
   |   IMP mapped   |                        1                         |
   | packet traffic |                                                  |
   |  ODUflex for   | 103 125 000 x 240/238 x n/20 kbit/s, where n is  |
   |  FlexE aware   | total number of available tributary slots among  |
   |   transport    | all PHYs which have been crunched and combined.  |
   +----------------+--------------------------------------------------+

     Note that this table doesn't include ODUCn -- since it cannot be
   generated by mapping a non-OTN signal.  An ODUCn is always formed by
                      multiplexing multiple LO-ODUs.

        Table 2: Types and rates of ODUs usable for client mappings












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    ==================================================================


                     Clients (e.g. SONET/SDH, Ethernet)
                          +       +      +
                          |       |      |
       +------------------+-------+------+------------------------+
       |                     OPUk                                 |
       +----------------------------------------------------------+
       |                     ODUk                                 |
       +-----------------------+---------------------------+------+
       | OTUk, OTUk.V, OTUkV   |          OPUk             |      |
       +----------+----------------------------------------+      |
       | OTLk.n   |            |          ODUk             |      |
       +----------+            +---------------------+-----+      |
                               | OTUk, OTUk.V, OTUkV |   OPUCn    |
                               +----------+-----------------------+
                               | OTLk.n   |          |   ODUCn    |
                               +----------+          +------------+
                                                     |   OTUCn    |
                                                     +------------+


    ==================================================================

   Figure 4: Digital Structure of OTN interfaces (from G.709:Figure 6-1)

4.  Usecases

   This section introduces various usecases that provide the rationale
   for the requirements that any solution must satisfy.  At a later
   point in time, it is possible to consolidate these usecases so that
   all the multiplexing (and demultiplexing) variants are encountered
   along the path of an end-to-end ODU circuit.

   Note-1: These usecases present scenarios in which OTUCn links are
   depicted.  These illustrations do not highlight how the OTUCn is
   transported between the 3R points.  That is, these usecases cover
   cases in which a standard FlexO interface (e.g. as defined in
   [ITU-T_G709.1]) is used, or whether a vendor specific mapping of
   OTUCn to OTSiG (as defined in [ITU-T_G872]) is used.  In other words,
   multiple variants of these usecases based on FlexO usage (or not) are
   not included in this document.

   Note-2: This version of the document covers many usecases in detail.
   Future versions of this document may combine multiple usecases (e.g.
   all cases involving ODUflex into one broad category), and retain only
   the minimal set of usecases.



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4.1.  100GE Client Service with a homogeneous chain of OTUC1 links

   In the scenario illustrated in Figure 5 a 100GBASE-R client is mapped
   into an ODU4 at NE1.  The resulting ODU4 signal is multiplexed into
   the ODUC1 server layer (using GMP) and further encapsulated to form
   the OTUC1 signal.  The links NE1-NE2, and NE2-NE3 are both OTUC1
   links -- and they can carry one 100GE client mapped into an ODU4
   server layer.  Actions performed at NE2 are: (a) terminate OTUC1, and
   ODUC1 towards NE1 (b) demultiplex the ODU4 signal from ODUC1 (c) map
   the ODU4 signal onto a different ODUC1/OTUC1 towards NE3.  NE3
   performs the inverse sequence of steps performed at NE1, and recovers
   the 100GBASE-R client from the ODU4 signal.  Note that the ODU4 and
   ODUC1 signals are not "interoperable" and that the ODUC1 is a server
   layer to the ODU4 signal.

   This illustration is also applicable to the usecase in which members
   of a FlexE group are transported in a flexe-unaware mode in the
   transport network.  Although this illustration included only OTUC1
   signals, any higher rate OTUCn signal can be substituted for these
   signals.  In this particular scenario, there are two adjacent ODUC1
   hops, and the NE2 demultiplexs (and multiplexes) the ODU4 onto the
   ODUC1.  It is possible to construct an alternative scenario in the
   case when NE2 acts as a regenerator, and doesn't terminate the ODUC1
   signals in the two hops, and instead repeats the ODUC1 signal; this
   scenario is specifically discussed in Section 4.6.

    ==================================================================


          +----------+                                  +----------+
          |  100GE   |                                  |  100GE   |
          +----------+        +---------------+         +----------+
          |  ODU4    |        |      ODU4     |         |  ODU4    |
          +----------+        +---------------+         +----------+
          |  ODUC1   |        | ODUC1 | ODUC1 |         |  ODUC1   |
          +----------+        +---------------+         +----------+
          |  OTUC1   +--------+ OTUC1 | OTUC1 +---------+  OTUC1   |
          +----------+        +---------------+         +----------+
             NE1                  NE2                     NE3

                   +------------->            +------------->
                      Scope of                    Scope of
                      OTUC1, ODUC1                OTUC1, ODUC1


    ==================================================================

                      Figure 5: 100GE Client service



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4.2.  100GE Client Service with a mix of OTU4, and OTUC1 links

   In the scenario illustrated in Figure 6 a 100GBASE-R client is mapped
   into an ODU4 at NE1.  The resulting ODU4 signal is encapsulated with
   an OTU layer to form the OTU4 signal.  Actions performed at NE2 are:
   (a) terminate OTU4 layer, and extract the ODU4 signal (b) map the
   ODU4 signal onto a different ODUC1/OTUC1 towards NE3.  NE3 performs
   the same set of actions that were performed by NE3 in Figure 5.  This
   usecase illustrates a scenario in which an ODU4 signal can span
   between network elements regardless of whether they support the OTUCn
   interfaces or not.

    ==================================================================


        +----------+                                  +----------+
        |  100GE   |                                  |  100GE   |
        +----------+        +---------------+         +----------+
        |  ODU4    |        |      ODU4     |         |  ODU4    |
        +----------+        +-------+-------+         +----------+
        |  OTU4    +--------+ OTU4  | ODUC1 |         |  ODUC1   |
        +----------+        +---------------+         +----------+
                                    | OTUC1 +---------+  OTUC1   |
                                    --------+         +----------+
             NE1                 NE2                     NE3

                +-------------->         +---------------->
                    Scope of                    Scope of
                    OTU4 layer                  OTUC1, ODUC1


    ==================================================================

    Figure 6: 100GE Client Service with a mix of OTU4, and OTUC1 links

4.3.  400GE Client Service with a mix of OTUCn links

   In the scenario illustrated in Figure 7 a 400GBASE-R client is mapped
   into an ODUflex at NE1.  The resulting ODUflex signal is multiplexed
   into an ODUC4 (using GMP), and then transformed into an OTUC4 signal.
   The links between NE1-NE2, and NE2-NE3 are OTUC4 and OTUC6
   (respectively).  Actions performed at NE2 are: (a) terminate OTUC4,
   and ODUC4 towards NE1 (b) demultiplex the ODUflex signal from ODUC4
   (c) map the ODUflex signal onto ODUC6/OTUC6 towards NE3.  NE3
   performs the inverse sequence of steps performed at NE1, and recovers
   the 400GBASE-R client from the ODUflex signal.





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   Although not specifically illustrated in this figure, the 200G of
   spare capacity in the NE2-NE3 links can be used to carry other client
   signals.. Although the scenario illustrated in Figure 7 is specific
   to 400GE, the treatment for packet clients at other rates (e.g. 25G,
   50G, 200G) follows a very similar processing sequence.  In the case
   of 25GBASE-R clients , the 25GE client signal will be mapped to an
   ODUflex, and can be multiplexed into an ODU4 signal, or an ODUCn
   signal as illustrated here.

    ==================================================================


        +----------+                                  +----------+
        |  400GE   |                                  |  400GE   |
        +----------+        +---------------+         +----------+
        |  ODUflex |        |    ODUflex    |         |  ODUflex |
        +----------+        +-------+-------+         +----------+
        |  ODUC4   |        | ODUC4 | ODUC6 |         |  ODUC6   |
        +----------+        +---------------+         +----------+
        |  OTUC4   +--------+ OTUC4 | OTUC6 +---------+  OTUC6   |
        +----------+        +-------+-------+         +----------+
           NE1                  NE2                     NE3

                 <------------->            <------------->
                    Scope of                    Scope of
                    OTUC4, ODUC4                OTUC6, ODUC6



    ==================================================================

                Figure 7: 400GE transport over OTUCn links

4.4.  FlexE aware transport over OTUCn links

   In the scenario illustrated in Figure 8 NE1 interfaces to a client
   equipment which includes the FlexE SHIM functions which originate/
   terminate a FlexE group.  The transport network edge node NE2 is
   FlexE aware -- but doesn't terminate the FlexE group.  NE1 may (as
   defined in the FlexE draft [I-D.izh-ccamp-flexe-fwk]), crunch the
   unavailable tributary slots in the FlexE PHY signals, and map the
   resultant stream to one or more ODUflex signals.  The links between
   NE1-NE2, and NE2-NE3 are OTUC4 and OTUC6 (respectively).  Actions
   performed at NE2 are: (a) terminate OTUC4, and ODUC4 towards NE1 (b)
   demultiplex the ODUflex signal from ODUC4 (c) map the ODUflex signal
   onto ODUC6/OTUC6 towards NE3.  NE3 recovers the Crunched and combined
   PHY(s) from the ODUflex signal, re-adds the unavailable calendar
   slots, and outputs the resulting stream towards the FlexE PHY(s).



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   In the scenario illustrated in Figure 8 the lowest rate OTUCn link is
   the OTUC4 link between NE1-NE2.  This means that the size of the
   FlexE group is at most 4.  FlexE groups with greater sizes can be
   handled by utilizing appropriate OTUCn links.  Note that at most 400G
   of the capacity of OTUC6 (or 600G) NE2-NE3 link is occupied by the
   ODUflex signal; the remaining bandwidth can be allocated to other
   client signals.

    ==================================================================


   FlexE    +----------+                       +----------+       FlexE
   group    | Crunched |                       | Crunche  |       Group
     +------> and      |                       | and      +-------->
            | Combined |                       | Combined | Add
            | PHY(s)   |                       | PHY(s)   | unavailable
            +----------+   +---------------+   +----------+ Calendar
            |  ODUflex |   |    ODUflex    |   |  ODUflex | slots
            +----------+   +-------+-------+   +----------+
            |  ODUC4   |   | ODUC4 | ODUC6 |   |  ODUC6   |
            +----------+   +---------------+   +----------+
            |  OTUC4   +---+ OTUC4 | OTUC6 +---+  OTUC6   |
            +----------+   +-------+-------+   +----------+
               NE1             NE2               NE3

                     <--------->        <----------->
                     Scope of            Scope of
                     OTUC4, ODUC4        OTUC6, ODUC6



    ==================================================================

             Figure 8: FlexE aware transport over OTUCn links

4.5.  FlexE Client transport over OTUCn links

   This use case (see Figure 9) concerns the scenario in which a FlexE
   group is terminated at the transport network edge node (via the FlexE
   SHIM function), and the FlexE clients are demultiplexed, and
   independently transported through the OTN network.  In the scenario
   illustrated in Figure 9 the lowest rate OTUCn link is the OTUC4 link
   between NE1-NE2.  This means that the maximum bit rate of the FlexE
   client is at most 400G.  FlexE clients with greater sizes can be
   handled by utilizing appropriate OTUCn links.  This figure
   illustrates the case in which one FlexE client is transported between
   NE1 and NE3.  Other FlexE clients recovered at NE1 can routed
   independently to NE3, or to other network elements.



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    ==================================================================



       +-----------------+                       +---------------+
       |     FlexE       |                       |    FlexE      |
       |     Client      |                       |    Client     |
       +-----------------+                       +---------------+
       | FlexE |         |   +---------------+   |       | Flex  |
       | SHIM  | ODUflex |   |    ODUflex    |   |ODUflex| SHIM  |
       +-----------------+   +---------------+   +---------------+
       | FlexE | ODUC4   |   | ODUC4 | ODUC6 |   | ODUC6 | FlexE |
  +----+ PHY(s +---------+   +---------------+   +-------+ PHY(s)+---->
 FlexE |       | OTUC4   +---+ OTUC4 | OTUC6 +---+ OTUC6 |       | FlexE
 Group +-----------------+   +---------------+   +---------------+ Group
                  NE1            NE2                 NE3

                    <------------>       <----------->
                       Scope of            Scope of
                       OTUC4, ODUC4        OTUC6, ODUC6


    ==================================================================

             Figure 9: FlexE client transport over OTUCn links

4.6.  Multihop ODUCn link

   As mentioned in the introductory section, the ODUCn is not a
   switchable entity.  The ODUCn layer is a server layer, which more-or-
   less occupies the position of a section layer in OTN networks.  As
   such, the ODUCn signal must be terminated and the contained low-order
   ODU flows can be switched independently to other OTN interfaces.
   G.709 and G.872 however allow for digital regenerators to terminate
   the OTUCn layer, and reinject the ODUCn layer towards another
   interface (where a new OTUCn section layer is started).  This
   scenario is illustrated in Figure 10.  In this figure, NE3 is the
   regenerator.  The ODUC2 signal is terminated at NE2, and NE4.  At the
   regeneration points, all the clients embedded inside the ODUCn signal
   are not touched (i.e. no TS changes can occur).  More specifically,
   the OPUC2 signal is not modified in any way.  However, the ODUC2 OH
   may be modified if intrusive TCM monitoring points are applied to the
   ODUC2 signal at NE3.  It is for this reason that the ODUC2 entity
   must be visible at NE3.

   In scenarios involving multi-hop ODUCn links, GMPLS signalling will
   be required to setup multiple ODUCn LSPs, each covering a regenerator
   section (since an end-to-end ODUCn LSP is not possible except in very



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   simple configurations).  A LO-ODU can then be switched across
   multiple ODUCn LSPs (possibly with different rates).

    ==================================================================


 +----------+                                               +----------+
 |  100GE   |                                               |  100GE   |
 +----------+     +---------------+                         +----------+
 |  ODU4    |     |      ODU4     |                         |  ODU4    |
 +----------+     +-------+-------+       +---------+       +----------+
 |  ODUC1   |     | ODUC1 | ODUC2 |       |  ODUC2  |       |  ODUC2   |
 +----------+     +---------------+       +---------+       +----------+
 |  OTUC1   +-----+ OTUC1 | OTUC2 +-------+  OTUC2  +-------+  OTUC2   |
 +----------+     +-------+-------+       +---------+       +----------+
    NE1               NE2                     NE3             NE4

          <------------->      <------------->     <------------->
             Scope of               OTUC2                OTUC2
             OTUC1, ODUC1

                               <--------------------------------->
                                             ODUC2



    ==================================================================

                      Figure 10: Multihop ODUCn link

4.7.  Use of OTUCn-M links

   The scenario illustrated in Figure 11 is a variant of the basic
   usecase presented in Figure 5.  The only difference is that the
   second hop of the ODU4 connection makes use of a OTUC2-30 link which
   has a capacity of 150G.















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    ==================================================================


          +----------+                                  +-----------+
          |  100GE   |                                  |  100GE    |
          +----------+        +------------------+      +-----------+
          |  ODU4    |        |      ODU4        |      |  ODU4     |
          +----------+        +-------+----------+      +-----------+
          |  ODUC1   |        | ODUC1 | ODUC2    |      |  ODUC2    |
          +----------+        +------------------+      +-----------+
          |  OTUC1   +--------+ OTUC1 | OTUC2-30 +------+  OTUC2-30 |
          +----------+        +-------+----------+      +-----------+
             NE1                  NE2                     NE3

                   +------------->            +------------->
                      Scope of                    Scope of
                      OTUC1, ODUC1                OTUC2-30
                                                  ODUC2



    ==================================================================

            Figure 11: 100GE Client service over OTUCn-M links

4.8.  Intermediate State of ODU mux

   The ODUCn links have a tributary slot granularity of 5G -- and this
   makes it a bit inefficient if a small number of ODU0 flows have to be
   switched across an ODUCn links.  In these cases, it is conceivable
   that the intermediate nodes may offer the convenience of a
   intermediate-stage multiplexing, whereby multiple ODU0 flows are
   first multiplexed into a higher rate container (e.g.  ODU2), and then
   multiplexed into an ODUCn signal.  This however assumes that all
   these ODU0 flows are co-routed in the network.  If this assumption
   cannot be made, the only solution is to multiplex these ODU0 flows
   into higher rate flows, from the source of the traffic.  This usecase
   isn't elaborated in this document.  We can add details if required.

5.  GMPLS Implications

5.1.  OTN ODUCn/OTUCn hierarchy

   As described in [ITU-T_G872], the digital layers of the OTN are
   divided into the OTU layer and a hierarchy of one or more ODU layers.
   As an ODUCn cannot be used to support non-OTN client signals, the OTN
   client signals (e.g.  ODU0, ODU1, ODU2, ODU2e, ODU3, ODU4, ODUflex)
   are first multiplexed into an ODUCn container, then the ODUCn



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   container is then mapped into OTUCn (see Figure 1).  The signal
   hierarchy supported by the ODUCn and OTUCn needs to be taken into
   consideration in control plane Routing and Signaling.

   ODUCn based connection management is concerned with controlling the
   connectivity of ODUCn paths.  According to [ITU-T_G872], the
   intermediate nodes with ODUCn do not support the switching of ODUCn
   tributary slot.  Intermediate ODUCn points are only considered as a
   forwarding node.  Once an ODUCn path is used to transport client
   signal, the TS occupied will not change across the ODUCn network.

5.2.  Implications for GMPLS Signaling

   [RFC7139] extends the base RSVP-TE signaling specification [RFC4328]
   to define RSVP-TE signaling extensions that can used to control OTN
   networks built in accordance with [ITU-T_G709_2012].
   [ITU-T_G709_2016] introduced some new containers, such as OPUCn,
   ODUCn, and OTUCn.  The mechanisms defined in [RFC7139] do not support
   these new OTN features.  Therefore, GMPLS signaling protocols MUST be
   extended to support this new functionality.  The following summarizes
   key aspects that should be considered for GMPLS signaling extensions:

   a.  Per the description in clause 7 of [ITU-T_G872], "the digital
       layers of the OTN are divided into the OTU layer and a hierarchy
       of one or more ODU layers".  In B100G links, the ODUCn layer is
       the bottom of the ODU hierarchy, and an ODUCn (induced) LSP needs
       to be established before the LO-ODUs can flow across this link.
       The traffic parameters in a signaling message should be extended
       to support the new signal type(s) for the ODUCn signals.  This
       approach keeps the treatment for ODUCn signals consistent with
       that of other ODU(s).

   b.  Support the new TS granularity: the signaling protocol should be
       able to identify the TS granularity (i.e., the new 5 Gbps TS
       granularity) to be used for establishing a Hierarchical LSP that
       will be used to carry service LSP(s) requiring a specific TS
       granularity.

   c.  Support for LSP setup of new ODUCn containers with related
       mapping and multiplexing capabilities.

   d.  A new label format MUST carry the information about the set of
       ODUCn tributary slots allocated to a specific LO-ODU.  It MUST be
       possible for a single LO-ODU to occupy an arbitrary set of
       tributary slots, selected from one or more OTUC/ODUC instances.

   e.  Support for TPN allocation and negotiation: TPN needs to be
       configured as part of the MSI information.  A signaling mechanism



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       must be identified to carry TPN information if the control plane
       is used to configure MSI information.  The range of TPN is
       [1..10*n] and the range of TPN is smaller than the number of
       tributary slots (20*n); e.g. it is not possible to carry 15 5G
       ODUflex signals in an ODUC1.  This constraint MUST be taken into
       account in the control plane supported).

   f.  Support for LSP setup of OTUCn sub rates (OTUCn-M) path: based on
       previous extensions, there should be new signal mechanism to
       declare the OTUCn-m information.  The GMPLS signalling protocol
       SHALL support the setup of OTUCn sub rates (OTUCn-M) LSP, which
       includes the negotiation of unavaliable slots number, slots
       postion and allocation of slot resources.

   g.  The GMPLS signalling protocol should be able to specify the new
       ODUCn/OTUCn signal types and related traffic information.  The
       traffic parameters should be extended in a signalling message to
       support the new ODUCn/OTUCn signal types

5.3.  Implications for GMPLS Routing

   The path computation process needs to select a suitable route for an
   ODUCn/OTUCn/OTUCn-M connection request.  In order to perform the path
   computation, it needs to evaluate the available bandwidth/slots
   available on one or more candidate links.  The routing protocol
   SHOULD be extended to carry sufficient information to represent ODU
   Traffic Engineering (TE) topology.

   The Interface Switching Capability Descriptors defined in [RFC4203]
   present a new constraint for LSP path computation.  [RFC4203] defines
   the Switching Capability, related Maximum LSP Bandwidth, and
   Switching Capability specific information.  [RFC7138] updates the
   ISCD to support ODU4, ODU2e and ODUflex.  The new Switching
   Capability specific information provided in [RFC7138] have to be
   adapted to support new features contained in [G709-2016].  The
   following requirements should be considered:

   a.  Support for carrying the link multiplexing capability: As
       discussed in Section 3.1.2, many different types of low-order
       ODU(s) (e.g.  ODUflex, ODU4) can be multiplexed into the ODUCn.
       An ODUCn path may support one or more types of ODUk signals.  The
       routing protocol should be capable of carrying this multiplexing
       capability.

   b.  Support for advertising 5G Tributary Slot Granularity introduced
       [ITU-T_G709_2016].





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   c.  Support for advertisement of available bandwidth in an ODUCn
       path.

6.  Open Issues

   1.  [Note (RSV)]: This document elaborates on several FlexE and 400GE
       usecases.  Since all these cases map the non-OTN client signals
       into ODUflex signals of various rates, it might be better to
       combine all these usecases into one category that handles ODUflex
       LSPs.  From a control plane point of view, the differences in the
       data plane processing are not relevant.  This change will be made
       in a future revision of this document (if there is agreement).

7.  Acknowledgements

8.  Authors (Full List)

      Qilei Wang (editor)

      ZTE

      Nanjing, China

      Email: wang.qilei@zte.com.cn




      Radha Valiveti (editor)

      Infinera Corp

      Sunnyvale, CA, USA

      Email: rvaliveti@infinera.com




      Haomian Zheng (editor)

      Huawei

      CN

      EMail: zhenghaomian@huawei.com





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      Huub van Helvoort

      Hai Gaoming B.V

      EMail: huubatwork@gmail.com

      Sergio Belotti

      Nokia

      EMail: sergio.belotti@nokia.com




      Iftekhar Hussain

      Infinera Corp

      Sunnyvale, CA, USA

      Email: IHussain@infinera.com




      Daniele Ceccarelli

      Ericsson

      Email: daniele.ceccarelli@ericsson.com

9.  Contributors

      Rajan Rao, Infinera Corp, Sunnyvale, USA, rrao@infinera.com

      Fatai Zhang, Huawei,zhangfatai@huawei.com

      Italo Busi, Huawei,italo.busi@huawei.com

      Zheyu Fan, Huawei, fanzheyu2@huawei.com

      Yuanbin Zhang, ZTE, Beiing, zhang.yuanbin@zte.com.cn

      Zafar Ali, Cisco Systems, zali@cisco.com

      Daniel King, d.king@lancaster.ac.uk




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      Manoj Kumar, Cisco Systems, manojk2@cisco.com

      Antonello Bonfanti, Cisco Systems, abonfant@cisco.com

      Akshaya Nadahalli, Cisco Systems, anadahal@cisco.com

10.  IANA Considerations

   This memo includes no request to IANA.

11.  Security Considerations

   None.

12.  References

12.1.  Normative References

   [ITU-T_G709.1]
              ITU-T, "ITU-T G.709.1: Flexible OTN short-reach interface;
              2016",  , 2016.

   [ITU-T_G709_2012]
              ITU-T, "ITU-T G.709: Optical Transport Network Interfaces;
              02/2012",
               http://www.itu.int/rec/T-REC-G..709-201202-S/en, February
              2012.

   [ITU-T_G709_2016]
              ITU-T, "ITU-T G.709: Optical Transport Network Interfaces;
              07/2016",
               http://www.itu.int/rec/T-REC-G..709-201606-P/en, July
              2016.

   [ITU-T_G872]
              ITU-T, "ITU-T G.872: The Architecture of Optical Transport
              Networks; 2017",  http://www.itu.int/rec/T-REC-G.872/en,
              January 2017.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.








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   [RFC4328]  Papadimitriou, D., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Extensions for G.709 Optical
              Transport Networks Control", RFC 4328,
              DOI 10.17487/RFC4328, January 2006,
              <http://www.rfc-editor.org/info/rfc4328>.

   [RFC7138]  Ceccarelli, D., Ed., Zhang, F., Belotti, S., Rao, R., and
              J. Drake, "Traffic Engineering Extensions to OSPF for
              GMPLS Control of Evolving G.709 Optical Transport
              Networks", RFC 7138, DOI 10.17487/RFC7138, March 2014,
              <http://www.rfc-editor.org/info/rfc7138>.

   [RFC7139]  Zhang, F., Ed., Zhang, G., Belotti, S., Ceccarelli, D.,
              and K. Pithewan, "GMPLS Signaling Extensions for Control
              of Evolving G.709 Optical Transport Networks", RFC 7139,
              DOI 10.17487/RFC7139, March 2014,
              <http://www.rfc-editor.org/info/rfc7139>.

12.2.  Informative References

   [I-D.izh-ccamp-flexe-fwk]
              Hussain, I., Valiveti, R., Pithewan, K., Wang, Q.,
              Andersson, L., Zhang, F., Chen, M., Dong, J., Du, Z.,
              zhenghaomian@huawei.com, z., Zhang, X., Huang, J., and Q.
              Zhong, "GMPLS Routing and Signaling Framework for Flexible
              Ethernet (FlexE)", draft-izh-ccamp-flexe-fwk-00 (work in
              progress), October 2016.

Authors' Addresses

   Qilei Wang (editor)
   ZTE
   Nanjing
   CN

   Email: wang.qilei@zte.com.cn


   Radha Valiveti (editor)
   Infinera Corp
   Sunnyvale
   USA

   Email: rvaliveti@infinera.com







Wang, et al.             Expires January 3, 2018               [Page 25]


Internet-Draft              B100G Extensions                   July 2017


   Haomian Zheng (editor)
   Huawei
   CN

   Email: zhenghaomian@huawei.com


   Huub van Helvoort
   Hai Gaoming B.V

   Email: huubatwork@gmail.com


   Sergio Belotti
   Nokia

   Email: sergio.belotti@nokia.com


































Wang, et al.             Expires January 3, 2018               [Page 26]


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