Internet Engineering Task Force                             Q. Wang, Ed.
Internet-Draft                                                       ZTE
Intended status: Informational                          R. Valiveti, Ed.
Expires: August 31, 2019 January 8, 2020                                   Infinera Corp
                                                           H. Zheng, Ed.
                                                                  Huawei
                                                             H. Helvoort
                                                         Hai Gaoming B.V
                                                              S. Belotti
                                                                   Nokia
                                                       February 27,
                                                            July 7, 2019

       Applicability of GMPLS for B100G Optical Transport Network
           draft-ietf-ccamp-gmpls-otn-b100g-applicability-00
           draft-ietf-ccamp-gmpls-otn-b100g-applicability-01

Abstract

   This document examines the applicability of using current existing
   GMPLS routing and signaling to set up ODUk/ODUflex over ODUCn link,
   as a result of the support of OTU/ODU links with rates larger than
   100G in the 2016 version of G.709.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     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 . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  OTUCn-M . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.4.  Time Slot Granularity . . . . . . . . . . . . . . . . . .   8
     3.5.  Structure of OPUCn MSI with Payload type 0x22 . . . . . .   8
     3.6.  Client Signal Mappings  . . . . . . . . . . . . . . . . .   8
   4.  Applicability and GMPLS Implications  . . . . . . . . . . . .  10
     4.1.  Applicability and Challenges  . . . . . . . . . . . . . .  10
     4.2.  GMPLS Implications and Applicability  . . . . . . . . . .  12
       4.2.1.  TE-Link Representation  . . . . . . . . . . . . . . .  12
       4.2.2.  Implications and Applicability for GMPLS Signalling .  12
       4.2.2.  13
       4.2.3.  Implications and Applicability for GMPLS Routing  . .  13  14
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14  15
   6.  Authors (Full List) . . . . . . . . . . . . . . . . . . . . .  14  15
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  15  16
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  16  17
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16  17
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  16  17
     10.2.  Informative References . . . . . . . . . . . . . . . . .  17  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17  18

1.  Introduction

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

   While the 2016 version of G.709 [ITU-T_G709_2016] introduces support
   for new higher rate ODU signals, termed ODUCn (which have a nominal
   rate of n x 100 Gbps), how to use GMPLS to configure ODUCn should be
   taken into consideration.  But it seems how to configure the ODUCn
   link needs more discussion, so this draft mainly focuses on the use
   of current GMPLS mechanisms to set up ODUk/ODUflex over an existing
   ODUCn link.

   This document presents an overview of the changes introduced in
   [ITU-T_G709_2016] to motivate the present topic and then analyzes how
   the current GMPLS routing and signalling mechanisms can be utilized
   to setup ODUk/ODUflex connections over ODUCn links.

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 is out of scope of this document.  But in order to
   facilitate the description of the challenges brought by
   [ITU-T_G709_2016] to B100G GMPLS routing and signalling, some general
   description about OTSi will be included in this draft.

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
       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.

   h.  OTSiG: see [ITU-T_G872]

   i.  OTSiA: see [ITU-T_G872]

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

   a.  The OTUCn signal contains one ODUCn.  The OTUCn and ODUCn signals
       perform digital section roles only (see
       [ITU-T_G709_2016]:Section 6.1.1)

   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 have a similar
       structure, i.e. they can be seen as being formed by interleaving
       n instances of ODUC signals (respectively).  The OTUC signal
       contains the ODUC 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.

   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
       >=1) is transferred, using bonded FlexO interfaces which belong
       to a FlexO group.  In its current form, Recommendation
       [ITU-T_G709.1] is limited to the case of transporting OTUCn
       signals using n 100G Ethernet PHY(s).  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

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 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 2).  In this case, the ODUCn is carried by 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.

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

+--------+           +--------+                +--------+          +--------+
|        +-----------+        |                |        +----------+        |
| OTN    |-----------| OTN    |                | OTN    |----------| OTN    |
| DXC    +-----------+ WXC    +----------------+ WXC    +----------+ DXC    |
|        |           | 3R     |                | 3R     |          |        |
+--------+           +--------+                +--------+          +--------+
    <--------------------------------ODUCn------------------------------>
     <------------------>  <----------------------> <-----------------------> <------------------>
             OTUCn                   OTUCn                  OTUCn

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

                          Figure 2: 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.  In other words, it is possible to
   extend the reach of an optical link (i.e. increase the physical
   distance covered) by lowering the bitrate of the client signal that
   is modulated onto the carrier(s).  By the very nature of the OTUCn
   signal, it is constrained to rates which are multiples of
   (approximately) 100G.  If it so happens that the total rate of the
   LO-ODUs carried over the ODUCn is smaller than n X 100G, it is
   possible to "crunch" the OTUCn to remove the unused capacity.  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) but only M tributary slots of capacity.

3.4.  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, 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).  It is worthwhile
   considering that the range of tributary port number (TPN) is 10*n,
   and not 20*n which would allow for a different client signal to be
   carried in each TS.  As an example, it will not be possible to embed
   15 5G ODUflex signals in a ODUC1.

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 availability of
   each TS.  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.  b.c.  The tributary port # in bits 2 to 8 and 10 to 16 indicates
       the port number of the client that is being carried in this
       specific TS; a flexible assignment of tributary port to tributary
       slots is possible.  Numbering of tributary ports are is from 1 to
       10n.

3.6.  Client Signal Mappings

   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
       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 3 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

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

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

4.  Applicability and GMPLS Implications

4.1.  Applicability and Challenges

   Two typical scenarios are depicted in Appendix XIII of
   [ITU-T_G709_2016], which are also introduced into this document to
   help analyze the potential extension to GMPLS needed.  Though these
   two scenarios are mainly introduced in G.709 to describe OTUCn sub
   rates application, they can also be used to describe general OTUCn
   application.  One thing that should be note is these two scenarios
   are a little different from those described in [ITU-T_G709_2016], as
   the figure in this section include the OTSi(G) in to facilitate the
   description of the challenge brought by [ITU-T_G709_2016].

   The first scenarios is depicted in Figure 4.  This scenario deploys
   OTUCn/OTUCn-M between two line ports connecting two L1/L0 ODU cross
   connects (XC) within one optical transport network.  One OTUCn is
   actually carried by one OTSi(G) or OTSiA.

   As defined in [ITU-T_G872], OTSiG is used to represent one or more
   OTSi as a group to carry a single client signal (e.g., OTUCn).  The
   OTSiG may have non-associated overhead, the combination of the OTSiG
   and OTSiG-O is represented by the OTSiA management/control
   abstraction.

   In this scenario, it is clear that the OTUCn and ODUCn link can be
   automatically established, after/together with the setup of OTSi(G)
   or OTSiA, as both OTUCn and ODUCn perform section layer only.  One
   client OTUCn signal is carried by one single huge OTSi signal or a
   group of OTSi.  There is a 1:1 mapping relationship between OTUCn and
   OTSi(G) or OTSiA.

   For example, one 400G OTUCn signal can be carried by one single 400G
   OTSi signal or one 400G OTUCn signal can be split into 4 different
   OTUC instances, with each instances carried by one OTSi.  Those four
   OTSi function as a group to carry a single 400G OTUCn signal.

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

                 +--------+                     +--------+
                 |        +---------------------+        |
                 | OTN    |---------------------| OTN    |
                 |  XC    +---------------------+  XC    |
                 |        |                     |        |
                 +--------+                     +--------+
                   <---------- ODUk/ODUflex ----------->
                    <------------ ODUCn -------------->
                     <------- OTUCn/OTUCn-M --------->
                      <--------OTSi(G)/OTSiA--------->

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

                           Figure 4: Scenario A

   The second scenarios is depicted in Figure 4.  This scenario deploys
   OTUCn/OTUCn-M between transponders which are in a different domain B,
   which are separated from the L1 ODU XCs in domain A and/or C. one
   end-to-end ODUCn is actually supported by three different OTUCn or
   OTUCn-M segments, which are in turn carried by OTSi(G) or OTSiA.

   In the second scenario, OTUCn links will be established automatically
   after/together with the setup of OTSi(G) or OTSiA, while there are
   still some doubts about how the ODUCn link is established.  In
   principle, it could/should be possible but it is not yet clear in
   details how the ODUCn link can be automatically setup.

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

                    +--------------------------------------+
     A              |                B                     |          A or C
     |              |                                      |             |
+--------+          | +--------+                +--------+ |        +--------+
|        +----------|-+        |                |        +-|--------+        |
| OTN    |----------|-| Transp |                | Transp |-|--------| OTN    |
|  XC    +----------|-+ onder  +----------------+ onder  +-|--------+  XC    |
|        |          | |        |                |        | |        |        |
+--------+          | +--------+                +--------+ |        +--------+
                    |                                      |
                    +--------------------------------------+

     <-----------------------------ODUk/ODUflex---------------------------->
      <----------------------------- ODUCn ------------------------------->
       <-------OTUCn-------><-----OTUCn/OTUCn-M-----><-------OTUCn------->
        <--OTSi(G)/OTSiA-->  <----OTSi(G)/OTSiA---->  <--OTSi(G)/OTSiA-->

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

                           Figure 5: Scenario B

   According to the above description, it can be concluded that some
   uncertainty about setup of ODUCn link still exist, and this
   uncertainty may have relationship with the progress in ITU-T.  Based
   on the analysis, it is suggested that the scope of this draft should
   mainly focus on how to set up ODUk/ODUflex LSPs over ODUCn links, as
   also indicated in the figure above.

4.2.  GMPLS Implications and Applicability

4.2.1.  TE-Link Representation

   Section 3 of RFC7138 describes how to represent G.709 OTUk/ODUk with
   TE-Links in GMPLS.  Similar to that, ODUCn links can also be
   represented as TE-Links, which can be seen in the figure below.

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

                                3R                      3R
+--------+              +--------+              +--------+              +--------+
|        |              |        |              |        |              |        |
| node A |<-OTUCn Link->| node B |<-OTUCn Link->| node C |<-OTUCn Link->| node D |
|        |              |        |              |        |              |        |
+--------+              +--------+              +--------+              +--------+
      |<--------------------------- ODUCn Link -------------------------->|
      |<----------------------------- TE-Link --------------------------->|

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

                             Figure 6: telink

   Two ends of a TE-Link is able to know whether the TE-Link is
   supported by an ODUCn or an ODUk or an OTUk, as well as the resource
   related information (e.g., slot granularity, number of tributary slot
   available).

4.2.2.  Implications and Applicability for GMPLS Signalling

   Once the ODUCn link is configured, the GMPLS mechanisms defined in
   RFC7139 can be reused to set up ODUk/ODUflex LSP with no/few changes.
   As the resource on the ODUCn link which can be seen by the client
   ODUk/ODUflex is a serial of 5G slots, the label defined in RFC7139 is
   able to accommodate the requirement of the setup of ODUk/ODUflex over
   ODUCn link.  The OTN-TDM GENERALIZED_LABEL object is used to indicate
   how the LO ODUj signal is multiplexed into the HO ODUk link.  The LO
   ODUj Signal Type is indicated by Traffic Parameters, while the type
   of HO ODUk link is identified by the selected interface carried in
   the IF_ID RSVP_HOP object.  IF_ID RSVP_HOP object provides a pointer
   to the interface associated with TE-Link and therefore the two nodes
   terminating the TE-link know (by internal/local configuration) the
   attributes of ODUCn TE-Link.

   One thing should be note is the TPN used in RFC7139 and defined in
   G.709-2016 for ODUCn link.  Since the TPN currently defined in G.709
   for ODUCn link has 14 bits, while this field in RFC7139 only has 12
   bits, some extension work is needed, but this is not so urgent since
   for today networks scenarios 12 bits are enough, as it can support a
   single ODUCn link up to n=400, namely 40Tbit.

   An example is given below to illustrate the label format defined in
   RFC7139 for multiplexing ODU4 onto ODUC10.  One ODUC10 has 200 5G
   slots, and twenty of them are allocated to the ODU4.  Along with the
   increase of "n", the label may become lengthy, an optimized label
   format may be needed.

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

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       TPN = 3         |   Reserved    |     Length = 200      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 0|               Padding Bits(0)                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

                          Figure 6: 7: Label format

4.2.2.

4.2.3.  Implications and Applicability for GMPLS Routing

   For routing, we think that no extension to current mechanisms defined
   in RFC7138 are needed.  Because, once one ODUCn link is up, we need
   to advertise only the resources that can be used on this ODUCn link
   and the multiplexing hierarchy on this link.  Considering ODUCn link
   is already configured, it's the ultimate hierarchy of this
   multiplexing, there is no need to explicitly extent the ODUCn signal
   type in the routing.

   The OSPF-TE extension defined in section 4 of RFC7138 can be used to
   advertise the resource information on the ODUCn link to direct the
   setup of ODUk/ODUflex.

5.  Acknowledgements

6.  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

      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

7.  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 Individual, zheyu2008@gmail.com

      Dieter Beller, Nokia, Dieter.Beller@nokia.com

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

      Zafar Ali, Cisco Systems, zali@cisco.com

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

      Manoj Kumar, Cisco Systems, manojk2@cisco.com

      Antonello Bonfanti, Cisco Systems, abonfant@cisco.com

      Akshaya Nadahalli, Cisco Systems, anadahal@cisco.com Individual, nadahalli@gmail.com

8.  IANA Considerations

   This memo includes no request to IANA.

9.  Security Considerations

   None.

10.  References

10.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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,
              <https://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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc7139>.

10.2.  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

   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