



Internet Engineering Task Force                             Q. Wang, Ed.
Internet-Draft                                           ZTE Corporation
Intended status: Informational                          R. Valiveti, Ed.
Expires: 22 May 2023                                       Infinera Corp
                                                           H. Zheng, Ed.
                                                                  Huawei
                                                             H. Helvoort
                                                         Hai Gaoming B.V
                                                              S. Belotti
                                                                   Nokia
                                                        18 November 2022


    Applicability of GMPLS for Beyond 100G Optical Transport Network
           draft-ietf-ccamp-gmpls-otn-b100g-applicability-15

Abstract

   This document examines the applicability of using existing GMPLS
   routing and signalling mechanisms to set up Optical Data Unit-k
   (ODUk) Label Switched Paths (LSPs) over Optical Data Unit-Cn (ODUCn)
   links as defined in the 2020 version of G.709.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 22 May 2023.

Copyright Notice

   Copyright (c) 2022 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
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   license-info) in effect on the date of publication of this document.



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   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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  OTN terminology used in this document . . . . . . . . . . . .   3
   3.  Overview of the OTUCn/ODUCn in G.709  . . . . . . . . . . . .   5
     3.1.  OTUCn . . . . . . . . . . . . . . . . . . . . . . . . . .   5
       3.1.1.  OTUCn-M . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  ODUCn . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.3.  Tributary Slot Granularity  . . . . . . . . . . . . . . .   8
     3.4.  Structure of OPUCn MSI with Payload type 0x22 . . . . . .   8
     3.5.  Client Signal Mappings  . . . . . . . . . . . . . . . . .   9
   4.  GMPLS Implications and Applicability  . . . . . . . . . . . .  10
     4.1.  TE-Link Representation  . . . . . . . . . . . . . . . . .  10
     4.2.  Implications and Applicability for GMPLS Signalling . . .  11
     4.3.  Implications and Applicability for GMPLS Routing  . . . .  12
   5.  Authors (Full List) . . . . . . . . . . . . . . . . . . . . .  13
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  13
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Appendix A.  Possible Future Work . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   The current GMPLS routing [RFC7138] and signalling [RFC7139]
   extensions support the control of Optical Transport Network (OTN)
   signals and capabilities that were defined in the 2012 version of
   G.709 [ITU-T_G709_2012].

   In 2016 a further version of G.709 was published: [ITU-T_G709_2016].
   This version introduced higher rate Optical Transport Unit (OTU) and
   Optical Data Unit (ODU) signals, termed OTUCn and ODUCn respectively,
   which have a nominal rate of n x 100 Gbit/s.  According to the
   definition in [ITU-T_G709_2016], OTUCn and ODUCn perform only the
   digital section layer role and ODUCn supports only ODUk clients.
   This document focuses on the use of existing GMPLS mechanisms to set
   up ODUk (e.g., ODUflex) Label Switched Paths (LSPs) over ODUCn links,
   independently from how these links have been set up.




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   Because [ITU-T_G709_2020] does not introduce any new features to
   OTUCn and ODUCn compared to [ITU-T_G709_2016], this document starts
   with [ITU-T_G709_2020] by first presenting an overview of the OTUCn
   and ODUCn signals, and then analyzing how the current GMPLS routing
   and signalling mechanisms can be utilized to set up ODUk (e.g.,
   ODUflex) LSPs over ODUCn links.

   This document assumes that the reader is familiar with OTN, GMPLS,
   and how GMPLS is applied in OTN networks.  As such, this document
   doesn't provide any background pertaining to OTN networks that
   included links with capacities of 100G or less; this background could
   be found in documents such as [RFC7062] and [RFC7096].  This document
   provides an overview of the dataplane primitives that enable links
   with capacities greater than 100G, and analyses the extensions that
   would be required in the current GMPLS routing & signaling mechanisms
   to support the evolution in OTN networks.

2.  OTN terminology used in this document

   *  FlexO: Flexible OTN information structure.  This information
      structure is usually with a specific bit rate and frame format,
      consisting of overhead and payload, which is used as a group for
      the transport of an OTUCn signal.

   *  LSP: Label Switched Path.

   *  ODU: Optical Data Unit.  An ODU has the frame structure and
      overhead, as defined in Figure 12-1 of [ITU-T_G709_2020].  ODUs
      can be formed in two ways: a) by encapsulating a single non-OTN
      client (such as SONET/SDH, Ethernet) b) multiplexing lower-rate
      ODUs.  In general, the ODU layer represents the path layer in OTN
      networks.  The only exception is the ODUCn signal (defined below)
      which is defined to be a section layer signal.  In the
      classification based on bitrates of the ODU signals, ODUs are of
      two types: Fixed rate, and flexible rate.  Flexible rate ODU(s),
      called "ODUFlex" have a rate that is 239/238 times the bit rate of
      the client signal it encapsulates.

   *  ODUk: Optical Data Unit-k, where k is one of {0, 1, 2, 2e, 3, 4}.
      The term ODUk references to an ODU whose bit rate is fully
      specified by the index k.  The bit rates of the ODUk signal for k
      = {0, 1, 2, 2e, 3, 4} are approximately 1.25G, 2.5G, 10G, 10.3G,
      40G, 100G respectively.








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   *  ODUflex: Optical Data Unit - flexible rate.  An ODUflex has the
      same frame structure as a "generic" ODU, but with rate that is a
      fixed multiple of the bitrate of the client signal it
      encapsulates.  ITU-T defines specific ODUflex containers that are
      required to transport specific clients such as 50GE, 200GE, 400GE,
      etc.

   *  ODUC: Optical Data Unit -C; this signal has a bandwidth of
      approximately 100G, and is of a slightly higher bit rate than the
      fixed rate ODU4 signal.  This signal has the format defined in
      Figure 12-1 of [ITU-T_G709_2020].  This signal represents the
      building block for constructing a higher rate signal called ODUCn
      (defined below).

   *  ODUCn: Optical Data Unit-Cn; Cn indicates the bit rate of
      approximately n*100G.  This frame structure consists of "n"
      interleaved, frame and multi-frame synchronous instances of the
      ODUC signal, each of which has the format defined in Figure 12-1
      of [ITU-T_G709_2020].

   *  OPUC: Optical Payload Unit -C; with a payload of approximately
      100G.  This structure represents the payload area of the ODUC
      signal.

   *  OPUCn: Optical Payload Unit-Cn.  Where Cn indicates that the bit
      rate is approximately n*100G.  This structure represents the
      payload area of the ODUCn signal.

   *  OTUC: Optical Transport Unit -C; with a bandwidth of approximately
      100G.  This signal forms the building block of the OTUCn signal
      defined below, which has a bandwidth of approximately n*100G.

   *  OTUCn: Fully standardized Optical Transport Unit-Cn.  This frame
      structure is realized by extending the ODUCn signal with the OTU
      layer overhead.  The structure of this signal is illustrated in
      Figure 11-1 of [ITU-T_G709_2020].  Note that the term "fully
      standardized" is defined by ITU-T in
      [ITU-T_G709_2020]:Section 6.1.1.

   *  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 5
      Gbit/s tributary slots - where M is less than 20*n, which is the
      number of tributary slots in the OTUCn signal.

   *  OTN: Optical Transport Network.




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   *  PSI: OPU Payload Structure Indicator.  This is a 256-byte signal
      that describes the composition of the OPU signal.  This field is a
      concatenation of the Payload type (PT) and the Multiplex Structure
      Indicator (MSI) defined below.

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

   *  TPN: Tributary Port Number.  The tributary port number is used to
      indicate the port number of the client signal that is being
      transported in one specific tributary slot.

   Detailed descriptions of these terms can be found in
   [ITU-T_G709_2020].

3.  Overview of the OTUCn/ODUCn in G.709

   This section provides an overview of OTUCn/ODUCn signals defined in
   [ITU-T_G709_2020].  The text in this section is purely descriptive
   and is not normative.  For a full description of OTUCn/ODUCn signals
   please refer to [ITU-T_G709_2020].  In the event of any discrepancy
   between this text and [ITU-T_G709_2020], that other document is
   definitive.

3.1.  OTUCn

   In order to carry client signals with rates greater than 100 Gbit/s,
   [ITU-T_G709_2020] takes a general and scalable approach that
   decouples the rates of OTU signals from the client rate.  The new OTU
   signal is called OTUCn, and this signal is defined to have a rate of
   (approximately) n*100G.  The following are the key characteristics of
   the OTUCn signal:

   *  The OTUCn signal contains one ODUCn.  The OTUCn and ODUCn signals
      perform digital section roles only (see
      [ITU-T_G709_2020]:Section 6.1.1)

   *  The OTUCn signals can be viewed as being formed by interleaving n
      synchronous OTUC signals (which are labeled 1, 2, ..., n).

   *  Each of the OTUC instances has the same overhead as the standard
      OTUk signal in [ITU-T_G709_2020].  Note that the OTUC signal
      doesn't include the FEC columns illustrated in
      [ITU-T_G709_2020]:Figure 11-1.  The OTUC signal includes an ODUC.




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   *  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.

   *  The combined signal OTUCn has n instances of OTUC overhead, and n
      instances of ODUC overhead.

   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.

   OTUCn interfaces can be categorized as follows, based on the type of
   peer network element:

   *  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
      Recommendation [ITU-T_G709.1] specifies a flexible interoperable
      short-reach OTN interface over which an OTUCn (n >=1) is
      transferred, using bonded Flexible OTN information structure
      (FlexO) interfaces which belong to a FlexO group.

   *  intra-domain interfaces: In these cases, the OTUCn is transported
      using a proprietary (vendor specific) encapsulation, FEC etc.  It
      is also possible to transport OTUCn for intra-domain links using
      FlexO.

3.1.1.  OTUCn-M

   The standard OTUCn signal has the same rate as that of the ODUCn
   signal.  This implies that the OTUCn signal can only be transported
   over wavelength groups which have a total capacity of multiples of
   (approximately) 100G.  Modern optical interfaces support a variety of
   bit rates per wavelength, depending on the reach requirements for the
   optical path.  If the total rate of the ODUk LSPs planned to be
   carried over an ODUCn link is smaller than n*100G, it is possible to
   "crunch" the OTUCn not to transmit the unused tributary slots.  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 instance) but with only
   M (M is less than 20*n) OPUCn tributary slots available to carry ODUk
   LSPs.









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3.2.  ODUCn

   The ODUCn signal defined in [ITU-T_G709_2020] 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 and payload areas, but has
   a higher rate since its payload area can embed an ODU4 signal.

   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-terminated, i.e.
   they will have identical source/sink locations (see Figure 1).  In
   this figure, the term "OTN Switch" has the same meaning as that used
   in [RFC7138]:Section 3.  [ITU-T_G709_2020] allows for the ODUCn
   signal to pass through one or more digital regenerator nodes (shown
   as Nodes B, C in Figure 2) 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.  This process is termed as "ODUCn regeneration" in
   [ITU-T_G872]:Section 7.1.  In this example, 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,
   tributary-slot allocation remains unchanged.

                      +--------+           +--------+
                      |        +-----------+        |
                      | OTN    |-----------| OTN    |
                      | Switch +-----------+ Switch |
                      | A      |           |  B     |
                      |        +-----------+        |
                      +--------+           +--------+
                          <--------ODUCn------->
                           <-------OTUCn------>

                           Figure 1: ODUCn signal














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    +---------+        +--------+        +--------+          +--------+
    |         +--------+        |        |        +----------+        |
    | OTN     |--------| OTN    |        | OTN    |----------| OTN    |
    | Switch  +--------+ Regen  +--------+ Regen  +----------+ Switch |
    | A       |        | B      |        | C      |          | D      |
    |         +--------+        |        |        +----------+        |
    +---------+        +--------+        +--------+          +--------+

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

                     Figure 2: ODUCn signal - multihop

3.3.  Tributary Slot Granularity

   [ITU-T_G709_2012] introduced the support for 1.25 Gbit/s granular
   tributary slots in OPU2, OPU3, and OPU4 signals.  [ITU-T_G709_2020]
   defined the OPUC with a 5 Gbit/s tributary slot granularity.  This
   means that the ODUCn signal has 20*n tributary slots (of 5 Gbit/s
   capacity).  The range of tributary port number (TPN) is 10*n instead
   of 20*n, which restricts the maximum client signals that could be
   carried over one single ODUC1.

3.4.  Structure of OPUCn MSI with Payload type 0x22

   As mentioned above, the OPUCn signal has 20*n 5 Gbit/s tributary
   slots (TSs).  The OPUCn MSI field has a fixed length of 40*n bytes
   and indicates the availability and occupation 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_2020]:Section 20.4.1):

   *  The TS availability bit indicates if the tributary slot is
      available or unavailable

   *  The TS occupation bit indicates if the tributary slot is allocated
      or unallocated

   *  The tributary port number (14 bits) of the client signal that is
      being carried in this specific TS.  A flexible assignment of
      tributary port to tributary slots is possible.  Numbering of
      tributary ports is from 1 to 10*n.

   The concatenation of the OPUCn payload type (PT) and the MSI field is
   carried over the overhead byte designated as PSI in
   [ITU-T_G709_2020]:Figure 15-6.




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3.5.  Client Signal Mappings

   The approach taken by the ITU-T to map non-OTN client signals to the
   appropriate ODU containers is as follows:

   *  All client signals are mapped into an ODUj, or ODUk (e.g.,
      ODUflex) as specified in clause 17 of [ITU-T_G709_2020].

   *  The terms ODUj & ODUk are used in a multiplexing scenario, with
      ODUj being a low-order ODU which is multiplexed into ODUk, a high-
      order ODU.  As Figure 3 illustrates, the ODUCn is also a high-
      order ODU into which other ODUs can be multiplexed; the ODUCn
      itself cannot be multiplexed into any higher rate ODU signal; it
      is defined to be a section level signal.

   *  ODUflex signals are low-order signals only.  If the ODUflex
      entities have rates of 100G or less, they can be transported over
      either an ODUk (k=1..4) or an ODUCn.  For ODUflex connections with
      rates greater than 100G, ODUCn is required.

   *  ODU Virtual Concatenation has been deprecated.  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.


























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                 Clients (e.g. SONET/SDH, Ethernet)

           |   |   |                           |   |   |
           |   |   |                           |   |   |
           |   |   |                           |   |   |
       +---+---+---+----+                      |   |   |
       |      OPUj      |                      |   |   |
       +----------------+                      |   |   |
       |      ODUj      |                      |   |   |
       +----------------+----------------------+---+---+----------+
       |                                                          |
       |                       OPUk                               |
       +----------------------------------------------------------+
       |                                                          |
       |                       ODUk       k in {0,1,2,2e,3,4,flex}|
       +-------------------------+-----+--------------------------+
       |                         |     |                          |
       | OTUk, OTUk-SC, OTUk-V   |     |          OPUCn           |
       +-------------------------+     +--------------------------+
                                       |                          |
                                       |          ODUCn           |
                                       +--------------------------+
                                       |                          |
                                       |          OTUCn           |
                                       +--------------------------+

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

4.  GMPLS Implications and Applicability

4.1.  TE-Link Representation

   Section 3 of RFC7138 describes how to represent G.709 OTUk/ODUk with
   TE-Links in GMPLS.  In the same manner, OTUCn links can also be
   represented as TE-links.  Figure 4 below provides an illustration of
   a one-hop OTUCn TE link.

                 +----------+                   +---------+
                 |  OTN     |                   |  OTN    |
                 |  Switch  +-------------------+  Switch |
                 |  A       |                   |  B      |
                 +----------+                   +---------+

                     |<---------OTUCn Link---------->|

                     |<---------TE-Link------------->|

                          Figure 4: OTUCn TE-Links



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   It is possible to create TE-links that span more than one hop by
   creating forward adjacencies (FA) between non-adjacent nodes (see
   Figure 5).  In this illustration, the nodes B and C are performing
   the ODUCn regeneration function described in
   [ITU-T_G872]:Section 7.1, and are not electrically switching the
   ODUCn signal from one interface to another.  As in the one-hop case,
   Multiple-hop TE-links advertise the ODU switching capability.

   +--------+         +--------+          +--------+         +---------+
   |  OTN   |         |  OTN   |          |  OTN   |         |  OTN    |
   | Switch |<------->|  regen |<-------->|  regen |<------->|  Switch |
   |   A    |  OTUCn  |   B    |   OTUCn  |   C    |  OTUCn  |   D     |
   +--------+  Link   +--------+   Link   +--------+  Link   +---------+

          |<-------------------- ODUCn Link -------------------->|

          |<---------------------- TE-Link --------------------->|

                    Figure 5: Multiple-hop ODUCn TE-Link

   The two endpoints of a TE-Link are configured with the supported
   resource information, which may include whether the TE-Link is
   supported by an ODUCn or an ODUk or an OTUk, as well as the link
   attribute information (e.g., slot granularity, list of available
   tributary slot).

4.2.  Implications and Applicability for GMPLS Signalling

   Once the ODUCn TE-Link is configured, the GMPLS mechanisms defined in
   [RFC7139] can be reused to set up ODUk/ODUflex LSPs with no changes.
   As the resource on the ODUCn link which can be seen by the client
   ODUk/ODUflex is a set of 5 Gbit/s slots, the label defined in
   [RFC7139] is able to accommodate the requirement of the setup of
   ODUk/ODUflex over ODUCn link.  In [RFC7139], the OTN-TDM
   GENERALIZED_LABEL object is used to indicate how the lower order (LO)
   ODUj signal is multiplexed into the higher order (HO) ODUk link.  In
   a similar manner, the OTN-TDM GENERALIZED_LABEL object is used to
   indicate how the ODUk signal is multiplexed into the ODUCn link.  The
   ODUk Signal Type is indicated by Traffic Parameters.  The 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 the ODUCn TE Link.

   Since the TPN defined in [ITU-T_G709_2020] for an ODUCn link has 14
   bits, while this field in [RFC7139] only has 12 bits, some extension
   work will eventually be needed.  Given that a 12-bit TPN field can
   support ODUCn links with up to n=400 (i.e. 40Tbit/s links), this need
   is not urgent.



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   An example is given in Figure 6 to illustrate the label format
   defined in [RFC7139] for multiplexing ODU4 onto ODUC10.  One ODUC10
   has 200 5 Gbit/s slots, and twenty of them are allocated to the ODU4.
   With this label encoding, only 20 out of the 200 bits mask are non-
   zero, and is very inefficient.  The inefficiency grows for larger
   values of "n" and an optimized label format may be desirable.

       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: Label format

4.3.  Implications and Applicability for GMPLS Routing

   For routing, it is deemed that no extension to current mechanisms
   defined in [RFC7138] is needed.  Because, once an ODUCn link is up,
   the resources that need to be advertised are the resources that are
   exposed by this ODUCn link and the multiplexing hierarchy on this
   link.  Since the ODUCn link is the lowest layer of the ODU
   multiplexing hierarchy involving multiple ODU layers, and there is a
   1:1 correspondence with the OTUCn signal, there is no need to
   explicitly define a new value to represent the ODUCn signal type in
   the OSPF-TE routing protocol.

   The OSPF-TE extension defined in section 4 of [RFC7138] can be reused
   to advertise the resource information on the ODUCn link to help
   finish the setup of ODUk/ODUflex.







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5.  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

6.  Contributors

      Iftekhar Hussain, Infinera Corp, Sunnyvale, CA, USA,
      IHussain@infinera.com

      Daniele Ceccarelli, Ericsson, daniele.ceccarelli@ericsson.com

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

      Fatai Zhang, Huawei,zhangfatai@huawei.com



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      Italo Busi, Huawei,italo.busi@huawei.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

      Yuji Tochio, Fujitsu, tochio@fujitsu.com

7.  IANA Considerations

   This memo includes no request to IANA.

8.  Security Considerations

   This document analyzed the applicability of protocol extensions in
   [RFC7138] and [RFC7139] for use in the 2020 version of G.709 [ITU-
   T_G709_2020] and found that no new extensions are needed.  Therefore,
   this document introduced no new security considerations to the
   existing signaling and routing protocols beyond those already
   described in [RFC7138] and [RFC7139].  Please refer to [RFC7138] and
   [RFC7139] for further details of the specific security measures.
   Additionally, [RFC5920] addresses the security aspects that are
   relevant in the context of GMPLS.

9.  References

9.1.  Normative References

   [ITU-T_G709_2020]
              ITU-T, "ITU-T G.709: Optical Transport Network Interfaces;
              06/2020", June 2020.

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
              <https://www.rfc-editor.org/info/rfc5920>.








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   [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>.

9.2.  Informative References

   [ITU-T_G709.1]
              ITU-T, "ITU-T G.709.1: Flexible OTN short-reach interface;
              2018", 2018.

   [ITU-T_G709_2012]
              ITU-T, "ITU-T G.709: Optical Transport Network Interfaces;
              02/2012", February 2012.

   [ITU-T_G709_2016]
              ITU-T, "ITU-T G.709: Optical Transport Network Interfaces;
              07/2016", July 2016.

   [ITU-T_G872]
              ITU-T, "ITU-T G.872: Architecture of Optical Transport
              Networks; 12/2019", December 2019.

   [RFC7062]  Zhang, F., Ed., Li, D., Li, H., Belotti, S., and D.
              Ceccarelli, "Framework for GMPLS and PCE Control of G.709
              Optical Transport Networks", RFC 7062,
              DOI 10.17487/RFC7062, November 2013,
              <https://www.rfc-editor.org/info/rfc7062>.

   [RFC7096]  Belotti, S., Ed., Grandi, P., Ceccarelli, D., Ed.,
              Caviglia, D., Zhang, F., and D. Li, "Evaluation of
              Existing GMPLS Encoding against G.709v3 Optical Transport
              Networks (OTNs)", RFC 7096, DOI 10.17487/RFC7096, January
              2014, <https://www.rfc-editor.org/info/rfc7096>.










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Appendix A.  Possible Future Work

   As noted in Section Section 4.2, the GMPLS TPN field in Section 6.1
   of [RFC7139] is only 12 bits whereas an ODUCn link could require up
   to 14 bits.  Although the need is not urgent, future work could
   extend the TPN field in GMPLS to use the Reserved bits immediately
   adjacent.  This would need to be done in a backward compatible way.

   Section Section 4.2 further notes that the current encoding of GMPLS
   labels can be inefficient for larger values of n in ODUCn.  Future
   work might examine a more compact, yet generalized label encoding to
   address this issue should it be felt, after analysis of the
   operational aspects, that the current encoding is causing problems.
   Introduction of a new label encoding would need to be done using a
   new LSP Encoding Type / G-PID pairing to ensure correct
   interoperability.

Authors' Addresses

   Qilei Wang (editor)
   ZTE Corporation
   Nanjing
   China
   Email: wang.qilei@zte.com.cn


   Radha Valiveti (editor)
   Infinera Corp
   Sunnyvale
   USA
   Email: rvaliveti@infinera.com


   Haomian Zheng (editor)
   Huawei
   China
   Email: zhenghaomian@huawei.com


   Huub van Helvoort
   Hai Gaoming B.V
   Almere
   Netherlands
   Email: huubatwork@gmail.com


   Sergio Belotti
   Nokia



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   Email: sergio.belotti@nokia.com


















































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