Network Working Group                                   Fatai Zhang, Ed.
Internet Draft                                                    Dan Li
Category: Informational                                           Huawei
                                                                  Han Li
                                                           D. Ceccarelli
Expires: March 22, 2014                               September 22, 2013

                 Framework for GMPLS and PCE Control of
                    G.709 Optical Transport Networks


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
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   This Internet-Draft will expire on March 22, 2014.


   This document provides a framework to allow the development of
   protocol extensions to support Generalized Multi-Protocol Label
   Switching (GMPLS) and Path Computation Element (PCE) control of

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   Optical Transport Networks (OTN) as specified in ITU-T Recommendation
   G.709 as published in 2012.

Table of Contents

   1. Introduction ................................................. 2
   2. Terminology .................................................. 3
   3. G.709 Optical Transport Network .............................. 4
      3.1. OTN Layer Network ....................................... 4
         3.1.1. Client signal mapping .............................. 5
         3.1.2. Multiplexing ODUj onto Links ....................... 7
   Structure of MSI information .................. 8
   4. Connection management in OTN ................................. 9
      4.1. Connection management of the ODU ........................ 10
   5. GMPLS/PCE Implications  ...................................... 12
      5.1. Implications for Label Switch Path (LSP) Hierarchy ...... 12
      5.2. Implications for GMPLS Signaling ........................ 13
      5.3. Implications for GMPLS Routing .......................... 15
      5.4. Implications for Link Management Protocol ............... 17
      5.5. Implications for Control Plane Backward Compatibility ... 18
      5.6. Implications for Path Computation Elements .............. 19
      5.7. Implications for Management of GMPLS Networks ........... 20
   6. Data Plane Backward Compatibility Considerations ............. 20
   7. Security Considerations  ..................................... 21
   8. IANA Considerations .......................................... 21
   9. Acknowledgments .............................................. 21
   10. References .................................................. 21
      10.1. Normative References ................................... 21
      10.2. Informative References  ................................ 23
   11. Authors' Addresses .......................................... 24
   12. Contributors ................................................ 25

1. Introduction

   Optical Transport Networks (OTN) has become a mainstream layer 1
   technology for the transport network. Operators want to introduce
   control plane capabilities based on GMPLS to OTN, to realize the
   benefits associated with a high-function control plane (e.g.,
   improved network resiliency, resource usage efficiency, etc.).

   GMPLS extends Multi-Protocol Label Switching (MPLS) to encompass time
   division multiplexing (TDM) networks (e.g., Synchronous Optical
   NETwork (SONET)/ Synchronous Digital Hierarchy (SDH), Plesiochronous

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   Digital Hierarchy (PDH), and G.709 sub-lambda), lambda switching
   optical networks, and spatial switching (e.g., incoming port or fiber
   to outgoing port or fiber). The GMPLS architecture is provided in
   [RFC3945], signaling function and Resource ReserVation Protocol-
   Traffic Engineering (RSVP-TE) extensions are described in [RFC3471]
   and [RFC3473], routing and Open Shortest Path First (OSPF) extensions
   are described in [RFC4202] and [RFC4203], and the Link Management
   Protocol (LMP) is described in [RFC4204].

   The GMPLS signaling extensions defined in [RFC4328] provide the
   mechanisms for basic GMPLS control of OTN based on the 2001 revision
   of the G.709 specification. The 2012 revision of the G.709
   specification, [G709-2012], includes new features, for example,
   various multiplexing structures, two types of Tributary Slots (TSs)
   (i.e., 1.25Gbps and 2.5Gbps), and extension of the Optical channel
   Data Unit-j (ODUj) definition to include the ODUflex function.

   This document reviews relevant aspects of OTN technology evolution
   that affect the GMPLS control plane protocols and examines why and
   how to update the mechanisms described in [RFC4328]. This document
   additionally provides a framework for the GMPLS control of OTN and
   includes a discussion of the implication for the use of the PCE

   For the purposes of the control plane the OTN can be considered as
   being comprised of ODU and wavelength (Optical Channel (OCh)) layers.
   This document focuses on the control of the ODU layer, with control
   of the wavelength layer considered out of the scope. Please refer to
   [RFC6163] for further information about the wavelength layer.

2. Terminology

   OTN: Optical Transport Network

   OPU: Optical channel Payload Unit

   ODU: Optical channel Data Unit

   OTU: Optical channel Transport Unit

   OMS: Optical multiplex section

   MSI: Multiplex Structure Identifier

   TPN: Tributary Port Number

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   LO ODU: Lower Order ODU. The LO ODUj (j can be 0, 1, 2, 2e, 3, 4,
   flex.) represents the container transporting a client of the OTN that
   is either directly mapped into an OTUk (k = j) or multiplexed into a
   server HO ODUk (k > j) container.

   HO ODU: Higher Order ODU. The HO ODUk (k can be 1, 2, 2e, 3, 4.)
   represents the entity transporting a multiplex of LO ODUj tributary
   signals in its OPUk area.

   ODUflex: Flexible ODU. A flexible ODUk can have any bit rate and a
   bit rate tolerance of +/-100 ppm (parts per million).

   In general, throughout this document, 'ODUj' is used to refer to ODU
   entities acting as LO ODU, and 'ODUk' is used to refer to ODU
   entities being used as HO ODU.

3. G.709 Optical Transport Network

   This section provides an informative overview of those aspects of the
   OTN impacting control plane protocols.  This overview is based on the
   ITU-T Recommendations that contain the normative definition of the
   OTN. Technical details regarding OTN architecture and interfaces are
   provided in the relevant ITU-T Recommendations.

   Specifically, [G872-2012] describes the functional architecture of
   optical transport networks providing optical signal transmission,
   multiplexing, routing, supervision, performance assessment, and
   network survivability. The legacy OTN referenced by [RFC4328] defines
   the interfaces of the optical transport network to be used within and
   between subnetworks of the optical network.  With the evolution and
   deployment of OTN technology many new features have been specified in
   ITU-T recommendations, including for example, new ODU0, ODU2e, ODU4
   and ODUflex containers as described in [G709-2012].

3.1. OTN Layer Network

   The simplified signal hierarchy of OTN is shown in Figure 1, which
   illustrates the layers that are of interest to the control plane.
   Other layers below OCh (e.g. Optical Transmission Section (OTS)) are
   not included in this Figure. The full signal hierarchy is provided in

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                               Client signal

                   Figure 1 - Basic OTN signal hierarchy

   Client signals are mapped into ODUj containers. These ODUj containers
   are multiplexed onto the OTU/OCh. The individual OTU/OCh signals are
   combined in the OMS using Wavelength Division Multiplexing (WDM), and
   this aggregated signal provides the link between the nodes.

3.1.1. Client signal mapping

   The client signals are mapped into a LO ODUj. The current values of j
   defined in [G709-2012] are: 0, 1, 2, 2e, 3, 4, Flex. The approximate
   bit rates of these signals are defined in [G709-2012] and are
   reproduced in Tables 1 and 2.

                     Table 1 - ODU types and bit rates
   |       ODU Type        |       ODU nominal bit rate        |
   |         ODU0          |         1,244,160 Kbps            |
   |         ODU1          |    239/238 x 2,488,320 Kbps       |
   |         ODU2          |    239/237 x 9,953,280 Kbps       |
   |         ODU3          |    239/236 x 39,813,120 Kbps      |
   |         ODU4          |    239/227 x 99,532,800 Kbps      |
   |         ODU2e         |    239/237 x 10,312,500 Kbps      |
   |                       |                                   |
   |     ODUflex for       |                                   |
   |Constant Bit Rate (CBR)| 239/238 x client signal bit rate  |
   |    Client signals     |                                   |
   |                       |                                   |
   |   ODUflex for Generic |                                   |
   |   Framing Procedure   |        Configured bit rate        |
   |   - Framed (GFP-F)    |                                   |
   | Mapped client signal  |                                   |

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   NOTE - The nominal ODUk rates are approximately: 2,498,775.126 Kbps
   (ODU1), 10,037,273.924 Kbps (ODU2), 40,319,218.983 Kbps (ODU3),
   104,794,445.815 Kbps (ODU4) and 10,399,525.316 Kbps (ODU2e).

                     Table 2 - ODU types and tolerance
   |      ODU Type         |       ODU bit-rate tolerance      |
   |        ODU0           |            +/-20 ppm              |
   |        ODU1           |            +/-20 ppm              |
   |        ODU2           |            +/-20 ppm              |
   |        ODU3           |            +/-20 ppm              |
   |        ODU4           |            +/-20 ppm              |
   |        ODU2e          |            +/-100 ppm             |
   |                       |                                   |
   |   ODUflex for CBR     |                                   |
   |   Client signals      |            +/-100 ppm             |
   |                       |                                   |
   |  ODUflex for GFP-F    |                                   |
   | Mapped client signal  |            +/-100 ppm             |

   One of two options is for mapping client signals into ODUflex
   depending on the client signal type:

   -  Circuit clients are proportionally wrapped. Thus the bit rate is
      defined by the client signal and the tolerance is fixed to +/-100

   -  Packet clients are mapped using the Generic Framing Procedure
      (GFP). [G709-2012] recommends that the ODUflex(GFP) will fill an
      integral number of tributary slots of the smallest HO ODUk path
      over which the ODUflex(GFP) may be carried, and the tolerance
      should be +/-100 ppm.

   Note that additional information on G.709 client mapping can be found
   in [G7041].

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3.1.2. Multiplexing ODUj onto Links

   The links between the switching nodes are provided by one or more
   wavelengths.  Each wavelength carries one OCh, which carries one OTU,
   which carries one ODU.  Since all of these signals have a 1:1:1
   relationship, we only refer to the OTU for clarity.  The ODUjs are
   mapped into the TSs (Tributary Slots) of the OPUk.  Note that in the
   case where j=k the ODUj is mapped into the OTU/OCh without

   The initial versions of G.709 referenced by [RFC4328] only provided a
   single TS granularity, nominally 2.5Gbps. [G709-2012] added an
   additional TS granularity, nominally 1.25Gbps. The number and type of
   TSs provided by each of the currently identified OTUk is provided

             Tributary Slot Granularity
                2.5Gbps     1.25Gbps           Nominal Bit rate
     OTU1         1             2                  2.5Gbps
     OTU2         4             8                   10Gbps
     OTU3        16            32                   40Gbps
     OTU4        --            80                  100Gbps

   To maintain backwards compatibility while providing the ability to
   interconnect nodes that support 1.25Gbps TS at one end of a link and
   2.5Gbps TS at the other, [G709-2012] requires 'new' equipment fall
   back to the use of a 2.5Gbps TS when connected to legacy equipment.
   This information is carried in band by the payload type.

   The actual bit rate of the TS in an OTUk depends on the value of k.
   Thus the number of TSs occupied by an ODUj may vary depending on the
   values of j and k. For example an ODU2e uses 9 TSs in an OTU3 but
   only 8 in an OTU4. Examples of the number of TSs used for various
   cases are provided below (Referring to Table 7-9 of [G709-2012]):

   -  ODU0 into ODU1, ODU2, ODU3 or ODU4 multiplexing with 1,25Gbps TS
      o  ODU0 occupies 1 of the 2, 8, 32 or 80 TSs for ODU1, ODU2, ODU3
         or ODU4

   -  ODU1 into ODU2, ODU3 or ODU4 multiplexing with 1,25Gbps TS
      o  ODU1 occupies 2 of the 8, 32 or 80 TSs for ODU2, ODU3 or ODU4

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   -  ODU1 into ODU2, ODU3 multiplexing with 2.5Gbps TS granularity
      o  ODU1 occupies 1 of the 4 or 16 TSs for ODU2 or ODU3

   -  ODU2 into ODU3 or ODU4 multiplexing with 1.25Gbps TS granularity
      o  ODU2 occupies 8 of the 32 or 80 TSs for ODU3 or ODU4

   -  ODU2 into ODU3 multiplexing with 2.5Gbps TS granularity
      o  ODU2 occupies 4 of the 16 TSs for ODU3

   -  ODU3 into ODU4 multiplexing with 1.25Gbps TS granularity
      o  ODU3 occupies 31 of the 80 TSs for ODU4

   -  ODUflex into ODU2, ODU3 or ODU4 multiplexing with 1.25Gbps TS
      o  ODUflex occupies n of the 8, 32 or 80 TSs for ODU2, ODU3 or
         ODU4 (n <= Total TS number of ODUk)

   -  ODU2e into ODU3 or ODU4 multiplexing with 1.25Gbps TS granularity
      o  ODU2e occupies 9 of the 32 TSs for ODU3 or 8 of the 80 TSs for

   In general the mapping of an ODUj (including ODUflex) into a specific
   OTUk TS is determined locally, and it can also be explicitly
   controlled by a specific entity (e.g., head end, Network Management
   System (NMS)) through Explicit Label Control [RFC3473]. Structure of MSI information

   When multiplexing an ODUj into a HO ODUk (k>j), G.709 specifies the
   information that has to be transported in-band in order to allow for
   correct demultiplexing. This information, known as MSI, is
   transported in the OPUk overhead and is local to each link. In case
   of bidirectional paths the association between TPN and TS must be the
   same in both directions.

   The MSI information is organized as a set of entries, with one entry
   for each HO ODUj TS. The information carried by each entry is:

   - Payload Type:  the type of the transported payload.

   - TPN:  the port number of the ODUj transported by the HO ODUk. The
      TPN is the same for all the TSs assigned to the transport of the
      same ODUj instance.

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   For example, an ODU2 carried by a HO ODU3 is described by 4 entries
   in the OPU3 overhead when the TS granularity is 2.5Gbps, and by 8
   entries when the TS granularity is 1.25Gbps.

   On each node and on every link, two MSI values have to be provisioned
   (Referring to [G798-V4]):

   - The Transmitted MSI (TxMSI) information inserted in OPU (e.g.,
      OPU3) overhead by the source of the HO ODUk trail.

   - The expected MSI (ExMSI) information that is used to check the
      accepted MSI (AcMSI) information. The AcMSI information is the MSI
      valued received in-band, after a three-frame integration.

   As described in [G798-V4], the sink of the HO ODU trail checks the
   complete content of the AcMSI information against the ExMSI. If the
   AcMSI is different from the ExMSI, then the traffic is dropped and a
   payload mismatch alarm is generated.

   Provisioning of TPN can be performed either by network management
   system or control plane. In the last case, control plane is also
   responsible for negotiating the provisioned values on a link by link

4. Connection management in OTN

   OTN-based connection management is concerned with controlling the
   connectivity of ODU paths and OCh. This document focuses on the
   connection management of ODU paths. The management of OCh paths is
   described in [RFC6163].

   While [G872-2001] considered the ODU as a set of layers in the same
   way as SDH has been modeled, recent ITU-T OTN architecture progress
   [G872-2012] includes an agreement to model the ODU as a single layer
   network with the bit rate as a parameter of links and connections.
   This allows the links and nodes to be viewed in a single topology as
   a common set of resources that are available to provide ODUj
   connections independent of the value of j. Note that when the bit
   rate of ODUj is less than the server bit rate, ODUj connections are
   supported by HO ODU (which has a one-to-one relationship with the

   From an ITU-T perspective, the ODU connection topology is represented
   by that of the OTU link layer, which has the same topology as that of
   the OCh layer (independent of whether the OTU supports HO ODU, where
   multiplexing is utilized, or LO ODU in the case of direct mapping).

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   Thus, the OTU and OCh layers should be visible in a single
   topological representation of the network, and from a logical
   perspective, the OTU and OCh may be considered as the same logical,
   switchable entity.

   Note that the OTU link layer topology may be provided via various
   infrastructure alternatives, including point-to-point optical
   connections, optical connections fully in the optical domain and
   optical connections involving hybrid sub-lambda/lambda nodes
   involving 3R, etc, see [RFC6163] for additional information.

4.1. Connection management of the ODU

   LO ODUj can be either mapped into the OTUk signal (j = k), or
   multiplexed with other LO ODUjs into an OTUk (j < k), and the OTUk is
   mapped into an OCh.

   From the perspective of control plane, there are two kinds of network
   topology to be considered.

   (1) ODU layer

   In this case, the ODU links are presented between adjacent OTN nodes,
   as illustrated in Figure 2. In this layer there are ODU links with a
   variety of TSs available, and nodes that are Optical Digital Cross
   Connects (ODXCs). LO ODU connections can be setup based on the
   network topology.

                  Link #5       +--+---+--+        Link #4
     +--------------------------|         |--------------------------+
     |                          |  ODXC   |                          |
     |                          +---------+                          |
     |                             Node E                            |
     |                                                               |
   +-++---+--+        +--+---+--+        +--+---+--+        +--+---+-++
   |         |Link #1 |         |Link #2 |         |Link #3 |         |
   |         |--------|         |--------|         |--------|         |
   |  ODXC   |        |  ODXC   |        |  ODXC   |        |  ODXC   |
   +---------+        +---------+        +---------+        +---------+
      Node A             Node B              Node C            Node D

        Figure 2 - Example Topology for LO ODU connection management

   If an ODUj connection is requested between Node C and Node E
   routing/path computation must select a path that has the required
   number of TS available and that offers the lowest cost.  Signaling is
   then invoked to set up the path and to provide the information (e.g.,

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   selected TSs) required by each transit node to allow the
   configuration of the ODUj to OTUk mapping (j = k) or multiplexing (j
   < k), and demapping (j = k) or demultiplexing (j < k).

   (2) ODU layer with OCh switching capability

   In this case, the OTN nodes interconnect with wavelength switched
   node (e.g., Reconfiguration Optical Add/Drop Multiplexer (ROADM),
   Optical Cross-Connect (OXC)) that are capable of OCh switching, which
   is illustrated in Figure 3 and Figure 4. There are ODU layer and OCh
   layer, so it is simply a Multi-Layer Networks (MLN) (see [RFC6001]).
   OCh connections may be created on demand, which is described in
   section 5.1.

   In this case, an operator may choose to allow the underlying OCh
   layer to be visible to the ODU routing/path computation process in
   which case the topology would be as shown in Figure 4. In Figure 3
   below, instead, a cloud representing OCh capable switching nodes is
   represented. In Figure 3, the operator choice is to hide the real OCh
   layer network topology.

                                Node E
         Link #5              +--------+       Link #4
     +------------------------|        |------------------------+
     |                          ------                          |
     |                       //        \\                       |
     |                      ||          ||                      |
     |                      | OCh domain |                      |
   +-+-----+        +------ ||          || ------+        +-----+-+
   |       |        |        \\        //        |        |       |
   |       |Link #1 |          --------          |Link #3 |       |
   |       +--------+         |        |         +--------+       +
   | ODXC  |        |  ODXC   +--------+  ODXC   |        | ODXC  |
   +-------+        +---------+Link #2 +---------+        +-------+
     Node A            Node B             Node C            Node D

      Figure 3 - OCh Hidden Topology for LO ODU connection management

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           Link #5            +---------+            Link #4
     +------------------------|         |-----------------------+
     |                   +----| ODXC    |----+                  |
     |                 +-++   +---------+   ++-+                |
     |         Node f  |  |     Node E      |  |  Node g        |
     |                 +-++                 ++-+                |
     |                   |       +--+        |                  |
   +-+-----+        +----+----+--|  |--+-----+---+        +-----+-+
   |       |Link #1 |         |  +--+  |         |Link #3 |       |
   |       +--------+         | Node h |         +--------+       |
   | ODXC  |        | ODXC    +--------+ ODXC    |        | ODXC  |
   +-------+        +---------+ Link #2+---------+        +-------+
     Node A            Node B            Node C             Node D

     Figure 4 - OCh Visible Topology for LO ODUj connection management

   In Figure 4, the cloud of previous figure is substituted by the real
   topology. The nodes f, g, h are nodes with OCh switching capability.

   In the examples (i.e., Figure 3 and Figure 4), we have considered the
   case in which LO ODUj connections are supported by OCh connection,
   and the case in which the supporting underlying connection can be
   also made by a combination of HO ODU/OCh connections.

   In this case, the ODU routing/path selection process will request an
   HO ODU/OCh connection between node C and node E from the OCh domain.
   The connection will appear at ODU level as a Forwarding Adjacency,
   which will be used to create the ODU connection.

5. GMPLS/PCE Implications

   The purpose of this section is to provide a set of requirements to be
   evaluated for extensions of the current GMPLS protocol suite and the
   PCE applications and protocols to encompass OTN enhancements and
   connection management.

5.1. Implications for Label Switch Path (LSP) Hierarchy

   The path computation for ODU connection request is based on the
   topology of ODU layer.

   The OTN path computation can be divided into two layers. One layer is
   OCh/OTUk, the other is ODUj. [RFC4206] and [RFC6107] define the
   mechanisms to accomplish creating the hierarchy of LSPs. The LSP

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   management of multiple layers in OTN can follow the procedures
   defined in [RFC4206], [RFC6001] and [RFC6107], etc.

   As discussed in section 4, the route path computation for OCh is in
   the scope of Wavelength Switched Optical Network (WSON) [RFC6163].
   Therefore, this document only considers ODU layer for ODU connection

   LSP hierarchy can also be applied within the ODU layers. One of the
   typical scenarios for ODU layer hierarchy is to maintain
   compatibility with introducing new [G709-2012] services (e.g., ODU0,
   ODUflex) into a legacy network configuration (i.e., the legacy OTN
   referenced by [RFC4328]). In this scenario, it may be needed to
   consider introducing hierarchical multiplexing capability in specific
   network transition scenarios. One method for enabling multiplexing
   hierarchy is by introducing dedicated boards in a few specific places
   in the network and tunneling these new services through the legacy
   containers (ODU1, ODU2, ODU3), thus postponing the need to upgrade
   every network element to [G709-2012] capabilities.

   In such case, one ODUj connection can be nested into another ODUk
   (j<k) connection, which forms the LSP hierarchy in ODU layer. The
   creation of the outer ODUk connection can be triggered via network
   planning, or by the signaling of the inner ODUj connection. For the
   former case, the outer ODUk connection can be created in advance
   based on network planning. For the latter case, the multi-layer
   network signaling described in [RFC4206], [RFC6107] and [RFC6001]
   (including related modifications, if needed) are relevant to create
   the ODU connections with multiplexing hierarchy. In both cases, the
   outer ODUk connection is advertised as a Forwarding Adjacency (FA).

5.2. Implications for GMPLS Signaling

   The signaling function and RSVP-TE extensions are described in
   [RFC3471] and [RFC3473]. For OTN-specific control, [RFC4328] defines
   signaling extensions to support control for the legacy G.709 Optical
   Transport Networks.

   As described in Section 3, [G709-2012] introduced some new features
   that include the ODU0, ODU2e, ODU4 and ODUflex containers. The
   mechanisms defined in [RFC4328] do not support such new OTN features,
   and protocol extensions will be necessary to allow them to be
   controlled by a GMPLS control plane.

   [RFC4328] defines the LSP Encoding Type, the Switching Type and the
   Generalized Protocol Identifier (Generalized-PID) constituting the
   common part of the Generalized Label Request. The G.709 Traffic

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   Parameters are also defined in [RFC4328]. The following signaling
   aspects should be considered additionally since [RFC4328] was

   - Support for specifying the new signal types and the related
      traffic information

      The traffic parameters should be extended in signaling message to
      support the new ODUj including:

         -  ODU0
         -  ODU2e
         -  ODU4
         -  ODUflex

      For ODUflex signal type, its bit rate must be carried additionally
      in the Traffic Parameter to setup an ODUflex connection.

      For other ODU signal types, their bit rates and tolerances are
      fixed and can be deduced from the signal types.

   - Support for LSP setup using different TS granularity

      The signaling protocol should be able to identify the TS
      granularity (i.e., the 2.5Gbps TS granularity and the new 1.25Gbps
      TS granularity) to be used for establishing an Hierarchical LSP
      which will be used to carry service LSP(s) requiring specific TS

   - Support for LSP setup of new ODUk/ODUflex containers with related
      mapping and multiplexing capabilities

      A new label format must be defined to carry the exact TSs
      allocation information related to the extended mapping and
      multiplexing hierarchy (For example, ODU0 into ODU2 multiplexing
      (with 1.25Gbps TS granularity)), in order to set up the ODU

   - Support for TPN allocation and negotiation

      TPN needs to be configured as part of the MSI information (see
      more information in Section A signaling mechanism must
      be identified to carry TPN information if control plane is used to
      configure MSI information.

   - Support for ODU Virtual Concatenation (VCAT) and Link Capacity
      Adjustment Scheme (LCAS)

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      GMPLS signaling should support the creation of Virtual
      Concatenation of ODUk signal with k=1, 2, 3. The signaling should
      also support the control of dynamic capacity changing of a VCAT
      container using LCAS ([G7042]). [RFC6344] has a clear description
      of VCAT and LCAS control in SONET/SDH and OTN.

   - Support for Control of Hitless Adjustment of ODUflex (GFP)

      [G7044] has been created in ITU-T to specify Hitless Adjustment of
      ODUflex (GFP) (HAO) that is used to increase or decrease the
      bandwidth of an ODUflex (GFP) that is transported in an OTN.

      The procedure of ODUflex (GFP) adjustment requires the
      participation of every node along the path. Therefore, it is
      recommended to use the control plane signaling to initiate the
      adjustment procedure in order to avoid the manual configuration at
      each node along the path.

      From the perspective of control plane, the control of ODUflex
      resizing is similar to control of bandwidth increasing and
      decreasing described in [RFC3209]. Therefore, the Shared Explicit
      (SE) style can be used for control of HAO.

   All the extensions above should consider the extensibility to match
   future evolvement of OTN.

5.3. Implications for GMPLS Routing

   The path computation process needs to select a suitable route for an
   ODUj connection request. In order to perform the path computation, it
   needs to evaluate the available bandwidth on each candidate link.
   The routing protocol should be extended to convey sufficient
   information to represent ODU Traffic Engineering (TE) topology.

   Interface Switching Capability Descriptors defined in [RFC4202]
   present a new constraint for LSP path computation. [RFC4203] defines
   the switching capability and related Maximum LSP Bandwidth and the
   Switching Capability specific information. When the Switching
   Capability field is TDM the Switching Capability Specific Information
   field includes Minimum LSP Bandwidth, an indication whether the
   interface supports Standard or Arbitrary SONET/SDH, and padding.
   Hence a new Switching Capability value needs to be defined for [G709-
   2012] ODU switching in order to allow the definition of a new
   Switching Capability Specific Information field definition. The
   following requirements should be considered:

   - Support for carrying the link multiplexing capability

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       As discussed in section 3.1.2, many different types of ODUj can
       be multiplexed into the same OTUk. For example, both ODU0 and
       ODU1 may be multiplexed into ODU2. An OTU link may support one or
       more types of ODUj signals. The routing protocol should be
       capable of carrying this multiplexing capability.

   - Support any ODU and ODUflex

       The bit rate (i.e., bandwidth) of each TS is dependent on the TS
       granularity and the signal type of the link. For example, the
       bandwidth of a 1.25G TS in an OTU2 is about 1.249409620Gbps,
       while the bandwidth of a 1.25G TS in an OTU3 is about

       One LO ODU may need different number of TSs when multiplexed into
       different HO ODUs. For example, for ODU2e, 9 TSs are needed when
       multiplexed into an ODU3, while only 8 TSs are needed when
       multiplexed into an ODU4. For ODUflex, the total number of TSs to
       be reserved in a HO ODU equals the maximum of [bandwidth of
       ODUflex / bandwidth of TS of the HO ODU].

       Therefore, the routing protocol should be capable of carrying the
       necessary link bandwidth information for performing accurate
       route computation for any of the fixed rate ODUs as well as

   - Support for differentiating between terminating and switching

       Due to internal constraints and/or limitations, the type of
       signal being advertised by an interface could be restricted to
       switched (i.e. forwarded to switching matrix without
       multiplexing/demultiplexing actions), restricted to terminated
       (demuxed) or both of them. The capability advertised by an
       interface needs further distinction in order to separate
       termination and switching capabilities.

       Therefore, to allow the required flexibility, the routing
       protocol should clearly distinguish the terminating and switching

   - Support for Tributary Slot Granularity advertisement

       [G709-2012] defines two types of TS but each link can only
       support a single type at a given time. In order to perform a
       correct path computation (i.e. the LSP end points have matching

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       Tributary Slot Granularity values) the Tributary Slot Granularity
       needs to be advertised.

   - Support different priorities for resource reservation

       How many priorities levels should be supported depends on the
       operator's policy. Therefore, the routing protocol should be
       capable of supporting up to 8 priority levels as defined in

   - Support link bundling

       As described in [RFC4201], link bundling can improve routing
       scalability by reducing the amount of TE links that has to be
       handled by routing protocol. The routing protocol should be
       capable of supporting bundling multiple OTU links, at the same
       line rate and muxing hierarchy, between a pair of nodes as a TE
       link. Note that link bundling is optional and is implementation

   - Support for Control of Hitless Adjustment of ODUflex (GFP)

       The control plane should support hitless adjustment of ODUflex,
       so the routing protocol should be capable of differentiating
       whether an ODU link can support hitless adjustment of ODUflex
       (GFP) or not, and how much resource can be used for resizing.
       This can be achieved by introducing a new signal type
       "ODUflex(GFP-F), resizable" that implies the support for hitless
       adjustment of ODUflex (GFP) by that link.

   As mentioned in Section 5.1, one method of enabling multiplexing
   hierarchy is via usage of dedicated boards to allow tunneling of new
   services through legacy ODU1, ODU2, ODU3 containers. Such dedicated
   boards may have some constraints with respect to switching matrix
   access; detection and representation of such constraints is for
   further study.

5.4. Implications for Link Management Protocol

   As discussed in section 5.3, Path computation needs to know the
   interface switching capability of links. The switching capability of
   two ends of the link may be different, so the link capability of two
   ends should be correlated.

   LMP [RFC4204] provides a control plane protocol for exchanging and
   correlating link capabilities.

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   Note that LO ODU type information can be, in principle, discovered by
   routing. Since in certain cases, routing is not present (e.g. User-
   Network Interface (UNI) case) we need to extend link management
   protocol capabilities to cover this aspect. In case of routing
   presence, the discovery via LMP could also be optional.

   - Correlating the granularity of the TS

       As discussed in section 3.1.2, the two ends of a link may support
       different TS granularity. In order to allow interconnection the
       node with 1.25Gbps granularity should fall back to 2.5Gbps

       Therefore, it is necessary for the two ends of a link to
       correlate the granularity of the TS. This ensures the correct use
       and of the TE link.

   - Correlating the supported LO ODU signal types and multiplexing
      hierarchy capability

       Many new ODU signal types have been introduced in [G709-2012],
       such as ODU0, ODU4, ODU2e and ODUflex. It is possible that
       equipment does not support all the LO ODU signal types introduced
       by those new standards or drafts. Furthermore, since multiplexing
       hierarchy may not be supported by the legacy OTN, it is possible
       that only one end of an ODU link can support multiplexing
       hierarchy capability, or the two ends of the link support
       different multiplexing hierarchy capabilities (e.g., one end of
       the link supports ODU0 into ODU1 into ODU3 multiplexing while the
       other end supports ODU0 into ODU2 into ODU3 multiplexing).

       For the control and management consideration, it is necessary for
       the two ends of an HO ODU link to correlate which types of LO ODU
       can be supported and what multiplexing hierarchy capabilities can
       be provided by the other end.

5.5. Implications for Control Plane Backward Compatibility

   With the introduction of [G709-2012], there may be OTN composed of a
   mixture of nodes, some of which support the legacy OTN and run
   control plane protocols defined in [RFC4328], while others support
   [G709-2012] and new OTN control plane characterized in this document.
   Note that a third case, for the sake of completeness, consists on
   nodes supporting the legacy OTN referenced by [RFC4328] with a new
   OTN control plane, but such nodes can be considered as new nodes with
   limited capabilities.

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   This section discusses the compatibility of nodes implementing the
   control plane procedures defined [RFC4328], in support of the legacy
   OTN, and the control plane procedures defined to support [G709-2012],
   as outlined by this document.

   Compatibility needs to be considered only when controlling ODU1 or
   ODU2 or ODU3 connection, because the legacy OTN only support these
   three ODU signal types. In such cases, there are several possible
   options including:

   - A node supporting [G709-2012] could support only the [G709-2012]
      related control plane procedures, in which case both types of
      nodes would be unable to jointly control an LSP for an ODU type
      that both nodes support in the data plane.

   - A node supporting [G709-2012] could support both the [G709-2012]
      related control plane and the control plane defined in [RFC4328].

      o Such a node could identify which set of procedure to follow
         when initiating an LSP based on the Switching Capability value
         advertised in routing.

      o Such a node could follow the set of procedures based on the
         Switching Type received in signaling messages from an upstream

      o Such a node, when processing a transit LSP, could select which
         signaling procedures to follow based on the Switching
         Capability value advertised in routing by the next hop node.

5.6. Implications for Path Computation Elements

   [RFC7025] describes the requirements for GMPLS applications of PCE in
   order to establish GMPLS LSP. PCE needs to consider the GMPLS TE
   attributes appropriately once a Path Computation Client (PCC) or
   another PCE requests a path computation. The TE attributes which can
   be contained in the path calculation request message from the PCC or
   the PCE defined in [RFC5440] includes switching capability, encoding
   type, signal type, etc.

   As described in section 5.2, new signal types and new signals with
   variable bandwidth information need to be carried in the extended
   signaling message of path setup. For the same consideration, PCE
   Communication Protocol (PCECP) also has a desire to be extended to
   carry the new signal type and related variable bandwidth information
   when a PCC requests a path computation.

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5.7. Implications for Management of GMPLS Networks

   From the management perspective, it should be capable of managing not
   only the legacy OTN referenced by [RFC4328], but also new management
   functions introduced by the new features as specified in [G709-2012]
   (see more in Sections 3&4). Regarding OTN Operations, Administration
   and Maintenance (OAM) configuration, it could be done through either
   Network Management Systems (NMS) or GMPLS control plane as defined in
   [TDM-OAM]. Further details of management aspects for GMPLS networks
   refer to [RFC3945].

   In case PCE is used to perform path computation in OTN, the PCE
   manageability should be considered (see more in Section 8 of

6. Data Plane Backward Compatibility Considerations

   If MI AUTOpayloadtype is activated (see [G798-V4]), a node supporting
   1.25Gbps TS can interwork with the other nodes that supporting
   2.5Gbps TS by combining Specific TSs together in data plane. The
   control plane must support this TS combination.

            +----------+   ------------>    +----------+
            |     TS1==|===========\--------+--TS1     |
            |     TS2==|=========\--\-------+--TS2     |
            |     TS3==|=======\--\--\------+--TS3     |
            |     TS4==|=====\--\--\--\-----+--TS4     |
            |          |      \  \  \  \----+--TS5     |
            |          |       \  \  \------+--TS6     |
            |          |        \  \--------+--TS7     |
            |          |         \----------+--TS8     |
            +----------+   <------------    +----------+
               node A           Resv           node B

         Figure 5 - Interworking between 1.25Gbps TS and 2.5Gbps TS

   Take Figure 5 as an example. Assume that there is an ODU2 link
   between node A and B, where node A only supports the 2.5Gbps TS while
   node B supports the 1.25Gbps TS. In this case, the TS#i and TS#i+4
   (where i<=4) of node B are combined together. When creating an ODU1
   service in this ODU2 link, node B reserves the TS#i and TS#i+4 with

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   the granularity of 1.25Gbps. But in the label sent from B to A, it is
   indicated that the TS#i with the granularity of 2.5Gbps is reserved.

   In the opposite direction, when receiving a label from node A
   indicating that the TS#i with the granularity of 2.5Gbps is reserved,
   node B will reserved the TS#i and TS#i+4 with the granularity of
   1.25Gbps in its data plane.

7. Security Considerations

   The use of control plane protocols for signaling, routing and path
   computation opens an OTN to security threats through attacks on those
   protocols. Although, this is not greater than the risks presented by
   the existing OTN control plane as defined by [RFC4203] and [RFC4328].
   Meanwhile, the Data Communication Network (DCN) for OTN GMPLS control
   plane protocols is likely to be in the in-fiber overhead, which
   together with access lists at the network edges, provides a
   significant security feature. For further details of the specific
   security measures refer to the documents that define the protocols
   ([RFC3473], [RFC4203], [RFC5307], [RFC4204] and [RFC5440]). [RFC5920]
   provides an overview of security vulnerabilities and protection
   mechanisms for the GMPLS control plane.

8. IANA Considerations

   This document makes not requests for IANA action.

9. Acknowledgments

   We would like to thank Maarten Vissers and Lou Berger for their
   review and useful comments.

10. References

10.1. Normative References

   [RFC3209]   Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.
               and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
               Tunnels", RFC 3209, December 2001.

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   [RFC3471]   Berger, L., Editor, "Generalized Multi-Protocol Label
               Switching (GMPLS) Signaling Functional Description", RFC
               3471, January 2003.

   [RFC3473]   L. Berger, Ed., "Generalized Multi-Protocol Label
               Switching (GMPLS) Signaling Resource ReserVation
               Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
               3473, January 2003.

   [RFC4201]   K. Kompella, Y. Rekhter, Ed., "Link Bundling in MPLS
               Traffic Engineering (TE)", RFC 4201, October 2005.

   [RFC4202]   K. Kompella, Y. Rekhter, Ed., "Routing Extensions in
               Support of Generalized Multi-Protocol Label Switching
               (GMPLS)", RFC 4202, October 2005.

   [RFC4203]   K. Kompella, Y. Rekhter, Ed., "OSPF Extensions in Support
               of Generalized Multi-Protocol Label Switching (GMPLS)",
               RFC 4203, October 2005.

   [RFC4204]   Lang, J., Ed., "Link Management Protocol (LMP)", RFC
               4204, October 2005.

   [RFC4206]   K. Kompella, Y. Rekhter, Ed., "Label Switched Paths (LSP)
               Hierarchy with Generalized Multi-Protocol Label Switching
               (GMPLS) Traffic Engineering (TE)", RFC 4206, October

   [RFC4328]   D. Papadimitriou, Ed. "Generalized Multi-Protocol
               LabelSwitching (GMPLS) Signaling Extensions for G.709
               Optical Transport Networks Control", RFC 4328, Jan 2006.

   [RFC5307]   K. Kompella, Y. Rekhter, Ed., "IS-IS Extensions in
               Support of Generalized Multi-Protocol Label Switching
               (GMPLS)", RFC 5307, October 2008.

   [RFC5440]   JP. Vasseur, JL. Le Roux, Ed.," Path Computation Element
               (PCE) Communication Protocol (PCEP)", RFC 5440, March

   [RFC6001]   Dimitri Papadimitriou et al, "Generalized Multi-Protocol
               Label Switching (GMPLS) Protocol Extensions for Multi-
               Layer and Multi-Region Networks (MLN/MRN)", RFC6001,
               February 21, 2010.

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   [RFC6107]   K. Shiomoto, A. Farrel, "Procedures for Dynamically
               Signaled Hierarchical Label Switched Paths", RFC6107,
               February 2011.

   [RFC6344]   G. Bernstein et al, "Operating Virtual Concatenation
               (VCAT) and the Link Capacity Adjustment Scheme (LCAS)
               with Generalized Multi-Protocol Label Switching (GMPLS)",
               RFC6344, August, 2011.

   [G709-2012] ITU-T, "Interface for the Optical Transport Network
               (OTN)", G.709/Y.1331 Recommendation, February 2012.

10.2. Informative References

   [G798-V4]   ITU-T, "Characteristics of optical transport network
               hierarchy equipment functional blocks", G.798
               Recommendation, October 2010.

   [G7042]     ITU-T, "Link capacity adjustment scheme (LCAS) for
               virtual concatenated signals", G.7042/Y.1305, March 2006.

   [G872-2001] ITU-T, "Architecture of optical transport networks",
               G.872 Recommendation, November 2001.

   [G872-2012] ITU-T, "Architecture of optical transport networks",
               G.872 Recommendation, October 2012.

   [G7044]     ITU-T, "Hitless adjustment of ODUflex", G.7044/Y.1347,
               October 2011.

   [G7041]     ITU-T, "Generic framing procedure", G.7041/Y.1303, April

   [RFC3945]   Mannie, E., "Generalized Multi-Protocol Label Switching
               (GMPLS) Architecture", RFC 3945, October 2004.

   [RFC4655]   Farrel, A., Vasseur, J., and J. Ash, "A Path
               Computation Element (PCE)-Based Architecture",
               RFC 4655, August 2006.

   [RFC6163]   Y. Lee, G. Bernstein, W. Imajuku, "Framework for GMPLS
               and PCE Control of Wavelength Switched Optical Networks
               (WSON)", RFC6163, April 2011.

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   [RFC5920]   Fang, L., Ed., "Security Framework for MPLS and GMPLS
               Networks", RFC5920, July 2010.

   [RFC7025]   Tomohiro Otani, Kenichi Ogaki, Diego Caviglia, and Fatai
               Zhang, "Requirements for GMPLS applications of PCE",
               RFC7025, September 2013.

   [TDM-OAM]   A. Kern, A. Takacs, "GMPLS RSVP-TE Extensions for
               SONET/SDH and OTN OAM Configuration", draft-ietf-ccamp-
               rsvp-te-sdh-otn-oam-ext, Work in Progress.

11. Authors' Addresses

   Fatai Zhang (editor)
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China

   Phone: +86-755-28972912

   Dan Li
   Huawei Technologies Co., Ltd.
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China

   Phone: +86-755-28973237

   Han Li
   China Mobile Communications Corporation
   53 A Xibianmennei Ave. Xuanwu District
   Beijing 100053 P.R. China

   Phone: +86-10-66006688

   Sergio Belotti
   Optics CTO

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   Via Trento 30 20059 Vimercate (Milano) Italy
   +39 039 6863033


   Daniele Ceccarelli
   Via A. Negrone 1/A
   Genova - Sestri Ponente


12. Contributors

   Jianrui Han
   Huawei Technologies Co., Ltd.
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China

   Phone: +86-755-28972913

   Malcolm Betts


   Pietro Grandi
   Optics CTO
   Via Trento 30 20059 Vimercate (Milano) Italy
   +39 039 6864930


   Eve Varma
   1A-261, 600-700 Mountain Av
   PO Box 636
   Murray Hill, NJ  07974-0636

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