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Internet Engineering Task Force (IETF) S. Belotti, Ed. Request for Comments: 7096 P. Grandi Category: Informational Alcatel-Lucent ISSN: 2070-1721 D. Ceccarelli, Ed.

                                                           D. Caviglia
                                                              Ericsson
                                                              F. Zhang
                                                                 D. Li
                                                   Huawei Technologies
                                                          January 2014
               Evaluation of Existing GMPLS Encoding
         against G.709v3 Optical Transport Networks (OTNs)

Abstract

 ITU-T recommendation G.709-2012 has introduced new fixed and flexible
 Optical channel Data Unit (ODU) containers in Optical Transport
 Networks (OTNs).
 This document provides an evaluation of existing Generalized
 Multiprotocol Label Switching (GMPLS) routing and signaling protocols
 against the G.709 OTNs.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7096.

Belotti, et al. Informational [Page 1] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

Copyright Notice

 Copyright (c) 2014 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1. Introduction ....................................................3
 2. G.709 Mapping and Multiplexing Capabilities .....................4
 3. Tributary Slot Granularity ......................................6
    3.1. Data-Plane Considerations ..................................7
         3.1.1. Payload Type and TS Granularity Relationship ........7
         3.1.2. Fallback Procedure ..................................8
    3.2. Control-Plane Considerations ...............................9
 4. Tributary Port Number ..........................................13
 5. Signal Type ....................................................13
 6. Bit Rate and Tolerance .........................................15
 7. Unreserved Resources ...........................................15
 8. Maximum LSP Bandwidth ..........................................15
 9. Distinction between Terminating and Switching Capabilities .....16
 10. Priority Support ..............................................18
 11. Multi-stage Multiplexing ......................................18
 12. Generalized Label .............................................19
 13. Security Considerations .......................................19
 14. Contributors ..................................................20
 15. Acknowledgements ..............................................20
 16. References ....................................................20
    16.1. Normative References .....................................20
    16.2. Informative References ...................................21

Belotti, et al. Informational [Page 2] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

1. Introduction

 GMPLS routing [RFC4203] [RFC5307] and signaling [RFC3473] [RFC4328]
 provide the mechanisms for basic GMPLS control of Optical Transport
 Networks (OTNs) based on the 2001 revision of the G.709 specification
 [G.709-2001].  The 2012 revision of the G.709 specification
 [G.709-2012] includes new OTN features that are not supported by
 GMPLS.
 This document provides an evaluation of exiting GMPLS signaling and
 routing protocols against G.709 requirements.  Background information
 and a framework for the GMPLS protocol extensions needed to support
 G.709 is provided in [RFC7062].  Specific routing and signaling
 extensions defined in [OTN-OSPF] and [OTN-RSVP] specifically address
 the gaps identified in this document.

Belotti, et al. Informational [Page 3] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

2. G.709 Mapping and Multiplexing Capabilities

 The digital OTN-layered structure is comprised of the digital path
 layer (ODU) and the digital section layer (OTU).  An OTU (Optical
 channel Transport Unit) section layer supports one ODU path layer as
 a client and provides monitoring capability for the Optical Channel
 (OCh), which is the optical path carrying the digital OTN structure.
 An ODU path layer may transport a heterogeneous assembly of ODU
 clients.  Some types of ODUs (i.e., ODU1, ODU2, ODU3, and ODU4) may
 assume either a client or server role within the context of a
 particular networking domain.  The terms ODU1, ODU2, ODU3, ODU4, and
 flexible ODU (ODUflex) are explained in G.709.  G.872 [G.872]
 provides two tables defining mapping and multiplexing capabilities of
 OTNs, which are reported below.
       +--------------------+--------------------+
       |     ODU client     |     OTU server     |
       +--------------------+--------------------+
       |        ODU0        |          -         |
       +--------------------+--------------------+
       |        ODU1        |        OTU 1       |
       +--------------------+--------------------+
       |        ODU2        |        OTU 2       |
       +--------------------+--------------------+
       |        ODU2e       |          -         |
       +--------------------+--------------------+
       |        ODU3        |        OTU 3       |
       +--------------------+--------------------+
       |        ODU4        |        OTU 4       |
       +--------------------+--------------------+
       |        ODUflex     |          -         |
       +--------------------+--------------------+
             Figure 1: OTN Mapping Capability

Belotti, et al. Informational [Page 4] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

     +=================================+=========================+
     |           ODU client            |       ODU server        |
     +---------------------------------+-------------------------+
     |        1.25 Gbit/s client       |                         |
     +---------------------------------+          ODU0           |
     |                 -               |                         |
     +=================================+=========================+
     |         2.5 Gbit/s client       |                         |
     +---------------------------------+          ODU1           |
     |              ODU0               |                         |
     +=================================+=========================+
     |         10 Gbit/s client        |                         |
     +---------------------------------+          ODU2           |
     |        ODU0,ODU1,ODUflex        |                         |
     +=================================+=========================+
     |        10.3125 Gbit/s client    |                         |
     +---------------------------------+          ODU2e          |
     |                 -               |                         |
     +=================================+=========================+
     |         40 Gbit/s client        |                         |
     +---------------------------------+          ODU3           |
     |  ODU0,ODU1,ODU2,ODU2e,ODUflex   |                         |
     +=================================+=========================+
     |        100 Gbit/s client        |                         |
     +---------------------------------+          ODU4           |
     |ODU0,ODU1,ODU2,ODU2e,ODU3,ODUflex|                         |
     +=================================+=========================+
     |CBR* clients from greater than   |                         |
     |2.5 Gbit/s to 100 Gbit/s: or     |                         |
     |GFP-F** mapped packet clients    |          ODUflex        |
     |from 1.25 Gbit/s to 100 Gbit/s.  |                         |
     +---------------------------------+                         |
     |                 -               |                         |
     +=================================+=========================+
     (*) - Constant Bit Rate
     (**) - Generic Framing Procedure - Framed (GFP-F)
                 Figure 2: OTN Multiplexing Capability
 In the following, the terms Optical channel Data Unit-j (ODUj) and
 Optical channel Data Unit-k (ODUk) are used in a multiplexing
 scenario to identify the lower order signal (ODUj) and the higher
 order signal (ODUk).  How an ODUk connection service is transported
 within an operator network is governed by operator policy.  For
 example, the ODUk connection service might be transported over an
 ODUk path over an Optical channel Transport Unit-k (OTUk) section,
 with the same path and section rates as that of the connection

Belotti, et al. Informational [Page 5] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

 service (see Figure 1).  In this case, an entire lambda of capacity
 is consumed in transporting the ODUk connection service.  On the
 other hand, the operator might exploit different multiplexing
 capabilities in the network to improve infrastructure efficiencies
 within any given networking domain.  In this case, ODUk multiplexing
 may be performed prior to transport over various rate ODU servers (as
 per Figure 2) over associated OTU sections.
 From the perspective of multiplexing relationships, a given ODUk may
 play different roles as it traverses various networking domains.
 As detailed in [RFC7062], client ODUk connection services can be
 transported over:
 Case A:  one or more wavelength subnetworks connected by optical
          links, or
 Case B:  one or more ODU links (having sub-lambda and/or lambda
          bandwidth granularity), or
 Case C:  a mix of ODU links and wavelength subnetworks.
 This document considers the Traffic Engineering (TE) information
 needed for ODU path computation and the parameters needed to be
 signaled for Label Switched Path (LSP) setup.
 The following sections list and analyze what GMPLS already has and
 what it is missing with regard to each type of data that needs to be
 advertised and signaled.

3. Tributary Slot Granularity

 G.709 defines two types of Tributary Slot (TS) granularities.  This
 TS granularity is defined per layer, meaning that both ends of a link
 can select proper TS granularity differently for each supported
 layer, based on the rules below:
 o  If both ends of a link are new cards supporting both 1.25 Gbit/s
    TS and 2.5 Gbit/s TS, then the link will work with 1.25 Gbit/s TS.
 o  If one end of a link is a new card supporting both the 1.25 Gbit/s
    and 2.5 Gbit/s TS granularities, and the other end is an old card
    supporting just the 2.5 Gbit/s TS granularity, the link will work
    with 2.5 Gbit/s TS granularity.

Belotti, et al. Informational [Page 6] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

3.1. Data-Plane Considerations

3.1.1. Payload Type and TS Granularity Relationship

 As defined in G.709, an ODUk container consists of an Optical channel
 Payload Unit-k (OPUk) plus a specific ODUk Overhead (OH).  OPUk OH
 information is added to the OPUk information payload to create an
 OPUk.  It includes information to support the adaptation of client
 signals.  Within the OPUk overhead, there is the payload structure
 identifier (PSI) that includes the payload type (PT).  The PT is used
 to indicate the composition of the OPUk signal.  When an ODUj signal
 is multiplexed into an ODUk, the ODUj signal is first extended with
 the frame alignment overhead and then mapped into an Optical channel
 Data Tributary Unit (ODTU).  Two different types of ODTUs are
 defined:
 o  ODTUjk ((j,k) = {(0,1), (1,2), (1,3), (2,3)}; ODTU01, ODTU12,
    ODTU13, and ODTU23) in which an ODUj signal is mapped via the
    Asynchronous Mapping Procedure (AMP), as defined in Section 19.5
    of [G.709-2012].
 o  ODTUk.ts ((k,ts) = (2,1..8), (3,1..32), (4,1..80)) in which a
    lower order ODU (ODU0, ODU1, ODU2, ODU2e, ODU3, and ODUflex)
    signal is mapped via the Generic Mapping Procedure (GMP), as
    defined in Section 19.6 of [G.709-2012].
 G.709 also introduces a logical entity, called Optical channel Data
 Tributary Unit Group (ODTUGk), characterizing the multiplexing of the
 various ODTU.  The ODTUGk is then mapped into OPUk.  Optical channel
 Data Tributary Unit j into k (ODTUjk) and Optical channel Data
 Tributary Unit k with ts tributary slots (ODTUk.ts) are directly
 time-division multiplexed into the tributary slots of an OH OPUk.
 When PT is assuming values 0x20 or 0x21, together with OPUk type
 (k=1, 2, 3, 4), it is used to discriminate two different ODU
 multiplex structures for ODTUGx:
 o  Value 0x20: supporting ODTUjk only
 o  Value 0x21: supporting ODTUk.ts or ODTUk.ts and ODTUjk
 The distinction is needed for OPUk with k=2 or 3 since OPU2 and OPU3
 are able to support both the different ODU multiplex structures.  For
 OPU4 and OPU1, only one type of ODTUG is supported: ODTUG4 with
 PT=0x21 and ODTUG1 with PT=0x20 (see Figure 6).  The relationship
 between PT and TS granularity is due to the fact that the two

Belotti, et al. Informational [Page 7] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

 different ODTUGk types discriminated by PT and OPUk are characterized
 by two different TS granularities of the related OPUk, the former at
 2.5 Gbit/s and the latter at 1.25 Gbit/s.
 In order to complete the picture, in the PSI OH, there is also the
 Multiplex Structure Identifier (MSI) that provides the information on
 which tributary slots of the different ODTUjk or ODTUk.ts are mapped
 into the related OPUk.  The following figure shows how the client
 traffic is multiplexed till the OPUk layer.
                 +--------+      +------------+
      +----+     |        !------| ODTUjk     |-----Client
      |    |     | ODTUGk |      +-----.------+
      |    |-----| PT=0x21|            .
      |    |     |        |      +-----.------+
      |    |     |        |------| ODTUk.ts   |-----Client
      |OPUk|     +--------+      +------------+
      |    |
      |    |     +--------+      +------------+
      |    |     |        |------| ODTUjk     |-----Client
      |    |-----|        |      +-----.------+
      +----+     | ODTUGk |            .
                 | PT=0x20|      +-----.------+
                 |        |------| ODTUjk     |-----Client
                 +--------+      +------------+
                   Figure 3: OTN Client Multiplexing

3.1.2. Fallback Procedure

 G.798 [G.798] describes the so-called PT=0x21-to-PT=0x20 interworking
 process that explains how two nodes with interfaces that have
 different payload types and, hence, different TS granularity (1.25
 Gbit/s vs. 2.5 Gbit/s), can be coordinated to permit the equipment
 with 1.25 Gbit/s TS granularity to adapt the TS allocation according
 to the different TS granularity (2.5 Gbit/s) of a neighbor.
 Therefore, in order to let the Network Element (NE) change TS
 granularity accordingly to the neighbor requirements, the
 AUTOpayloadtype [G.798] needs to be set.  When both the neighbors
 (link or trail) have been configured as structured, the payload type
 received in the overhead is compared to the transmitted PT.  If they
 are different and the transmitted one is PT=0x21, the node must fall
 back to PT=0x20.  In this case, the fallback process makes the system
 self-consistent, and the only reason for signaling the TS granularity
 is to provide the correct label (i.e., the label for PT=0x21 has
 twice the TS number of PT=0x20).  On the other side, if the

Belotti, et al. Informational [Page 8] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

 AUTOpayloadtype is not configured, the Resource Reservation Protocol-
 Traffic Engineering (RSVP-TE) consequent actions need to be defined
 in case of a TS mismatch.

3.2. Control-Plane Considerations

 When setting up an ODUj over an ODUk, it is possible to identify two
 types of TS granularity (TSG): the server and the client.  The server
 TS granularity is used to map an end-to-end ODUj onto a server ODUk
 LSP or links.  This parameter cannot be influenced in any way from
 the ODUj LSP: the ODUj LSP will be mapped on tributary slots
 available on the different links / ODUk LSPs.  When setting up an
 ODUj at a given rate, the fact that it is carried over a path
 composed by links / Forwarding Adjacencies (FAs) structured with 1.25
 Gbit/s or 2.5 Gbit/s TS granularity is completely transparent to the
 end-to-end ODUj.
 The client TS granularity information is one of the parameters needed
 to correctly select the adaptation towards the client layers at the
 end nodes, and this is the only thing that the ODUj has to guarantee.
 In Figure 4, an example of client and server TS granularity
 utilization in a scenario with mixed OTN [RFC4328] and OTN interfaces
 [G.709-2012] is shown.
                          ODU1-LSP
         .........................................
    TSG-C|                                       |TSG-C
     1.25|                   ODU2-H-LSP          |1.25 Gbit/s
   Gbit/s+------------X--------------------------+
         |       TSG-S|                          |TSG-S
         |         2.5|                          |2.5 Gbit/s
         |      Gbit/s|       ODU3-H-LSP         |
         |            |------------X-------------|
         |            |                          |
      +--+--+      +--+--+                   +---+-+
      |     |      |     |     +-+   +-+     |     |
      |  A  +------+  B  +-----+ +***+ +-----+  Z  |
      | V.3 | OTU2 | V.1 |OTU3 +-+   +-+ OTU3| V.3 |
      +-----+      +-----+                   +-----+
       ... Service LSP
       --- Hierarchical-LSP (H-LSP)
       Figure 4: Client-Server TS Granularity Example

Belotti, et al. Informational [Page 9] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

 In this scenario, an ODU3 LSP is set up from nodes B to Z.  Node B
 has an old interface that is able to support 2.5 Gbit/s TS
 granularity; hence, only client TS granularity equal to 2.5 Gbit/s
 can be exported to ODU3 H-LSP-possible clients.  An ODU2 LSP is set
 up from nodes A to Z with client TS granularity 1.25 Gbit/s signaled
 and exported towards clients.  The ODU2 LSP is carried by ODU3 H-LSP
 from nodes B to Z.  Due to the limitations of the old node B
 interface, the ODU2 LSP is mapped with 2.5 Gbit/s TS granularity over
 the ODU3 H-LSP.  Then, an ODU1 LSP is set up from nodes A to Z, which
 is carried by the ODU2 H-LSP and mapped over it using 1.25 Gbit/s TS
 granularity.
 What is shown in the example is that the TS granularity processing is
 a per-layer issue: even if the ODU3 H-LSP is created with the TS
 granularity client at 2.5 Gbit/s, the ODU2 H-LSP must guarantee a
 1.25 Gbit/s TS granularity client.  The ODU3 H-LSP is eligible from
 an ODU2 LSP perspective since it is known from the routing that this
 ODU3 interface at node Z supports an ODU2 termination exporting a TS
 granularity at 1.25 Gbit/s / 2.5 Gbit/s.
 The TS granularity information is needed in the routing protocol as
 the ingress node (A in the previous example) needs to know if the
 interfaces at the last hop can support the required TS granularity.
 In case they cannot, A will compute an alternate path from itself to
 Z (see Figure 4).
 Moreover, TS granularity information also needs to be signaled.  As
 an example, consider the setup of an ODU3 forwarding adjacency that
 is going to carry an ODU0; hence, the support of 1.25 Gbit/s TS is
 needed.  The information related to the TS granularity has to be
 carried in the signaling to permit node C (see Figure 5) to choose
 the right one among the different interfaces (with different TS
 granularities) towards D.  In case the full Explicit Route Object
 (ERO) is provided in the signaling with explicit interface
 declaration, there is no need for C to choose the right interface
 towards D as it has been already decided by the ingress node or by
 the Path Computation Element (PCE).

Belotti, et al. Informational [Page 10] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

                              ODU3
                             <---------------------->
                              ODU0
             <-------------------------------------->
             |                                      |
    +--------+      +--------+      +--------+      +--------+
    |        |      |        |      |        | 1.25 |        |
    |  Node  |      |  Node  |      |  Node  +------+  Node  |
    |   A    +------+   B    +------+   C    | ODU3 |   D    |
    |        | ODU3 |        | ODU3 |        +------+        |
    +--------+ 1.25 +--------+ 2.5  +--------+ 2.5  +--------+
                 Figure 5: TS Granularity in Signaling
 In case an ODUk FA_LSP needs to be set up as nesting another ODUj (as
 depicted in Figure 5), there might be the need to know the hierarchy
 of nested LSPs in addition to TS granularity to permit the
 penultimate hop (i.e., C) to choose the correct interface towards the
 egress node or any intermediate node (i.e., B) to choose the right
 path when performing the ERO expansion.  This is not needed in case
 we allow bundling only component links with homogeneous hierarchies.
 In the case in which a specific implementation does not specify the
 last hop interface in the ERO, crankback can be a solution.
 In a multi-stage multiplexing environment, any layer can have a
 different TS granularity structure; for example, in a multiplexing
 hierarchy such as ODU0->ODU2->ODU3, the ODU3 can be structured at TS
 granularity = 2.5 Gbit/s in order to support an ODU2 connection, but
 this ODU2 connection can be a tunnel for ODU0 and, hence, structured
 with 1.25 Gbit/s TS granularity.  Therefore, any multiplexing level
 has to advertise its TS granularity capabilities in order to allow a
 correct path computation by the end nodes (both the ODUk trail and
 the H-LSP/FA).
 The following table shows the different mapping possibilities
 depending on the TS granularity types.  The client types are shown in
 the left column, while the different OPUk server and related TS
 granularities are listed in the top row.  The table also shows the
 relationship between the TS granularity and the payload type.

Belotti, et al. Informational [Page 11] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

               +------------------------------------------------+
               | 2.5 Gbit/s TS ||     1.25 Gbit/s TS            |
               | OPU2  | OPU3  || OPU1  | OPU2  | OPU3  | OPU4  |
       +-------+------------------------------------------------+
       |       |   -   |   -   ||  AMP  |  GMP  |  GMP  |  GMP  |
       | ODU0  |       |       ||PT=0x20|PT=0x21|PT=0x21|PT=0x21|
       +-------+------------------------------------------------+
       |       |  AMP  |  AMP  ||   -   |  AMP  |  AMP  |  GMP  |
       | ODU1  |PT=0x20|PT=0x20||       |PT=0x21|PT=0x21|PT=0x21|
       +-------+------------------------------------------------+
       |       |   -   |  AMP  ||   -   |   -   |  AMP  |  GMP  |
       | ODU2  |       |PT=0x20||       |       |PT=0x21|PT=0x21|
       +-------+------------------------------------------------+
       |       |   -   |   -   ||   -   |   -   |  GMP  |  GMP  |
       | ODU2e |       |       ||       |       |PT=0x21|PT=0x21|
       +-------+------------------------------------------------+
       |       |   -   |   -   ||   -   |   -   |   -   |  GMP  |
       | ODU3  |       |       ||       |       |       |PT=0x21|
       +-------+------------------------------------------------+
       |       |   -   |   -   ||   -   |  GMP  |  GMP  |  GMP  |
       | ODUfl |       |       ||       |PT=0x21|PT=0x21|PT=0x21|
       +-------+------------------------------------------------+
                Figure 6: ODUj into OPUk Mapping Types
                  (Source: [G.709-2012], Tables7-10)
 Specific information could be defined in order to carry the
 multiplexing hierarchy and adaptation information (i.e., TS
 granularity / PT and AMP / GMP) to enable precise path selection.
 That way, when the penultimate node (or the intermediate node
 performing the ERO expansion) receives such an object, together with
 the Traffic Parameters Object, it is possible to choose the correct
 interface towards the egress node.
 In conclusion, both routing and signaling need to be extended to
 appropriately represent the TS granularity/PT information.  Routing
 needs to represent a link's TS granularity and PT capabilities as
 well as the supported multiplexing hierarchy.  Signaling needs to
 represent the TS granularity/PT and multiplexing hierarchy encoding.

Belotti, et al. Informational [Page 12] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

4. Tributary Port Number

 [RFC4328] supports only the deprecated auto-MSI mode, which assumes
 that the Tributary Port Number (TPN) is automatically assigned in the
 transmit direction and is not checked in the receive direction.
 As described in [G.709-2012] and [G.798], the OPUk overhead in an
 OTUk frame contains n (n = the total number of TSs of the ODUk) MSI
 bytes (in the form of multiframe), each of which is used to indicate
 the association between the TPN and TS of the ODUk.
 The association between the TPN and TS has to be configured by the
 control plane and checked by the data plane on each side of the link.
 (Please refer to [RFC7062] for further details.)  As a consequence,
 the RSVP-TE signaling needs to be extended to support the TPN
 assignment function.

5. Signal Type

 From a routing perspective, GMPLS OSPF [RFC4203] and GMPLS IS-IS
 [RFC5307] only allow advertising interfaces [RFC4328] (the single TS
 type) without the capability of providing precise information about
 bandwidth-specific allocation.  For example, in case of link
 bundling, when dividing the unreserved bandwidth by the MAX LSP
 bandwidth, it is not possible to know the exact number of LSPs at MAX
 LSP bandwidth size that can be set up (see the example in Figure 3).
 The lack of spatial allocation heavily impacts the restoration
 process because the lack of information on free resources highly
 increases the number of crankbacks affecting network convergence
 time.
 Moreover, actual tools provided by [RFC4203] and [RFC5307] only allow
 advertising signal types with fixed bandwidth and implicit hierarchy
 (e.g., Synchronous Digital Hierarchy (SDH) networks / Synchronous
 Optical Networks (SONETs)) or variable bandwidth with no hierarchy
 (e.g., packet switching networks); but, they do not provide the means
 for advertising networks with a mixed approach (e.g., ODUflex
 Constant Bit Rate (CBR) and ODUflex packet).
 For example, when advertising ODU0 as MIN LSP bandwidth and ODU4 as
 MAX LSP bandwidth, it is not possible to state whether the advertised
 link supports ODU4 and ODUflex or ODU4, ODU3, ODU2, ODU1, ODU0, and
 ODUflex.  Such ambiguity is not present in SDH networks where the
 hierarchy is implicit and flexible containers like ODUflex do not
 exist.  The issue could be resolved by declaring 1 Interface
 Switching Capability Descriptor (ISCD) for each signal type actually
 supported by the link.

Belotti, et al. Informational [Page 13] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

 Suppose, for example, there is an equivalent ODU2 unreserved
 bandwidth in a TE link (with bundling capability) distributed on 4
 ODU1; it would be advertised via the ISCD in this way:
    MAX LSP Bandwidth: ODU1
    MIN LSP Bandwidth: ODU1
  1. Maximum Reservable Bandwidth (of the bundle) set to ODU2
  1. Unreserved Bandwidth (of the bundle) set to ODU2
 In conclusion, the routing extensions defined in [RFC4203] and
 [RFC5307] require a different ISCD per signal type in order to
 advertise each supported container.  This motivates an attempt to
 look for a more optimized solution without proliferation of the
 number of ISCDs advertised.
 Per [RFC2328], OSPF messages are directly encapsulated in IP
 datagrams and depend on IP fragmentation when transmitting packets
 larger than the network's MTU.  [RFC2328] recommends that "IP
 fragmentation should be avoided whenever possible".  This
 recommendation further constrains solutions since OSPF does not
 support any generic mechanism to fragment OSPF Link State
 Advertisements (LSAs).  Even when used in IP environments, IS-IS
 [RFC1195] does not support message sizes larger than a link's maximum
 frame size.
 With respect to link bundling [RFC4201], the utilization of the ISCD
 as it is would not allow precise advertising of spatial bandwidth
 allocation information unless using only one component link per TE
 link.
 On the other hand, from a signaling point of view, [RFC4328]
 describes GMPLS signaling extensions to support the control of G.709
 OTNs defined before 2011 [G.709-2001].  However, [RFC4328] needs to
 be updated because it does not provide the means to signal all the
 new signal types and related mapping and multiplexing
 functionalities.

Belotti, et al. Informational [Page 14] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

6. Bit Rate and Tolerance

 In the current traffic parameters signaling, bit rate and tolerance
 are implicitly defined by the signal type.  ODUflex CBR and ODUflex
 packet can have variable bit rates (please refer to [RFC7062],
 Table 2); hence, signaling traffic parameters need to be upgraded.
 With respect to tolerance, there is no need to upgrade GMPLS
 protocols as a fixed value (+/-100 parts per million (ppm) or +/-20
 ppm depending on the signal type) is defined for each signal type.

7. Unreserved Resources

 Unreserved resources need to be advertised per priority and per
 signal type in order to allow the correct functioning of the
 restoration process.  [RFC4203] only allows advertising unreserved
 resources per priority; this leads to uncertainty about how many LSPs
 of a specific signal type can be restored.  As an example, consider
 the scenario depicted in the following figure.
                +------+ component link 1 +------+
                |      +------------------+      |
                |      | component link 2 |      |
                |  N1  +------------------+  N2  |
                |      | component link 3 |      |
                |      +------------------+      |
                +------+                  +---+--+
                 Figure 7: Concurrent Path Computation
 Consider the case where a TE link is composed of three ODU3 component
 links with 32 TSs available on the first one, 24 TSs on the second,
 and 24 TSs on the third and is supporting ODU2 and ODU3 signal types.
 The node would advertise a TE link with unreserved bandwidth equal to
 80 TSs and a MAX LSP bandwidth equal to 32 TSs.  In case of
 restoration, the network could try to restore two ODU3s (64 TSs) in
 such a TE link while only a single ODU3 can be set up, and a
 crankback would be originated.  In more complex network scenarios,
 the number of crankbacks can be much higher.

8. Maximum LSP Bandwidth

 Maximum LSP bandwidth is currently advertised per priority in the
 common part of the ISCD.  Section 5 reviews some of the implications
 of advertising OTN information using ISCDs and identifies the need
 for a more optimized solution.  While strictly not required, such an
 optimization effort should also consider the optimization of the per-
 priority maximum LSP bandwidth advertisement of both fixed and
 variable ODU types.

Belotti, et al. Informational [Page 15] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

9. Distinction between Terminating and Switching Capabilities

 The capability advertised by an interface needs further distinction
 in order to separate terminating and switching capabilities.  Due to
 internal constraints and/or limitations, the type of signal being
 advertised by an interface could just be switched (i.e., forwarded to
 the switching matrix without multiplexing/demultiplexing actions),
 terminated (demultiplexed), or both.  The following figures help
 explain the switching and terminating capabilities.
           MATRIX                   LINE INTERFACE
     +-----------------+          +-----------------+
     |    +-------+    |   ODU2   |                 |
    ----->| ODU2  |----|----------|--------\        |
     |    +-------+    |          |      +----+     |
     |                 |          |       \__/      |
     |                 |          |        \/       |
     |    +-------+    |   ODU3   |         | ODU3  |
    ----->| ODU3  |----|----------|------\  |       |
     |    +-------+    |          |       \ |       |
     |                 |          |        \|       |
     |                 |          |      +----+     |
     |                 |          |       \__/      |
     |                 |          |        \/       |
     |                 |          |         ---------> OTU3
     +-----------------+          +-----------------+
       Figure 8: Switching and Terminating Capabilities
 The figure in the example shows a line interface that is able to:
 o  Multiplex an ODU2 coming from the switching matrix into an ODU3
    and map it into an OTU3
 o  Map an ODU3 coming from the switching matrix into an OTU3
 In this case, the interface bandwidth advertised is ODU2 with
 switching capability and ODU3 with both switching and terminating
 capabilities.
 This piece of information needs to be advertised together with the
 related unreserved bandwidth and signal type.  As a consequence,
 signaling must have the capability to set up an LSP, allowing the
 local selection of resources to be consistent with the limitations
 considered during the path computation.

Belotti, et al. Informational [Page 16] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

 In Figure 9 and Figure 10, there are two examples of the terminating/
 switching capability differentiation.  In both examples, all nodes
 only support single-stage capability.  Figure 9 represents a scenario
 in which a failure on link B-C forces node A to calculate another
 ODU2 LSP carrying ODU0 service along the nodes B-E-D.  As node D is a
 single stage capable node, it is able to extract ODU0 service only
 from the ODU2 interface.  Node A has to know that from E to D exists
 an available OTU2 link from which node D can extract the ODU0
 service.  This information is required in order to avoid the OTU3
 link being considered in the path computation.
             ODU0 Transparently Transported
     +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
     |           ODU2 LSP Carrying ODU0 Service                  |
     |       |'''''''''''''''''''''''''''''''''''''''''''|       |
     |       |                                           |       |
     |  +----++  OTU2   +-----+   OTU2  +-----+  OTU2   ++----+  |
   ODU0 |     |  Link   |     |   Link  |     |  Link   |     | ODU0
   ---->|  A  |_________|  B  |_________|  C  |_________|  D  |---->
        |     |         |     |         |     |         |     |
        +-----+         +--+--+         +-----+         ++--+-+
                           |                             |  |
                       OTU3|                             |  |
                       Link|    +-----+__________________|  |
                           |    |     |    OTU3 Link        |
                           |____|  E  |                     |
                                |     |_____________________|
                                +-----+    OTU2 Link
     Figure 9: Switching and Terminating Capabilities - Example 1
 Figure 10 addresses the scenario in which the restoration of the ODU2
 LSP (A-B-C-D) is required.  The two bundled component links between B
 and E could be used, but the ODU2 over the OTU2 component link can
 only be terminated and not switched.  This implies that it cannot be
 used to restore the ODU2 LSP (A-B-C-D).  However, such ODU2
 unreserved bandwidth must be advertised since it can be used for a
 different ODU2 LSP terminating on E, e.g., F-B-E.  Node A has to know
 that the ODU2 capability on the OTU2 link can only be terminated, and
 that the restoration of A-B-C-D can only be performed using the ODU2
 bandwidth available on the OTU3 link.

Belotti, et al. Informational [Page 17] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

             ODU0 Transparently Transported
     +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
     |           ODU2 LSP Carrying ODU0 Service                  |
     |       |'''''''''''''''''''''''''''''''''''''''''''|       |
     |       |                                           |       |
     |  +----++  OTU2   +-----+   OTU2  +-----+  OTU2   ++----+  |
   ODU0 |     |  Link   |     |   Link  |     |  Link   |     | ODU0
   ---->|  A  |_________|  B  |_________|  C  |_________|  D  |---->
        |     |         |     |         |     |         |     |
        +-----+         ++-+-++         +-----+         +--+--+
                         | | |                             |
                     OTU2| | |                             |
           +-----+   Link| | |   OTU3    +-----+           |
           |     |       | | |   Link    |     |           |
           |  F  |_______| | |___________|  E  |___________|
           |     |         |_____________|     | OTU2 Link
           +-----+            OTU2 Link  +-----+
     Figure 10: Switching and Terminating Capabilities - Example 2
 The issue shown above is analyzed in an OTN context, but it is a
 general technology-independent GMPLS limitation.

10. Priority Support

 [RFC4202] defines eight priorities for resource availability and
 usage.  As defined, each is advertised independent of the number of
 priorities supported by a network, and even unsupported priorities
 are included.  As is the case in Section 8, addressing any
 inefficiency with such advertisements is not required to support
 OTNs.  But, any such inefficiency should also be considered as part
 of the optimization effort identified in Section 5.

11. Multi-stage Multiplexing

 With reference to [RFC7062], the introduction of multi-stage
 multiplexing implies the advertisement of cascaded adaptation
 capabilities together with the matrix access constraints.  The
 structure defined by the IETF for the advertisement of adaptation
 capabilities is the Interface Adaptation Capability Descriptor
 (IACD), as defined in [RFC6001].
 With respect to routing, please note that in case of multi-stage
 multiplexing hierarchy (e.g., ODU1->ODU2->ODU3), not only the ODUk/
 OTUk bandwidth (ODU3) and service-layer bandwidth (ODU1) are needed
 but also the intermediate one (ODU2).  This is a typical case of a
 spatial allocation problem.

Belotti, et al. Informational [Page 18] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

 In this scenario, suppose the following advertisement:
    Hierarchy: ODU1->ODU2->ODU3
    Number of ODU1==5
 The number of ODU1 suggests that it is possible to have an ODU2 FA,
 but it depends on the spatial allocation of such ODU1s.
 It is possible that two links are bundled together and three
 ODU1->ODU2->ODU3 are available on a component link and two on the
 other one; in such a case, the ODU2 FA could not be set up.  The
 advertisement of the ODU2 is needed because in case of ODU1 spatial
 allocation (3+2), the ODU2 available bandwidth would be 0 (ODU2 FA
 cannot be created), while in case of ODU1 spatial allocation (4+1),
 the ODU2 available bandwidth would be 1 (1 ODU2 FA can be created).
 The information stated above implies augmenting both the ISCD and the
 IACD.

12. Generalized Label

 The ODUk label format defined in [RFC4328] could be updated to
 support new signal types as defined in [G.709-2012], but it would be
 difficult to further enhance it to support possible new signal types.
 Furthermore, such a label format may have scalability issues due to
 the high number of labels needed when signaling large LSPs.  For
 example, when an ODU3 is mapped into an ODU4 with 1.25 Gbit/s
 tributary slots, it would require the utilization of 31 labels
 (31*4*8=992 bits) to be allocated, while an ODUflex into an ODU4 may
 need up to 80 labels (80*4*8=2560 bits).
 A new flexible and scalable ODUk label format needs to be defined.

13. Security Considerations

 This document provides an evaluation of OTN requirements against
 actual routing ([RFC4202], [RFC4203], and [RFC5307]) and signaling
 mechanisms ([RFC3471], [RFC3473], and [RFC4328]) in GMPLS.
 This document defines new types of information to be carried that
 describes OTN containers and hierarchies.  It does not define any new
 protocol elements, and from a security standpoint, this memo does not
 introduce further risks with respect to the information that can be
 currently conveyed via GMPLS protocols.  For a general discussion on
 MPLS and GMPLS-related security issues, see the MPLS/GMPLS security
 framework [RFC5920].

Belotti, et al. Informational [Page 19] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

14. Contributors

 Jonathan Sadler
 Tellabs
 EMail: jonathan.sadler@tellabs.com
 John Drake
 Juniper
 EMail: jdrake@juniper.net
 Francesco Fondelli
 Ericsson
 Via Moruzzi 1
 Pisa - 56100
 EMail: francesco.fondelli@ericsson.com

15. Acknowledgements

 The authors would like to thank Lou Berger, Eve Varma, and Sergio
 Lanzone for their precious collaboration and review.

16. References

16.1. Normative References

 [G.709-2001]  ITU-T, "Interfaces for the Optical Transport Network
               (OTN)", G.709/Y.1331 Recommendation, February 2001.
 [G.709-2012]  ITU-T, "Interfaces for the Optical Transport Network
               (OTN)", G.709/Y.1331 Recommendation, February 2012.
 [G.798]       ITU-T, "Characteristics of Optical Transport Network
               Hierarchy Equipment Functional Blocks", G.798
               Recommendation, December 2012.
 [G.872]       ITU-T, "Architecture of Optical Transport Networks",
               G.872 Recommendation, October 2012.
 [RFC1195]     Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
               dual environments", RFC 1195, December 1990.
 [RFC3471]     Berger, L., "Generalized Multi-Protocol Label Switching
               (GMPLS) Signaling Functional Description", RFC 3471,
               January 2003.

Belotti, et al. Informational [Page 20] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

 [RFC3473]     Berger, L., "Generalized Multi-Protocol Label Switching
               (GMPLS) Signaling Resource ReserVation Protocol-Traffic
               Engineering (RSVP-TE) Extensions", RFC 3473, January
               2003.
 [RFC4202]     Kompella, K. and Y. Rekhter, "Routing Extensions in
               Support of Generalized Multi-Protocol Label Switching
               (GMPLS)", RFC 4202, October 2005.
 [RFC4203]     Kompella, K. and Y. Rekhter, "OSPF Extensions in
               Support of Generalized Multi-Protocol Label Switching
               (GMPLS)", RFC 4203, October 2005.
 [RFC4328]     Papadimitriou, D., "Generalized Multi-Protocol Label
               Switching (GMPLS) Signaling Extensions for G.709
               Optical Transport Networks Control", RFC 4328, January
               2006.
 [RFC5307]     Kompella, K. and Y. Rekhter, "IS-IS Extensions in
               Support of Generalized Multi-Protocol Label Switching
               (GMPLS)", RFC 5307, October 2008.
 [RFC6001]     Papadimitriou, D., Vigoureux, M., Shiomoto, K.,
               Brungard, D., and JL. Le Roux, "Generalized MPLS
               (GMPLS) Protocol Extensions for Multi-Layer and
               Multi-Region Networks (MLN/ MRN)", RFC 6001, October
               2010.

16.2. Informative References

 [OTN-OSPF]    Ceccarelli, D., Ed., Zhang, F., Belotti, S., Rao, R.,
               and J.  Drake, "Traffic Engineering Extensions to OSPF
               for Generalized MPLS (GMPLS) Control of Evolving G.709
               OTN Networks", Work in Progress, December 2013.
 [OTN-RSVP]    Zhang, F., Ed., Zhang, G., Belotti, S., Ceccarelli, D.,
               and K.  Pithewan, "Generalized Multi-Protocol Label
               Switching (GMPLS) Signaling Extensions for the evolving
               G.709 Optical Transport Networks Control", Work in
               Progress, September 2013.
 [RFC2328]     Moy, J., "OSPF Version 2", STD 54, RFC 2328, April
               1998.
 [RFC4201]     Kompella, K., Rekhter, Y., and L. Berger, "Link
               Bundling in MPLS Traffic Engineering (TE)", RFC 4201,
               October 2005.

Belotti, et al. Informational [Page 21] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

 [RFC5920]     Fang, L., "Security Framework for MPLS and GMPLS
               Networks", RFC 5920, July 2010.
 [RFC7062]     Zhang, F., Li, D., Li, H., Belotti, S., and D.
               Ceccarelli, "Framework for GMPLS and PCE Control of
               G.709 Optical Transport Networks", RFC 7062, November
               2013.

Belotti, et al. Informational [Page 22] RFC 7096 GMPLS Evaluation against G.709v3 OTNs January 2014

Authors' Addresses

 Sergio Belotti (editor)
 Alcatel-Lucent
 Via Trento, 30
 Vimercate
 Italy
 EMail: sergio.belotti@alcatel-lucent.com
 Pietro Vittorio Grandi
 Alcatel-Lucent
 Via Trento, 30
 Vimercate
 Italy
 EMail: pietro_vittorio.grandi@alcatel-lucent.com
 Daniele Ceccarelli (editor)
 Ericsson
 Via A. Negrone 1/A
 Genova - Sestri Ponente
 Italy
 EMail: daniele.ceccarelli@ericsson.com
 Diego Caviglia
 Ericsson
 Via A. Negrone 1/A
 Genova - Sestri Ponente
 Italy
 EMail: diego.caviglia@ericsson.com
 Fatai Zhang
 Huawei Technologies
 F3-5-B R&D Center, Huawei Base
 Bantian, Longgang District
 Shenzhen  518129
 P.R. China
 Phone: +86-755-28972912
 EMail: zhangfatai@huawei.com
 Dan Li
 Huawei Technologies
 F3-5-B R&D Center, Huawei Base
 Bantian, Longgang District
 Shenzhen  518129
 P.R. China
 Phone: +86-755-28973237
 EMail: danli@huawei.com

Belotti, et al. Informational [Page 23]

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