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RFC 7096

Evaluation of Existing GMPLS Encoding against G.709v3 Optical Transport Networks (OTNs)

Pages: 23

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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
                                                                F. Zhang
                                                                   D. Li
                                                     Huawei Technologies
                                                            January 2014

                 Evaluation of Existing GMPLS Encoding
           against G.709v3 Optical Transport Networks (OTNs)


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
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Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
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   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
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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.
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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
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       |           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
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   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.
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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
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   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
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   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
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   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

   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).
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               |                                      |
      +--------+      +--------+      +--------+      +--------+
      |        |      |        |      |        | 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.
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                 | 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.
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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.
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   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

      - Maximum Reservable Bandwidth (of the bundle) set to ODU2

      - 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

   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
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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.
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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.
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   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.
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               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.
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   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

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].
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14. Contributors

Jonathan Sadler Tellabs EMail: John Drake Juniper EMail: Francesco Fondelli Ericsson Via Moruzzi 1 Pisa - 56100 EMail:

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

   [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

   [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

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.
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   [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
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Authors' Addresses

Sergio Belotti (editor) Alcatel-Lucent Via Trento, 30 Vimercate Italy EMail: Pietro Vittorio Grandi Alcatel-Lucent Via Trento, 30 Vimercate Italy EMail: Daniele Ceccarelli (editor) Ericsson Via A. Negrone 1/A Genova - Sestri Ponente Italy EMail: Diego Caviglia Ericsson Via A. Negrone 1/A Genova - Sestri Ponente Italy EMail: 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: 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: