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Versions: (draft-bccg-ccamp-otn-g709-info-model) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 7096

CCAMP Working Group                                      S. Belotti, Ed.
Internet-Draft                                                 P. Grandi
Intended status: Informational                            Alcatel-Lucent
Expires: October 6, 2013                              D. Ceccarelli, Ed.
                                                             D. Caviglia
                                                                Ericsson
                                                                F. Zhang
                                                                   D. Li
                                                     Huawei Technologies
                                                           April 4, 2013


Evaluation of existing GMPLS encoding against G.709v3 Optical Transport
                             Networks (OTN)
                draft-ietf-ccamp-otn-g709-info-model-07

Abstract

   ITU-T recommendation G.709 [G.709-2012] has introduced new fixed and
   flexible Optical Data Unit (ODU) containers in Optical Transport
   Networks (OTNs).

   This document provides an evaluation of existing Generalized
   Multiprotocol Label Switching (GMPLS) routing and signaling methods
   against the G.709 [G.709-2012] OTN networks.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 6, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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  . . . . . . . . .  3
   3.  Tributary Slot Granularity . . . . . . . . . . . . . . . . . .  6
     3.1.  Data Plane Considerations  . . . . . . . . . . . . . . . .  6
       3.1.1.  Payload Type and TSG relationship  . . . . . . . . . .  6
       3.1.2.  Fall-back procedure  . . . . . . . . . . . . . . . . .  8
     3.2.  Control Plane considerations . . . . . . . . . . . . . . .  8
   4.  Tributary Port Number  . . . . . . . . . . . . . . . . . . . . 12
   5.  Signal type  . . . . . . . . . . . . . . . . . . . . . . . . . 12
   6.  Bit rate and tolerance . . . . . . . . . . . . . . . . . . . . 14
   7.  Unreserved Resources . . . . . . . . . . . . . . . . . . . . . 14
   8.  Maximum LSP Bandwidth  . . . . . . . . . . . . . . . . . . . . 15
   9.  Distinction between terminating and switching capability . . . 15
   10. Priority Support . . . . . . . . . . . . . . . . . . . . . . . 17
   11. Multi-stage multiplexing . . . . . . . . . . . . . . . . . . . 17
   12. Generalized Label  . . . . . . . . . . . . . . . . . . . . . . 18
   13. Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   14. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   15. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 19
   16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     17.1. Normative References . . . . . . . . . . . . . . . . . . . 20
     17.2. Informative References . . . . . . . . . . . . . . . . . . 21
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21














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1.  Introduction

   GMPLS[RFC3945] extends MPLS to include Layer-2 Switching (L2SC),
   Time-Division Multiplexing (e.g., SONET/SDH, PDH, and OTN),
   Wavelength (OCh, Lambdas) Switching and Spatial Switching (e.g.
   incoming port or fiber to outgoing port or fiber).

   This document provides an evaluation of GMPLS signaling and routing
   processes against G.709 [G.709-2012] requirements.

   OSPF-TE and RSVP-TE requirements are defined in [OTN-FWK], while
   protocol extensions are defined in [OTN-OSPF] and [OTN-RSVP].


2.  G.709 Mapping and Multiplexing Capabilities

   The digital OTN layered structure is comprised of digital path layer
   (ODU) and digital section layer (OTU).  An OTU (Optical Transport
   Unit) section layer supports one ODU path layer as client and
   provides monitoring capability for the OCh.  An ODU path layer may
   transport a heterogeneous assembly of ODU clients.  Some types of
   ODUs (i.e., ODU1, ODU2, ODU3, ODU4) may assume either a client or
   server role within the context of a particular networking domain.
   ITU-T G.872 recommendation [G.872] provides two tables defining
   mapping and multiplexing capabilities of OTNs, which are reported
   below.

























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         +--------------------+--------------------+
         |     ODU client     |     OTU server     |
         +--------------------+--------------------+
         |        ODU 0       |          -         |
         +--------------------+--------------------+
         |        ODU 1       |        OTU 1       |
         +--------------------+--------------------+
         |        ODU 2       |        OTU 2       |
         +--------------------+--------------------+
         |        ODU 2e      |          -         |
         +--------------------+--------------------+
         |        ODU 3       |        OTU 3       |
         +--------------------+--------------------+
         |        ODU 4       |        OTU 4       |
         +--------------------+--------------------+
         |        ODU flex    |          -         |
         +--------------------+--------------------+


                     Figure 1: OTN mapping capability































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       +=================================+=========================+
       |           ODU client            |       ODU server        |
       +---------------------------------+-------------------------+
       |        1.25 Gbps client         |                         |
       +---------------------------------+          ODU 0          |
       |                 -               |                         |
       +=================================+=========================+
       |         2.5 Gbps client         |                         |
       +---------------------------------+          ODU 1          |
       |              ODU 0              |                         |
       +=================================+=========================+
       |         10 Gbps client          |                         |
       +---------------------------------+          ODU 2          |
       |        ODU0,ODU1,ODUflex        |                         |
       +=================================+=========================+
       |        10.3125 Gbps client      |                         |
       +---------------------------------+          ODU 2e         |
       |                 -               |                         |
       +=================================+=========================+
       |         40 Gbps client          |                         |
       +---------------------------------+          ODU 3          |
       |  ODU0,ODU1,ODU2,ODU2e,ODUflex   |                         |
       +=================================+=========================+
       |        100 Gbps client          |                         |
       +---------------------------------+          ODU 4          |
       |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 from |          ODUflex        |
       |1.25 Gbit/s to 100 Gbit/s.       |                         |
       +---------------------------------+                         |
       |                 -               |                         |
       +=================================+=========================+



                   Figure 2: OTN multiplexing capability

   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
   OTUk section, with the path and section being at the same rate as
   that of the connection service (see Table 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



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   this case, ODUk multiplexing may be performed prior to transport over
   various rate ODU servers (as per Table 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 [OTN-FWK], client ODUk connection services can be
   transported over:

      o Case A) one or more wavelength sub-networks connected by optical
      links or

      o Case B) one or more ODU links (having sub-lambda and/or lambda
      bandwidth granularity)

      o Case C) a mix of ODU links and wavelength sub-networks.

   This document considers the TE information needed for ODU path
   computation and parameters needed to be signaled for LSP setup.

   The following sections list and analyze, for each type of data that
   needs to be advertised and signaled, what is already there in GMPLS
   and what is missing.


3.  Tributary Slot Granularity

   ITU-T recommendation defines two types of Tributary Slot (TS)
   granularity.  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:

      - If both ends of a link are new cards supporting both 1.25Gbps TS
      and 2.5Gbps TS, then the link will work with 1.25Gbps TS.

      - If one end is a new card supporting both the 1.25Gbps and
      2,5Gbps TS, and the other end is an old card supporting just the
      2.5Gbps TS, the link will work with 2.5Gbps TS.

3.1.  Data Plane Considerations

3.1.1.  Payload Type and TSG relationship

   As defined in G.709-2012 an ODUk container consist of an Optical
   Payload Unit (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



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   signals.  Within the OPUk overhead there is the payload structure
   identifier (PSI) that includes the payload type (PT).  The payload
   type (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 frame alignment overhead and then mapped into an
   Optical channel Data Tributary Unit (ODTU).  Two different types of
   ODTU are defined:

      - 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), defined in clause 19.5 of
      G.709-2012.

      - ODTUk.ts ((k,ts) = (2,1..8), (3,1..32), (4,1..80)) in which a
      lower order ODU (ODU0, ODU1, ODU2, ODU2e, ODU3, ODUflex) signal is
      mapped via the Generic Mapping Procedure (GMP), defined in clause
      19.6 of G.709-2012.

   G.709-2012 introduces also a logical entity, called Optical Data
   Tributary Unit Group (ODTUGk), characterizing the multiplexing of the
   various ODTU.  The ODTUGk is then mapped into OPUK.  ODTUjk and
   ODTUk.ts signals are directly time-division multiplexed into the
   tributary slots of an HO OPUk.

   When PT is assuming value 20 or 21,together with OPUk type (K=
   1,2,3,4), it is used to discriminate two different ODU multiplex
   structure ODTUGx :

      - Value 20: supporting ODTUjk only,

      - Value 21: supporting ODTUk.ts or ODTUk.ts and ODTUjk.

   The discrimination 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=21 and ODTUG1 with PT=20. (see table Figure 6).The relationship
   between PT and TS granularity, is in the fact that the two different
   ODTUGk discriminated by PT and OPUk are characterized by two
   different TS granularities of the related OPUk, the former at 2.5
   Gbps, the latter at 1.25Gbps.

   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 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.





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                   +--------+      +------------+
        +----+     |        !------| ODTUjk     |-----Client
        |    |     | ODTUGk |      +-----.------+
        |    |-----| PT=21  |            .
        |    |     |        |      +-----.------+
        |    |     |        |------| ODTUk.TS   |-----Client
        |OPUk|     +--------+      +------------+
        |    |
        |    |     +--------+      +------------+
        |    |     |        |------| ODTUjk     |-----Client
        |    |-----|        |      +-----.------+
        +----+     | ODTUGk |            .
                   | PT=20  |      +-----.------+
                   |        |------| ODTUjk     |-----Client
                   +--------+      +------------+


                     Figure 3: OTN client multiplexing

3.1.2.  Fall-back procedure

   ITU-T G.798 r[G.798] describes the so called PT=21-to-PT=20
   interworking process that explains how two equipments with interfaces
   with different PayloadType, and hence different TS granularity
   (1.25Gbps vs. 2.5Gbps), can be coordinated so to permit the equipment
   with 1.25 TS granularity to adapt his TS allocation accordingly to
   the different TS granularity (2.5Gbps) of a neighbor.

   Therefore, in order to let the NE change TS granularity accordingly
   to the neighbor requirements, the AUTOpayloadtype 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 PT=21,
   the node must fallback to PT=20.  In this case the fall-back process
   makes the system self consistent and the only reason for signaling
   the TS granularity is to provide the correct label (i.e. label for
   PT=21 has twice the TS number of PT=20).  On the other side, if the
   AUTOpayloadtype is not configured, the RSVP-TE consequent actions in
   case of TS mismatch need to be defined.

3.2.  Control Plane considerations

   When setting up an ODUj over an ODUk, it is possible to identify two
   types of TSG, the server and the client one.  The server TSG is used
   to map an end to end ODUj onto a server ODUk LSP or links.  This
   parameter can not be influenced in any way from the ODUj LSP: 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



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   that it is carried over a path composed by links/Forwarding
   Adjacencies(FAs) structured with 1.25Gbps or 2.5Gbps TS size is
   completely transparent to the end to end ODUj.

   On the other side the client TSG is the tributary slot size that is
   exported towards the client layer.  The client TSG 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 TSG utilization in a
   scenario with mixed [RFC4328] OTN and [G.709-2012] OTN interfaces is
   shown.


                            ODU1-LSP
           .........................................
      TSG-C|                                       |TSG-C
       1.25|                   ODU2-H-LSP          |1.25
           +------------X--------------------------+
           |       TSG-S|                          |TSG-S
           |         2.5|                          |2.5
           |            |       ODU3-H-LSP         |
           |            |------------X-------------|
           |            |                          |
        +--+--+      +--+--+                   +---+-+
        |     |      |     |     +-+   +-+     |     |
        |  A  +------+  B  +-----+ +***+ +-----+  Z  |
        | V.3 | OTU2 | V.1 |OTU3 +-+   +-+ OTU3| V.3 |
        +-----+      +-----+                   +-----+

         ... Service LSP
         --- H-LSP


                    Figure 4: Client-Server TSG example

   In this scenario, an ODU3 LSP is setup from node B to Z. Node B has
   an old interface able to support 2.5 TSG granularity, hence only
   client TSG equal to 2.5Gbps can be exported to ODU3 H-LSP possible
   clients.  An ODU2 LSP is setup from node A to node Z with client TSG
   1.25 signaled and exported towards clients.  The ODU2 LSP is carried
   by ODU3 H-LSP from B to Z. Due to the limitations of old node B
   interface, the ODU2 LSP is mapped with 2.5Gbps TSG over the ODU3
   H-LSP.  Then an ODU1 LSP is setup from A to Z, carried by the ODU2
   H-LSP and mapped over it using a 1.25Gbps TSG.

   What is shown in the example is that the TSG processing is a per



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   layer issue: even if the ODU3 H-LSP is created with TSG client at
   2.5Gbps, the ODU2 H-LSP must guarantee a 1.25Gbps TSG client.  ODU3
   H-LSP is eligible from ODU2 LSP perspective since from the routing it
   is known that this ODU3 interface at node Z, supports an ODU2
   termination exporting a TSG 1.25/2.5.

   The TSG 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 TSG.  In case they cannot, A
   will compute an alternate path from itself to Z (see figure 4).

   Moreover, also TSG information needs to be signaled.  Consider as
   example the setup of an ODU3 forwarding adjacency that is going to
   carry an ODU0, hence the support of 1.25 GBps TS is needed.  The
   information related to the TSG has to be carried in the signaling to
   permit node C (see figure 5) choose the right one among the different
   interfaces (with different TSGs) towards D. In case the full 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 PCE.


                                ODU3
                               <---------------------->

                                ODU0
               <-------------------------------------->
               |                                      |
      +--------+      +--------+      +--------+      +--------+
      |        |      |        |      |        | 1.25 |        |
      |  Node  |      |  Node  |      |  Node  +------+  Node  |
      |   A    +------+   B    +------+   C    | ODU3 |   D    |
      |        | ODU3 |        | ODU3 |        +------+        |
      +--------+ 1.25 +--------+ 2.5  +--------+ 2.5  +--------+


                        Figure 5: TSG in signaling

   In case an ODUk FA_LSP needs to be set up nesting another ODUj (as
   depicted in figure 4), there might be the need to know the hierarchy
   of nested LSPs in addition to TSG, to permit the penultimate hop
   (i.e.  C) choosing the correct interface towards the egress node or
   any intermediate node (i.e.  B) choosing the right path when
   performing ERO expansion.  This is not needed in case we allow
   bundling only component links with homogeneous hierarchies.  In case
   of specific implementation not specifying in the ERO the last hop
   interface, crank-back can be a solution.




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   In a multi-stage multiplexing environment any layer can have a
   different TSG structure, e.g. in a multiplexing hierarchy like
   ODU0->ODU2->ODU3, the ODU3 can be structured at TSG=2.5 in order to
   support an ODU2 connection, but this ODU2 connection can be a tunnel
   for ODU0, and hence structured with 1.25 TSG.  Therefore any
   multiplexing level has to advertise his TSG capabilities in order to
   allow a correct path computation by the end nodes (both of the ODUk
   trail and of the H-LSP/FA).

   The following table shows the different mapping possibilities
   depending on the TSG types.  The client types are shown in the left
   column, while the different OPUk server and related TSGs are listed
   in the top row.  The table also shows the relationship between the
   TSG and the payload type.


                 +------------------------------------------------+
                 |    2.5G TS    ||          1.25G TS             |
                 | OPU2  | OPU3  || OPU1  | OPU2  | OPU3  | OPU4  |
         +-------+------------------------------------------------+
         |       |   -   |   -   ||  AMP  |  GMP  |  GMP  |  GMP  |
         | ODU0  |       |       || PT=20 | PT=21 | PT=21 | PT=21 |
         +-------+------------------------------------------------+
         |       |  AMP  |  AMP  ||   -   |  AMP  |  AMP  |  GMP  |
         | ODU1  | PT=20 | PT=20 ||       | PT=21 | PT=21 | PT=21 |
         +-------+------------------------------------------------+
         |       |   -   |  AMP  ||   -   |   -   |  AMP  |  GMP  |
         | ODU2  |       | PT=20 ||       |       | PT=21 | PT=21 |
         +-------+------------------------------------------------+
         |       |   -   |   -   ||   -   |   -   |  GMP  |  GMP  |
         | ODU2e |       |       ||       |       | PT=21 | PT=21 |
         +-------+------------------------------------------------+
         |       |   -   |   -   ||   -   |   -   |   -   |  GMP  |
         | ODU3  |       |       ||       |       |       | PT=21 |
         +-------+------------------------------------------------+
         |       |   -   |   -   ||   -   |  GMP  |  GMP  |  GMP  |
         | ODUfl |       |       ||       | PT=21 | PT=21 | PT=21 |
         +-------+------------------------------------------------+


    Figure 6: ODUj into OPUk mapping types (Source: Table 7-10 [G.709-
                                  2012])

   The signaled TSGs information is not enough to have a complete choice
   since the penultimate hop node (or any intermediate node performing
   ERO expansion) has to distinguish between interfaces with the same
   TSG (e.g. 1.25Gbps) whether the interface is able to support the
   right hierarchy, i.e. it is possible to have two interfaces both at



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   1.25 TSG but only one is supporting ODU0.

   A specifi information could be defined in order to carry the
   multiplexing hierarchy and adaptation information (i.e.  TSG/PT, AMP/
   GMP) so to have a more precise choice capability.  In this way, when
   the penultimate node (or the intermediate node performing ERO
   expansion) receives such object, together with the Traffic Parameters
   Object, it is allowed to choose the correct interface towards the
   egress node.

   In conclusion both routing and signaling needs to be extended to
   appropriately represent the TSG/PT information.  Routing needs to
   represent a link's TSG and PT capabilities as well as the supported
   multiplexing hierarchy.  Signaling needs to represent the TSG/PT and
   multiplexing hierarchy encoding.


4.  Tributary Port Number

   [RFC4328] supports only the deprecated auto-MSI mode which assumes
   that the Tributary Port Number is automatically assigned in the
   transmit direction and 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
   (Multiplex Structure Identifier) bytes (in the form of multi-frame),
   each of which is used to indicate the association between tributary
   port number and tributary slot of the ODUk.

   The association between 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 [OTN-FWK] 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, [RFC4203] allows advertising [RFC4328]
   interfaces (single TS type) without the capability of providing
   precise information about bandwidth specific allocation.  For
   example, in case of link bundling, 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 example
   fig. 3)

   The lack of spatial allocation heavily impacts the restoration
   process, because the lack of information of free resources highly



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   increases the number of crank-backs affecting network convergence
   time.

   Moreover actual tools provided by [RFC4203] only allow advertising
   signal types with fixed bandwidth and implicit hierarchy (e.g.  SDH/
   SONET networks) or variable bandwidth with no hierarchy (e.g. packet
   switching networks) but do not provide the means for advertising
   networks with mixed approach (e.g.  ODUflex CBR and ODUflex packet).

   For example, 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 ISCD for each
   signal type actually supported by the link.

   Supposing for example to have 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 Bw: ODU1

      MIN LSP Bw: ODU1

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

      - Unreserved Bandwidth (of the bundle) set to ODU2

   In conclusion, the OSPF-TE extensions defined in [RFC4203] require a
   different ISCD per signal type in order to advertise each supported
   container.  This motivates attempting to look for a more optimized
   solution, without proliferations of the number of ISCD advertised.
   Per [RFC2328], OSPF messages are directly encapsulated in IP
   datagrams and depend on IP fragmentation when transmitting packets
   larger than the network MTU.  [RFC2328] recommends that "IP
   fragmentation should be avoided whenever possible."  This
   recommendation further constraints solutions as OSPF does not support
   any generic mechanism to fragment OSPF LSAs.

   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 for pre-
   G.709-2012 OTNs.  However, [RFC4328] needs to be updated because it



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   does not provide the means to signal all the new signal types and
   related mapping and multiplexing functionalities.


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 Packet
   can have variable bit rates(please refer to [OTN-FWK] table 2); hence
   signaling traffic parameters need to be upgraded.  With respect to
   the tolerance there is no need to upgrade GMPLS protocols as a fixed
   value (+/-100 ppm or +/-20ppm 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 not to know how many LSPs of a
   specific signal type can be restored.  As example it is possible to
   consider the scenario depicted in the following figure.


                  +------+ component link 1 +------+
                  |      +------------------+      |
                  |      | component link 2 |      |
                  |  N1  +------------------+  N2  |
                  |      | component link 3 |      |
                  |      +------------------+      |
                  +------+                  +---+--+


                   Figure 7: Concurrent path computation

   Suppose to have a TE link comprising 3 ODU3 component links with
   32TSs available on the first one, 24TSs on the second, 24TSs on the
   third and supporting ODU2 and ODU3 signal types.  The node would
   advertise a TE link 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 2 ODU3 (64TSs) in such TE-link while only a
   single ODU3 can be set up and a crank-back would be originated.  In
   more complex network scenarios the number of crank-backs can be much
   higher.






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8.  Maximum LSP Bandwidth

   Maximum LSP bandwidth is currently advertised in the common part of
   the ISCD and advertised per priority, while in OTN networks it is
   only required for ODUflex advertising.  This leads to a significant
   waste of bits inside each LSA.


9.  Distinction between terminating and switching capability

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



             MATRIX                   LINE INTERFACE
       +-----------------+          +-----------------+
       |    +-------+    |   ODU2   |                 |
      ----->| ODU-2 |----|----------|--------\        |
       |    +-------+    |          |      +----+     |
       |                 |          |       \__/      |
       |                 |          |        \/       |
       |    +-------+    |   ODU3   |         | ODU3  |
      ----->| ODU-3 |----|----------|------\  |       |
       |    +-------+    |          |       \ |       |
       |                 |          |        \|       |
       |                 |          |      +----+     |
       |                 |          |       \__/      |
       |                 |          |        \/       |
       |                 |          |         ---------> OTU-3
       +-----------------+          +-----------------+


             Figure 8: Switching and Terminating capabilities

   The figure in the example shows a line interface able to:

      - Multiplex an ODU2 coming from the switching matrix into and ODU3
      and map it into an OTU3

      - Map an ODU3 coming from the switching matrix into an OTU3

   In this case the interface bandwidth advertised is ODU2 with



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   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 possibility to setup an LSP allowing the
   local selection of resources consistent with the limitations
   considered during the path computation.

   In figures 9 and 10 there are two examples of the need of
   termination/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 path 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 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 that
   the OTU3 link is 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 7 addresses the scenario in which the restoration of the ODU2
   LSP (ABCD) 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



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   used to restore the ODU2 LSP (ABCD).  However such ODU2 unreserved
   bandwidth must be advertised since it can be used for a different
   ODU2 LSP terminating on E, e.g.  (FBE).  Node A has to know that the
   ODU2 capability on the OTU2 link can only be terminated and that the
   restoration of (ABCD) can only be performed using the ODU2 bandwidth
   available on the OTU3 link.



               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


10.  Priority Support

   The IETF foresees that up to eight priorities must be supported and
   that all of them have to be advertised independently on the number of
   priorities supported by the implementation.  Considering that the
   advertisement of all the different supported signal types will
   originate large LSAs, it is advised to advertise only the information
   related to the really supported priorities.


11.  Multi-stage multiplexing

   With reference to the [OTN-FWK], introduction of multi-stage
   multiplexing implies the advertisement of cascaded adaptation
   capabilities together with the matrix access constraints.  The
   structure defined by IETF for the advertisement of adaptation



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   capabilities is ISCD/IACD as in [RFC4202] and [RFC5339].
   Modifications to ISCD/IACD, if needed, have to be addressed in the
   related encoding documents.

   With respect to the routing, please note that in case of multi stage
   muxing 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 spatial
   allocation problem.

   Suppose in this scenario to have 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 2 links are bundled together and 3
   ODU1->ODU2->ODU3 are available on a component link and 2 on the other
   one, in such a case no ODU2 FA could 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 (no ODU2 FA can be created),
   while in case of ODU1 spatial allocation (4+1) the ODU2 available
   bandwidth would be 1 (1 ODU2 FA can be created).


12.  Generalized Label

   The ODUk label format defined in [RFC4328] could be updated to
   support new signal types defined in [G.709-2012] but would hardly be
   further enhanced to support possible new signal types.

   Furthermore such 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 1.25G tributary slots, it
   would require the utilization of thirty-one labels (31*4*8=992 bits)
   to be allocated while an ODUflex into an ODU4 may need up to eighty
   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] and [RFC4203] and signaling mechanism



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   [RFC3471], [RFC3473] and [RFC4328]in GMPLS.

   New types of information to be conveyed regard OTN containers and
   hierarchies 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].


14.  IANA Considerations

   This informational document does not make any requests for IANA
   action.


15.  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




16.  Acknowledgements

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




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17.  References

17.1.  Normative References

   [OTN-OSPF]
              D.Ceccarelli,D.Caviglia,F.Zhang,D.Li,Y.Xu,P.Grandi,S.Belot
              ti, "Traffic Engineering Extensions to OSPF for
              Generalized MPLS (GMPLS) Control of Evolutive G.709 OTN
              Networks", work in
              progress draft-ietf-ccamp-gmpls-ospf-g709v3-04, November
              2012.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

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

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

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              September 2003.

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

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

   [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.

   [RFC5250]  Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
              OSPF Opaque LSA Option", RFC 5250, July 2008.

   [RFC5339]  Le Roux, JL. and D. Papadimitriou, "Evaluation of Existing



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              GMPLS Protocols against Multi-Layer and Multi-Region
              Networks (MLN/MRN)", RFC 5339, September 2008.

   [RFC5920]  Fang, L., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, July 2010.

17.2.  Informative References

   [G.709-2012]
              ITU-T, "Rec G.709, version 4", approved by ITU-T in 2012.

   [G.798]    ITU-T, "Revised version of G.798 Characteristics of
              optical transport network hierarchy equipment functional
              blocks", consented by ITU-T on December 2012.

   [G.872]    ITU-T, "Revised version of G.872: Architecture of optical
              transport networks for consent", consented by ITU-T on
              December 2012.

   [OTN-FWK]  F.Zhang, D.Li, H.Li, S.Belotti, D.Ceccarelli, "Framework
              for GMPLS and PCE Control of G.709 Optical Transport
              Networks", work in
              progress draft-ietf-ccamp-gmpls-g709-framework-11,
              November 2012.

   [OTN-RSVP]
              F.Zhang, G.Zhang, S.Belotti, D.Ceccarelli, K.Pithewan,
              "Generalized Multi-Protocol Label Switching (GMPLS)
              Signaling Extensions for the evolving G.709 Optical
              Transport Networks Control, work in progress
              draft-ietf-ccamp-gmpls-signaling-g709v3-05",
              November 2012.


Authors' Addresses

   Sergio Belotti (editor)
   Alcatel-Lucent
   Via Trento, 30
   Vimercate
   Italy

   Email: sergio.belotti@alcatel-lucent.com








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   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
   Shenzhen 518129 P.R.China  Bantian, Longgang District
   Phone: +86-755-28972912

   Email: zhangfatai@huawei.com


   Dan Li
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Shenzhen 518129 P.R.China  Bantian, Longgang District
   Phone: +86-755-28973237

   Email: danli@huawei.com








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