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

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7062.
Authors Fatai Zhang , Dan Li , Han Li , Sergio Belotti , Daniele Ceccarelli
Last updated 2013-09-12 (Latest revision 2013-08-02)
Replaces draft-zhang-ccamp-gmpls-g709-framework
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Document shepherd Lou Berger
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Network Working Group                                   Fatai Zhang, Ed. 
Internet Draft                                                    Dan Li 
Category: Informational                                           Huawei 
                                                                  Han Li 
                                                           D. Ceccarelli 
Expires: February 2, 2014                                 August 2, 2013 
                 Framework for GMPLS and PCE Control of  
                    G.709 Optical Transport Networks 

Status of this Memo 

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

   Internet-Drafts are working documents of the Internet Engineering   
   Task Force (IETF), its areas, and its working groups.  Note that   
   other groups may also distribute working documents as Internet-   

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   and may be updated, replaced, or obsoleted by other documents at any   
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   material or to cite them other than as "work in progress." 

   The list of current Internet-Drafts can be accessed at 

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   This Internet-Draft will expire on February 2, 2014. 


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

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


Table of Contents 

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

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

   GMPLS extends Multi-Protocol Label Switching (MPLS) to encompass time 
   division multiplexing (TDM) networks (e.g., Synchronous Optical 
   NETwork (SONET)/ Synchronous Digital Hierarchy (SDH), Plesiochronous 
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   Digital Hierarchy (PDH), and G.709 sub-lambda), lambda switching 
   optical networks, and spatial switching (e.g., incoming port or fiber 
   to outgoing port or fiber). The GMPLS architecture is provided in 
   [RFC3945], signaling function and Resource ReserVation Protocol-
   Traffic Engineering (RSVP-TE) extensions are described in [RFC3471] 
   and [RFC3473], routing and Open Shortest Path First (OSPF) extensions 
   are described in [RFC4202] and [RFC4203], and the Link Management 
   Protocol (LMP) is described in [RFC4204].  

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

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

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


2. Terminology 

   OTN: Optical Transport Network 

   OPU: Optical channel Payload Unit 

   ODU: Optical channel Data Unit 

   OTU: Optical channel Transport Unit 

   OMS: Optical multiplex section 

   MSI: Multiplex Structure Identifier 

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

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

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

3. G.709 Optical Transport Network 

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

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

3.1. OTN Layer Network 

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

                               Client signal 

                   Figure 1 - Basic OTN signal hierarchy 
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   Client signals are mapped into ODUj containers. These ODUj containers 
   are multiplexed onto the OTU/OCh. The individual OTU/OCh signals are 
   combined in the OMS using Wavelength Division Multiplexing (WDM), and 
   this aggregated signal provides the link between the nodes. 


3.1.1. Client signal mapping 

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

                     Table 1 - ODU types and bit rates 
   |       ODU Type        |       ODU nominal bit rate        | 
   |         ODU0          |         1,244,160 Kbps            | 
   |         ODU1          |    239/238 x 2,488,320 Kbps       | 
   |         ODU2          |    239/237 x 9,953,280 Kbps       | 
   |         ODU3          |    239/236 x 39,813,120 Kbps      | 
   |         ODU4          |    239/227 x 99,532,800 Kbps      | 
   |         ODU2e         |    239/237 x 10,312,500 Kbps      | 
   |                       |                                   | 
   |     ODUflex for       |                                   | 
   |Constant Bit Rate (CBR)| 239/238 x client signal bit rate  | 
   |    Client signals     |                                   | 
   |                       |                                   | 
   |   ODUflex for Generic |                                   | 
   |   Framing Procedure   |        Configured bit rate        | 
   |   - Framed (GFP-F)    |                                   | 
   | Mapped client signal  |                                   | 
   NOTE - The nominal ODUk rates are approximately: 2,498,775.126 Kbps 
   (ODU1), 10,037,273.924 Kbps (ODU2), 40,319,218.983 Kbps (ODU3), 
   104,794,445.815 Kbps (ODU4) and 10,399,525.316 Kbps (ODU2e). 
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                     Table 2 - ODU types and tolerance 
   |      ODU Type         |       ODU bit-rate tolerance      | 
   |        ODU0           |            +/-20 ppm              | 
   |        ODU1           |            +/-20 ppm              | 
   |        ODU2           |            +/-20 ppm              | 
   |        ODU3           |            +/-20 ppm              | 
   |        ODU4           |            +/-20 ppm              | 
   |        ODU2e          |            +/-100 ppm             | 
   |                       |                                   | 
   |   ODUflex for CBR     |                                   | 
   |   Client signals      |            +/-100 ppm             | 
   |                       |                                   | 
   |  ODUflex for GFP-F    |                                   | 
   | Mapped client signal  |            +/-100 ppm             | 
   One of two options is for mapping client signals into ODUflex 
   depending on the client signal type:  

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

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

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

3.1.2. Multiplexing ODUj onto Links 

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

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

             Tributary Slot Granularity 
                2.5Gbps     1.25Gbps           Nominal Bit rate  
     OTU1         1             2                  2.5Gbps 
     OTU2         4             8                   10Gbps 
     OTU3        16            32                   40Gbps 
     OTU4        --            80                  100Gbps 
   To maintain backwards compatibility while providing the ability to 
   interconnect nodes that support 1.25Gbps TS at one end of a link and 
   2.5Gbps TS at the other, [G709-2012] requires 'new' equipment fall 
   back to the use of a 2.5Gbps TS when connected to legacy equipment.  
   This information is carried in band by the payload type. 

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

   -  ODU0 into ODU1, ODU2, ODU3 or ODU4 multiplexing with 1,25Gbps TS 
      o  ODU0 occupies 1 of the 2, 8, 32 or 80 TSs for ODU1, ODU2, ODU3 
         or ODU4  
   -  ODU1 into ODU2, ODU3 or ODU4 multiplexing with 1,25Gbps TS 
      o  ODU1 occupies 2 of the 8, 32 or 80 TSs for ODU2, ODU3 or ODU4  
   -  ODU1 into ODU2, ODU3 multiplexing with 2.5Gbps TS granularity  
      o  ODU1 occupies 1 of the 4 or 16 TSs for ODU2 or ODU3  
   -  ODU2 into ODU3 or ODU4 multiplexing with 1.25Gbps TS granularity  
      o  ODU2 occupies 8 of the 32 or 80 TSs for ODU3 or ODU4 
   -  ODU2 into ODU3 multiplexing with 2.5Gbps TS granularity  
      o  ODU2 occupies 4 of the 16 TSs for ODU3  
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   -  ODU3 into ODU4 multiplexing with 1.25Gbps TS granularity  
      o  ODU3 occupies 31 of the 80 TSs for ODU4  
   -  ODUflex into ODU2, ODU3 or ODU4 multiplexing with 1.25Gbps TS 
      o  ODUflex occupies n of the 8, 32 or 80 TSs for ODU2, ODU3 or 
         ODU4 (n <= Total TS number of ODUk)  
   -  ODU2e into ODU3 or ODU4 multiplexing with 1.25Gbps TS granularity  
      o  ODU2e occupies 9 of the 32 TSs for ODU3 or 8 of the 80 TSs for 
   In general the mapping of an ODUj (including ODUflex) into a specific 
   OTUk TS is determined locally, and it can also be explicitly 
   controlled by a specific entity (e.g., head end, Network Management 
   System (NMS)) through Explicit Label Control [RFC3473]. Structure of MSI information 

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

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

   -  Payload Type:  the type of the transported payload. 

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

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

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

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

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

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

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

4. Connection management in OTN  

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

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

   From an ITU-T perspective, the ODU connection topology is represented 
   by that of the OTU link layer, which has the same topology as that of 
   the OCh layer (independent of whether the OTU supports HO ODU, where 
   multiplexing is utilized, or LO ODU in the case of direct mapping). 
   Thus, the OTU and OCh layers should be visible in a single 
   topological representation of the network, and from a logical 
   perspective, the OTU and OCh may be considered as the same logical, 
   switchable entity.   

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

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

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

   (1) ODU layer  

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

                  Link #5       +--+---+--+        Link #4 
     +--------------------------|         |--------------------------+ 
     |                          |  ODXC   |                          | 
     |                          +---------+                          | 
     |                             Node E                            | 
     |                                                               | 
   +-++---+--+        +--+---+--+        +--+---+--+        +--+---+-++ 
   |         |Link #1 |         |Link #2 |         |Link #3 |         | 
   |         |--------|         |--------|         |--------|         | 
   |  ODXC   |        |  ODXC   |        |  ODXC   |        |  ODXC   | 
   +---------+        +---------+        +---------+        +---------+ 
      Node A             Node B              Node C            Node D 
        Figure 2 - Example Topology for LO ODU connection management 

   If an ODUj connection is requested between Node C and Node E 
   routing/path computation must select a path that has the required 
   number of TS available and that offers the lowest cost.  Signaling is 
   then invoked to set up the path and to provide the information (e.g., 
   selected TSs) required by each transit node to allow the 
   configuration of the ODUj to OTUk mapping (j = k) or multiplexing (j 
   < k), and demapping (j = k) or demultiplexing (j < k). 

   (2) ODU layer with OCh switching capability 

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

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

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

      Figure 3 - OCh Hidden Topology for LO ODU connection management 


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

     Figure 4 - OCh Visible Topology for LO ODUj connection management 

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

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

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


5. GMPLS/PCE Implications 

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

5.1. Implications for Label Switch Path (LSP) Hierarchy 

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

   The OTN path computation can be divided into two layers. One layer is 
   OCh/OTUk, the other is ODUj. [RFC4206] and [RFC6107] define the 
   mechanisms to accomplish creating the hierarchy of LSPs. The LSP 
   management of multiple layers in OTN can follow the procedures 
   defined in [RFC4206], [RFC6001] and [RFC6107], etc. 

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

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

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

5.2. Implications for GMPLS Signaling 

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

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

   [RFC4328] defines the LSP Encoding Type, the Switching Type and the 
   Generalized Protocol Identifier (Generalized-PID) constituting the 
   common part of the Generalized Label Request. The G.709 Traffic 
   Parameters are also defined in [RFC4328]. The following signaling 
   aspects should be considered additionally since [RFC4328] was 

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

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

         -  ODU0 
         -  ODU2e 
         -  ODU4 
         -  ODUflex 

      For ODUflex signal type, its bit rate must be carried additionally 
      in the Traffic Parameter to setup an ODUflex connection. 
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      For other ODU signal types, their bit rates and tolerances are 
      fixed and can be deduced from the signal types. 

   -  Support for LSP setup using different TS granularity  

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

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

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

   -  Support for TPN allocation and negotiation 

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

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

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

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

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

      The procedure of ODUflex (GFP) adjustment requires the 
      participation of every node along the path. Therefore, it is 
      recommended to use the control plane signaling to initiate the 
      adjustment procedure in order to avoid the manual configuration at 
      each node along the path. 
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      From the perspective of control plane, the control of ODUflex 
      resizing is similar to control of bandwidth increasing and 
      decreasing described in [RFC3209]. Therefore, the Shared Explicit 
      (SE) style can be used for control of HAO. 

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

5.3. Implications for GMPLS Routing 

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

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

   -  Support for carrying the link multiplexing capability 

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

   -  Support any ODU and ODUflex 

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

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

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

   -  Support for differentiating between terminating and switching 

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

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

   -  Support for Tributary Slot Granularity advertisement 

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

   -  Support different priorities for resource reservation 

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

   -  Support link bundling 

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

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       link. Note that link bundling is optional and is implementation 

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

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

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

5.4. Implications for Link Management Protocol 

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

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

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

   -  Correlating the granularity of the TS 

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

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

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

       Many new ODU signal types have been introduced in [G709-2012], 
       such as ODU0, ODU4, ODU2e and ODUflex. It is possible that 
       equipment does not support all the LO ODU signal types introduced 
       by those new standards or drafts. Furthermore, since multiplexing 
       hierarchy was not allowed by the legacy OTN referenced by 
       [RFC4328], it is possible that only one end of an ODU link can 
       support multiplexing hierarchy capability, or the two ends of the 
       link support different multiplexing hierarchy capabilities (e.g., 
       one end of the link supports ODU0 into ODU1 into ODU3 
       multiplexing while the other end supports ODU0 into ODU2 into 
       ODU3 multiplexing). 

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

5.5. Implications for Control Plane Backward Compatibility 

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

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

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

   -  A node supporting [G709-2012] could support only the [G709-2012] 
      related control plane procedures, in which case both types of 
      nodes would be unable to jointly control an LSP for an ODU type 
      that both nodes support in the data plane. Note that this case is 
      supported by the procedures defined in [RFC3473] as a different 
      Switching Capability/Type value is used for the different control 
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      plane versions. 

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

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

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

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

5.6. Implications for Path Computation Elements 

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

   As described in section 5.2.1, new signal types and new signals with 
   variable bandwidth information need to be carried in the extended 
   signaling message of path setup. For the same consideration, PCE 
   Communication Protocol (PCECP) also has a desire to be extended to 
   carry the new signal type and related variable bandwidth information 
   when a PCC requests a path computation.  


5.7. Implications for Management of GMPLS Networks 

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

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


6. Data Plane Backward Compatibility Considerations  

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

            +----------+   ------------>    +----------+  
            |     TS1==|===========\--------+--TS1     |  
            |     TS2==|=========\--\-------+--TS2     |  
            |     TS3==|=======\--\--\------+--TS3     |  
            |     TS4==|=====\--\--\--\-----+--TS4     |  
            |          |      \  \  \  \----+--TS5     |  
            |          |       \  \  \------+--TS6     |  
            |          |        \  \--------+--TS7     |  
            |          |         \----------+--TS8     |  
            +----------+   <------------    +----------+  
               node A           Resv           node B  
         Figure 5 - Interworking between 1.25Gbps TS and 2.5Gbps TS 
   Take Figure 5 as an example. Assume that there is an ODU2 link 
   between node A and B, where node A only supports the 2.5Gbps TS while 
   node B supports the 1.25Gbps TS. In this case, the TS#i and TS#i+4 
   (where i<=4) of node B are combined together. When creating an ODU1 
   service in this ODU2 link, node B reserves the TS#i and TS#i+4 with 
   the granularity of 1.25Gbps. But in the label sent from B to A, it is 
   indicated that the TS#i with the granularity of 2.5Gbps is reserved. 

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


7. Security Considerations 

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


8. IANA Considerations 

   This document makes not requests for IANA action. 


9. Acknowledgments 

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


10. References 

10.1. Normative References 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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10.2. Informative References 

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

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

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

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

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

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

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

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

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

   [PCE-APS]   Tomohiro Otani, Kenichi Ogaki, Diego Caviglia, and Fatai 
               Zhang, "Requirements for GMPLS applications of PCE", 
               draft-ietf-pce-gmpls-aps-req, Work in Progress. 

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

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


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11. Authors' Addresses 

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

   Phone: +86-755-28972912

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

   Phone: +86-755-28973237

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

   Phone: +86-10-66006688

   Sergio Belotti
   Optics CTO
   Via Trento 30 20059 Vimercate (Milano) Italy
   +39 039 6863033


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

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12. Contributors 

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

   Phone: +86-755-28972913

   Malcolm Betts
   Huawei Technologies Co., Ltd.

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


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

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