Internet Engineering Task Force (IETF)
Request for Comments: 7446
Category: Informational
ISSN: 2070-1721
Y. Lee, Ed.
G. Bernstein, Ed.
Grotto Networking
D. Li
W. Imajuku
February 2015

Routing and Wavelength Assignment Information Model

for Wavelength Switched Optical Networks


This document provides a model of information needed by the Routing and Wavelength Assignment (RWA) process in Wavelength Switched Optical Networks (WSONs). The purpose of the information described in this model is to facilitate constrained optical path computation in WSONs. This model takes into account compatibility constraints between WSON signal attributes and network elements but does not include constraints due to optical impairments. Aspects of this information that may be of use to other technologies utilizing a GMPLS control plane are discussed.

Status of This Memo

This document is not an Internet Standards Track specification; it is published for informational purposes.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at

Copyright Notice

Copyright © 2015 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( 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. Terminology .....................................................3
   3. Routing and Wavelength Assignment Information Model .............3
      3.1. Dynamic and Relatively Static Information ..................4
   4. Node Information (General) ......................................4
      4.1. Connectivity Matrix ........................................5
   5. Node Information (WSON Specific) ................................5
      5.1. Resource Accessibility/Availability ........................7
      5.2. Resource Signal Constraints and Processing Capabilities ...11
      5.3. Compatibility and Capability Details ......................12
           5.3.1. Shared Input or Output Indication ..................12
           5.3.2. Optical Interface Class List .......................12
           5.3.3. Acceptable Client Signal List ......................13
           5.3.4. Processing Capability List .........................13
   6. Link Information (General) .....................................13
      6.1. Administrative Group ......................................14
      6.2. Interface Switching Capability Descriptor .................14
      6.3. Link Protection Type (for This Link) ......................14
      6.4. Shared Risk Link Group Information ........................14
      6.5. Traffic Engineering Metric ................................15
      6.6. Port Label Restrictions ...................................15
           6.6.1. Port-Wavelength Exclusivity Example ................17
   7. Dynamic Components of the Information Model ....................18
      7.1. Dynamic Link Information (General) ........................19
      7.2. Dynamic Node Information (WSON Specific) ..................19
   8. Security Considerations ........................................19
   9. References .....................................................20
      9.1. Normative References ......................................20
      9.2. Informative References ....................................21
   Contributors ......................................................22
   Authors' Addresses ................................................23

1. Introduction

The purpose of the WSON information model described in this document is to facilitate constrained optical path computation, and as such it is not a general-purpose network management information model. This constraint is frequently referred to as the "wavelength continuity" constraint, and the corresponding constrained optical path computation is known as the Routing and Wavelength Assignment (RWA) problem. Hence, the information model must provide sufficient topology and wavelength restriction and availability information to support this computation. More details on the RWA process and WSON subsystems and their properties can be found in [RFC6163]. The model defined here includes constraints between WSON signal attributes and network elements but does not include optical impairments.

In addition to presenting an information model suitable for path computation in WSON, this document also highlights model aspects that may have general applicability to other technologies utilizing a GMPLS control plane. The portion of the information model applicable to technologies beyond WSON is referred to as "general" to distinguish it from the "WSON-specific" portion that is applicable only to WSON technology.

2. Terminology

Refer to [RFC6163] for definitions of Reconfigurable Optical Add/Drop Multiplexer (ROADM), RWA, Wavelength Conversion, Wavelength Division Multiplexing (WDM), WSON, and other related terminology used in this document.

3. Routing and Wavelength Assignment Information Model

The WSON RWA information model in this document comprises four categories of information. The categories are independent of whether the information comes from a switching subsystem or from a line subsystem -- a switching subsystem refers to WSON nodes such as a ROADM or an Optical Add/Drop Multiplexer (OADM), and a line subsystem refers to devices such as WDM or Optical Amplifier. The categories are these:

  • Node Information
  • Link Information
  • Dynamic Node Information
  • Dynamic Link Information

Note that this is roughly the categorization used in Section 7 of [G.7715].

In the following, where applicable, the Reduced Backus-Naur Form (RBNF) syntax of [RBNF] is used to aid in defining the RWA information model.

3.1. Dynamic and Relatively Static Information

All the RWA information of concern in a WSON network is subject to change over time. Equipment can be upgraded; links may be placed in or out of service and the like. However, from the point of view of RWA computations, there is a difference between information that can change with each successive connection establishment in the network and information that is relatively static and independent of connection establishment. A key example of the former is link wavelength usage since this can change with connection setup/teardown and this information is a key input to the RWA process. Examples of relatively static information are the potential port connectivity of a WDM ROADM, and the channel spacing on a WDM link.

This document separates, where possible, dynamic and static information so that these can be kept separate in possible encodings. This allows for separate updates of these two types of information, thereby reducing processing and traffic load caused by the timely distribution of the more dynamic RWA WSON information.

4. Node Information (General)

The node information described here contains the relatively static information related to a WSON node. This includes connectivity constraints amongst ports and wavelengths since WSON switches can exhibit asymmetric switching properties. Additional information could include properties of wavelength converters in the node, if any are present. In [Switch] it was shown that the wavelength connectivity constraints for a large class of practical WSON devices can be modeled via switched and fixed connectivity matrices along with corresponding switched and fixed port constraints. These connectivity matrices are included with the node information, while the switched and fixed port wavelength constraints are included with the link information.


   <Node_Information> ::= <Node_ID> [<ConnectivityMatrix>...]

Where the Node_ID would be an appropriate identifier for the node within the WSON RWA context.

Note that multiple connectivity matrices are allowed and hence can fully support the most-general cases enumerated in [Switch].

4.1. Connectivity Matrix

The connectivity matrix (ConnectivityMatrix) represents either the potential connectivity matrix for asymmetric switches (e.g., ROADMs and such) or fixed connectivity for an asymmetric device such as a multiplexer. Note that this matrix does not represent any particular internal blocking behavior but indicates which input ports and wavelengths could possibly be connected to a particular output port. For a switch or ROADM, representing blocking that is dependent on the internal state is beyond the scope of this document. Due to its highly implementation-dependent nature, it would most likely not be subject to standardization in the future. The connectivity matrix is a conceptual M by N matrix representing the potential switched or fixed connectivity, where M represents the number of input ports and N the number of output ports. This is a "conceptual" matrix since the matrix tends to exhibit structure that allows for very compact representations that are useful for both transmission and path computation.

Note that the connectivity matrix information element can be useful in any technology context where asymmetric switches are utilized.

   <ConnectivityMatrix> ::= <MatrixID>



<MatrixID> is a unique identifier for the matrix.

<ConnType> can be either 0 or 1 depending upon whether the connectivity is either fixed or switched.

<Matrix> represents the fixed or switched connectivity in that Matrix(i, j) = 0 or 1 depending on whether input port i can connect to output port j for one or more wavelengths.

5. Node Information (WSON Specific)

As discussed in [RFC6163], a WSON node may contain electro-optical subsystems such as regenerators, wavelength converters or entire switching subsystems. The model present here can be used in characterizing the accessibility and availability of limited resources such as regenerators or wavelength converters as well as WSON signal attribute constraints of electro-optical subsystems. As such, this information element is fairly specific to WSON technologies.

In this document, the term "resource" is used to refer to a physical component of a WSON node such as a regenerator or a wavelength converter. Multiple instances of such components are often present within a single WSON node. This term is not to be confused with the concept of forwarding or switching resources such as bandwidth or lambdas.

A WSON node may include regenerators or wavelength converters arranged in a shared pool. As discussed in [RFC6163], a WSON node can also include WDM switches that use optical-electronic-optical (OEO) processing. There are a number of different approaches used in the design of WDM switches containing regenerator or converter pools. However, from the point of view of path computation, the following need to be known:

  1. The nodes that support regeneration or wavelength conversion.
  1. The accessibility and availability of a wavelength converter to convert from a given input wavelength on a particular input port to a desired output wavelength on a particular output port.
  1. Limitations on the types of signals that can be converted and the conversions that can be performed.

Since resources tend to be packaged together in blocks of similar devices, e.g., on line cards or other types of modules, the fundamental unit of identifiable resource in this document is the "resource block".

A resource block is a collection of resources from the same WSON node that are grouped together for administrative reasons and for ease of encoding in the protocols. All resources in the same resource block behave in the same way and have similar characteristics relevant to the optical system, e.g., processing properties, accessibility, etc.

A resource pool is a collection of resource blocks for the purpose of representing throughput or cross-connect capabilities in a WSON node. A resource pool associates input ports or links on the node with output ports or links and is used to indicate how signals may be passed from an input port or link to an output port or link by way of a resource block (in other words, by way of a resource). A resource pool may, therefore, be modeled as a matrix.

A resource block may be present in multiple resource pools.

This leads to the following formal high-level model:

   <Node_Information> ::= <Node_ID>



<ResourcePool> ::= <ResourceBlockInfo>...




First, the accessibility of resource blocks is addressed; then, their properties are discussed.

5.1. Resource Accessibility/Availability

A similar technique as used to model ROADMs, and optical switches can be used to model regenerator/converter accessibility. This technique was generally discussed in [RFC6163] and consisted of a matrix to indicate possible connectivity along with wavelength constraints for links/ports. Since regenerators or wavelength converters may be considered a scarce resource, it is desirable that the model include, if desired, the usage state (availability) of individual regenerators or converters in the pool. Models that incorporate more state to further reveal blocking conditions on input or output to particular converters are for further study and not included here.

The three-stage model is shown schematically in Figures 1 and 2. The difference between the two figures is that in Figure 1 it's assumed that each signal that can get to a resource block may do so, while in Figure 2 the access to sets of resource blocks is via a shared fiber that imposes its own wavelength collision constraint. Figure 1 shows that there can be more than one input to each resource block since each input represents a single wavelength signal, while Figure 2 shows a single WDM input or output, e.g., a fiber, to/from each set of blocks.

This model assumes N input ports (fibers), P resource blocks containing one or more identical resources (e.g., wavelength converters), and M output ports (fibers). Since not all input ports can necessarily reach each resource block, the model starts with a resource pool input matrix RI(i,p) = {0,1} depending on whether input port i can potentially reach resource block p.

Since not all wavelengths can necessarily reach all the resources or the resources may have limited input wavelength range, the model has a set of relatively static input port constraints for each resource. In addition, if the access to a set of resource blocks is via a shared fiber (Figure 2), this would impose a dynamic wavelength availability constraint on that shared fiber. The resource block input port constraint is modeled via a static wavelength set mechanism, and the case of shared access to a set of blocks is modeled via a dynamic wavelength set mechanism.

Next, a state vector RA(j) = {0,...,k} is used to track the number of resources in resource block j in use. This is the only state kept in the resource pool model. This state is not necessary for modeling "fixed" transponder system or full OEO switches with WDM interfaces, i.e., systems where there is no sharing.

After that, a set of static resource output wavelength constraints and possibly dynamic shared output fiber constraints maybe used. The static constraints indicate what wavelengths a particular resource block can generate or is restricted to generating, e.g., a fixed regenerator would be limited to a single lambda. The dynamic constraints would be used in the case where a single shared fiber is used to output the resource block (Figure 2).

Finally, to complete the model, a resource pool output matrix RE(p,k) = {0,1} depending on whether the output from resource block p can reach output port k, may be used.

      I1   +-------------+                       +-------------+ O1
     ----->|             |      +--------+       |             |----->
      I2   |             +------+ Rb #1  +-------+             | O2
     ----->|             |      +--------+       |             |----->
           |             |                       |             |
           | Resource    |      +--------+       |  Resource   |
           | Pool        +------+        +-------+  Pool       |
           |             |      + Rb #2  +       |             |
           | Input       +------+        +-------|  Output     |
           | Connection  |      +--------+       |  Connection |
           | Matrix      |           .           |  Matrix     |
           |             |           .           |             |
           |             |           .           |             |
      IN   |             |      +--------+       |             | OM
     ----->|             +------+ Rb #P  +-------+             |----->
           |             |      +--------+       |             |
           +-------------+   ^               ^   +-------------+
                             |               |
                             |               |
                             |               |
                             |               |
                    Input wavelength      Output wavelength
                    constraints for       constraints for
                    each resource         each resource


Rb is a resource block.

Figure 1: Schematic Diagram of the Resource Pool Model

    I1   +-------------+                       +-------------+ O1
   ----->|             |      +--------+       |             |----->
    I2   |             +======+ Rb #1  +-+     |             | O2
   ----->|             |      +--------+ |     |             |----->
         |             |                 |=====|             |
         | Resource    |      +--------+ |     |  Resource   |
         | Pool        |    +-+ Rb #2  +-+     |  Pool       |
         |             |    | +--------+       |             |
         | Input       |====|                  |  Output     |
         | Connection  |    | +--------+       |  Connection |
         | Matrix      |    +-| Rb #3  |=======|  Matrix     |
         |             |      +--------+       |             |
         |             |           .           |             |
         |             |           .           |             |
         |             |           .           |             |
    IN   |             |      +--------+       |             | OM
   ----->|             +======+ Rb #P  +=======+             |----->
         |             |      +--------+       |             |
         +-------------+   ^               ^   +-------------+
                           |               |
                           |               |
                           |               |
               Single (shared) fibers for block input and output

Input wavelength Output wavelength

availability for availability for

each block input fiber each block output fiber


Rb is a resource block.

Figure 2: Schematic Diagram of the Resource Pool Model with

Shared Block Accessibility

Formally, the model can be specified as:

   <ResourceAccessibility> ::= <PoolInputMatrix>
   <ResourceWaveConstraints> ::= <InputWaveConstraints>
   <RBSharedAccessWaveAvailability> ::= [<InAvailableWavelengths>]
   <RBPoolState> ::=    <ResourceBlockID>



Note that, except for <RBPoolState>, all the components of <ResourcePool> are relatively static. Also, the <InAvailableWavelengths> and <OutAvailableWavelengths> are only used in the cases of shared input or output access to the particular block. See the resource block information in the next section for how this is specified.

5.2. Resource Signal Constraints and Processing Capabilities

The wavelength conversion abilities of a resource (e.g., regenerator, wavelength converter) were modeled in the <OutputWaveConstraints> previously discussed. As discussed in [RFC6163], the constraints on an electro-optical resource can be modeled in terms of input constraints, processing capabilities, and output constraints:

   <ResourceBlockInfo> ::= <ResourceBlockSet>




   Where  <ResourceBlockSet> is a list of resource block identifiers
   with the same characteristics.  If this set is missing, the
   constraints are applied to the entire network element.

The <InputConstraints> are constraints are based on signal compatibility and/or shared access constraint indication. The details of these constraints are defined in Section 5.3.

   <InputConstraints> ::= <SharedInput>


The <ProcessingCapabilities> are important operations that the resource (or network element) can perform on the signal. The details of these capabilities are defined in Section 5.3.

   <ProcessingCapabilities> ::= [<NumResources>]

The <OutputConstraints> are either restrictions on the properties of the signal leaving the block, options concerning the signal properties when leaving the resource, or shared fiber output constraint indication.

   <OutputConstraints> := <SharedOutput>


5.3. Compatibility and Capability Details

5.3.1. Shared Input or Output Indication

As discussed in Section 5.2 and shown in Figure 2, the input or output access to a resource block may be via a shared fiber. The <SharedInput> and <SharedOutput> elements are indicators for this condition with respect to the block being described.

5.3.2. Optical Interface Class List

<OpticalInterfaceClassList> ::= <OpticalInterfaceClass> ...

The Optical Interface Class is a unique number that identifies all information related to optical characteristics of a physical interface. The class may include other optical parameters related to other interface properties. A class always includes signal compatibility information.

The content of each class is out of the scope of this document and can be defined by other entities (e.g., the ITU, optical equipment vendors, etc.).

Since even current implementation of physical interfaces may support different optical characteristics, a single interface may support multiple interface classes. Which optical interface class is used among all the ones available for an interface is out of the scope of this document but is an output of the RWA process.

5.3.3. Acceptable Client Signal List

The list is simply:


Where the Generalized Protocol Identifiers (G-PID) object represents one of the IETF-standardized G-PID values as defined in [RFC3471] and [RFC4328].

5.3.4. Processing Capability List

The ProcessingCapabilities are defined in Section 5.2.

The processing capability list sub-TLV is a list of processing functions that the WSON network element (NE) can perform on the signal including:

  1. number of resources within the block
  1. regeneration capability
  1. fault and performance monitoring
  1. vendor-specific capability

Note that the code points for fault and performance monitoring and vendor-specific capability are subject to further study.

6. Link Information (General)

MPLS-TE routing protocol extensions for OSPF [RFC3630] and IS-IS [RFC5305], along with GMPLS routing protocol extensions for OSPF [RFC4203] and IS-IS [RFC5307] provide the bulk of the relatively static link information needed by the RWA process. However, WSONs bring in additional link-related constraints. These stem from characterizing WDM line systems, restricting laser transmitter tuning, and switching subsystem port wavelength constraints, e.g., "colored" ROADM drop ports.

The following syntax summarizes both information from existing GMPLS routing protocols and new information that may be needed by the RWA process.

   <LinkInfo> ::=  <LinkID>



Note that these additional link characteristics only apply to line- side ports of a WDM system or add/drop ports pertaining to the resource pool (e.g., regenerator or wavelength converter pool). The advertisement of input/output tributary ports is not intended here.

6.1. Administrative Group

Administrative Group: Defined in [RFC3630] and extended for MPLS-TE [RFC7308]. Each set bit corresponds to one administrative group assigned to the interface. A link may belong to multiple groups. This is a configured quantity and can be used to influence routing decisions.

6.2. Interface Switching Capability Descriptor

InterfaceSwCapDesc: Defined in [RFC4202]; lets us know the different switching capabilities on this GMPLS interface. In both [RFC4203] and [RFC5307], this information gets combined with the maximum Link State Protocol Data Unit (LSP) bandwidth that can be used on this link at eight different priority levels.

6.3. Link Protection Type (for This Link)

Protection: Defined in [RFC4202] and implemented in [RFC4203] and [RFC5307]. Used to indicate what protection, if any, is guarding this link.

6.4. Shared Risk Link Group Information

SRLG: Defined in [RFC4202] and implemented in [RFC4203] and [RFC5307]. This allows for the grouping of links into shared risk groups, i.e., those links that are likely, for some reason, to fail at the same time.

6.5. Traffic Engineering Metric

TrafficEngineeringMetric: Defined in [RFC3630] and [RFC5305]. This allows for the identification of a data-channel link metric value for traffic engineering that is separate from the metric used for path cost computation of the control plane.

Note that multiple "link metric values" could find use in optical networks; however, it would be more useful to the RWA process to assign these specific meanings such as "link mile" metric, "probability of failure" metric, etc.

6.6. Port Label Restrictions

Port label restrictions could be applied generally to any label types in GMPLS by adding new kinds of restrictions. Wavelength is a type of label.

Port label (wavelength) restrictions (PortLabelRestriction) model the label (wavelength) restrictions that the link and various optical devices, such as Optical Cross-Connects (OXCs), ROADMs, and waveband multiplexers, may impose on a port. These restrictions tell us what wavelength may or may not be used on a link and are relatively static. This plays an important role in fully characterizing a WSON switching device [Switch]. Port wavelength restrictions are specified relative to the port in general or to a specific connectivity matrix (Section 4.1). [Switch] gives an example where both switch and fixed connectivity matrices are used and both types of constraints occur on the same port.

   <PortLabelRestriction> ::= <MatrixID>
                              <Restriction parameters list>

<Restriction parameters list> ::=

<Simple label restriction parameters> |

<Channel count restriction parameters> |

<Label range restriction parameters> |

<Simple+channel restriction parameters> |

<Exclusive label restriction parameters>

<Simple label restriction parameters> ::= <LabelSet> ...

<Channel count restriction parameters> ::= <MaxNumChannels>

<Label range restriction parameters> ::= <MaxLabelRange>

                                            (<LabelSet> ...)
   <Simple+channel restriction parameters> ::= <MaxNumChannels>
                                               (<LabelSet> ...)

<Exclusive label restriction parameters> ::= <LabelSet> ...


MatrixID is the ID of the corresponding connectivity matrix (Section 4.1).

The RestrictionType parameter is used to specify general port restrictions and matrix-specific restrictions. It can take the following values and meanings:

      SIMPLE_LABEL:   Simple label (wavelength) set restriction; the
         LabelSet parameter is required.

CHANNEL_COUNT: The number of channels is restricted to be less

than or equal to the MaxNumChannels parameter (which is required).

      LABEL_RANGE:  Used to indicate a restriction on a range of labels
         that can be switched.  For example, a waveband device with a
         tunable center frequency and passband.  This constraint is
         characterized by the MaxLabelRange parameter, which indicates
         the maximum range of the labels, e.g., which may represent a
         waveband in terms of channels.  Note that an additional
         parameter can be used to indicate the overall tuning range.
         Specific center frequency tuning information can be obtained
         from information about the dynamic channel in use.  It is
         assumed that both center frequency and bandwidth (Q) tuning can
         be done without causing faults in existing signals.

SIMPLE LABEL and CHANNEL COUNT: In this case, the accompanying

label set and MaxNumChannels indicate labels permitted on the port and the maximum number of labels that can be simultaneously used on the port.

LINK LABEL_EXCLUSIVITY: A label (wavelength) can be used at most

once among a given set of ports. The set of ports is specified as a parameter to this constraint.

Restriction-specific parameters are used with one or more of the previously listed restriction types. The currently defined parameters are:

LabelSet is a conceptual set of labels (wavelengths).

MaxNumChannels is the maximum number of channels that can be

simultaneously used (relative to either a port or a matrix).

LinkSet is a conceptual set of ports.

MaxLabelRange indicates the maximum range of the labels. For example, if the port is a "colored" drop port of a ROADM, then there are two restrictions: (a) CHANNEL_COUNT, with MaxNumChannels = 1, and (b) SIMPLE_WAVELENGTH, with the wavelength set consisting of a single member corresponding to the frequency of the permitted wavelength. See [Switch] for a complete waveband example.

This information model for port wavelength (label) restrictions is fairly general in that it can be applied to ports that have label restrictions only or to ports that are part of an asymmetric switch and have label restrictions. In addition, the types of label restrictions that can be supported are extensible.

6.6.1. Port-Wavelength Exclusivity Example

Although there can be many different ROADM or switch architectures that can lead to the constraint where a lambda (label) maybe used at most once on a set of ports, Figure 3 shows a ROADM architecture based on components known as Wavelength Selective Switches (WSSes) [OFC08]. This ROADM is composed of splitters, combiners, and WSSes. This ROADM has 11 output ports, which are numbered in the diagram. Output ports 1-8 are known as drop ports and are intended to support a single wavelength. Drop ports 1-4 output from WSS 2, which is fed from WSS 1 via a single fiber. Due to this internal structure, a constraint is placed on the output ports 1-4 that a lambda can be used only once over the group of ports (assuming unicast and not multicast operation). The output ports 5-8 have a similar constraint due to the internal structure.

                            |               A
                            v            10 |
                        +-------+        +-------+
                        | Split |        |WSS  6 |
                        +-------+        +-------+
     +----+              | | | |          | | | |
     | W  |              | | | |          | | | +-------+   +----+
     | S  |--------------+ | | |    +-----+ | +----+    |   | S  |
   9 | S  |----------------|---|----|-------|------|----|---| p  |
   --|    |----------------|---|----|-------|----+ |    +---| l  |<
     | 5  |--------------+ |   |    | +-----+    | |     +--| i  |
     +----+              | |   |    | |   +------|-|-----|--| t  |
                +--------|-+   +----|-|---|------|----+  |  +----+
     +----+     |        |          | |   |      | |  |  |
     | S  |-----|--------|----------+ |   |      | |  |  |  +----+
     | p  |-----|--------|------------|---|------|----|--|--| W  |
   ->| l  |-----|-----+  | +----------+   |      | |  +--|--| S  |11
     | i  |---+ |     |  | | +------------|------|-------|--| S  |->
     | t  |   | |     |  | | |            |      | | +---|--|    |
     +----+   | | +---|--|-|-|------------|------|-|-|---+  | 7  |
              | | |   +--|-|-|--------+ | |      | | |      +----+
              | | |      | | |        | | |      | | |
             +------+   +------+     +------+   +------+
             | WSS 1|   | Split|     | WSS 3|   | Split|
             +--+---+   +--+---+     +--+---+   +--+---+
                |          A            |          A
                v          |            v          |
             +-------+  +--+----+    +-------+  +--+----+
             | WSS 2 |  | Comb. |    | WSS 4 |  | Comb. |
             +-------+  +-------+    +-------+  +-------+
             1|2|3|4|    A A A A     5|6|7|8|    A A A A
              v v v v    | | | |      v v v v    | | | |

Figure 3: A ROADM Composed from Splitter, Combiners, and WSSes

7. Dynamic Components of the Information Model

In the previously presented information model, there are a limited number of information elements that are dynamic, i.e., subject to change with subsequent establishment and teardown of connections. Depending on the protocol used to convey this overall information model, it may be possible to send this dynamic information separately from the relatively larger amount of static information needed to characterize WSONs and their network elements.

7.1. Dynamic Link Information (General)

For WSON links, the wavelength availability and which wavelengths are in use for shared backup purposes can be considered dynamic information and hence are grouped with the dynamic information in the following set:

   <DynamicLinkInfo> ::=  <LinkID>



AvailableLabels is a set of labels (wavelengths) currently available on the link. Given this information and the port wavelength restrictions, one can also determine which wavelengths are currently in use. This parameter could potentially be used with other technologies that GMPLS currently covers or may cover in the future.

SharedBackupLabels is a set of labels (wavelengths) currently used for shared backup protection on the link. An example usage of this information in a WSON setting is given in [Shared]. This parameter could potentially be used with other technologies that GMPLS currently covers or may cover in the future.

Note that the above does not dictate a particular encoding or placement for available label information. In some routing protocols, it may be advantageous or required to place this information within another information element such as the Interface Switching Capability Descriptor (ISCD). Consult the extensions that are specific to each routing protocol for details of placement of information elements.

7.2. Dynamic Node Information (WSON Specific)

Currently the only node information that can be considered dynamic is the resource pool state, and it can be isolated into a dynamic node information element as follows:

   <DynamicNodeInfo> ::=  <NodeID> [<ResourcePool>]

8. Security Considerations

This document discusses an information model for RWA computation in WSONs. From a security standpoint, such a model is very similar to the information that can be currently conveyed via GMPLS routing protocols. Such information includes network topology, link state and current utilization, as well as the capabilities of switches and routers within the network. As such, this information should be protected from disclosure to unintended recipients. In addition, the intentional modification of this information can significantly affect network operations, particularly due to the large capacity of the optical infrastructure to be controlled. A general discussion on security in GMPLS networks can be found in [RFC5920].

9. References

9.1. Normative References

   [G.7715]  ITU-T, "Architecture and requirements for routing in the
             automatically switched optical networks", ITU-T
             Recommendation G.7715, June 2002.
   [RBNF]    Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax Used
             to Form Encoding Rules in Various Routing Protocol
             Specifications", RFC 5511, April 2009,
   [RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label
             Switching (GMPLS) Signaling Functional Description", RFC
             3471, January 2003,
   [RFC3630] van der Meer, J., Mackie, D., Swaminathan, V., Singer, D.,
             and P. Gentric, "RTP Payload Format for Transport of MPEG-4
             Elementary Streams", RFC 3640, November 2003,
   [RFC4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing Extensions
             in Support of Generalized Multi-Protocol Label Switching
             (GMPLS)", RFC 4202, October 2005,
   [RFC4203] Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions in
             Support of Generalized Multi-Protocol Label Switching
             (GMPLS)", RFC 4203, October 2005,
   [RFC4328] Papadimitriou, D., Ed., "Generalized Multi-Protocol Label
             Switching (GMPLS) Signaling Extensions for G.709 Optical
             Transport Networks Control", RFC 4328, January 2006,
   [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
             Engineering", RFC 5305, October 2008,
   [RFC5307] Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS Extensions
             in Support of Generalized Multi-Protocol Label Switching
             (GMPLS)", RFC 5307, October 2008,
   [RFC6163] Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku,
             "Framework for GMPLS and Path Computation Element (PCE)
             Control of Wavelength Switched Optical Networks (WSONs)",
             RFC 6163, April 2011,
   [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS
             Traffic Engineering (MPLS-TE)", RFC 7308, July 2014,

9.2. Informative References

   [OFC08]   Roorda, P., and B. Collings, "Evolution to Colorless and
             Directionless ROADM Architectures", Optical Fiber
             Communication / National Fiber Optic Engineers Conference
             (OFC/NFOEC), 2008, pp. 1-3.
   [RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
             Networks", RFC 5920, July 2010,
   [Shared]  Bernstein, G., and Y. Lee, "Shared Backup Mesh Protection
             in PCE-based WSON Networks", iPOP 2008.
   [Switch]  Bernstein, G., Lee, Y., Gavler, A., and J. Martensson,
             "Modeling WDM Wavelength Switching Systems for Use in GMPLS
             and Automated Path Computation", Journal of Optical
             Communications and Networking, vol. 1, June 2009, pp.


Diego Caviglia
Via A. Negrone 1/A 16153
Genoa, Italy

   Phone: +39 010 600 3736
   EMail: diego.caviglia@(,

Anders Gavler
Acreo AB
Electrum 236
SE - 164 40 Kista


Jonas Martensson
Acreo AB
Electrum 236
SE - 164 40 Kista

   Itaru Nishioka
   NEC Corp.
   1753 Simonumabe, Nakahara-ku, Kawasaki, Kanagawa 211-8666
   Phone: +81 44 396 3287
   Lyndon Ong
   Cyril Margaria

Authors' Addresses

   Young Lee (editor)
   Huawei Technologies
   5369 Legacy Drive, Building 3
   Plano, TX  75023
   United States
   Phone: (469) 277-5838

Greg M. Bernstein (editor)
Grotto Networking
Fremont, CA
United States

   Phone: (510) 573-2237
   Dan Li
   Huawei Technologies Co., Ltd.
   F3-5-B R&D Center, Huawei Base,
   Bantian, Longgang District
   Shenzhen 518129
   Phone: +86-755-28973237
   Wataru Imajuku
   NTT Network Innovation Labs
   1-1 Hikari-no-oka, Yokosuka, Kanagawa
   Phone: +81-(46) 859-4315