Network Working Group                                      G. Bernstein                                            Y. Lee
Internet Draft                                        Grotto Networking                                                   Huawei
Intended status: Informational                                   Y. Lee                             G. Bernstein
Expires: May September 2009                               Grotto Networking
                                                                  D. Li
                                                             W. Imajuku


                                                          March 3, 2008 2009

    Routing and Wavelength Assignment Information Model for Wavelength
                         Switched Optical Networks



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   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 lightpath computation in
   WSONs, particularly in cases where there are no or a limited number
   of wavelength converters available. This model currently does not include
   optical impairments.

Table of Contents

   1. Introduction...................................................3
      1.1. Revision History..........................................3
         1.1.1. Changes from 01......................................3
   2. Terminology....................................................3
   3. Routing and Wavelength Assignment Information Model............4
      3.1. Dynamic and Relatively Static Information.................4
      3.2. Node Information..........................................4 Information..........................................5
         3.2.1. Switched Connectivity Matrix.........................5
         3.2.2. Fixed Connectivity Matrix............................5 Matrix............................6
         3.2.3. Shared Risk Node Group...............................6
         3.2.4. Wavelength Converter Pool............................6
   OEO Wavelength Converter Info...................9
      3.3. Link Information..........................................9
         3.3.1. Link ID.............................................10
         3.3.2. Administrative Group................................10
         3.3.3. Interface Switching Capability Descriptor...........10
         3.3.4. Link Protection Type (for this link)................10
         3.3.5. Shared Risk Link Group Information..................10
         3.3.6. Traffic Engineering Metric..........................11
         3.3.7. Maximum Bandwidth Per Channel.......................11
         3.3.8. Switched and Fixed Port Wavelength Restrictions.....11
      3.4. Dynamic Link Information.................................12
      3.5. Dynamic Node Information.................................12
   4. Security Considerations.......................................13
   5. IANA Considerations...........................................13
   6. Acknowledgments...............................................13
   7. References....................................................14
      7.1. Normative References.....................................14
      7.2. Informative References...................................14
   8. Contributors..................................................15
   Author's Addresses...............................................16
   Intellectual Property Statement..................................16
   Disclaimer of Validity...........................................17

1. Introduction

   The purpose of the following information model for WSONs is to
   facilitate constrained lightpath computation and as such is not a
   general purpose network management information model. In particular
   this model has particular value in the cases where there are no or a
   limited number of wavelength converters available in the WSON. This
   constraint is frequently referred to as the "wavelength continuity"
   constraint, and the corresponding constrained lightpath 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 [WSON-Frame]. The model defined here
   does not currently include impairments however optical impairments
   can be accommodated by the general framework presented here.

1.1. Revision History

   1.1.1. Changes from 01

   Added text on multiple fixed and switched connectivity matrices.

   Added text on the relationship between SRNG and SRLG and encoding

   Added clarifying text on the meaning and use of port/wavelength

   Added clarifying text on wavelength availability information and how
   to derive wavelengths currently in use.

2. Terminology

   CWDM: Coarse Wavelength Division Multiplexing.

   DWDM: Dense Wavelength Division Multiplexing.

   FOADM: Fixed Optical Add/Drop Multiplexer.

   ROADM: Reconfigurable Optical Add/Drop Multiplexer. A reduced port
   count wavelength selective switching element featuring ingress and
   egress line side ports as well as add/drop side ports.

   RWA: Routing and Wavelength Assignment.

   Wavelength Conversion. The process of converting an information
   bearing optical signal centered at a given wavelength to one with
   "equivalent" content centered at a different wavelength. Wavelength
   conversion can be implemented via an optical-electronic-optical (OEO)
   process or via a strictly optical process.

   WDM: Wavelength Division Multiplexing.

   Wavelength Switched Optical Network (WSON): A WDM based optical
   network in which switching is performed selectively based on the
   center wavelength of an optical signal.

3. Routing and Wavelength Assignment Information Model

   We group the following WSON RWA information model into four
   categories regardless of whether they stem from a switching subsystem
   or from a line subsystem:

   o  Node Information

   o  Link Information

   o  Dynamic Node Information

   o  Dynamic Link Information

   Note that this is roughly the categorization used in [G.7715] section

   In the following we use where applicable the reduced Backus-Naur form
   (RBNF) syntax of [RBNF] 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 that information that is relatively static on the time scales 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.

   In this document we will separate, where possible, dynamic and static
   information so that these can be kept separate in possible encodings
   and hence allowing 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.

3.2. Node Information

   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. We include these
   connectivity matrices with our node information the switched and
   fixed port wavelength constraints with the link information.


   <Node_Information> ::= <Node_ID> [<SwitchedConnectivityMatrix>]
   [<FixedConnectivityMatrix>], [<SRNG>] [<WavelengthConverterPool>]

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

   It is TBD whether multiple switched and fixed connectivity matrices
   should optionally be allowed to fully support the most general cases
   enumerated in [Switch]. To support multiple matrices each of the
   matrices below would need an identifier so that its particular
   port/wavelength constraints can be associated.

   3.2.1. Switched Connectivity Matrix

   The switched connectivity matrix (SwitchConnectivityMatrix)
   represents the potential connectivity matrix for asymmetric switches
   (e.g. ROADMs and such). Note that this matrix does not represent any
   particular internal blocking behavior but indicates which ingress
   ports and wavelengths could possibly be connected to a particular
   output port. Representing internal state dependent blocking for a
   switch or ROADM is beyond the scope of this document and due to its
   highly implementation dependent nature would not be subject to
   standardization. This is a conceptual M by N matrix representing the
   potential switched connectivity, where M represents the number of
   ingress ports and N the number of egress ports. We say this is a
   "conceptual" since this matrix tends to exhibit structure that allows
   for very compact representations that are useful for both
   transmission and path computation [Encode].

   SwitchedConnectivityMatrix(i, j) = 0 or 1 depending on whether
   ingress port i can connect to egress port j for one or more

   3.2.2. Fixed Connectivity Matrix

   The fixed connectivity matrix (FixedConnectivityMatrix) represents
   the connectivity for asymmetric fixed devices or the fixed part of a
   "hybrid" device [Switch]. This is a conceptual M by N matrix, where M
   represents the number of ingress ports and N the number of egress
   ports. We say this is a "conceptual" since this matrix tends to
   exhibit structure that allows for very compact representations.

   FixedConnectivityMatrix(i, j) = 0 or 1 depending on whether ingress
   port i is connected to egress port j for one or more wavelengths.

   3.2.3. Shared Risk Node Group

   SRNG: Shared risk group for nodes. The concept of a shared risk link
   group was defined in [RFC4202]. This can be used to achieve a desired
   "amount" of link diversity. It is also desirable to have a similar
   capability to achieve various degrees of node diversity. This is
   explained in [G.7715]. Typical risk groupings for nodes can include
   those nodes in the same building, within the same city, or geographic

   Since the failure of a node implies the failure of all links
   associated with that node a sufficiently general shared risk link
   group (SRLG) encoding, such as that used in GMPLS routing extensions
   can explicitly incorporate SRNG information.

   3.2.4. Wavelength Converter Pool

   A WSON node may include wavelength converters. These are usually
   arranged into some type of pool to promote resource sharing. There
   are a number of different approaches used in the design of switches
   with converter pools. However, from the point of view of path
   computation we need to know the following:

   1. The nodes that support wavelength conversion.

   2. The accessibility and availability of a wavelength converter to
      convert from a given ingress wavelength on a particular ingress
      port to a desired egress wavelength on a particular egress port.

   3. Limitations on the types of signals that can be converted and the
      conversions that can be performed.

   To model point 2 above we can use a similar technique as used to
   model ROADMs and optical switches this technique was generally
   discussed in [WSON-Frame] and consisted of a matrix to indicate
   possible connectivity along with wavelength constraints for
   links/ports. Since wavelength converters are considered a scarce
   resource we will also want to our model to include as a minimum the
   usage state of individual wavelength converters in the pool. Models
   that incorporate more state to further reveal blocking conditions on
   ingress or egress to particular converters are for further study.

   We utilize a three stage model as shown schematically in Figure 1. In
   this model we assume N ingress ports (fibers), P wavelength
   converters, and M egress ports (fibers). Since not all ingress ports
   can necessarily reach the converter pool, the model starts with a
   wavelength pool ingress matrix WI(i,p) = {0,1} whether ingress port i
   can reach potentially reach wavelength converter p.

   Since not all wavelength can necessarily reach all the converters or
   the converters may have limited input wavelength range we have a set
   of ingress port constraints for each wavelength converter. Currently
   we assume that a wavelength converter can only take a single
   wavelength on input. We can model each wavelength converter ingress
   port constraint via a wavelength set mechanism.

   Next we have a state vector WC(j) = {0,1} dependent upon whether
   wavelength converter j in the pool is in use. This is the only state
   kept in the converter pool model. This state is not necessary for
   modeling "fixed" transponder system, i.e., systems where there is no
   sharing.  In addition, this state information may be encoded in a
   much more compact form depending on the overall connectivity
   structure [WC-Pool].

   After that, we have a set of wavelength converter egress wavelength
   constraints. These constraints indicate what wavelengths a particular
   wavelength converter can generate or are restricted to generating due
   to internal switch structure.

   Finally, we have a wavelength pool egress matrix WE(p,k) = {0,1}
   depending on whether the output from wavelength converter p can reach
   egress port k. Examples of this method being used to model wavelength
   converter pools for several switch architectures from the literature
   are given in reference [WC-Pool].

      I1   +-------------+                       +-------------+ E1
     ----->|             |      +--------+       |             |----->
      I2   |             +------+ WC #1  +-------+             | E2
     ----->|             |      +--------+       |             |----->
           | Wavelength  |                       |  Wavelength |
           | Converter   |      +--------+       |  Converter  |
           | Pool        +------+ WC #2  +-------+  Pool       |
           |             |      +--------+       |             |
           | Ingress     |                       |  Egress     |
           | Connection  |           .           |  Connection |
           | Matrix      |           .           |  Matrix     |
           |             |           .           |             |
           |             |                       |             |
      IN   |             |      +--------+       |             | EM
     ----->|             +------+ WC #P  +-------+             |----->
           |             |      +--------+       |             |
           +-------------+   ^               ^   +-------------+
                             |               |
                             |               |
                             |               |
                             |               |

                    Ingress wavelength    Egress wavelength
                    constraints for       constraints for
                    each converter        each converter

      Figure 1 Schematic diagram of wavelength converter pool model.

   Formally we can specify the model as:

   <WavelengthConverterPool> ::= <IngressPoolMatrix> <PoolIngressMatrix>
   <IngressPoolConstraints> [<WCPoolState>] <EgressPoolConstraints>
   Note that except for <WCPoolState> all the other components of
   <WavelengthConverterPool> are relatively static. In addition
   <WCPoolState> is a relatively small structure compared potentially to
   the others and hence in a future revision of this document maybe
   moved to a new section on dynamic node information. OEO Wavelength Converter Info

   An OEO based wavelength converter can be characterized by an input
   wavelength set and an output wavelength set.  In addition any
   constraints on the signal formats and rates accommodated by the
   converter must be described. Such a wavelength converter can be
   modeled by:

   <OEOWavelengthConverterInfo> ::= <RegeneratorType>  [<BitRateRange>]

   Where the RegeneratorType is used to model an OEO regenerator.
   Regenerators are usually classified into three types [G.sup39]. Level
   1 provides signal amplification, level 2 amplification and pulse
   shaping, and level 3 amplification, pulse shaping and timing
   regeneration. Level 2 regenerators can have a restricted bit rate
   range, while level 3 regenerators can also be specialized to a
   particular signal type.

   BitRateRange: indicates the range of bit rates that can be
   accommodated by the wavelength converter.

   AcceptableSignals: is a list of signals that the wavelength converter
   can handle. This could be fairly general for Level 1 and Level 2
   regenerators, e.g., characterized by general signal properties such
   as modulation type and related parameters, or fairly specific signal
   types for Level 3 based regenerators.

3.3. Link Information

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

   In the following summarize both information from existing route
   protocols and new information that maybe needed by the RWA process.

   <LinkInfo> ::=  <LinkID> [<AdministrativeGroup>] [<InterfaceCapDesc>]
   [<Protection>] [<SRLG>]... [<TrafficEngineeringMetric>]
   [<MaximumBandwidthPerChannel>] <[SwitchedPortWavelengthRestriction>]

   3.3.1. Link ID

   <LinkID> ::=  <LocalLinkID> <LocalNodeID> <RemoteLinkID>

   Here we can generally identify a link via a combination of local and
   remote node identifiers along with the corresponding local and remote
   link identifiers per [RFC4202, RFC4203, RFC5307]. Note that reference
   [RFC3630] provides other ways to identify local and remote link ends
   in the case of numbered links.

   3.3.2. Administrative Group

   AdministrativeGroup: Defined in [RFC3630]. 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.

   3.3.3. 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 LSP
   bandwidth that can be used on this link at eight different priority

   3.3.4. Link Protection Type (for this link)

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

   3.3.5. Shared Risk Link Group Information

   SRLG: Defined in [RFC4202] and implemented in [RFC4203, 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

   3.3.6. Traffic Engineering Metric

   TrafficEngineeringMetric: Defined in [RFC3630].  This allows for the
   definition of one additional link metric value for traffic
   engineering separate from the IP link state routing protocols link
   metric. 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, or
   probability of failure metric, etc...

   3.3.7.  Maximum Bandwidth Per Channel

   TBD: Need to check if we still want this.

   3.3.8. Switched and Fixed Port Wavelength Restrictions

   Switch and fixed port wavelength restrictions
   (SwitchedPortWavelengthRestriction, FixedPortWavelengthRestriction)
   model the wavelength restrictions that various optical devices such
   as OXCs, ROADMs, and waveband mulitplexers 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]. The
   SwitchedPortWavelengthRestriction is used with ports specified in the
   SwitchedConnectivityMatrix while the FixedPortWavelengthRestriction
   is used with ports specified in the FixedConnectivityMatrix.
   Reference [Switch] gives an example where both switch and fixed
   connectivity matrices are used and both types of constraints occur on
   the same port.

   <SwitchedPortWavelengthRestriction> ::= <port wavelength restriction>

   <FixedPortWavelengthRestriction> ::= <port wavelength restriction>

   <port wavelength restriction> ::= <RestrictionKind>
   <RestrictionParameters> <WavelengthSet>

   <RestrictionParameters> ::= <MaxNumChannels> [<OthersTBD>]...

   Where WavelengthSet is a conceptual set of wavelengths,
   MaxNumChannels is the number of channels permitted on the port, and
   RestrictionKind can take the following values and meanings:

   SIMPLE:   Simple wavelength selective restriction. Max number of
   channels indicates the number of wavelengths permitted on the port
   and the accompanying wavelength set indicates the permitted values.

   WAVEBAND1:   Waveband device with a tunable center frequency and
   passband. In this case the maximum number of channels indicates the
   maximum width of the waveband in terms of the channels spacing given
   in the wavelength set. The corresponding wavelength set is used to
   indicate the overall tuning range. Specific center frequency tuning
   information can be obtained from dynamic channel in use information.
   It is assumed that both center frequency and bandwidth (Q) tuning can
   be done without causing faults in existing signals.

   For example, if the port is a "colored" drop port of a ROADM then the
   value of RestrictionKind = SIMPLE for a simple wavelength selective
   restriction, the MaxNumberOfChannels = 1, and the wavelength
   restriction is just a wavelength set consisting of a single member
   corresponding to the frequency of the permitted wavelength. See
   [Switch] for a complete waveband example.

3.4. Dynamic Link Information

   By dynamic information we mean information that is subject to change
   on a link with subsequent connection establishment or teardown.
   Currently for WSON the only information we currently envision is
   wavelength availability and wavelength in use for shared backup

   <DynamicLinkInfo> ::=  <LinkID> <AvailableWavelengths>


   <LinkID> ::= <LocalLinkID> <LocalNodeID> <RemoteLinkID>

   AvailableWavelengths is a set of wavelengths currently available on
   the link. Given this information and the port wavelength restrictions
   we can also determine which wavelengths are currently in use.

   SharedBackupWavelengths is a set of wavelengths currently used for
   shared backup protection on the link. An example usage of this
   information in a WSON setting is given in [Shared].

3.5. Dynamic Node Information

   Dynamic node information is used to hold information for a node that
   can change frequently.  Currently only wavelength converter pool
   information is included as a possible (but not required) information

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

   Where NodeID is a node identifier and the exact form of the
   wavelength converter pool status information is TBD.

4. Security Considerations

   This document discussed an information model for RWA computation in
   WSONs. Such a model is very similar from a security standpoint of the
   information that can be currently conveyed via GMPLS routing
   protocols.  Such information includes network topology, link state
   and current utilization, and 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.

5. IANA Considerations

   This informational document does not make any requests for IANA

6. Acknowledgments

   This document was prepared using

7. References

7.1. Normative References

   [Encode] Reference the encoding draft here.

   [RBNF]   A. Farrel, "Reduced Backus-Naur Form (RBNF) A Syntax Used in
             Various Protocol Specifications", work in progress: draft-
             farrel-rtg-common-bnf-07.txt, October 2008.

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

   [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.

   [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.

   [WSON-Frame] G. Bernstein, Y. Lee, W. Imajuku, "Framework for GMPLS
             and PCE Control of Wavelength Switched Optical Networks",
             work in progress: draft-ietf-ccamp-wavelength-switched-
             framework-01.txt, October 2008.

7.2. Informative References

   [Shared] G. Bernstein, Y. Lee, "Shared Backup Mesh Protection in PCE-
         based WSON Networks", iPOP 2008, http://www.grotto- .

   [Switch] G. Bernstein, Y. Lee, A. Gavler, J. Martensson, " Modeling
         WDM Wavelength Switching Systems for use in Automated Path
         Computation", http://www.grotto- , June, 2008
   [G.Sup39] ITU-T Series G Supplement 39, Optical system design and
             engineering considerations, February 2006.

   [WC-Pool] G. Bernstein, Y. Lee, "Modeling WDM Switching Systems
             including Wavelength Converters" to appear www.grotto-
   , 2008.

8. Contributors

   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 Sweden


   Jonas Martensson
   Acreo AB
   Electrum 236
   SE - 164 40 Kista, Sweden


   Itaru Nishioka
   NEC Corp.
   1753 Simonumabe, Nakahara-ku, Kawasaki, Kanagawa 211-8666

   Phone: +81 44 396 3287

   Lyndon Ong

Author's Addresses

   Greg M. Bernstein (ed.)
   Grotto Networking
   Fremont California, USA

   Phone: (510) 573-2237

   Young Lee (ed.)
   Huawei Technologies
   1700 Alma Drive, Suite 100
   Plano, TX 75075

   Phone: (972) 509-5599 (x2240)

   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

   Wataru Imajuku
   NTT Network Innovation Labs
   1-1 Hikari-no-oka, Yokosuka, Kanagawa

   Phone: +81-(46) 859-4315

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