Network Working Group Y. Lee (ed.) Internet Draft Huawei Intended status: Informational G. Bernstein (ed.) Expires: April 2010 Grotto Networking Wataru Imajuku NTT October 9, 2009 Framework for GMPLS and PCE Control of Wavelength Switched Optical Networks (WSON) draft-ietf-ccamp-rwa-wson-framework-04.txt 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- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 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Abstract This memo provides a framework for applying Generalized Multi- Protocol Label Switching (GMPLS) and the Path Computation Element (PCE) architecture to the control of wavelength switched optical networks (WSON). In particular we provide control plane models for key wavelength switched optical network subsystems and processes. The subsystems include wavelength division multiplexed links, tunable laser transmitters, reconfigurable optical add/drop multiplexers (ROADM) and wavelength converters. Lightpath provisioning, in general, requires the routing and wavelength assignment (RWA) process. This process is reviewed and the information requirements, both static and dynamic for this process are presented, along with alternative implementation architectures that could be realized via various combinations of extended GMPLS and PCE protocols. This memo focuses on topological elements and path selection constraints that are common across different WSON environments as such it does not address optical impairments in any depth nor does it address potential incompatibilities between some types of optical signals and some types of network elements and links. Table of Contents 1. Introduction...................................................4 1.1. Revision History..........................................4 1.1.1. Changes from 00......................................4 1.1.2. Changes from 01......................................5 1.1.3. Changes from 02......................................5 1.2. Related Documents ........................................6 2. Terminology....................................................6 3. Wavelength Switched Optical Networks...........................7 3.1. WDM and CWDM Links........................................7 3.2. Optical Transmitters......................................9 3.2.1. Lasers...............................................9 3.2.2. WSON Signal Parameters..............................10 3.3. ROADMs, OXCs, Splitters, Combiners and FOADMs............10 3.3.1. Reconfigurable Add/Drop Multiplexers and OXCs.......10 3.3.2. Splitters...........................................13 3.3.3. Combiners...........................................14 Bernstein and Lee Expires April 9, 2010[Page 2] Internet-Draft Wavelength Switched Optical Networks October 2009 3.3.4. Fixed Optical Add/Drop Multiplexers.................14 3.4. Wavelength Converters....................................15 3.4.1. Wavelength Converter Pool Modeling..................16 4. Routing and Wavelength Assignment and the Control Plane.......20 4.1. Architectural Approaches to RWA..........................21 4.1.1. Combined RWA (R&WA).................................22 4.1.2. Separated R and WA (R+WA)...........................22 4.1.3. Routing and Distributed WA (R+DWA)..................23 4.2. Conveying information needed by RWA......................23 4.3. Lightpath Temporal Characteristics.......................24 5. Modeling Examples and Control Plane Use Cases.................25 5.1. Network Modeling for GMPLS/PCE Control...................25 5.1.1. Describing the WSON nodes...........................26 5.1.2. Describing the links................................28 5.2. RWA Path Computation and Establishment...................29 5.3. Resource Optimization....................................30 5.4. Support for Rerouting....................................31 6. GMPLS & PCE Implications......................................31 6.1. Implications for GMPLS signaling.........................31 6.1.1. Identifying Wavelengths and Signals.................32 6.1.2. Combined RWA/Separate Routing WA support............32 6.1.3. Distributed Wavelength Assignment: Unidirectional, No Converters.................................................32 6.1.4. Distributed Wavelength Assignment: Unidirectional, Limited Converters.........................................33 6.1.5. Distributed Wavelength Assignment: Bidirectional, No Converters.................................................33 6.2. Implications for GMPLS Routing...........................34 6.2.1. Wavelength-Specific Availability Information........34 6.2.2. WSON Routing Information Summary....................35 6.3. Optical Path Computation and Implications for PCE........36 6.3.1. Lightpath Constraints and Characteristics...........36 6.3.2. Discovery of RWA Capable PCEs.......................37 6.4. Summary of Impacts by RWA Architecture...................37 7. Security Considerations.......................................38 8. IANA Considerations...........................................39 9. Acknowledgments...............................................39 10. References...................................................40 10.1. Normative References....................................40 10.2. Informative References..................................41 11. Contributors.................................................44 Author's Addresses...............................................45 Intellectual Property Statement..................................45 Disclaimer of Validity...........................................46 Bernstein and Lee Expires April 9, 2010[Page 3] Internet-Draft Wavelength Switched Optical Networks October 2009 1. Introduction This memo provides a framework for applying GMPLS and the Path Computation Element (PCE) architecture to the control of WSONs. In particular we provide control plane models for key wavelength switched optical network subsystems and processes. The subsystems include wavelength division multiplexed links, tunable laser transmitters, reconfigurable optical add/drop multiplexers (ROADM) and wavelength converters. Lightpath provisioning, in general, requires the routing and wavelength assignment (RWA) process. This process is reviewed and the information requirements, both static and dynamic for this process are presented, along with alternative implementation architectures that could be realized via various combinations of extended GMPLS and PCE protocols. This document will focus on the unique properties of links, switches and path selection constraints that occur in WSONs. Different WSONs such as access, metro and long haul may apply different techniques for dealing with optical impairments hence this document will not address optical impairments in any depth, but instead focus on properties that are common across a variety of WSONs. For more on how the GMPLS control plane can aid in dealing with optical impairments see [WSON-Imp]. For the purposes of this document we assume that all signals used in a WSON are compatible with all network elements and links within the WSON. This can arise in practice for a number of reasons including: (a) in some WSONs only one class of signal is used throughout the network, or (b) only "relatively" transparent network elements are utilized in the WSON. How the GMPLS control plane can deal with situations where this assumption is not true (i.e., where not all of the optical signals in the network are compatible with all network elements and limited to processing only certain types of WSON signals) is addressed in a separate draft [WSON-Compat]. 1.1. Revision History 1.1.1. Changes from 00 o Added new first level section on modeling examples and control plane use cases. o Added new third level section on wavelength converter pool modeling o Editorial clean up of English and updated references. Bernstein and Lee Expires April 9, 2010[Page 4] Internet-Draft Wavelength Switched Optical Networks October 2009 1.1.2. Changes from 01 Fixed error in wavelength converter pool example. 1.1.3. Changes from 02 Updated the abstract to emphasize the focus of this draft and differentiate it from WSON impairment [WSON-Imp] and WSON compatibility [WSON-Compat] drafts. Added references to [WSON-Imp] and [WSON-Compat]. Updated the introduction to explain the relationship between this document and the [WSON-Imp] and [WSON-Compat] documents. In section 3.1 removed discussion of optical impairments in fibers. Merged section 3.2.2 and section 3.2.3. Deferred much of the discussion of signal types and standards to [WSON-Compat]. In section 3.4 on Wavelength converters removed paragraphs dealing with signal compatibility discussion as this is addressed in [WSON- Compat]. In section 6.1 removed discussion of signaling extensions to deal with different WSON signal types. This is deferred to [WSON-Compat]. In section 6 removed discussion of "Need for Wavelength Specific Maximum Bandwidth Information". In section 6 removed discussion of "Relationship to link bundling and layering". In section 6 removed discussion of "Computation Architecture Implications" as this material was redundant with text that occurs earlier in the document. In section 6 removed discussion of "Scaling Implications" as this material was redundant with text that occurs earlier in the document. 1.1.4. Changes from 03 In Section 3.3.1 added 4-degree ROADM example and its connectivity matrix. Bernstein and Lee Expires April 9, 2010[Page 5] Internet-Draft Wavelength Switched Optical Networks October 2009 1.2. Related Documents This framework document covers essential concepts and models for the application and extension of the control plane to WSONs. The following documents address specific aspects of WSONs and complement this draft. o [WSON-Info] This document provides an information model needed by the routing and wavelength assignment (RWA) process in WSON. o [WSON-Encode] This document provides efficient, protocol-agnostic encodings for the information elements necessary to support the routing and wavelength assignment (RWA) process in WSONs. o [WSON-Imp] This document provides a framework for the support of impairment aware Routing and Wavelength Assignment (RWA) in WSON. o [WSON-Compat] This document provides an overview of signal compatibility constraints associated with WSON network elements including regenerators. o [PCEP-RWA] This document provides application-specific requirements for the Path Computation Element communication Protocol (PCEP) for the support of RWA in WSON. 2. Terminology CWDM: Coarse Wavelength Division Multiplexing. DWDM: Dense Wavelength Division Multiplexing. FOADM: Fixed Optical Add/Drop Multiplexer. OXC: Optical cross connect. A symmetric optical switching element in which a signal on any ingress port can reach any egress port. ROADM: Reconfigurable Optical Add/Drop Multiplexer. An asymmetric 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/Converters: 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. Bernstein and Lee Expires April 9, 2010[Page 6] Internet-Draft Wavelength Switched Optical Networks October 2009 WDM: Wavelength Division Multiplexing. Wavelength Switched Optical Networks (WSON): WDM based optical networks in which switching is performed selectively based on the center wavelength of an optical signal. 3. Wavelength Switched Optical Networks WSONs come in a variety of shapes and sizes from continent spanning long haul networks, to metropolitan networks, to residential access networks. In all these cases we are concerned with those properties that constrain the choice of wavelengths that can be used, i.e., restrict the wavelength label set, impact the path selection process, and limit the topological connectivity. In the following we examine and model some major subsystems of a WSON with an emphasis on those aspects that are of relevance to the control plane. In particular we look at WDM links, Optical Transmitters, ROADMs, and Wavelength Converters. 3.1. WDM and CWDM Links WDM and CWDM links run over optical fibers, and optical fibers come in a wide range of types that tend to be optimized for various applications from access networks, metro, long haul, and submarine links to name a few. ITU-T standards exist for various types of fibers. For the purposes here we are concerned only with single mode fibers (SMF). The following SMF fiber types are typically encountered in optical networks: ITU-T Standard | Common Name ------------------------------------------------------------ G.652 [G.652] | Standard SMF | G.653 [G.653] | Dispersion shifted SMF | G.654 [G.654] | Cut-off shifted SMF | G.655 [G.655] | Non-zero dispersion shifted SMF | G.656 [G.656] | Wideband non-zero dispersion shifted SMF | ------------------------------------------------------------ Typically WDM links operate in one or more of the approximately defined optical bands [G.Sup39]: Band Range (nm) Common Name Raw Bandwidth (THz) O-band 1260-1360 Original 17.5 E-band 1360-1460 Extended 15.1 S-band 1460-1530 Short 9.4 C-band 1530-1565 Conventional 4.4 L-band 1565-1625 Long 7.1 U-band 1625-1675 Ultra-long 5.5 Bernstein and Lee Expires April 9, 2010[Page 7] Internet-Draft Wavelength Switched Optical Networks October 2009 Not all of a band may be usable, for example in many fibers that support E-band there is significant attenuation due to a water absorption peak at 1383nm. Hence we can have a discontinuous acceptable wavelength range for a particular link. Also some systems will utilize more than one band. This is particularly true for coarse WDM (CWDM) systems. Current technology breaks up the bandwidth capacity of fibers into distinct channels based on either wavelength or frequency. There are two standards covering wavelengths and channel spacing. ITU-T recommendation [G.694.1] describes a DWDM grid defined in terms of frequency grids of 12.5GHz, 25GHz, 50GHz, 100GHz, and other multiples of 100GHz around a 193.1THz center frequency. At the narrowest channel spacing this provides less than 4800 channels across the O through U bands. ITU-T recommendation [G.694.2] describes a CWDM grid defined in terms of wavelength increments of 20nm running from 1271nm to 1611nm for 18 or so channels. The number of channels is significantly smaller than the 32 bit GMPLS label space allocated to lambda switching. A label representation for these ITU-T grids is given in [Otani] and allows a common vocabulary to be used in signaling lightpaths. Further, these ITU-T grid based labels can also be used to describe WDM links, ROADM ports, and wavelength converters for the purposes path selection. With a tremendous existing base of fiber many WDM links are designed to take advantage of particular fiber characteristics or to try to avoid undesirable properties. For example dispersion shifted SMF [G.653] was originally designed for good long distance performance in single channel systems, however putting WDM over this type of fiber requires much system engineering and a fairly limited range of wavelengths. Hence for our basic, impairment unaware, modeling of a WDM link we will need the following information: o Wavelength range(s): Given a mapping between labels and the ITU-T grids each range could be expressed in terms of a doublet (lambda1, lambda2) or (freq1, freq1) where the lambdas or frequencies can be represented by 32 bit integers. o Channel spacing: currently there are about five channel spacings used in DWDM systems 12.5GHz to 200GHz and one defined CWDM spacing. For a particular link this information is relatively static, i.e., changes to these properties generally require hardware upgrades. Such information could be used locally during wavelength assignment via signaling, similar to label restrictions in MPLS or used by a PCE in solving the combined routing and wavelength assignment problem. Bernstein and Lee Expires April 9, 2010[Page 8] Internet-Draft Wavelength Switched Optical Networks October 2009 3.2. Optical Transmitters 3.2.1. Lasers WDM optical systems make use of laser transmitters utilizing different wavelengths (frequencies). Some laser transmitters were and are manufactured for a specific wavelength of operation, that is, the manufactured frequency cannot be changed. First introduced to reduce inventory costs, tunable optical laser transmitters are becoming widely deployed in some systems [Coldren04], [Buus06]. This allows flexibility in the wavelength used for optical transmission and aids in path selection. Fundamental modeling parameters from the control plane perspective optical transmitters are: o Tunable: Is this transmitter tunable or fixed. o Tuning range: This is the frequency or wavelength range over which the laser can be tuned. With the fixed mapping of labels to lambdas of [Otani] this can be expressed as a doublet (lambda1, lambda2) or (freq1, freq2) where lambda1 and lambda2 or freq1 and freq2 are the labels representing the lower and upper bounds in wavelength or frequency. o Tuning time: Tuning times highly depend on the technology used. Thermal drift based tuning may take seconds to stabilize, whilst electronic tuning might provide sub-ms tuning times. Depending on the application this might be critical. For example, thermal drift might not be applicable for fast protection applications. o Spectral Characteristics and stability: The spectral shape of the laser's emissions and its frequency stability put limits on various properties of the overall WDM system. One relatively easy to characterize constraint is the finest channel spacing on which the transmitter can be used. Note that ITU-T recommendations specify many aspects of a laser transmitter.. Many of these parameters, such as spectral characteristics and stability, are used in the design of WDM subsystems consisting of transmitters, WDM links and receivers however they do not furnish additional information that will influence label switched path (LSP) provisioning in a properly designed system. Also note that lasers transmitters as a component can degrade and fail over time. This presents the possibility of the failure of a LSP (lightpath) without either a node or link failure. Hence, additional Bernstein and Lee Expires April 9, 2010[Page 9] Internet-Draft Wavelength Switched Optical Networks October 2009 mechanisms may be necessary to detect and differentiate this failure from the others, e.g., one doesn't not want to initiate mesh restoration if the source transmitter has failed, since the laser transmitter will still be failed on the alternate optical path. 3.2.2. WSON Signal Parameters As pointed out in the introduction, for the purposes of this document we assume that all optical signals used in a WSON are compatible with all links, network elements, and receivers in that WSON. In [WSON- Compat] we discuss how the GMPLS control plane can be extended to deal with incompatibilities between signals and network elements. Key WSON signal parameters include modulation type, bit rate and forward error correction coding technique. Multiple modulation formats have been standardized [G.959.1] and many others are used industry and discussed in the literature [Winzer06]. When signals with different modulation types are used in a WSON then it can be important to check these signals for compatibility with network elements such as regenerators, OEO switches, wavelength converters and receivers [WSON-Compat]. 3.3. ROADMs, OXCs, Splitters, Combiners and FOADMs Definitions of various optical devices and their parameters can be found in [G.671], we only look at a subset of these and their non- impairment related properties. 3.3.1. Reconfigurable Add/Drop Multiplexers and OXCs Reconfigurable add/drop optical multiplexers (ROADM) have matured and are available in different forms and technologies [Basch06]. This is a key technology that allows wavelength based optical switching. A classic degree-2 ROADM is shown in Figure 1. Bernstein and Lee Expires April 9, 2010[Page 10] Internet-Draft Wavelength Switched Optical Networks October 2009 Line side ingress +---------------------+ Line side egress --->| |---> | | | ROADM | | | | | +---------------------+ | | | | o o o o | | | | | | | | O O O O | | | | Tributary Side: Drop (egress) Add (ingress) Figure 1 Degree-2 ROADM The key feature across all ROADM types is their highly asymmetric switching capability. In the ROADM of Figure 1, the "add" ingress ports can only egress on the line side egress port and not on any of the "drop" egress ports. The degree of a ROADM or switch is given by the number of line side ports (ingress and egress) and does not include the number of "add" or "drop" ports. Sometimes the "add" "drop" ports are also called tributary ports. As the degree of the ROADM increases beyond two it can have properties of both a switch (OXC) and a multiplexer and hence we must know the switched connectivity offered by such a network element to effectively utilize it. A straight forward way to do this is via a "switched connectivity" matrix A where Amn = 0 or 1, depending upon whether a wavelength on ingress port m can be connected to egress port n [Imajuku]. For the ROADM of Figure 1 the switched connectivity matrix can be expressed as Ingress Egress Port Port #1 #2 #3 #4 #5 -------------- #1: 1 1 1 1 1 #2 1 0 0 0 0 A = #3 1 0 0 0 0 #4 1 0 0 0 0 #5 1 0 0 0 0 Where ingress ports 2-5 are add ports, egress ports 2-5 are drop ports and ingress port #1 and egress port #1 are the line side (WDM) ports. For ROADMs this matrix will be very sparse, and for OXCs the complement of the matrix will be very sparse, compact encodings and examples, including high degree ROADMs/OXCs, are given in [WSON- Encode]. A classic degree-4 ROADM is shown in Figure 2. Bernstein and Lee Expires April 9, 2010[Page 11] Internet-Draft Wavelength Switched Optical Networks October 2009 +-----------------------+ Line side-1 --->| |---> Line side-2 ingress (I1) | | egress (E2) Line side-1 <---| |<--- Line side-2 Egress (E1) | | Ingress (I2) | ROADM | Line side-3 --->| |---> Line side-4 ingress (I3) | | egress (E4) Line side-3 <---| |<--- Line side-4 Egress (E3) | | Ingress (I4) | | +-----------------------+ | O | O | O | O | | | | | | | | O | O | O | O | Tributary Side: E5 I5 E6 I6 E7 I7 E8 I8 Figure 2 Degree-4 ROADM Note that this example is 4-degree example with one (potentially multi-channel) add/drop per line side port. Note also that the connectivity constraints for typical ROADM designs are "bi-directional", i.e. if ingress port X can be connected to egress port Y, typically ingress port Y can be connected to egress port X, assuming the numbering is done in such a way that ingress X and egress X correspond to the same line side direction or the same add/drop port. This makes the connectivity matrix symmetrical as shown below. Ingress Egress Port Port E1 E2 E3 E4 E5 E6 E7 E8 ----------------------- I1 0 1 1 1 0 1 0 0 I2 1 0 1 1 0 0 1 0 A = I3 1 1 0 1 1 0 0 0 I4 1 1 1 0 0 0 0 1 I5 0 0 1 0 0 0 0 0 I6 1 0 0 0 0 0 0 0 I7 0 1 0 0 0 0 0 0 I8 0 0 0 1 0 0 0 0 where I5/E5 are add/drop ports to/from line side-3, I6/E6 are add/drop ports to/from line side-1, I7/E7 are add/drop ports to/from Bernstein and Lee Expires April 9, 2010[Page 12] Internet-Draft Wavelength Switched Optical Networks October 2009 line side-2 and I8/E8 are add/drop ports to/from line side-4. Note that diagonal elements are zero since I assume that loopback is not supported. If ports support loopback, diagonal elements would be one. Additional constraints may also apply to the various ports in a ROADM/OXC. In the literature of optical switches and ROADMs the following restrictions/terms are used: Colored port: An ingress or more typically an egress (drop) port restricted to a single channel of fixed wavelength. Colorless port: An ingress or more typically an egress (drop) port restricted to a single channel of arbitrary wavelength. In general a port on a ROADM could have any of the following wavelength restrictions: o Multiple wavelengths, full range port o Single wavelength, full range port o Single wavelength, fixed lambda port o Multiple wavelengths, reduced range port (for example wave band switching) To model these restrictions we need two pieces of information for each port: (a) number of wavelengths, (b) wavelength range and spacing. Note that this information is relatively static. More complicated wavelength constraints are modeled in [WSON-Info]. 3.3.2. Splitters An optical splitter consists of a single ingress port and two or more egress ports. The ingress optical signaled is essentially copied (with loss) to all egress ports. Using the modeling notions of section 3.3.1. the ingress and egress ports of a splitter would have the same wavelength restrictions. In addition we can describe a splitter by a connectivity matrix Amn as follows: Bernstein and Lee Expires April 9, 2010[Page 13] Internet-Draft Wavelength Switched Optical Networks October 2009 Ingress Egress Port Port #1 #2 #3 ... #N ----------------- A = #1 1 1 1 ... 1 The difference from a simple ROADM is that this is not a switched (potential) connectivity matrix but the fixed connectivity matrix of the device. 3.3.3. Combiners A optical combiner is somewhat the dual of a splitter in that it has a single multi-wavelength egress port and multiple ingress ports. The contents of all the ingress ports are copied and combined to the single egress port. The various ports may have different wavelength restrictions. It is generally the responsibility of those using the combiner to assure that wavelength collision does not occur on the egress port. The fixed connectivity matrix Amn for a combiner would look like: Ingress Egress Port Port #1 --- #1: 1 #2 1 A = #3 1 ... 1 #N 1 3.3.4. Fixed Optical Add/Drop Multiplexers A fixed optical add/drop multiplexer can alter the course of an ingress wavelength in a preset way. In particular a given wavelength (or waveband) from a line side ingress port would be dropped to a fixed "tributary" egress port. Depending on the device's construction that same wavelength may or may not be "continued" to the line side egress port ("drop and continue" operation). Further there may exist tributary ingress ports ("add" ports) whose signals are combined with each other and "continued" line side signals. In general to represent the routing properties of an FOADM we need a fixed connectivity matrix Amn as previously discussed and we need the precise wavelength restrictions for all ingress and egress ports. From the wavelength restrictions on the tributary egress ports (drop ports) we can see what wavelengths have been dropped. From the wavelength restrictions on the tributary ingress (add) ports we can Bernstein and Lee Expires April 9, 2010[Page 14] Internet-Draft Wavelength Switched Optical Networks October 2009 see which wavelengths have been added to the line side egress port. Finally from the added wavelength information and the line side egress wavelength restrictions we can infer which wavelengths have been continued. To summarize, the modeling methodology introduced in section 3.3.1. consisting of a connectivity matrix and port wavelength restrictions can be used to describe a large set of fixed optical devices such as combiners, splitters and FOADMs. Hybrid devices consisting of both switched and fixed parts are modeled in [WSON-Info]. 3.4. Wavelength Converters Wavelength converters take an ingress optical signal at one wavelength and emit an equivalent content optical signal at another wavelength on egress. There are currently two approaches to building wavelength converters. One approach is based on optical to electrical to optical (OEO) conversion with tunable lasers on egress. This approach can be dependent upon the signal rate and format, i.e., this is basically an electrical regenerator combined with a tunable laser. The other approach performs the wavelength conversion, optically via non-linear optical effects, similar in spirit to the familiar frequency mixing used in radio frequency systems, but significantly harder to implement. Such processes/effects may place limits on the range of achievable conversion. These may depend on the wavelength of the input signal and the properties of the converter as opposed to only the properties of the converter in the OEO case. Different WSON system designs may choose to utilize this component to varying degrees or not at all. Current or envisioned contexts for wavelength converters are: 1. Wavelength conversion associated with OEO switches and tunable laser transmitters. In this case there are plenty of converters to go around since we can think of each tunable output laser transmitter on an OEO switch as a potential wavelength converter. 2. Wavelength conversion associated with ROADMs/OXCs. In this case we may have a limited pool of wavelength converters available. Conversion could be either all optical or via an OEO method. 3. Wavelength conversion associated with fixed devices such as FOADMs. In this case we may have a limited amount of conversion. Also in this case the conversion may be used as part of light path routing. Based on the above contexts a modeling approach for wavelength converters could be as follows: Bernstein and Lee Expires April 9, 2010[Page 15] Internet-Draft Wavelength Switched Optical Networks October 2009 1. Wavelength converters can always be modeled as associated with network elements. This includes fixed wavelength routing elements. 2. A network element may have full wavelength conversion capability, i.e., any ingress port and wavelength, or a limited number of wavelengths and ports. On a box with a limited number of converters there also may exist restrictions on which ports can reach the converters. Hence regardless of where the converters actually are we can associate them with ingress ports. 3. Wavelength converters have range restrictions that are either independent or dependent upon the ingress wavelength. In WSONs where wavelength converters are sparse we may actually see a light path appear to loop or "backtrack" upon itself in order to reach a wavelength converter prior to continuing on to its destination. The lambda used on the "detour" out to the wavelength converter would be different from that coming back from the "detour" to the wavelength converter. A model for an individual O-E-O wavelength converter would consist of: o Input lambda or frequency range o Output lambda or frequency range 3.4.1. Wavelength Converter Pool Modeling A WSON node may include multiple 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, i.e., matrices to indicate Bernstein and Lee Expires April 9, 2010[Page 16] Internet-Draft Wavelength Switched Optical Networks October 2009 possible connectivity along with wavelength constraints for links/ports. Since wavelength converters are considered a scarce resource we will also want our model to include as a minimum the usage state of individual wavelength converters in the pool. We utilize a three stage model as shown schematically in Figure 3. 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]. Bernstein and Lee Expires April 9, 2010[Page 17] Internet-Draft Wavelength Switched Optical Networks October 2009 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 3 Schematic diagram of wavelength converter pool model. Example: Shared Per Node In Figure 4 below we show a simple optical switch in a four wavelength DWDM system sharing wavelength converters in a general "per node" fashion. Bernstein and Lee Expires April 9, 2010[Page 18] Internet-Draft Wavelength Switched Optical Networks October 2009 ___________ +------+ | |--------------------------->| | | |--------------------------->| C | /| | |--------------------------->| o | E1 I1 /D+--->| |--------------------------->| m | + e+--->| | | b |====> ====>| M| | Optical | +-----------+ +----+ | i | + u+--->| Switch | | WC Pool | |O S|-->| n | \x+--->| | | +-----+ | |p w|-->| e | \| | +----+->|WC #1|--+->|t i| | r | | | | +-----+ | |i t| +------+ | | | | |c c| +------+ /| | | | +-----+ | |a h|-->| | I2 /D+--->| +----+->|WC #2|--+->|l |-->| C | E2 + e+--->| | | +-----+ | | | | o | ====>| M| | | +-----------+ +----+ | m |====> + u+--->| | | b | \x+--->| |--------------------------->| i | \| | |--------------------------->| n | | |--------------------------->| e | |___________|--------------------------->| r | +------+ Figure 4 An optical switch featuring a shared per node wavelength converter pool architecture. In this case the ingress and egress pool matrices are simply: +-----+ +-----+ | 1 1 | | 1 1 | WI =| |, WE =| | | 1 1 | | 1 1 | +-----+ +-----+ Example: Shared Per Link In Figure 5 we show a different wavelength pool architecture know as "shared per fiber". In this case the ingress and egress pool matrices are simply: Bernstein and Lee Expires April 9, 2010[Page 19] Internet-Draft Wavelength Switched Optical Networks October 2009 +-----+ +-----+ | 1 1 | | 1 0 | WI =| |, WE =| | | 1 1 | | 0 1 | +-----+ +-----+ ___________ +------+ | |--------------------------->| | | |--------------------------->| C | /| | |--------------------------->| o | E1 I1 /D+--->| |--------------------------->| m | + e+--->| | | b |====> ====>| M| | Optical | +-----------+ | i | + u+--->| Switch | | WC Pool | | n | \x+--->| | | +-----+ | | e | \| | +----+->|WC #1|--+---------->| r | | | | +-----+ | +------+ | | | | +------+ /| | | | +-----+ | | | I2 /D+--->| +----+->|WC #2|--+---------->| C | E2 + e+--->| | | +-----+ | | o | ====>| M| | | +-----------+ | m |====> + u+--->| | | b | \x+--->| |--------------------------->| i | \| | |--------------------------->| n | | |--------------------------->| e | |___________|--------------------------->| r | +------+ Figure 5 An optical switch featuring a shared per fiber wavelength converter pool architecture. 4. Routing and Wavelength Assignment and the Control Plane In wavelength switched optical networks consisting of tunable lasers and wavelength selective switches with wavelength converters on every interface, path selection is similar to the MPLS and TDM circuit switched cases in that the labels, in this case wavelengths (lambdas), have only local significance. That is, a wavelength- convertible network with full wavelength-conversion capability at each node is equivalent to a circuit-switched TDM network with full time slot interchange capability; thus, the routing problem needs to be addressed only at the level of the traffic engineered (TE) link Bernstein and Lee Expires April 9, 2010[Page 20] Internet-Draft Wavelength Switched Optical Networks October 2009 choice, and wavelength assignment can be resolved locally by the switches on a hop-by-hop basis. However, in the limiting case of an optical network with no wavelength converters, a light path (optical signal) needs a route from source to destination and must pick a single wavelength that can be used along that path without "colliding" with the wavelength used by any other light path that may share an optical fiber. This is sometimes referred to as a "wavelength continuity constraint". To ease up on this constraint while keeping network costs in check a limited number of wavelength converters may be introduced at key points in the network [Chu03]. In the general case of limited or no wavelength converters this computation is known as the Routing and Wavelength Assignment (RWA) problem [HZang00]. The "hardness" of this problem is well documented. There, however, exist a number of reasonable approximate methods for its solution [HZang00]. The inputs to the basic RWA problem are the requested light paths source and destination, the network's topology, the locations and capabilities of any wavelength converters, and the wavelengths available on each optical link. The output from an algorithm solving the RWA problem is an explicit route through ROADMs, a wavelength for the optical transmitter, and a set of locations (generally associated with ROADMs or switches) where wavelength conversion is to occur and the new wavelength to be used on each component link after that point in the route. It is to be noted that choice of specific RWA algorithm is out of the scope for this document. However there are a number of different approaches to dealing with the RWA algorithm that can affect the division of effort between signaling, routing and PCE. 4.1. Architectural Approaches to RWA Two general computational approaches are taken to solving the RWA problem. Some algorithms utilize a two step procedure of path selection followed by wavelength assignment, and others solve the problem in a combined fashion. In the following, three different ways of performing RWA in conjunction with the control plane are considered. The choice of one of these architectural approaches over another generally impacts the demands placed on the various control plane protocols. Bernstein and Lee Expires April 9, 2010[Page 21] Internet-Draft Wavelength Switched Optical Networks October 2009 4.1.1. Combined RWA (R&WA) In this case, a unique entity is in charge of performing routing and wavelength assignment. This approach relies on a sufficient knowledge of network topology, of available network resources and of network nodes capabilities. This solution is compatible with most known RWA algorithms, and in particular those concerned with network optimization. On the other hand, this solution requires up-to-date and detailed network information. Such a computational entity could reside in two different logical places: o In a separate Path Computation Element (PCE) which hence owns the complete and updated knowledge of network state and provides path computation services to node. o In the Ingress node, in that case all nodes have the R&WA functionality; the knowledge of the network state is obtained by a periodic flooding of information provided by the other nodes. 4.1.2. Separated R and WA (R+WA) In this case a first entity performs routing, while a second performs wavelength assignment. The first entity furnishes one or more paths to the second entity that will perform wavelength assignment and possibly final path selection. As the entities computing the path and the wavelength assignment are separated, this constrains the class of RWA algorithms that may be implemented. Although it may seem that algorithms optimizing a joint usage of the physical and spectral paths are excluded from this solution, many practical optimization algorithms only consider a limited set of possible paths, e.g., as computed via a k-shortest path algorithm [Ozdaglar03]. Hence although there is no guarantee that the selected final route and wavelength offers the optimal solution, by allowing multiple routes to pass to the wavelength selection process reasonable optimization can be performed. The entity performing the routing assignment needs the topology information of the network, whereas the entity performing the wavelength assignment needs information on the network's available resources and on network node capabilities. Bernstein and Lee Expires April 9, 2010[Page 22] Internet-Draft Wavelength Switched Optical Networks October 2009 4.1.3. Routing and Distributed WA (R+DWA) In this case a first entity performs routing, while wavelength assignment is performed on a hop-by-hop manner along the previously computed route. This mechanism relies on updating of a list of potential wavelengths used to ensure conformance with the wavelength continuity constraint. As currently specified, the GMPLS protocol suite signaling protocol can accommodate such an approach. Per [RFC3471], the Label Set selection works according to an AND scheme. Each hop restricts the Label Set sent to the next hop from the one received from the previous hop by performing an AND operation between the wavelength referred by the labels the message includes with the one available on the ongoing interface. The constraint to perform this AND operation is up to the node local policy (even if one expects a consistent policy configuration throughout a given transparency domain). When wavelength conversion is performed at an intermediate node, a new Label Set is generated. The egress nodes selects one label in the Label Set received at the node, which is also up to the node local policy. Depending on these policies a spectral assignment may not be found or one consuming too many conversion resources relative to what a dedicated wavelength assignment policy would have achieved. Hence, this approach may generate higher blocking probabilities in a heavily loaded network. On the one hand, this solution may be empowered with some signaling extensions to ease its functioning and possibly enhance its performances relatively to blocking. Note that this approach requires less information dissemination than the others. The first entity may be a PCE or the ingress node of the LSP. This solution is applicable inside networks where resource optimization is not as critical. 4.2. Conveying information needed by RWA The previous sections have characterized WSONs and lightpath requests. In particular, high level models of the information used by the RWA process were presented. We can view this information as either static, changing with hardware changes (including possibly failures), or dynamic, those that can change with subsequent lightpath provisioning. The timeliness in which an entity involved in the RWA process is notified of such changes is fairly situational. For example, for network restoration purposes, learning of a hardware failure or of new hardware coming online to provide restoration Bernstein and Lee Expires April 9, 2010[Page 23] Internet-Draft Wavelength Switched Optical Networks October 2009 capability can be critical. Currently there are various methods for communicating RWA relevant information, these include, but are not limited to: o Existing control plane protocols such as GMPLS routing and signaling. Note that routing protocols can be used to convey both static and dynamic information. Static information currently conveyed includes items like router options and such. o Management protocols such as NetConf, SNMPv3, CLI, CORBA, or others. o Directory services and accompanying protocols. These are good for the dissemination of relatively static information. Not intended for dynamic information. o Other techniques for dynamic information: messaging straight from NEs to PCE to avoid flooding. This would be useful if the number of PCEs is significantly less than number of WSON NEs. Or other ways to limit flooding to "interested" NEs. Mechanisms to improve scaling of dynamic information: o Tailor message content to WSON. For example the use of wavelength ranges, or wavelength occupation bit maps. Utilize incremental updates if feasible. 4.3. Lightpath Temporal Characteristics The temporal characteristics of a light path connection can affect the choice of solution to the RWA process. For our purposes here we look at the timeliness of connection establishment/teardown, and the duration of the connection. Connection Establishment/Teardown Timeliness can be thought of in approximately three time frames: 1. Time Critical: For example those lightpath establishments used for restoration of service or other high priority real time service requests. 2. Soft time bounds: This is a more typical new connection request. While expected to be responsive, there should be more time to take into account network optimization. 3. Scheduled or Advanced reservations. Here lightpath connections are requested significantly ahead of their intended "in service" time. Bernstein and Lee Expires April 9, 2010[Page 24] Internet-Draft Wavelength Switched Optical Networks October 2009 There is the potential for significant network optimization if multiple lightpaths can be computed concurrently to achieve network optimization objectives. Lightpath connection duration has typically been thought of as approximately three time frames: 1. Dynamic: those lightpaths with relatively short duration (holding times). 2. Pseudo-static: lightpaths with moderately long durations. 3. Static: lightpaths with long durations. Different types of RWA algorithms have been developed for dealing with dynamic versus pseudo-static conditions. These can address service provider's needs for: (a) network optimization, (b) restoration, and (c) highly dynamic lightpath provisioning. Hence we can model timescale related lightpath requirements via the following notions: o Batch or Sequential light path connection requests o Timeliness of Connection establishment o Duration of lightpath connection 5. Modeling Examples and Control Plane Use Cases This section provides examples of the fixed and switch optical node and wavelength constraint models of section 3. and WSON control plane use cases related to path computation, establishment, rerouting, and optimization. 5.1. Network Modeling for GMPLS/PCE Control Consider a network containing three routers (R1 through R3), eight WSON nodes (N1 through N8) and 18 links (L1 through L18) and one OEO converter (O1) in a topology shown below. Bernstein and Lee Expires April 9, 2010[Page 25] Internet-Draft Wavelength Switched Optical Networks October 2009 +--+ +--+ +--+ +--------+ +-L3-+N2+-L5-+ +--------L12--+N6+--L15--+ N8 +-- | +--+ |N4+-L8---+ +--+ ++--+---++ | | +-L9--+| | | | +--+ +-+-+ ++-+ || | L17 L18 | ++-L1--+ | | ++++ +----L16---+ | | |R1| | N1| L7 |R2| | | | | ++-L2--+ | | ++-+ | ++---++ +--+ +-+-+ | | | + R3 | | +--+ ++-+ | | +-----+ +-L4-+N3+-L6-+N5+-L10-+ ++----+ +--+ | +--------L11--+ N7 +---- +--+ ++---++ | | L13 L14 | | ++-+ | |O1+-+ +--+ 5.1.1. Describing the WSON nodes The eight WSON nodes in this example have the following properties: o Nodes N1, N2, N3 have fixed OADMs (FOADMs) installed and can therefore only access a static and pre-defined set of wavelengths o All other nodes contain ROADMs and can therefore access all wavelengths. o Nodes N4, N5, N7 and N8 are multi-degree nodes, allowing any wavelength to be optically switched between any of the links. Note however, that this does not automatically apply to wavelengths that are being added or dropped at the particular node. o Node N4 is an exception to that: This node can switch any wavelength from its add/drop ports to any of its outgoing links (L5, L7 and L12 in this case) o The links from the routers are always only able to carry one wavelength with the exception of links L8 and L9 which are capable to add/drop any wavelength. o Node N7 contains an OEO transponder (O1) connected to the node via links L13 and L14. That transponder operates in 3R mode and does not change the wavelength of the signal. Assume that it can regenerate any of the client signals, however only for a specific wavelength. Bernstein and Lee Expires April 9, 2010[Page 26] Internet-Draft Wavelength Switched Optical Networks October 2009 Given the above restrictions, the node information for the eight nodes can be expressed as follows: (where ID == identifier, SCM == switched connectivity matrix, and FCM == fixed connectivity matrix). Bernstein and Lee Expires April 9, 2010[Page 27] Internet-Draft Wavelength Switched Optical Networks October 2009 +ID+SCM +FCM + | | |L1 |L2 |L3 |L4 | | |L1 |L2 |L3 |L4 | | | |L1 |0 |0 |0 |0 | |L1 |0 |0 |1 |0 | | |N1|L2 |0 |0 |0 |0 | |L2 |0 |0 |0 |1 | | | |L3 |0 |0 |0 |0 | |L3 |1 |0 |0 |1 | | | |L4 |0 |0 |0 |0 | |L4 |0 |1 |1 |0 | | +--+---+---+---+---+---+---+---+---+---+---+---+---+ | | |L3 |L5 | | | | |L3 |L5 | | | | |N2|L3 |0 |0 | | | |L3 |0 |1 | | | | | |L5 |0 |0 | | | |L5 |1 |0 | | | | +--+---+---+---+---+---+---+---+---+---+---+---+---+ | | |L4 |L6 | | | | |L4 |L6 | | | | |N3|L4 |0 |0 | | | |L4 |0 |1 | | | | | |L6 |0 |0 | | | |L6 |1 |0 | | | | +--+---+---+---+---+---+---+---+---+---+---+---+---+ | | |L5 |L7 |L8 |L9 |L12| |L5 |L7 |L8 |L9 |L12| | |L5 |0 |1 |1 |1 |1 |L5 |0 |0 |0 |0 |0 | |N4|L7 |1 |0 |1 |1 |1 |L7 |0 |0 |0 |0 |0 | | |L8 |1 |1 |0 |1 |1 |L8 |0 |0 |0 |0 |0 | | |L9 |1 |1 |1 |0 |1 |L9 |0 |0 |0 |0 |0 | | |L12|1 |1 |1 |1 |0 |L12|0 |0 |0 |0 |0 | +--+---+---+---+---+---+---+---+---+---+---+---+---+ | | |L6 |L7 |L10|L11| | |L6 |L7 |L10|L11| | | |L6 |0 |1 |0 |1 | |L6 |0 |0 |1 |0 | | |N5|L7 |1 |0 |0 |1 | |L7 |0 |0 |0 |0 | | | |L10|0 |0 |0 |0 | |L10|1 |0 |0 |0 | | | |L11|1 |1 |0 |0 | |L11|0 |0 |0 |0 | | +--+---+---+---+---+---+---+---+---+---+---+---+---+ | | |L12|L15| | | | |L12|L15| | | | |N6|L12|0 |1 | | | |L12|0 |0 | | | | | |L15|1 |0 | | | |L15|0 |0 | | | | +--+---+---+---+---+---+---+---+---+---+---+---+---+ | | |L11|L13|L14|L16| | |L11|L13|L14|L16| | | |L11|0 |1 |0 |1 | |L11|0 |0 |0 |0 | | |N7|L13|1 |0 |0 |0 | |L13|0 |0 |1 |0 | | | |L14|0 |0 |0 |1 | |L14|0 |1 |0 |0 | | | |L16|1 |0 |1 |0 | |L16|0 |0 |1 |0 | | +--+---+---+---+---+---+---+---+---+---+---+---+---+ | | |L15|L16|L17|L18| | |L15|L16|L17|L18| | | |L15|0 |1 |0 |0 | |L15|0 |0 |0 |1 | | |N8|L16|1 |0 |0 |0 | |L16|0 |0 |1 |0 | | | |L17|0 |0 |0 |0 | |L17|0 |1 |0 |0 | | | |L18|0 |0 |0 |0 | |L18|1 |0 |1 |0 | | +--+---+---+---+---+---+---+---+---+---+---+---+---+ 5.1.2. Describing the links For the following discussion some simplifying assumptions are made: Bernstein and Lee Expires April 9, 2010[Page 28] Internet-Draft Wavelength Switched Optical Networks October 2009 o It is assumed that the WSON node support a total of four wavelengths designated WL1 through WL4. o It is assumed that the impairment feasibility of a path or path segment is independent from the wavelength chosen. For the discussion of the RWA operation to build LSPs between two routers, the wavelength constraints on the links between the routers and the WSON nodes as well as the connectivity matrix of these links needs to be specified: +Link+WLs supported +Possible egress links+ | L1 | WL1 | L3 | +----+-----------------+---------------------+ | L2 | WL2 | L4 | +----+-----------------+---------------------+ | L8 | WL1 WL2 WL3 WL4 | L5 L7 L12 | +----+-----------------+---------------------+ | L9 | WL1 WL2 WL3 WL4 | L5 L7 L12 | +----+-----------------+---------------------+ | L10| WL2 | L6 | +----+-----------------+---------------------+ | L13| WL1 WL2 WL3 WL4 | L11 L14 | +----+-----------------+---------------------+ | L14| WL1 WL2 WL3 WL4 | L13 L16 | +----+-----------------+---------------------+ | L17| WL2 | L16 | +----+-----------------+---------------------+ | L18| WL1 | L15 | +----+-----------------+---------------------+ Note that the possible egress links for the links connecting to the routers is inferred from the Switched Connectivity Matrix and the Fixed Connectivity Matrix of the Nodes N1 through N8 and is show here for convenience, i.e., this information does not need to be repeated. 5.2. RWA Path Computation and Establishment The calculation of optical impairment feasible routes is outside the scope of this framework document. In general impairment feasible routes serve as an input to the RWA algorithm. For the example use case shown here, assume the following feasible routes: Bernstein and Lee Expires April 9, 2010[Page 29] Internet-Draft Wavelength Switched Optical Networks October 2009 +Endpoint 1+Endpoint 2+Feasible Route + | R1 | R2 | L1 L3 L5 L8 | | R1 | R2 | L1 L3 L5 L9 | | R1 | R2 | L2 L4 L6 L7 L8 | | R1 | R2 | L2 L4 L6 L7 L9 | | R1 | R2 | L2 L4 L6 L10 | | R1 | R3 | L1 L3 L5 L12 L15 L18 | | R1 | N7 | L2 L4 L6 L11 | | N7 | R3 | L16 L17 | | N7 | R2 | L16 L15 L12 L9 | | R2 | R3 | L8 L12 L15 L18 | | R2 | R3 | L8 L7 L11 L16 L17 | | R2 | R3 | L9 L12 L15 L18 | | R2 | R3 | L9 L7 L11 L16 L17 | Given a request to establish a LSP between R1 and R2 the RWA algorithm finds the following possible solutions: +WL + Path + | WL1| L1 L3 L5 L8 | | WL1| L1 L3 L5 L9 | | WL2| L2 L4 L6 L7 L8| | WL2| L2 L4 L6 L7 L9| | WL2| L2 L4 L6 L10 | Assume now that the RWA chooses WL1 and the Path L1 L3 L5 L8 for the requested LSP. Next, another LSP is signaled from R1 to R2. Given the established LSP using WL1, the following table shows the available paths: +WL + Path + | WL2| L2 L4 L6 L7 L9| | WL2| L2 L4 L6 L10 | Assume now that the RWA chooses WL2 and the path L2 L4 L6 L7 L9 for the establishment of the new LSP. Faced with another LSP request -this time from R2 to R3 - can not be fulfilled since the only four possible paths (starting at L8 and L9) are already in use. 5.3. Resource Optimization The preceding example gives rise to another use case: The optimization of network resources. Optimization can be achieved on a number of layers (e.g. through electrical or optical multiplexing of Bernstein and Lee Expires April 9, 2010[Page 30] Internet-Draft Wavelength Switched Optical Networks October 2009 client signals) or by re-optimizing the solutions found by the RWA algorithm. Given the above example again, assume that the RWA algorithm should find a path between R2 and R3. The only possible path to reach R3 from R2 needs to use L9. L9 however is blocked by one of the LSPs from R1. 5.4. Support for Rerouting It is also envisioned that the extensions to GMPLS and PCE support rerouting of wavelengths in case of failures. Assume for this discussion that the only two LSPs in use in the system are: LSP1: WL1 L1 L3 L5 L8 LSP2: WL2 L2 L4 L6 L7 L9 Assume furthermore that the link L5 fails. The RWA can now find the following alternate path and and establish that path: R1 -> N7 -> R2 Level 3 regeneration will take place at N7, so that the complete path looks like this: R1 -> L2 L4 L6 L11 L13 -> O1 -> L14 L16 L15 L12 L9 -> R2 6. GMPLS & PCE Implications The presence and amount of wavelength conversion available at a wavelength switching interface has an impact on the information that needs to be transferred by the control plane (GMPLS) and the PCE architecture. Current GMPLS and PCE standards can address the full wavelength conversion case so the following will only address the limited and no wavelength conversion cases. 6.1. Implications for GMPLS signaling Basic support for WSON signaling already exists in GMPLS with the lambda (value 9) LSP encoding type [RFC3471], or for G.709 compatible optical channels, the LSP encoding type (value = 13) "G.709 Optical Channel" from [RFC4328]. However a number of practical issues arise Bernstein and Lee Expires April 9, 2010[Page 31] Internet-Draft Wavelength Switched Optical Networks October 2009 in the identification of wavelengths and signals, and distributed wavelength assignment processes which are discussed below. 6.1.1. Identifying Wavelengths and Signals As previously stated a global fixed mapping between wavelengths and labels simplifies the characterization of WDM links and WSON devices. Furthermore such a mapping as described in [Otani] eases communication between PCE and WSON PCCs. 6.1.2. Combined RWA/Separate Routing WA support In either the combined RWA or separate routing WA cases, the node initiating the signaling will have a route from the source to destination along with the wavelengths (generalized labels) to be used along portions of the path. Current GMPLS signaling supports an explicit route object (ERO) and within an ERO an ERO Label subobject can be use to indicate the wavelength to be used at a particular node. In case the local label map approach is used the label sub- object entry in the ERO has to be translated appropriately. 6.1.3. Distributed Wavelength Assignment: Unidirectional, No Converters GMPLS signaling for a uni-directional lightpath LSP allows for the use of a label set object in the RSVP-TE path message. The processing of the label set object to take the intersection of available lambdas along a path can be performed resulting in the set of available lambda being known to the destination that can then use a wavelength selection algorithm to choose a lambda. For example, the following is a non-exhaustive subset of wavelength assignment (WA) approaches discussed in [HZang00]: 1. Random: Looks at all available wavelengths for the light path then chooses from those available at random. 2. First Fit: Wavelengths are ordered, first available (on all links) is chosen. 3. Most Used: Out of the wavelengths available on the path attempts to select most use wavelength in network. 4. Least Loaded: For multi-fiber networks. Chooses the wavelength j that maximizes minimum of the difference between the number of fibers on link l and the number of fibers on link l with wavelength j occupied. Bernstein and Lee Expires April 9, 2010[Page 32] Internet-Draft Wavelength Switched Optical Networks October 2009 As can be seen from the above short list, wavelength assignment methods have differing information or processing requirements. The information requirements of these methods are as follows: 1. Random: nothing more than the available wavelength set. 2. First Fit: nothing more than the available wavelength set. 3. Most Used: the available wavelength set and information on global wavelength use in the network. 4. Least Loaded: the available wavelength set and information concerning the wavelength dependent loading for each link (this applies to multi-fiber links). This could be obtained via global information or via supplemental information passed via the signaling protocol. In case (3) above the global information needed by the wavelength assignment could be derived from suitably enhanced GMPLS routing. Note however this information need not be accurate enough for combined RWA computation. GMPLS signaling does not provide a way to indicate that a particular wavelength assignment algorithm should be used. 6.1.4. Distributed Wavelength Assignment: Unidirectional, Limited Converters The previous outlined the case with no wavelength converters. In the case of wavelength converters, nodes with wavelength converters would need to make the decision as to whether to perform conversion. One indicator for this would be that the set of available wavelengths which is obtained via the intersection of the incoming label set and the egress links available wavelengths is either null or deemed too small to permit successful completion. At this point the node would need to remember that it will apply wavelength conversion and will be responsible for assigning the wavelength on the previous lambda-contiguous segment when the RSVP-TE RESV message passes by. The node will pass on an enlarged label set reflecting only the limitations of the wavelength converter and the egress link. The record route option in RVSP-TE signaling can be used to show where wavelength conversion has taken place. 6.1.5. Distributed Wavelength Assignment: Bidirectional, No Converters There are potential issues in the case of a bi-directional lightpath which requires the use of the same lambda in both directions. We can Bernstein and Lee Expires April 9, 2010[Page 33] Internet-Draft Wavelength Switched Optical Networks October 2009 try to use the above procedure to determine the available bidirectional lambda set if we use the interpretation that the available label set is available in both directions. However, a problem, arises in that bidirectional LSPs setup, according to [RFC3471] section 4.1, is indicated by the presence of an upstream label in the path message. However, until the intersection of the available label sets is obtained, e.g., at the destination node and the wavelength assignment algorithm has been run the upstream label information will not be available. Hence currently distributed wavelength assignment with bidirectional lightpaths is not supported. 6.2. Implications for GMPLS Routing GMPLS routing [RFC4202] currently defines an interface capability descriptor for "lambda switch capable" (LSC) which we can use to describe the interfaces on a ROADM or other type of wavelength selective switch. In addition to the topology information typically conveyed via an IGP, we would need to convey the following subsystem properties to minimally characterize a WSON: 1. WDM Link properties (allowed wavelengths). 2. Laser Transmitters (wavelength range). 3. ROADM/FOADM properties (connectivity matrix, port wavelength restrictions). 4. Wavelength Converter properties (per network element, may change if a common limited shared pool is used). This information is modeled in detail in [WSON-Info] and a compact encoding is given in [WSON-Encode]. 6.2.1. Wavelength-Specific Availability Information For wavelength assignment we need to know which specific wavelengths are available and which are occupied if we are going to run a combined RWA process or separate WA process as discussed in sections 4.1.1. 4.1.2. This is currently not possible with GMPLS routing extensions. In the routing extensions for GMPLS [RFC4202], requirements for layer-specific TE attributes are discussed. The RWA problem for optical networks without wavelength converters imposes an additional requirement for the lambda (or optical channel) layer: that of Bernstein and Lee Expires April 9, 2010[Page 34] Internet-Draft Wavelength Switched Optical Networks October 2009 knowing which specific wavelengths are in use. Note that current dense WDM (DWDM) systems range from 16 channels to 128 channels with advanced laboratory systems with as many as 300 channels. Given these channel limitations and if we take the approach of a global wavelength to label mapping or furnishing the local mappings to the PCEs then representing the use of wavelengths via a simple bit-map is feasible [WSON-Encode]. 6.2.2. WSON Routing Information Summary The following table summarizes the WSON information that could be conveyed via GMPLS routing and attempts to classify that information as to its static or dynamic nature and whether that information would tend to be associated with either a link or a node. Information Static/Dynamic Node/Link ------------------------------------------------------------------ Connectivity matrix Static Node Per port wavelength restrictions Static Node(1) WDM link (fiber) lambda ranges Static Link WDM link channel spacing Static Link Laser Transmitter range Static Link(2) Wavelength conversion capabilities Static(3) Node Maximum bandwidth per Wavelength Static Link Wavelength Availability Dynamic(4) Link Notes: 1. These are the per port wavelength restrictions of an optical device such as a ROADM and are independent of any optical constraints imposed by a fiber link. 2. This could also be viewed as a node capability. 3. This could be dynamic in the case of a limited pool of converters where the number available can change with connection establishment. Note we may want to include regeneration capabilities here since OEO converters are also regenerators. 4. Not necessarily needed in the case of distributed wavelength assignment via signaling. While the full complement of the information from the previous table is needed in the Combined RWA and the separate Routing and WA Bernstein and Lee Expires April 9, 2010[Page 35] Internet-Draft Wavelength Switched Optical Networks October 2009 architectures, in the case of Routing + distribute WA via signaling we only need the following information: Information Static/Dynamic Node/Link ------------------------------------------------------------------ Connectivity matrix Static Node Wavelength conversion capabilities Static(3) Node Information models and compact encodings for this information is provided in [WSON-Info] and [WSON-Encode]. 6.3. Optical Path Computation and Implications for PCE As previously noted the RWA problem can be computationally intensive [HZang00]. Such computationally intensive path computations and optimizations were part of the impetus for the PCE (path computation element) architecture. As the PCEP defines the procedures necessary to support both sequential [RFC5440] and global concurrent path computations [RFC5557], PCE is well positioned to support WSON-enabled RWA computation with some protocol enhancement. Implications for PCE generally fall into two main categories: (a) lightpath constraints and characteristics, (b) computation architectures. 6.3.1. Lightpath Constraints and Characteristics For the varying degrees of optimization that may be encountered in a network the following models of bulk and sequential lightpath requests are encountered: o Batch optimization, multiple lightpaths requested at one time. o Lightpath(s) and backup lightpath(s) requested at one time. o Single lightpath requested at a time. PCEP and PCE-GCO can be readily enhanced to support all of the potential models of RWA computation. Lightpath constraints include: o Bidirectional Assignment of wavelengths Bernstein and Lee Expires April 9, 2010[Page 36] Internet-Draft Wavelength Switched Optical Networks October 2009 o Possible simultaneous assignment of wavelength to primary and backup paths. o Tuning range constraint on optical transmitter. Lightpath characteristics can include: o Duration information (how long this connection may last) o Timeliness/Urgency information (how quickly is this connection needed) 6.3.2. Discovery of RWA Capable PCEs The algorithms and network information needed for solving the RWA are somewhat specialized and computationally intensive hence not all PCEs within a domain would necessarily need or want this capability. Hence, it would be useful via the mechanisms being established for PCE discovery [RFC5088] to indicate that a PCE has the ability to deal with the RWA problem. Reference [RFC5088] indicates that a sub- TLV could be allocated for this purpose. Recent progress on objective functions in PCE [RFC5541] would allow the operators to flexibly request differing objective functions per their need and applications. For instance, this would allow the operator to choose an objective function that minimizes the total network cost associated with setting up a set of paths concurrently. This would also allow operators to choose an objective function that results in a most evenly distributed link utilization. This implies that PCEP would easily accommodate wavelength selection algorithm in its objective function to be able to optimize the path computation from the perspective of wavelength assignment if chosen by the operators. 6.4. Summary of Impacts by RWA Architecture The following table summarizes for each RWA strategy the list of mandatory ("M") and optional ("O") control plane features according to GMPLS architectural blocks: o Information required by the path computation entity, o LSP request parameters used in either PCC to PCE situations or in signaling, o RSVP-TE LSP signaling parameters used in LSP establishment. Bernstein and Lee Expires April 9, 2010[Page 37] Internet-Draft Wavelength Switched Optical Networks October 2009 The table shows which enhancements are common to all architectures (R&WA, R+WA, R+DWA), which apply only to R&WA and R+WA (R+&WA), and which apply only to R+DWA. Note that this summary serves for the purpose of a generic reference. +-------------------------------------+-----+-------+-------+-------+ | | |Common | R+&WA | R+DWA | | Feature | ref +---+---+---+---+---+---+ | | | M | O | M | O | M | O | +-------------------------------------+-----+---+---+---+---+---+---+ | Generalized Label for Wavelength |5.1.1| x | | | | | | +-------------------------------------+-----+---+---+---+---+---+---+ | Flooding of information for the | | | | | | | | | routing phase | | | | | | | | | Node features | 3.3 | | | | | | | | Node type | | | x | | | | | | spectral X-connect constraint | | | | x | | | | | port X-connect constraint | | | | x | | | | | Transponders availability | | | x | | | | | | Transponders features | 3.2 | | x | | | | | | Converter availability | | | | x | | | | | Converter features | 3.4 | | | x | | | x | | TE-parameters of WDM links | 3.1 | x | | | | | | | Total Number of wavelength | | x | | | | | | | Number of wavelengths available | | x | | | | | | | Grid spacing | | x | | | | | | | Wavelength availability on links | 5.2 | | | x | | | | +-------------------------------------+-----+---+---+---+---+---+---+ | LSP request parameters | | | | | | | | | Signal features | 5.1 | | x | | | x | | | Modulation format | | | x | | | x | | | Modulation parameters | | | x | | | x | | | Specification of RWA method | 5.1 | | x | | | x | | | LSP time features | 4.3 | | x | | | | | +-------------------------------------+-----+---+---+---+---+---+---+ | Enriching signaling messages | | | | | | | | | Signal features | 5.1 | | | | | x | | +-------------------------------------+-----+---+---+---+---+---+---+ 7. Security Considerations This document has no requirement for a change to the security models within GMPLS and associated protocols. That is the OSPF-TE, RSVP-TE, and PCEP security models could be operated unchanged. However satisfying the requirements for RWA using the existing protocols may significantly affect the loading of those protocols. This makes the operation of the network more vulnerable to denial of Bernstein and Lee Expires April 9, 2010[Page 38] Internet-Draft Wavelength Switched Optical Networks October 2009 service attacks. Therefore additional care maybe required to ensure that the protocols are secure in the WSON environment. Furthermore the additional information distributed in order to address the RWA problem represents a disclosure of network capabilities that an operator may wish to keep private. Consideration should be given to securing this information. 8. IANA Considerations This document makes no request for IANA actions. 9. Acknowledgments The authors would like to thank Adrian Farrel for many helpful comments that greatly improved the contents of this draft. This document was prepared using 2-Word-v2.0.template.dot. Bernstein and Lee Expires April 9, 2010[Page 39] Internet-Draft Wavelength Switched Optical Networks October 2009 10. References 10.1. Normative References [RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, January 2003. [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering (TE) Extensions to OSPF Version 2", RFC 3630, September 2003. [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004. [RFC4201] Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling in MPLS Traffic Engineering (TE)", RFC 4201, October 2005. [RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4202, October 2005. [RFC4328] Papadimitriou, D., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Extensions for G.709 Optical Transport Networks Control", RFC 4328, January 2006. [G.694.1] ITU-T Recommendation G.694.1, "Spectral grids for WDM applications: DWDM frequency grid", June, 2002. [RFC5088] J.L. Le Roux, J.P. Vasseur, Yuichi Ikejiri, and Raymond Zhang, "OSPF protocol extensions for Path Computation Element (PCE) Discovery", January 2008. [RFC5557] Y. Lee, J.L. Le Roux, D. King, and E. Oki, "Path Computation Element Communication Protocol (PCECP) Requirements and Protocol Extensions In Support of Global Concurrent Optimization", RFC 5557, July 2009. [RFC5440] J.P. Vasseur and J.L. Le Roux (Editors), "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, May 2009. [RFC5541] J.L. Le Roux, J.P. Vasseur, and Y. Lee, "Encoding of Objective Functions in Path Computation Element (PCE) communication and discovery protocols", RFC 5541, July 2009. Bernstein and Lee Expires April 9, 2010[Page 40] Internet-Draft Wavelength Switched Optical Networks October 2009 [WSON-Compat] G. Bernstein, Y. Lee, B. Mack-Crane, "WSON Signal Characteristics and Network Element Compatibility Constraints for GMPLS", draft-bernstein-ccamp-wson- compatibility, work in progress. [WSON-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "Routing and Wavelength Assignment Information Encoding for Wavelength Switched Optical Networks", draft-bernstein- ccamp-wson-encode, work in progress. [WSON-Imp] Y. Lee, G. Bernstein, D. Li, G. Martinelli, "A Framework for the Control of Wavelength Switched Optical Networks (WSON) with Impairments", draft-ietf-ccamp-wson- impairments, work in progress. [WSON-Info] Y. Lee, G. Bernstein, D. Li, W. Imajuku, "Routing and Wavelength Assignment Information for Wavelength Switched Optical Networks", draft-bernstein-ccamp-wson-info, work in progress [PCEP-RWA] Y. Lee, G. Bernstein, J. Martensson, T. Takeda, T. Otani, "PCEP Requirements for WSON Routing and Wavelength Assignment", draft-lee-pce-wson-routing-wavelength, work in progress. 10.2. Informative References [HZang00] H. Zang, J. Jue and B. Mukherjeee, "A review of routing and wavelength assignment approaches for wavelength-routed optical WDM networks", Optical Networks Magazine, January 2000. [Coldren04] Larry A. Coldren, G. A. Fish, Y. Akulova, J. S. Barton, L. Johansson and C. W. Coldren, "Tunable Seiconductor Lasers: A Tutorial", Journal of Lightwave Technology, vol. 22, no. 1, pp. 193-202, January 2004. [Chu03] Xiaowen Chu, Bo Li and Chlamtac I, "Wavelength converter placement under different RWA algorithms in wavelength- routed all-optical networks", IEEE Transactions on Communications, vol. 51, no. 4, pp. 607-617, April 2003. [Buus06] Jens Buus EJM, "Tunable Lasers in Optical Networks", Journal of Lightware Technology, vol. 24, no. 1, pp. 5-11, January 2006. Bernstein and Lee Expires April 9, 2010[Page 41] Internet-Draft Wavelength Switched Optical Networks October 2009 [Basch06] E. Bert Bash, Roman Egorov, Steven Gringeri and Stuart Elby, "Architectural Tradeoffs for Reconfigurable Dense Wavelength-Division Multiplexing Systems", IEEE Journal of Selected Topics in Quantum Electronics, vol. 12, no. 4, pp. 615-626, July/August 2006. [Otani] T. Otani, H. Guo, K. Miyazaki, D. Caviglia, "Generalized Labels of Lambda-Switching Capable Label Switching Routers (LSR)", work in progress: draft-otani-ccamp-gmpls-g-694- lambda-labels, work in progress. [Winzer06] Peter J. Winzer and Rene-Jean Essiambre, "Advanced Optical Modulation Formats", Proceedings of the IEEE, vol. 94, no. 5, pp. 952-985, May 2006. [G.652] ITU-T Recommendation G.652, Characteristics of a single-mode optical fibre and cable, June 2005. [G.653] ITU-T Recommendation G.653, Characteristics of a dispersion- shifted single-mode optical fibre and cable, December 2006. [G.654] ITU-T Recommendation G.654, Characteristics of a cut-off shifted single-mode optical fibre and cable, December 2006. [G.655] ITU-T Recommendation G.655, Characteristics of a non-zero dispersion-shifted single-mode optical fibre and cable, March 2006. [G.656] ITU-T Recommendation G.656, Characteristics of a fibre and cable with non-zero dispersion for wideband optical transport, December 2006. [G.671] ITU-T Recommendation G.671, Transmission characteristics of optical components and subsystems, January 2005. [G.872] ITU-T Recommendation G.872, Architecture of optical transport networks, November 2001. [G.959.1] ITU-T Recommendation G.959.1, Optical Transport Network Physical Layer Interfaces, March 2006. [G.694.1] ITU-T Recommendation G.694.1, Spectral grids for WDM applications: DWDM frequency grid, June 2002. [G.694.2] ITU-T Recommendation G.694.2, Spectral grids for WDM applications: CWDM wavelength grid, December 2003. Bernstein and Lee Expires April 9, 2010[Page 42] Internet-Draft Wavelength Switched Optical Networks October 2009 [G.Sup39] ITU-T Series G Supplement 39, Optical system design and engineering considerations, February 2006. [G.Sup43] ITU-T Series G Supplement 43, Transport of IEEE 10G base-R in optical transport networks (OTN), November 2006. [Imajuku] W. Imajuku, Y. Sone, I. Nishioka, S. Seno, "Routing Extensions to Support Network Elements with Switching Constraint", work in progress: draft-imajuku-ccamp-rtg- switching-constraint-02.txt, July 2007. [Ozdaglar03] Asuman E. Ozdaglar and Dimitri P. Bertsekas, "Routing and wavelength assignment in optical networks," IEEE/ACM Transactions on Networking, vol. 11, 2003, pp. 259 -272. [RFC4054] Strand, J. and A. Chiu, "Impairments and Other Constraints on Optical Layer Routing", RFC 4054, May 2005. [RFC4606] Mannie, E. and D. Papadimitriou, "Generalized Multi- Protocol Label Switching (GMPLS) Extensions for Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) Control", RFC 4606, August 2006. [WC-Pool] G. Bernstein, Y. Lee, "Modeling WDM Switching Systems including Wavelength Converters" to appear www.grotto- networking.com, 2008. Bernstein and Lee Expires April 9, 2010[Page 43] Internet-Draft Wavelength Switched Optical Networks October 2009 11. Contributors Snigdho Bardalai Fujitsu Email: Snigdho.Bardalai@us.fujitsu.com Diego Caviglia Ericsson Via A. Negrone 1/A 16153 Genoa Italy Phone: +39 010 600 3736 Email: diego.caviglia@(marconi.com, ericsson.com) Daniel King Aria Networks Email: daniel.king@aria-networks.com Itaru Nishioka NEC Corp. 1753 Simonumabe, Nakahara-ku, Kawasaki, Kanagawa 211-8666 Japan Phone: +81 44 396 3287 Email: i-nishioka@cb.jp.nec.com Lyndon Ong Ciena Email: Lyong@Ciena.com Pierre Peloso Alcatel-Lucent Route de Villejust - 91620 Nozay - France Email: pierre.peloso@alcatel-lucent.fr Jonathan Sadler Tellabs Email: Jonathan.Sadler@tellabs.com Dirk Schroetter Cisco Email: dschroet@cisco.com Jonas Martensson Acreo Electrum 236 16440 Kista, Sweden Email:Jonas.Martensson@acreo.se Bernstein and Lee Expires April 9, 2010[Page 44] Internet-Draft Wavelength Switched Optical Networks October 2009 Author's Addresses Greg M. Bernstein (ed.) Grotto Networking Fremont California, USA Phone: (510) 573-2237 Email: gregb@grotto-networking.com Young Lee (ed.) Huawei Technologies 1700 Alma Drive, Suite 100 Plano, TX 75075 USA Phone: (972) 509-5599 (x2240) Email: ylee@huawei.com Wataru Imajuku NTT Network Innovation Labs 1-1 Hikari-no-oka, Yokosuka, Kanagawa Japan Phone: +81-(46) 859-4315 Email: imajuku.wataru@lab.ntt.co.jp Intellectual Property Statement The IETF Trust takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in any IETF Document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Copies of Intellectual Property disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or Bernstein and Lee Expires April 9, 2010[Page 45] Internet-Draft Wavelength Switched Optical Networks October 2009 users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement any standard or specification contained in an IETF Document. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity All IETF Documents and the information contained therein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Bernstein and Lee Expires April 9, 2010[Page 46]