Network Working Group Y. Lee (ed.) Internet Draft Huawei Intended status: Informational G. Bernstein (ed.) Expires: August 2011 Grotto Networking Wataru Imajuku NTT February 8, 2011 Framework for GMPLS and PCE Control of Wavelength Switched Optical Networks (WSON) draft-ietf-ccamp-rwa-wson-framework-12.txt Abstract This document 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, it examines Routing and Wavelength Assignment (RWA) of optical paths. This document 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. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt Bernstein and Lee Expires August 8, 2011 [Page 1] Internet-Draft Wavelength Switched Optical Networks February 2011 The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 8, 2011. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction...................................................4 2. Terminology....................................................5 3. Wavelength Switched Optical Networks...........................6 3.1. WDM and CWDM Links........................................6 3.2. Optical Transmitters and Receivers........................8 3.3. Optical Signals in WSONs..................................9 3.3.1. Optical Tributary Signals...........................10 3.3.2. WSON Signal Characteristics.........................10 3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs............11 3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs.......11 3.4.2. Splitters...........................................14 3.4.3. Combiners...........................................15 3.4.4. Fixed Optical Add/Drop Multiplexers.................15 3.5. Electro-Optical Systems..................................16 3.5.1. Regenerators........................................16 3.5.2. OEO Switches........................................19 3.6. Wavelength Converters....................................19 3.6.1. Wavelength Converter Pool Modeling..................21 3.7. Characterizing Electro-Optical Network Elements..........25 3.7.1. Input Constraints...................................26 3.7.2. Output Constraints..................................26 3.7.3. Processing Capabilities.............................27 Bernstein and Lee Expires August 8, 2011 [Page 2] Internet-Draft Wavelength Switched Optical Networks February 2011 4. Routing and Wavelength Assignment and the Control Plane.......28 4.1. Architectural Approaches to RWA..........................28 4.1.1. Combined RWA (R&WA).................................29 4.1.2. Separated R and WA (R+WA)...........................29 4.1.3. Routing and Distributed WA (R+DWA)..................30 4.2. Conveying information needed by RWA......................30 5. Modeling Examples and Control Plane Use Cases.................31 5.1. Network Modeling for GMPLS/PCE Control...................31 5.1.1. Describing the WSON nodes...........................32 5.1.2. Describing the links................................34 5.2. RWA Path Computation and Establishment...................35 5.3. Resource Optimization....................................36 5.4. Support for Rerouting....................................37 5.5. Electro-Optical Networking Scenarios.....................37 5.5.1. Fixed Regeneration Points...........................37 5.5.2. Shared Regeneration Pools...........................38 5.5.3. Reconfigurable Regenerators.........................38 5.5.4. Relation to Translucent Networks....................38 6. GMPLS and PCE Implications....................................39 6.1. Implications for GMPLS signaling.........................39 6.1.1. Identifying Wavelengths and Signals.................39 6.1.2. WSON Signals and Network Element Processing.........40 6.1.3. Combined RWA/Separate Routing WA support............40 6.1.4. Distributed Wavelength Assignment: Unidirectional, No Converters.................................................41 6.1.5. Distributed Wavelength Assignment: Unidirectional, Limited Converters.........................................41 6.1.6. Distributed Wavelength Assignment: Bidirectional, No Converters.................................................41 6.2. Implications for GMPLS Routing...........................42 6.2.1. Electro-Optical Element Signal Compatibility........42 6.2.2. Wavelength-Specific Availability Information........43 6.2.3. WSON Routing Information Summary....................43 6.3. Optical Path Computation and Implications for PCE........45 6.3.1. Optical path Constraints and Characteristics........45 6.3.2. Electro-Optical Element Signal Compatibility........45 6.3.3. Discovery of RWA Capable PCEs.......................46 7. Security Considerations.......................................46 8. IANA Considerations...........................................47 9. Acknowledgments...............................................47 10. References...................................................48 10.1. Normative References....................................48 10.2. Informative References..................................49 11. Contributors.................................................51 Author's Addresses...............................................52 Intellectual Property Statement..................................52 Disclaimer of Validity...........................................53 Bernstein and Lee Expires August 8, 2011 [Page 3] Internet-Draft Wavelength Switched Optical Networks February 2011 1. Introduction Wavelength Switched Optical Networks (WSONs) are constructed from subsystems that include Wavelength Division Multiplexed (WDM) links, tunable transmitters and receivers, Reconfigurable Optical Add/Drop Multiplexers (ROADM), wavelength converters, and electro-optical network elements. A WSON is a WDM-based optical network in which switching is performed selectively based on the center wavelength of an optical signal. WSONs can differ from other types of GMPLS networks in that many types of WSON nodes are highly asymmetric with respect to their switching capabilities, compatibility of signal types and network elements may need to be considered, and label assignment can be non- local. In order to provision an optical connection (an optical path) through a WSON certain wavelength continuity and resource availability constraints must be met to determine viable and optimal paths through the WSON. The determination of paths is known as Routing and Wavelength Assignment (RWA). Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes an architecture and a set of control plane protocols that can be used to operate data networks ranging from packet switch capable networks, through those networks that use time division multiplexing, to WDM networks. The Path Computation Element (PCE) architecture [RFC4655] defines functional components that can be used to compute and suggest appropriate paths in connection-oriented traffic-engineered networks. This document provides a framework for applying the GMPLS architecture and protocols [RFC3945], and the PCE architecture [RFC4655] to the control and operation of WSONs. To aid in this process this document also provides an overview of the subsystems and processes that comprise WSONs, and describes RWA so that the information requirements, both static and dynamic, can be identified to explain how the information can be modeled for use by GMPLS and PCE systems. This work will facilitate the development of protocol solution models and protocol extensions within the GMPLS and PCE protocol families. Different WSONs such as access, metro, and long haul may apply different techniques for dealing with optical impairments hence this document does not address optical impairments in any depth. Note that this document focuses on the generic properties of links, switches and path selection constraints that occur in many types of WSONs. See [WSON-Imp] for more information on optical impairments and GMPLS. Bernstein and Lee Expires August 8, 2011 [Page 4] Internet-Draft Wavelength Switched Optical Networks February 2011 2. Terminology Add/Drop Multiplexers (ADM): An optical device used in WDM networks composed of one or more line side ports and typically many tributary ports. CWDM: Coarse Wavelength Division Multiplexing. DWDM: Dense Wavelength Division Multiplexing. Degree: The degree of an optical device (e.g., ROADM) is given by a count of its line side ports. Drop and continue: A simple multi-cast feature of some ADM where a selected wavelength can be switched out of both a tributary (drop) port and a line side port. FOADM: Fixed Optical Add/Drop Multiplexer. GMPLS: Generalized Multi-Protocol Label Switching. Line side: In WDM system line side ports and links typically can carry the full multiplex of wavelength signals, as compared to tributary (add or drop ports) that typically carry a few (typically one) wavelength signals. OXC: Optical cross connect. An optical switching element in which a signal on any input port can reach any output port. PCC: Path Computation Client. Any client application requesting a path computation to be performed by the Path Computation Element. PCE: Path Computation Element. An entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints. PCEP: PCE Communication Protocol. The communication protocol between a Path Computation Client and Path Computation Element. ROADM: Reconfigurable Optical Add/Drop Multiplexer. A wavelength selective switching element featuring input and output line side ports as well as add/drop tributary ports. RWA: Routing and Wavelength Assignment. Transparent Network: A wavelength switched optical network that does not contain regenerators or wavelength converters. Bernstein and Lee Expires August 8, 2011 [Page 5] Internet-Draft Wavelength Switched Optical Networks February 2011 Translucent Network: A wavelength switched optical network that is predominantly transparent but may also contain limited numbers of regenerators and/or wavelength converters. Tributary: A link or port on a WDM system that can carry significantly less than the full multiplex of wavelength signals found on the line side links/ports. Typical tributary ports are the add and drop ports on an ADM and these support only a single wavelength channel. 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. WDM: Wavelength Division Multiplexing. Wavelength Switched Optical Networks (WSONs): 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 range in size from continent spanning long haul networks, to metropolitan networks, to residential access networks. In all these cases, the main concern is 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 addition, if electro-optical network elements are used in the WSON, additional compatibility constraints may be imposed by the network elements on various optical signal parameters. The subsequent sections review and model some of the major subsystems of a WSON with an emphasis on those aspects that are of relevance to the control plane. In particular, WDM links, optical transmitters, ROADMs, and wavelength converters are examined. 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. Examples include access networks, metro, long haul, and submarine links. International Telecommunication Union - Telecommunication Standardization Sector (ITU-T) standards exist for various types of fibers. Although fiber can be categorized into Single mode fibers (SMF) and Multi-mode fibers (MMF), the latter are typically used for short-reach campus and premise applications. SMF are used for longer-reach applications and therefore are the primary Bernstein and Lee Expires August 8, 2011 [Page 6] Internet-Draft Wavelength Switched Optical Networks February 2011 concern of this document. 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 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 a discontinuous acceptable wavelength range for a particular link may be needed and is modeled. Also some systems will utilize more than one band. This is particularly true for CWDM systems. Current technology subdivides 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, Spectral grids for WDM applications: DWDM frequency grid [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, Spectral grids for WDM applications: CWDM wavelength grid [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 defined for GMPLS, see [RFC3471]. A label representation for these ITU-T grids is given in [Otani] and provides a common label format to be used in Bernstein and Lee Expires August 8, 2011 [Page 7] Internet-Draft Wavelength Switched Optical Networks February 2011 signaling optical paths. Further, these ITU-T grid based labels can also be used to describe WDM links, ROADM ports, and wavelength converters for the purposes of path selection. 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 significant system engineering and a fairly limited range of wavelengths. Hence the following information is needed as parameters to perform basic, impairment unaware, modeling of a WDM link: o Wavelength range(s): Given a mapping between labels and the ITU-T grids each range could be expressed in terms of a tuple (lambda1, lambda2) or (freq1, freq1) where the lambdas or frequencies can be represented by 32 bit integers. o Channel spacing: Currently there are five channel spacings used in DWDM systems and a single channel spacing defined for CWDM systems. For a particular link this information is relatively static, as changes to these properties generally require hardware upgrades. Such information may be used locally during wavelength assignment via signaling, similar to label restrictions in MPLS or used by a PCE in providing combined RWA. 3.2. Optical Transmitters and Receivers WDM optical systems make use of optical transmitters and receivers utilizing different wavelengths (frequencies). Some transmitters are manufactured for a specific wavelength of operation, that is, the manufactured frequency cannot be changed. First introduced to reduce inventory costs, tunable optical transmitters and receivers are deployed in some systems, and allow flexibility in the wavelength used for optical transmission/reception. Such tunable optics aid in path selection. Fundamental modeling parameters from the control plane perspective optical transmitters and receivers are: o Tunable: Do the transmitter and receivers operate at variable or fixed wavelength. Bernstein and Lee Expires August 8, 2011 [Page 8] Internet-Draft Wavelength Switched Optical Networks February 2011 o Tuning range: This is the frequency or wavelength range over which the optics can be tuned. With the fixed mapping of labels to lambdas as proposed in [Otani] this can be expressed as a tuple (lambda1, lambda2) or (freq1, freq2) where lambda1 and lambda2 or freq1 and freq2 are the labels representing the lower and upper bounds in wavelength. 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 usable for fast protection applications. o Spectral characteristics and stability: The spectral shape of a 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 closest channel spacing with which the transmitter can be used. Note that ITU-T recommendations specify many aspects of an optical 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 the Label Switched Path (LSP) provisioning in a properly designed system. Also note that optical components can degrade and fail over time. This presents the possibility of the failure of a LSP (optical path) without either a node or link failure. Hence, additional mechanisms may be necessary to detect and differentiate this failure from the others, e.g., one doesn't want to initiate mesh restoration if the source transmitter has failed, since the optical transmitter will still be failed on the alternate optical path. 3.3. Optical Signals in WSONs In WSONs the fundamental unit of switching is intuitively that of a "wavelength". The transmitters and receivers in these networks will deal with one wavelength at a time, while the switching systems themselves can deal with multiple wavelengths at a time. Hence multichannel DWDM networks with single channel interfaces are the prime focus of this document as opposed to multi-channel interfaces. Interfaces of this type are defined in ITU-T recommendations [G.698.1] and [G.698.2]. Key non-impairment related parameters defined in [G.698.1] and [G.698.2] are: (a) Minimum channel spacing (GHz) Bernstein and Lee Expires August 8, 2011 [Page 9] Internet-Draft Wavelength Switched Optical Networks February 2011 (b) Minimum and maximum central frequency (c) Bit-rate/Line coding (modulation) of optical tributary signals For the purposes of modeling the WSON in the control plane, (a) and (b) are considered as properties of the link and restrictions on the GMPLS labels while (c) is a property of the "signal". 3.3.1. Optical Tributary Signals The optical interface specifications [G.698.1], [G.698.2], and [G.959.1] all use the concept of an optical tributary signal which is defined as "a single channel signal that is placed within an optical channel for transport across the optical network". Note the use of the qualifier "tributary" to indicate that this is a single channel entity and not a multichannel optical signal. There are currently a number of different types of optical tributary signals, which are known as "optical tributary signal classes". These are currently characterized by a modulation format and bit rate range [G.959.1]: (a) Optical tributary signal class NRZ 1.25G (b) Optical tributary signal class NRZ 2.5G (c) Optical tributary signal class NRZ 10G (d) Optical tributary signal class NRZ 40G (e) Optical tributary signal class RZ 40G Note that with advances in technology more optical tributary signal classes may be added and that this is currently an active area for development and standardization. In particular at the 40G rate there are a number of non-standardized advanced modulation formats that have seen significant deployment including Differential Phase Shift Keying (DPSK) and Phase Shaped Binary Transmission (PSBT). According to [G.698.2] it is important to fully specify the bit rate of the optical tributary signal. Hence it is seen that modulation format (optical tributary signal class) and bit rate are key parameters in characterizing the optical tributary signal. 3.3.2. WSON Signal Characteristics An optical tributary signal referenced in ITU-T [G.698.1] and [G.698.2] is referred to as the "signal" in this document. This Bernstein and Lee Expires August 8, 2011 [Page 10] Internet-Draft Wavelength Switched Optical Networks February 2011 corresponds to the "lambda" LSP in GMPLS. For signal compatibility purposes with electro-optical network elements, the following signal characteristics are considered: 1. Optical tributary signal class (modulation format). 2. FEC: whether forward error correction is used in the digital stream and what type of error correcting code is used. 3. Center frequency (wavelength). 4. Bit rate. 5. G-PID: general protocol identifier for the information format. The first three items on this list can change as a WSON signal traverses the optical network with elements that include regenerators, Optical-to-Electrical (OEO) switches, or wavelength converters. Bit rate and G-PID would not change since they describe the encoded bit stream. A set of G-PID values is already defined for lambda switching in [RFC3471] and [RFC4328]. Note that a number of non-standard or proprietary modulation formats and FEC codes are commonly used in WSONs. For some digital bit streams the presence of Forward Error Correction (FEC) can be detected, e.g., in [G.707] this is indicated in the signal itself via the FEC Status Indication (FSI) byte, while in [G.709] this can be inferred from whether the FEC field of the Optical Channel Transport Unit-k (OTUk) is all zeros or not. 3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs Definitions of various optical devices such as ROADMs, Optical Cross- connects (OXCs), splitters, combiners and Fixed Optical Add-Drop Multiplexers (FOADMs) and their parameters can be found in [G.671]. Only a subset of these relevant to the control plane and their non- impairment related properties are considered in the following sections. 3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs ROADMs are available in different forms and technologies. 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 August 8, 2011 [Page 11] Internet-Draft Wavelength Switched Optical Networks February 2011 Line side input +---------------------+ Line side output --->| |---> | | | ROADM | | | | | +---------------------+ | | | | o o o o | | | | | | | | O O O O | | | | Tributary Side: Drop (output) Add (input) Figure 1. Degree-2 unidirectional ROADM The key feature across all ROADM types is their highly asymmetric switching capability. In the ROADM of Figure 1, signals introduced via the add ports can only be sent on the line side output port and not on any of the drop ports. The term "degree" is used to refer to the number of line side ports (input and output) of a ROADM, and does not include the number of "add" or "drop" ports. The add and drop ports are sometimes 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 it is necessary to know the switched connectivity offered by such a network element to effectively utilize it. A straightforward way to represent this is via a "switched connectivity" matrix A where Amn = 0 or 1, depending upon whether a wavelength on input port m can be connected to output port n [Imajuku]. For the ROADM shown in Figure 1 the switched connectivity matrix can be expressed as: Input Output 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 input ports 2-5 are add ports, output ports 2-5 are drop ports and input port #1 and output port #1 are the line side (WDM) ports. For ROADMs, this matrix will be very sparse, and for OXCs the matrix will be very dense. Compact encodings and examples, including high degree ROADMs/OXCs, are given in [Gen-Encode]. A degree-4 ROADM is shown in Figure 2. Bernstein and Lee Expires August 8, 2011 [Page 12] Internet-Draft Wavelength Switched Optical Networks February 2011 +-----------------------+ Line side-1 --->| |---> Line side-2 Input (I1) | | Output (E2) Line side-1 <---| |<--- Line side-2 Output (E1) | | Input (I2) | ROADM | Line side-3 --->| |---> Line side-4 Input (I3) | | Output (E4) Line side-3 <---| |<--- Line side-4 Output (E3) | | Input (I4) | | +-----------------------+ | O | O | O | O | | | | | | | | O | O | O | O | Tributary Side: E5 I5 E6 I6 E7 I7 E8 I8 Figure 2. Degree-4 bidirectional 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 "bidirectional", i.e. if input port X can be connected to output port Y, typically input port Y can be connected to output port X, assuming the numbering is done in such a way that input X and output X correspond to the same line side direction or the same add/drop port. This makes the connectivity matrix symmetrical as shown below. Input Output 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 line side-2 and I8/E8 are add/drop ports to/from line side-4. Note Bernstein and Lee Expires August 8, 2011 [Page 13] Internet-Draft Wavelength Switched Optical Networks February 2011 that diagonal elements are zero since loopback is not supported in the example. If ports support loopback, diagonal elements would be set to one. Additional constraints may also apply to the various ports in a ROADM/OXC. The following restrictions and terms may be used: Colored port: an input or more typically an output (drop) port restricted to a single channel of fixed wavelength. Colorless port: an input or more typically an output (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 it is necessary to have 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]. 3.4.2. Splitters An optical splitter consists of a single input port and two or more output ports. The input optical signaled is essentially copied (with power loss) to all output ports. Using the modeling notions of Section 3.4.1. (Reconfigurable Add/Drop Multiplexers and OXCs) the input and output ports of a splitter would have the same wavelength restrictions. In addition a splitter is modeled by a connectivity matrix Amn as follows: Input Output 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 connectivity matrix but the fixed connectivity matrix of the device. Bernstein and Lee Expires August 8, 2011 [Page 14] Internet-Draft Wavelength Switched Optical Networks February 2011 3.4.3. Combiners An optical combiner is a device that combines the optical wavelengths carried by multiple input ports into a single multi-wavelength output 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 output port. The fixed connectivity matrix Amn for a combiner would look like: Input Output Port Port #1 --- #1: 1 #2 1 A = #3 1 ... 1 #N 1 3.4.4. Fixed Optical Add/Drop Multiplexers A fixed optical add/drop multiplexer can alter the course of an input wavelength in a preset way. In particular a given wavelength (or waveband) from a line side input port would be dropped to a fixed "tributary" output port. Depending on the device's construction that same wavelength may or may not also be sent out the line side output port. This is commonly referred to as "drop and continue" operation. There also may exist tributary input ports ("add" ports) whose signals are combined with each other and other line side signals. In general, to represent the routing properties of an FOADM it is necessary to have both a fixed connectivity matrix Amn as previously discussed and the precise wavelength restrictions for all input and output ports. From the wavelength restrictions on the tributary output ports, what wavelengths have been selected can be derived. From the wavelength restrictions on the tributary input ports, it can be seen which wavelengths have been added to the line side output port. Finally from the added wavelength information and the line side output wavelength restrictions it can be inferred which wavelengths have been continued. To summarize, the modeling methodology introduced in Section 3.4.1. (Reconfigurable Add/Drop Multiplexers and OXCs) 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]. Bernstein and Lee Expires August 8, 2011 [Page 15] Internet-Draft Wavelength Switched Optical Networks February 2011 3.5. Electro-Optical Systems This section describes how Electro-Optical Systems (e.g., OEO switches, wavelength converters, and regenerators) interact with the WSON signal characteristics listed in Section 3.3.2. (WSON Signal Characteristics) OEO switches, wavelength converters and regenerators all share a similar property: they can be more or less "transparent" to an "optical signal" depending on their functionality and/or implementation. Regenerators have been fairly well characterized in this regard and hence their properties can be described first. 3.5.1. Regenerators The various approaches to regeneration are discussed in ITU-T G.872 Annex A [G.872]. They map a number of functions into the so-called 1R, 2R and 3R categories of regenerators as summarized in Table 1 below: Table 1. Regenerator functionality mapped to general regenerator classes from [G.872]. --------------------------------------------------------------------- 1R | Equal amplification of all frequencies within the amplification | bandwidth. There is no restriction upon information formats. +----------------------------------------------------------------- | Amplification with different gain for frequencies within the | amplification bandwidth. This could be applied to both single- | channel and multi-channel systems. +----------------------------------------------------------------- | Dispersion compensation (phase distortion). This analogue | process can be applied in either single-channel or multi- | channel systems. --------------------------------------------------------------------- 2R | Any or all 1R functions. Noise suppression. +----------------------------------------------------------------- | Digital reshaping (Schmitt Trigger function) with no clock | recovery. This is applicable to individual channels and can be | used for different bit rates but is not transparent to line | coding (modulation). -------------------------------------------------------------------- 3R | Any or all 1R and 2R functions. Complete regeneration of the | pulse shape including clock recovery and retiming within | required jitter limits. -------------------------------------------------------------------- From this table it is seen that 1R regenerators are generally independent of signal modulation format (also known as line coding), but may work over a limited range of wavelength/frequencies. 2R Bernstein and Lee Expires August 8, 2011 [Page 16] Internet-Draft Wavelength Switched Optical Networks February 2011 regenerators are generally applicable to a single digital stream and are dependent upon modulation format (line coding) and to a lesser extent are limited to a range of bit rates (but not a specific bit rate). Finally, 3R regenerators apply to a single channel, are dependent upon the modulation format and generally sensitive to the bit rate of digital signal, i.e., either are designed to only handle a specific bit rate or need to be programmed to accept and regenerate a specific bit rate. In all these types of regenerators the digital bit stream contained within the optical or electrical signal is not modified. It is common for regenerators to modify the digital bit stream for performance monitoring and fault management purposes. Synchronous Optical Networking (SONET), Synchronous Digital Hierarchy (SDH) and Interfaces for the Optical Transport Network (G.709) all have digital signal "envelopes" designed to be used between "regenerators" (in this case 3R regenerators). In SONET this is known as the "section" signal, in SDH this is known as the "regenerator section" signal, in G.709 this is known as an OTUk. These signals reserve a portion of their frame structure (known as overhead) for use by regenerators. The nature of this overhead is summarized in Table 2 below. Bernstein and Lee Expires August 8, 2011 [Page 17] Internet-Draft Wavelength Switched Optical Networks February 2011 Table 2. SONET, SDH, and G.709 regenerator related overhead. +-----------------------------------------------------------------+ |Function | SONET/SDH | G.709 OTUk | | | Regenerator | | | | Section | | |------------------+----------------------+-----------------------| |Signal | J0 (section | Trail Trace | |Identifier | trace) | Identifier (TTI) | |------------------+----------------------+-----------------------| |Performance | BIP-8 (B1) | BIP-8 (within SM) | |Monitoring | | | |------------------+----------------------+-----------------------| |Management | D1-D3 bytes | GCC0 (general | |Communications | | communications | | | | channel) | |------------------+----------------------+-----------------------| |Fault Management | A1, A2 framing | FAS (frame alignment | | | bytes | signal), BDI(backward| | | | defect indication)BEI| | | | (backward error | | | | indication) | +------------------+----------------------+-----------------------| |Forward Error | P1,Q1 bytes | OTUk FEC | |Correction (FEC) | | | +-----------------------------------------------------------------+ In the previous table it is seen that frame alignment, signal identification, and FEC are supported. What table 2 also shows by its omission is that no switching or multiplexing occurs at this layer. This is a significant simplification for the control plane since control plane standards require a multi-layer approach when there are multiple switching layers, but not for "layering" to provide the management functions of Table 2. That is, many existing technologies covered by GMPLS contain extra management related layers that are essentially ignored by the control plane (though not by the management plane!). Hence, the approach here is to include regenerators and other devices at the WSON layer unless they provide higher layer switching and then a multi-layer or multi-region approach [RFC5212] is called for. However, this can result in regenerators having a dependence on the client signal type. Hence depending upon the regenerator technology the following constraints may be imposed by a regenerator device: Table 3. Regenerator Compatibility Constraints. Bernstein and Lee Expires August 8, 2011 [Page 18] Internet-Draft Wavelength Switched Optical Networks February 2011 +--------------------------------------------------------+ | Constraints | 1R | 2R | 3R | +--------------------------------------------------------+ | Limited Wavelength Range | x | x | x | +--------------------------------------------------------+ | Modulation Type Restriction | | x | x | +--------------------------------------------------------+ | Bit Rate Range Restriction | | x | x | +--------------------------------------------------------+ | Exact Bit Rate Restriction | | | x | +--------------------------------------------------------+ | Client Signal Dependence | | | x | +--------------------------------------------------------+ Note that the limited wavelength range constraint can be modeled for GMPLS signaling with the label set defined in [RFC3471] and that the modulation type restriction constraint includes FEC. 3.5.2. OEO Switches A common place where OEO processing may take place is within WSON switches that utilize (or contain) regenerators. This may be to convert the signal to an electronic form for switching then reconverting to an optical signal prior to output from the switch. Another common technique is to add regenerators to restore signal quality either before or after optical processing (switching). In the former case the regeneration is applied to adapt the signal to the switch fabric regardless of whether or not it is needed from a signal quality perspective. In either case these optical switches have essentially the same compatibility constraints as those which are described for regenerators in Table 3. 3.6. Wavelength Converters Wavelength converters take an input optical signal at one wavelength and emit an equivalent content optical signal at another wavelength on output. There are multiple approaches to building wavelength converters. One approach is based on OEO conversion with fixed or tunable optics on output. This approach can be dependent upon the signal rate and format, i.e., this is basically an electrical regenerator combined with a laser/receiver. Hence, this type of wavelength converter has signal processing restrictions that are Bernstein and Lee Expires August 8, 2011 [Page 19] Internet-Draft Wavelength Switched Optical Networks February 2011 essentially the same as those described for regenerators in Table 3 of section 3.5.1. Another 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 fixed or tunable optics. In this case there are typically multiple converters available since each use of an OEO switch can be thought of as a potential wavelength converter. 2. Wavelength conversion associated with ROADMs/OXCs. In this case there may be 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 there may be a limited amount of conversion. Also in this case the conversion may be used as part of optical path routing. Based on the above considerations, wavelength converters are modeled as follows: 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 input 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 they can be associated with input ports. 3. Wavelength converters have range restrictions that are either independent or dependent upon the input wavelength. In WSONs where wavelength converters are sparse an optical path may appear to loop or "backtrack" upon itself in order to reach a wavelength converter prior to continuing on to its destination. The Bernstein and Lee Expires August 8, 2011 [Page 20] Internet-Draft Wavelength Switched Optical Networks February 2011 lambda used on input to the wavelength converter would be different from the lambda coming back from 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. 3.6.1. 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 it is necessary 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 input wavelength on a particular input port to a desired output wavelength on a particular output port. 3. Limitations on the types of signals that can be converted and the conversions that can be performed. To model point 2 above, a technique similar to that used to model ROADMs and optical switches can be used, i.e., matrices to indicate possible connectivity along with wavelength constraints for links/ports. Since wavelength converters are considered a scarce resource it will be desirable to include as a minimum the usage state of individual wavelength converters in the pool. A three stage model is used as shown schematically in Figure 3. (Schematic diagram of wavelength converter pool model). This model represents N input ports (fibers), P wavelength converters, and M output ports (fibers). Since not all input ports can necessarily reach the converter pool, the model starts with a wavelength pool input matrix WI(i,p) = {0,1} where input port i can potentially reach wavelength converter p. Since not all wavelengths can necessarily reach all the converters or the converters may have limited input wavelength range there is a set of input port constraints for each wavelength converter. Currently it is assumed that a wavelength converter can only take a single Bernstein and Lee Expires August 8, 2011 [Page 21] Internet-Draft Wavelength Switched Optical Networks February 2011 wavelength on input. Each wavelength converter input port constraint can be modeled via a wavelength set mechanism. Next 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 [Gen- Encode]. After that, a set of wavelength converter output wavelength constraints is used. These constraints indicate what wavelengths a particular wavelength converter can generate or are restricted to generating due to internal switch structure. Finally, a wavelength pool output matrix WE(p,k) = {0,1} indicating whether the output from wavelength converter p can reach output port k. Examples of this method being used to model wavelength converter pools for several switch architectures are given in reference [Gen- Encode]. Bernstein and Lee Expires August 8, 2011 [Page 22] Internet-Draft Wavelength Switched Optical Networks February 2011 I1 +-------------+ +-------------+ E1 ----->| | +--------+ | |-----> I2 | +------+ WC #1 +-------+ | E2 ----->| | +--------+ | |-----> | Wavelength | | Wavelength | | Converter | +--------+ | Converter | | Pool +------+ WC #2 +-------+ Pool | | | +--------+ | | | Input | | Output | | Connection | . | Connection | | Matrix | . | Matrix | | | . | | | | | | IN | | +--------+ | | EM ----->| +------+ WC #P +-------+ |-----> | | +--------+ | | +-------------+ ^ ^ +-------------+ | | | | | | | | Input wavelength Output wavelength constraints for constraints for each converter each converter Figure 3. Schematic diagram of wavelength converter pool model. Figure 4 below shows a simple optical switch in a four wavelength DWDM system sharing wavelength converters in a general shared "per node" fashion. Bernstein and Lee Expires August 8, 2011 [Page 23] Internet-Draft Wavelength Switched Optical Networks February 2011 +-----------+ ___________ +------+ | |--------------------------->| | | |--------------------------->| 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 input and output pool matrices are simply: +-----+ +-----+ | 1 1 | | 1 1 | WI =| |, WE =| | | 1 1 | | 1 1 | +-----+ +-----+ Figure 5 shows a different wavelength pool architecture known as "shared per fiber". In this case the input and output pool matrices are simply: +-----+ +-----+ | 1 1 | | 1 0 | WI =| |, WE =| | | 1 1 | | 0 1 | +-----+ +-----+ Bernstein and Lee Expires August 8, 2011 [Page 24] Internet-Draft Wavelength Switched Optical Networks February 2011 +-----------+ +------+ | |--------------------------->| | | |--------------------------->| 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. 3.7. Characterizing Electro-Optical Network Elements In this section electro-optical WSON network elements are characterized by the three key functional components: input constraints, output constraints and processing capabilities. WSON Network Element +-----------------------+ WSON Signal | | | | WSON Signal | | | | ---------------> | | | | -----------------> | | | | +-----------------------+ <-----> <-------> <-----> Input Processing Output Figure 6. WSON Network Element Bernstein and Lee Expires August 8, 2011 [Page 25] Internet-Draft Wavelength Switched Optical Networks February 2011 3.7.1. Input Constraints Section 3. (Wavelength Switched Optical Networks) discussed the basic properties regenerators, OEO switches and wavelength converters. From these the following possible types of input constraints and properties are derived: 1. Acceptable Modulation formats. 2. Client Signal (G-PID) restrictions. 3. Bit Rate restrictions. 4. FEC coding restrictions. 5. Configurability: (a) none, (b) self-configuring, (c) required. These constraints are represented via simple lists. Note that the device may need to be "provisioned" via signaling or some other means to accept signals with some attributes versus others. In other cases the devices maybe relatively transparent to some attributes, e.g., such as a 2R regenerator to bit rate. Finally, some devices may be able to auto-detect some attributes and configure themselves, e.g., a 3R regenerator with bit rate detection mechanisms and flexible phase locking circuitry. To account for these different cases item 5 has been added, which describes the devices configurability. Note that such input constraints also apply to the termination of the WSON signal. 3.7.2. Output Constraints None of the network elements considered here modifies either the bit rate or the basic type of the client signal. However, they may modify the modulation format or the FEC code. Typically the following types of output constraints are seen: 1. Output modulation is the same as input modulation (default). 2. A limited set of output modulations is available. 3. Output FEC is the same as input FEC code (default). 4. A limited set of output FEC codes is available. Note that in cases (2) and (4) above, where there is more than one choice in the output modulation or FEC code then the network element Bernstein and Lee Expires August 8, 2011 [Page 26] Internet-Draft Wavelength Switched Optical Networks February 2011 will need to be configured on a per LSP basis as to which choice to use. 3.7.3. Processing Capabilities A general WSON network element (NE) can perform a number of signal processing functions including: (A) Regeneration (possibly different types). (B) Fault and Performance Monitoring. (C) Wavelength Conversion. (D) Switching. An NE may or may not have the ability to perform regeneration (of the one of the types previously discussed). In addition some nodes may have limited regeneration capability, i.e., a shared pool, which may be applied to selected signals traversing the NE. Hence to describe the regeneration capability of a link or node it is necessary to have at a minimum: 1. Regeneration capability: (a)fixed, (b) selective, (c) none. 2. Regeneration type: 1R, 2R, 3R. 3. Regeneration pool properties for the case of selective regeneration (input and output restrictions, availability). Note that the properties of shared regenerator pools would be essentially the same as that of wavelength converter pools modeled in section 3.6.1. (Wavelength Pool Convertor Modeling). Item (B), fault and performance monitoring, is typically outside the scope of the control plane. However, when the operations are to be performed on an LSP basis or on part of an LSP then the control plane can be of assistance in their configuration. Per LSP, per node, fault and performance monitoring examples include setting up a "section trace" (a regenerator overhead identifier) between two nodes, or intermediate optical performance monitoring at selected nodes along a path. Bernstein and Lee Expires August 8, 2011 [Page 27] Internet-Draft Wavelength Switched Optical Networks February 2011 4. Routing and Wavelength Assignment and the Control Plane From a control plane perspective, a wavelength-convertible network with full wavelength-conversion capability at each node can be controlled much like a packet MPLS-labeled network or a circuit- switched Time-division multiplexing (TDM) network with full time slot interchange capability is controlled. In this case, the path selection process needs to identify the Traffic Engineered (TE) links to be used by an optical path, and wavelength assignment can be made on a hop-by-hop basis. However, in the case of an optical network without wavelength converters, an optical path needs to be routed from source to destination and must use a single wavelength that is available along that path without "colliding" with a wavelength used by any other optical path that may share an optical fiber. This is sometimes referred to as a "wavelength continuity constraint". In the general case of limited or no wavelength converters the computation of both the links and wavelengths is known as RWA. The inputs to basic RWA are the requested optical path's source and destination, the network topology, the locations and capabilities of any wavelength converters, and the wavelengths available on each optical link. The output from an algorithm providing RWA is an explicit route through ROADMs, a wavelength for 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 the choice of specific RWA algorithm is out of the scope for this document. However there are a number of different approaches to dealing with RWA algorithm that can affect the division of effort between path computation/routing and signaling. 4.1. Architectural Approaches to RWA Two general computational approaches are taken to performing RWA. Some algorithms utilize a two-step procedure of path selection followed by wavelength assignment, and others perform RWA 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. The approaches Bernstein and Lee Expires August 8, 2011 [Page 28] Internet-Draft Wavelength Switched Optical Networks February 2011 are provided for reference purposes only, and other approaches are possible. 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 places: o In a PCE which maintains a complete and updated view of network state and provides path computation services to nodes (PCCs). o In an ingress node, in which case all nodes have the R&WA functionality and 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, one entity performs routing, while a second performs wavelength assignment. The first entity furnishes one or more paths to the second entity which will perform wavelength assignment and 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 wavelength 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. Hence, while 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 specific network node capabilities. Bernstein and Lee Expires August 8, 2011 [Page 29] Internet-Draft Wavelength Switched Optical Networks February 2011 4.1.3. Routing and Distributed WA (R+DWA) In this case, one entity performs routing, while wavelength assignment is performed on a hop-by-hop, distributed manner along the previously computed path. 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. GMPLS, per [RFC3471], includes support for the communication of the set of labels (wavelengths) that may be used between nodes via a Label Set. When conversion is not performed at an intermediate node, a hop generates the Label Set it sends to the next hop based on the intersection of the Label Set received from the previous hop and the wavelengths available on the node's switch and ongoing interface. The generation of the outgoing Label Set 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 node selects one label in the Label Set which it received; additionally the node can apply local policy during label selection. GMPLS also provides support for the signaling of bidirectional optical paths. Depending on these policies a wavelength assignment may not be found or one may be found that consumes 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. This solution may be facilitated via signaling extensions which ease its functioning and possibly enhance its performance with respect to blocking probability. Note that this approach requires less information dissemination than the other techniques described. The first entity may be a PCE or the ingress node of the LSP. 4.2. Conveying information needed by RWA The previous sections have characterized WSONs and optical path requests. In particular, high level models of the information used by RWA process were presented. This information can be viewed as either relatively static, i.e., changing with hardware changes (including possibly failures), or relatively dynamic, i.e., those that can change with optical path provisioning. The time requirement in which an entity involved in RWA process needs to be notified of such changes is fairly situational. For example, for network restoration Bernstein and Lee Expires August 8, 2011 [Page 30] Internet-Draft Wavelength Switched Optical Networks February 2011 purposes, learning of a hardware failure or of new hardware coming online to provide restoration 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, i.e., GMPLS routing and signaling. Note that routing protocols can be used to convey both static and dynamic information. o Management protocols such as NetConf, SNMPv3, CLI, and CORBA. o Directory services and accompanying protocols. These are typically used for the dissemination of relatively static information. Directory services are not suited to manage information in dynamic and fluid environments. o Other techniques for dynamic information, e.g., sending information directly from NEs to PCE to avoid flooding. This would be useful if the number of PCEs is significantly less than number of WSON NEs. There may be other ways to limit flooding to "interested" NEs. Possible mechanisms to improve scaling of dynamic information include: o Tailor message content to WSON. For example the use of wavelength ranges, or wavelength occupation bit maps. o Utilize incremental updates if feasible. 5. Modeling Examples and Control Plane Use Cases This section provides examples of the fixed and switched optical node and wavelength constraint models of Section 3. and use cases for WSON control plane 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 August 8, 2011 [Page 31] Internet-Draft Wavelength Switched Optical Networks February 2011 +--+ +--+ +--+ +--------+ +-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+-+ +--+ Figure 7. Routers and WSON nodes in a GMPLS and PCE Environment. 5.1.1. Describing the WSON nodes The eight WSON nodes described in Figure 7 have the following properties: o Nodes N1, N2, N3 have 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 output links (L5, L7 and L12 in this case). o The links from the routers are only able to carry one wavelength with the exception of links L8 and L9 which are capable to add/drop any wavelength. Bernstein and Lee Expires August 8, 2011 [Page 32] Internet-Draft Wavelength Switched Optical Networks February 2011 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. 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 August 8, 2011 [Page 33] Internet-Draft Wavelength Switched Optical Networks February 2011 +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 August 8, 2011 [Page 34] Internet-Draft Wavelength Switched Optical Networks February 2011 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 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 output 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 output 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 document. In general optical impairment feasible routes serve as an input to RWA algorithm. For the example use case shown here, assume the following feasible routes: Bernstein and Lee Expires August 8, 2011 [Page 35] Internet-Draft Wavelength Switched Optical Networks February 2011 +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 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 RWA algorithm yields 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 RWA algorithm yields WL2 and the path L2 L4 L6 L7 L9 for the establishment of the new LSP. A 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 August 8, 2011 [Page 36] Internet-Draft Wavelength Switched Optical Networks February 2011 client signals) or by re-optimizing the solutions found by a RWA algorithm. Given the above example again, assume that a RWA algorithm should identify 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. An RWA algorithm can now compute the following alternate path 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 5.5. Electro-Optical Networking Scenarios In the following various networking scenarios are considered involving regenerators, OEO switches and wavelength converters. These scenarios can be grouped roughly by type and number of extensions to the GMPLS control plane that would be required. 5.5.1. Fixed Regeneration Points In the simplest networking scenario involving regenerators, regeneration is associated with a WDM link or an entire node and is not optional, i.e., all signals traversing the link or node will be regenerated. This includes OEO switches since they provide regeneration on every port. There may be input constraints and output constraints on the regenerators. Hence the path selection process will need to know from routing or other means the regenerator constraints so that it can Bernstein and Lee Expires August 8, 2011 [Page 37] Internet-Draft Wavelength Switched Optical Networks February 2011 choose a compatible path. For impairment aware routing and wavelength assignment (IA-RWA) the path selection process will also need to know which links/nodes provide regeneration. Even for "regular" RWA, this regeneration information is useful since wavelength converters typically perform regeneration and the wavelength continuity constraint can be relaxed at such a point. Signaling does not need to be enhanced to include this scenario since there are no reconfigurable regenerator options on input, output or with respect to processing. 5.5.2. Shared Regeneration Pools In this scenario there are nodes with shared regenerator pools within the network in addition to fixed regenerators of the previous scenario. These regenerators are shared within a node and their application to a signal is optional. There are no reconfigurable options on either input or output. The only processing option is to "regenerate" a particular signal or not. Regenerator information in this case is used in path computation to select a path that ensures signal compatibility and IA-RWA criteria. To setup an LSP that utilizes a regenerator from a node with a shared regenerator pool it is necessary to indicate that regeneration is to take place at that particular node along the signal path. Such a capability currently does not exist in GMPLS signaling. 5.5.3. Reconfigurable Regenerators This scenario is concerned with regenerators that require configuration prior to use on an optical signal. As discussed previously, this could be due to a regenerator that must be configured to accept signals with different characteristics, for regenerators with a selection of output attributes, or for regenerators with additional optional processing capabilities. As in the previous scenarios it is necessary to have information concerning regenerator properties for selection of compatible paths and for IA-RWA computations. In addition during LSP setup it is necessary to be able configure regenerator options at a particular node along the path. Such a capability currently does not exist in GMPLS signaling. 5.5.4. Relation to Translucent Networks Networks that contain both transparent network elements such as reconfigurable optical add drop multiplexers (ROADMs) and electro- Bernstein and Lee Expires August 8, 2011 [Page 38] Internet-Draft Wavelength Switched Optical Networks February 2011 optical network elements such regenerators or OEO switches are frequently referred to as translucent optical networks. Three main types of translucent optical networks have been discussed: 1. Transparent "islands" surrounded by regenerators. This is frequently seen when transitioning from a metro optical sub- network to a long haul optical sub-network. 2. Mostly transparent networks with a limited number of OEO ("opaque") nodes strategically placed. This takes advantage of the inherent regeneration capabilities of OEO switches. In the planning of such networks one has to determine the optimal placement of the OEO switches. 3. Mostly transparent networks with a limited number of optical switching nodes with "shared regenerator pools" that can be optionally applied to signals passing through these switches. These switches are sometimes called translucent nodes. All three types of translucent networks fit within the networking scenarios of Section 5.5.1. and Section 5.5.2. above. And hence, can be accommodated by the GMPLS extensions envisioned in this document. 6. GMPLS and 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 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. Bernstein and Lee Expires August 8, 2011 [Page 39] Internet-Draft Wavelength Switched Optical Networks February 2011 Furthermore such a mapping as described in [Otani] provides such a fixed mapping for communication between PCE and WSON PCCs. 6.1.2. WSON Signals and Network Element Processing As discussed in Section 3.3.2. a WSON signal at any point along its path can be characterized by the (a) modulation format, (b) FEC, (c) wavelength, (d)bit rate, and (d)G-PID. Currently G-PID, wavelength (via labels), and bit rate (via bandwidth encoding) are supported in [RFC3471] and [RFC3473]. These RFCs can accommodate the wavelength changing at any node along the LSP and can thus provide explicit control of wavelength converters. In the fixed regeneration point scenario described in Section 5.5.1. (Fixed Regeneration Points) no enhancements are required to signaling since there are no additional configuration options for the LSP at a node. In the case of shared regeneration pools described in Section 5.5.2. (Shared Regeneration Pools) it is necessary to indicate to a node that it should perform regeneration on a particular signal. Viewed another way, for an LSP, it is desirable to specify that certain nodes along the path perform regeneration. Such a capability currently does not exist in GMPLS signaling. The case of configurable regenerators described in Section 5.5.3. (Reconfigurable Regenerators) is very similar to the previous except that now there are potentially many more items that can be configured on a per node basis for an LSP. Note that the techniques of [RFC5420] which allow for additional LSP attributes and their recording in a Record Route Object (RRO) object could be extended to allow for additional LSP attributes in an ERO. This could allow one to indicate where optional 3R regeneration should take place along a path, any modification of LSP attributes such as modulation format, or any enhance processing such as performance monitoring. 6.1.3. 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 used to indicate the wavelength to be used at a particular Bernstein and Lee Expires August 8, 2011 [Page 40] Internet-Draft Wavelength Switched Optical Networks February 2011 node. In case the local label map approach is used the label sub- object entry in the ERO has to be interpreted appropriately. 6.1.4. Distributed Wavelength Assignment: Unidirectional, No Converters GMPLS signaling for a unidirectional optical path LSP allows for the use of a label set object in the Resource Reservation Protocol - Traffic Engineering (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. 6.1.5. Distributed Wavelength Assignment: Unidirectional, Limited 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 output 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 is processed. The node will pass on an enlarged label set reflecting only the limitations of the wavelength converter and the output link. The record route option in RSVP-TE signaling can be used to show where wavelength conversion has taken place. 6.1.6. Distributed Wavelength Assignment: Bidirectional, No Converters There are cases of a bidirectional optical path which requires the use of the same lambda in both directions. The above procedure can be used to determine the available bidirectional lambda set if it is interpreted that the available label set is available in both directions. In bidirectional LSPs setup, according to [RFC3471] Section 4.1. (Architectural Approaches to RWA), is indicated by the presence of an upstream label in the path message. However, until the intersection of the available label sets is determined along the path and at the destination node the upstream label information may not be correct. This case can be supported using current GMPLS mechanisms, but may not be as efficient as an Bernstein and Lee Expires August 8, 2011 [Page 41] Internet-Draft Wavelength Switched Optical Networks February 2011 optimized bidirectional single-label allocation mechanism. 6.2. Implications for GMPLS Routing GMPLS routing [RFC4202] currently defines an interface capability descriptor for "lambda switch capable" (LSC) which can be used 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, it would be necessary to convey the following subsystem properties to minimally characterize a WSON: 1. WDM Link properties (allowed wavelengths). 2. Optical 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. Electro-Optical Element Signal Compatibility In network scenarios where signal compatibility is a concern it is necessary to add parameters to our existing node and link models to take into account electro-optical input constraints, output constraints, and the signal processing capabilities of a NE in path computations. Input constraints: 1. Permitted optical tributary signal classes: A list of optical tributary signal classes that can be processed by this network element or carried over this link. (configuration type) 2. Acceptable FEC codes. (configuration type) 3. Acceptable Bit Rate Set: a list of specific bit rates or bit rate ranges that the device can accommodate. Coarse bit rate info is included with the optical tributary signal class restrictions. 4. Acceptable G-PID list: a list of G-PIDs corresponding to the "client" digital streams that is compatible with this device. Bernstein and Lee Expires August 8, 2011 [Page 42] Internet-Draft Wavelength Switched Optical Networks February 2011 Note that the bit rate of the signal does not change over the LSP. This can be communicated as an LSP parameter and hence this information would be available for any NE that needs to use it for configuration. Hence it is not necessary to have "configuration type" for the NE with respect to bit rate. Output constraints: 1. Output modulation: (a)same as input, (b) list of available types 2. FEC options: (a) same as input, (b) list of available codes Processing capabilities: 1. Regeneration: (a) 1R, (b) 2R, (c) 3R, (d)list of selectable regeneration types 2. Fault and performance monitoring: (a) G-PID particular capabilities, (b) optical performance monitoring capabilities. Note that such parameters could be specified on an (a) Network element wide basis, (b) a per port basis, (c) on a per regenerator basis. Typically such information has been on a per port basis; see the GMPLS interface switching capability descriptor [RFC4202]. 6.2.2. Wavelength-Specific Availability Information For wavelength assignment it is necessary to know which specific wavelengths are available and which are occupied if a combined RWA process or separate WA process is run as discussed in sections 4.1.1. 4.1.2. This is currently not possible with GMPLS routing. In the routing extensions for GMPLS [RFC4202], requirements for layer-specific TE attributes are discussed. RWA for optical networks without wavelength converters imposes an additional requirement for the lambda (or optical channel) layer: that of knowing which specific wavelengths are in use. Note that current 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 the approach of a global wavelength to label mapping or furnishing the local mappings to the PCEs is taken then representing the use of wavelengths via a simple bit-map is feasible [Gen-Encode]. 6.2.3. WSON Routing Information Summary The following table summarizes the WSON information that could be conveyed via GMPLS routing and attempts to classify that information Bernstein and Lee Expires August 8, 2011 [Page 43] Internet-Draft Wavelength Switched Optical Networks February 2011 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 Optical transmitter range Static Link(2) Wavelength conversion capabilities Static(3) Node Maximum bandwidth per wavelength Static Link Wavelength availability Dynamic(4) Link Signal compatibility and processing Static/Dynamic Node 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 it may be desirable 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 architectures, in the case of Routing + distributed WA via signaling only the following information is needed: 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], [Gen-Encode] and [WSON-Encode]. Bernstein and Lee Expires August 8, 2011 [Page 44] Internet-Draft Wavelength Switched Optical Networks February 2011 6.3. Optical Path Computation and Implications for PCE As previously noted RWA can be computationally intensive. Such computationally intensive path computations and optimizations were part of the impetus for the PCE architecture [RFC4655]. The Path Computation Element Protocol (PCEP) defines the procedures necessary to support both sequential [RFC5440] and global concurrent path computations (PCE-GCO) [RFC5557]. The PCEP is well positioned to support WSON-enabled RWA computation with some protocol enhancement. Implications for PCE generally fall into two main categories: (a) optical path constraints and characteristics, (b) computation architectures. 6.3.1. Optical path Constraints and Characteristics For the varying degrees of optimization that may be encountered in a network the following models of bulk and sequential optical path requests are encountered: o Batch optimization, multiple optical paths requested at one time (PCE-GCO). o Optical path(s) and backup optical path(s) requested at one time (PCEP). o Single optical path requested at a time (PCEP). PCEP and PCE-GCO can be readily enhanced to support all of the potential models of RWA computation. Optical path constraints include: o Bidirectional Assignment of wavelengths. o Possible simultaneous assignment of wavelength to primary and backup paths. o Tuning range constraint on optical transmitter. 6.3.2. Electro-Optical Element Signal Compatibility When requesting a path computation to PCE, the PCC should be able to indicate the following: Bernstein and Lee Expires August 8, 2011 [Page 45] Internet-Draft Wavelength Switched Optical Networks February 2011 o The G-PID type of an LSP. o The signal attributes at the transmitter (at the source): (i) modulation type; (ii) FEC type. o The signal attributes at the receiver (at the sink): (i) modulation type; (ii) FEC type. The PCE should be able to respond to the PCC with the following: o The conformity of the requested optical characteristics associated with the resulting LSP with the source, sink and NE along the LSP. o Additional LSP attributes modified along the path (e.g., modulation format change, etc.). 6.3.3. Discovery of RWA Capable PCEs The algorithms and network information needed for 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 RWA. 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. 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 Bernstein and Lee Expires August 8, 2011 [Page 46] Internet-Draft Wavelength Switched Optical Networks February 2011 protocols may significantly affect the loading of those protocols. This may make the operation of the network more vulnerable to denial of 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 RWA represents a disclosure of network capabilities that an operator may wish to keep private. Consideration should be given to securing this information. For a general discussion on MPLS and GMPLS related security issues, see the MPLS/GMPLS security framework [RFC5920]. 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 August 8, 2011 [Page 47] Internet-Draft Wavelength Switched Optical Networks February 2011 10. References 10.1. Normative References [RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, January 2003. [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol- Traffic Engineering (RSVP-TE) Extensions", RFC 3473, January 2003. [RFC3945] Mannie, E. "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004. [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. [RFC4655] Farrel, A., Vasseur, JP., and Ash, J., "A Path Computation Element (PCE)-Based Architecture ", RFC 4655, August 2006. [RFC5088] J.L. Le Roux, J.P. Vasseur, Yuichi Ikejiri, and Raymond Zhang, "OSPF protocol extensions for Path Computation Element (PCE) Discovery", January 2008. [RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux, M., and D. Brungard, "Requirements for GMPLS-Based Multi- Region and Multi-Layer Networks (MRN/MLN)", RFC 5212, July 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. [RFC5420] Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A. Ayyangarps, "Encoding of Attributes for MPLS LSP Establishment Using Resource Reservation Protocol Traffic Engineering (RSVP-TE)", RFC 5420, February 2009. Bernstein and Lee Expires August 8, 2011 [Page 48] Internet-Draft Wavelength Switched Optical Networks February 2011 [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. 10.2. Informative References [Gen-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "General Network Element Constraint Encoding for GMPLS Controlled Networks", draft-ietf-ccamp-general-constraint-encode, work in progress. [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.694.1] ITU-T Recommendation G.694.1, "Spectral grids for WDM applications: DWDM frequency grid", June, 2002. [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. Bernstein and Lee Expires August 8, 2011 [Page 49] Internet-Draft Wavelength Switched Optical Networks February 2011 [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. [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. [Otani] T. Otani, H. Guo, K. Miyazaki, D. Caviglia, "Generalized Labels of Lambda-Switching Capable Label Switching Routers (LSR)", work in progress: draft-ietf-ccamp-gmpls-g-694- lambda-labels, work in progress. [RFC5920] Fang, L., "Security Framework for MPLS and GMPLS Networks", RFC 5920, July 2010.[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. [WSON-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "Routing and Wavelength Assignment Information Encoding for Wavelength Switched Optical Networks", draft-ietf-ccamp- rwa-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 Bernstein and Lee Expires August 8, 2011 [Page 50] Internet-Draft Wavelength Switched Optical Networks February 2011 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 Old Dog Consulting UK Email: daniel@olddog.co.uk 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 Bernstein and Lee Expires August 8, 2011 [Page 51] Internet-Draft Wavelength Switched Optical Networks February 2011 Cisco Email: dschroet@cisco.com Jonas Martensson Acreo Electrum 236 16440 Kista, Sweden Email:Jonas.Martensson@acreo.se 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 Bernstein and Lee Expires August 8, 2011 [Page 52] Internet-Draft Wavelength Switched Optical Networks February 2011 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 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 August 8, 2011 [Page 53]