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diff --git a/doc/rfc/rfc6163.txt b/doc/rfc/rfc6163.txt new file mode 100644 index 0000000..837dacc --- /dev/null +++ b/doc/rfc/rfc6163.txt @@ -0,0 +1,2859 @@ + + + + + + +Internet Engineering Task Force (IETF) Y. Lee, Ed. +Request for Comments: 6163 Huawei +Category: Informational G. Bernstein, Ed. +ISSN: 2070-1721 Grotto Networking + W. Imajuku + NTT + April 2011 + + + Framework for GMPLS and Path Computation Element (PCE) Control + of Wavelength Switched Optical Networks (WSONs) + +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 (WSONs). 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 document is not an Internet Standards Track specification; it is + published for informational purposes. + + This document is a product of the Internet Engineering Task Force + (IETF). It represents the consensus of the IETF community. It has + received public review and has been approved for publication by the + Internet Engineering Steering Group (IESG). Not all documents + approved by the IESG are a candidate for any level of Internet + Standard; see Section 2 of RFC 5741. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + http://www.rfc-editor.org/info/rfc6163. + + + + + + + + + + + + +Lee, et al. Informational [Page 1] + +RFC 6163 Wavelength Switched Optical Networks April 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 Optical 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 ...........24 + 3.7.1. Input Constraints ..................................25 + 3.7.2. Output Constraints .................................25 + 3.7.3. Processing Capabilities ............................26 + 4. Routing and Wavelength Assignment and the Control Plane ........26 + 4.1. Architectural Approaches to RWA ...........................27 + 4.1.1. Combined RWA (R&WA) ................................27 + 4.1.2. Separated R and WA (R+WA) ..........................28 + 4.1.3. Routing and Distributed WA (R+DWA) .................28 + 4.2. Conveying Information Needed by RWA .......................29 + + + + + +Lee, et al. Informational [Page 2] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 5. Modeling Examples and Control Plane Use Cases ..................30 + 5.1. Network Modeling for GMPLS/PCE Control ....................30 + 5.1.1. Describing the WSON Nodes ..........................31 + 5.1.2. Describing the Links ...............................34 + 5.2. RWA Path Computation and Establishment ....................34 + 5.3. Resource Optimization .....................................36 + 5.4. Support for Rerouting .....................................36 + 5.5. Electro-Optical Networking Scenarios ......................36 + 5.5.1. Fixed Regeneration Points ..........................37 + 5.5.2. Shared Regeneration Pools ..........................37 + 5.5.3. Reconfigurable Regenerators ........................37 + 5.5.4. Relation to Translucent Networks ...................38 + 6. GMPLS and PCE Implications .....................................38 + 6.1. Implications for GMPLS Signaling ..........................39 + 6.1.1. Identifying Wavelengths and Signals ................39 + 6.1.2. WSON Signals and Network Element Processing ........39 + 6.1.3. Combined RWA/Separate Routing WA support ...........40 + 6.1.4. Distributed Wavelength Assignment: + Unidirectional, No Converters ......................40 + 6.1.5. Distributed Wavelength Assignment: + Unidirectional, Limited Converters .................40 + 6.1.6. Distributed Wavelength Assignment: + Bidirectional, No Converters .......................40 + 6.2. Implications for GMPLS Routing ............................41 + 6.2.1. Electro-Optical Element Signal Compatibility .......41 + 6.2.2. Wavelength-Specific Availability Information .......42 + 6.2.3. WSON Routing Information Summary ...................43 + 6.3. Optical Path Computation and Implications for PCE .........44 + 6.3.1. Optical Path Constraints and Characteristics .......44 + 6.3.2. Electro-Optical Element Signal Compatibility .......45 + 6.3.3. Discovery of RWA-Capable PCEs ......................45 + 7. Security Considerations ........................................46 + 8. Acknowledgments ................................................46 + 9. References .....................................................46 + 9.1. Normative References ......................................46 + 9.2. Informative References ....................................47 + + + + + + + + + + + + + + + +Lee, et al. Informational [Page 3] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + +1. Introduction + + Wavelength Switched Optical Networks (WSONs) are constructed from + subsystems that include Wavelength Division Multiplexing (WDM) links, + tunable transmitters and receivers, Reconfigurable Optical Add/Drop + Multiplexers (ROADMs), 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. + + + + + +Lee, et al. Informational [Page 4] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + +2. Terminology + + Add/Drop Multiplexer (ADM): An optical device used in WDM networks + and 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 multicast feature of some ADMs 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 a WDM system, line side ports and links can typically + carry the full multiplex of wavelength signals, as compared to + tributary (add or drop) ports that typically carry a few (usually + 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 application of 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. + + + +Lee, et al. Informational [Page 5] + +RFC 6163 Wavelength Switched Optical Networks April 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 (SMFs) and Multi-Mode Fibers (MMFs), the latter + are typically used for short-reach campus and premise applications. + SMFs are used for longer-reach applications and are therefore the + + + +Lee, et al. Informational [Page 6] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + primary concern of this document. The following SMF 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 1383 nm. 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 12.5 GHz, 25 GHz, 50 GHz, 100 GHz, and other + multiples of 100 GHz around a 193.1 THz 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 20 nm running from 1271 nm to 1611 nm 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 [RFC6205] and + provides a common label format to be used in signaling optical paths. + + + + + +Lee, et al. Informational [Page 7] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 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, freq2), 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 for optical transmitters and + receivers from the control plane perspective are: + + o Tunable: Do the transmitters and receivers operate at variable or + fixed wavelength? + + 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 [RFC6205], this can be expressed as a + + + +Lee, et al. Informational [Page 8] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 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 constraint that + is relatively easy to characterize 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 an 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; for example, one does not 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 + + The fundamental unit of switching in WSONs 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, + multi-channel 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) + + (b) Minimum and maximum central frequency + + + + +Lee, et al. Informational [Page 9] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + (c) Bitrate/Line coding (modulation) of optical tributary signals + + For the purposes of modeling the WSON in the control plane, (a) and + (b) are considered 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 multi-channel 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 bitrate + range [G.959.1]: + + (a) Optical tributary signal class Non-Return-to-Zero (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 Return-to-Zero (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 bitrate + of the optical tributary signal. Hence, modulation format (optical + tributary signal class) and bitrate are key parameters in + characterizing the optical tributary signal. + +3.3.2. WSON Signal Characteristics + + The optical tributary signal referenced in ITU-T Recommendations + [G.698.1] and [G.698.2] is referred to as the "signal" in this + document. This corresponds to the "lambda" LSP in GMPLS. For signal + + + + +Lee, et al. Informational [Page 10] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + compatibility purposes with electro-optical network elements, the + following signal characteristics are considered: + + 1. Optical tributary signal class (modulation format) + + 2. Forward Error Correction (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. Bitrate + + 5. General Protocol Identifier (G-PID) 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, OEO switches, or wavelength converters. + + Bitrate and G-PID would not change since they describe the encoded + bitstream. 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 + bitstreams, the presence of FEC can be detected; for example, 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 or not the FEC field of the Optical Channel Transport Unit-k + (OTUk) is all zeros. + +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 Optical 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. + + + + + + +Lee, et al. Informational [Page 11] + +RFC 6163 Wavelength Switched Optical Networks April 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; 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. + + + + + +Lee, et al. Informational [Page 12] + +RFC 6163 Wavelength Switched Optical Networks April 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 is a 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"; that is, 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 + that diagonal elements are zero since loopback is not supported in + the example. If ports support loopback, diagonal elements would be + set to one. + + + +Lee, et al. Informational [Page 13] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + Additional constraints may also apply to the various ports in a + ROADM/OXC. The following restrictions and terms may be used: + + o Colored port: an input or, more typically, an output (drop) port + restricted to a single channel of fixed wavelength + + o 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) the number of wavelengths and (b) the + 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, 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. + + + + + + +Lee, et al. Informational [Page 14] + +RFC 6163 Wavelength Switched Optical Networks April 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 + ensure 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 a "drop and continue" + operation. Tributary input ports ("add" ports) whose signals are + combined with each other and other line side signals may also exist. + + 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, the wavelengths that 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, + which consists 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]. + + + + + +Lee, et al. Informational [Page 15] + +RFC 6163 Wavelength Switched Optical Networks April 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. 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. 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 bitrates 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. + -------------------------------------------------------------------- + + This table shows that 1R regenerators are generally independent of + signal modulation format (also known as line coding) but may work + over a limited range of wavelengths/frequencies. 2R regenerators are + + + +Lee, et al. Informational [Page 16] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 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 bitrates (but not a specific bitrate). + Finally, 3R regenerators apply to a single channel, are dependent + upon the modulation format, and are generally sensitive to the + bitrate of digital signal, i.e., either are designed to only handle a + specific bitrate or need to be programmed to accept and regenerate a + specific bitrate. In all these types of regenerators, the digital + bitstream contained within the optical or electrical signal is not + modified. + + It is common for regenerators to modify the digital bitstream 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; and, 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. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Lee, et al. Informational [Page 17] + +RFC 6163 Wavelength Switched Optical Networks April 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) | | | + +-----------------------------------------------------------------+ + + Table 2 shows that frame alignment, signal identification, and FEC + are supported. By omission, Table 2 also shows 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 do not require the "layering" to provide the management + functions shown in 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; 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 constraints + listed in Table 3 may be imposed by a regenerator device: + + + + + + + +Lee, et al. Informational [Page 18] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + Table 3. Regenerator Compatibility Constraints + + +--------------------------------------------------------+ + | Constraints | 1R | 2R | 3R | + +--------------------------------------------------------+ + | Limited Wavelength Range | x | x | x | + +--------------------------------------------------------+ + | Modulation Type Restriction | | x | x | + +--------------------------------------------------------+ + | Bitrate Range Restriction | | x | x | + +--------------------------------------------------------+ + | Exact Bitrate 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 reconvert + 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 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; that is, this is basically an electrical + regenerator combined with a laser/receiver. Hence, this type of + wavelength converter has signal-processing restrictions that are + essentially the same as those described for regenerators in Table 3 + of Section 3.5.1. + + + +Lee, et al. Informational [Page 19] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 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, 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 + lambda used on input to the wavelength converter would be different + from the lambda coming back from the wavelength converter. + + + +Lee, et al. Informational [Page 20] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + A model for an individual OEO 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 is desirable to include, at a minimum, the usage state + of individual wavelength converters in the pool. + + A three stage model is used as shown schematically in Figure 3. 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 a 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 wavelength on input. Each wavelength converter input port + constraint can be modeled via a wavelength set mechanism. + + Next, there is 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 + + + +Lee, et al. Informational [Page 21] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 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} indicates + 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 [Gen-Encode]. + + 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 shows a simple optical switch in a four-wavelength DWDM + system sharing wavelength converters in a general shared "per-node" + fashion. + + + + + + +Lee, et al. Informational [Page 22] + +RFC 6163 Wavelength Switched Optical Networks April 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 | + +-----+ +-----+ + + + + + + + + +Lee, et al. Informational [Page 23] + +RFC 6163 Wavelength Switched Optical Networks April 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 + + + + + + + +Lee, et al. Informational [Page 24] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + +3.7.1. Input Constraints + + Sections 3.5 and 3.6 discuss the basic properties of 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. Bitrate 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 may be relatively transparent to some attributes, + e.g., a 2R regenerator to bitrate. Finally, some devices may be able + to auto-detect some attributes and configure themselves, e.g., a 3R + regenerator with bitrate detection mechanisms and flexible phase + locking circuitry. To account for these different cases, item 5 has + been added, which describes the device's 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 + bitrate 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, the network element will need + to be configured on a per-LSP basis as to which choice to use. + + + + +Lee, et al. Informational [Page 25] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + +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 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. + + 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, the control plane can + be of assistance in their configuration. Per-LSP, per-node, and + 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. + +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 + + + + +Lee, et al. Informational [Page 26] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 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 a specific RWA algorithm is out + of the scope of this document. However, there are a number of + different approaches to dealing with RWA algorithms 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 sections, 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 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 + + + +Lee, et al. Informational [Page 27] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + network nodes' capabilities. This solution is compatible with most + known RWA algorithms, particularly 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 that maintains a complete and updated view of network + state and provides path computation services to nodes + + 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. + + The separation of the entities computing the path and the wavelength + assignment 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 offer the optimal solution, reasonable + optimization can be performed by allowing multiple routes to pass to + the wavelength selection process. + + 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. + +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 + + + +Lee, et al. Informational [Page 28] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 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 that 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 that 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 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, the following: + + 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, and CORBA. + + + +Lee, et al. Informational [Page 29] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + o Methods to access configuration and status information such as a + command line interface (CLI). + + 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 PCEs to avoid flooding. This + would be useful if the number of PCEs is significantly less than + the 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 Tailoring message content to WSON, e.g., the use of wavelength + ranges or wavelength occupation bit maps + + o Utilizing 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), 18 links (L1 through L18), and one OEO + converter (O1) in a topology shown in Figure 7. + + + + + + + + + + + + + + + + + +Lee, et al. Informational [Page 30] + +RFC 6163 Wavelength Switched Optical Networks April 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, and 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. + + + + + +Lee, et al. Informational [Page 31] + +RFC 6163 Wavelength Switched Optical Networks April 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 but 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): + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Lee, et al. Informational [Page 32] + +RFC 6163 Wavelength Switched Optical Networks April 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 | | + +--+---+---+---+---+---+---+---+---+---+---+---+---+ + + + + + + + +Lee, et al. Informational [Page 33] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + +5.1.2. Describing the Links + + For the following discussion, some simplifying assumptions are made: + + o It is assumed that the WSON node supports 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 + need 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 shown + here for convenience; that is, 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 an RWA algorithm. + + + + + +Lee, et al. Informational [Page 34] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + For the example use case shown here, assume the following feasible + routes: + + +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 an LSP between R1 and R2, an 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 an 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 an RWA algorithm yields WL2 and the path L2 L4 L6 L7 + L9 for the establishment of the new LSP. + + An LSP request -- this time from R2 to R3 -- cannot be fulfilled + since the four possible paths (starting at L8 and L9) are already in + use. + + + + + + + +Lee, et al. Informational [Page 35] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + +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 + client signals) or by re-optimizing the solutions found by an RWA + algorithm. + + Given the above example again, assume that an 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. + + For this discussion, assume that the only two LSPs in use in the + system are: + + LSP1: WL1 L1 L3 L5 L8 + + LSP2: WL2 L2 L4 L6 L7 L9 + + Furthermore, assume that the L5 fails. An RWA algorithm can now + compute and establish the following alternate 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 subsections, 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. + + + + + + + + + +Lee, et al. Informational [Page 36] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + +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; that is, 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 + the regenerator constraints from routing or other means so that it + can 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 + processing. + +5.5.2. Shared Regeneration Pools + + In this scenario, there are nodes with shared regenerator pools + within the network in addition to the 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. + + In this case, regenerator information is used in path computation to + select a path that ensures signal compatibility and IA-RWA criteria. + + To set up 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 does not currently 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. + + + +Lee, et al. Informational [Page 37] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 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 to configure regenerator options at a particular + node along the path. Such a capability does not currently 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- + optical network elements such as 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 + subnetwork to a long-haul optical subnetwork. + + 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 Sections 5.5.1 and 5.5.2. Hence, they 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 have an impact on the information that + needs to be transferred by the control plane (GMPLS) and the PCE + architecture. Current GMPLS and PCE standards address the full + wavelength conversion case, so the following subsections will only + address the limited and no wavelength conversion cases. + + + + + + + + +Lee, et al. Informational [Page 38] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + +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 in distributed + wavelength assignment processes, which are discussed below. + +6.1.1. Identifying Wavelengths and Signals + + As previously stated, a global-fixed mapping between wavelengths and + labels simplifies the characterization of WDM links and WSON devices. + Furthermore, a mapping like the one described in [RFC6205] provides + 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) bitrate, and (e) G-PID. + + Currently, G-PID, wavelength (via labels), and bitrate (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, + 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, + 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 does not currently exist in GMPLS + signaling. + + The case of reconfigurable regenerators described in Section 5.5.3 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] that allow for additional LSP + attributes and their recording in a Record Route Object (RRO) could + be extended to allow for additional LSP attributes in an Explicit + Route Object (ERO). This could allow one to indicate where optional + + + + +Lee, et al. Informational [Page 39] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 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 case or the separate routing WA case, 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 node. In case the local label map approach is used, the + label subobject 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. 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 lambdas being + known to the destination, which 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 that 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 that require 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 + + + +Lee, et al. Informational [Page 40] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + interpreted that the available Label Set is available in both + directions. According to [RFC3471], Section 4.1, the setup of + bidirectional LSPs 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 + 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) that 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 Interior Gateway Protocol (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 an 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) + + + + +Lee, et al. Informational [Page 41] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 2. Acceptable FEC codes (configuration type) + + 3. Acceptable bitrate set: a list of specific bitrates or bitrate + ranges that the device can accommodate. Coarse bitrate 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 + + Note that the bitrate of the signal does not change over the LSP. + This can be communicated as an LSP parameter; therefore, 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 bitrate. + + 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 (a) a network- + element-wide basis, (b) a per-port basis, or (c) 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 + and 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, if the + + + +Lee, et al. Informational [Page 42] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + approach of a global wavelength to label mapping or furnishing the + local mappings to the PCEs is taken, representing the use of + wavelengths via a simple bitmap 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 + according to its static or dynamic nature and its association 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 that it may be desirable to include + regeneration capabilities here since OEO converters are also + regenerators. + + 4. This is 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: + + + + + + + +Lee, et al. Informational [Page 43] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + Information Static/Dynamic Node/Link + ------------------------------------------------------------------ + Connectivity matrix Static Node + Wavelength conversion capabilities Static(3) Node + + Information models and compact encodings for this information are + provided in [WSON-Info], [Gen-Encode], and [WSON-Encode]. + +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 Communication Protocol (PCEP) defines + the procedures necessary to support both sequential [RFC5440] and + Global Concurrent Optimization (GCO) path computations [RFC5557]. + With some protocol enhancement, the PCEP is well positioned to + support WSON-enabled RWA computation. + + 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. + + + + + + + + + + + +Lee, et al. Informational [Page 44] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 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: + + 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) + +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. Therefore, + it would be useful to indicate that a PCE has the ability to deal + with RWA via the mechanisms being established for PCE discovery + [RFC5088]. [RFC5088] indicates that a sub-TLV could be allocated for + this purpose. + + Recent progress on objective functions in PCE [RFC5541] would allow + 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 + the most evenly distributed link utilization. + + + + +Lee, et al. Informational [Page 45] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + This implies that PCEP would easily accommodate a 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 does not require changes to the security models within + GMPLS and associated protocols. That is, the OSPF-TE, RSVP-TE, and + PCEP security models could be operated unchanged. + + However, satisfying the requirements for RWA using the existing + protocols may significantly affect the loading of those protocols. + This 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. Acknowledgments + + The authors would like to thank Adrian Farrel for many helpful + comments that greatly improved the contents of this document. + +9. References + +9.1. Normative References + + [RFC3471] Berger, L., Ed., "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., Ed., "Generalized Multi-Protocol Label + Switching (GMPLS) Architecture", RFC 3945, October + 2004. + + + + + + +Lee, et al. Informational [Page 46] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + [RFC4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing + Extensions in Support of Generalized Multi-Protocol + Label Switching (GMPLS)", RFC 4202, October 2005. + + [RFC4328] Papadimitriou, D., Ed., "Generalized Multi-Protocol + Label Switching (GMPLS) Signaling Extensions for G.709 + Optical Transport Networks Control", RFC 4328, January + 2006. + + [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path + Computation Element (PCE)-Based Architecture", RFC + 4655, August 2006. + + [RFC5088] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and + R. Zhang, "OSPF Protocol Extensions for Path + Computation Element (PCE) Discovery", RFC 5088, 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] Lee, Y., Le Roux, JL., King, D., and E. Oki, "Path + Computation Element Communication Protocol (PCEP) + 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. + + [RFC5440] Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path + Computation Element (PCE) Communication Protocol + (PCEP)", RFC 5440, March 2009. + + [RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of + Objective Functions in the Path Computation Element + Communication Protocol (PCEP)", RFC 5541, June 2009. + +9.2. Informative References + + [Gen-Encode] Bernstein, G., Lee, Y., Li, D., and W. Imajuku, + "General Network Element Constraint Encoding for GMPLS + Controlled Networks", Work in Progress, December 2010. + + + + +Lee, et al. Informational [Page 47] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + [G.652] ITU-T Recommendation G.652, "Characteristics of a + single-mode optical fibre and cable", November 2009. + + [G.653] ITU-T Recommendation G.653, "Characteristics of a + dispersion-shifted single-mode optical fibre and + cable", July 2010. + + [G.654] ITU-T Recommendation G.654, "Characteristics of a cut- + off shifted single-mode optical fibre and cable", July + 2010. + + [G.655] ITU-T Recommendation G.655, "Characteristics of a non- + zero dispersion-shifted single-mode optical fibre and + cable", November 2009. + + [G.656] ITU-T Recommendation G.656, "Characteristics of a fibre + and cable with non-zero dispersion for wideband optical + transport", July 2010. + + [G.671] ITU-T Recommendation G.671, "Transmission + characteristics of optical components and subsystems", + January 2009. + + [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.698.1] ITU-T Recommendation G.698.1, "Multichannel DWDM + applications with single-channel optical interfaces", + November 2009. + + [G.698.2] ITU-T Recommendation G.698.2, "Amplified multichannel + dense wavelength division multiplexing applications + with single channel optical interfaces ", November + 2009. + + [G.707] ITU-T Recommendation G.707, "Network node interface for + the synchronous digital hierarchy (SDH)", January 2007. + + [G.709] ITU-T Recommendation G.709, "Interfaces for the Optical + Transport Network (OTN)", December 2009. + + [G.872] ITU-T Recommendation G.872, "Architecture of optical + transport networks", November 2001. + + + + + +Lee, et al. Informational [Page 48] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + [G.959.1] ITU-T Recommendation G.959.1, "Optical transport + network physical layer interfaces", November 2009. + + [G.Sup39] ITU-T Series G Supplement 39, "Optical system design + and engineering considerations", December 2008. + + [Imajuku] Imajuku, W., Sone, Y., Nishioka, I., and S. Seno, + "Routing Extensions to Support Network Elements with + Switching Constraint", Work in Progress, July 2007. + + [RFC6205] Otani, T., Ed. and D. Li, Ed., "Generalized Labels of + Lambda-Switch Capable (LSC) Label Switching Routers", + RFC 6205, March 2011. + + [RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS + Networks", RFC 5920, July 2010. + + [WSON-Encode] Bernstein, G., Lee, Y., Li, D., and W. Imajuku, + "Routing and Wavelength Assignment Information Encoding + for Wavelength Switched Optical Networks", Work in + Progress, March 2011. + + [WSON-Imp] Lee, Y., Bernstein, G., Li, D., and G. Martinelli, "A + Framework for the Control of Wavelength Switched + Optical Networks (WSON) with Impairments", Work in + Progress, April 2011. + + [WSON-Info] Bernstein, G., Lee, Y., Li, D., and W. Imajuku, + "Routing and Wavelength Assignment Information Model + for Wavelength Switched Optical Networks", Work in + Progress, July 2008. + +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, diego.caviglia@ericsson.com + + + + + + +Lee, et al. Informational [Page 49] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + + 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 + Cisco + EMail: dschroet@cisco.com + + Jonas Martensson + Acreo + Electrum 236 + 16440 Kista + Sweden + EMail: Jonas.Martensson@acreo.se + + + + + + + + + + + + + + +Lee, et al. Informational [Page 50] + +RFC 6163 Wavelength Switched Optical Networks April 2011 + + +Authors' Addresses + + Young Lee (editor) + Huawei Technologies + 1700 Alma Drive, Suite 100 + Plano, TX 75075 + USA + + Phone: (972) 509-5599 (x2240) + EMail: ylee@huawei.com + + + Greg M. Bernstein (editor) + Grotto Networking + Fremont, CA + USA + + Phone: (510) 573-2237 + EMail: gregb@grotto-networking.com + + + Wataru Imajuku + NTT Network Innovation Labs + 1-1 Hikari-no-oka, Yokosuka, Kanagawa + Japan + + Phone: +81-(46) 859-4315 + EMail: wataru.imajuku@ieee.org + + + + + + + + + + + + + + + + + + + + + + + +Lee, et al. Informational [Page 51] + |