Network Working Group Y. Lee
Internet DraftHuawei G. Bernstein Grotto Networking D. Li Huawei G. Martinelli Cisco Internet Draft Intended status: Informational October 21, 2010March 9, 2011 Expires: AprilSeptember 2011 A Framework for the Control of Wavelength Switched Optical Networks (WSON) with Impairments draft-ietf-ccamp-wson-impairments-04.txtdraft-ietf-ccamp-wson-impairments-05.txt Status of this Memo This Internet-Draft is submitted to IETFin full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 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Abstract The operation ofAs an optical networks requires information onsignal progresses along its path it may be altered by the various physical characterization ofprocesses in the optical network elements, subsystems, devices,fibers and cabling.devices it encounters. When such alterations result in signal degradation, we usually refer to these processes as "impairments". These physical characteristics may be important constraints to consider when using a GMPLS control plane to support path setup and maintenance.maintenance in wavelength switched optical networks. This document discusses how the definition and characterization of optical fiber, devices, subsystems, and network elements contained in various ITU-T recommendations can be combined withprovides a framework for applying GMPLS control planeprotocols and mechanismsthe PCE architecture to support Impairment Aware Routing and Wavelength Assignment (IA-RWA) in wavelength switched optical networks. Table of Contents 1. Introduction...................................................4 1.1. Revision History..........................................5Introduction...................................................3 2. Motivation.....................................................5Terminology....................................................4 3. Applicability..................................................5 4. Impairment Aware Optical Path Computation......................6 220.127.116.11. Optical Network Requirements and Constraints..............7 18.104.22.168.1.1. Impairment Aware Computation Scenarios...............7 22.214.171.124.1.2. Impairment Computation and Information Sharing Constraints.................................................8 126.96.36.199.1.3. Impairment Estimation Process.......................10 188.8.131.52. IA-RWA Computation and Control Plane Architectures.......11 184.108.40.206.2.1. Combined Routing, WA, and IV........................13 220.127.116.11.2.2. Separate Routing, WA, or IV.........................13 18.104.22.168.2.3. Distributed WA and/or IV............................13 3.3.IV............................14 4.3. Mapping Network Requirements to Architectures............14 4.Architectures............15 5. Protocol Implications.........................................17 22.214.171.124. Information Model for Impairments........................17 126.96.36.199. Routing..................................................18 4.3. Signaling................................................18 188.8.131.52. Signaling................................................19 5.4. PCE......................................................19 184.108.40.206.4.1. Combined IV & RWA...................................19 220.127.116.11.4.2. IV-Candidates + RWA.................................19 4.4.3. Approximate IA-RWA + Separate Detailed IV...........21 5. Security Considerations.......................................23RWA.................................20 6. IANA Considerations...........................................23Security Considerations.......................................22 7. Acknowledgments...............................................23IANA Considerations...........................................22 8. References....................................................31References....................................................22 8.1. Normative References.....................................31References.....................................22 8.2. Informative References...................................33References...................................24 9. Acknowledgments...............................................24 1. Introduction Wavelength Switched Optical Networks (WSONs) are constructed from subsystems that may include Wavelength Division Multiplexed (WDM) links, tunable transmitters and receivers, Reconfigurable Optical Add/Drop Multiplexers (ROADM), wavelength converters, and electro- optical network elements. A WSON is a wavelength division multiplexed (WDM)-based optical network in which switching is performed selectively based on the center wavelength of an optical signal. As an optical signal progresses along its path it may be altered by the various physical processes in the optical fibers and devices it encounters. When such alterations result in signal degradation, we usually refer tothese processes are usually referred to as "impairments". An overview of some critical optical impairments and their routing (path selection) implications can be found in [RFC4054]. Roughly speaking, opticalOptical impairments accumulate along the path (without 3R regeneration) traversed by the signal. They are influenced by the type of fiber used, the types and placement of various optical devices and the presence of other optical signals that may share a fiber segment along the signal's path. The degradation of the optical signals due to impairments can result in unacceptable bit error rates or even a complete failure to demodulate and/or detect the received signal. Therefore, path selection in any WSON requires consideration of optical impairments so that the signal will be propagated from the network ingress pointIn order to the egress point withprovision an acceptable signal quality. Someoptical subnetworks are designed such that over any path the degradation to anconnection (an optical signal due topath) through a WSON certain path continuity, resource availability and impairments never exceeds prescribed bounds. This mayconstraints must be duemet to determine viable and optimal paths through the limited geographic extentnetwork. The determination of the network, the network topology, and/or the quality of the fiber and devices employed. In such networks the path selection problem reduces to determining a continuous wavelength from source to destination (thepaths is known as Impairment Aware Routing and Wavelength Assignment problem). These(IA-RWA). Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes a set of control plane protocols that can be used to operate data networks are discussed in [WSON-Frame]. In other opticalranging from packet switch capable networks, impairments are importantthrough those networks that use time division multiplexing, and the path selection process must be impairment-aware. AlthoughWDM. [RFC4054] describes a number of key optical impairments, a more complete descriptiongives an overview of some critical optical impairments and processestheir routing (path selection) implications for GMPLS. The Path Computation Element (PCE) architecture [RFC4655] defines functional components that can be foundused to compute and suggest appropriate paths in connection-oriented traffic-engineered networks. This document provides a framework for applying GMPLS protocols and the ITU-T Recommendations. Appendix APCE architecture to the control and operation of IA-RWA for WSONs. To aid in this process this document also provides an overview of the extensive ITU-T documentation in this area. The benefits of operating networks using the Generalized Multiprotocol Label Switching (GMPLS) control plane is described in [RFC3945]. The advantages of using a path computation element (PCE) to perform complex path computations are discussed in [RFC4655]. Based on the existing ITU-T standards covering optical characteristics (impairments)subsystems and processes that comprise WSONs, and describes IA-RWA so that the knowledge ofinformation requirements can be identified to explain how the impact of impairments mayinformation can be estimated along a path, this document provides a frameworkmodeled for impairment aware path computation and establishment utilizinguse by GMPLS protocolsand thePCE architecture. As insystems. This work will facilitate the impairment free case covered in [WSON-Frame], a number of different control plane architectural options are described. 1.1. Revision History Changes from 00 to 01: Added discussion of regenerators to section 3. Added to discussion of interface parameters in section 3.1.3. Added to discussiondevelopment of IV Candidates function in section 3.2. Changes from 01 to 02: Correctprotocol solution models and refine use of "black link" concept based on liaison with ITU-T and WG feedback. Changes from 02 to 03: Insert additional information on useprotocol extensions within the GMPLS and considerations for regenerators in section 3.PCE protocol families. 2. Motivation There are deployment scenarios for WSONTerminology Add/Drop Multiplexers (ADM): An optical device used in WDM networks where not all possible paths will yield suitable signal quality. There are multiple reasons behind this choice; here below is a non- exhaustive listcomposed of examples: o WSON is evolving using multi-degree opticalone or more line side ports and typically many tributary ports. CWDM: Coarse Wavelength Division Multiplexing. DWDM: Dense Wavelength Division Multiplexing. FOADM: Fixed Optical Add/Drop Multiplexer. GMPLS: Generalized Multi-Protocol Label Switching. IA-RWA: Impairment Aware Routing and Wavelength Assignment Line side: In WDM system line side ports and links typically can carry the full multiplex of wavelength signals, as compared to tributary (add or drop ports) that typically carry a few (typically one) wavelength signals. OXC: Optical cross connectsconnect. An optical switching element in which a way that network topologies are changing from rings (and interconnected rings)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 full mesh. Addingnetwork equipment such as amplifierspath or regenerators, to make all paths feasible, leads to an over-provisioned network. Indeed, even with over provisioning, theroute based on a network could still have some infeasible paths. o Withingraph and applying computational constraints. PCEP: PCE Communication Protocol. The communication protocol between a given network, thePath 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 physical interface may change over thenetwork life, e.g., thethat does not contain regenerators or wavelength converters. 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 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. Applicability There are deployment scenarios for WSON networks where not all possible paths will yield suitable signal quality. There are multiple reasons behind this choice; here below is a non-exhaustive list of examples: o WSON is evolving using multi-degree optical cross connects in a way that network topologies are changing from rings (and interconnected rings) to general mesh. Adding network equipment such as amplifiers or regenerators, to make all paths feasible, leads to an over-provisioned network. Indeed, even with over provisioning, the network could still have some infeasible paths. o Within a given network, the optical physical interface may change over the network life, e.g., the optical interfaces might be upgraded to higher bit-rates. Such changes could result in paths being unsuitable for the optical signal. Although the same considerations may apply to other network equipment upgrades,Moreover, the optical physical interfaces are a typical case because they aretypically provisioned at various stages of the network's life span as needed by traffic demands. o There are cases where a network is upgraded by adding new optical cross connects to increase network flexibility. In such cases existing paths will have their feasibility modified while new paths will need to have their feasibility assessed. o With the recent bit rate increases from 10G to 40G and 100G over a single wavelength, WSON networks will likely be operated with a mix of wavelengths at different bit rates. This operational scenario will impose someimpairment considerationsconstraints due to different physical behavior of different bit rates and associated modulation formats. Not having an impairment aware control plane for such networks will require a more complex network design phase that, since the beginning,that takes into account evolving network status in term of equipments and traffic.traffic at the beginning stage. This could result in over-engineering the DWDM network with additional regenerators nodesand optical amplifiers. Optical impairment awareness allows for the concept of photonic switching where possible and provides regeneration when it is a must.In addition, network operations such as path establishment, will require significant pre-design via non-control plane processes resulting in significantly slower network provisioning. 3.4. Impairment Aware Optical Path Computation The basic criteria for path selection is whether one can successfully transmit the signal from a transmitter to a receiver within a prescribed error tolerance, usually specified as a maximum permissible bit error ratio (BER). This generally depends on the nature of the signal transmitted between the sender and receiver and the nature of the communications channel between the sender and receiver. The optical path utilized (along with the wavelength) determines the communications channel. The optical impairments incurred by the signal along the fiber and at each optical network element along the path determine whether the BER performance or any other measure of signal quality can be met for a signal on a particular end-to-end path. This could include parameters such as the Q factor to correlate both linear and non-linear parameters into one value. The impairment-awareImpairment-aware path calculation needsalso needs to take into account when regeneration happensis used along the path. [WSON-Frame] introducesprovides background on the concept of Opticaloptical translucent network thatnetworks which contains transparent elements and electro-optical elements such as OEO regenerations. In such networks a generic light path can go through a certainnumber of regeneration points. Regeneration points could happen for two reasons: (i) wavelength conversion to assist theRWA processto avoid wavelength blocking. This is the impairment free case covered by[WSON-Frame].by [WSON-Frame]. (ii) the optical signal iswithout regeneration would be too degraded.degraded to meet end to end BER requirements. This is the case when theRWA taketakes into consideration impairment estimation covered by this document. In the latter case a lightan optical path can be seen as a set of transparent segments. The optical impairments calculation needs to be reset at each regeneration point so each transparent segment will have its own impairment evaluation. +---+ +----+ +----+ +---++-----+ +----+ +---+ | I |----| N1 |---| N2 |-----| RREG |-----| N3 |----| E | +--++---+ +----+ +----+ +---++-----+ +----+ +---+ |.--------------------------.|.------------------.||<----------------------------->|<-------------------->| Segment 1 Segment 2 Figure 1 LightOptical path as a set of transparent segments For example, Figure 1 represents a Lightan optical path from node I to node E with a regeneration point RREG in between. It is feasible from an impairment validation perspective if both segments (I, N1, N2, R)REG) and (R,(REG, N3, E) are feasible. 18.104.22.168. Optical Network Requirements and Constraints This section examines the various optical network requirements and constraints that an impairment aware optical control plane may have to operate under. These requirements and constraints motivate the IA-RWAIA- RWA architectural alternatives to be presented in the following section. We can break the differentDifferent optical networks contexts up alongcan be broken into two main criteria: (a) the accuracy required in the estimation of impairment effects, and (b) the constraints on the impairment estimation computation and/or sharing of impairment information. 22.214.171.124.1.1. Impairment Aware Computation Scenarios A. No concern for impairments or Wavelength Continuity Constraints This situation is covered by existing GMPLS with local wavelength (label) assignment. B. No concern for impairments but Wavelength Continuity Constraints This situation is applicable to networks designed such that every possible path is valid for the signal types permitted on the network. In this case impairments are only taken into account during network design and after that, for example during optical path computation, they can be ignored. This is the case discussed in [WSON-Frame] where impairments may be ignored by the control plane and only optical parameters related to signal compatibility are considered. C. Approximated Impairment Estimation This situation is applicable to networks in which impairment effects need to be considered but there is sufficient margin such that they can be estimated via approximation techniques such as link budgets and dispersion[G.680],[G.sup39].dispersion [G.680],[G.sup39]. The viability of optical paths for a particular class of signals can be estimated using well defined approximation techniques [G.680], [G.sup39]. This is the generally known as linear case where only linear effects are taken into account. AddingNote that adding or removing an optical signal on the path willshould not render any of the existing signals in the network as non-viable.non- viable. For example, one form of non-viability is the occurrence of transients in existing links of sufficient magnitude to impact the BER of thoseexisting signals. Much work at ITU-T has gone into developing impairment models at this and more detailed levels. Impairment characterization of network elements could thenmay be used to calculate which paths are conformant with a specified BER for a particular signal type. In such a case, we can combine the impairment aware (IA) path computation with the RWA process to permit more optimal IA-RWA computations. Note,Note that the IA path computation may also take place in a separate entity, i.e., a PCE. D. Detailed Impairment Computation This situation is applicable to networks in which impairment effects must be more accurately computed. For these networks, a full computation and evaluation of the impact to any existing paths needs to be performed prior to the addition of a new path. Currently no impairment models are available from ITU-T and this scenario is outside the scope of this document. 126.96.36.199.1.2. Impairment Computation and Information Sharing Constraints In GMPLS, information used for path computation is standardized for distribution amongst the elements participating in the control plane and any appropriately equipped PCE can perform path computation. For optical systems this may not be possible. This is typically due to only portions of an optical system being subject to standardization. In ITU-T recommendations [G.698.1] and [G.698.2] which specify single channel interfaces to multi-channel DWDM systems only the single channel interfaces (transmit and receive) are specified while the multi-channel links are not standardized. These DWDM links are referred to as "black links" since their details are not generally available. Note however the overall impact of a black link at the single channel interface points is limited by [G.698.1] and [G.698.2]. Typically a vendor might use proprietary impairment models for DWDM spans and to estimate the validity of optical paths. For example, models of optical nonlinearities are not currently standardized. Vendors may also choose not to publish impairment details for links or a set of network elements in order not to divulge their optical system designs. In general, the impairment estimation/validation of an optical path for optical networks with "black links" (path) could not be performed by a general purpose impairment aware (IA) computation entity since it would not have access to or understand the "black link" impairment parameters. However, impairment estimation (optical path validation) could be performed by a vendor specific impairment aware computation entity. Such a vendor specific IA computation, could utilize standardized impairment information imported from other network elements in these proprietary computations. In the following we will usethe term "black links" will be used to describe these computation and information sharing constraints in optical networks. From the control plane perspective we havethe following options: A.options are considered: 1. The authority in control of the "black links" can furnish a list of all viable paths between all viable node pairs to a computational entity. This information would be particularly useful as an input to RWA optimization to be performed by another computation entity. The difficulty here is for larger networks such a list of paths along with any wavelength constraints could get unmanageably large. B.2. The authority in control of the "black links" could provide a PCE like entity that would furnish a list of viable paths/wavelengths between two requested nodes. This is useful as an input to RWA optimizations and can reduce the scaling issue previously mentioned. Such a PCE like entity would not need to perform a full RWA computation, i.e., it would not need to take into account current wavelength availability on links. Such an approach may require PCEP extensions for both the request and response information. C.3. The authority in control of the "black links" can provide a PCE that performs full IA-RWA services. The difficulty is this requires the one authority to also become the sole source of all RWA optimization algorithms and such. In all the above cases it would be the responsibility of the authority in control of the "black links" to import the shared impairment information from the other NEs via the control plane or other means as necessary. 188.8.131.52.1.3. Impairment Estimation Process The Impairment Estimation Process can be modeled through the following functional blocks. These blocks are independent fromof any Control Plane architecture, that is, they can be implemented by the same or by different control plane functions as detailed in following sections. +-----------------+ +------------+ +-----------+ | +------------+ | | | | | | | | | | Optical | | Optical | | | Optical | | | Interface |------->| Impairment|--->| | Channel | | | (Transmit/ | | Path | | | Estimation | | | Receive) | | | | | | | +------------+ +-----------+ | +------------+ | | || | | || | | Estimation | | || | | \/ | | +------------+ | | | BER / | | | | Q Factor | | | +------------+ | +-----------------+ Starting from functional block on the left the Optical Interface represents where the optical signal is transmitted or received and defines the properties at the end points path. Even the no- impairmentno-impairment case like scenario B in section 184.108.40.206.1 needs to consider a minimum set of interface characteristics. In such case only a few parameters used to assess the signal compatibility will be taken into account (see [WSON-Frame]). For the impairment-awarenessimpairment-aware case signal compatibilitythese parameters may be sufficient or not depending on the accepted level of approximation (scenarios C and D). This functional block highlights the need to consider a set of interface parameters during an Impairment Validation Process. The block "Optical Impairment Path" represents all kinds of impairments affecting a wavelength as it traverses the networks through links and nodes. In the case where the control plane has no IV this block will not be present. Otherwise, this function must be implemented in some way via the control plane. Options for this will be given in the next section on architectural alternatives. This block implementation (e.g. through routing, signaling or PCE) may influence the way the control plane distributes impairment information within the network. The last block implements the decision function for path feasibility. Depending on the IA level of approximation this function can be more or less complex. For example in case of no IA only the signal class compatibility will be verified. In addition to feasible/not-feasible result, it may be worthworthwhile for decision functions to consider the case in which paths can be likely-to-be- feasiblelikely-to-be-feasible within some degree of confidence. The optical impairments are usually not fixed values as they may vary within ranges of values according to the approach taken in the physical modeling (worst-case, statistical or based on typical values). For example, the utilization of the worst-case value for each parameter within impairment validation process may lead to marking some paths as not-feasible while they are very likely to be feasible in reality. 220.127.116.11. IA-RWA Computation and Control Plane Architectures From a control plane point of view optical impairments are additional constraints to the impairment-free RWA process described in [WSON-Frame].[WSON- Frame]. In impairment aware routing and wavelength assignment (IA-RWA),(IA- RWA), there are conceptually three general classes of processes to be considered: Routing (R), Wavelength Assignment (WA), and Impairment Validation (estimation) (IV). Impairment validation may come in many forms, and maybe invoked at different levels of detail in the IA-RWA process. From a process point of view we will consider the following three forms of impairment validation: o IV-Candidates In this case an Impairment Validation (IV) process furnishes a set of paths between two nodes along with any wavelength restrictions such that the paths are valid with respect to optical impairments. These paths and wavelengths may not be actually available in the network due to its current usage state. This set of paths wouldcould be returned in response to a request for a set of at most K valid paths between two specified nodes. Note that such a process never directly discloses optical impairment information. Note that that this case includes any paths between source and destination that may have been "pre-validated". In this case the control plane simply makes use of candidate paths but does not know any optical impairment information. Another option is when the path validity is assessed within the control plane. The following cases highlight this situation. o IV-Approximate Verification Here approximation methods are used to estimate the impairments experienced by a signal. Impairments are typically approximated by linear and/or statistical characteristics of individual or combined components and fibers along the signal path. o IV-Detailed Verification In this case an IV process is given a particular path and wavelength through an optical network and is asked to verify whether the overall quality objectives for the signal over this path can be met. Note that such a process never directly discloses optical impairment information. The next two cases refer to the way an impairment validation computation can be performed. o IV-Centralized In this case impairments to a path are computed at a single entity. The information concerning impairmentsimpairments, however, may still be gathered from network elements however.elements. Depending how information areis gathered this may put additional requirements on routing protocols. This will be detailed in followinglater sections. o IV-Distributed In the distributed IV process, impairmentapproximate degradation measures such as OSNR, dispersion, DGD, etc. are accumulated along the path via a signaling like protocol. Each node on the path may already perform some part of the impairment computation (i.e. distributed). When the accumulated measures reach the destination node a decision on the impairment validity of the path can be made. Note that such a process would entail revealing an individual network element's impairment information but it does not generally require spreadingdistributing optical parameters at network level.to the entire network. The Control Plane must not preclude the possibility to operate one or all the above cases concurrently in the same network. For example there could be cases where a certain number of paths are already pre-validatespre- validated (IV-Candidates) so the control plane may setup one of those path without requesting any impairment validation procedure. On the same network however the control plane may compute a path outside the set of IV-Candidates for which an impairment evaluation can be necessary. The following subsections present three major classes of IA-RWA path computation architectures and reviews some of their respective advantages and disadvantages. 18.104.22.168.2.1. Combined Routing, WA, and IV From the point of view of optimality, the "best"reasonably good IA-RWA solutions can be achieved if the path computation entity (PCE) can conceptually/algorithmically combine the processes of routing, wavelength assignment and impairment validation. Such a combination can take place if the PCE is given: (a) the impairment-free WSON network information as discussed in [WSON- Frame][WSON-Frame] and (b) impairment information to validate potential paths. 22.214.171.124.2.2. Separate Routing, WA, or IV Separating the processes of routing, WA and/or IV can reduce the need for sharing of different types of information used in path computation. This was discussed for routing separate from WA in [WSON-Frame]. In addition, as will bewas discussed in the section on network contextssome impairment information may not be shared and this may lead to the need to separate IV from RWA. In addition, as also discussed in the section on network contexts,if IV needs to be done at a high level of precision it may be advantageous to offload this computation to a specialized server. The following conceptual architectures belong in this general category: o R+WA+IV -- separate routing, wavelength assignment, and impairment validation. o R + (WA & IV) -- routing separate from a combined wavelength assignment and impairment validation process. Note that impairment validation is typically wavelength dependent hence combining WA with IV can lead to efficiencies. o (RWA)+IV - combined routing and wavelength assignment with a separate impairment validation process. Note that the IV process may come before or after the RWA processes. If RWA comes first then IV is just rendering a yes/no decision on the selected path and wavelength. If IV comes first it would need to furnish a list of possible (valid with respect to impairments) routes and wavelengths to the RWA processes. 126.96.36.199.2.3. Distributed WA and/or IV In the non-impairment RWA situation [WSON-Frame] it was shown that a distributed wavelength assignment (WA) process carried out via signaling can eliminate the need to distribute wavelength availability information via an IGP.interior gateway protocol (IGP). A similar approach can allow for the distributed computation of impairment effects and avoid the need to distribute impairment characteristics of network elements and links via routerouting protocols or by other means. An example of such an approach is given in [Martinelli] and utilizes enhancements to RSVP signaling to carry accumulated impairment related information. So the following conceptual options belong to this category: o RWA+D(IV)RWA + D(IV) - Combined routing and wavelength assignment and distributed impairment validation. o R + D(WA & IV) -- routing separate from a distributed wavelength assignment and impairment validation process. A distributedDistributed impairment validation for a prescribed network path requires that the effects of impairments canbe calculated by approximate models with cumulative quality measures such as those given in [G.680]. For such a system to be interoperable the various impairment measures to be accumulatedexact encoding of the techniques from [G.680] would need to be agreed according to [G.680].upon. If distributed WA is being done at the same time as distributed IV then we may need to accumulate impairment related information for all wavelengths that could be used. This is somewhat winnowed down as potential wavelengths are discovered to be in use, but could be a significant burden for lightly loaded high channel count networks. 188.8.131.52. Mapping Network Requirements to Architectures InFigure 2 we showshows process flows for three main architectural alternatives to IA-RWA when approximate impairment validation suffices. InFigure 3 we showshows process flows for two main architectural alternatives when detailed impairment verification is required. +-----------------------------------+ | +--+ +-------+ +--+ | | |IV| |Routing| |WA| | | +--+ +-------+ +--+ | | | | Combined Processes | +-----------------------------------+ (a) +--------------+ +----------------------+ | +----------+ | | +-------+ +--+ | | | IV | | | |Routing| |WA| | | |candidates| |----->| +-------+ +--+ | | +----------+ | | Combined Processes | +--------------+ +----------------------+ (b) +-----------+ +----------------------+ | +-------+ | | +--+ +--+ | | |Routing| |------->| |WA| |IV| | | +-------+ | | +--+ +--+ | +-----------+ | Distributed Processes| +----------------------+ (c) Figure 2 Process flows for the three main approximate impairment architectural alternatives. The advantages, requirements and suitability of these options are as follows: o Combined IV & RWA process This alternative combines RWA and IV within a single computation entity enabling highest potential optimality and efficiency in IA- RWA. This alternative requires that the computational entity knows impairment information as well as non-impairment RWA information. This alternative can be used with "black links", but would then need to be provided by the authority controlling the "black links". o IV-Candidates + RWA process This alternative allows separation of impairment information into two computational entities while still maintaining a high degree of potential optimality and efficiency in IA-RWA. The candidates IV process needs to know impairment information from all optical network elements, while the RWA process needs to know non- impairmentnon-impairment RWA information from the network elements. This alternative can be used with "black links", but the authority in control of the "black links" would need to provide the functionality of the IV-candidates process. Note that this is still very useful since the algorithmic areas of IV and RWA are very different and prone to specialization. o Routing + Distributed WA and IV In this alternative a signaling protocol is extended and leveraged in the wavelength assignment and impairment validation processes. Although this doesn't enable as high a potential degree of optimality of optimality as (a) or (b), it does not require distribution of either link wavelength usage or link/node impairment information. Note that this is most likely not suitable for "black links". +-----------------------------------+ +------------+ | +-----------+ +-------+ +--+ | | +--------+ | | | IV | |Routing| |WA| | | | IV | | | |approximate| +-------+ +--+ |---->| |Detailed| | | +-----------+ | | +--------+ | | Combined Processes | | | +-----------------------------------+ +------------+ (a) +--------------+ +----------------------+ +------------+ | +----------+ | | +-------+ +--+ | | +--------+ | | | IV | | | |Routing| |WA| |---->| | IV | | | |candidates| |----->| +-------+ +--+ | | |Detailed| | | +----------+ | | Combined Processes | | +--------+ | +--------------+ +----------------------+ | | (b) +------------+ Figure 3 Process flows for the two main detailed impairment validation architectural options. The advantages, requirements and suitability of these detailed validation options are as follows: o Combined approximate IV & RWA + Detailed-IV This alternative combines RWA and approximate IV within a single computation entity enabling highest potential optimality and efficiency in IA-RWA; then has a separate entity performing detailed impairment validation. In the case of "black links" the authority controlling the "black links" would need to provide all functionality. o Candidates-IV + RWA + Detailed-IV This alternative allows separation of approximate impairment information into a computational entity while still maintaining a high degree of potential optimality and efficiency in IA-RWA; then a separate computation entity performs detailed impairment validation. Note that detailed impairment estimation is not standardized. 4.5. Protocol Implications The previous IA-RWA architectural alternatives and process flows make differing demands on a GMPLS/PCE based control plane. In this section we discuss the use of (a) an impairment information model, (b) PCE as computational entity assuming the various process roles and consequences for PCEP, (c)any needed extensions to signaling, and (d) extensions to routing. The impacts to the control plane for IA-RWA are summarized in Figure 4. +-------------------+----+----+----------+--------+ | IA-RWA Option |PCE |Sig |Info Model| Routing| +-------------------+----+----+----------+--------+ | Combined |Yes | No | Yes | Yes | | IV & RWA | | | | | +-------------------+----+----+----------+--------+- | IV-Candidates |Yes | No | Yes | Yes | | + RWA | | | | | +-------------------+----+----+----------+--------+ | Routing + |No | Yes| Yes | No | |Distributed IV, RWA| | | | | +-------------------+----+----+----------+--------+ | Detailed IV |Yes | No | Yes | Yes | +-------------------+----+----+----------+--------+Figure 4 IA-RWA architectural options and control plane impacts. 184.108.40.206. Information Model for Impairments As previously discussed all IA-RWA scenarios to a greater or lesser extent rely on a common impairment information model. A number of ITU-T recommendations cover detailed as well as approximate impairment characteristics of fibers and a variety of devices and subsystems. A well integrated impairment model for optical network elements is given in [G.680] and is used to form the basis for an optical impairment model in a companion document [Imp-Info]. It should be noted that the current version of [G.680] is limited to the networks composed of a single WDM line system vendor combined with OADMs and/or PXCs from potentially multiple other vendors, this is known as situation 1 and is shown in Figure 1-1 of [G.680]. It is planed in the future that [G.680] will include networks incorporating line systems from multiple vendors as well as OADMs and/or PXCs from potentially multiple other vendors, this is known as situation 2 and is shown in Figure 1-2 of [G.680]. The case of distributed impairment validation actually requires a bit more than an impairment information model. In particular, it needs a common impairment "computation" model. In the distributed IV case one needs to standardize the accumulated impairment measures that will be conveyed and updated at each node. Section 9 of [G.680] provides guidance in this area with specific formulas given for OSNR, residual dispersion, polarization mode dispersion/polarization dependent loss, effects of channel uniformity, etc... However, specifics of what intermediate results are kept and in what form would need to be standardized. 220.127.116.11. Routing Different approaches to path/wavelength impairment validation gives rise to different demands placed on GMPLS routing protocols. In the case where approximate impairment information is used to validate paths GMPLS routing may be used to distribute the impairment characteristics of the network elements and links based on the impairment information model previously discussed. Depending on the computational alternative the routing protocol may need to advertise information necessary to impairment validation process. This can potentially cause scalability issues due to the high amount of data that need to be advertised. Such issue can be addressed separating data that need to be advertised rarely and data that need to be advertised more frequently or adopting other form of awareness solutions described in previous sections (e.g. centralized and/or external IV entity). In term of approximated scenario (see Section 18.104.22.168.1.1. ) the model defined by [G.680] will apply and routing protocol will need to gather information required for such computation. In the case of distributed-IV no new demands would be placed on the routing protocol. 22.214.171.124. Signaling The largest impacts on signaling occur in the cases where distributed impairment validation is performed. In this we need to accumulate impairment information as previously discussed. In addition, since the characteristics of the signal itself, such as modulation type, can play a major role in the tolerance of impairments, this type of information will need to be implicitly or explicitly signaled so that an impairment validation decision can be made at the destination node. It remains for further study if it may be beneficial to include additional information to a connection request such as desired egress signal quality (defined in some appropriate sense) in non- distributednon-distributed IV scenarios. 126.96.36.199. PCE In section 188.8.131.52. we gave a number of computation architectural alternatives that could be used to meet the various requirements and constraints of section 184.108.40.206. Here we look at how these alternatives could be implemented via either a single PCE or a set of two or more cooperating PCEs, and the impacts on the PCEP protocol. 220.127.116.11.4.1. Combined IV & RWA In this situation, shown in Figure 2(a), a single PCE performs all the computations needed for IA-RWA. o TE Database Requirements WSON Topology and switching capabilities, WSON WDM link wavelength utilization, and WSON impairment information o PCC to PCE Request Information Signal characteristics/type, required quality, source node, destination node o PCE to PCC Reply Information If the computations completed successfully then the PCE returns the path and its assigned wavelength. If the computations could not complete successfully it would be potentially useful to know the reason why. At a very crude level we'd like to know if this was due to lack of wavelength availability or impairment considerations or a bit of both. The information to be conveyed is for further study. 18.104.22.168.4.2. IV-Candidates + RWA In this situation, shown in Figure 2(b), we have two separate processes involved in the IA-RWA computation. This requires at leasttwo cooperating PCEs: one for the Candidates-IV process and another for the RWA process. In addition, the overall process needs to be coordinated. This could be done with yet another PCE or we can add this functionality to one of previously defined PCEs. We choose this later option and require the RWA PCE to also act as the overall process coordinator. The roles, responsibilities and information requirements for these two PCEs are given below. RWA and Coordinator PCE (RWA-Coord-PCE): Responsible for interacting with PCC and for utilizing Candidates- PCECandidates-PCE as needed during RWA computations. In particular it needs to know to use the Candidates-PCE to obtain potential set of routes and wavelengths. o TE Database Requirements WSON Topology and switching capabilities and WSON WDM link wavelength utilization (no impairment information). o PCC to RWA-PCE request: same as in the combined case. o RWA-PCE to PCC reply: same as in the combined case. o RWA-PCE to IV-Candidates-PCE request The RWA-PCE asks for a set of at most K routes along with acceptable wavelengths between nodes specified in the original PCC request. o IV-Candidates-PCE reply to RWA-PCE The Candidates-PCE returns a set of at most K routes along with acceptable wavelengths between nodes specified in the RWA-PCE request. IV-Candidates-PCE: The IV-Candidates-PCE is responsible for impairment aware path computation. It needs not take into account current link wavelength utilization, but this is not prohibited. The Candidates-PCE is only required to interact with the RWA-PCE as indicated above and not the PCC. o TE Database Requirements WSON Topology and switching capabilities and WSON impairment information (no information link wavelength utilization required). In Figure 5 we show a sequence diagram for the interactions between the PCC, RWA-PCERWA-Coord PCE and IV-Candidates-PCE.IV-Candidates PCE. +---+ +-------------+ +----------------- ++-----------------+ |PCC| |RWA-Coord-PCE| |IV-Candidates-|RWA-Coord PCE| |IV-Candidates PCE| +-+-+ +------+------+ +---------+------- ++---------+-------+ ...___ (a) | | | ````---...____ | | | ```-->| | | | | | |--..___ (b) | | | ```---...___ | | | ```---->| | | | | | | | | (c) ___...| | | ___....---'''' | | |<--'''' | | | | | | | | (d) ___...| | | ___....---''' | | |<--''' | | | | | | | | Figure 5 Sequence diagram for the interactions between PCC, RWA- Coordinating-PCE and the IV-Candidates-PCE. In step (a) the PCC requests a path meeting specified quality constraints between two nodes (A and Z) for a given signal represented either by a specific type or a general class with associated parameters. In step (b) the RWA-Coordinating-PCE requests up to K candidate paths between nodes A and Z and associated acceptable wavelengths. In step (c) The IV-Candidates-IV-Candidates PCE returns this list to the RWA-Coordinating PCE which then uses this set of paths and wavelengths as input (e.g. a constraint) to its RWA computation. In step (d) the RWA-Coordinating-PCE returns the overall IA-RWA computation results to the PCC. 4.4.3. Approximate IA-RWA + Separate Detailed IV In Figure 3 we showed two cases where a separate detailed impairment validation process could be utilized. We can place the detailed validation process into a separate PCE. Assuming that a different PCE assumes a coordinating role and interacts with the PCC we can keep the interactions with this separate IV-Detailed- PCE very simple. IV-Detailed-PCE: o TE Database Requirements The IV-Detailed-PCE will need optical impairment information, WSON topology, and possibly WDM link wavelength usage information. This document puts no restrictions on the type of information that may be used in these computations. o Coordinating-PCE to IV-Detailed-PCE request The coordinating-PCE will furnish signal characteristics, quality requirements, path and wavelength to the IV-Detailed-PCE. o IV-Detailed-PCE to Coordinating-PCE reply The reply is essential an yes/no decision as to whether the requirements could actually be met. In the case where the impairment validation fails it would be helpful to convey information related to cause or quantify the failure, e.g., so a judgment can be made whether to try a different signal or adjust signal parameters. In Figure 6 we show a sequence diagram for the interactions for the process shown in Figure 3(b). This involves interactions between the PCC, RWA-PCE (acting as coordinator), IV-Candidates- PCE and the IV-Detailed-PCE. In step (a) the PCC requests a path meeting specified quality constraints between two nodes (A and Z) for a given signal represented either by a specific type or a general class with associated parameters. In step (b) the RWA-Coordinating-PCE requests up to K candidate paths between nodes A and Z and associated acceptable wavelengths. In step (c) The IV-Candidates- PCE returns this list to the RWA-Coordinating PCE which then uses this set of paths and wavelengths as input (e.g. a constraint) to its RWA computation. In step (d) the RWA-Coordinating-PCE request a detailed verification of the path and wavelength that it has computed. In step (e) the IV-Detailed-PCE returns the results of the validation to the RWA-Coordinating-PCE. Finally in step (f)IA- RWA-Coordinating PCE returns the final results (either a path and wavelength or cause for the failure to compute a path and wavelength) to the PCC. +----------+ +--------------+ +------------ + +---+ |RWA-Coord | |IV-Candidates | |IV-Detailed | |PCC| | PCE | | PCE | | PCE | +-+-+ +----+-----+ +------+-------+ +-----+------ + |.._ (a) | | | | ``--.__ | | | | `-->| | | | | (b) | | | |--....____ | | | | ````---.>| | | | | | | | (c) __..-| | | | __..---'' | | | |<--'' | | | | | | |...._____ (d) | | | `````-----....._____ | | | `````----->| | | | | | (e) _____.....+ | | _____.....-----''''' | | |<----''''' | | (f) __.| | | __.--'' | |<-'' | | | Figure 6 Sequence diagram for the interactions between PCC, RWA- Coordinating-PCE, IV-Candidates-PCE and IV-Detailed-PCE. 5. Security Considerations This document discusses a number of control plane architectures that incorporate knowledge of impairments in optical networks. If such architecture is put into use within a network it will by its nature contain details of the physical characteristics of an optical network. Such information would need to be protected from intentional or unintentional disclosure. 6. IANA Considerations This draft does not currently require any consideration from IANA. 7. Acknowledgments This document was prepared using 2-Word-v2.0.template.dot. APPENDIX A: Overview of Optical Layer ITU-T Recommendations For optical fiber, devices, subsystems and network elements the ITU-T has a variety of recommendations that include definitions, characterization parameters and test methods. In the following we take a bottom up survey to emphasize the breadth and depth of the existing recommendations. We focus on digital communications over single mode optical fiber. A.1. Fiber and Cables Fibers and cables form a key component of what from the control plane perspective could be termed an optical link. Due to the wide range of uses of optical networks a fairly wide range of fiber types are used in practice. The ITU-T has three main recommendations covering the definition of attributes and test methods for single mode fiber: o Definitions and test methods for linear, deterministic attributes of single-mode fibre and cable [G.650.1] o Definitions and test methods for statistical and non-linear related attributes of single-mode fibre and cable [G.650.2] o Test methods for installed single-mode fibre cable sections [G.650.3] General Definitions[G.650.1]: Mechanical Characteristics (numerous), Mode field characteristics(mode field, mode field diameter, mode field centre, mode field concentricity error, mode field non-circularity), Glass geometry characteristics, Chromatic dispersion definitions (chromatic dispersion, group delay, chromatic dispersion coefficient, chromatic dispersion slope, zero-dispersion wavelength, zero-dispersion slope), cut-off wavelength, attenuation. Definition of equations and fitting coefficients for chromatic dispersion (Annex A). [G.650.2] polarization mode dispersion (PMD) - phenomenon of PMD, principal states of polarization (PSP), differential group delay (DGD), PMD value, PMD coefficient, random mode coupling, negligible mode coupling, mathematical definitions in terms of Stokes or Jones vectors. Nonlinear attributes: Effective area, correction factor k, non-linear coefficient (refractive index dependent on intensity), Stimulated Billouin scattering. Tests defined [G.650.1]: Mode field diameter, cladding diameter, core concentricity error, cut-off wavelength, attenuation, chromatic dispersion. [G.650.2]: test methods for polarization mode dispersion. [G.650.3] Test methods for characteristics of fibre cable sections following installation: attenuation, splice loss, splice location, fibre uniformity and length of cable sections (these are OTDR based), PMD, Chromatic dispersion. With these definitions a variety of single mode fiber types are defined as shown in the table below: 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 | ------------------------------------------------------------ A.2. Devices A.2.1. Optical Amplifiers Optical amplifiers greatly extend the transmission distance of optical signals in both single channel and multi channel (WDM) subsystems. The ITU-T has the following recommendations: o Definition and test methods for the relevant generic parameters of optical amplifier devices and subsystems [G.661] o Generic characteristics of optical amplifier devices and subsystems [G.662] o Application related aspects of optical amplifier devices and subsystems [G.663] o Generic characteristics of Raman amplifiers and Raman amplified subsystems [G.665] Reference [G.661] starts with general classifications of optical amplifiers based on technology and usage, and include a near exhaustive list of over 60 definitions for optical amplifier device attributes and parameters. In references [G.662] and [G.665] we have characterization of specific devices, e.g., semiconductor optical amplifier, used in a particular setting, e.g., line amplifier. For example reference[G.662] gives the following minimum list of relevant parameters for the specification of an optical amplifier device used as line amplifier in a multichannel application: a) Channel allocation. b) Total input power range. c) Channel input power range. d) Channel output power range. e) Channel signal-spontaneous noise figure. f) Input reflectance. g) Output reflectance. h) Maximum reflectance tolerable at input. i) Maximum reflectance tolerable at output. j) Maximum total output power. k) Channel addition/removal (steady-state) gain response. l) Channel addition/removal (transient) gain response. m) Channel gain. n) Multichannel gain variation (inter-channel gain difference). o) Multichannel gain-change difference (inter-channel gain-change difference). p) Multichannel gain tilt (inter-channel gain-change ratio). q) Polarization Mode Dispersion (PMD). A.2.2. Dispersion Compensation In optical systems two forms of dispersion are commonly encountered [RFC4054] chromatic dispersion and polarization mode dispersion (PMD). There are a number of techniques and devices used for compensating for these effects. The following ITU-T recommendations characterize such devices: o Characteristics of PMD compensators and PMD compensating receivers [G.666] o Characteristics of Adaptive Chromatic Dispersion Compensators [G.667] The above furnish definitions as well as parameters and characteristics. For example in [G.667] adaptive chromatic dispersion compensators are classified as being receiver, transmitter or line based, while in [G.666] PMD compensators are only defined for line and receiver configurations. Parameters that are common to both PMD and chromatic dispersion compensators include: line fiber type, maximum and minimum input power, maximum and minimum bit rate, and modulation type. In addition there are a great many parameters that apply to each type of device and configuration. A.2.3. Optical Transmitters The definitions of the characteristics of optical transmitters can be found in references [G.957], [G.691], [G.692] and [G.959.1]. In addition references [G.957], [G.691], and [G.959.1] define specific parameter values or parameter ranges for these characteristics for interfaces for use in particular situations. We generally have the following types of parameters Wavelength related: Central frequency, Channel spacing, Central frequency deviation[G.692]. Spectral characteristics of the transmitter: Nominal source type (LED, MLM lasers, SLM lasers) [G.957], Maximum spectral width, Chirp parameter, Side mode suppression ratio, Maximum spectral power density [G.691]. Power related: Mean launched power, Extinction ration, Eye pattern mask [G.691], Maximum and minimum mean channel output power [G.959.1]. A.2.4. Optical Receivers References [G.959.1], [G.691], [G.692] and [G.957], define optical receiver characteristics and [G.959.1], [G.691] and [G.957]give specific values of these parameters for particular interface types and network contexts. The receiver parameters include: Receiver sensitivity: minimum value of average received power to achieve a 1x10-10 BER [G.957] or 1x10-12 BER [G.691]. See [G.957] and [G.691] for assumptions on signal condition. Receiver overload: Receiver overload is the maximum acceptable value of the received average power for a 1x10.10 BER [G.957] or a 1x10-12 BER [G.691]. Receiver reflectance: "Reflections from the receiver back to the cable plant are specified by the maximum permissible reflectance of the receiver measured at reference point R." Optical path power penalty: "The receiver is required to tolerate an optical path penalty not exceeding X dB to account for total degradations due to reflections, intersymbol interference, mode partition noise, and laser chirp." When dealing with multi-channel systems or systems with optical amplifiers we may also need: Optical signal-to-noise ratio: "The minimum value of optical SNR required to obtain a 1x10-12 BER."[G.692] Receiver wavelength range: "The receiver wavelength range is defined as the acceptable range of wavelengths at point Rn. This range must be wide enough to cover the entire range of central frequencies over the OA passband." [G.692] Minimum equivalent sensitivity: "This is the minimum sensitivity that would be required of a receiver placed at MPI-RM in multichannel applications to achieve the specified maximum BER of the application code if all except one of the channels were to be removed (with an ideal loss-less filter) at point MPI-RM." [G.959.1] A.3. Components and Subsystems Reference [G.671] "Transmission characteristics of optical components and subsystems" covers the following components: o optical add drop multiplexer (OADM) subsystem; o asymmetric branching component; o optical attenuator; o optical branching component (wavelength non-selective); o optical connector; o dynamic channel equalizer (DCE); o optical filter; o optical isolator; o passive dispersion compensator; o optical splice; o optical switch; o optical termination; o tuneable filter; o optical wavelength multiplexer (MUX)/demultiplexer (DMUX); - coarse WDM device; - dense WDM device; - wide WDM device. Reference [G.671] then specifies applicable parameters for these components. For example an OADM subsystem will have parameters such as: insertion loss (input to output, input to drop, add to output), number of add, drop and through channels, polarization dependent loss, adjacent channel isolation, allowable input power, polarization mode dispersion, etc... A.4. Network Elements The previously cited ITU-T recommendations provide a plethora of definitions and characterizations of optical fiber, devices, components and subsystems. Reference [G.Sup39] "Optical system design and engineering considerations" provides useful guidance on the use of such parameters. In many situations the previous models while good don't encompass the higher level network structures that one typically deals with in the control plane, i.e, "links" and "nodes". In addition such models include the full range of network applications from planning, installation, and possibly day to day network operations, while with the control plane we are generally concerned with a subset of the later. In particular for many control plane applications we are interested in formulating the total degradation to an optical signal as it travels through multiple optical subsystems, devices and fiber segments. In reference [G.680] "Physical transfer functions of optical networks elements", a degradation function is currently defined for the following optical network elements: (a) DWDM Line segment, (b) Optical Add/Drop Multiplexers (OADM), and (c) Photonic cross- connect (PXC). The scope of [G.680] is currently for optical networks consisting of one vendors DWDM line systems along with another vendors OADMs or PXCs. The DWDM line system of [G.680] consistsuses this set of the optical fiber, line amplifierspaths and any embedded dispersion compensators. Similarlywavelengths as input (e.g. a constraint) to its RWA computation. In step (d) the OADM/PXC network element may consist ofRWA-Coordinating PCE returns the basic OADM component and optionally included optical amplifiers. The parameters for theseoverall IA-RWA computation results to the PCC. 6. Security Considerations This document discusses a number of control plane architectures that incorporate knowledge of impairments in optical networks. If such architecture is put into use within a network elements (ONE) are given underit will by its nature contain details of the following circumstances: o General ONE without optical amplifiers o General ONE with optical amplifiers o OADM without optical amplifiers o OADM with optical amplifiers o Reconfigurable OADM (ROADM) without optical amplifiers o ROADM with optical amplifiers o PXC without optical amplifiers o PXC withphysical characteristics of an optical amplifiersnetwork. Such information would need to be protected from intentional or unintentional disclosure. 7. IANA Considerations This draft does not currently require any consideration from IANA. 8. References 8.1. Normative References [G.650.1] ITU-T Recommendation G.650.1, Definitions and test methods for linear, deterministic attributes of single- modesingle-mode fibre and cable, June 2004. [650.2][G.650.2] ITU-T Recommendation G.650.2, Definitions and test methods for statistical and non-linear related attributes of single-mode fibre and cable, July 2007. [650.3][G.650.3] ITU-T Recommendation G.650.3 [G.652] ITU-T Recommendation G.652, Characteristics of a single- modesingle-mode optical fibre and cable, June 2005. [G.653] ITU-T Recommendation G.653, Characteristics of a dispersion-shifteddispersion- shifted single-mode optical fibre and cable, December 2006. [G.654] ITU-T Recommendation G.654, Characteristics of a cut-off shifted single-mode optical fibre and cable, December 2006. [G.655] ITU-T Recommendation G.655, Characteristics of a non-zero dispersion-shifted single-mode optical fibre and cable, March 2006. [G.656] ITU-T Recommendation G.656, Characteristics of a fibre and cable with non-zero dispersion for wideband optical transport, December 2006. [G.661] ITU-T Recommendation G.661, Definition and test methods for the relevant generic parameters of optical amplifier devices and subsystems, March 2006. [G.662] ITU-T Recommendation G.662, Generic characteristics of optical amplifier devices and subsystems, July 2005. [G.671] ITU-T Recommendation G.671, Transmission characteristics of optical components and subsystems, January 2005. [G.680] ITU-T Recommendation G.680, Physical transfer functions of optical network elements, July 2007. [G.691] ITU-T Recommendation G.691, Optical interfaces for multichannel systems with optical amplifiers, November 1998. [G.692] ITU-T Recommendation G.692, Optical interfaces for single channel STM-64 and other SDH systems with optical amplifiers, March 2006. [G.872] ITU-T Recommendation G.872, Architecture of optical transport networks, November 2001. [G.957] ITU-T Recommendation G.957, Optical interfaces for equipments and systems relating to the synchronous digital hierarchy, March 2006. [G.959.1] ITU-T Recommendation G.959.1, Optical Transport Network Physical Layer Interfaces, March 2006. [G.694.1] ITU-T Recommendation G.694.1, Spectral grids for WDM applications: DWDM frequency grid, June 2002. [G.694.2] ITU-T Recommendation G.694.2, Spectral grids for WDM applications: CWDM wavelength grid, December 2003. [G.698.1] ITU-T Recommendation G.698.1, Multichannel DWDM applications with Single-Channel optical interface, December 2006. [G.698.2] ITU-T Recommendation G.698.2, Amplified multichannel DWDM applications with Single-Channel optical interface, July 2007. [G.Sup39] ITU-T Series G Supplement 39, Optical system design and engineering considerations, February 2006. [RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004. [RFC4054] Strand, J., Ed., and A. Chiu, Ed., "Impairments and Other Constraints on Optical Layer Routing", RFC 4054, May 2005. [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006. 8.2. Informative References [WSON-Frame] G. Bernstein,Y. Lee, G. Bernstein, W. Imajuku, "Framework for GMPLS and PCE Control of Wavelength Switched Optical Networks", work in progress: draft-ietf-ccamp- wavelength-switched-framework-02.txt, March 2009. 8.2. Informative Referencesdraft-ietf-ccamp-wavelength-switched- framework. [Imp-Info] G. Bernstein, Y. Lee, D. Li, "A Framework for the Control and Measurement of Wavelength Switched Optical Networks (WSON) with Impairments", work in progress: draft-bernstein-wson-impairment-info.draft- bernstein-wson-impairment-info. [Martinelli] G. Martinelli (ed.) and A. Zanardi (ed.), "GMPLS Signaling Extensions for Optical Impairment Aware Lightpath Setup", Work in Progress: draft-martinelli- ccamp-optical-imp-signaling-02.txt, February 2008. [WSON-Comp] G. Bernstein, Y. Lee, Ben Mack-Crane, "WSON Signal Characteristicsdraft-martinelli-ccamp-optical- imp-signaling. 9. Acknowledgments This document was prepared using 2-Word-v2.0.template.dot. Copyright (c) 2011 IETF Trust and Network Element Compatibility Constraints for GMPLS", workthe persons identified as authors of the code. All rights reserved. Redistribution and use in progress: draft- bernstein-ccamp-wson-signal. Author'ssource and binary forms, with or without modification, are permitted provided that the following conditions are met: o Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. o Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. o Neither the name of Internet Society, IETF or IETF Trust, nor the names of specific contributors, may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 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