Network Working Group Y. Lee Huawei G. Bernstein Grotto Networking D. Li Huawei G. Martinelli Cisco Internet Draft Intended status: Informational January 5, 2012 Expires: July 2012 A Framework for the Control of Wavelength Switched Optical Networks (WSON) with Impairments draft-ietf-ccamp-wson-impairments-10.txt Abstract 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, these processes are usually referred to as "impairments". These physical characteristics may be important constraints to consider when using a GMPLS control plane to support path setup and maintenance in wavelength switched optical networks. This document provides a framework for applying GMPLS protocols and the PCE architecture to support Impairment Aware Routing and Wavelength Assignment (IA-RWA) in wavelength switched optical networks. Specifically, this document discusses key computing constraints, scenarios and architectural processes: Routing, Wavelength Assignment, and Impairment Validation. This document does not define optical data plane aspects; impairment parameters, measurement of, or assessment and qualification of a route, but rather it describes the architectural and information components for protocol solutions. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Lee & Bernstein Expires July 5, 2012 [Page 1] Internet-Draft Framework for Optical Impairments January 2012 Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on July 5, 2012. Copyright Notice Copyright (c) 2012 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...................................................3 2. Terminology....................................................4 3. Applicability..................................................6 4. Impairment Aware Optical Path Computation......................7 4.1. Optical Network Requirements and Constraints..............8 4.1.1. Impairment Aware Computation Scenarios...............8 4.1.2. Impairment Computation and Information Sharing Constraints.................................................9 Lee & Bernstein Expires July 5, 2012 [Page 2] Internet-Draft Framework for Optical Impairments January 2012 4.1.3. Impairment Estimation Process.......................11 4.2. IA-RWA Computation and Control Plane Architectures.......12 4.2.1. Combined Routing, WA, and IV........................14 4.2.2. Separate Routing, WA, or IV.........................14 4.2.3. Distributed WA and/or IV............................15 4.3. Mapping Network Requirements to Architectures............16 5. Protocol Implications.........................................18 5.1. Information Model for Impairments........................19 5.2. Routing..................................................20 5.3. Signaling................................................20 5.4. PCE......................................................21 5.4.1. Combined IV & RWA...................................21 5.4.2. IV-Candidates + RWA.................................21 5.4.3. Approximate IA-RWA + Separate Detailed IV...........23 6. Manageability and Operations..................................25 7. Security Considerations.......................................26 8. IANA Considerations...........................................27 9. References....................................................27 9.1. Normative References.....................................27 9.2. Informative References...................................27 10. Acknowledgments..............................................28 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, these processes are usually referred to as "impairments". Optical 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. In order to provision an optical connection (an optical path) through a WSON, a combination of path continuity, resource availability, and impairments constraints must be met to determine Lee & Bernstein Expires July 5, 2012 [Page 3] Internet-Draft Framework for Optical Impairments January 2012 viable and optimal paths through the network. The determination of appropriate paths is known as Impairment Aware Routing and Wavelength Assignment (IA-RWA). Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] provides a set of control plane protocols that can be used to operate networks ranging from packet switch capable networks, through those networks that use time division multiplexing and WDM. The Path Computation Element (PCE) architecture [RFC4655] defines functional computation components that can be used in cooperation with the GMPLS control plane to compute and suggest appropriate paths. [RFC4054] provides an overview of optical impairments and their routing (path selection) implications for GMPLS. This document uses as reference [G.680] and other ITU-T Recommendations for the optical data plane aspects. This document provides a framework for applying GMPLS protocols and the PCE architecture to the control and operation of IA-RWA for WSONs. To aid in this evaluation, this document provides an overview of the subsystems and processes that comprise WSONs and describes IA-RWA models based on the corresponding ITU-T Recommendations, so that the information requirements for use by GMPLS and PCE systems can be identified. This work will facilitate the development of protocol extensions in support of IA-RWA within the GMPLS and PCE protocol families. 2. Terminology ADM: Add/Drop Multiplexers - An optical device used in WDM networks composed of one or more line side ports and typically many tributary ports. Black links: Black links refer to tributary interfaces where only link characteristics are defined. This approach enables transverse compatibility at the single-channel point using a direct wavelength- multiplexing configuration. CWDM: Coarse Wavelength Division Multiplexing DGD: Differential Group Delay DWDM: Dense Wavelength Division Multiplexing FOADM: Fixed Optical Add/Drop Multiplexer Lee & Bernstein Expires July 5, 2012 [Page 4] Internet-Draft Framework for Optical Impairments January 2012 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. NEs: Network Elements OADMs: Optical Add Drop Multiplexers OSNR: Optical Signal to Noise Ratio OXC: Optical cross connect - An optical switching element in which a signal on any input port can reach any output port. PCC: Path Computation Client - Any client application requesting a path computation to be performed by the Path Computation Element. PCE: Path Computation Element - An entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints. PCEP: PCE Communication Protocol - The communication protocol between a Path Computation Client and Path Computation Element. PXC: Photonic Cross Connects Q-factor: The Q-factor provides a qualitative description of the receiver performance. It is a function of the signal to optical noise ratio. The Q-factor suggests the minimum SNR (Signal Noise Ratio) required to obtain a specific BER for a given signal. 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. Translucent Network: A wavelength switched optical network that is predominantly transparent but may also contain limited numbers of regenerators and/or wavelength converters. Lee & Bernstein Expires July 5, 2012 [Page 5] Internet-Draft Framework for Optical Impairments January 2012 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; 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 ensure all paths are 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. Moreover, the optical physical interfaces are typically 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. Lee & Bernstein Expires July 5, 2012 [Page 6] Internet-Draft Framework for Optical Impairments January 2012 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 impairment constraints 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 needs to take into account the evolving network status in term of equipments and traffic at the beginning stage. In addition, network operations such as path establishment, will require significant pre-design via non- control plane processes resulting in significantly slower network provisioning. It should be highlighted that the impact of impairments and use in determination of path viability is not sufficiently well established for general applicability [G.680]; it will depend on network implementations. The use of an impairment aware control plane and set of information distributed will need to be evaluated on a case by case scenario. 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. Impairment-aware path calculation also needs to take into account when regeneration is used along the path. [RFC6163] provides background on the concept of optical translucent networks which contains transparent elements and electro-optical elements such as OEO regenerations. In such networks, a generic light path can go through a number of regeneration points. Regeneration points could happen for two reasons: Lee & Bernstein Expires July 5, 2012 [Page 7] Internet-Draft Framework for Optical Impairments January 2012 (i) Due to wavelength conversion to assist RWA to avoid wavelength blocking. This is the impairment free case covered by [RFC6163]. (ii) The optical signal without regeneration would be too degraded to meet end to end BER requirements. This is the case when RWA takes into consideration impairment estimation covered by this document. In the latter case, an 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 |-----| REG |-----| N3 |----| E | +---+ +----+ +----+ +-----+ +----+ +---+ |<----------------------------->|<-------------------->| Segment 1 Segment 2 Figure 1 Optical path as a set of transparent segments For example, Figure 1 represents an optical path from node I to node E with a regeneration point REG in between. It is feasible from an impairment validation perspective if both segments (I, N1, N2, REG) and (REG, N3, E) are feasible. 4.1. Optical Network Requirements and Constraints This section examines the various optical network requirements and constraints under which an impairment aware optical control plane may have to operate under. These requirements and constraints motivate the IA-RWA architectural alternatives to be presented in the following section. Different optical networks contexts can 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. 4.1.1. 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 Lee & Bernstein Expires July 5, 2012 [Page 8] Internet-Draft Framework for Optical Impairments January 2012 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 [RFC6163] 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]. 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. Note that adding or removing an optical signal on the path should not render any of the existing signals in the network as 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 existing signals. Much work at ITU-T has gone into developing impairment models at this and more detailed levels. Impairment characterization of network elements may be used to calculate which paths are conformant with a specified BER for a particular signal type. In such a case, the impairment aware (IA) path computation can be combined with the RWA process to permit more optimal IA-RWA computations. Note that the IA path computation may also take place in a separate entity, i.e., a PCE. D. Accurate 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. 4.1.2. 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 Lee & Bernstein Expires July 5, 2012 [Page 9] Internet-Draft Framework for Optical Impairments January 2012 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. However, note that 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 in order 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" in the 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, the term "black links" will be used to describe these computation and information sharing constraints in optical networks. From the control plane perspective the following 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 that such a list of paths along with any wavelength constraints could get unmanageably large as the size of the network increases. Lee & Bernstein Expires July 5, 2012 [Page 10] Internet-Draft Framework for Optical Impairments January 2012 2. The authority in control of the "black links" could provide a PCE-like entity 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. 3. The authority in control of the "black links" provides 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. 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. 4.1.3. Impairment Estimation Process The Impairment Estimation Process can be modeled through the following functional blocks. These blocks are independent of 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 | | | +------------+ | +-----------------+ Lee & Bernstein Expires July 5, 2012 [Page 11] Internet-Draft Framework for Optical Impairments January 2012 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 path end points. Even the impairment- free case, like scenario B in section 4.1.1, 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 [RFC6163]). For the impairment-aware case, these 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 the Impairment Validation Process. The block "Optical Impairment Path" represents the types of impairments affecting a wavelength as it traverses the networks through links and nodes. In the case of a network where there are no impairments (Scenario A), this block will not be present. Otherwise, this function must be implemented in some way via the control plane. Architectural alternatives to accomplish this are provided in section 4.2. 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 worthwhile for decision functions to consider the case in which paths can be likely-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, in reality, feasible. 4.2. 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 [RFC6163]. In impairment aware routing and wavelength assignment (IA-RWA), there are conceptually three general classes of processes to be considered: Routing (R), Wavelength Assignment (WA), and Impairment Validation (IV), i.e., estimation. Impairment validation may come in many forms, and may be invoked at different levels of detail in the IA-RWA process. All the variations of impairment validation discussed in this section is based on Lee & Bernstein Expires July 5, 2012 [Page 12] Internet-Draft Framework for Optical Impairments January 2012 Scenario C (Approximated Impairment Estimation) as discussed in Section 4.1.1. From a process point of view, the following three forms of impairment validation will be considered: 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 could 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 impairments, however, may still be gathered from network elements. Depending how information is Lee & Bernstein Expires July 5, 2012 [Page 13] Internet-Draft Framework for Optical Impairments January 2012 gathered, this may put additional requirements on routing protocols. This will be detailed in later sections. o IV-Distributed In the distributed IV process, approximate degradation measures such as OSNR, dispersion, DGD, etc., may be accumulated along the path via signaling. 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 distributing optical parameters to the entire network. The Control Plane must not preclude the possibility to concurrently perform one or all the above cases in the same network. For example, there could be cases where a certain number of paths are already pre-validated (IV-Candidates) so the control plane may setup one of those paths 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. 4.2.1. Combined Routing, WA, and IV From the point of view of optimality, 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 [RFC6163] and (b) impairment information to validate potential paths. 4.2.2. 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 [RFC6163]. In addition, as was discussed, some impairment information may not be shared and this may lead to the need to separate IV from RWA. In addition, if IV needs to be done at a high Lee & Bernstein Expires July 5, 2012 [Page 14] Internet-Draft Framework for Optical Impairments January 2012 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. 4.2.3. Distributed WA and/or IV In the non-impairment RWA situation [RFC6163], 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 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 by routing protocols or by other means. So the following conceptual options belong to this category: o 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. Distributed impairment validation for a prescribed network path requires that the effects of impairments be calculated by approximate models with cumulative quality measures such as those given in [G.680]. The protocol encoding of the impairment related information from [G.680] would need to be agreed upon. Lee & Bernstein Expires July 5, 2012 [Page 15] Internet-Draft Framework for Optical Impairments January 2012 If distributed WA is being done at the same time as distributed IV then it is necessary to accumulate impairment related information for all wavelengths that could be used. The amount of information is reduced somewhat as potential wavelengths are discovered to be in use, but could be a significant burden for lightly loaded high channel count networks. 4.3. Mapping Network Requirements to Architectures Figure 2 shows process flows for the three main architectural alternatives to IA-RWA when approximate impairment validation is sufficient. Figure 3 shows process flows for the 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 Lee & Bernstein Expires July 5, 2012 [Page 16] Internet-Draft Framework for Optical Impairments January 2012 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-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 conducive to specialization. o Routing + Distributed WA and IV In this alternative, a signaling protocol may be extended and leveraged in the wavelength assignment and impairment validation processes. Although this doesn't enable as high a potential degree 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". Lee & Bernstein Expires July 5, 2012 [Page 17] Internet-Draft Framework for Optical Impairments January 2012 +-----------------------------------+ +------------+ | +-----------+ +-------+ +--+ | | +--------+ | | | 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 the highest potential optimality and efficiency in IA-RWA while keeping 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. 5. Protocol Implications The previous IA-RWA architectural alternatives and process flows make differing demands on a GMPLS/PCE based control plane. This section discusses the use of (a) an impairment information model, (b) PCE as computational entity assuming the various process roles and consequences for PCEP, (c) possible extensions to signaling, and (d) possible extensions to routing. This document is providing this evaluation to aid protocol solutions work. The protocol Lee & Bernstein Expires July 5, 2012 [Page 18] Internet-Draft Framework for Optical Impairments January 2012 specifications may deviate from this assessment. The assessment of the impacts to the control plane for IA-RWA is 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| | | | | +-------------------+----+----+----------+--------+ Figure 4 IA-RWA architectural options and control plane impacts. 5.1. Information Model for Impairments As previously discussed, most IA-RWA scenarios rely, to a greater or lesser extent, 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. An impairment model which can be used as a guideline for optical network elements and assessment of path viability is given in [G.680]. It should be noted that the current version of [G.680] is limited to 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 planned 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]. For the case of distributed impairment validation (distributed IV), this would require more than an impairment information model. It would need 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 Lee & Bernstein Expires July 5, 2012 [Page 19] Internet-Draft Framework for Optical Impairments January 2012 formulas given for OSNR, residual dispersion, polarization mode dispersion/polarization dependent loss, and effects of channel uniformity. However, specifics of what intermediate results are kept and in what form would need to be standardized for interoperability. As noted in [G.680], this information may possibly not be sufficient, and in such case the applicability would be network dependent. 5.2. Routing Different approaches to path/wavelength impairment validation give 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 the impairment validation process. This can potentially cause scalability issues due to the high volume of data that need to be advertised. Such issue can be addressed separating data that need to be advertised rarely from 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 4.1.1.), the model defined by [G.680] will apply and the 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. 5.3. Signaling The largest impacts on signaling occur in the cases where distributed impairment validation is performed. In this case, it is necessary 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 Lee & Bernstein Expires July 5, 2012 [Page 20] Internet-Draft Framework for Optical Impairments January 2012 egress signal quality (defined in some appropriate sense) in non- distributed IV scenarios. 5.4. PCE In section 4.3. a number of computation architectural alternatives were given that could be used to meet the various requirements and constraints of section 4.1. Here the focus is 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. This document provides this evaluation to aid solutions work. The protocol specifications may deviate from this assessment. 5.4.1. 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 minimum, it is of interest to know if this was due to lack of wavelength availability, impairment considerations, or both. The information to be conveyed is for further study. 5.4.2. IV-Candidates + RWA In this situation, as shown in Figure 2(b), two separate processes are involved in the IA-RWA computation. This requires two cooperating path computation entities: 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 this functionality could be added to one of previously defined entities. This later option requires the RWA entity to also act as the overall process coordinator. The roles, responsibilities, and information requirements for these two entities when instantiated as PCEs are given below. Lee & Bernstein Expires July 5, 2012 [Page 21] Internet-Draft Framework for Optical Impairments January 2012 RWA and Coordinator PCE (RWA-Coord-PCE): Responsible for interacting with PCC and for utilizing Candidates- 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 need 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 initiating PCC. Note: RWA-Coord PCE is also a PCC with respect to the IV-Candidate. o TE Database Requirements: WSON Topology and switching capabilities and WSON impairment information (no information link wavelength utilization required). Figure 5 shows a sequence diagram for the possible interactions between the PCC, RWA-Coord PCE, and IV-Candidates PCE. Lee & Bernstein Expires July 5, 2012 [Page 22] Internet-Draft Framework for Optical Impairments January 2012 +---+ +-------------+ +-----------------+ |PCC| |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. The term "K candidate paths" is associated with K-shortest path algorithm. It refers to an algorithm that finds multiple K short paths connecting the source and the destination in a graph allowing repeated vertices and edges in the paths. See details in [Eppstein]. 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 returns the overall IA-RWA computation results to the PCC. 5.4.3. Approximate IA-RWA + Separate Detailed IV Previously, Figure 3 showed two cases where a separate detailed impairment validation process could be utilized. It is possible to Lee & Bernstein Expires July 5, 2012 [Page 23] Internet-Draft Framework for Optical Impairments January 2012 place the detailed validation process into a separate PCE. Assuming that a different PCE assumes a coordinating role and interacts with the PCC, it is possible to keep the interactions with this separate IV-Detailed-PCE very simple. Please note that there is some inefficiency by separating the IV-Candidates-PCE from the IV- Detailed-PCE from a message flow perspective in order to achieve a high degree of potential optimality. 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 essentially a 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 that a judgment can be made whether to try a different signal or adjust signal parameters. Figure 6 shows a sequence diagram for the interactions corresponding to 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), the 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. Lee & Bernstein Expires July 5, 2012 [Page 24] Internet-Draft Framework for Optical Impairments January 2012 +----------+ +--------------+ +------------+ +---+ |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. 6. Manageability and Operations The issues concerning manageability and operations are beyond the scope of this document. The details of manageability and operational issues will have to be deferred to future protocol implementation. On a high-level, the GMPLS-routing based architecture discussed in Section 5.2. may have to deal with how to resolve potential scaling issues associated with disseminating a large amount of impairment characteristics of the network elements and links. From a scaling point of view, the GMPLS-signaling based architecture discussed in Section 5.3. would be more scalable than other alternatives as this architecture would avoid the dissemination of a large amount of data to the networks. This benefit may come, however, at the expense of potentially inefficient use of network resources. Lee & Bernstein Expires July 5, 2012 [Page 25] Internet-Draft Framework for Optical Impairments January 2012 The PCE-based architectures discussed in Section 5.4. would have to consider operational complexity when implementing options that require the use of multiple PCE servers. The most serious case is the option discussed in Section 5.4.3., namely, "Approximate IA-RWA + Separate Detailed IV". The combined IV & RWA option (which was discussed on Section 5.4.1.), on the other hand, is simpler than other alternatives to operate as one PCE server handles all functionality; however, this option may suffer from a heavy computation and processing burden compared to other alternatives. Interoperability may be a hurdle to overcome when trying to agree on some impairment parameters especially those which are associated with the black links. This work has been in progress in ITU-T and needs some more time to mature. 7. 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 similar to other network information used within intra-domain protocols. 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 impairment information dissemination using the existing protocols may significantly affect the loading of those protocols. This may make the operation of the network more vulnerable to active attacks such as injections, impersonation, and MITMs. Therefore, additional care may be required to ensure that the protocols are secure in the impairment-aware WSON environment. Furthermore, the additional information distributed in order to address impairment information 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] and, in particular, text detailing security issues when Control Plane is physically separated from Data Plane. Lee & Bernstein Expires July 5, 2012 [Page 26] Internet-Draft Framework for Optical Impairments January 2012 8. IANA Considerations This draft does not currently require any consideration from IANA. 9. References 9.1. Normative References [G.680] ITU-T Recommendation G.680, Physical transfer functions of optical network elements, July 2007. [RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004. [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006. 9.2. Informative References [G.Sup39] ITU-T Series G Supplement 39, Optical system design and engineering considerations, February 2006. [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. [RFC4054] Strand, J., Ed., and A. Chiu, Ed., "Impairments and Other Constraints on Optical Layer Routing", RFC 4054, May 2005. [RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks", RFC 5920, July 2010. [RFC6163] Lee, Y., Ed., G. Bernstein, Ed., and W. Imajuku, "Framework for GMPLS and PCE Control of Wavelength Switched Optical Networks", RFC 6163, April 2011. [Eppstein] Eppstein, D., "Finding the k shortest paths", 35th IEEE Symp. Foundations of Comp. Sci., Santa Fe, pp. 154-165, 1994. Lee & Bernstein Expires July 5, 2012 [Page 27] Internet-Draft Framework for Optical Impairments January 2012 10. Acknowledgments This document was prepared using 2-Word-v2.0.template.dot. Copyright (c) 2012 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source 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. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Lee & Bernstein Expires July 5, 2012 [Page 28] Internet-Draft Framework for Optical Impairments January 2012 Authors' Addresses Young Lee (ed.) Huawei Technologies 1700 Alma Drive, Suite 100 Plano, TX 75075 USA Phone: (972) 509-5599 (x2240) Email: ylee@huawei.com Greg M. Bernstein (ed.) Grotto Networking Fremont California, USA Phone: (510) 573-2237 Email: gregb@grotto-networking.com Dan Li Huawei Technologies Co., Ltd. F3-5-B R&D Center, Huawei Base, Bantian, Longgang District Shenzhen 518129 P.R.China Phone: +86-755-28973237 Email: danli@huawei.com Giovanni Martinelli Cisco Via Philips 12 20052 Monza, Italy Phone: +39 039 2092044 Email: giomarti@cisco.com Contributor's Addresses Ming Chen Huawei Technologies Co., Ltd. F3-5-B R&D Center, Huawei Base, Bantian, Longgang District Shenzhen 518129 P.R.China Lee & Bernstein Expires July 5, 2012 [Page 29] Internet-Draft Framework for Optical Impairments January 2012 Phone: +86-755-28973237 Email: mchen@huawei.com Rebecca Han Huawei Technologies Co., Ltd. F3-5-B R&D Center, Huawei Base, Bantian, Longgang District Shenzhen 518129 P.R.China Phone: +86-755-28973237 Email: hanjianrui@huawei.com Gabriele Galimberti Cisco Via Philips 12, 20052 Monza, Italy Phone: +39 039 2091462 Email: ggalimbe@cisco.com Alberto Tanzi Cisco Via Philips 12, 20052 Monza, Italy Phone: +39 039 2091469 Email: altanzi@cisco.com David Bianchi Cisco Via Philips 12, 20052 Monza, Italy Email: davbianc@cisco.com Moustafa Kattan Cisco Dubai 500321 United Arab Emirates Email: mkattan@cisco.com Dirk Schroetter Cisco Email: dschroet@cisco.com Lee & Bernstein Expires July 5, 2012 [Page 30] Internet-Draft Framework for Optical Impairments January 2012 Daniele Ceccarelli Ericsson Via A. Negrone 1/A Genova - Sestri Ponente Italy Email: daniele.ceccarelli@ericsson.com Elisa Bellagamba Ericsson Farogatan 6, Kista 164 40 Sweeden Email: elisa.bellagamba@ericcson.com Diego Caviglia Ericsson Via A. negrone 1/A Genova - Sestri Ponente Italy Email: diego.caviglia@ericcson.com Lee & Bernstein Expires July 5, 2012 [Page 31]