Network Working Group Y. Lee Huawei G. Bernstein Grotto Networking D. Li Huawei G. Martinelli Cisco Internet Draft Intended status: Informational March 9, 2011 Expires: September 2011 A Framework for the Control of Wavelength Switched Optical Networks (WSON) with Impairments draft-ietf-ccamp-wson-impairments-05.txt Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 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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. 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, 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 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. Table of Contents 1. Introduction...................................................3 2. Terminology....................................................4 3. Applicability..................................................5 4. Impairment Aware Optical Path Computation......................6 4.1. Optical Network Requirements and Constraints..............7 4.1.1. Impairment Aware Computation Scenarios...............7 4.1.2. Impairment Computation and Information Sharing Constraints.................................................8 4.1.3. Impairment Estimation Process.......................10 4.2. IA-RWA Computation and Control Plane Architectures.......11 4.2.1. Combined Routing, WA, and IV........................13 4.2.2. Separate Routing, WA, or IV.........................13 4.2.3. Distributed WA and/or IV............................14 4.3. Mapping Network Requirements to Architectures............15 5. Protocol Implications.........................................17 5.1. Information Model for Impairments........................17 5.2. Routing..................................................18 5.3. Signaling................................................19 5.4. PCE......................................................19 5.4.1. Combined IV & RWA...................................19 Lee & Bernstein Expires September 9, 2011 [Page 2] Internet-Draft Framework for Optical Impairments March 2011 5.4.2. IV-Candidates + RWA.................................20 6. Security Considerations.......................................22 7. IANA Considerations...........................................22 8. References....................................................22 8.1. Normative References.....................................22 8.2. Informative References...................................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, 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 certain path continuity, resource availability and impairments constraints must be met to determine viable and optimal paths through the network. The determination of paths is known as Impairment Aware Routing and Wavelength Assignment (IA-RWA). Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes a set of control plane protocols that can be used to operate data networks ranging from packet switch capable networks, through those networks that use time division multiplexing, and WDM. [RFC4054] gives an overview of some critical optical impairments and their routing (path selection) implications for GMPLS. The Path Computation Element (PCE) architecture [RFC4655] defines functional components that can be used to compute and suggest appropriate paths in connection-oriented traffic-engineered networks. Lee & Bernstein Expires September 9, 2011 [Page 3] Internet-Draft Framework for Optical Impairments March 2011 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 process this document also provides an overview of the subsystems and processes that comprise WSONs, and describes IA-RWA so that the information requirements can be identified to explain how the information can be modeled for use by GMPLS and PCE systems. This work will facilitate the development of protocol solution models and protocol extensions within the GMPLS and PCE protocol families. 2. Terminology Add/Drop Multiplexers (ADM): An optical device used in WDM networks composed of one or more line side ports and typically many tributary ports. CWDM: Coarse Wavelength Division Multiplexing. DWDM: Dense Wavelength Division Multiplexing. 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 connect. An optical switching element in which a signal on any input port can reach any output port. PCC: Path Computation Client. Any client application requesting a path computation to be performed by the Path Computation Element. PCE: Path Computation Element. An entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints. PCEP: PCE Communication Protocol. The communication protocol between a Path Computation Client and Path Computation Element. ROADM: Reconfigurable Optical Add/Drop Multiplexer. A wavelength selective switching element featuring input and output line side ports as well as add/drop tributary ports. Lee & Bernstein Expires September 9, 2011 [Page 4] Internet-Draft Framework for Optical Impairments March 2011 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. 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. Moreover, the optical physical interfaces are typically provisioned at various stages of the network's life span as needed by traffic demands. Lee & Bernstein Expires September 9, 2011 [Page 5] Internet-Draft Framework for Optical Impairments March 2011 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 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 takes into account evolving network status in term of equipments and traffic at the beginning stage. This could result in over-engineering the DWDM network with additional regenerators and optical amplifiers. In addition, network operations such as path establishment, will require significant pre-design via non-control plane processes resulting in significantly slower network provisioning. 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. [WSON-Frame] 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: (i) wavelength conversion to assist RWA to avoid wavelength blocking. This is the impairment free case covered by [WSON-Frame]. Lee & Bernstein Expires September 9, 2011 [Page 6] Internet-Draft Framework for Optical Impairments March 2011 (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 that 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 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, Lee & Bernstein Expires September 9, 2011 [Page 7] Internet-Draft Framework for Optical Impairments March 2011 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]. 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, we can combine the impairment aware (IA) path computation 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. 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. 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 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 Lee & Bernstein Expires September 9, 2011 [Page 8] Internet-Draft Framework for Optical Impairments March 2011 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 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 for larger networks such a list of paths along with any wavelength constraints could get unmanageably large. 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. Lee & Bernstein Expires September 9, 2011 [Page 9] Internet-Draft Framework for Optical Impairments March 2011 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. 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 | | | +------------+ | +-----------------+ 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-impairment 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 [WSON-Frame]). 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 Lee & Bernstein Expires September 9, 2011 [Page 10] Internet-Draft Framework for Optical Impairments March 2011 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 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 feasible in reality. 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 [WSON- Frame]. 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 (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 Lee & Bernstein Expires September 9, 2011 [Page 11] Internet-Draft Framework for Optical Impairments March 2011 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 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. 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 Lee & Bernstein Expires September 9, 2011 [Page 12] Internet-Draft Framework for Optical Impairments March 2011 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 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- 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. 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 [WSON-Frame] 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 [WSON-Frame]. 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 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. Lee & Bernstein Expires September 9, 2011 [Page 13] Internet-Draft Framework for Optical Impairments March 2011 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 [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 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 routing 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) - 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]. For such a system to be interoperable the exact encoding of the techniques from [G.680] would need to be agreed 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. Lee & Bernstein Expires September 9, 2011 [Page 14] Internet-Draft Framework for Optical Impairments March 2011 4.3. Mapping Network Requirements to Architectures Figure 2 shows process flows for three main architectural alternatives to IA-RWA when approximate impairment validation suffices. Figure 3 shows 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 Lee & Bernstein Expires September 9, 2011 [Page 15] Internet-Draft Framework for Optical Impairments March 2011 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 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 Lee & Bernstein Expires September 9, 2011 [Page 16] Internet-Draft Framework for Optical Impairments March 2011 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. 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| | | | | +-------------------+----+----+----------+--------+ Figure 4 IA-RWA architectural options and control plane impacts. 5.1. 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 Lee & Bernstein Expires September 9, 2011 [Page 17] Internet-Draft Framework for Optical Impairments March 2011 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. 5.2. 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 4.1.1. ) the model defined by [G.680] will apply and routing protocol will need to gather information required for such computation. Lee & Bernstein Expires September 9, 2011 [Page 18] Internet-Draft Framework for Optical Impairments March 2011 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 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-distributed IV scenarios. 5.4. PCE In section 4.3. we gave a number of computation architectural alternatives that could be used to meet the various requirements and constraints of section 4.1. 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. 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 Lee & Bernstein Expires September 9, 2011 [Page 19] Internet-Draft Framework for Optical Impairments March 2011 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. 5.4.2. 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 two 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-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: Lee & Bernstein Expires September 9, 2011 [Page 20] Internet-Draft Framework for Optical Impairments March 2011 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-Coord PCE and IV-Candidates PCE. +---+ +-------------+ +-----------------+ |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. In step (c) The IV-Candidates PCE returns this list to the RWA-Coordinating PCE which then uses this set of Lee & Bernstein Expires September 9, 2011 [Page 21] Internet-Draft Framework for Optical Impairments March 2011 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. 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 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. 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-mode fibre and cable, June 2004. [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. [G.650.3] ITU-T Recommendation G.650.3 [G.652] ITU-T Recommendation G.652, Characteristics of a single-mode optical fibre and cable, June 2005. [G.653] ITU-T Recommendation G.653, Characteristics of a dispersion- shifted single-mode optical fibre and cable, December 2006. [G.654] ITU-T Recommendation G.654, Characteristics of a cut-off shifted single-mode optical fibre and cable, December 2006. [G.655] ITU-T Recommendation G.655, Characteristics of a non-zero dispersion-shifted single-mode optical fibre and cable, March 2006. Lee & Bernstein Expires September 9, 2011 [Page 22] Internet-Draft Framework for Optical Impairments March 2011 [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. Lee & Bernstein Expires September 9, 2011 [Page 23] Internet-Draft Framework for Optical Impairments March 2011 [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] 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. [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. [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. 9. Acknowledgments This document was prepared using 2-Word-v2.0.template.dot. Copyright (c) 2011 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. Lee & Bernstein Expires September 9, 2011 [Page 24] Internet-Draft Framework for Optical Impairments March 2011 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 September 9, 2011 [Page 25] Internet-Draft Framework for Optical Impairments March 2011 Authors' Addresses Greg M. Bernstein (ed.) Grotto Networking Fremont California, USA Phone: (510) 573-2237 Email: gregb@grotto-networking.com Young Lee (ed.) Huawei Technologies 1700 Alma Drive, Suite 100 Plano, TX 75075 USA Phone: (972) 509-5599 (x2240) Email: ylee@huawei.com 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 Phone: +86-755-28973237 Email: mchen@huawei.com Rebecca Han Huawei Technologies Co., Ltd. Lee & Bernstein Expires September 9, 2011 [Page 26] Internet-Draft Framework for Optical Impairments March 2011 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 Daniele Ceccarelli Ericsson Via A. Negrone 1/A Genova - Sestri Ponente Italy Lee & Bernstein Expires September 9, 2011 [Page 27] Internet-Draft Framework for Optical Impairments March 2011 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 September 9, 2011 [Page 28]