Network Working Group S. Seno Internet Draft Mitsubishi Electric Intended status: Informational Expires: April 19, 2010 October 19, 2009 Requirement of Impairment Compensation Control in WSON draft-seno-ccamp-wson-impairment-compensate-cntl-01.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on April 19, 2010. Abstract This memo describes requirements of compensation control of optical impairments such as chromatic dispersion for dynamic optical paths, as well as automatic discovery of fiber-related impairments over links by collaboration of a pair of adjacent nodes upon installation. It is intended as a supplement to the wavelength switched optical networks (WSON) framework with impairments, because GMPLS-based automatic adjustment of impairment compensation and automatic discovery of link impairments will improve usability of WSON. S. Seno Expires April 19, 2010 [Page 1] Internet Drafts WSON Compensation Control Oct 2009 Table of Contents 1. Introduction....................................................2 1.1. Problem Statements............................................3 1.2. Organization of This Memo.....................................3 2. GMPLS-based Impairment Compensation Control.....................4 2.1. Impairment Compensation Control by the Control Plane..........4 2.2. Impairment Compensation Procedure.............................7 2.3. Impairment Compensation Control Requirements..................8 3. GMPLS-based Impairment Discovery................................9 3.1. Link Impairment Discovery Procedure...........................9 3.2. IA-RWA and Link Impairment Discovery.........................10 3.3. Link Impairment Discovery Requirements.......................11 4. Conclusion.....................................................11 5. Security Considerations........................................12 6. IANA Considerations............................................12 7. Acknowledgments................................................12 8. References.....................................................12 8.1. Normative References.........................................12 8.2. Informative References.......................................13 Authors' and Contributors' Addresses..............................14 Intellectual Property Statement...................................15 Copyright Notice..................................................15 1. Introduction The Wavelength Switched Optical Networks (WSON) framework with impairments [WSON-Imp-Frame] discusses how Impairment Aware Routing and Wavelength Assignment (IA-RWA) in optical networks is supported by the Control Plane with considerations on various impairments encountered by an optical path. It identifies major issues with IA- RWA, such as impairment estimation, impairment information sharing, IA-RWA architectures, and protocol implications of IA-RWA to the GMPLS (Generalized Multi-Protocol Label Switching) [RFC3471] [RFC3473] [RFC4328] and PCE (Path Computation Element) protocols. To deal with various impairments encountered by optical paths, various impairment compensation technologies have been developed. For example, chromatic dispersion may be compensated by dispersion compensation fiber (DCF) or an electronic or optical compensation device at the transmitter or the receiver of the signal. Insertion of 3R repeaters or an optical amplifier at an optical path's transient node may also be regarded as a compensation effort. S. Seno Expires April 19, 2010 [Page 2] Internet Drafts WSON Compensation Control Oct 2009 Although some compensation technologies offer fixed or limited compensation ranges against impairments, compensation technologies with wide and dynamically tunable compensation ranges have been developing. Such compensation technologies are especially suited for a dynamically established optical path because impairment compensation by them can be automatically adjusted as adequate corresponding to a requested path's impairments. 1.1 Problem Statements The emerging tunable compensation technologies against optical impairments will be able to support dynamically established optical paths which may traverse different routes and different optical fiber types, because their compensation parameters can be adjusted to meet different impairments corresponding to optical paths. However, there are is a problem that no Control Plane mechanisms have been defined to automatically adjust compensation parameters according to dynamic optical paths. Because benefit of automatic establishment of optical paths is well recognized, it is obvious that associated control of automatic impairment compensation adjustment is also beneficial. According to the IA-RWA architectures, Impairment Validation (IV) process collects and evaluates impairments of a requested optical path. Such impairment information is essential for impairment compensation adjustment described above, and can be used in its process. Another problem is that there are no means to automatically discover impairment information, although it is required by the IA-RWA process. 1.2 Organization of This Memo Based upon the above observation, this memo discusses how compensation control for tunable compensation technologies is handled within the WSON framework in Section 2. Section 2 also includes requirements of impairment compensation control to the Control Plane. This memo also discusses automatic discovery of fiber-related impairments over links for use by IA-RWA in Section 3. Link impairments are basic components of end-to-end impairments of an optical path, and their automatic discovery by collaboration of a pair of adjacent nodes upon installation will be beneficial to the WSON framework with impairments. Section 3 also includes requirements S. Seno Expires April 19, 2010 [Page 3] Internet Drafts WSON Compensation Control Oct 2009 of link impairment discovery to the Control Plane. It is the intension of this memo to explain impairment compensation control and link impairment discovery with regard to the WSON framework with impairments so that they will be properly placed within it. 2. GMPLS-based Impairment Compensation Control 2.1. Impairment Compensation Control by the Control Plane Optical Impairments such as fiber chromatic dispersion are discussed in [WSON-Imp-Info]. Such impairments on the optical signal over a dynamic optical path may be compensated at the signal's transmitter node, receiver node, or transient nodes by means of some compensation technologies applicable to one or more impairment types to be dealt with. For example, chromatic dispersion may be compensated at the transmitter node by electronic pre-distortion device, by dispersion compensation fiber (DCF) at the transient nodes, and by electronic dispersion compensator at the receiver node. Please note that the transmitter node will be the ingress node of the path and the receiver node will be the egress node of the path, respectively, for the downstream signal. The transmitter node will be the egress node of the path and the receiver node will be the ingress node of the path, respectively, for the upstream signal. Note that more than one compensation technologies may be applied at more than one nodes traversed by a single optical path. In the case of chromatic dispersion, DCF may be used repeatedly at transient nodes as well as at the receiver node. Different compensation technologies offer different administrative characteristics for optical paths. Whereas DCF is statically inserted into an optical path and its compensation value is fixed, other compensation technologies offer wider tuning ranges which enable their compensation capabilities promptly adjusted to a dynamic optical path. This means prompt adjustment control is required. Various impairments may be encountered in the course of IA-RWA process [WSON-Imp-Frame] when an optical path is newly requested. To evaluate implications of impairments on transmitted signal quality by S. Seno Expires April 19, 2010 [Page 4] Internet Drafts WSON Compensation Control Oct 2009 Impairment Validation, the IA-RWA entity may accumulate impairments over candidate route and wavelength pairs for a requested path, based on information gathered at the IA-RWA entity in advance or signaling- based impairment collection [Optical-Evidence] [Optical-Signaling]. Such accumulated impairments are useful for selection of appropriate compensation devices, when more than one compensation devices are available, and for adjustment of compensation devices which will be used against the impairments. To effectively and rapidly select and adjust compensation devices for a dynamic optical path upon its request, GMPLS signaling-based distributed compensation control over the Control Plane will be beneficial. As compensation devices may be applied not only at an optical path's terminating nodes but also at its transient nodes, conveyance of compensation control objects by signaling messages has an advantage that they naturally reach each node of an optical path. In the following, how distributed compensation control is used for selection and adjustment of compensation devices is described: (i) Selection of compensation devices As shown above, more than one compensation technologies may be applied at more than one nodes traversed by a single optical path. Because compensation technologies will evolve while an optical network is built and expanded, and compensation devices' cost will differ corresponding to different compensation capabilities, it is reasonably assumed that compensation devices with different capabilities will co-exist in a single network and even in a single node. For example, a terminating node of a newly requested path's will have a pool of compensation devices with different capabilities. It is obvious that optimized selection of compensation devices, where each path is assigned a compensation device with just sufficient capability to compensate for it, will provide better utilization of compensation devices. On the other hand, if compensation devices are assigned without consideration on their compensation capabilities, a device with high capability may be assigned to a path which can be compensated for by a device with less capability, and it will not be available when a path with large impairment is requested. To achieve optimized selection of compensation devices, each node where compensation is applied should know how much compensation is required at it, and this information can effectively distributed by signaling conveying accumulated impairments of a requested path. As S. Seno Expires April 19, 2010 [Page 5] Internet Drafts WSON Compensation Control Oct 2009 an example, consider a case where chromatic dispersion is collected along a path's route by signaling and delivered to its egress nodes. If the egress node has a pool of dispersion compensation devices for downstream signal received by it, the egress node can select an appropriate device from the pool based on accumulated chromatic dispersion. As for the upstream signal transmitted to the opposite direction, its accumulated dispersion should be conveyed from the egress node to the ingress node by signaling so that it will be used for selection of an appropriate device from the ingress node's device pool. (ii) Initial setting of compensation parameters The IA-RWA entity may accumulate impairments over a candidate route and wavelength pair for a requested path, based on information gathered at the IA-RWA entity in advance or signaling-based impairment collection [Optical-Evidence] [Optical-Signaling]. Such accumulated impairments can be translated to compensation parameters of tunable compensation devices and used for initial setting of them upon path establishment. This will reduce time necessary to adjust compensation parameters of the compensation devices, because compensation parameters are already near their optimal values. However, without such a priori knowledge, adjustment may take a long time because compensation parameters may be set far from their optimal values. Adjustment process of compensation parameters is further discussed in (iii) below. Reduction of compensation adjustment time based on estimated impairments of a path by IA-RWA will shorten overall path establishment time from a path's request to its release, and will contribute to effective use of network resources. (iii) Optimization of compensation parameters Initial setting of compensation parameters based on estimated impairments by IA-RWA may not be the best one because of residual impairments, errors due to accumulation, and so on. Thus further adjustment of compensation parameters may be performed before a path's Data Plane is ready for release to its users. An adjustment process of compensation parameters often involves measurement of sample signal transmitted over the Data Plane with feed-back control over the Control Plane, as shown in Figure 1. In the first step (A), measurement is agreed by sample signal's transmitter and receiver by exchange of messages in the Control S. Seno Expires April 19, 2010 [Page 6] Internet Drafts WSON Compensation Control Oct 2009 Plane. In the next step (B), the transmitter sends sample signal to the receiver in the Data Plane and its performance is measured by the receiver. In the last step (C), the measured performance results or more desirable setting parameters for compensation devices are fed back to the transmitter by the receiver in the Control Plane. Such a feed-back loop may take considerable time, especially when the sample signal has to traverse a long distance or measurement time is long. The more optimized the initial setting of the compensation devices, the less feed-back loops may be needed, and adjustment time will be shortened. +-------------+ +-------------+ | Transmitter | | Receiver | +-------------+ +-------------+ | (A) measurement agreement | | <------------------------------------> | | | | (B) sample signal | | =====================================> | | | | (C) measurement result | | <------------------------------------- | | | -----> : Control Plane messages =====> : Data Plane sample signal Figure 1 A Typical Measurement Process. As shown above, the Control Plane helps compensation adjustment process by providing the means for controlling measurement process as well as exchange of the measured performance results or desirable compensation parameters. Measurement of optical performance parameters controlled by RSVP-TE extensions was proposed by [Optical- Evidence] as optical impairment collection. 2.2. Impairment Compensation Procedure A general procedure of impairment compensation control is as follows: S. Seno Expires April 19, 2010 [Page 7] Internet Drafts WSON Compensation Control Oct 2009 (1) Request of an optical path which may encounter impairments. (2) Selection of the path's route and wavelength with an estimate of accumulated impairments. Here some type of the IA-RWA procedures is used for route and wavelength selection, and it is assumed that it can estimate how much impairments will be accumulated over each pair of route and wavelength selected. (3) Assignment of compensation devices with initial setting of compensation parameters. Estimated accumulated impairments, or desirable compensation device parameters derived from them, may be notified from the IA-RWA entity to the path's ingress node and egress node by PCE-based or GMPLS- based protocols. If the path's terminating nodes include compensation devices with different compensation capabilities and the IA-RWA entity has knowledge of up-to-date assignment of the compensation devices, the entity may be able to select compensation devices just sufficient for compensation of the path, so that such assignment is optimized. How the entity derives compensation device parameters or how it selects compensation devices according to estimated accumulated impairments are outside the scope of this memo. (4) Optimization of compensation parameters through measurement of residual impairments and adjustment of the compensation devices. Here adjustment feed-back loops between signal's transmitter and receiver may be controlled by GMPLS-based signaling. 2.3. Impairment Compensation Control Requirements From the above argument, the following requirements for GMPLS-based impairment compensation control over the Control Plane are obtained: (a) Transmission of an estimate of accumulated impairments of a path from the IA-RWA entity to nodes where the IA-RWA entity is capable of such estimate. (b) Transmission of an estimate of accumulated impairments between nodes. (c) Transmission of compensation device selection information, and S. Seno Expires April 19, 2010 [Page 8] Internet Drafts WSON Compensation Control Oct 2009 optionally, compensation device setting parameters, from the IA-RWA entity to nodes. (d) Transmission of compensation device selection information, and optionally, compensation device setting parameters, between nodes. (e) Transmission of measurement control information between sample signal's transmitter and receiver. In (e), the control information may include measurement initiation and measurement synchronization, and, optionally, conflict resolution of optical resources suggested by [Optical-Evidence]. It may also include measurement results from the receiver to the transmitter. 3. GMPLS-based Impairment Discovery 3.1. Link Impairment Discovery Procedure Automatic configuration of optical Network Elements (NEs) has attracted considerable attentions and standardization efforts in recent years have produced neighbor discovery and service discovery protocols such as LMP [RFC4204] and OIF-UNI [OIF-UNI-1.0]. Automatic discovery of fiber-related link impairments will be achieved if each node has impairment measurement functions and a pair of adjacent nodes collaborates to measure link impairments between them and to notify the results each other. As the measurement process shown in Figure 1 is generic and also applicable to link impairment measurement, a link impairment discovery protocol can also be designed based on it. However, a GMPLS signaling-based mechanism, such as [Optical- Evidence] and [Optical-Signaling], can not be applied to link impairment discovery upon installation of a new NE or a new link, because signaling assumes node and link information is available for specification of an optical path, but such information with respect to a new NE or a new link becomes available only after their discovery process has completed. Therefore, link impairment discovery should be realized as an extension to the standardized neighbor discovery protocol, such as LMP, so that discovery of a new NE or a new link by neighbor discovery will smoothly lead to discovery of link impairments. S. Seno Expires April 19, 2010 [Page 9] Internet Drafts WSON Compensation Control Oct 2009 Link impairment discovery can be integrated into LMP as a procedure similar to link verification. This is because link verification was designed to correlate Data Plane information, i.e. link connectivity, with Control Plane identifiers, and link impairments are also Data Plane information to be correlated with such identifiers. Link impairment discovery protocol may use the same encoding for link impairment information as encoding of impairment information by signaling-based impairment collection. 3.2. IA-RWA and Link Impairment Discovery Collection of link impairments by the IA-RWA entity, in case if it does not reside in NEs, may be achieved by advertisement of link impairments by the routing protocol or other means. Link impairment discovery may be incorporated into the IA-RWA architectures as in the following models: (i) Centralized IA-RWA When the IA-RWA entity is centralized as a PCE, each node performing link impairment discovery should notify discovered link impairments to the PCE. The PCE may be able to validate a requested path's route and wavelength selection, evaluating link impairments accumulated along each candidate route of the path. (ii) Distributed IA-RWA When the IA-RWA entity is distributed among nodes, a requested path's terminating nodes validate the path's route and wavelength selection. This model is further divided to the two cases below according to how link impairments are collected for validation. (ii-1) Routing-based collection Each node advertises discovered link impairments by a routing protocol such as an extended OSPF-TE. Because link impairments are link-specific property, they may be encoded as TE-link information. Advertised link impairments will be stored in routing information base of all nodes. When an optical path is requested, its ingress node will validate the path's route and wavelength selection with evaluation of link impairments accumulated along each candidate route S. Seno Expires April 19, 2010 [Page 10] Internet Drafts WSON Compensation Control Oct 2009 of the path. (ii-2) Signaling-based collection When an optical path is requested, GMPLS-based signaling from its ingress node to its egress node along a candidate route also accumulates discovered link impairments along the route. The egress node evaluates the accumulated impairments to decide whether the candidate route is acceptable or not, as described in [WSON-Imp- Frame] 2.2. 3.3. Link Impairment Discovery Requirements From the above argument, the following requirements for GMPLS-based link impairment discovery are obtained: (a) Transmission of link impairment measurement control information between a link's terminating nodes. Such control may include measurement initiation and measurement synchronization. Link impairment measurement is typically performed for each direction of a link individually, because different directions usually use different fibers. Thus link impairment discovery is defined as a uni- directional procedure, where sample signal is transmitted by the transmitter and its measurement result is obtained by the receiver. (b) Transmission of measurement results from the receiver to the transmitter. Sharing of measurement results between a link's terminating nodes will facilitates impairment validation. 4. Conclusion Although the current WSON framework with impairments [WSON-Imp-Frame] includes reference to dispersion compensation in A.2.2, it does not address how impairment compensation is controlled within the WSON framework. Because impairment compensation control described in Section 2 is useful for effective and rapid establishment of optical paths with impairment compensation, it is recommended that the WSON framework should include it. Because automatic discovery of link impairments described in Section 3 will contribute to automatic processing of IA-RWA, its inclusion to the WSON framework with impairments is also recommended. S. Seno Expires April 19, 2010 [Page 11] Internet Drafts WSON Compensation Control Oct 2009 5. Security Considerations This document has no requirement for a change to the security models within GMPLS and associated protocols. However, the additional information exchanged for impairment compensation control and automatic discovery of impairments represents a disclosure of network capabilities that an operator may wish to keep private. Consideration should be given to securing such information. 6. IANA Considerations TBD. 7. Acknowledgments The authors would like to thank Young Lee and Daniel King for their supoprt. 8. References 8.1. Normative References [RFC3471] L. Berger, Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, January 2003. [RFC3473] L. Berger, Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC 3473, January 2003. [RFC4204] J. Lang, Ed., "Link Management Protocol (LMP)", RFC 4204, October 2005. [RFC4328] D. Papadimitriou, "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Extensions for G.709 Optical Transport Networks Control", RFC 4328, January 2006. S. Seno Expires April 19, 2010 [Page 12] Internet Drafts WSON Compensation Control Oct 2009 [WSON-Imp-Frame] G. Bernstein, Y. Lee, and D. Li, "A Framework for the Control of Wavelength Switched Optical Networks (WSON) with Impairments", work in progress: draft-ietf-ccamp-wson- impairments-00.txt, June 2009. [WSON-Imp-Info] G. Bernstein, and Y. Lee, "Information Model for Impaired Optical Path Validation", work in progress: draft- bernstein-wson-impairment-info-02.txt, July 2009. [OIF-UNI-1.0] Optical Internetworking Forum, "User Network Interface (UNI) 1.0 Signaling Specification", OIF-UNI-01.0, October 2001. 8.2. Informative References [Optical-Signaling] G. Martinelli and A. Zanardi, Ed., "GMPLS Signaling Extensions for Optical Impairment Aware Lightpath Setup", work in progress: draft-martinelli-ccamp-optical- imp-signaling-02.txt, July 2009. [PCEP-Imp] Y. Lee, G. Bernstein, J. Martensson, T. Takeda and T. Otani, "PCEP Requirements for WSON Impairments", work in progress: draft-lee-pce-wson-impairments-00.txt, June 2009. [Winzer06] P. J. Winzer and R-J Essiambre, "Advanced Optical Modulation Formats", Proceedings of the IEEE, vol. 94, no. 5, pp. 952-985, May 2006. [Seno06] S. Seno, Y. Baba, T. Mizuochi, T. Sugihara, K. Motoshima and T. Ideguchi, "Dynamic Compensation Control by GMPLS- Plus," Technology Digest, OECC 2006, 5E4-4, Kaohsiung, Taiwan, July 2006. S. Seno Expires April 19, 2010 [Page 13] Internet Drafts WSON Compensation Control Oct 2009 Authors' Addresses Shoichiro Seno Information Technology R&D Center Mitsubishi Electric Corporation 5-1-1 Ofuna, Kamakura, Japan Email: Senoo.Shoichiro@dc.MitsubishiElectric.co.jp Phone: +81 (467) 41-2881 Contributors' Addresses Yoshimasa Baba Information Technology R&D Center Mitsubishi Electric Corporation 5-1-1 Ofuna, Kamakura, Japan Email: Baba.Yoshimasa@dp.MitsubishiElectric.co.jp Phone: +81 (467) 41-2430 Eiichi Horiuchi Information Technology R&D Center Mitsubishi Electric Corporation 5-1-1 Ofuna, Kamakura, Japan Email: Horiuchi.Eiichi@cw.MitsubishiElectric.co.jp Phone: +81 (467) 41-2430 Kazuo Kubo Information Technology R&D Center Mitsubishi Electric Corporation 5-1-1 Ofuna, Kamakura, Japan Email: Kubo.Kazuo@cj.MitsubishiElectric.co.jp Phone: +81 (467) 41-2443 S. Seno Expires April 19, 2010 [Page 14] Internet Drafts WSON Compensation Control Oct 2009 Intellectual Property Statement The IETF Trust takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in any IETF Document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Copies of Intellectual Property disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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