Network Working Group G. Bernstein Internet Draft Grotto Networking Intended status: Informational Y. Lee Huawei October 26, 2008 Expires: April 2009 Information Model for Impaired Optical Path Validation draft-bernstein-wson-impairment-info-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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/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 April 26, 2009. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This document provides an information model for the optical impairment characteristics of optical network elements for use in path computation and optical path validation. This model is based on Bernstein Expires April 26, 2009 [Page 1] Internet-Draft Optical Impairment Info Model October 2008 ITU-T defined optical network element characteristics as given in ITU-T recommendation G.680 and related specifications. This model is intentionally compatible with a previous impairment free optical information model used in optical path computations and wavelength assignment. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [RFC2119]. Table of Contents 1. Introduction...................................................2 2. Optical Impairment Information Model...........................3 2.1. Network Element Wide Parameters...........................3 2.2. Per Port Parameters.......................................4 2.3. Port to Port Parameters...................................4 3. Encoding Considerations........................................5 4. Usage of Parameters in Optical Path Validation.................5 5. Security Considerations........................................5 6. IANA Considerations............................................6 7. Conclusions....................................................6 8. Acknowledgments................................................6 APPENDIX A: Optical Parameters....................................7 A.1. Parameters for NEs without optical amplifiers.............7 A.2. Additional parameters for NEs with optical amplifiers.....9 9. References....................................................11 9.1. Normative References.....................................11 9.2. Informative References...................................11 Author's Addresses...............................................12 Intellectual Property Statement..................................12 Disclaimer of Validity...........................................13 1. Introduction Impairments in optical networks can be accounted for in a number of ways as discussed in reference [Imp-Frame]. This document provides an information model for path validation in optical networks utilizing approximate computations. The definitions, characteristics and usage of the optical parameters that form this model are based on ITU-T recommendation G.680 [G.680]. This impairment related model is intentionally compatible with the impairment free model of reference [RWA-Info]. Although this document focuses on the optical impairment parameters from a control plane point of view, Appendix A provides a Bernstein Expires April 26, 2009 [Page 2] Internet-Draft Optical Impairment Info Model October 2008 list of optical parameters and their definition from ITU-T G.680 and related documents. 2. Optical Impairment Information Model The definitions of optical impairment parameters of network elements and examples of their use can be found in [G.680] and related documents (also see Appendix A). From an information modeling and control plane perspective, one basic aspect of a given parameter is the scope of its applicability within a network element. In particular we need to know which parameters will (a) apply to the network element as a whole, (b) can vary on a per port basis for a network element, and (c)can vary based on ingress to egress port pairs. 2.1. Network Element Wide Parameters Based on the definitions in [G.680] and related documents we have the following parameters apply to the network element as a whole. At most one of these parameters is required per network element. 1. Channel frequency range (GHz, Max, Min) 2. Channel insertion loss deviation (dB, Max) 3. Ripple (dB, Max) 4. Channel chromatic dispersion (ps/nm, Max, Min) 5. Differential group delay (ps, Max) 6. Polarization dependent loss (dB, Max) 7. Reflectance (passive component) (dB, Max) 8. Reconfigure time/Switching time (ms, Max, Min) 9. Channel uniformity (dB, Max) 10.Channel addition/removal (steady-state) gain response (dB, Max, Min) 11.Transient duration (ms, Max) 12.Transient gain increase (dB, Max) Bernstein Expires April 26, 2009 [Page 3] Internet-Draft Optical Impairment Info Model October 2008 13.Transient gain reduction (dB, Max) 14.Multichannel gain-change difference (inter-channel gain-change difference) (dB, Max) 15.Multichannel gain tilt (inter-channel gain-change ratio)(dB, Max) 2.2. Per Port Parameters The following optical parameters may exhibit per port dependence, hence may be specified a most once for each port of the network element. 1. Total input power range (dBm, Max, Min) 2. Channel input power range (dBm, Max, Min) 3. Channel output power range (dBm, Max, Min) 4. Input reflectance (dB, Max) (with amplifiers) 5. Output reflectance (dB, Max) (with amplifiers) 6. Maximum reflectance tolerable at input (dB, Min) 7. Maximum reflectance tolerable at output (dB, Min) 8. Maximum total output power (dBm, Max) 2.3. Port to Port Parameters The following optical parameters may exhibit a port-to-port dependence and hence may be specified at most once for each ingress/egress port pair of the network element. 1. Insertion loss (dB, Max, Min) 2. Isolation, adjacent channel (dB, Min) 3. Isolation, non-adjacent channel (dB, Min) 4. Channel extinction (dB, Min) 5. Channel signal-spontaneous noise figure (dB, Max) 6. Channel gain (dB, Max, Min) Bernstein Expires April 26, 2009 [Page 4] Internet-Draft Optical Impairment Info Model October 2008 3. Encoding Considerations The units for the various parameters include GHz, dB, dBm, ms, ps, and ps/nm. These are typically expressed as floating point numbers. Due to the measurement limitations inherent in these parameters single precision floating point, e.g., 32 bit IEEE floating point, numbers should be sufficient. For realistic optical network elements the per port and port-to-port parameters typically only assume a few values. For example, the channel gain of a ROADM is usually specified in terms of input to drop, add to output, and input to output. This implies that many port and port-to-port parameters could be efficiently specified, stored and transported by making use of the Link Set Sub-TLV and Connectivity Matrix Sub-TLV of reference [Encode]. 4. Usage of Parameters in Optical Path Validation Given an optical path and the optical characteristics of each network element along the path we then need to use these characteristics to validate the path. We envisage that these parameters will be made available via some mechanism to the entity in which optical path validation takes place. Refer to [Imp-Frame] for architectural options in which impairment validation for an optical path is defined. Section 9 and 10 of G.680 gives techniques and formulas for use in calculating the impact of a cascade of network elements. These range from relatively simple bounds on the sum of uncompensated chromatic dispersion (residual dispersion) to more elaborate formulas for overall optical signal to noise ration (OSNR) computations based on multiple parameters including noise factor. To further aid understanding and use of these optical parameters Appendix I of [G.680] furnishes example parameter values for different network element types and appendix II provides examples of computations involving the cascades of network elements along a path. 5. Security Considerations This document defines an information model for impairments in optical networks. If such a model 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. Bernstein Expires April 26, 2009 [Page 5] Internet-Draft Optical Impairment Info Model October 2008 6. IANA Considerations This draft does not currently require any consideration from IANA. 7. Conclusions The state of standardization of optical device characteristics has matured from when initial IETF work concerning optical impairments was investigated in [RFC4054]. Relatively recent ITU-T recommendations provide a standardized based of optical characteristic definitions and parameters that control plane technologies such as GMPLS and PCE can make use of in performing optical path validation. The enclosed information model shows how readily such ITU-T optical work can be utilized within the control plane. 8. Acknowledgments This document was prepared using 2-Word-v2.0.template.dot. Bernstein Expires April 26, 2009 [Page 6] Internet-Draft Optical Impairment Info Model October 2008 APPENDIX A: Optical Parameters The following provides an annotated list of optical characteristics from ITU-T recommendation G.680 [G.680] for use in optical path impairment computations. For each parameter we specify the units to be used, whether minimum or maximum values are used, and whether the parameters applies to the optical network element as a whole, on a per port basis or on a port-to-port pair basis. Not all these parameters will apply to all devices. The main differentiation in G.680 comes from those network elements that include or do not include optical amplifiers. A.1. Parameters for NEs without optical amplifiers Channel frequency range (GHz, Max, Min): [G.671] The frequency range within which a DWDM device is required to operate with a specified performance. For a particular nominal channel central frequency, fnomi, this frequency range is from fimin = (fnomi - dfmax) to fimax = (fnomi + dfmax), where dfmax is the maximum channel central frequency deviation. Nominal channel central frequency and maximum channel central frequency deviation are defined in ITU-T Rec. G.692. Insertion loss (dB, Port-Port, Max, Min):[G.671] It is the reduction in optical power between an input and output port of a WDM device in decibels (dB). Channel insertion loss deviation (dB, Max):[G.671] This is the maximum variation of insertion loss at any frequency within the channel frequency range (DWDM devices) or channel wavelength range (CWDM and WWDM devices). Ripple (dB, Max): [G.671] For WDM devices and tuneable filters, the peak-to-peak difference in insertion loss within a channel frequency (or wavelength) range. Channel chromatic dispersion (ps/nm, Max, Min): [G.650.1] Change of the group delay of a light pulse for a unit fibre length caused by a unit wavelength change. Differential group delay (ps, Max): [G.671] Polarization Mode Dispersion (PMD) is usually described in terms of a Differential Group Delay (DGD), which is the time difference between the principal States of Polarization (SOPs) of an optical signal at a particular wavelength and time. Bernstein Expires April 26, 2009 [Page 7] Internet-Draft Optical Impairment Info Model October 2008 Polarization dependent loss (dB, Max): [G.671] Maximum variation of insertion loss due to a variation of the state of polarization (SOP) over all SOPs. Reflectance (dB, Max): [G.671] The ratio of reflected power Pr to incident power, Pi at a given port of a passive component, for given conditions of spectral composition, polarization and geometrical distribution. Isolation, adjacent channel (dB, Min, Port-Port): [G.671] The adjacent channel isolation (of a WDM device) is defined to be equal to the unidirectional (far-end) isolation of that device with the restriction that x, the isolation wavelength number, is restricted to the channels immediately adjacent to the (channel) wavelength number associated with port o. Isolation, non-adjacent channel (dB, Min, Port-Port): [G.671] The non-adjacent channel isolation (of a WDM device) is defined to be equal to the unidirectional (far-end) isolation of that device with the restriction that x, the isolation wavelength number, is restricted to each of the channels not immediately adjacent to the (channel) wavelength number associated with port o. Note: [G.671] In a WDM device able to separate k wavelengths (w1, w2, ... , wk) radiation coming from one input port into k output ports, each one nominally passing radiation at one specific wavelength only. The unidirectional (far-end) isolation is a measure of the part of the optical power at each wavelength exiting from the port at wavelengths different from the nominal wavelength relative to the power at the nominal wavelength. Channel extinction (dB, Min, Port-Port): [G.671] Within the operating wavelength range, the difference (in dB) between the maximum insertion loss for the non-extinguished (non-blocked) channels and the minimum insertion loss for the extinguished (blocked) channels. Reconfigure time (ms, Max, Min): [G.680] The reconfigure time (of an ROADM) is the elapsed time measured from the earliest point that the actuation energy is applied to reconfigure the ONE to the time when the channel insertion loss for all wanted channels has settled to within 0.5 dB of its final steady state value and all other parameters of the device (e.g., isolation and channel extinction)are within the allowed limits. Switching time (for PXC) (ms, Max, Min): [G.671] The elapsed time it takes the switch to turn path io on or off from a particular initial Bernstein Expires April 26, 2009 [Page 8] Internet-Draft Optical Impairment Info Model October 2008 state, measured from the time the actuation energy is applied or removed. Channel uniformity (dB, Max): [G.671] The difference (in dB) between the powers of the channel with the most power (in dBm) and the channel with the least power (in dBm). This applies to a multichannel signal across the operating wavelength range. A.2. Additional parameters for NEs with optical amplifiers Total input power range (dBm, Max, Min, Port): [G.661] The range of optical power levels at the input for which the corresponding output signal optical power lies in the specified output power range, where the OA performance is ensured. Channel input power range (dBm, Max, Min, Port): see above. Channel output power range (dBm, Max, Min, Port): [G.661] The range of optical power levels at the output of the OA for which the corresponding input signal power lies in the specified input power range, where the OA performance is ensured. Channel signal-spontaneous noise figure (dB, Max, Port-Port) [G.661] The signal-spontaneous beat noise contribution to the noise figure, expressed in dB. Input reflectance (dB, Max, Port): [G.661] The maximum fraction of incident optical power, at the operating wavelength and over all states of input light polarization, reflected by the OA from the input port, under nominal specified operating conditions, expressed in dB. Output reflectance (dB, Max, Port): [G.661] The fraction of incident optical power at the operating wavelength reflected by the OA from the output port, under nominal operating conditions, expressed in dB. Maximum reflectance tolerable at input (dB, Min, Port): [G.661] The maximum fraction of power, expressed in dB, exiting the optical input port of the OA which, when reflected back into the OA, allows the device to still meet its specifications. Maximum reflectance tolerable at output (dB, Min, Port): [G.661] The maximum fraction of power, expressed in dB, exiting the optical output port of the OA which, when reflected back into the OA, allows the device to still meet its specifications. Bernstein Expires April 26, 2009 [Page 9] Internet-Draft Optical Impairment Info Model October 2008 Maximum total output power (dBm, Max, Port): [G.661] The highest signal optical power at the output that can be obtained from the OA under nominal operating conditions. Channel addition/removal (steady-state) gain response (dB, Max, Min): [G.661] For a specified multichannel configuration, the steady-state change in channel gain of any one of the channels due to the addition/removal of one or more other channels, expressed in dB. Transient duration (ms, Max): [G.661] The time period from the addition/removal of a channel to the time when the output power level of that or another channel reaches and remains within +- N dB from its steady-state value. Transient gain increase (dB, Max): [G.661] For a specified multichannel configuration, the maximum change in channel gain of any one of the channels due to the addition/removal of one or more other channels during the transient period after channel addition/removal, expressed in dB. Transient gain reduction (dB, Max): see above. Channel gain (dB, Max, Min, Port-Port): [G.661] Gain for each channel (at wavelength wj) in a specified multichannel configuration, expressed in dB. Multichannel gain-change difference (inter-channel gain-change difference) (dB, Max): [G.661] For a specified channel allocation, the difference of change in gain in one channel with respect to the change in gain of another channel for two specified sets of channel input powers, expressed in dB. Multichannel gain tilt (inter-channel gain-change ratio)(dB, Max): [G.661] The ratio of the changes in gain in each channel to the change in gain at a reference channel as the input conditions are varied from one set of input channel powers to a second set of input channel powers, expressed in dB per dB. Bernstein Expires April 26, 2009 [Page 10] Internet-Draft Optical Impairment Info Model October 2008 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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.661] ITU-T Recommendation G.661, Definition and test methods for the relevant generic parameters of optical amplifier devices and subsystems, March 2006. [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. [Imp-Frame] G. Bernstein, Y. Lee, D. Li, A Framework for the Control and Measurement of Wavelength Switched Optical Networks (WSON) with Impairments, Work in Progress, October 2008. [RWA-Info] G. Bernstein, Y. Lee, D. Li, W. Imajuku, Routing and Wavelength Assignment Information Model for Wavelength Switched Optical Networks, Work in Progress: draft-ietf- ccamp-rwa-info-00.txt, August 2008. 9.2. Informative References [RFC4054] Strand, J., Ed., and A. Chiu, Ed., "Impairments and Other Constraints on Optical Layer Routing", RFC 4054, May 2005. [Encode] G. Bernstein, Y. Lee, D. Li, W. Imajuku, "Routing and Wavelength Assignment Information Encoding for Wavelength Switched Optical Networks" Work in progress: draft- bernstein-ccamp-wson-encode-00.txt, July 2008. Bernstein Expires April 26, 2009 [Page 11] Internet-Draft Optical Impairment Info Model October 2008 Author's Addresses Greg Bernstein Grotto Networking Fremont CA, 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 Intellectual Property Statement The IETF 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 this 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. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR 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. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Bernstein Expires April 26, 2009 [Page 12] Internet-Draft Optical Impairment Info Model October 2008 Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Bernstein Expires April 26, 2009 [Page 13]