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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Ayan Banerjee (Calient Networks) 2 Internet Draft Angela Chiu (Celion Networks) 3 Expiration Date: November 2001 John Drake (Calient Networks) 4 Dan Blumenthal (Calient Networks) 5 Andre Fredette (Photonex) 7 Impairment Constraints for Routing in All-Optical Networks 9 draft-banerjee-routing-impairments-00.txt 11 1. Status of this Memo 13 This document is an Internet-Draft and is in full conformance with 14 all provisions of Section 10 of RFC2026 [Bra96]. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six 22 months and may be updated, replaced, or obsoleted by other documents 23 at any time. It is inappropriate to use Internet- Drafts as 24 reference material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 2. Abstract 34 In the not too distant future, signals carried between two endpoints 35 will be transmitted in an all-optical domain over a multi-hop path. 36 Such transparent networks consist of photonic switches, optical 37 add/drop multiplexers, optical amplifiers, optical regenerators, and 38 fiber. Signaling for such routes needs to account for optical 39 impairments in the path. This draft discusses a number of optical 40 parameters and proposes optical constraints as enhancements to the 41 routing protocols (for a subset of the parameters). 43 3. Introduction 45 Recently, a lot of work has been done to use the Generalized MPLS 46 control plane [ABB01] to dynamically provision resources and to 47 provide network survivability using protection and restoration 48 techniques for all-optical networks. The optical networks presently 49 being deployed may be called "opaque" ([TGN98]) - each link is 50 optically isolated by transponders doing O/E/O conversions from 51 other links. These transponders are quite expensive and they also 52 constrain the rapid evolution to new services - for example, they 53 tend to be bit rate and format specific. Thus there are strong 54 motivators to introduce "domains of transparency" - all-optical 55 networks. Such _transparent_ networks consist of photonic switches, 56 optical add/drop multiplexers, optical amplifiers, optical 57 regenerators, and fiber. 59 Current proposals on routing protocol extensions (see [KRB01a] and 60 [KRB01b]) consider opaque networks where all routes have adequate 61 signal quality. Here, we consider all-optical networks. In order to 62 take full advantages of potential cost and operational efficiencies 63 offered by the all-optical networks, we assume that a domain of 64 transparency may be too large to ensure that all potential routes 65 have adequate signal quality for all connections. In order to obtain 66 paths for the connections, physical impairments of various links in 67 the all-optical network need to be accounted for. Our goal is to 68 understand the impacts of the various types of impairments in this 69 environment and to recommend a practical set of parameters that need 70 to be accounted for. This necessitates enhancing the routing 71 protocols to advertise the selected attributes which are necessary 72 to compute constrained shortest paths. 74 The organization of the remainder of this document is as follows. 75 In Section 4, we discuss the various optical parameters that may 76 need to be announced. Furthermore, we outline the TLVs for the 77 (specifically for the OSPF and IS-IS routing protocols) parameters 78 that are to be flooded into the routing database. 80 4. Optical Parameters 82 In this section, we identify the various attributes that are 83 potential candidates for being flooded using the routing protocols. 84 We are only concerned with the impairments that may have impacts on 85 possible routes chosen through a transparent network. According to 86 the requirements specified in [CST00], we account for two key linear 87 impairments, namely Polarization Mode Dispersion (PMD) and Optical 88 Signal to Noise Ratio (OSNR). There are other performance related 89 parameters, e.g., modulator extinction ratio, jitter, Q-factor, etc 90 outlined in [CBD00], that need to be taken into account when 91 designing the transmission system. These parameters are either not 92 route dependent, or implicitly reflected by the PMD and OSNR 93 constraints or included in the OSNR margin described in section 4.3. 95 4.1. Polarization Mode Dispersion (PMD) 96 PMD management requires that the time-average differential group 97 delay (DGD) between two orthogonal state of polarizations, tau be 98 less than a fraction a of the bit duration, T = 1/B, where B is the 99 bit rate. The value of a depends on three major factors, 1) margin 100 allocated to PMD, e.g., 1dB; 2) targeting outage probability, e.g., 101 4x10-5; 3) sensitivity of receiver to DGD. A typical value for a is 102 0.1[ITU]. 104 Assume that the transparent segment consists of K links, with each 105 link k having a PMD value of tau(k). The PMD value of a link tau(k) 106 is a function of the length and fiber PMD parameter of each fiber 107 span on the link. The constraint on overall path PMD becomes the sum 108 of squares of the PMD parameter across all links to be less than 109 a^2/B^2. Hence, for routing constraint checking purposes regarding 110 PMD, the only link dependent information that needs to be propagated 111 or is tau(k)^2 (the square of the polarization mode dispersion). 113 In OSPF, the PMD parameter is represented as a sub-TLV of the Link 114 TLV in the Traffic Engineering LSA, with type 15. The length of the 115 sub-TLV is four-octets and specifies the square of the polarization 116 mode dispersion (in IEEE floating point format, the unit being pico 117 seconds squared). The format of the PMD sub-TLV is as shown: 119 0 1 2 3 120 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 121 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 122 | Type = 15 | Length = 4 | 123 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 124 | Polarization Mode Dispersion Square | 125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 127 In IS-IS, we enhance the sub-TLVs for the extended IS reachability 128 TLV. The length of the PMD sub-TLV is four-octets and specifies the 129 square of the polarization mode dispersion (in IEEE floating point 130 format, the unit being pico seconds squared). Specifically, we add 131 the following sub-TLV: 132 Sub-TLV type Length(in bytes) Name 133 21 4 PMD Type 135 4.2 Optical Signal to Noise Ratio (OSNR) 137 Amplifier Spontaneous Emission (ASE) degrades the signal to noise 138 ratio. An acceptable optical SNR level (SNRmin) which depends on the 139 bit rate, transmitter-receiver technology (e.g., FEC), and margins 140 allocated for other impairments, needs to be maintained at the 141 receiver. Vendors currently provide OTS engineering rules defining 142 maximum span length and number of spans that ensure that all routes 143 meet this requirement. For larger transparent domains, more detailed 144 OSNR computations will be needed to determine whether the OSNR level 145 on a given all-optical service or restoration route has acceptable 146 OSNR. 148 Assume P is the average optical power launched at the transmitter, 149 and each link k generates noise power N(k). The OSNR constraint for 150 path computation becomes the sum of the noise power across all links 151 in the path must be less than P/ SNRmin. 153 In OSPF, the Noise parameter is represented as a sub-TLV of the Link 154 TLV in the Traffic Engineering LSA, with type 16. The length of the 155 sub-TLV is four-octets and specifies the noise power (in IEEE 156 floating point format, the unit being dBm). The format of the Noise 157 sub-TLV is as shown: 159 0 1 2 3 160 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 162 | Type = 16 | Length = 4 | 163 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 164 | Noise Parameter | 165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 167 In IS-IS, we enhance the sub-TLVs for the extended IS reachability 168 TLV. The length of the noise sub-TLV is four-octets and specifies 169 the noise power of the link (in IEEE floating point format, the unit 170 being dBm ). Specifically, we add the following sub-TLV: 171 Sub-TLV type Length(in bytes) Name 172 21 4 Noise parameter Type 174 4.3 OSNR Margin and Receiver OSNR requirements 176 As an additional constraint, a network-wide margin on the OSNR 177 accounts for a number of other additional parameters that are not 178 spelled out explicitly in the above TLVs. For example, other major 179 impairments are: 180 1. Polarization-Dependent Loss (PDL): It is required that the total 181 PDL on the path to be within some acceptable limit, typically 1dB 182 margin in OSNR. 183 2. Chromatic Dispersion: In general, this impairment can be 184 adequately (but not optimally) compensated for on a per-link 185 basis, and/or at system initial setup time. 186 3. Crosstalk: Since crosstalk in the system affects Q, it can be 187 factored in with some margin in Q. As a result, one can increase 188 the OSNR requirement by some modified margin. 189 4. Nonlinear Impairments: One could assume that nonlinear 190 impairments are bounded and increase the required OSNR level by X 191 dB, where X for performance reasons would be limited to 1 or 2 192 dB, consequently setting a limit on the maximum number of spans. 193 For the approach described here to be useful, it is desirable for 194 this span limit to be longer than that imposed by the constraints 195 which can be treated explicitly. 197 Furthermore, it is assumed that all nodes in the network have a 198 table of the minimum value of the OSNR required to transmit 199 information at a specified bit rate for a given transceiver 200 technology (e.g. FEC). 202 5. Security Considerations 204 The enhancements do not introduce any additional security 205 considerations. 207 6. Acknowledgments 209 This document has benefited from discussions with Michael Eiselt and 210 Jonathan Lang. 212 7. References 214 [ABB01] Ashwood-Smith, P., et. al., "Generalized MPLS Signaling 215 Functional Description,_ Internet draft, draft-ietf- 216 generalized-mpls-signaling-00.txt, work in progress, March 217 2001. 218 [Bra96] Bradner, S., "The Internet Standards Process -- Revision 3," 219 BCP 9, RFC 2026, October 1996. 220 [CBD00] Ceuppens, L., Blumenthal, D., Drake, J., Chrostowski, J., 221 Edwards, W., "Performance Monitoring in Photonic Networks in 222 Support of MPL(ambda)S", Internet draft, work in progress, 223 March 2000. 224 [CST00] A. Chiu, J. Strand, and R. Tkach, "Unique Features and 225 Requirements for The Optical Layer Control Plane", Internet 226 Draft, draft-chiu-strand-unique-olcp-01.txt, work in 227 progress, November 2000. 228 [KRB01a] Kompella, K., et.al., "IS-IS extensions in support of 229 Generalized MPLS," Internet Draft, draft-ietf-gmpls- 230 extensions-01.txt, work in progress, 2001. 231 [KRB01b] Kompella, K., et. al., "OSPF extensions in support of 232 Generalized MPLS," Internet draft, draft-ospf-generalized- 233 mpls-00.txt, work in progress, March 2001. 234 [TGN98] Tkach, K., Goldstein, E., Nagel, J., and Strand, J., 235 "Fundamental Limits of Optical Transparency," Optical Fiber 236 Communication Conference, February 1998. 238 7. Author's Addresses 240 Ayan Banerjee Angela Chiu 241 Calient Networks Celion Networks 242 5853 Rue Ferrari 1 Sheila Drive, Suite 2 243 San Jose, CA 95138 Tinton Falls, NJ 07724 244 Email: abanerjee@calient.net email: angela.chiu@celion.com 246 John Drake Dan Blumenthal 247 Calient Networks Calient Networks 248 5853 Rue Ferrari 5853 Rue Ferrari 249 San Jose, CA 95138 San Jose, CA 95138 250 Email: jdrake@calient.net Email: dblumenthal@calient.net 251 Andre Fredette 252 8C Preston Court 253 Bedford, MA 01730 254 Photonex Corporation 255 Email: fredette@photonex.com