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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Y. Lee (ed.) 2 Internet Draft Huawei 3 Intended status: Informational G. Bernstein (ed.) 4 Expires: June 2011 Grotto Networking 5 Wataru Imajuku 6 NTT 8 December 17, 2010 10 Framework for GMPLS and PCE Control of Wavelength Switched Optical 11 Networks (WSON) 12 draft-ietf-ccamp-rwa-wson-framework-08.txt 14 Abstract 16 This document provides a framework for applying Generalized Multi- 17 Protocol Label Switching (GMPLS) and the Path Computation Element 18 (PCE) architecture to the control of wavelength switched optical 19 networks (WSON). In particular, it examines Routing and Wavelength 20 Assignment (RWA) of optical paths. 22 This document focuses on topological elements and path selection 23 constraints that are common across different WSON environments as 24 such it does not address optical impairments in any depth. 26 Status of this Memo 28 This Internet-Draft is submitted to IETF in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF), its areas, and its working groups. Note that 33 other groups may also distribute working documents as Internet- 34 Drafts. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 The list of current Internet-Drafts can be accessed at 42 http://www.ietf.org/ietf/1id-abstracts.txt 43 The list of Internet-Draft Shadow Directories can be accessed at 44 http://www.ietf.org/shadow.html. 46 This Internet-Draft will expire on June 17, 2009. 48 Copyright Notice 50 Copyright (c) 2010 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (http://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with 58 respect to this document. Code Components extracted from this 59 document must include Simplified BSD License text as described in 60 Section 4.e of the Trust Legal Provisions and are provided without 61 warranty as described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction...................................................4 66 2. Terminology....................................................4 67 3. Wavelength Switched Optical Networks...........................6 68 3.1. WDM and CWDM Links........................................6 69 3.2. Optical Transmitters and Receivers........................8 70 3.3. Optical Signals in WSONs..................................9 71 3.3.1. Optical Tributary Signals...........................10 72 3.3.2. WSON Signal Characteristics.........................10 73 3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs............11 74 3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs.......11 75 3.4.2. Splitters...........................................14 76 3.4.3. Combiners...........................................15 77 3.4.4. Fixed Optical Add/Drop Multiplexers.................15 78 3.5. Electro-Optical Systems..................................16 79 3.5.1. Regenerators........................................16 80 3.5.2. OEO Switches........................................19 81 3.6. Wavelength Converters....................................19 82 3.6.1. Wavelength Converter Pool Modeling..................21 83 3.7. Characterizing Electro-Optical Network Elements..........25 84 3.7.1. Input Constraints...................................26 85 3.7.2. Output Constraints..................................26 86 3.7.3. Processing Capabilities.............................27 88 4. Routing and Wavelength Assignment and the Control Plane.......28 89 4.1. Architectural Approaches to RWA..........................28 90 4.1.1. Combined RWA (R&WA).................................29 91 4.1.2. Separated R and WA (R+WA)...........................29 92 4.1.3. Routing and Distributed WA (R+DWA)..................30 93 4.2. Conveying information needed by RWA......................30 94 5. Modeling Examples and Control Plane Use Cases.................31 95 5.1. Network Modeling for GMPLS/PCE Control...................31 96 5.1.1. Describing the WSON nodes...........................32 97 5.1.2. Describing the links................................34 98 5.2. RWA Path Computation and Establishment...................35 99 5.3. Resource Optimization....................................36 100 5.4. Support for Rerouting....................................37 101 5.5. Electro-Optical Networking Scenarios.....................37 102 5.5.1. Fixed Regeneration Points...........................37 103 5.5.2. Shared Regeneration Pools...........................38 104 5.5.3. Reconfigurable Regenerators.........................38 105 5.5.4. Relation to Translucent Networks....................38 106 6. GMPLS and PCE Implications....................................39 107 6.1. Implications for GMPLS signaling.........................39 108 6.1.1. Identifying Wavelengths and Signals.................39 109 6.1.2. WSON Signals and Network Element Processing.........40 110 6.1.3. Combined RWA/Separate Routing WA support............40 111 6.1.4. Distributed Wavelength Assignment: Unidirectional, No 112 Converters.................................................41 113 6.1.5. Distributed Wavelength Assignment: Unidirectional, 114 Limited Converters.........................................41 115 6.1.6. Distributed Wavelength Assignment: Bidirectional, No 116 Converters.................................................41 117 6.2. Implications for GMPLS Routing...........................42 118 6.2.1. Electro-Optical Element Signal Compatibility........42 119 6.2.2. Wavelength-Specific Availability Information........43 120 6.2.3. WSON Routing Information Summary....................43 121 6.3. Optical Path Computation and Implications for PCE........45 122 6.3.1. Optical path Constraints and Characteristics........45 123 6.3.2. Electro-Optical Element Signal Compatibility........45 124 6.3.3. Discovery of RWA Capable PCEs.......................46 125 7. Security Considerations.......................................46 126 8. IANA Considerations...........................................47 127 9. Acknowledgments...............................................47 128 10. References...................................................48 129 10.1. Normative References....................................48 130 10.2. Informative References..................................49 131 11. Contributors.................................................52 132 Author's Addresses...............................................53 133 Intellectual Property Statement..................................53 134 Disclaimer of Validity...........................................54 135 12. Appendix A Revision History..................................54 137 1. Introduction 139 Wavelength Switched Optical Networks (WSONs) are constructed from 140 subsystems that include Wavelength Division Multiplexed (WDM) links, 141 tunable transmitters and receivers, Reconfigurable Optical Add/Drop 142 Multiplexers (ROADM), wavelength converters, and electro-optical 143 network elements. A WSON is a WDM-based optical network in which 144 switching is performed selectively based on the center wavelength of 145 an optical signal. 147 In order to provision an optical connection (an optical path) through 148 a WSON certain path continuity and resource availability constraints 149 must be met to determine viable and optimal paths through the 150 network. The determination of paths is known as Routing and 151 Wavelength Assignment (RWA). 153 Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes 154 a set of control plane protocols that can be used to operate data 155 networks ranging from packet switch capable networks, through those 156 networks that use time division multiplexing, to WDM networks. The 157 Path Computation Element (PCE) architecture [RFC4655] defines 158 functional components that can be used to compute and suggest 159 appropriate paths in connection-oriented traffic-engineered networks. 161 This document provides a framework for applying GMPLS protocols and 162 the PCE architecture to the control and operation of WSONs. To aid 163 in this process this document also provides an overview of the 164 subsystems and processes that comprise WSONs, and describes RWA so 165 that the information requirements, both static and dynamic, can be 166 identified to explain how the information can be modeled for use by 167 GMPLS and PCE systems. This work will facilitate the development of 168 protocol solution models and protocol extensions within the GMPLS and 169 PCE protocol families. 171 Note that this document focuses on the generic properties of links, 172 switches and path selection constraints that occur in WSONs. 173 Different WSONs such as access, metro, and long haul may apply 174 different techniques for dealing with optical impairments hence this 175 document does not address optical impairments in any depth. See 176 [WSON-Imp] for more information on optical impairments and GMPLS. 178 2. Terminology 180 Add/Drop Multiplexers (ADM): An optical device used in WDM networks 181 composed of one or more line side ports and typically many tributary 182 ports. 184 CWDM: Coarse Wavelength Division Multiplexing. 186 DWDM: Dense Wavelength Division Multiplexing. 188 Degree: The degree of an optical device (e.g., ROADM) is given by a 189 count of its line side ports. 191 Drop and continue: A simple multi-cast feature of some ADM where a 192 selected wavelength can be switched out of both a tributary (drop) 193 port and a line side port. 195 FOADM: Fixed Optical Add/Drop Multiplexer. 197 GMPLS: Generalized Multi-Protocol Label Switching. 199 Line side: In WDM system line side ports and links typically can 200 carry the full multiplex of wavelength signals, as compared to 201 tributary (add or drop ports) that typically carry a few (typically 202 one) wavelength signals. 204 OXC: Optical cross connect. An optical switching element in which a 205 signal on any input port can reach any output port. 207 PCC: Path Computation Client. Any client application requesting a 208 path computation to be performed by the Path Computation Element. 210 PCE: Path Computation Element. An entity (component, application, or 211 network node) that is capable of computing a network path or route 212 based on a network graph and applying computational constraints. 214 PCEP: PCE Communication Protocol. The communication protocol between 215 a Path Computation Client and Path Computation Element. 217 ROADM: Reconfigurable Optical Add/Drop Multiplexer. A wavelength 218 selective switching element featuring input and output line side 219 ports as well as add/drop tributary ports. 221 RWA: Routing and Wavelength Assignment. 223 Transparent Network: A wavelength switched optical network that does 224 not contain regenerators or wavelength converters. 226 Translucent Network: A wavelength switched optical network that is 227 predominantly transparent but may also contain limited numbers of 228 regenerators and/or wavelength converters. 230 Tributary: A link or port on a WDM system that can carry 231 significantly less than the full multiplex of wavelength signals 232 found on the line side links/ports. Typical tributary ports are the 233 add and drop ports on an ADM and these support only a single 234 wavelength channel. 236 Wavelength Conversion/Converters: The process of converting an 237 information bearing optical signal centered at a given wavelength to 238 one with "equivalent" content centered at a different wavelength. 239 Wavelength conversion can be implemented via an optical-electronic- 240 optical (OEO) process or via a strictly optical process. 242 WDM: Wavelength Division Multiplexing. 244 Wavelength Switched Optical Networks (WSONs): WDM based optical 245 networks in which switching is performed selectively based on the 246 center wavelength of an optical signal. 248 3. Wavelength Switched Optical Networks 250 WSONs range in size from continent spanning long haul networks, to 251 metropolitan networks, to residential access networks. In all these 252 cases, the main concern is those properties that constrain the choice 253 of wavelengths that can be used, i.e., restrict the wavelength label 254 set, impact the path selection process, and limit the topological 255 connectivity. In addition, if electro-optical network elements are 256 used in the WSON, additional compatibility constraints may be imposed 257 by the network elements on various optical signal parameters. The 258 subsequent sections review and model some of the major subsystems of 259 a WSON with an emphasis on those aspects that are of relevance to the 260 control plane. In particular, WDM links, optical transmitters, 261 ROADMs, and wavelength converters are examined. 263 3.1. WDM and CWDM Links 265 WDM and CWDM links run over optical fibers, and optical fibers come 266 in a wide range of types that tend to be optimized for various 267 applications examples include access networks, metro, long haul, and 268 submarine links. International Telecommunication Union - 269 Telecommunication Standardization Sector (ITU-T) standards exist for 270 various types of fibers. Although fiber can be categorized into 271 Single mode fibers (SMF) and Multi-mode fibers (MMF), the latter are 272 typically used for short-reach campus and premise applications. SMF 273 are used for longer-reach applications and therefore are the primary 274 concern of this document. The following SMF fiber types are typically 275 encountered in optical networks: 277 ITU-T Standard | Common Name 278 ------------------------------------------------------------ 279 G.652 [G.652] | Standard SMF | 280 G.653 [G.653] | Dispersion shifted SMF | 281 G.654 [G.654] | Cut-off shifted SMF | 282 G.655 [G.655] | Non-zero dispersion shifted SMF | 283 G.656 [G.656] | Wideband non-zero dispersion shifted SMF | 284 ------------------------------------------------------------ 286 Typically WDM links operate in one or more of the approximately 287 defined optical bands [G.Sup39]: 289 Band Range (nm) Common Name Raw Bandwidth (THz) 290 O-band 1260-1360 Original 17.5 291 E-band 1360-1460 Extended 15.1 292 S-band 1460-1530 Short 9.4 293 C-band 1530-1565 Conventional 4.4 294 L-band 1565-1625 Long 7.1 295 U-band 1625-1675 Ultra-long 5.5 297 Not all of a band may be usable, for example in many fibers that 298 support E-band there is significant attenuation due to a water 299 absorption peak at 1383nm. Hence a discontinuous acceptable 300 wavelength range for a particular link may be needed and is modeled. 301 Also some systems will utilize more than one band. This is 302 particularly true for CWDM systems. 304 Current technology subdivides the bandwidth capacity of fibers into 305 distinct channels based on either wavelength or frequency. There are 306 two standards covering wavelengths and channel spacing. ITU-T 307 Recommendation G.694.1, Spectral grids for WDM applications: DWDM 308 frequency grid [G.694.1] describes a DWDM grid defined in terms of 309 frequency grids of 12.5GHz, 25GHz, 50GHz, 100GHz, and other multiples 310 of 100GHz around a 193.1THz center frequency. At the narrowest 311 channel spacing this provides less than 4800 channels across the O 312 through U bands. ITU-T Recommendation G.694.2, Spectral grids for WDM 313 applications: CWDM wavelength grid [G.694.2] describes a CWDM grid 314 defined in terms of wavelength increments of 20nm running from 1271nm 315 to 1611nm for 18 or so channels. The number of channels is 316 significantly smaller than the 32 bit GMPLS label space defined for 317 GMPLS, see [RFC3471]. A label representation for these ITU-T grids 318 is given in [Otani] and provides a common label format to be used in 319 signaling optical paths. Further, these ITU-T grid based labels can 320 also be used to describe WDM links, ROADM ports, and wavelength 321 converters for the purposes of path selection. 323 Many WDM links are designed to take advantage of particular fiber 324 characteristics or to try to avoid undesirable properties. For 325 example dispersion shifted SMF [G.653] was originally designed for 326 good long distance performance in single channel systems, however 327 putting WDM over this type of fiber requires significant system 328 engineering and a fairly limited range of wavelengths. Hence the 329 following information is needed as parameters to perform basic, 330 impairment unaware, modeling of a WDM link: 332 o Wavelength range(s): Given a mapping between labels and the ITU-T 333 grids each range could be expressed in terms of a tuple (lambda1, 334 lambda2) or (freq1, freq1) where the lambdas or frequencies can be 335 represented by 32 bit integers. 337 o Channel spacing: Currently there are five channel spacings used in 338 DWDM systems and a single channel spacing defined for CWDM 339 systems. 341 For a particular link this information is relatively static, as 342 changes to these properties generally require hardware upgrades. Such 343 information may be used locally during wavelength assignment via 344 signaling, similar to label restrictions in MPLS or used by a PCE in 345 providing combined RWA. 347 3.2. Optical Transmitters and Receivers 349 WDM optical systems make use of optical transmitters and receivers 350 utilizing different wavelengths (frequencies). Some transmitters are 351 manufactured for a specific wavelength of operation, that is, the 352 manufactured frequency cannot be changed. First introduced to reduce 353 inventory costs, tunable optical transmitters and receivers are 354 deployed in some systems, and allow flexibility in the wavelength 355 used for optical transmission/reception. Such tunable optics aid in 356 path selection. 358 Fundamental modeling parameters from the control plane perspective 359 optical transmitters and receivers are: 361 o Tunable: Do the transmitter and receivers operate at variable or 362 fixed wavelength. 364 o Tuning range: This is the frequency or wavelength range over which 365 the optics can be tuned. With the fixed mapping of labels to 366 lambdas as proposed in [Otani] this can be expressed as a tuple 367 (lambda1, lambda2) or (freq1, freq2) where lambda1 and lambda2 or 368 freq1 and freq2 are the labels representing the lower and upper 369 bounds in wavelength. 371 o Tuning time: Tuning times highly depend on the technology used. 372 Thermal drift based tuning may take seconds to stabilize, whilst 373 electronic tuning might provide sub-ms tuning times. Depending on 374 the application this might be critical. For example, thermal drift 375 might not be usable for fast protection applications. 377 o Spectral characteristics and stability: The spectral shape of a 378 laser's emissions and its frequency stability put limits on 379 various properties of the overall WDM system. One relatively easy 380 to characterize constraint is the closest channel spacing with 381 which the transmitter can be used. 383 Note that ITU-T recommendations specify many aspects of an optical 384 transmitter. Many of these parameters, such as spectral 385 characteristics and stability, are used in the design of WDM 386 subsystems consisting of transmitters, WDM links and receivers 387 however they do not furnish additional information that will 388 influence the Label Switched Path (LSP) provisioning in a properly 389 designed system. 391 Also note that optical components can degrade and fail over time. 392 This presents the possibility of the failure of a LSP (optical path) 393 without either a node or link failure. Hence, additional mechanisms 394 may be necessary to detect and differentiate this failure from the 395 others, e.g., one doesn't not want to initiate mesh restoration if 396 the source transmitter has failed, since the optical transmitter will 397 still be failed on the alternate optical path. 399 3.3. Optical Signals in WSONs 401 In WSONs the fundamental unit of switching is intuitively that of a 402 "wavelength". The transmitters and receivers in these networks will 403 deal with one wavelength at a time, while the switching systems 404 themselves can deal with multiple wavelengths at a time. Hence 405 multichannel DWDM networks with single channel interfaces are the 406 prime focus of this document general concern as opposed to multi- 407 channel interfaces. Interfaces of this type are defined in ITU-T 408 recommendations [G.698.1] and [G.698.2]. Key non-impairment related 409 parameters defined in [G.698.1] and [G.698.2] are: 411 (a) Minimum channel spacing (GHz) 413 (b) Minimum and maximum central frequency 415 (c) Bit-rate/Line coding (modulation) of optical tributary signals 416 For the purposes of modeling the WSON in the control plane, (a) and 417 (b) are considered as properties of the link and restrictions on the 418 GMPLS labels while (c) is a property of the "signal". 420 3.3.1. Optical Tributary Signals 422 The optical interface specifications [G.698.1], [G.698.2], and 423 [G.959.1] all use the concept of an optical tributary signal which is 424 defined as "a single channel signal that is placed within an optical 425 channel for transport across the optical network". Note the use of 426 the qualifier "tributary" to indicate that this is a single channel 427 entity and not a multichannel optical signal. 429 There are currently a number of different types of optical tributary 430 signals, which are known as "optical tributary signal classes". These 431 are currently characterized by a modulation format and bit rate range 432 [G.959.1]: 434 (a) Optical tributary signal class NRZ 1.25G 436 (b) Optical tributary signal class NRZ 2.5G 438 (c) Optical tributary signal class NRZ 10G 440 (d) Optical tributary signal class NRZ 40G 442 (e) Optical tributary signal class RZ 40G 444 Note that with advances in technology more optical tributary signal 445 classes may be added and that this is currently an active area for 446 development and standardization. In particular at the 40G rate there 447 are a number of non-standardized advanced modulation formats that 448 have seen significant deployment including Differential Phase Shift 449 Keying (DPSK) and Phase Shaped Binary Transmission (PSBT). 451 According to [G.698.2] it is important to fully specify the bit rate 452 of the optical tributary signal. Hence it is seen that modulation 453 format (optical tributary signal class) and bit rate are key 454 parameters in characterizing the optical tributary signal. 456 3.3.2. WSON Signal Characteristics 458 An optical tributary signal referenced in ITU-T [G.698.1] and 459 [G.698.2] is referred to as the "signal" in this document. This 460 corresponds to the "lambda" LSP in GMPLS. For signal compatibility 461 purposes with electro-optical network elements, the following signal 462 characteristics are considered: 464 1. Optical tributary signal class (modulation format). 465 2. FEC: whether forward error correction is used in the digital stream 466 and what type of error correcting code is used. 467 3. Center frequency (wavelength). 468 4. Bit rate. 469 5. G-PID: general protocol identifier for the information format. 471 The first three items on this list can change as a WSON signal 472 traverses the optical network with elements that include 473 regenerators, Optical-to-Electrical (OEO) switches, or wavelength 474 converters. 476 Bit rate and G-PID would not change since they describe the encoded 477 bit stream. A set of G-PID values is already defined for lambda 478 switching in [RFC3471] and [RFC4328]. 480 Note that a number of non-standard or proprietary modulation formats 481 and FEC codes are commonly used in WSONs. For some digital bit 482 streams the presence of Forwarding Equivalence Class (FEC) can be 483 detected, e.g., in [G.707] this is indicated in the signal itself via 484 the FEC Status Indication (FSI) byte, while in [G.709] this can be 485 inferred from whether the FEC field of the Optical Channel Transport 486 Unit-k (OTUk) is all zeros or not. 488 3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs 490 Definitions of various optical devices such as ROADMs, Optical Cross- 491 connects (OXCs), splitters, combiners and Fixed Optical Add-Drop 492 Multiplexers (FOADMs) and their parameters can be found in [G.671]. 493 Only a subset of these and their non-impairment related properties 494 are considered in the following sections. 496 3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs 498 ROADMs are available in different forms and technologies. This is a 499 key technology that allows wavelength based optical switching. A 500 classic degree-2 ROADM is shown in Figure 1. 502 Line side input +---------------------+ Line side output 503 --->| |---> 504 | | 505 | ROADM | 506 | | 507 | | 508 +---------------------+ 509 | | | | o o o o 510 | | | | | | | | 511 O O O O | | | | 512 Tributary Side: Drop (output) Add (input) 514 Figure 1. Degree-2 ROADM 516 The key feature across all ROADM types is their highly asymmetric 517 switching capability. In the ROADM of Figure 1, signals introduced 518 via the add ports can only be sent on the line side output port and 519 not on any of the drop ports. The term "degree" is used to refer to 520 the number of line side ports (input and output) of a ROADM, and does 521 not include the number of "add" or "drop" ports. The add and drop 522 ports are sometimes also called tributary ports. As the degree of the 523 ROADM increases beyond two it can have properties of both a switch 524 (OXC) and a multiplexer and hence it is necessary to know the 525 switched connectivity offered by such a network element to 526 effectively utilize it. A straightforward way to represent this is 527 via a "switched connectivity" matrix A where Amn = 0 or 1, depending 528 upon whether a wavelength on input port m can be connected to output 529 port n [Imajuku]. For the ROADM shown in Figure 1 the switched 530 connectivity matrix can be expressed as: 532 Input Output Port 533 Port #1 #2 #3 #4 #5 534 -------------- 535 #1: 1 1 1 1 1 536 #2 1 0 0 0 0 537 A = #3 1 0 0 0 0 538 #4 1 0 0 0 0 539 #5 1 0 0 0 0 541 Where input ports 2-5 are add ports, output ports 2-5 are drop ports 542 and input port #1 and output port #1 are the line side (WDM) ports. 544 For ROADMs, this matrix will be very sparse, and for OXCs the matrix 545 will be very dense, compact encodings and examples, including high 546 degree ROADMs/OXCs, are given in [WSON-Encode]. A degree-4 ROADM is 547 shown in Figure 2. 549 +-----------------------+ 550 Line side-1 --->| |---> Line side-2 551 Input (I1) | | Output (E2) 552 Line side-1 <---| |<--- Line side-2 553 Output (E1) | | Input (I2) 554 | ROADM | 555 Line side-3 --->| |---> Line side-4 556 Input (I3) | | Output (E4) 557 Line side-3 <---| |<--- Line side-4 558 Output (E3) | | Input (I4) 559 | | 560 +-----------------------+ 561 | O | O | O | O 562 | | | | | | | | 563 O | O | O | O | 564 Tributary Side: E5 I5 E6 I6 E7 I7 E8 I8 566 Figure 2. Degree-4 ROADM 568 Note that this example is 4-degree example with one (potentially 569 multi-channel) add/drop per line side port. 571 Note also that the connectivity constraints for typical ROADM designs 572 are "bidirectional", i.e. if input port X can be connected to output 573 port Y, typically input port Y can be connected to output port X, 574 assuming the numbering is done in such a way that input X and output 575 X correspond to the same line side direction or the same add/drop 576 port. This makes the connectivity matrix symmetrical as shown below. 578 Input Output Port 579 Port E1 E2 E3 E4 E5 E6 E7 E8 580 ----------------------- 581 I1 0 1 1 1 0 1 0 0 582 I2 1 0 1 1 0 0 1 0 583 A = I3 1 1 0 1 1 0 0 0 584 I4 1 1 1 0 0 0 0 1 585 I5 0 0 1 0 0 0 0 0 586 I6 1 0 0 0 0 0 0 0 587 I7 0 1 0 0 0 0 0 0 588 I8 0 0 0 1 0 0 0 0 590 Where I5/E5 are add/drop ports to/from line side-3, I6/E6 are 591 add/drop ports to/from line side-1, I7/E7 are add/drop ports to/from 592 line side-2 and I8/E8 are add/drop ports to/from line side-4. Note 593 that diagonal elements are zero since loopback is not supported in 594 the example. If ports support loopback, diagonal elements would be 595 set to one. 597 Additional constraints may also apply to the various ports in a 598 ROADM/OXC. The following restrictions and terms may be used: 600 Colored port: an input or more typically an output (drop) port 601 restricted to a single channel of fixed wavelength. 603 Colorless port: an input or more typically an output (drop) port 604 restricted to a single channel of arbitrary wavelength. 606 In general a port on a ROADM could have any of the following 607 wavelength restrictions: 609 o Multiple wavelengths, full range port. 611 o Single wavelength, full range port. 613 o Single wavelength, fixed lambda port. 615 o Multiple wavelengths, reduced range port (for example wave band 616 switching). 618 To model these restrictions it is necessary to have two pieces of 619 information for each port: (a) number of wavelengths, (b) wavelength 620 range and spacing. Note that this information is relatively static. 621 More complicated wavelength constraints are modeled in [WSON-Info]. 623 3.4.2. Splitters 625 An optical splitter consists of a single input port and two or more 626 output ports. The input optical signaled is essentially copied (with 627 power loss) to all output ports. 629 Using the modeling notions of Section 3.4.1. (Reconfigurable Add/Drop 630 Multiplexers and OXCs) the input and output ports of a splitter would 631 have the same wavelength restrictions. In addition a splitter is 632 modeled by a connectivity matrix Amn as follows: 634 Input Output Port 635 Port #1 #2 #3 ... #N 636 ----------------- 637 A = #1 1 1 1 ... 1 639 The difference from a simple ROADM is that this is not a switched 640 connectivity matrix but the fixed connectivity matrix of the device. 642 3.4.3. Combiners 644 An optical combiner is a device that combines the optical wavelengths 645 carried by multiple input ports into a single multi-wavelength output 646 port. The various ports may have different wavelength restrictions. 647 It is generally the responsibility of those using the combiner to 648 assure that wavelength collision does not occur on the output port. 649 The fixed connectivity matrix Amn for a combiner would look like: 651 Input Output Port 652 Port #1 653 --- 654 #1: 1 655 #2 1 656 A = #3 1 657 ... 1 658 #N 1 660 3.4.4. Fixed Optical Add/Drop Multiplexers 662 A fixed optical add/drop multiplexer can alter the course of an input 663 wavelength in a preset way. In particular a given wavelength (or 664 waveband) from a line side input port would be dropped to a fixed 665 "tributary" output port. Depending on the device's construction that 666 same wavelength may or may not also be sent out the line side output 667 port. This is commonly referred to as "drop and continue" operation. 668 There also may exist tributary input ports ("add" ports) whose 669 signals are combined with each other and other line side signals. 671 In general, to represent the routing properties of an FOADM it is 672 necessary to have both a fixed connectivity matrix Amn as previously 673 discussed and the precise wavelength restrictions for all input and 674 output ports. From the wavelength restrictions on the tributary 675 output ports, what wavelengths have been selected can be derived. 676 From the wavelength restrictions on the tributary input ports, it can 677 be seen which wavelengths have been added to the line side output 678 port. Finally from the added wavelength information and the line side 679 output wavelength restrictions it can be inferred which wavelengths 680 have been continued. 682 To summarize, the modeling methodology introduced in Section 3.4.1. 683 (Reconfigurable Add/Drop Multiplexers and OXCs) consisting of a 684 connectivity matrix and port wavelength restrictions can be used to 685 describe a large set of fixed optical devices such as combiners, 686 splitters and FOADMs. Hybrid devices consisting of both switched and 687 fixed parts are modeled in [WSON-Info]. 689 3.5. Electro-Optical Systems 691 This section describes how Electro-Optical Systems (e.g., OEO 692 switches, wavelength converters, and regenerators) interact with the 693 WSON signal characteristics listed in Section 3.3.2. (WSON Signal 694 Characteristics) OEO switches, wavelength converters and regenerators 695 all share a similar property: they can be more or less "transparent" 696 to an "optical signal" depending on their functionality and/or 697 implementation. Regenerators have been fairly well characterized in 698 this regard and hence their properties can be described first. 700 3.5.1. Regenerators 702 The various approaches to regeneration are discussed in ITU-T G.872 703 Annex A [G.872]. They map a number of functions into the so-called 704 1R, 2R and 3R categories of regenerators as summarized in Table 1 705 below: 707 Table 1. Regenerator functionality mapped to general regenerator 708 classes from [G.872]. 710 --------------------------------------------------------------------- 711 1R | Equal amplification of all frequencies within the amplification 712 | bandwidth. There is no restriction upon information formats. 713 +----------------------------------------------------------------- 714 | Amplification with different gain for frequencies within the 715 | amplification bandwidth. This could be applied to both single- 716 | channel and multi-channel systems. 717 +----------------------------------------------------------------- 718 | Dispersion compensation (phase distortion). This analogue 719 | process can be applied in either single-channel or multi- 720 | channel systems. 721 --------------------------------------------------------------------- 722 2R | Any or all 1R functions. Noise suppression. 723 +----------------------------------------------------------------- 724 | Digital reshaping (Schmitt Trigger function) with no clock 725 | recovery. This is applicable to individual channels and can be 726 | used for different bit rates but is not transparent to line 727 | coding (modulation). 728 -------------------------------------------------------------------- 729 3R | Any or all 1R and 2R functions. Complete regeneration of the 730 | pulse shape including clock recovery and retiming within 731 | required jitter limits. 732 -------------------------------------------------------------------- 734 From this table it is seen that 1R regenerators are generally 735 independent of signal modulation format (also known as line coding), 736 but may work over a limited range of wavelength/frequencies. 2R 737 regenerators are generally applicable to a single digital stream and 738 are dependent upon modulation format (line coding) and to a lesser 739 extent are limited to a range of bit rates (but not a specific bit 740 rate). Finally, 3R regenerators apply to a single channel, are 741 dependent upon the modulation format and generally sensitive to the 742 bit rate of digital signal, i.e., either are designed to only handle 743 a specific bit rate or need to be programmed to accept and regenerate 744 a specific bit rate. In all these types of regenerators the digital 745 bit stream contained within the optical or electrical signal is not 746 modified. 748 It is common for regenerators to modify the digital bit stream for 749 performance monitoring and fault management purposes. Synchronous 750 Optical Networking (SONET), Synchronous Digital Hierarchy (SDH) and 751 Interfaces for the Optical Transport Network (G.709) all have digital 752 signal "envelopes" designed to be used between "regenerators" (in 753 this case 3R regenerators). In SONET this is known as the "section" 754 signal, in SDH this is known as the "regenerator section" signal, in 755 G.709 this is known as an OTUk. These signals reserve a portion of 756 their frame structure (known as overhead) for use by regenerators. 757 The nature of this overhead is summarized in Table 2 below. 759 Table 2. SONET, SDH, and G.709 regenerator related overhead. 761 +-----------------------------------------------------------------+ 762 |Function | SONET/SDH | G.709 OTUk | 763 | | Regenerator | | 764 | | Section | | 765 |------------------+----------------------+-----------------------| 766 |Signal | J0 (section | Trail Trace | 767 |Identifier | trace) | Identifier (TTI) | 768 |------------------+----------------------+-----------------------| 769 |Performance | BIP-8 (B1) | BIP-8 (within SM) | 770 |Monitoring | | | 771 |------------------+----------------------+-----------------------| 772 |Management | D1-D3 bytes | GCC0 (general | 773 |Communications | | communications | 774 | | | channel) | 775 |------------------+----------------------+-----------------------| 776 |Fault Management | A1, A2 framing | FAS (frame alignment | 777 | | bytes | signal), BDI(backward| 778 | | | defect indication)BEI| 779 | | | (backward error | 780 | | | indication) | 781 +------------------+----------------------+-----------------------| 782 |Forward Error | P1,Q1 bytes | OTUk FEC | 783 |Correction (FEC) | | | 784 +-----------------------------------------------------------------+ 786 In the previous table it is seen that frame alignment, signal 787 identification, and FEC are supported. What this table also shows by 788 its omission is that no switching or multiplexing occurs at this 789 layer. This is a significant simplification for the control plane 790 since control plane standards require a multi-layer approach when 791 there are multiple switching layers, but not for "layering" to 792 provide the management functions of Table 2. That is, many existing 793 technologies covered by GMPLS contain extra management related layers 794 that are essentially ignored by the control plane (though not by the 795 management plane!). Hence, the approach here is to include 796 regenerators and other devices at the WSON layer unless they provide 797 higher layer switching and then a multi-layer or multi-region 798 approach [RFC5212] is called for. However, this can result in 799 regenerators having a dependence on the client signal type. 801 Hence depending upon the regenerator technology the following 802 constraints may be imposed by a regenerator device: 804 Table 3. Regenerator Compatibility Constraints. 806 +--------------------------------------------------------+ 807 | Constraints | 1R | 2R | 3R | 808 +--------------------------------------------------------+ 809 | Limited Wavelength Range | x | x | x | 810 +--------------------------------------------------------+ 811 | Modulation Type Restriction | | x | x | 812 +--------------------------------------------------------+ 813 | Bit Rate Range Restriction | | x | x | 814 +--------------------------------------------------------+ 815 | Exact Bit Rate Restriction | | | x | 816 +--------------------------------------------------------+ 817 | Client Signal Dependence | | | x | 818 +--------------------------------------------------------+ 820 Note that the limited wavelength range constraint can be modeled for 821 GMPLS signaling with the label set defined in [RFC3471] and that the 822 modulation type restriction constraint includes FEC. 824 3.5.2. OEO Switches 826 A common place where OEO processing may take place is within WSON 827 switches that utilize (or contain) regenerators. Regenerators may be 828 added to a switching system for a number of reasons. One common 829 reason is to restore signal quality either before or after optical 830 processing (switching). Another reason may be to convert the signal 831 to an electronic form for switching then reconverting to an optical 832 signal prior to output from the switch. In this later case the 833 regeneration is applied to adapt the signal to the switch fabric 834 regardless of whether or not it is needed from a signal quality 835 perspective. 837 In either case these optical switches have essentially the same 838 compatibility constraints as those which are described for 839 regenerators in Table 3. 841 3.6. Wavelength Converters 843 Wavelength converters take an input optical signal at one wavelength 844 and emit an equivalent content optical signal at another wavelength 845 on output. There are multiple approaches to building wavelength 846 converters. One approach is based on OEO conversion with fixed or 847 tunable optics on output. This approach can be dependent upon the 848 signal rate and format, i.e., this is basically an electrical 849 regenerator combined with a laser/receiver. Hence, this type of 850 wavelength converter has signal processing restrictions that are 851 essentially the same as those described for regenerators in Table 3 852 of section 3.5.1. 854 Another approach performs the wavelength conversion, optically via 855 non-linear optical effects, similar in spirit to the familiar 856 frequency mixing used in radio frequency systems, but significantly 857 harder to implement. Such processes/effects may place limits on the 858 range of achievable conversion. These may depend on the wavelength of 859 the input signal and the properties of the converter as opposed to 860 only the properties of the converter in the OEO case. Different WSON 861 system designs may choose to utilize this component to varying 862 degrees or not at all. 864 Current or envisioned contexts for wavelength converters are: 866 1. Wavelength conversion associated with OEO switches and fixed or 867 tunable optics. In this case there are typically multiple 868 converters available since each on the use of an OEO switch can be 869 thought of as a potential wavelength converter. 871 2. Wavelength conversion associated with ROADMs/OXCs. In this case 872 there may be a limited pool of wavelength converters available. 873 Conversion could be either all optical or via an OEO method. 875 3. Wavelength conversion associated with fixed devices such as FOADMs. 876 In this case there may be a limited amount of conversion. Also in 877 this case the conversion may be used as part of optical path 878 routing. 880 Based on the above considerations, wavelength converters are modeled 881 as follows: 883 1. Wavelength converters can always be modeled as associated with 884 network elements. This includes fixed wavelength routing elements. 886 2. A network element may have full wavelength conversion capability, 887 i.e., any input port and wavelength, or a limited number of 888 wavelengths and ports. On a box with a limited number of 889 converters there also may exist restrictions on which ports can 890 reach the converters. Hence regardless of where the converters 891 actually are they can be associated with input ports. 893 3. Wavelength converters have range restrictions that are either 894 independent or dependent upon the input wavelength. 896 In WSONs where wavelength converters are sparse an optical path may 897 appear to loop or "backtrack" upon itself in order to reach a 898 wavelength converter prior to continuing on to its destination. The 899 lambda used on input to the wavelength converter would be different 900 the lambda coming back from the wavelength converter. 902 A model for an individual O-E-O wavelength converter would consist 903 of: 905 o Input lambda or frequency range. 907 o Output lambda or frequency range. 909 3.6.1. Wavelength Converter Pool Modeling 911 A WSON node may include multiple wavelength converters. These are 912 usually arranged into some type of pool to promote resource sharing. 913 There are a number of different approaches used in the design of 914 switches with converter pools. However, from the point of view of 915 path computation it is necessary to know the following: 917 1. The nodes that support wavelength conversion. 919 2. The accessibility and availability of a wavelength converter to 920 convert from a given input wavelength on a particular input port 921 to a desired output wavelength on a particular output port. 923 3. Limitations on the types of signals that can be converted and the 924 conversions that can be performed. 926 To model point 2 above, a similar technique can be used to model 927 ROADMs and optical switches, i.e., matrices to indicate possible 928 connectivity along with wavelength constraints for links/ports. Since 929 wavelength converters are considered a scarce resource it will be 930 desirable to include as a minimum the usage state of individual 931 wavelength converters in the pool. 933 A three stage model is used as shown schematically in Figure 3. 934 (Schematic diagram of wavelength converter pool model). This model 935 represents N input ports (fibers), P wavelength converters, and M 936 output ports (fibers). Since not all input ports can necessarily 937 reach the converter pool, the model starts with a wavelength pool 938 input matrix WI(i,p) = {0,1} where input port i can reach potentially 939 reach wavelength converter p. 941 Since not all wavelength can necessarily reach all the converters or 942 the converters may have limited input wavelength range there is a set 943 of input port constraints for each wavelength converter. Currently it 944 is assumed that a wavelength converter can only take a single 945 wavelength on input. Each wavelength converter input port constraint 946 can be modeled via a wavelength set mechanism. 948 Next a state vector WC(j) = {0,1} dependent upon whether wavelength 949 converter j in the pool is in use. This is the only state kept in the 950 converter pool model. This state is not necessary for modeling 951 "fixed" transponder system, i.e., systems where there is no sharing. 952 In addition, this state information may be encoded in a much more 953 compact form depending on the overall connectivity structure [WSON- 954 Encode]. 956 After that, a set of wavelength converter output wavelength 957 constraints is used. These constraints indicate what wavelengths a 958 particular wavelength converter can generate or are restricted to 959 generating due to internal switch structure. 961 Finally, a wavelength pool output matrix WE(p,k) = {0,1} indicating 962 whether the output from wavelength converter p can reach output port 963 k. Examples of this method being used to model wavelength converter 964 pools for several switch architectures are given in reference [WSON- 965 Encode]. 967 I1 +-------------+ +-------------+ E1 968 ----->| | +--------+ | |-----> 969 I2 | +------+ WC #1 +-------+ | E2 970 ----->| | +--------+ | |-----> 971 | Wavelength | | Wavelength | 972 | Converter | +--------+ | Converter | 973 | Pool +------+ WC #2 +-------+ Pool | 974 | | +--------+ | | 975 | Input | | Output | 976 | Connection | . | Connection | 977 | Matrix | . | Matrix | 978 | | . | | 979 | | | | 980 IN | | +--------+ | | EM 981 ----->| +------+ WC #P +-------+ |-----> 982 | | +--------+ | | 983 +-------------+ ^ ^ +-------------+ 984 | | 985 | | 986 | | 987 | | 989 Input wavelength Output wavelength 990 constraints for constraints for 991 each converter each converter 993 Figure 3. Schematic diagram of wavelength converter pool model. 995 Figure 4 below shows a simple optical switch in a four wavelength 996 DWDM system sharing wavelength converters in a general shared "per 997 node" fashion. 999 +-----------+ ___________ +------+ 1000 | |--------------------------->| | 1001 | |--------------------------->| C | 1002 /| | |--------------------------->| o | E1 1003 I1 /D+--->| |--------------------------->| m | 1004 + e+--->| | | b |====> 1005 ====>| M| | Optical | +-----------+ +----+ | i | 1006 + u+--->| Switch | | WC Pool | |O S|-->| n | 1007 \x+--->| | | +-----+ | |p w|-->| e | 1008 \| | +----+->|WC #1|--+->|t i| | r | 1009 | | | +-----+ | |i t| +------+ 1010 | | | | |c c| +------+ 1011 /| | | | +-----+ | |a h|-->| | 1012 I2 /D+--->| +----+->|WC #2|--+->|l |-->| C | E2 1013 + e+--->| | | +-----+ | | | | o | 1014 ====>| M| | | +-----------+ +----+ | m |====> 1015 + u+--->| | | b | 1016 \x+--->| |--------------------------->| i | 1017 \| | |--------------------------->| n | 1018 | |--------------------------->| e | 1019 |___________|--------------------------->| r | 1020 +-----------+ +------+ 1022 Figure 4. An optical switch featuring a shared per node wavelength 1023 converter pool architecture. 1025 In this case the input and output pool matrices are simply: 1027 +-----+ +-----+ 1028 | 1 1 | | 1 1 | 1029 WI =| |, WE =| | 1030 | 1 1 | | 1 1 | 1031 +-----+ +-----+ 1033 Figure 5 shows a different wavelength pool architecture known as 1034 "shared per fiber". In this case the input and output pool matrices 1035 are simply: 1037 +-----+ +-----+ 1038 | 1 1 | | 1 0 | 1039 WI =| |, WE =| | 1040 | 1 1 | | 0 1 | 1041 +-----+ +-----+ 1042 +-----------+ +------+ 1043 | |--------------------------->| | 1044 | |--------------------------->| C | 1045 /| | |--------------------------->| o | E1 1046 I1 /D+--->| |--------------------------->| m | 1047 + e+--->| | | b |====> 1048 ====>| M| | Optical | +-----------+ | i | 1049 + u+--->| Switch | | WC Pool | | n | 1050 \x+--->| | | +-----+ | | e | 1051 \| | +----+->|WC #1|--+---------->| r | 1052 | | | +-----+ | +------+ 1053 | | | | +------+ 1054 /| | | | +-----+ | | | 1055 I2 /D+--->| +----+->|WC #2|--+---------->| C | E2 1056 + e+--->| | | +-----+ | | o | 1057 ====>| M| | | +-----------+ | m |====> 1058 + u+--->| | | b | 1059 \x+--->| |--------------------------->| i | 1060 \| | |--------------------------->| n | 1061 | |--------------------------->| e | 1062 |___________|--------------------------->| r | 1063 +-----------+ +------+ 1064 Figure 5. An optical switch featuring a shared per fiber wavelength 1065 converter pool architecture. 1067 3.7. Characterizing Electro-Optical Network Elements 1069 In this section electro-optical WSON network elements are 1070 characterized by the three key functional components: input 1071 constraints, output constraints and processing capabilities. 1073 WSON Network Element 1074 +-----------------------+ 1075 WSON Signal | | | | WSON Signal 1076 | | | | 1077 ---------------> | | | | -----------------> 1078 | | | | 1079 +-----------------------+ 1080 <-----> <-------> <-----> 1082 Input Processing Output 1084 Figure 6. WSON Network Element 1086 3.7.1. Input Constraints 1088 Section 3. (Wavelength Switched Optical Networks) discussed the basic 1089 properties regenerators, OEO switches and wavelength converters. From 1090 these the following possible types of input constraints and 1091 properties are derived: 1093 1. Acceptable Modulation formats. 1095 2. Client Signal (G-PID) restrictions. 1097 3. Bit Rate restrictions. 1099 4. FEC coding restrictions. 1101 5. Configurability: (a) none, (b) self-configuring, (c) required. 1103 These constraints are represented via simple lists. Note that the 1104 device may need to be "provisioned" via signaling or some other means 1105 to accept signals with some attributes versus others. In other cases 1106 the devices maybe relatively transparent to some attributes, e.g., 1107 such as a 2R regenerator to bit rate. Finally, some devices may be 1108 able to auto-detect some attributes and configure themselves, e.g., a 1109 3R regenerator with bit rate detection mechanisms and flexible phase 1110 locking circuitry. To account for these different cases item 5 has 1111 been added, which describes the devices configurability. 1113 Note that such input constraints also apply to the termination of the 1114 WSON signal. 1116 3.7.2. Output Constraints 1118 None of the network elements considered here modifies either the bit 1119 rate or the basic type of the client signal. However, they may modify 1120 the modulation format or the FEC code. Typically the following types 1121 of output constraints are seen: 1123 1. Output modulation is the same as input modulation (default). 1125 2. A limited set of output modulations is available. 1127 3. Output FEC is the same as input FEC code (default). 1129 4. A limited set of output FEC codes is available. 1131 Note that in cases (2) and (4) above, where there is more than one 1132 choice in the output modulation or FEC code then the network element 1133 will need to be configured on a per LSP basis as to which choice to 1134 use. 1136 3.7.3. Processing Capabilities 1138 A general WSON network element (NE) can perform a number of signal 1139 processing functions including: 1141 (A) Regeneration (possibly different types). 1143 (B) Fault and Performance Monitoring. 1145 (C) Wavelength Conversion. 1147 (D) Switching. 1149 An NE may or may not have the ability to perform regeneration (of the 1150 one of the types previously discussed). In addition some nodes may 1151 have limited regeneration capability, i.e., a shared pool, which may 1152 be applied to selected signals traversing the NE. Hence to describe 1153 the regeneration capability of a link or node it is necessary to have 1154 at a minimum: 1156 1. Regeneration capability: (a)fixed, (b) selective, (c) none. 1158 2. Regeneration type: 1R, 2R, 3R. 1160 3. Regeneration pool properties for the case of selective 1161 regeneration (input and output restrictions, availability). 1163 Note that the properties of shared regenerator pools would be 1164 essentially the same at that of wavelength converter pools modeled in 1165 section 3.6.1. (Wavelength Pool Convertor Modeling). 1167 Item (B), fault and performance monitoring, is typically outside the 1168 scope of the control plane. However, when the operations are to be 1169 performed on an LSP basis or on part of an LSP then the control plane 1170 can be of assistance in their configuration. Per LSP, per node, fault 1171 and performance monitoring examples include setting up a "section 1172 trace" (a regenerator overhead identifier) between two nodes, or 1173 intermediate optical performance monitoring at selected nodes along a 1174 path. 1176 4. Routing and Wavelength Assignment and the Control Plane 1178 From a control plane perspective, a wavelength-convertible network 1179 with full wavelength-conversion capability at each node can be 1180 controlled much like a packet MPLS-labeled network or a circuit- 1181 switched Time-division multiplexing (TDM) network with full time slot 1182 interchange capability is controlled. In this case, the path 1183 selection process needs to identify the Traffic Engineered (TE) links 1184 to be used by an optical path, and wavelength assignment can be made 1185 on a hop-by-hop basis. 1187 However, in the case of an optical network without wavelength 1188 converters, an optical path needs to be routed from source to 1189 destination and must use a single wavelength that is available along 1190 that path without "colliding" with a wavelength used by any other 1191 optical path that may share an optical fiber. This is sometimes 1192 referred to as a "wavelength continuity constraint". 1194 In the general case of limited or no wavelength converters the 1195 computation of both the links and wavelengths is known as RWA. 1197 The inputs to basic RWA are the requested optical path's source and 1198 destination, the network topology, the locations and capabilities of 1199 any wavelength converters, and the wavelengths available on each 1200 optical link. The output from an algorithm providing RWA is an 1201 explicit route through ROADMs, a wavelength for optical transmitter, 1202 and a set of locations (generally associated with ROADMs or switches) 1203 where wavelength conversion is to occur and the new wavelength to be 1204 used on each component link after that point in the route. 1206 It is to be noted that the choice of specific RWA algorithm is out of 1207 the scope for this document. However there are a number of different 1208 approaches to dealing with RWA algorithm that can affect the division 1209 of effort between path computation/routing and signaling. 1211 4.1. Architectural Approaches to RWA 1213 Two general computational approaches are taken to performing RWA. 1214 Some algorithms utilize a two-step procedure of path selection 1215 followed by wavelength assignment, and others perform RWA in a 1216 combined fashion. 1218 In the following, three different ways of performing RWA in 1219 conjunction with the control plane are considered. The choice of one 1220 of these architectural approaches over another generally impacts the 1221 demands placed on the various control plane protocols. The approaches 1222 are provided for reference purposes only, and other approaches are 1223 possible. 1225 4.1.1. Combined RWA (R&WA) 1227 In this case, a unique entity is in charge of performing routing and 1228 wavelength assignment. This approach relies on a sufficient knowledge 1229 of network topology, of available network resources and of network 1230 nodes capabilities. This solution is compatible with most known RWA 1231 algorithms, and in particular those concerned with network 1232 optimization. On the other hand, this solution requires up-to-date 1233 and detailed network information. 1235 Such a computational entity could reside in two different places: 1237 o In a PCE which maintains a complete and updated view of network 1238 state and provides path computation services to nodes (PCCs). 1240 o In an ingress node, in which case all nodes have the R&WA 1241 functionality and network state is obtained by a periodic flooding 1242 of information provided by the other nodes. 1244 4.1.2. Separated R and WA (R+WA) 1246 In this case, one entity performs routing, while a second performs 1247 wavelength assignment. The first entity furnishes one or more paths 1248 to the second entity which will perform wavelength assignment and 1249 final path selection. 1251 As the entities computing the path and the wavelength assignment are 1252 separated, this constrains the class of RWA algorithms that may be 1253 implemented. Although it may seem that algorithms optimizing a joint 1254 usage of the physical and wavelength paths are excluded from this 1255 solution, many practical optimization algorithms only consider a 1256 limited set of possible paths, e.g., as computed via a k-shortest 1257 path algorithm. Hence, while there is no guarantee that the selected 1258 final route and wavelength offers the optimal solution, by allowing 1259 multiple routes to pass to the wavelength selection process 1260 reasonable optimization can be performed. 1262 The entity performing the routing assignment needs the topology 1263 information of the network, whereas the entity performing the 1264 wavelength assignment needs information on the network's available 1265 resources and specific network node capabilities. 1267 4.1.3. Routing and Distributed WA (R+DWA) 1269 In this case, one entity performs routing, while wavelength 1270 assignment is performed on a hop-by-hop, distributed, manner along 1271 the previously computed path. This mechanism relies on updating of a 1272 list of potential wavelengths used to ensure conformance with the 1273 wavelength continuity constraint. 1275 As currently specified, the GMPLS protocol suite signaling protocol 1276 can accommodate such an approach. GMPLS, per [RFC3471], includes 1277 support for the communication of the set of labels (wavelengths) that 1278 may be used between nodes via a Label Set. When conversion is not 1279 performed at an intermediate node, a hop generates the Label Set it 1280 sends to the next hop based on the intersection of the Label Set 1281 received from the previous hop and the wavelengths available on the 1282 node's switch and ongoing interface. The generation of the outgoing 1283 Label Set is up to the node local policy (even if one expects a 1284 consistent policy configuration throughout a given transparency 1285 domain). When wavelength conversion is performed at an intermediate 1286 node, a new Label Set is generated. The egress node selects one label 1287 in the Label Set which it received; additionally the node can apply 1288 local policy during label selection. GMPLS also provides support for 1289 the signaling of bidirectional optical paths. 1291 Depending on these policies a wavelength assignment may not be found 1292 or one consuming too many conversion resources relative to what a 1293 dedicated wavelength assignment policy would have achieved. Hence, 1294 this approach may generate higher blocking probabilities in a heavily 1295 loaded network. 1297 This solution may be facilitated via signaling extensions which ease 1298 its functioning and possibly enhance its performance relatively to 1299 blocking. Note that this approach requires less information 1300 dissemination than the other techniques described. 1302 The first entity may be a PCE or the ingress node of the LSP. 1304 4.2. Conveying information needed by RWA 1306 The previous sections have characterized WSONs and optical path 1307 requests. In particular, high level models of the information used by 1308 RWA process were presented. This information can be viewed as either 1309 relatively static, i.e., changing with hardware changes (including 1310 possibly failures), or relatively dynamic, i.e., those that can 1311 change with optical path provisioning. The time requirement in which 1312 an entity involved in RWA process needs to be notified of such 1313 changes is fairly situational. For example, for network restoration 1314 purposes, learning of a hardware failure or of new hardware coming 1315 online to provide restoration capability can be critical. 1317 Currently there are various methods for communicating RWA relevant 1318 information, these include, but are not limited to: 1320 o Existing control plane protocols, i.e., GMPLS routing and 1321 signaling. Note that routing protocols can be used to convey both 1322 static and dynamic information. 1324 o Management protocols such as NetConf, SNMPv3, CLI, and CORBA. 1326 o Directory services and accompanying protocols. These are typically 1327 used for the dissemination of relatively static information. 1328 Directory services are not suited to manage information in dynamic 1329 and fluid environments. 1331 o Other techniques for dynamic information, e.g., sending 1332 information directly from NEs to PCE to avoid flooding. This would 1333 be useful if the number of PCEs is significantly less than number 1334 of WSON NEs. Or other ways to limit flooding to "interested" NEs. 1336 Possible mechanisms to improve scaling of dynamic information 1337 include: 1339 o Tailor message content to WSON. For example the use of wavelength 1340 ranges, or wavelength occupation bit maps. 1342 o Utilize incremental updates if feasible. 1344 5. Modeling Examples and Control Plane Use Cases 1346 This section provides examples of the fixed and switch optical node 1347 and wavelength constraint models of Section 3. and WSON control 1348 plane use cases related to path computation, establishment, 1349 rerouting, and optimization. 1351 5.1. Network Modeling for GMPLS/PCE Control 1353 Consider a network containing three routers (R1 through R3), eight 1354 WSON nodes (N1 through N8) and 18 links (L1 through L18) and one OEO 1355 converter (O1) in a topology shown below. 1357 +--+ +--+ +--+ +--------+ 1358 +-L3-+N2+-L5-+ +--------L12--+N6+--L15--+ N8 + 1359 | +--+ |N4+-L8---+ +--+ ++--+---++ 1360 | | +-L9--+| | | | 1361 +--+ +-+-+ ++-+ || | L17 L18 1362 | ++-L1--+ | | ++++ +----L16---+ | | 1363 |R1| | N1| L7 |R2| | | | 1364 | ++-L2--+ | | ++-+ | ++---++ 1365 +--+ +-+-+ | | | + R3 | 1366 | +--+ ++-+ | | +-----+ 1367 +-L4-+N3+-L6-+N5+-L10-+ ++----+ 1368 +--+ | +--------L11--+ N7 + 1369 +--+ ++---++ 1370 | | 1371 L13 L14 1372 | | 1373 ++-+ | 1374 |O1+-+ 1375 +--+ 1377 Figure 7. Routers and WSON nodes in a GMPLS and PCE Environment. 1379 5.1.1. Describing the WSON nodes 1381 The eight WSON nodes described in Figure 7 have the following 1382 properties: 1384 o Nodes N1, N2, N3 have FOADMs installed and can therefore only 1385 access a static and pre-defined set of wavelengths. 1387 o All other nodes contain ROADMs and can therefore access all 1388 wavelengths. 1390 o Nodes N4, N5, N7 and N8 are multi-degree nodes, allowing any 1391 wavelength to be optically switched between any of the links. Note 1392 however, that this does not automatically apply to wavelengths 1393 that are being added or dropped at the particular node. 1395 o Node N4 is an exception to that: This node can switch any 1396 wavelength from its add/drop ports to any of its output links (L5, 1397 L7 and L12 in this case). 1399 o The links from the routers are only able to carry one wavelength 1400 with the exception of links L8 and L9 which are capable to 1401 add/drop any wavelength. 1403 o Node N7 contains an OEO transponder (O1) connected to the node via 1404 links L13 and L14. That transponder operates in 3R mode and does 1405 not change the wavelength of the signal. Assume that it can 1406 regenerate any of the client signals, however only for a specific 1407 wavelength. 1409 Given the above restrictions, the node information for the eight 1410 nodes can be expressed as follows: (where ID == identifier, SCM == 1411 switched connectivity matrix, and FCM == fixed connectivity matrix). 1413 +ID+SCM +FCM + 1414 | | |L1 |L2 |L3 |L4 | | |L1 |L2 |L3 |L4 | | 1415 | |L1 |0 |0 |0 |0 | |L1 |0 |0 |1 |0 | | 1416 |N1|L2 |0 |0 |0 |0 | |L2 |0 |0 |0 |1 | | 1417 | |L3 |0 |0 |0 |0 | |L3 |1 |0 |0 |1 | | 1418 | |L4 |0 |0 |0 |0 | |L4 |0 |1 |1 |0 | | 1419 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1420 | | |L3 |L5 | | | | |L3 |L5 | | | | 1421 |N2|L3 |0 |0 | | | |L3 |0 |1 | | | | 1422 | |L5 |0 |0 | | | |L5 |1 |0 | | | | 1423 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1424 | | |L4 |L6 | | | | |L4 |L6 | | | | 1425 |N3|L4 |0 |0 | | | |L4 |0 |1 | | | | 1426 | |L6 |0 |0 | | | |L6 |1 |0 | | | | 1427 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1428 | | |L5 |L7 |L8 |L9 |L12| |L5 |L7 |L8 |L9 |L12| 1429 | |L5 |0 |1 |1 |1 |1 |L5 |0 |0 |0 |0 |0 | 1430 |N4|L7 |1 |0 |1 |1 |1 |L7 |0 |0 |0 |0 |0 | 1431 | |L8 |1 |1 |0 |1 |1 |L8 |0 |0 |0 |0 |0 | 1432 | |L9 |1 |1 |1 |0 |1 |L9 |0 |0 |0 |0 |0 | 1433 | |L12|1 |1 |1 |1 |0 |L12|0 |0 |0 |0 |0 | 1434 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1435 | | |L6 |L7 |L10|L11| | |L6 |L7 |L10|L11| | 1436 | |L6 |0 |1 |0 |1 | |L6 |0 |0 |1 |0 | | 1437 |N5|L7 |1 |0 |0 |1 | |L7 |0 |0 |0 |0 | | 1438 | |L10|0 |0 |0 |0 | |L10|1 |0 |0 |0 | | 1439 | |L11|1 |1 |0 |0 | |L11|0 |0 |0 |0 | | 1440 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1441 | | |L12|L15| | | | |L12|L15| | | | 1442 |N6|L12|0 |1 | | | |L12|0 |0 | | | | 1443 | |L15|1 |0 | | | |L15|0 |0 | | | | 1444 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1445 | | |L11|L13|L14|L16| | |L11|L13|L14|L16| | 1446 | |L11|0 |1 |0 |1 | |L11|0 |0 |0 |0 | | 1447 |N7|L13|1 |0 |0 |0 | |L13|0 |0 |1 |0 | | 1448 | |L14|0 |0 |0 |1 | |L14|0 |1 |0 |0 | | 1449 | |L16|1 |0 |1 |0 | |L16|0 |0 |1 |0 | | 1450 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1451 | | |L15|L16|L17|L18| | |L15|L16|L17|L18| | 1452 | |L15|0 |1 |0 |0 | |L15|0 |0 |0 |1 | | 1453 |N8|L16|1 |0 |0 |0 | |L16|0 |0 |1 |0 | | 1454 | |L17|0 |0 |0 |0 | |L17|0 |1 |0 |0 | | 1455 | |L18|0 |0 |0 |0 | |L18|1 |0 |1 |0 | | 1456 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1458 5.1.2. Describing the links 1460 For the following discussion some simplifying assumptions are made: 1462 o It is assumed that the WSON node support a total of four 1463 wavelengths designated WL1 through WL4. 1465 o It is assumed that the impairment feasibility of a path or path 1466 segment is independent from the wavelength chosen. 1468 For the discussion of RWA operation to build LSPs between two 1469 routers, the wavelength constraints on the links between the routers 1470 and the WSON nodes as well as the connectivity matrix of these links 1471 needs to be specified: 1473 +Link+WLs supported +Possible output links+ 1474 | L1 | WL1 | L3 | 1475 +----+-----------------+---------------------+ 1476 | L2 | WL2 | L4 | 1477 +----+-----------------+---------------------+ 1478 | L8 | WL1 WL2 WL3 WL4 | L5 L7 L12 | 1479 +----+-----------------+---------------------+ 1480 | L9 | WL1 WL2 WL3 WL4 | L5 L7 L12 | 1481 +----+-----------------+---------------------+ 1482 | L10| WL2 | L6 | 1483 +----+-----------------+---------------------+ 1484 | L13| WL1 WL2 WL3 WL4 | L11 L14 | 1485 +----+-----------------+---------------------+ 1486 | L14| WL1 WL2 WL3 WL4 | L13 L16 | 1487 +----+-----------------+---------------------+ 1488 | L17| WL2 | L16 | 1489 +----+-----------------+---------------------+ 1490 | L18| WL1 | L15 | 1491 +----+-----------------+---------------------+ 1493 Note that the possible output links for the links connecting to the 1494 routers is inferred from the switched connectivity matrix and the 1495 fixed connectivity matrix of the Nodes N1 through N8 and is show here 1496 for convenience, i.e., this information does not need to be repeated. 1498 5.2. RWA Path Computation and Establishment 1500 The calculation of optical impairment feasible routes is outside the 1501 scope of this document. In general impairment feasible routes serve 1502 as an input to RWA algorithm. 1504 For the example use case shown here, assume the following feasible 1505 routes: 1507 +Endpoint 1+Endpoint 2+Feasible Route + 1508 | R1 | R2 | L1 L3 L5 L8 | 1509 | R1 | R2 | L1 L3 L5 L9 | 1510 | R1 | R2 | L2 L4 L6 L7 L8 | 1511 | R1 | R2 | L2 L4 L6 L7 L9 | 1512 | R1 | R2 | L2 L4 L6 L10 | 1513 | R1 | R3 | L1 L3 L5 L12 L15 L18 | 1514 | R1 | N7 | L2 L4 L6 L11 | 1515 | N7 | R3 | L16 L17 | 1516 | N7 | R2 | L16 L15 L12 L9 | 1517 | R2 | R3 | L8 L12 L15 L18 | 1518 | R2 | R3 | L8 L7 L11 L16 L17 | 1519 | R2 | R3 | L9 L12 L15 L18 | 1520 | R2 | R3 | L9 L7 L11 L16 L17 | 1522 Given a request to establish a LSP between R1 and R2 RWA algorithm 1523 finds the following possible solutions: 1525 +WL + Path + 1526 | WL1| L1 L3 L5 L8 | 1527 | WL1| L1 L3 L5 L9 | 1528 | WL2| L2 L4 L6 L7 L8| 1529 | WL2| L2 L4 L6 L7 L9| 1530 | WL2| L2 L4 L6 L10 | 1532 Assume now that RWA algorithm yields WL1 and the Path L1 L3 L5 L8 for 1533 the requested LSP. 1535 Next, another LSP is signaled from R1 to R2. Given the established 1536 LSP using WL1, the following table shows the available paths: 1538 +WL + Path + 1539 | WL2| L2 L4 L6 L7 L9| 1540 | WL2| L2 L4 L6 L10 | 1542 Assume now that RWA algorithm yields WL2 and the path L2 L4 L6 L7 L9 1543 for the establishment of the new LSP. 1545 A LSP request -this time from R2 to R3 - can not be fulfilled since 1546 the only four possible paths (starting at L8 and L9) are already in 1547 use. 1549 5.3. Resource Optimization 1551 The preceding example gives rise to another use case: the 1552 optimization of network resources. Optimization can be achieved on a 1553 number of layers (e.g. through electrical or optical multiplexing of 1554 client signals) or by re-optimizing the solutions found by a RWA 1555 algorithm. 1557 Given the above example again, assume that a RWA algorithm should 1558 identify a path between R2 and R3. The only possible path to reach R3 1559 from R2 needs to use L9. L9 however is blocked by one of the LSPs 1560 from R1. 1562 5.4. Support for Rerouting 1564 It is also envisioned that the extensions to GMPLS and PCE support 1565 rerouting of wavelengths in case of failures. 1567 Assume for this discussion that the only two LSPs in use in the 1568 system are: 1570 LSP1: WL1 L1 L3 L5 L8 1572 LSP2: WL2 L2 L4 L6 L7 L9 1574 Assume furthermore that the link L5 fails. An RWA algorithm can now 1575 compute the following alternate path and establish that path: 1577 R1 -> N7 -> R2 1579 Level 3 regeneration will take place at N7, so that the complete path 1580 looks like this: 1582 R1 -> L2 L4 L6 L11 L13 -> O1 -> L14 L16 L15 L12 L9 -> R2 1584 5.5. Electro-Optical Networking Scenarios 1586 In the following various networking scenarios are considered 1587 involving regenerators, OEO switches and wavelength converters. These 1588 scenarios can be grouped roughly by type and number of extensions to 1589 the GMPLS control plane that would be required. 1591 5.5.1. Fixed Regeneration Points 1593 In the simplest networking scenario involving regenerators, 1594 regeneration is associated with a WDM link or an entire node and is 1595 not optional, i.e., all signals traversing the link or node will be 1596 regenerated. This includes OEO switches since they provide 1597 regeneration on every port. 1599 There may be input constraints and output constraints on the 1600 regenerators. Hence the path selection process will need to know from 1601 routing or other means the regenerator constraints so that it can 1602 choose a compatible path. For impairment aware routing and wavelength 1603 assignment (IA-RWA) the path selection process will also need to know 1604 which links/nodes provide regeneration. Even for "regular" RWA, this 1605 regeneration information is useful since wavelength converters 1606 typically perform regeneration and the wavelength continuity 1607 constraint can be relaxed at such a point. 1609 Signaling does not need to be enhanced to include this scenario since 1610 there are no reconfigurable regenerator options on input, output or 1611 with respect to processing. 1613 5.5.2. Shared Regeneration Pools 1615 In this scenario there are nodes with shared regenerator pools within 1616 the network in addition to fixed regenerators of the previous 1617 scenario. These regenerators are shared within a node and their 1618 application to a signal is optional. There are no reconfigurable 1619 options on either input or output. The only processing option is to 1620 "regenerate" a particular signal or not. 1622 Regenerator information in this case is used in path computation to 1623 select a path that ensures signal compatibility and IA-RWA criteria. 1625 To setup an LSP that utilizes a regenerator from a node with a shared 1626 regenerator pool it is necessary to indicate that regeneration is to 1627 take place at that particular node along the signal path. Such a 1628 capability currently does not exist in GMPLS signaling. 1630 5.5.3. Reconfigurable Regenerators 1632 This scenario is concerned with regenerators that require 1633 configuration prior to use on an optical signal. As discussed 1634 previously, this could be due to a regenerator that must be 1635 configured to accept signals with different characteristics, for 1636 regenerators with a selection of output attributes, or for 1637 regenerators with additional optional processing capabilities. 1639 As in the previous scenarios it is necessary to have information 1640 concerning regenerator properties for selection of compatible paths 1641 and for IA-RWA computations. In addition during LSP setup it is 1642 necessary to be able configure regenerator options at a particular 1643 node along the path. Such a capability currently does not exist in 1644 GMPLS signaling. 1646 5.5.4. Relation to Translucent Networks 1648 Networks that contain both transparent network elements such as 1649 reconfigurable optical add drop multiplexers (ROADMs) and electro- 1650 optical network elements such regenerators or OEO switches are 1651 frequently referred to as translucent optical networks. 1653 Three main types of translucent optical networks have been discussed: 1655 1. Transparent "islands" surrounded by regenerators. This is 1656 frequently seen when transitioning from a metro optical sub- 1657 network to a long haul optical sub-network. 1659 2. Mostly transparent networks with a limited number of OEO 1660 ("opaque") nodes strategically placed. This takes advantage of the 1661 inherent regeneration capabilities of OEO switches. In the 1662 planning of such networks one has to determine the optimal 1663 placement of the OEO switches. 1665 3. Mostly transparent networks with a limited number of optical 1666 switching nodes with "shared regenerator pools" that can be 1667 optionally applied to signals passing through these switches. 1668 These switches are sometimes called translucent nodes. 1670 All three types of translucent networks fit within the networking 1671 scenarios of Section 5.5.1. and Section 5.5.2. above. And hence, 1672 can be accommodated by the GMPLS extensions envisioned in this 1673 document. 1675 6. GMPLS and PCE Implications 1677 The presence and amount of wavelength conversion available at a 1678 wavelength switching interface has an impact on the information that 1679 needs to be transferred by the control plane (GMPLS) and the PCE 1680 architecture. Current GMPLS and PCE standards can address the full 1681 wavelength conversion case so the following will only address the 1682 limited and no wavelength conversion cases. 1684 6.1. Implications for GMPLS signaling 1686 Basic support for WSON signaling already exists in GMPLS with the 1687 lambda (value 9) LSP encoding type [RFC3471], or for G.709 compatible 1688 optical channels, the LSP encoding type (value = 13) "G.709 Optical 1689 Channel" from [RFC4328]. However a number of practical issues arise 1690 in the identification of wavelengths and signals, and distributed 1691 wavelength assignment processes which are discussed below. 1693 6.1.1. Identifying Wavelengths and Signals 1695 As previously stated a global fixed mapping between wavelengths and 1696 labels simplifies the characterization of WDM links and WSON devices. 1698 Furthermore such a mapping as described in [Otani] provides such a 1699 fixed mapping for communication between PCE and WSON PCCs. 1701 6.1.2. WSON Signals and Network Element Processing 1703 As discussed in Section 3.3.2. a WSON signal at any point along its 1704 path can be characterized by the (a) modulation format, (b) FEC, (c) 1705 wavelength, (d)bit rate, and (d)G-PID. 1707 Currently G-PID, wavelength (via labels), and bit rate (via bandwidth 1708 encoding) are supported in [RFC3471] and [RFC3473]. These RFCs can 1709 accommodate the wavelength changing at any node along the LSP and can 1710 thus provide explicit control of wavelength converters. 1712 In the fixed regeneration point scenario described in Section 5.5.1. 1713 (Fixed Regeneration Points) no enhancements are required to signaling 1714 since there are no additional configuration options for the LSP at a 1715 node. 1717 In the case of shared regeneration pools described in Section 5.5.2. 1718 (Shared Regeneration Pools) it is necessary to indicate to a node 1719 that it should perform regeneration on a particular signal. Viewed 1720 another way, for an LSP, it is desirable to specify that certain 1721 nodes along the path perform regeneration. Such a capability 1722 currently does not exist in GMPLS signaling. 1724 The case of configurable regenerators described in Section 5.5.3. 1725 (Reconfigurable Regenerators) is very similar to the previous except 1726 that now there are potentially many more items that can be configured 1727 on a per node basis for an LSP. 1729 Note that the techniques of [RFC5420] which allow for additional LSP 1730 attributes and their recording in a Record Route Object (RRO) object 1731 could be extended to allow for additional LSP attributes in an ERO. 1732 This could allow one to indicate where optional 3R regeneration 1733 should take place along a path, any modification of LSP attributes 1734 such as modulation format, or any enhance processing such as 1735 performance monitoring. 1737 6.1.3. Combined RWA/Separate Routing WA support 1739 In either the combined RWA or separate routing WA cases, the node 1740 initiating the signaling will have a route from the source to 1741 destination along with the wavelengths (generalized labels) to be 1742 used along portions of the path. Current GMPLS signaling supports an 1743 Explicit Route Object (ERO) and within an ERO an ERO Label subobject 1744 can be used to indicate the wavelength to be used at a particular 1745 node. In case the local label map approach is used the label sub- 1746 object entry in the ERO has to be interpreted appropriately. 1748 6.1.4. Distributed Wavelength Assignment: Unidirectional, No 1749 Converters 1751 GMPLS signaling for a unidirectional optical path LSP allows for the 1752 use of a label set object in the Resource Reservation Protocol - 1753 Traffic Engineering (RSVP-TE) path message. The processing of the 1754 label set object to take the intersection of available lambdas along 1755 a path can be performed resulting in the set of available lambda 1756 being known to the destination that can then use a wavelength 1757 selection algorithm to choose a lambda. 1759 6.1.5. Distributed Wavelength Assignment: Unidirectional, Limited 1760 Converters 1762 In the case of wavelength converters, nodes with wavelength 1763 converters would need to make the decision as to whether to perform 1764 conversion. One indicator for this would be that the set of available 1765 wavelengths which is obtained via the intersection of the incoming 1766 label set and the output links available wavelengths is either null 1767 or deemed too small to permit successful completion. 1769 At this point the node would need to remember that it will apply 1770 wavelength conversion and will be responsible for assigning the 1771 wavelength on the previous lambda-contiguous segment when the RSVP-TE 1772 RESV message is processed. The node will pass on an enlarged label 1773 set reflecting only the limitations of the wavelength converter and 1774 the output link. The record route option in RSVP-TE signaling can be 1775 used to show where wavelength conversion has taken place. 1777 6.1.6. Distributed Wavelength Assignment: Bidirectional, No 1778 Converters 1780 There are cases of a bidirectional optical path which requires the 1781 use of the same lambda in both directions. The above procedure can be 1782 used to determine the available bidirectional lambda set if it is 1783 interpreted that the available label set is available in both 1784 directions. In bidirectional LSPs setup, according to [RFC3471] 1785 Section 4.1. (Architectural Approaches to RWA), is indicated by the 1786 presence of an upstream label in the path message. 1788 However, until the intersection of the available label sets is 1789 determined along the path and at the destination node the upstream 1790 label information may not be correct. This case can be supported 1791 using current GMPLS mechanisms, but may not be as efficient as an 1792 optimized bidirectional single-label allocation mechanism. 1794 6.2. Implications for GMPLS Routing 1796 GMPLS routing [RFC4202] currently defines an interface capability 1797 descriptor for "lambda switch capable" (LSC) which can be used to 1798 describe the interfaces on a ROADM or other type of wavelength 1799 selective switch. In addition to the topology information typically 1800 conveyed via an IGP, it would be necessary to convey the following 1801 subsystem properties to minimally characterize a WSON: 1803 1. WDM Link properties (allowed wavelengths). 1805 2. Optical transmitters (wavelength range). 1807 3. ROADM/FOADM Properties (connectivity matrix, port wavelength 1808 restrictions). 1810 4. Wavelength converter properties (per network element, may change if 1811 a common limited shared pool is used). 1813 This information is modeled in detail in [WSON-Info] and a compact 1814 encoding is given in [WSON-Encode]. 1816 6.2.1. Electro-Optical Element Signal Compatibility 1818 In network scenarios where signal compatibility is a concern it is 1819 necessary to add parameters to our existing node and link models to 1820 take into account electro-optical input constraints, output 1821 constraints, and the signal processing capabilities of a NE in path 1822 computations. 1824 Input constraints: 1826 1. Permitted optical tributary signal classes: A list of optical 1827 tributary signal classes that can be processed by this network 1828 element or carried over this link. (configuration type) 1829 2. Acceptable FEC codes. (configuration type) 1830 3. Acceptable Bit Rate Set: a list of specific bit rates or bit rate 1831 ranges that the device can accommodate. Coarse bit rate info is 1832 included with the optical tributary signal class restrictions. 1833 4. Acceptable G-PID list: a list of G-PIDs corresponding to the 1834 "client" digital streams that is compatible with this device. 1836 Note that since the bit rate of the signal does not change over the 1837 LSP. This can be communicated as an LSP parameter and hence this 1838 information would be available for any NE that needs to use it for 1839 configuration. Hence it is not necessary to have "configuration type" 1840 for the NE with respect to bit rate. 1842 Output constraints: 1844 1. Output modulation: (a)same as input, (b) list of available types 1846 2. FEC options: (a) same as input, (b) list of available codes 1848 Processing capabilities: 1850 1. Regeneration: (a) 1R, (b) 2R, (c) 3R, (d)list of selectable 1851 regeneration types 1853 2. Fault and performance monitoring: (a) G-PID particular 1854 capabilities, (b) optical performance monitoring capabilities. 1856 Note that such parameters could be specified on an (a) Network 1857 element wide basis, (b) a per port basis, (c) on a per regenerator 1858 basis. Typically such information has been on a per port basis, see, 1859 the GMPLS interface switching capability descriptor [RFC4202]. 1861 6.2.2. Wavelength-Specific Availability Information 1863 For wavelength assignment it is necessary to know which specific 1864 wavelengths are available and which are occupied if a combined RWA 1865 process or separate WA process is run as discussed in sections 4.1.1. 1866 4.1.2. This is currently not possible with GMPLS routing. 1868 In the routing extensions for GMPLS [RFC4202], requirements for 1869 layer-specific TE attributes are discussed. RWA for optical networks 1870 without wavelength converters imposes an additional requirement for 1871 the lambda (or optical channel) layer: that of knowing which specific 1872 wavelengths are in use. Note that current DWDM systems range from 16 1873 channels to 128 channels with advanced laboratory systems with as 1874 many as 300 channels. Given these channel limitations and if the 1875 approach of a global wavelength to label mapping or furnishing the 1876 local mappings to the PCEs is taken then representing the use of 1877 wavelengths via a simple bit-map is feasible [WSON-Encode]. 1879 6.2.3. WSON Routing Information Summary 1881 The following table summarizes the WSON information that could be 1882 conveyed via GMPLS routing and attempts to classify that information 1883 as to its static or dynamic nature and whether that information would 1884 tend to be associated with either a link or a node. 1886 Information Static/Dynamic Node/Link 1887 ------------------------------------------------------------------ 1888 Connectivity matrix Static Node 1889 Per port wavelength restrictions Static Node(1) 1890 WDM link (fiber) lambda ranges Static Link 1891 WDM link channel spacing Static Link 1892 Optical transmitter range Static Link(2) 1893 Wavelength conversion capabilities Static(3) Node 1894 Maximum bandwidth per wavelength Static Link 1895 Wavelength availability Dynamic(4) Link 1896 Signal compatibility and processing Static/Dynamic Node 1898 Notes: 1900 1. These are the per port wavelength restrictions of an optical 1901 device such as a ROADM and are independent of any optical 1902 constraints imposed by a fiber link. 1904 2. This could also be viewed as a node capability. 1906 3. This could be dynamic in the case of a limited pool of converters 1907 where the number available can change with connection 1908 establishment. Note it may be desirable to include regeneration 1909 capabilities here since OEO converters are also regenerators. 1911 4. Not necessarily needed in the case of distributed wavelength 1912 assignment via signaling. 1914 While the full complement of the information from the previous table 1915 is needed in the Combined RWA and the separate Routing and WA 1916 architectures, in the case of Routing + distributed WA via signaling 1917 only the following information is needed: 1919 Information Static/Dynamic Node/Link 1920 ------------------------------------------------------------------ 1921 Connectivity matrix Static Node 1922 Wavelength conversion capabilities Static(3) Node 1924 Information models and compact encodings for this information is 1925 provided in [WSON-Info], [Gen-Encode] and [WSON-Encode]. 1927 6.3. Optical Path Computation and Implications for PCE 1929 As previously noted RWA can be computationally intensive. Such 1930 computationally intensive path computations and optimizations were 1931 part of the impetus for the PCE architecture [RFC4655]. 1933 The Path Computation Element Protocol (PCEP) defines the procedures 1934 necessary to support both sequential [RFC5440] and global concurrent 1935 path computations (PCE-GCO) [RFC5557], PCE is well positioned to 1936 support WSON-enabled RWA computation with some protocol enhancement. 1938 Implications for PCE generally fall into two main categories: (a) 1939 optical path constraints and characteristics, (b) computation 1940 architectures. 1942 6.3.1. Optical path Constraints and Characteristics 1944 For the varying degrees of optimization that may be encountered in a 1945 network the following models of bulk and sequential optical path 1946 requests are encountered: 1948 o Batch optimization, multiple optical paths requested at one time 1949 (PCE-GCO). 1951 o Optical path(s) and backup optical path(s) requested at one time 1952 (PCEP). 1954 o Single optical path requested at a time (PCEP). 1956 PCEP and PCE-GCO can be readily enhanced to support all of the 1957 potential models of RWA computation. 1959 Optical path constraints include: 1961 o Bidirectional Assignment of wavelengths. 1963 o Possible simultaneous assignment of wavelength to primary and 1964 backup paths. 1966 o Tuning range constraint on optical transmitter. 1968 6.3.2. Electro-Optical Element Signal Compatibility 1970 When requesting a path computation to PCE, the PCC should be able to 1971 indicate the following: 1973 o The G-PID type of an LSP. 1975 o The signal attributes at the transmitter (at the source): (i) 1976 modulation type; (ii) FEC type. 1978 o The signal attributes at the receiver (at the sink): (i) 1979 modulation type; (ii) FEC type. 1981 The PCE should be able to respond to the PCC with the following: 1983 o The conformity of the requested optical characteristics associated 1984 with the resulting LSP with the source, sink and NE along the LSP. 1986 o Additional LSP attributes modified along the path (e.g., 1987 modulation format change, etc.). 1989 6.3.3. Discovery of RWA Capable PCEs 1991 The algorithms and network information needed for RWA are somewhat 1992 specialized and computationally intensive hence not all PCEs within a 1993 domain would necessarily need or want this capability. Hence, it 1994 would be useful via the mechanisms being established for PCE 1995 discovery [RFC5088] to indicate that a PCE has the ability to deal 1996 with RWA. Reference [RFC5088] indicates that a sub-TLV could be 1997 allocated for this purpose. 1999 Recent progress on objective functions in PCE [RFC5541] would allow 2000 the operators to flexibly request differing objective functions per 2001 their need and applications. For instance, this would allow the 2002 operator to choose an objective function that minimizes the total 2003 network cost associated with setting up a set of paths concurrently. 2004 This would also allow operators to choose an objective function that 2005 results in a most evenly distributed link utilization. 2007 This implies that PCEP would easily accommodate wavelength selection 2008 algorithm in its objective function to be able to optimize the path 2009 computation from the perspective of wavelength assignment if chosen 2010 by the operators. 2012 7. Security Considerations 2014 This document has no requirement for a change to the security models 2015 within GMPLS and associated protocols. That is the OSPF-TE, RSVP-TE, 2016 and PCEP security models could be operated unchanged. 2018 However satisfying the requirements for RWA using the existing 2019 protocols may significantly affect the loading of those protocols. 2020 This may make the operation of the network more vulnerable to denial 2021 of service attacks. Therefore additional care maybe required to 2022 ensure that the protocols are secure in the WSON environment. 2024 Furthermore the additional information distributed in order to 2025 address RWA represents a disclosure of network capabilities that an 2026 operator may wish to keep private. Consideration should be given to 2027 securing this information. For a general discussion on MPLS and GMPLS 2028 related security issues, see the MPLS/GMPLS security framework 2029 [RFC5920]. 2031 8. IANA Considerations 2033 This document makes no request for IANA actions. 2035 9. Acknowledgments 2037 The authors would like to thank Adrian Farrel for many helpful 2038 comments that greatly improved the contents of this draft. 2040 This document was prepared using 2-Word-v2.0.template.dot. 2042 10. References 2044 10.1. Normative References 2046 [RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching 2047 (GMPLS) Signaling Functional Description", RFC 3471, 2048 January 2003. 2050 [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label 2051 Switching (GMPLS) Signaling Resource ReserVation Protocol- 2052 Traffic Engineering (RSVP-TE) Extensions", RFC 3473, 2053 January 2003. 2055 [RFC3945] Mannie, E. "Generalized Multi-Protocol Label Switching 2056 (GMPLS) Architecture", RFC 3945, October 2004. 2058 [RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in Support 2059 of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 2060 4202, October 2005. 2062 [RFC4328] Papadimitriou, D., "Generalized Multi-Protocol Label 2063 Switching (GMPLS) Signaling Extensions for G.709 Optical 2064 Transport Networks Control", RFC 4328, January 2006. 2066 [RFC4655] Farrel, A., Vasseur, JP., and Ash, J., "A Path Computation 2067 Element (PCE)-Based Architecture ", RFC 4655, August 2006. 2069 [RFC5088] J.L. Le Roux, J.P. Vasseur, Yuichi Ikejiri, and Raymond 2070 Zhang, "OSPF protocol extensions for Path Computation 2071 Element (PCE) Discovery", January 2008. 2073 [RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux, 2074 M., and D. Brungard, "Requirements for GMPLS-Based Multi- 2075 Region and Multi-Layer Networks (MRN/MLN)", RFC 5212, July 2076 2008. 2078 [RFC5557] Y. Lee, J.L. Le Roux, D. King, and E. Oki, "Path 2079 Computation Element Communication Protocol (PCECP) 2080 Requirements and Protocol Extensions In Support of Global 2081 Concurrent Optimization", RFC 5557, July 2009. 2083 [RFC5420] Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A. 2084 Ayyangarps, "Encoding of Attributes for MPLS LSP 2085 Establishment Using Resource Reservation Protocol Traffic 2086 Engineering (RSVP-TE)", RFC 5420, February 2009. 2088 [RFC5440] J.P. Vasseur and J.L. Le Roux (Editors), "Path Computation 2089 Element (PCE) Communication Protocol (PCEP)", RFC 5440, May 2090 2009. 2092 [RFC5541] J.L. Le Roux, J.P. Vasseur, and Y. Lee, "Encoding of 2093 Objective Functions in Path Computation Element (PCE) 2094 communication and discovery protocols", RFC 5541, July 2095 2009. 2097 10.2. Informative References 2099 [Gen-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "General 2100 Network Element Constraint Encoding for GMPLS Controlled 2101 Networks", draft-ietf-ccamp-general-constraint-encode, work 2102 in progress. 2104 [G.652] ITU-T Recommendation G.652, Characteristics of a single-mode 2105 optical fibre and cable, June 2005. 2107 [G.653] ITU-T Recommendation G.653, Characteristics of a dispersion- 2108 shifted single-mode optical fibre and cable, December 2006. 2110 [G.654] ITU-T Recommendation G.654, Characteristics of a cut-off 2111 shifted single-mode optical fibre and cable, December 2006. 2113 [G.655] ITU-T Recommendation G.655, Characteristics of a non-zero 2114 dispersion-shifted single-mode optical fibre and cable, 2115 March 2006. 2117 [G.656] ITU-T Recommendation G.656, Characteristics of a fibre and 2118 cable with non-zero dispersion for wideband optical 2119 transport, December 2006. 2121 [G.671] ITU-T Recommendation G.671, Transmission characteristics of 2122 optical components and subsystems, January 2005. 2124 [G.694.1] ITU-T Recommendation G.694.1, "Spectral grids for WDM 2125 applications: DWDM frequency grid", June, 2002. 2127 [G.872] ITU-T Recommendation G.872, Architecture of optical 2128 transport networks, November 2001. 2130 [G.959.1] ITU-T Recommendation G.959.1, Optical Transport Network 2131 Physical Layer Interfaces, March 2006. 2133 [G.694.1] ITU-T Recommendation G.694.1, Spectral grids for WDM 2134 applications: DWDM frequency grid, June 2002. 2136 [G.694.2] ITU-T Recommendation G.694.2, Spectral grids for WDM 2137 applications: CWDM wavelength grid, December 2003. 2139 [G.Sup39] ITU-T Series G Supplement 39, Optical system design and 2140 engineering considerations, February 2006. 2142 [G.Sup43] ITU-T Series G Supplement 43, Transport of IEEE 10G base-R 2143 in optical transport networks (OTN), November 2006. 2145 [Imajuku] W. Imajuku, Y. Sone, I. Nishioka, S. Seno, "Routing 2146 Extensions to Support Network Elements with Switching 2147 Constraint", work in progress: draft-imajuku-ccamp-rtg- 2148 switching-constraint. 2150 [Otani] T. Otani, H. Guo, K. Miyazaki, D. Caviglia, "Generalized 2151 Labels of Lambda-Switching Capable Label Switching Routers 2152 (LSR)", work in progress: draft-otani-ccamp-gmpls-g-694- 2153 lambda-labels, work in progress. 2155 [RFC5920] Fang, L., "Security Framework for MPLS and GMPLS 2156 Networks", RFC 5920, July 2010.[Otani]T. Otani, H. Guo, K. 2157 Miyazaki, D. Caviglia, "Generalized Labels of Lambda- 2158 Switching Capable Label Switching Routers (LSR)", work in 2159 progress: draft-otani-ccamp-gmpls-g-694-lambda-labels, work 2160 in progress. 2162 [WSON-Compat] G. Bernstein, Y. Lee, B. Mack-Crane, "WSON Signal 2163 Characteristics and Network Element Compatibility 2164 Constraints for GMPLS", draft-bernstein-ccamp-wson- 2165 compatibility, work in progress. 2167 [WSON-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "Routing 2168 and Wavelength Assignment Information Encoding for 2169 Wavelength Switched Optical Networks", draft-ietf-ccamp- 2170 wson-encode, work in progress. 2172 [WSON-Imp] Y. Lee, G. Bernstein, D. Li, G. Martinelli, "A Framework 2173 for the Control of Wavelength Switched Optical Networks 2174 (WSON) with Impairments", draft-ietf-ccamp-wson- 2175 impairments, work in progress. 2177 [WSON-Info] Y. Lee, G. Bernstein, D. Li, W. Imajuku, "Routing and 2178 Wavelength Assignment Information for Wavelength Switched 2179 Optical Networks", draft-bernstein-ccamp-wson-info, work in 2180 progress 2182 11. Contributors 2184 Snigdho Bardalai 2185 Fujitsu 2187 Email: Snigdho.Bardalai@us.fujitsu.com 2189 Diego Caviglia 2190 Ericsson 2191 Via A. Negrone 1/A 16153 2192 Genoa Italy 2194 Phone: +39 010 600 3736 2195 Email: diego.caviglia@(marconi.com, ericsson.com) 2197 Daniel King 2198 Old Dog Consulting 2199 UK 2201 Email: daniel@olddog.co.uk 2203 Itaru Nishioka 2204 NEC Corp. 2205 1753 Simonumabe, Nakahara-ku 2206 Kawasaki, Kanagawa 211-8666 2207 Japan 2209 Phone: +81 44 396 3287 2210 Email: i-nishioka@cb.jp.nec.com 2212 Lyndon Ong 2213 Ciena 2215 Email: Lyong@Ciena.com 2217 Pierre Peloso 2218 Alcatel-Lucent 2219 Route de Villejust, 91620 Nozay 2220 France 2222 Email: pierre.peloso@alcatel-lucent.fr 2224 Jonathan Sadler 2225 Tellabs 2226 Email: Jonathan.Sadler@tellabs.com 2228 Dirk Schroetter 2229 Cisco 2230 Email: dschroet@cisco.com 2232 Jonas Martensson 2233 Acreo 2234 Electrum 236 2235 16440 Kista, Sweden 2237 Email:Jonas.Martensson@acreo.se 2239 Author's Addresses 2241 Greg M. Bernstein (ed.) 2242 Grotto Networking 2243 Fremont California, USA 2245 Phone: (510) 573-2237 2246 Email: gregb@grotto-networking.com 2248 Young Lee (ed.) 2249 Huawei Technologies 2250 1700 Alma Drive, Suite 100 2251 Plano, TX 75075 2252 USA 2254 Phone: (972) 509-5599 (x2240) 2255 Email: ylee@huawei.com 2257 Wataru Imajuku 2258 NTT Network Innovation Labs 2259 1-1 Hikari-no-oka, Yokosuka, Kanagawa 2260 Japan 2262 Phone: +81-(46) 859-4315 2263 Email: imajuku.wataru@lab.ntt.co.jp 2265 Intellectual Property Statement 2267 The IETF Trust takes no position regarding the validity or scope of 2268 any Intellectual Property Rights or other rights that might be 2269 claimed to pertain to the implementation or use of the technology 2270 described in any IETF Document or the extent to which any license 2271 under such rights might or might not be available; nor does it 2272 represent that it has made any independent effort to identify any 2273 such rights. 2275 Copies of Intellectual Property disclosures made to the IETF 2276 Secretariat and any assurances of licenses to be made available, or 2277 the result of an attempt made to obtain a general license or 2278 permission for the use of such proprietary rights by implementers or 2279 users of this specification can be obtained from the IETF on-line IPR 2280 repository at http://www.ietf.org/ipr 2282 The IETF invites any interested party to bring to its attention any 2283 copyrights, patents or patent applications, or other proprietary 2284 rights that may cover technology that may be required to implement 2285 any standard or specification contained in an IETF Document. Please 2286 address the information to the IETF at ietf-ipr@ietf.org. 2288 Disclaimer of Validity 2290 All IETF Documents and the information contained therein are provided 2291 on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 2292 REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE 2293 IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL 2294 WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY 2295 WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE 2296 ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS 2297 FOR A PARTICULAR PURPOSE. 2299 Acknowledgment 2301 Funding for the RFC Editor function is currently provided by the 2302 Internet Society. 2304 12. Appendix A Revision History 2306 This appendix to be removed before publication as an RFC. 2308 A.1 Changes from 00 2310 o Added new first level section on modeling examples and control 2311 plane use cases. 2313 o Added new third level section on wavelength converter pool 2314 modeling 2316 o Editorial clean up of English and updated references. 2318 A.2 Changes from 01 2320 Fixed error in wavelength converter pool example. 2322 A.3 Changes from 02 2324 Updated the abstract to emphasize the focus of this draft and 2325 differentiate it from WSON impairment [WSON-Imp] and WSON 2326 compatibility [WSON-Compat] drafts. 2328 Added references to [WSON-Imp] and [WSON-Compat]. 2330 Updated the introduction to explain the relationship between this 2331 document and the [WSON-Imp] and [WSON-Compat] documents. 2333 In section 3.1 removed discussion of optical impairments in fibers. 2335 Merged section 3.2.2 and section 3.2.3. Deferred much of the 2336 discussion of signal types and standards to [WSON-Compat]. 2338 In section 3.4 on Wavelength converters removed paragraphs dealing 2339 with signal compatibility discussion as this is addressed in [WSON- 2340 Compat]. 2342 In section 6.1 removed discussion of signaling extensions to deal 2343 with different WSON signal types. This is deferred to [WSON-Compat]. 2345 In section 6 removed discussion of "Need for Wavelength Specific 2346 Maximum Bandwidth Information". 2348 In section 6 removed discussion of "Relationship to link bundling and 2349 layering". 2351 In section 6 removed discussion of "Computation Architecture 2352 Implications" as this material was redundant with text that occurs 2353 earlier in the document. 2355 In section 6 removed discussion of "Scaling Implications" as this 2356 material was redundant with text that occurs earlier in the document. 2358 A.4 Changes from 03 2360 In Section 3.3.1 added 4-degree ROADM example and its connectivity 2361 matrix. 2363 A.5 Changes from 04 2365 Added and enhanced sections on signal type and network element 2366 compatibility. 2368 Merged section 3.2.1 into section 3.2. 2370 Created new section 3.3 on Optical signals with material from [WSON- 2371 Compat]. 2373 Created new section 3.5 on Electro-Optical systems with material from 2374 [WSON-Compat]. 2376 Created new section 3.7 on Characterizing Electro-Optical Network 2377 Elements with material from [WSON-Compat]. 2379 Created new section 5.5 on Electro-Optical Networking Scenarios with 2380 material from [WSON-Compat]. 2382 Created new section 6.1.2 on WSON Signals and Network Element 2383 Processing with material from [WSON-Compat]. 2385 Created new section 6.3.2. Electro-Optical Related PCEP Extensions 2386 with material from [WSON-Compat]. 2388 A.6 Changes from 05 2390 Removal of Section 1.2; Removal of section on optical path temporal 2391 characteristics; Removal of details on wavelength assignment 2392 algorithms; Removal of redundant summary in section 6.