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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: April 2011 Grotto Networking 5 Wataru Imajuku 6 NTT 8 October 8, 2010 10 Framework for GMPLS and PCE Control of Wavelength Switched Optical 11 Networks (WSON) 12 draft-ietf-ccamp-rwa-wson-framework-07.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 the Routing and 20 Wavelength Assignment (RWA) problem. 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 April 8, 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 87 4. Routing and Wavelength Assignment and the Control Plane.......28 88 4.1. Architectural Approaches to RWA..........................28 89 4.1.1. Combined RWA (R&WA).................................29 90 4.1.2. Separated R and WA (R+WA)...........................29 91 4.1.3. Routing and Distributed WA (R+DWA)..................30 92 4.2. Conveying information needed by RWA......................30 93 5. Modeling Examples and Control Plane Use Cases.................31 94 5.1. Network Modeling for GMPLS/PCE Control...................31 95 5.1.1. Describing the WSON nodes...........................32 96 5.1.2. Describing the links................................34 97 5.2. RWA Path Computation and Establishment...................35 98 5.3. Resource Optimization....................................36 99 5.4. Support for Rerouting....................................37 100 5.5. Electro-Optical Networking Scenarios.....................37 101 5.5.1. Fixed Regeneration Points...........................37 102 5.5.2. Shared Regeneration Pools...........................38 103 5.5.3. Reconfigurable Regenerators.........................38 104 5.5.4. Relation to Translucent Networks....................38 105 6. GMPLS and PCE Implications....................................39 106 6.1. Implications for GMPLS signaling.........................39 107 6.1.1. Identifying Wavelengths and Signals.................39 108 6.1.2. WSON Signals and Network Element Processing.........40 109 6.1.3. Combined RWA/Separate Routing WA support............40 110 6.1.4. Distributed Wavelength Assignment: Unidirectional, No 111 Converters.................................................41 112 6.1.5. Distributed Wavelength Assignment: Unidirectional, 113 Limited Converters.........................................41 114 6.1.6. Distributed Wavelength Assignment: Bidirectional, No 115 Converters.................................................41 116 6.2. Implications for GMPLS Routing...........................42 117 6.2.1. Electro-Optical Element Signal Compatibility........42 118 6.2.2. Wavelength-Specific Availability Information........43 119 6.2.3. WSON Routing Information Summary....................43 120 6.3. Optical Path Computation and Implications for PCE........45 121 6.3.1. Lightpath Constraints and Characteristics...........45 122 6.3.2. Electro-Optical Element Signal Compatibility........46 123 6.3.3. Discovery of RWA Capable PCEs.......................46 124 7. Security Considerations.......................................47 125 8. IANA Considerations...........................................47 126 9. Acknowledgments...............................................47 127 10. References...................................................48 128 10.1. Normative References....................................48 129 10.2. Informative References..................................49 130 11. Contributors.................................................51 131 Author's Addresses...............................................52 132 Intellectual Property Statement..................................52 133 Disclaimer of Validity...........................................53 134 12. Appendix A Revision History..................................53 136 1. Introduction 138 Wavelength Switched Optical Networks (WSONs) are constructed from 139 subsystems that include Wavelength Division Multiplexed (WDM) links, 140 tunable transmitters and receivers, Reconfigurable Optical Add/Drop 141 Multiplexers (ROADM), wavelength converters, and electro-optical 142 network elements. A WSON is a WDM-based optical network in which 143 switching is performed selectively based on the center wavelength of 144 an optical signal. 146 In order to provision an optical connection (a lightpath) through a 147 WSON certain path continuity and resource availability constraints 148 must be met to determine viable and optimal paths through the 149 network. The generic problem of determining such paths is known as 150 the Routing and Wavelength Assignment (RWA) problem. 152 Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes 153 a set of control plane protocols that can be used to operate data 154 networks ranging from packet switch capable networks, through those 155 networks that use time division multiplexing, to WDM networks. The 156 Path Computation Element (PCE) architecture [RFC4655] defines 157 functional components that can be used to compute and suggest 158 appropriate paths in connection-oriented traffic-engineered networks. 160 This document provides a framework for applying GMPLS protocols and 161 the PCE architecture to the control and operation of WSONs. To aid 162 in this process this document also provides an overview of the 163 subsystems and processes that comprise WSONs, and describes the RWA 164 problem so that the information requirements, both static and 165 dynamic, can be identified to explain how the information can be 166 modeled for use by GMPLS and PCE systems. This work will facilitate 167 the development of protocol solution models and protocol extensions 168 within the GMPLS and PCE protocol families. 170 Note that this document focuses on the generic properties of links, 171 switches and path selection constraints that occur in WSONs. 172 Different WSONs such as access, metro, and long haul may apply 173 different techniques for dealing with optical impairments hence this 174 document does not address optical impairments in any depth. See 175 [WSON-Imp] for more information on optical impairments and GMPLS. 177 2. Terminology 179 Add/Drop Multiplexers (ADM): An optical device used in WDM networks 180 composed of one or more line side ports and typically many tributary 181 ports. 183 CWDM: Coarse Wavelength Division Multiplexing. 185 DWDM: Dense Wavelength Division Multiplexing. 187 Degree: The degree of an optical device (e.g., ROADM) is given by a 188 count of its line side ports. 190 Drop and continue: A simple multi-cast feature of some ADM where a 191 selected wavelength can be switched out of both a tributary (drop) 192 port and a line side port. 194 FOADM: Fixed Optical Add/Drop Multiplexer. 196 GMPLS: Generalized Multi-Protocol Label Switching. 198 Line side: In WDM system line side ports and links typically can 199 carry the full multiplex of wavelength signals, as compared to 200 tributary (add or drop ports) that typically carry a few (typically 201 one) wavelength signals. 203 OXC: Optical cross connect. An optical switching element in which a 204 signal on any input port can reach any output port. 206 PCC: Path Computation Client. Any client application requesting a 207 path computation to be performed by the Path Computation Element. 209 PCE: Path Computation Element. An entity (component, application, or 210 network node) that is capable of computing a network path or route 211 based on a network graph and applying computational constraints. 213 PCEP: PCE Communication Protocol. The communication protocol between 214 a Path Computation Client and Path Computation Element. 216 ROADM: Reconfigurable Optical Add/Drop Multiplexer. An wavelength 217 selective switching element featuring input and output line side 218 ports as well as add/drop side ports. 220 RWA: Routing and Wavelength Assignment. 222 Transparent Network: A wavelength switched optical network that does 223 not contain regenerators or wavelength converters. 225 Translucent Network: A wavelength switched optical network that is 226 predominantly transparent but may also contain limited numbers of 227 regenerators and/or wavelength converters. 229 Tributary: A link or port on a WDM system that can carry 230 significantly less than the full multiplex of wavelength signals 231 found on the line side links/ports. Typical tributary ports are the 232 add and drop ports on an ADM and these support only a single 233 wavelength channel. 235 Wavelength Conversion/Converters: The process of converting an 236 information bearing optical signal centered at a given wavelength to 237 one with "equivalent" content centered at a different wavelength. 238 Wavelength conversion can be implemented via an optical-electronic- 239 optical (OEO) process or via a strictly optical process. 241 WDM: Wavelength Division Multiplexing. 243 Wavelength Switched Optical Networks (WSONs): WDM based optical 244 networks in which switching is performed selectively based on the 245 center wavelength of an optical signal. 247 3. Wavelength Switched Optical Networks 249 WSONs range in size from continent spanning long haul networks, to 250 metropolitan networks, to residential access networks. In all these 251 cases, the main concern is those properties that constrain the choice 252 of wavelengths that can be used, i.e., restrict the wavelength label 253 set, impact the path selection process, and limit the topological 254 connectivity. In addition, if electro-optical network elements are 255 used in the WSON, additional compatibility constraints may be imposed 256 by the network elements on various optical signal parameters. The 257 subsequent sections review and model some of the major subsystems of 258 a WSON with an emphasis on those aspects that are of relevance to the 259 control plane. In particular, WDM links, optical transmitters, 260 ROADMs, and wavelength converters are examined. 262 3.1. WDM and CWDM Links 264 WDM and CWDM links run over optical fibers, and optical fibers come 265 in a wide range of types that tend to be optimized for various 266 applications examples include access networks, metro, long haul, and 267 submarine links. International Telecommunication Union - 268 Telecommunication Standardization Sector (ITU-T) standards exist for 269 various types of fibers. Although fiber can be categorized into 270 Single mode fibers (SMF) and Multi-mode fibers (MMF), the latter are 271 typically used for short-reach campus and premise applications. SMF 272 are used for longer-reach applications and therefore are the primary 273 concern of this document. The following SMF fiber types are typically 274 encountered in optical networks: 276 ITU-T Standard | Common Name 277 ------------------------------------------------------------ 278 G.652 [G.652] | Standard SMF | 279 G.653 [G.653] | Dispersion shifted SMF | 280 G.654 [G.654] | Cut-off shifted SMF | 281 G.655 [G.655] | Non-zero dispersion shifted SMF | 282 G.656 [G.656] | Wideband non-zero dispersion shifted SMF | 283 ------------------------------------------------------------ 285 Typically WDM links operate in one or more of the approximately 286 defined optical bands [G.Sup39]: 288 Band Range (nm) Common Name Raw Bandwidth (THz) 289 O-band 1260-1360 Original 17.5 290 E-band 1360-1460 Extended 15.1 291 S-band 1460-1530 Short 9.4 292 C-band 1530-1565 Conventional 4.4 293 L-band 1565-1625 Long 7.1 294 U-band 1625-1675 Ultra-long 5.5 296 Not all of a band may be usable, for example in many fibers that 297 support E-band there is significant attenuation due to a water 298 absorption peak at 1383nm. Hence a discontinuous acceptable 299 wavelength range for a particular link may be needed and is modeled. 300 Also some systems will utilize more than one band. This is 301 particularly true for CWDM systems. 303 Current technology subdivides the bandwidth capacity of fibers into 304 distinct channels based on either wavelength or frequency. There are 305 two standards covering wavelengths and channel spacing. ITU-T 306 Recommendation G.694.1, Spectral grids for WDM applications: DWDM 307 frequency grid [G.694.1] describes a DWDM grid defined in terms of 308 frequency grids of 12.5GHz, 25GHz, 50GHz, 100GHz, and other multiples 309 of 100GHz around a 193.1THz center frequency. At the narrowest 310 channel spacing this provides less than 4800 channels across the O 311 through U bands. ITU-T Recommendation G.694.2, Spectral grids for WDM 312 applications: CWDM wavelength grid [G.694.2] describes a CWDM grid 313 defined in terms of wavelength increments of 20nm running from 1271nm 314 to 1611nm for 18 or so channels. The number of channels is 315 significantly smaller than the 32 bit GMPLS label space defined for 316 GMPLS, see [RFC3471]. A label representation for these ITU-T grids 317 is given in [Otani] and provides a common label format to be used in 318 signaling lightpaths. Further, these ITU-T grid based labels can also 319 be used to describe WDM links, ROADM ports, and wavelength converters 320 for the purposes of path selection. 322 Many WDM links are designed to take advantage of particular fiber 323 characteristics or to try to avoid undesirable properties. For 324 example dispersion shifted SMF [G.653] was originally designed for 325 good long distance performance in single channel systems, however 326 putting WDM over this type of fiber requires significant system 327 engineering and a fairly limited range of wavelengths. Hence the 328 following information is needed as parameters to perform basic, 329 impairment unaware, modeling of a WDM link: 331 o Wavelength range(s): Given a mapping between labels and the ITU-T 332 grids each range could be expressed in terms of a tuple (lambda1, 333 lambda2) or (freq1, freq1) where the lambdas or frequencies can be 334 represented by 32 bit integers. 336 o Channel spacing: Currently there are five channel spacings used in 337 DWDM systems and a single channel spacing defined for CWDM 338 systems. 340 For a particular link this information is relatively static, as 341 changes to these properties generally require hardware upgrades. Such 342 information may be used locally during wavelength assignment via 343 signaling, similar to label restrictions in MPLS or used by a PCE in 344 solving the combined RWA problem. 346 3.2. Optical Transmitters and Receivers 348 WDM optical systems make use of optical transmitters and receivers 349 utilizing different wavelengths (frequencies). Some transmitters are 350 manufactured for a specific wavelength of operation, that is, the 351 manufactured frequency cannot be changed. First introduced to reduce 352 inventory costs, tunable optical transmitters and receivers are 353 deployed in some systems, and allow flexibility in the wavelength 354 used for optical transmission/reception. Such tunable optics aid in 355 path selection. 357 Fundamental modeling parameters from the control plane perspective 358 optical transmitters and receivers are: 360 o Tunable: Do the transmitter and receivers operate at variable or 361 fixed wavelength. 363 o Tuning range: This is the frequency or wavelength range over which 364 the optics can be tuned. With the fixed mapping of labels to 365 lambdas as proposed in [Otani] this can be expressed as a tuple 366 (lambda1, lambda2) or (freq1, freq2) where lambda1 and lambda2 or 367 freq1 and freq2 are the labels representing the lower and upper 368 bounds in wavelength. 370 o Tuning time: Tuning times highly depend on the technology used. 371 Thermal drift based tuning may take seconds to stabilize, whilst 372 electronic tuning might provide sub-ms tuning times. Depending on 373 the application this might be critical. For example, thermal drift 374 might not be usable for fast protection applications. 376 o Spectral characteristics and stability: The spectral shape of a 377 laser's emissions and its frequency stability put limits on 378 various properties of the overall WDM system. One relatively easy 379 to characterize constraint is the closest channel spacing with 380 which the transmitter can be used. 382 Note that ITU-T recommendations specify many aspects of an optical 383 transmitter. Many of these parameters, such as spectral 384 characteristics and stability, are used in the design of WDM 385 subsystems consisting of transmitters, WDM links and receivers 386 however they do not furnish additional information that will 387 influence the Label Switched Path (LSP) provisioning in a properly 388 designed system. 390 Also note that optical components can degrade and fail over time. 391 This presents the possibility of the failure of a LSP (lightpath) 392 without either a node or link failure. Hence, additional mechanisms 393 may be necessary to detect and differentiate this failure from the 394 others, e.g., one doesn't not want to initiate mesh restoration if 395 the source transmitter has failed, since the optical transmitter will 396 still be failed on the alternate optical path. 398 3.3. Optical Signals in WSONs 400 In WSONs the fundamental unit of switching is intuitively that of a 401 "wavelength". The transmitters and receivers in these networks will 402 deal with one wavelength at a time, while the switching systems 403 themselves can deal with multiple wavelengths at a time. Hence 404 multichannel DWDM networks with single channel interfaces are the 405 prime focus of this document general concern as opposed to multi- 406 channel interfaces. Interfaces of this type are defined in ITU-T 407 recommendations [G.698.1] and [G.698.2]. Key non-impairment related 408 parameters defined in [G.698.1] and [G.698.2] are: 410 (a) Minimum channel spacing (GHz) 412 (b) Minimum and maximum central frequency 414 (c) Bit-rate/Line coding (modulation) of optical tributary signals 415 For the purposes of modeling the WSON in the control plane, (a) and 416 (b) are considered as properties of the link and restrictions on the 417 GMPLS labels while (c) is a property of the "signal". 419 3.3.1. Optical Tributary Signals 421 The optical interface specifications [G.698.1], [G.698.2], and 422 [G.959.1] all use the concept of an optical tributary signal which is 423 defined as "a single channel signal that is placed within an optical 424 channel for transport across the optical network". Note the use of 425 the qualifier "tributary" to indicate that this is a single channel 426 entity and not a multichannel optical signal. 428 There are currently a number of different types of optical tributary 429 signals, which are known as "optical tributary signal classes". These 430 are currently characterized by a modulation format and bit rate range 431 [G.959.1]: 433 (a) Optical tributary signal class NRZ 1.25G 435 (b) Optical tributary signal class NRZ 2.5G 437 (c) Optical tributary signal class NRZ 10G 439 (d) Optical tributary signal class NRZ 40G 441 (e) Optical tributary signal class RZ 40G 443 Note that with advances in technology more optical tributary signal 444 classes may be added and that this is currently an active area for 445 development and standardization. In particular at the 40G rate there 446 are a number of non-standardized advanced modulation formats that 447 have seen significant deployment including Differential Phase Shift 448 Keying (DPSK) and Phase Shaped Binary Transmission (PSBT). 450 According to [G.698.2] it is important to fully specify the bit rate 451 of the optical tributary signal. Hence it is seen that modulation 452 format (optical tributary signal class) and bit rate are key 453 parameters in characterizing the optical tributary signal. 455 3.3.2. WSON Signal Characteristics 457 An optical tributary signal defined in ITU-T [G.698.1] and [G.698.2] 458 is referred to as the "signal" in this document. This corresponds to 459 the "lambda" LSP in GMPLS. For signal compatibility purposes with 460 electro-optical network elements, the following signal 461 characteristics are considered: 463 1. Optical tributary signal class (modulation format). 464 2. FEC: whether forward error correction is used in the digital stream 465 and what type of error correcting code is used. 466 3. Center frequency (wavelength). 467 4. Bit rate. 468 5. G-PID: general protocol identifier for the information format. 470 The first three items on this list can change as a WSON signal 471 traverses the optical network with elements that include 472 regenerators, Optical-to-Electrical (OEO) switches, or wavelength 473 converters. 475 Bit rate and G-PID would not change since they describe the encoded 476 bit stream. A set of G-PID values is already defined for lambda 477 switching in [RFC3471] and [RFC4328]. 479 Note that a number of non-standard or proprietary modulation formats 480 and FEC codes are commonly used in WSONs. For some digital bit 481 streams the presence of Forwarding Equivalence Class (FEC) can be 482 detected, e.g., in [G.707] this is indicated in the signal itself via 483 the FEC Status Indication (FSI) byte, while in [G.709] this can be 484 inferred from whether the FEC field of the Optical Channel Transport 485 Unit-k (OTUk) is all zeros or not. 487 3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs 489 Definitions of various optical devices such as ROADMs, Optical Cross- 490 connects (OXCs), splitters, combiners and Fixed Optical Add-Drop 491 Multiplexers (FOADMs) and their parameters can be found in [G.671]. 492 Only a subset of these and their non-impairment related properties 493 are considered in the following sections. 495 3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs 497 ROADMs are available in different forms and technologies. This is a 498 key technology that allows wavelength based optical switching. A 499 classic degree-2 ROADM is shown in Figure 1. 501 Line side input +---------------------+ Line side output 502 --->| |---> 503 | | 504 | ROADM | 505 | | 506 | | 507 +---------------------+ 508 | | | | o o o o 509 | | | | | | | | 510 O O O O | | | | 511 Tributary Side: Drop (output) Add (input) 513 Figure 1. Degree-2 ROADM 515 The key feature across all ROADM types is their highly asymmetric 516 switching capability. In the ROADM of Figure 1, signals introduced 517 via the add ports can only be sent on the line side output port and 518 not on any of the drop ports. The term "degree" is used to refer to 519 the number of line side ports (input and output) of a ROADM, and does 520 not include the number of "add" or "drop" ports. The add and drop 521 ports are sometimes also called tributary ports. As the degree of the 522 ROADM increases beyond two it can have properties of both a switch 523 (OXC) and a multiplexer and hence it is necessary to know the 524 switched connectivity offered by such a network element to 525 effectively utilize it. A straightforward way to represent this is 526 via a "switched connectivity" matrix A where Amn = 0 or 1, depending 527 upon whether a wavelength on input port m can be connected to output 528 port n [Imajuku]. For the ROADM shown in Figure 1 the switched 529 connectivity matrix can be expressed as: 531 Input Output Port 532 Port #1 #2 #3 #4 #5 533 -------------- 534 #1: 1 1 1 1 1 535 #2 1 0 0 0 0 536 A = #3 1 0 0 0 0 537 #4 1 0 0 0 0 538 #5 1 0 0 0 0 540 Where input ports 2-5 are add ports, output ports 2-5 are drop ports 541 and input port #1 and output port #1 are the line side (WDM) ports. 543 For ROADMs, this matrix will be very sparse, and for OXCs the matrix 544 will be very dense, compact encodings and examples, including high 545 degree ROADMs/OXCs, are given in [WSON-Encode]. A degree-4 ROADM is 546 shown in Figure 2. 548 +-----------------------+ 549 Line side-1 --->| |---> Line side-2 550 Input (I1) | | Output (E2) 551 Line side-1 <---| |<--- Line side-2 552 Output (E1) | | Input (I2) 553 | ROADM | 554 Line side-3 --->| |---> Line side-4 555 Input (I3) | | Output (E4) 556 Line side-3 <---| |<--- Line side-4 557 Output (E3) | | Input (I4) 558 | | 559 +-----------------------+ 560 | O | O | O | O 561 | | | | | | | | 562 O | O | O | O | 563 Tributary Side: E5 I5 E6 I6 E7 I7 E8 I8 565 Figure 2. Degree-4 ROADM 567 Note that this example is 4-degree example with one (potentially 568 multi-channel) add/drop per line side port. 570 Note also that the connectivity constraints for typical ROADM designs 571 are "bidirectional", i.e. if input port X can be connected to output 572 port Y, typically input port Y can be connected to output port X, 573 assuming the numbering is done in such a way that input X and output 574 X correspond to the same line side direction or the same add/drop 575 port. This makes the connectivity matrix symmetrical as shown below. 577 Input Output Port 578 Port E1 E2 E3 E4 E5 E6 E7 E8 579 ----------------------- 580 I1 0 1 1 1 0 1 0 0 581 I2 1 0 1 1 0 0 1 0 582 A = I3 1 1 0 1 1 0 0 0 583 I4 1 1 1 0 0 0 0 1 584 I5 0 0 1 0 0 0 0 0 585 I6 1 0 0 0 0 0 0 0 586 I7 0 1 0 0 0 0 0 0 587 I8 0 0 0 1 0 0 0 0 589 Where I5/E5 are add/drop ports to/from line side-3, I6/E6 are 590 add/drop ports to/from line side-1, I7/E7 are add/drop ports to/from 591 line side-2 and I8/E8 are add/drop ports to/from line side-4. Note 592 that diagonal elements are zero since loopback is not supported in 593 the example. If ports support loopback, diagonal elements would be 594 set to one. 596 Additional constraints may also apply to the various ports in a 597 ROADM/OXC. The following restrictions and terms may be used: 599 Colored port: an input or more typically an output (drop) port 600 restricted to a single channel of fixed wavelength. 602 Colorless port: an input or more typically an output (drop) port 603 restricted to a single channel of arbitrary wavelength. 605 In general a port on a ROADM could have any of the following 606 wavelength restrictions: 608 o Multiple wavelengths, full range port. 610 o Single wavelength, full range port. 612 o Single wavelength, fixed lambda port. 614 o Multiple wavelengths, reduced range port (for example wave band 615 switching). 617 To model these restrictions it is necessary to have two pieces of 618 information for each port: (a) number of wavelengths, (b) wavelength 619 range and spacing. Note that this information is relatively static. 620 More complicated wavelength constraints are modeled in [WSON-Info]. 622 3.4.2. Splitters 624 An optical splitter consists of a single input port and two or more 625 output ports. The input optical signaled is essentially copied (with 626 power loss) to all output ports. 628 Using the modeling notions of Section 3.4.1. (Reconfigurable Add/Drop 629 Multiplexers and OXCs) the input and output ports of a splitter would 630 have the same wavelength restrictions. In addition a splitter is 631 modeled by a connectivity matrix Amn as follows: 633 Input Output Port 634 Port #1 #2 #3 ... #N 635 ----------------- 636 A = #1 1 1 1 ... 1 638 The difference from a simple ROADM is that this is not a switched 639 connectivity matrix but the fixed connectivity matrix of the device. 641 3.4.3. Combiners 643 An optical combiner is a device that combines the optical wavelengths 644 carried by multiple input ports into a single multi-wavelength output 645 output port. The various ports may have different wavelength 646 restrictions. It is generally the responsibility of those using the 647 combiner to assure that wavelength collision does not occur on the 648 output port. The fixed connectivity matrix Amn for a combiner would 649 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 -------------------------------------------------------------------- 733 From this table it is seen that 1R regenerators are generally 734 independent of signal modulation format (also known as line coding), 735 but may work over a limited range of wavelength/frequencies. 2R 736 regenerators are generally applicable to a single digital stream and 737 are dependent upon modulation format (line coding) and to a lesser 738 extent are limited to a range of bit rates (but not a specific bit 739 rate). Finally, 3R regenerators apply to a single channel, are 740 dependent upon the modulation format and generally sensitive to the 741 bit rate of digital signal, i.e., either are designed to only handle 742 a specific bit rate or need to be programmed to accept and regenerate 743 a specific bit rate. In all these types of regenerators the digital 744 bit stream contained within the optical or electrical signal is not 745 modified. 747 It is common for regenerators to modify the digital bit stream for 748 performance monitoring and fault management purposes. Synchronous 749 Optical Networking (SONET), Synchronous Digital Hierarchy (SDH) and 750 Interfaces for the Optical Transport Network (G.709) all have digital 751 signal "envelopes" designed to be used between "regenerators" (in 752 this case 3R regenerators). In SONET this is known as the "section" 753 signal, in SDH this is known as the "regenerator section" signal, in 754 G.709 this is known as an OTUk. These signals reserve a portion of 755 their frame structure (known as overhead) for use by regenerators. 756 The nature of this overhead is summarized in Table 2 below. 758 Table 2. SONET, SDH, and G.709 regenerator related overhead. 760 +-----------------------------------------------------------------+ 761 |Function | SONET/SDH | G.709 OTUk | 762 | | Regenerator | | 763 | | Section | | 764 |------------------+----------------------+-----------------------| 765 |Signal | J0 (section | Trail Trace | 766 |Identifier | trace) | Identifier (TTI) | 767 |------------------+----------------------+-----------------------| 768 |Performance | BIP-8 (B1) | BIP-8 (within SM) | 769 |Monitoring | | | 770 |------------------+----------------------+-----------------------| 771 |Management | D1-D3 bytes | GCC0 (general | 772 |Communications | | communications | 773 | | | channel) | 774 |------------------+----------------------+-----------------------| 775 |Fault Management | A1, A2 framing | FAS (frame alignment | 776 | | bytes | signal), BDI(backward| 777 | | | defect indication)BEI| 778 | | | (backward error | 779 | | | indication) | 780 +------------------+----------------------+-----------------------| 781 |Forward Error | P1,Q1 bytes | OTUk FEC | 782 |Correction (FEC) | | | 783 +-----------------------------------------------------------------+ 785 In the previous table it is seen that frame alignment, signal 786 identification, and FEC are supported. What this table also shows by 787 its omission is that no switching or multiplexing occurs at this 788 layer. This is a significant simplification for the control plane 789 since control plane standards require a multi-layer approach when 790 there are multiple switching layers, but not for "layering" to 791 provide the management functions of Table 2. That is, many existing 792 technologies covered by GMPLS contain extra management related layers 793 that are essentially ignored by the control plane (though not by the 794 management plane!). Hence, the approach here is to include 795 regenerators and other devices at the WSON layer unless they provide 796 higher layer switching and then a multi-layer or multi-region 797 approach [RFC5212] is called for. However, this can result in 798 regenerators having a dependence on the client signal type. 800 Hence depending upon the regenerator technology the following 801 constraints may be imposed by a regenerator device: 803 Table 3. Regenerator Compatibility Constraints. 805 +--------------------------------------------------------+ 806 | Constraints | 1R | 2R | 3R | 807 +--------------------------------------------------------+ 808 | Limited Wavelength Range | x | x | x | 809 +--------------------------------------------------------+ 810 | Modulation Type Restriction | | x | x | 811 +--------------------------------------------------------+ 812 | Bit Rate Range Restriction | | x | x | 813 +--------------------------------------------------------+ 814 | Exact Bit Rate Restriction | | | x | 815 +--------------------------------------------------------+ 816 | Client Signal Dependence | | | x | 817 +--------------------------------------------------------+ 819 Note that the limited wavelength range constraint can be modeled for 820 GMPLS signaling with the label set defined in [RFC3471] and that the 821 modulation type restriction constraint includes FEC. 823 3.5.2. OEO Switches 825 A common place where OEO processing may take place is within WSON 826 switches that utilize (or contain) regenerators. Regenerators may be 827 added to a switching system for a number of reasons. One common 828 reason is to restore signal quality either before or after optical 829 processing (switching). Another reason may be to convert the signal 830 to an electronic form for switching then reconverting to an optical 831 signal prior to output from the switch. In this later case the 832 regeneration is applied to adapt the signal to the switch fabric 833 regardless of whether or not it is needed from a signal quality 834 perspective. 836 In either case these optical switches have essentially the same 837 compatibility constraints as those which are described for 838 regenerators in Table 3. 840 3.6. Wavelength Converters 842 Wavelength converters take an input optical signal at one wavelength 843 and emit an equivalent content optical signal at another wavelength 844 on output. There are multiple approaches to building wavelength 845 converters. One approach is based on OEO conversion with fixed or 846 tunable optics on output. This approach can be dependent upon the 847 signal rate and format, i.e., this is basically an electrical 848 regenerator combined with a laser/receiver. Hence, this type of 849 wavelength converter has signal processing restrictions that are 850 essentially the same as those described for regenerators in Table 3 851 of section 3.5.1. 853 Another approach performs the wavelength conversion, optically via 854 non-linear optical effects, similar in spirit to the familiar 855 frequency mixing used in radio frequency systems, but significantly 856 harder to implement. Such processes/effects may place limits on the 857 range of achievable conversion. These may depend on the wavelength of 858 the input signal and the properties of the converter as opposed to 859 only the properties of the converter in the OEO case. Different WSON 860 system designs may choose to utilize this component to varying 861 degrees or not at all. 863 Current or envisioned contexts for wavelength converters are: 865 1. Wavelength conversion associated with OEO switches and fixed or 866 tunable optics. In this case there are typically multiple 867 converters available since each on the use of an OEO switch can be 868 thought of as a potential wavelength converter. 870 2. Wavelength conversion associated with ROADMs/OXCs. In this case 871 there may be a limited pool of wavelength converters available. 872 Conversion could be either all optical or via an OEO method. 874 3. Wavelength conversion associated with fixed devices such as FOADMs. 875 In this case there may be a limited amount of conversion. Also in 876 this case the conversion may be used as part of light path routing. 878 Based on the above considerations, wavelength converters are modeled 879 as follows: 881 1. Wavelength converters can always be modeled as associated with 882 network elements. This includes fixed wavelength routing elements. 884 2. A network element may have full wavelength conversion capability, 885 i.e., any input port and wavelength, or a limited number of 886 wavelengths and ports. On a box with a limited number of 887 converters there also may exist restrictions on which ports can 888 reach the converters. Hence regardless of where the converters 889 actually are they can be associated with input ports. 891 3. Wavelength converters have range restrictions that are either 892 independent or dependent upon the input wavelength. 894 In WSONs where wavelength converters are sparse a light path may 895 appear to loop or "backtrack" upon itself in order to reach a 896 wavelength converter prior to continuing on to its destination. The 897 lambda used on input to the wavelength converter would be different 898 the lambda coming back from the wavelength converter. 900 A model for an individual O-E-O wavelength converter would consist 901 of: 903 o Input lambda or frequency range. 905 o Output lambda or frequency range. 907 3.6.1. Wavelength Converter Pool Modeling 909 A WSON node may include multiple wavelength converters. These are 910 usually arranged into some type of pool to promote resource sharing. 911 There are a number of different approaches used in the design of 912 switches with converter pools. However, from the point of view of 913 path computation it is necessary to know the following: 915 1. The nodes that support wavelength conversion. 917 2. The accessibility and availability of a wavelength converter to 918 convert from a given input wavelength on a particular input port 919 to a desired output wavelength on a particular output port. 921 3. Limitations on the types of signals that can be converted and the 922 conversions that can be performed. 924 To model point 2 above, a similar technique can be used to model 925 ROADMs and optical switches, i.e., matrices to indicate possible 926 connectivity along with wavelength constraints for links/ports. Since 927 wavelength converters are considered a scarce resource it will be 928 desirable to include as a minimum the usage state of individual 929 wavelength converters in the pool. 931 A three stage model is used as shown schematically in Figure 3. 932 (Schematic diagram of wavelength converter pool model). In this model 933 it is assumed N input ports (fibers), P wavelength converters, and M 934 output ports (fibers). Since not all input ports can necessarily 935 reach the converter pool, the model starts with a wavelength pool 936 input matrix WI(i,p) = {0,1} where input port i can reach potentially 937 reach wavelength converter p. 939 Since not all wavelength can necessarily reach all the converters or 940 the converters may have limited input wavelength range there is a set 941 of input port constraints for each wavelength converter. Currently it 942 is assumed that a wavelength converter can only take a single 943 wavelength on input. Each wavelength converter input port constraint 944 can be modeled via a wavelength set mechanism. 946 Next a state vector WC(j) = {0,1} dependent upon whether wavelength 947 converter j in the pool is in use. This is the only state kept in the 948 converter pool model. This state is not necessary for modeling 949 "fixed" transponder system, i.e., systems where there is no sharing. 950 In addition, this state information may be encoded in a much more 951 compact form depending on the overall connectivity structure [WSON- 952 Encode]. 954 After that, a set of wavelength converter output wavelength 955 constraints is used. These constraints indicate what wavelengths a 956 particular wavelength converter can generate or are restricted to 957 generating due to internal switch structure. 959 Finally, a wavelength pool output matrix WE(p,k) = {0,1} indicating 960 whether the output from wavelength converter p can reach output port 961 k. Examples of this method being used to model wavelength converter 962 pools for several switch architectures are given in reference [WSON- 963 Encode]. 965 I1 +-------------+ +-------------+ E1 966 ----->| | +--------+ | |-----> 967 I2 | +------+ WC #1 +-------+ | E2 968 ----->| | +--------+ | |-----> 969 | Wavelength | | Wavelength | 970 | Converter | +--------+ | Converter | 971 | Pool +------+ WC #2 +-------+ Pool | 972 | | +--------+ | | 973 | Input | | Output | 974 | Connection | . | Connection | 975 | Matrix | . | Matrix | 976 | | . | | 977 | | | | 978 IN | | +--------+ | | EM 979 ----->| +------+ WC #P +-------+ |-----> 980 | | +--------+ | | 981 +-------------+ ^ ^ +-------------+ 982 | | 983 | | 984 | | 985 | | 987 Input wavelength Output wavelength 988 constraints for constraints for 989 each converter each converter 991 Figure 3. Schematic diagram of wavelength converter pool model. 993 Figure 4 below shows a simple optical switch in a four wavelength 994 DWDM system sharing wavelength converters in a general shared "per 995 node" fashion. 997 +-----------+ ___________ +------+ 998 | |--------------------------->| | 999 | |--------------------------->| C | 1000 /| | |--------------------------->| o | E1 1001 I1 /D+--->| |--------------------------->| m | 1002 + e+--->| | | b |====> 1003 ====>| M| | Optical | +-----------+ +----+ | i | 1004 + u+--->| Switch | | WC Pool | |O S|-->| n | 1005 \x+--->| | | +-----+ | |p w|-->| e | 1006 \| | +----+->|WC #1|--+->|t i| | r | 1007 | | | +-----+ | |i t| +------+ 1008 | | | | |c c| +------+ 1009 /| | | | +-----+ | |a h|-->| | 1010 I2 /D+--->| +----+->|WC #2|--+->|l |-->| C | E2 1011 + e+--->| | | +-----+ | | | | o | 1012 ====>| M| | | +-----------+ +----+ | m |====> 1013 + u+--->| | | b | 1014 \x+--->| |--------------------------->| i | 1015 \| | |--------------------------->| n | 1016 | |--------------------------->| e | 1017 |___________|--------------------------->| r | 1018 +-----------+ +------+ 1020 Figure 4. An optical switch featuring a shared per node wavelength 1021 converter pool architecture. 1023 In this case the input and output pool matrices are simply: 1025 +-----+ +-----+ 1026 | 1 1 | | 1 1 | 1027 WI =| |, WE =| | 1028 | 1 1 | | 1 1 | 1029 +-----+ +-----+ 1031 Figure 5 shows a different wavelength pool architecture known as 1032 "shared per fiber". In this case the input and output pool matrices 1033 are simply: 1035 +-----+ +-----+ 1036 | 1 1 | | 1 0 | 1037 WI =| |, WE =| | 1038 | 1 1 | | 0 1 | 1039 +-----+ +-----+ 1040 +-----------+ +------+ 1041 | |--------------------------->| | 1042 | |--------------------------->| C | 1043 /| | |--------------------------->| o | E1 1044 I1 /D+--->| |--------------------------->| m | 1045 + e+--->| | | b |====> 1046 ====>| M| | Optical | +-----------+ | i | 1047 + u+--->| Switch | | WC Pool | | n | 1048 \x+--->| | | +-----+ | | e | 1049 \| | +----+->|WC #1|--+---------->| r | 1050 | | | +-----+ | +------+ 1051 | | | | +------+ 1052 /| | | | +-----+ | | | 1053 I2 /D+--->| +----+->|WC #2|--+---------->| C | E2 1054 + e+--->| | | +-----+ | | o | 1055 ====>| M| | | +-----------+ | m |====> 1056 + u+--->| | | b | 1057 \x+--->| |--------------------------->| i | 1058 \| | |--------------------------->| n | 1059 | |--------------------------->| e | 1060 |___________|--------------------------->| r | 1061 +-----------+ +------+ 1062 Figure 5. An optical switch featuring a shared per fiber wavelength 1063 converter pool architecture. 1065 3.7. Characterizing Electro-Optical Network Elements 1067 In this section electro-optical WSON network elements are 1068 characterized by the three key functional components: input 1069 constraints, output constraints and processing capabilities. 1071 WSON Network Element 1072 +-----------------------+ 1073 WSON Signal | | | | WSON Signal 1074 | | | | 1075 ---------------> | | | | -----------------> 1076 | | | | 1077 +-----------------------+ 1078 <-----> <-------> <-----> 1080 Input Processing Output 1082 Figure 6. WSON Network Element 1084 3.7.1. Input Constraints 1086 Section 3. (Wavelength Switched Optical Networks) discussed the basic 1087 properties regenerators, OEO switches and wavelength converters. From 1088 these the following possible types of input constraints and 1089 properties are derived: 1091 1. Acceptable Modulation formats. 1093 2. Client Signal (G-PID) restrictions. 1095 3. Bit Rate restrictions. 1097 4. FEC coding restrictions. 1099 5. Configurability: (a) none, (b) self-configuring, (c) required. 1101 These constraints are represented via simple lists. Note that the 1102 device may need to be "provisioned" via signaling or some other means 1103 to accept signals with some attributes versus others. In other cases 1104 the devices maybe relatively transparent to some attributes, e.g., 1105 such as a 2R regenerator to bit rate. Finally, some devices maybe 1106 able to auto-detect some attributes and configure themselves, e.g., a 1107 3R regenerator with bit rate detection mechanisms and flexible phase 1108 locking circuitry. To account for these different cases item 5 has 1109 been added, which describes the devices configurability. 1111 Note that such input constraints also apply to the termination of the 1112 WSON signal. 1114 3.7.2. Output Constraints 1116 None of the network elements considered here modifies either the bit 1117 rate or the basic type of the client signal. However, they may modify 1118 the modulation format or the FEC code. Typically the following types 1119 of output constraints are seen: 1121 1. Output modulation is the same as input modulation (default). 1123 2. A limited set of output modulations is available. 1125 3. Output FEC is the same as input FEC code (default). 1127 4. A limited set of output FEC codes is available. 1129 Note that in cases (2) and (4) above, where there is more than one 1130 choice in the output modulation or FEC code then the network element 1131 will need to be configured on a per LSP basis as to which choice to 1132 use. 1134 3.7.3. Processing Capabilities 1136 A general WSON network element (NE) can perform a number of signal 1137 processing functions including: 1139 (A) Regeneration (possibly different types). 1141 (B) Fault and Performance Monitoring. 1143 (C) Wavelength Conversion. 1145 (D) Switching. 1147 An NE may or may not have the ability to perform regeneration (of the 1148 one of the types previously discussed). In addition some nodes may 1149 have limited regeneration capability, i.e., a shared pool, which may 1150 be applied to selected signals traversing the NE. Hence to describe 1151 the regeneration capability of a link or node it is necessary to have 1152 at a minimum: 1154 1. Regeneration capability: (a)fixed, (b) selective, (c) none. 1156 2. Regeneration type: 1R, 2R, 3R. 1158 3. Regeneration pool properties for the case of selective 1159 regeneration (input and output restrictions, availability). 1161 Note that the properties of shared regenerator pools would be 1162 essentially the same at that of wavelength converter pools modeled in 1163 section 3.6.1. (Wavelength Pool Convertor Modeling). 1165 Item (B), fault and performance monitoring, is typically outside the 1166 scope of the control plane. However, when the operations are to be 1167 performed on an LSP basis or on part of an LSP then the control plane 1168 can be of assistance in their configuration. Per LSP, per node, fault 1169 and performance monitoring examples include setting up a "section 1170 trace" (a regenerator overhead identifier) between two nodes, or 1171 intermediate optical performance monitoring at selected nodes along a 1172 path. 1174 4. Routing and Wavelength Assignment and the Control Plane 1176 A wavelength-convertible network with full wavelength-conversion 1177 capability at each node is equivalent to packet MPLS-labeled network 1178 or a circuit-switched Time-division multiplexing (TDM) network with 1179 full time slot interchange capability. In this case, the routing 1180 problem needs to be addressed only at the level of the Traffic 1181 Engineered (TE) link choice, and wavelength assignment can be 1182 resolved locally by the switches on a hop-by-hop basis. 1184 However, in the limiting case of an optical network with no 1185 wavelength converters, a light path (optical signal) needs a route 1186 from source to destination and must pick a single wavelength that can 1187 be used along that path without "colliding" with the wavelength used 1188 by any other light path that may share an optical fiber. This is 1189 sometimes referred to as a "wavelength continuity constraint". 1191 In the general case of limited or no wavelength converters this 1192 computation is known as the RWA problem. 1194 The inputs to the basic RWA problem are the requested light path's 1195 source and destination, the network topology, the locations and 1196 capabilities of any wavelength converters, and the wavelengths 1197 available on each optical link. The output from an algorithm solving 1198 the RWA problem is an explicit route through ROADMs, a wavelength for 1199 the optical transmitter, and a set of locations (generally associated 1200 with ROADMs or switches) where wavelength conversion is to occur and 1201 the new wavelength to be used on each component link after that point 1202 in the route. 1204 It is to be noted that the choice of specific RWA algorithm is out of 1205 the scope for this document. However there are a number of different 1206 approaches to dealing with the RWA algorithm that can affect the 1207 division of effort between path computation/routing and signaling. 1209 4.1. Architectural Approaches to RWA 1211 Two general computational approaches are taken to solving the RWA 1212 problem. Some algorithms utilize a two step procedure of path 1213 selection followed by wavelength assignment, and others solve the 1214 problem in a combined fashion. 1216 In the following, three different ways of performing RWA in 1217 conjunction with the control plane are considered. The choice of one 1218 of these architectural approaches over another generally impacts the 1219 demands placed on the various control plane protocols. 1221 4.1.1. Combined RWA (R&WA) 1223 In this case, a unique entity is in charge of performing routing and 1224 wavelength assignment. This approach relies on a sufficient knowledge 1225 of network topology, of available network resources and of network 1226 nodes capabilities. This solution is compatible with most known RWA 1227 algorithms, and in particular those concerned with network 1228 optimization. On the other hand, this solution requires up-to-date 1229 and detailed network information. 1231 Such a computational entity could reside in two different logical 1232 places: 1234 o The PCE, which maintains a complete and updated view of network 1235 state, provides path computation services to nodes (PCCs). 1237 o In the ingress node, in that case all nodes have the R&WA 1238 functionality; the knowledge of the network state is obtained by a 1239 periodic flooding of information provided by the other nodes. 1241 4.1.2. Separated R and WA (R+WA) 1243 In this case a first entity performs routing, while a second performs 1244 wavelength assignment. The first entity furnishes one or more paths 1245 to the second entity that will perform wavelength assignment and 1246 possibly final path selection. 1248 As the entities computing the path and the wavelength assignment are 1249 separated, this constrains the class of RWA algorithms that may be 1250 implemented. Although it may seem that algorithms optimizing a joint 1251 usage of the physical and spectral paths are excluded from this 1252 solution, many practical optimization algorithms only consider a 1253 limited set of possible paths, e.g., as computed via a k-shortest 1254 path algorithm. Hence although there is no guarantee that the 1255 selected final route and wavelength offers the optimal solution, by 1256 allowing multiple routes to pass to the wavelength selection process 1257 reasonable optimization can be performed. 1259 The entity performing the routing assignment needs the topology 1260 information of the network, whereas the entity performing the 1261 wavelength assignment needs information on the network's available 1262 resources and specific network node capabilities. 1264 4.1.3. Routing and Distributed WA (R+DWA) 1266 In this case a first entity performs routing, while wavelength 1267 assignment is performed on a hop-by-hop, distributed, manner along 1268 the previously computed route. This mechanism relies on updating of a 1269 list of potential wavelengths used to ensure conformance with the 1270 wavelength continuity constraint. 1272 As currently specified, the GMPLS protocol suite signaling protocol 1273 can accommodate such an approach. Per [RFC3471], the Label Set 1274 selection works according to an AND scheme. Each hop restricts the 1275 Label Set sent to the next hop from the one received from the 1276 previous hop by performing an AND operation between the wavelength 1277 referred by the labels the message includes with the one available on 1278 the ongoing interface. The constraint to perform this AND operation 1279 is up to the node local policy (even if one expects a consistent 1280 policy configuration throughout a given transparency domain). When 1281 wavelength conversion is performed at an intermediate node, a new 1282 Label Set is generated. The output node selects one label in the 1283 Label Set which it received; additionally the node can apply local 1284 policy during label selection. 1286 Depending on these policies a spectral assignment may not be found or 1287 one consuming too many conversion resources relative to what a 1288 dedicated wavelength assignment policy would have achieved. Hence, 1289 this approach may generate higher blocking probabilities in a heavily 1290 loaded network. 1292 On the one hand, this solution may be empowered with some signaling 1293 extensions to ease its functioning and possibly enhance its 1294 performance relatively to blocking. Note that this approach requires 1295 less information dissemination than the other techniques described. 1297 The first entity may be a PCE or the ingress node of the LSP. This 1298 solution is applicable inside networks where resource optimization is 1299 not as critical. 1301 4.2. Conveying information needed by RWA 1303 The previous sections have characterized WSONs and lightpath 1304 requests. In particular, high level models of the information used by 1305 the RWA process were presented. This information can be viewed as 1306 either static, changing with hardware changes (including possibly 1307 failures), or dynamic, those that can change with subsequent 1308 lightpath provisioning. The timeliness in which an entity involved in 1309 the RWA process is notified of such changes is fairly situational. 1310 For example, for network restoration purposes, learning of a hardware 1311 failure or of new hardware coming online to provide restoration 1312 capability can be critical. 1314 Currently there are various methods for communicating RWA relevant 1315 information, these include, but are not limited to: 1317 o Existing control plane protocols such as GMPLS routing and 1318 signaling. Note that routing protocols can be used to convey both 1319 static and dynamic information. 1321 o Management protocols such as NetConf, SNMPv3, CLI, CORBA, or 1322 others. 1324 o Directory services and accompanying protocols. These are good for 1325 the dissemination of relatively static information. Directory 1326 services are not suited to manage information in dynamic and fluid 1327 environments. 1329 o Other techniques for dynamic information: messaging straight from 1330 NEs to PCE to avoid flooding. This would be useful if the number 1331 of PCEs is significantly less than number of WSON NEs. Or other 1332 ways to limit flooding to "interested" NEs. 1334 Mechanisms to improve scaling of dynamic information: 1336 o Tailor message content to WSON. For example the use of wavelength 1337 ranges, or wavelength occupation bit maps. 1339 o Utilize incremental updates if feasible. 1341 5. Modeling Examples and Control Plane Use Cases 1343 This section provides examples of the fixed and switch optical node 1344 and wavelength constraint models of Section 3. and WSON control 1345 plane use cases related to path computation, establishment, 1346 rerouting, and optimization. 1348 5.1. Network Modeling for GMPLS/PCE Control 1350 Consider a network containing three routers (R1 through R3), eight 1351 WSON nodes (N1 through N8) and 18 links (L1 through L18) and one OEO 1352 converter (O1) in a topology shown below. 1354 +--+ +--+ +--+ +--------+ 1355 +-L3-+N2+-L5-+ +--------L12--+N6+--L15--+ N8 + 1356 | +--+ |N4+-L8---+ +--+ ++--+---++ 1357 | | +-L9--+| | | | 1358 +--+ +-+-+ ++-+ || | L17 L18 1359 | ++-L1--+ | | ++++ +----L16---+ | | 1360 |R1| | N1| L7 |R2| | | | 1361 | ++-L2--+ | | ++-+ | ++---++ 1362 +--+ +-+-+ | | | + R3 | 1363 | +--+ ++-+ | | +-----+ 1364 +-L4-+N3+-L6-+N5+-L10-+ ++----+ 1365 +--+ | +--------L11--+ N7 + 1366 +--+ ++---++ 1367 | | 1368 L13 L14 1369 | | 1370 ++-+ | 1371 |O1+-+ 1372 +--+ 1374 Figure 7. Routers and WSON nodes in a GMPLS and PCE Environment. 1376 5.1.1. Describing the WSON nodes 1378 The eight WSON nodes described in Figure 7 have the following 1379 properties: 1381 o Nodes N1, N2, N3 have FOADMs installed and can therefore only 1382 access a static and pre-defined set of wavelengths. 1384 o All other nodes contain ROADMs and can therefore access all 1385 wavelengths. 1387 o Nodes N4, N5, N7 and N8 are multi-degree nodes, allowing any 1388 wavelength to be optically switched between any of the links. Note 1389 however, that this does not automatically apply to wavelengths 1390 that are being added or dropped at the particular node. 1392 o Node N4 is an exception to that: This node can switch any 1393 wavelength from its add/drop ports to any of its outgoing links 1394 (L5, L7 and L12 in this case). 1396 o The links from the routers are always only able to carry one 1397 wavelength with the exception of links L8 and L9 which are capable 1398 to add/drop any wavelength. 1400 o Node N7 contains an OEO transponder (O1) connected to the node via 1401 links L13 and L14. That transponder operates in 3R mode and does 1402 not change the wavelength of the signal. Assume that it can 1403 regenerate any of the client signals, however only for a specific 1404 wavelength. 1406 Given the above restrictions, the node information for the eight 1407 nodes can be expressed as follows: (where ID == identifier, SCM == 1408 switched connectivity matrix, and FCM == fixed connectivity matrix). 1410 +ID+SCM +FCM + 1411 | | |L1 |L2 |L3 |L4 | | |L1 |L2 |L3 |L4 | | 1412 | |L1 |0 |0 |0 |0 | |L1 |0 |0 |1 |0 | | 1413 |N1|L2 |0 |0 |0 |0 | |L2 |0 |0 |0 |1 | | 1414 | |L3 |0 |0 |0 |0 | |L3 |1 |0 |0 |1 | | 1415 | |L4 |0 |0 |0 |0 | |L4 |0 |1 |1 |0 | | 1416 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1417 | | |L3 |L5 | | | | |L3 |L5 | | | | 1418 |N2|L3 |0 |0 | | | |L3 |0 |1 | | | | 1419 | |L5 |0 |0 | | | |L5 |1 |0 | | | | 1420 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1421 | | |L4 |L6 | | | | |L4 |L6 | | | | 1422 |N3|L4 |0 |0 | | | |L4 |0 |1 | | | | 1423 | |L6 |0 |0 | | | |L6 |1 |0 | | | | 1424 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1425 | | |L5 |L7 |L8 |L9 |L12| |L5 |L7 |L8 |L9 |L12| 1426 | |L5 |0 |1 |1 |1 |1 |L5 |0 |0 |0 |0 |0 | 1427 |N4|L7 |1 |0 |1 |1 |1 |L7 |0 |0 |0 |0 |0 | 1428 | |L8 |1 |1 |0 |1 |1 |L8 |0 |0 |0 |0 |0 | 1429 | |L9 |1 |1 |1 |0 |1 |L9 |0 |0 |0 |0 |0 | 1430 | |L12|1 |1 |1 |1 |0 |L12|0 |0 |0 |0 |0 | 1431 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1432 | | |L6 |L7 |L10|L11| | |L6 |L7 |L10|L11| | 1433 | |L6 |0 |1 |0 |1 | |L6 |0 |0 |1 |0 | | 1434 |N5|L7 |1 |0 |0 |1 | |L7 |0 |0 |0 |0 | | 1435 | |L10|0 |0 |0 |0 | |L10|1 |0 |0 |0 | | 1436 | |L11|1 |1 |0 |0 | |L11|0 |0 |0 |0 | | 1437 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1438 | | |L12|L15| | | | |L12|L15| | | | 1439 |N6|L12|0 |1 | | | |L12|0 |0 | | | | 1440 | |L15|1 |0 | | | |L15|0 |0 | | | | 1441 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1442 | | |L11|L13|L14|L16| | |L11|L13|L14|L16| | 1443 | |L11|0 |1 |0 |1 | |L11|0 |0 |0 |0 | | 1444 |N7|L13|1 |0 |0 |0 | |L13|0 |0 |1 |0 | | 1445 | |L14|0 |0 |0 |1 | |L14|0 |1 |0 |0 | | 1446 | |L16|1 |0 |1 |0 | |L16|0 |0 |1 |0 | | 1447 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1448 | | |L15|L16|L17|L18| | |L15|L16|L17|L18| | 1449 | |L15|0 |1 |0 |0 | |L15|0 |0 |0 |1 | | 1450 |N8|L16|1 |0 |0 |0 | |L16|0 |0 |1 |0 | | 1451 | |L17|0 |0 |0 |0 | |L17|0 |1 |0 |0 | | 1452 | |L18|0 |0 |0 |0 | |L18|1 |0 |1 |0 | | 1453 +--+---+---+---+---+---+---+---+---+---+---+---+---+ 1455 5.1.2. Describing the links 1457 For the following discussion some simplifying assumptions are made: 1459 o It is assumed that the WSON node support a total of four 1460 wavelengths designated WL1 through WL4. 1462 o It is assumed that the impairment feasibility of a path or path 1463 segment is independent from the wavelength chosen. 1465 For the discussion of the RWA operation to build LSPs between two 1466 routers, the wavelength constraints on the links between the routers 1467 and the WSON nodes as well as the connectivity matrix of these links 1468 needs to be specified: 1470 +Link+WLs supported +Possible output links+ 1471 | L1 | WL1 | L3 | 1472 +----+-----------------+---------------------+ 1473 | L2 | WL2 | L4 | 1474 +----+-----------------+---------------------+ 1475 | L8 | WL1 WL2 WL3 WL4 | L5 L7 L12 | 1476 +----+-----------------+---------------------+ 1477 | L9 | WL1 WL2 WL3 WL4 | L5 L7 L12 | 1478 +----+-----------------+---------------------+ 1479 | L10| WL2 | L6 | 1480 +----+-----------------+---------------------+ 1481 | L13| WL1 WL2 WL3 WL4 | L11 L14 | 1482 +----+-----------------+---------------------+ 1483 | L14| WL1 WL2 WL3 WL4 | L13 L16 | 1484 +----+-----------------+---------------------+ 1485 | L17| WL2 | L16 | 1486 +----+-----------------+---------------------+ 1487 | L18| WL1 | L15 | 1488 +----+-----------------+---------------------+ 1490 Note that the possible output links for the links connecting to the 1491 routers is inferred from the switched connectivity matrix and the 1492 fixed connectivity matrix of the Nodes N1 through N8 and is show here 1493 for convenience, i.e., this information does not need to be repeated. 1495 5.2. RWA Path Computation and Establishment 1497 The calculation of optical impairment feasible routes is outside the 1498 scope of this framework document. In general impairment feasible 1499 routes serve as an input to the RWA algorithm. 1501 For the example use case shown here, assume the following feasible 1502 routes: 1504 +Endpoint 1+Endpoint 2+Feasible Route + 1505 | R1 | R2 | L1 L3 L5 L8 | 1506 | R1 | R2 | L1 L3 L5 L9 | 1507 | R1 | R2 | L2 L4 L6 L7 L8 | 1508 | R1 | R2 | L2 L4 L6 L7 L9 | 1509 | R1 | R2 | L2 L4 L6 L10 | 1510 | R1 | R3 | L1 L3 L5 L12 L15 L18 | 1511 | R1 | N7 | L2 L4 L6 L11 | 1512 | N7 | R3 | L16 L17 | 1513 | N7 | R2 | L16 L15 L12 L9 | 1514 | R2 | R3 | L8 L12 L15 L18 | 1515 | R2 | R3 | L8 L7 L11 L16 L17 | 1516 | R2 | R3 | L9 L12 L15 L18 | 1517 | R2 | R3 | L9 L7 L11 L16 L17 | 1519 Given a request to establish a LSP between R1 and R2 the RWA 1520 algorithm finds the following possible solutions: 1522 +WL + Path + 1523 | WL1| L1 L3 L5 L8 | 1524 | WL1| L1 L3 L5 L9 | 1525 | WL2| L2 L4 L6 L7 L8| 1526 | WL2| L2 L4 L6 L7 L9| 1527 | WL2| L2 L4 L6 L10 | 1529 Assume now that the RWA chooses WL1 and the Path L1 L3 L5 L8 for the 1530 requested LSP. 1532 Next, another LSP is signaled from R1 to R2. Given the established 1533 LSP using WL1, the following table shows the available paths: 1535 +WL + Path + 1536 | WL2| L2 L4 L6 L7 L9| 1537 | WL2| L2 L4 L6 L10 | 1539 Assume now that the RWA chooses WL2 and the path L2 L4 L6 L7 L9 for 1540 the establishment of the new LSP. 1542 Faced with another LSP request -this time from R2 to R3 - can not be 1543 fulfilled since the only four possible paths (starting at L8 and L9) 1544 are already in use. 1546 5.3. Resource Optimization 1548 The preceding example gives rise to another use case: the 1549 optimization of network resources. Optimization can be achieved on a 1550 number of layers (e.g. through electrical or optical multiplexing of 1551 client signals) or by re-optimizing the solutions found by the RWA 1552 algorithm. 1554 Given the above example again, assume that the RWA algorithm should 1555 find a path between R2 and R3. The only possible path to reach R3 1556 from R2 needs to use L9. L9 however is blocked by one of the LSPs 1557 from R1. 1559 5.4. Support for Rerouting 1561 It is also envisioned that the extensions to GMPLS and PCE support 1562 rerouting of wavelengths in case of failures. 1564 Assume for this discussion that the only two LSPs in use in the 1565 system are: 1567 LSP1: WL1 L1 L3 L5 L8 1569 LSP2: WL2 L2 L4 L6 L7 L9 1571 Assume furthermore that the link L5 fails. The RWA can now find the 1572 following alternate path and and establish that path: 1574 R1 -> N7 -> R2 1576 Level 3 regeneration will take place at N7, so that the complete path 1577 looks like this: 1579 R1 -> L2 L4 L6 L11 L13 -> O1 -> L14 L16 L15 L12 L9 -> R2 1581 5.5. Electro-Optical Networking Scenarios 1583 In the following various networking scenarios are considered 1584 involving regenerators, OEO switches and wavelength converters. These 1585 scenarios can be grouped roughly by type and number of extensions to 1586 the GMPLS control plane that would be required. 1588 5.5.1. Fixed Regeneration Points 1590 In the simplest networking scenario involving regenerators, the 1591 regeneration is associated with a WDM link or entire node and is not 1592 optional, i.e., all signals traversing the link or node will be 1593 regenerated. This includes OEO switches since they provide 1594 regeneration on every port. 1596 There maybe input constraints and output constraints on the 1597 regenerators. Hence the path selection process will need to know from 1598 an IGP or other means the regenerator constraints so that it can 1599 choose a compatible path. For impairment aware routing and wavelength 1600 assignment (IA-RWA) the path selection process will also need to know 1601 which links/nodes provide regeneration. Even for "regular" RWA, this 1602 regeneration information is useful since wavelength converters 1603 typically perform regeneration and the wavelength continuity 1604 constraint can be relaxed at such a point. 1606 Signaling does not need to be enhanced to include this scenario since 1607 there are no reconfigurable regenerator options on input, output or 1608 with respect to processing. 1610 5.5.2. Shared Regeneration Pools 1612 In this scenario there are nodes with shared regenerator pools within 1613 the network in addition to fixed regenerators of the previous 1614 scenario. These regenerators are shared within a node and their 1615 application to a signal is optional. There are no reconfigurable 1616 options on either input or output. The only processing option is to 1617 "regenerate" a particular signal or not. 1619 Regenerator information in this case is used in path computation to 1620 select a path that ensures signal compatibility and IA-RWA criteria. 1622 To setup an LSP that utilizes a regenerator from a node with a shared 1623 regenerator pool one should be able to indicate that regeneration is 1624 to take place at that particular node along the signal path. Such a 1625 capability currently does not exist in GMPLS signaling. 1627 5.5.3. Reconfigurable Regenerators 1629 This scenario is concerned with regenerators that require 1630 configuration prior to use on an optical signal. As discussed 1631 previously, this could be due to a regenerator that must be 1632 configured to accept signals with different characteristics, for 1633 regenerators with a selection of output attributes, or for 1634 regenerators with additional optional processing capabilities. 1636 As in the previous scenarios it is necessary to have information 1637 concerning regenerator properties for selection of compatible paths 1638 and for IA-RWA computations. In addition during LSP setup it is 1639 necessary to be able configure regenerator options at a particular 1640 node along the path. Such a capability currently does not exist in 1641 GMPLS signaling. 1643 5.5.4. Relation to Translucent Networks 1645 Networks that contain both transparent network elements such as 1646 reconfigurable optical add drop multiplexers (ROADMs) and electro- 1647 optical network elements such regenerators or OEO switches are 1648 frequently referred to as translucent optical networks. 1650 Three main types of translucent optical networks have been discussed: 1652 1. Transparent "islands" surrounded by regenerators. This is 1653 frequently seen when transitioning from a metro optical sub- 1654 network to a long haul optical sub-network. 1656 2. Mostly transparent networks with a limited number of OEO 1657 ("opaque") nodes strategically placed. This takes advantage of the 1658 inherent regeneration capabilities of OEO switches. In the 1659 planning of such networks one has to determine the optimal 1660 placement of the OEO switches. 1662 3. Mostly transparent networks with a limited number of optical 1663 switching nodes with "shared regenerator pools" that can be 1664 optionally applied to signals passing through these switches. 1665 These switches are sometimes called translucent nodes. 1667 All three of these types of translucent networks fit within the 1668 networking scenarios of Section 5.5.1. and Section 5.5.2. above. 1669 And hence, can be accommodated by the GMPLS extensions suggested in 1670 this document. 1672 6. GMPLS and PCE Implications 1674 The presence and amount of wavelength conversion available at a 1675 wavelength switching interface has an impact on the information that 1676 needs to be transferred by the control plane (GMPLS) and the PCE 1677 architecture. Current GMPLS and PCE standards can address the full 1678 wavelength conversion case so the following will only address the 1679 limited and no wavelength conversion cases. 1681 6.1. Implications for GMPLS signaling 1683 Basic support for WSON signaling already exists in GMPLS with the 1684 lambda (value 9) LSP encoding type [RFC3471], or for G.709 compatible 1685 optical channels, the LSP encoding type (value = 13) "G.709 Optical 1686 Channel" from [RFC4328]. However a number of practical issues arise 1687 in the identification of wavelengths and signals, and distributed 1688 wavelength assignment processes which are discussed below. 1690 6.1.1. Identifying Wavelengths and Signals 1692 As previously stated a global fixed mapping between wavelengths and 1693 labels simplifies the characterization of WDM links and WSON devices. 1695 Furthermore such a mapping as described in [Otani] eases 1696 communication between PCE and WSON PCCs. 1698 6.1.2. WSON Signals and Network Element Processing 1700 It was seen in Section 3.3.2. that a WSON signal at any point along 1701 its path can be characterized by the (a) modulation format, (b) FEC, 1702 (c) wavelength, (d)bit rate, and (d)G-PID. 1704 Currently G-PID, wavelength (via labels), and bit rate (via bandwidth 1705 encoding) are supported in [RFC3471] and [RFC3473]. These RFCs can 1706 accommodate the wavelength changing at any node along the LSP and can 1707 thus provide explicit control of wavelength converters. 1709 In the fixed regeneration point scenario described in Section 5.5.1. 1710 (Fixed Regeneration Points) no enhancements are required to signaling 1711 since there are no additional configuration options for the LSP at a 1712 node. 1714 In the case of shared regeneration pools described in Section 5.5.2. 1715 (Shared Regeneration Pools) it is necessary to indicate to a node 1716 that it should perform regeneration on a particular signal. Viewed 1717 another way, for an LSP, it is desirable to specify that certain 1718 nodes along the path perform regeneration. Such a capability 1719 currently does not exist in GMPLS signaling. 1721 The case of configurable regenerators described in Section 5.5.3. 1722 (Reconfigurable Regenerators) is very similar to the previous except 1723 that now there are potentially many more items that can be configured 1724 on a per node basis for an LSP. 1726 Note that the techniques of [RFC5420] which allow for additional LSP 1727 attributes and their recording in an Record Route Object (RRO) object 1728 could be extended to allow for additional LSP attributes in an ERO. 1729 This could allow one to indicate where optional 3R regeneration 1730 should take place along a path, any modification of LSP attributes 1731 such as modulation format, or any enhance processing such as 1732 performance monitoring. 1734 6.1.3. Combined RWA/Separate Routing WA support 1736 In either the combined RWA or separate routing WA cases, the node 1737 initiating the signaling will have a route from the source to 1738 destination along with the wavelengths (generalized labels) to be 1739 used along portions of the path. Current GMPLS signaling supports an 1740 Explicit Route Object (ERO) and within an ERO an ERO Label subobject 1741 can be use to indicate the wavelength to be used at a particular 1742 node. In case the local label map approach is used the label sub- 1743 object entry in the ERO has to be translated appropriately. 1745 6.1.4. Distributed Wavelength Assignment: Unidirectional, No 1746 Converters 1748 GMPLS signaling for a uni-directional lightpath LSP allows for the 1749 use of a label set object in the Resource Reservation Protocol - 1750 Traffic Engineering (RSVP-TE) path message. The processing of the 1751 label set object to take the intersection of available lambdas along 1752 a path can be performed resulting in the set of available lambda 1753 being known to the destination that can then use a wavelength 1754 selection algorithm to choose a lambda. 1756 6.1.5. Distributed Wavelength Assignment: Unidirectional, Limited 1757 Converters 1759 In the case of wavelength converters, nodes with wavelength 1760 converters would need to make the decision as to whether to perform 1761 conversion. One indicator for this would be that the set of available 1762 wavelengths which is obtained via the intersection of the incoming 1763 label set and the output links available wavelengths is either null 1764 or deemed too small to permit successful completion. 1766 At this point the node would need to remember that it will apply 1767 wavelength conversion and will be responsible for assigning the 1768 wavelength on the previous lambda-contiguous segment when the RSVP-TE 1769 RESV message passes by. The node will pass on an enlarged label set 1770 reflecting only the limitations of the wavelength converter and the 1771 output link. The record route option in RVSP-TE signaling can be used 1772 to show where wavelength conversion has taken place. 1774 6.1.6. Distributed Wavelength Assignment: Bidirectional, No 1775 Converters 1777 There are potential issues in the case of a bi-directional lightpath 1778 which requires the use of the same lambda in both directions. The 1779 above procedure can be used to determine the available bidirectional 1780 lambda set if it is interpreted that the available label set is 1781 available in both directions. However, a problem, arises in that 1782 bidirectional LSPs setup, according to [RFC3471] Section 4.1. 1783 (Architectural Approaches to RWA), is indicated by the presence of an 1784 upstream label in the path message. 1786 However, until the intersection of the available label sets is 1787 obtained, e.g., at the destination node and the wavelength assignment 1788 algorithm has been run the upstream label information will not be 1789 available. Hence currently distributed wavelength assignment with 1790 bidirectional lightpaths is not supported. 1792 6.2. Implications for GMPLS Routing 1794 GMPLS routing [RFC4202] currently defines an interface capability 1795 descriptor for "lambda switch capable" (LSC) which can be used to 1796 describe the interfaces on a ROADM or other type of wavelength 1797 selective switch. In addition to the topology information typically 1798 conveyed via an IGP, it would be necessary to convey the following 1799 subsystem properties to minimally characterize a WSON: 1801 1. WDM Link properties (allowed wavelengths). 1803 2. Optical transmitters (wavelength range). 1805 3. ROADM/FOADM Properties (connectivity matrix, port wavelength 1806 restrictions). 1808 4. Wavelength converter properties (per network element, may change if 1809 a common limited shared pool is used). 1811 This information is modeled in detail in [WSON-Info] and a compact 1812 encoding is given in [WSON-Encode]. 1814 6.2.1. Electro-Optical Element Signal Compatibility 1816 In network scenarios where signal compatibility is a concern it is 1817 necessary to add parameters to our existing node and link models to 1818 take into account electro-optical input constraints, output 1819 constraints, and the signal processing capabilities of a NE in path 1820 computations. 1822 Input constraints: 1824 1. Permitted optical tributary signal classes: A list of optical 1825 tributary signal classes that can be processed by this network 1826 element or carried over this link. (configuration type) 1827 2. Acceptable FEC codes. (configuration type) 1828 3. Acceptable Bit Rate Set: a list of specific bit rates or bit rate 1829 ranges that the device can accommodate. Coarse bit rate info is 1830 included with the optical tributary signal class restrictions. 1831 4. Acceptable G-PID list: a list of G-PIDs corresponding to the 1832 "client" digital streams that is compatible with this device. 1834 Note that since the bit rate of the signal does not change over the 1835 LSP. This can be made as an LSP parameter and hence this information 1836 would be available for any NE that needs to use it for configuration. 1837 Hence it is not necessary to have "configuration type" for the NE 1838 with respect to bit rate. 1840 Output constraints: 1842 1. Output modulation: (a)same as input, (b) list of available types 1844 2. FEC options: (a) same as input, (b) list of available codes 1846 Processing capabilities: 1848 1. Regeneration: (a) 1R, (b) 2R, (c) 3R, (d)list of selectable 1849 regeneration types 1851 2. Fault and performance monitoring: (a) G-PID particular 1852 capabilities, (b) optical performance monitoring capabilities. 1854 Note that such parameters could be specified on an (a) Network 1855 element wide basis, (b) a per port basis, (c) on a per regenerator 1856 basis. Typically such information has been on a per port basis, 1857 e.g., the GMPLS interface switching capability descriptor [RFC4202]. 1859 6.2.2. Wavelength-Specific Availability Information 1861 For wavelength assignment it is necessary to know which specific 1862 wavelengths are available and which are occupied if a combined RWA 1863 process or separate WA process is run as discussed in sections 4.1.1. 1864 4.1.2. This is currently not possible with GMPLS routing extensions. 1866 In the routing extensions for GMPLS [RFC4202], requirements for 1867 layer-specific TE attributes are discussed. The RWA problem for 1868 optical networks without wavelength converters imposes an additional 1869 requirement for the lambda (or optical channel) layer: that of 1870 knowing which specific wavelengths are in use. Note that currentDWDM 1871 systems range from 16 channels to 128 channels with advanced 1872 laboratory systems with as many as 300 channels. Given these channel 1873 limitations and if the approach of a global wavelength to label 1874 mapping or furnishing the local mappings to the PCEs is taken then 1875 representing the use of wavelengths via a simple bit-map is feasible 1876 [WSON-Encode]. 1878 6.2.3. WSON Routing Information Summary 1880 The following table summarizes the WSON information that could be 1881 conveyed via GMPLS routing and attempts to classify that information 1882 as to its static or dynamic nature and whether that information would 1883 tend to be associated with either a link or a node. 1885 Information Static/Dynamic Node/Link 1886 ------------------------------------------------------------------ 1887 Connectivity matrix Static Node 1888 Per port wavelength restrictions Static Node(1) 1889 WDM link (fiber) lambda ranges Static Link 1890 WDM link channel spacing Static Link 1891 Optical transmitter range Static 1892 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 the RWA problem can be computationally intensive. 1930 Such computationally intensive path computations and optimizations 1931 were 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 lightpath constraints and characteristics, (b) computation 1940 architectures. 1942 6.3.1. Lightpath 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 lightpath 1946 requests are encountered: 1948 o Batch optimization, multiple lightpaths requested at one time 1949 (PCE-GCO). 1951 o Lightpath(s) and backup lightpath(s) requested at one time (PCEP). 1953 o Single lightpath requested at a time (PCEP). 1955 PCEP and PCE-GCO can be readily enhanced to support all of the 1956 potential models of RWA computation. 1958 Lightpath constraints include: 1960 o Bidirectional Assignment of wavelengths. 1962 o Possible simultaneous assignment of wavelength to primary and 1963 backup paths. 1965 o Tuning range constraint on optical transmitter. 1967 6.3.2. Electro-Optical Element Signal Compatibility 1969 When requesting a path computation to PCE, the PCC should be able to 1970 indicate the following: 1972 o The G-PID type of an LSP. 1974 o The signal attributes at the transmitter (at the source): (i) 1975 modulation type; (ii) FEC type. 1977 o The signal attributes at the receiver (at the sink): (i) 1978 modulation type; (ii) FEC type. 1980 The PCE should be able to respond to the PCC with the following: 1982 o The conformity of the requested optical characteristics associated 1983 with the resulting LSP with the source, sink and NE along the LSP. 1985 o Additional LSP attributes modified along the path (e.g., 1986 modulation format change, etc.). 1988 6.3.3. Discovery of RWA Capable PCEs 1990 The algorithms and network information needed for solving the RWA are 1991 somewhat specialized and computationally intensive hence not all PCEs 1992 within a domain would necessarily need or want this capability. 1993 Hence, it would be useful via the mechanisms being established for 1994 PCE discovery [RFC5088] to indicate that a PCE has the ability to 1995 deal with the RWA problem. Reference [RFC5088] indicates that a sub- 1996 TLV could be allocated for this purpose. 1998 Recent progress on objective functions in PCE [RFC5541] would allow 1999 the operators to flexibly request differing objective functions per 2000 their need and applications. For instance, this would allow the 2001 operator to choose an objective function that minimizes the total 2002 network cost associated with setting up a set of paths concurrently. 2003 This would also allow operators to choose an objective function that 2004 results in a most evenly distributed link utilization. 2006 This implies that PCEP would easily accommodate wavelength selection 2007 algorithm in its objective function to be able to optimize the path 2008 computation from the perspective of wavelength assignment if chosen 2009 by the operators. 2011 7. Security Considerations 2013 This document has no requirement for a change to the security models 2014 within GMPLS and associated protocols. That is the OSPF-TE, RSVP-TE, 2015 and PCEP security models could be operated unchanged. 2017 However satisfying the requirements for RWA using the existing 2018 protocols may significantly affect the loading of those protocols. 2019 This makes the operation of the network more vulnerable to denial of 2020 service attacks. Therefore additional care maybe required to ensure 2021 that the protocols are secure in the WSON environment. 2023 Furthermore the additional information distributed in order to 2024 address the RWA problem represents a disclosure of network 2025 capabilities that an operator may wish to keep private. Consideration 2026 should be given to securing this information. 2028 8. IANA Considerations 2030 This document makes no request for IANA actions. 2032 9. Acknowledgments 2034 The authors would like to thank Adrian Farrel for many helpful 2035 comments that greatly improved the contents of this draft. 2037 This document was prepared using 2-Word-v2.0.template.dot. 2039 10. References 2041 10.1. Normative References 2043 [RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching 2044 (GMPLS) Signaling Functional Description", RFC 3471, 2045 January 2003. 2047 [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label 2048 Switching (GMPLS) Signaling Resource ReserVation Protocol- 2049 Traffic Engineering (RSVP-TE) Extensions", RFC 3473, 2050 January 2003. 2052 [RFC3945] Mannie, E. "Generalized Multi-Protocol Label Switching 2053 (GMPLS) Architecture", RFC 3945, October 2004. 2055 [RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in Support 2056 of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 2057 4202, October 2005. 2059 [RFC4328] Papadimitriou, D., "Generalized Multi-Protocol Label 2060 Switching (GMPLS) Signaling Extensions for G.709 Optical 2061 Transport Networks Control", RFC 4328, January 2006. 2063 [G.694.1] ITU-T Recommendation G.694.1, "Spectral grids for WDM 2064 applications: DWDM frequency grid", June, 2002. 2066 [RFC5088] J.L. Le Roux, J.P. Vasseur, Yuichi Ikejiri, and Raymond 2067 Zhang, "OSPF protocol extensions for Path Computation 2068 Element (PCE) Discovery", January 2008. 2070 [RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux, 2071 M., and D. Brungard, "Requirements for GMPLS-Based Multi- 2072 Region and Multi-Layer Networks (MRN/MLN)", RFC 5212, July 2073 2008. 2075 [RFC5557] Y. Lee, J.L. Le Roux, D. King, and E. Oki, "Path 2076 Computation Element Communication Protocol (PCECP) 2077 Requirements and Protocol Extensions In Support of Global 2078 Concurrent Optimization", RFC 5557, July 2009. 2080 [RFC5420] Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A. 2081 Ayyangarps, "Encoding of Attributes for MPLS LSP 2082 Establishment Using Resource Reservation Protocol Traffic 2083 Engineering (RSVP-TE)", RFC 5420, February 2009. 2085 [RFC5440] J.P. Vasseur and J.L. Le Roux (Editors), "Path Computation 2086 Element (PCE) Communication Protocol (PCEP)", RFC 5440, May 2087 2009. 2089 [RFC5541] J.L. Le Roux, J.P. Vasseur, and Y. Lee, "Encoding of 2090 Objective Functions in Path Computation Element (PCE) 2091 communication and discovery protocols", RFC 5541, July 2092 2009. 2094 [WSON-Compat] G. Bernstein, Y. Lee, B. Mack-Crane, "WSON Signal 2095 Characteristics and Network Element Compatibility 2096 Constraints for GMPLS", draft-bernstein-ccamp-wson- 2097 compatibility, work in progress. 2099 [WSON-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "Routing 2100 and Wavelength Assignment Information Encoding for 2101 Wavelength Switched Optical Networks", draft-ietf-ccamp- 2102 wson-encode, work in progress. 2104 [Gen-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "General 2105 Network Element Constraint Encoding for GMPLS Controlled 2106 Networks", draft-ietf-ccamp-general-constraint-encode, work 2107 in progress. 2109 [WSON-Imp] Y. Lee, G. Bernstein, D. Li, G. Martinelli, "A Framework 2110 for the Control of Wavelength Switched Optical Networks 2111 (WSON) with Impairments", draft-ietf-ccamp-wson- 2112 impairments, work in progress. 2114 [WSON-Info] Y. Lee, G. Bernstein, D. Li, W. Imajuku, "Routing and 2115 Wavelength Assignment Information for Wavelength Switched 2116 Optical Networks", draft-bernstein-ccamp-wson-info, work in 2117 progress 2119 10.2. Informative References 2121 [RFC4655] Farrel, A., Vasseur, JP., and Ash, J., "A Path Computation 2122 Element (PCE)-Based Architecture ", RFC 4655, August 2006. 2124 [Otani] T. Otani, H. Guo, K. Miyazaki, D. Caviglia, "Generalized 2125 Labels of Lambda-Switching Capable Label Switching Routers 2126 (LSR)", work in progress: draft-otani-ccamp-gmpls-g-694- 2127 lambda-labels, work in progress. 2129 [G.652] ITU-T Recommendation G.652, Characteristics of a single-mode 2130 optical fibre and cable, June 2005. 2132 [G.653] ITU-T Recommendation G.653, Characteristics of a dispersion- 2133 shifted single-mode optical fibre and cable, December 2006. 2135 [G.654] ITU-T Recommendation G.654, Characteristics of a cut-off 2136 shifted single-mode optical fibre and cable, December 2006. 2138 [G.655] ITU-T Recommendation G.655, Characteristics of a non-zero 2139 dispersion-shifted single-mode optical fibre and cable, 2140 March 2006. 2142 [G.656] ITU-T Recommendation G.656, Characteristics of a fibre and 2143 cable with non-zero dispersion for wideband optical 2144 transport, December 2006. 2146 [G.671] ITU-T Recommendation G.671, Transmission characteristics of 2147 optical components and subsystems, January 2005. 2149 [G.872] ITU-T Recommendation G.872, Architecture of optical 2150 transport networks, November 2001. 2152 [G.959.1] ITU-T Recommendation G.959.1, Optical Transport Network 2153 Physical Layer Interfaces, March 2006. 2155 [G.694.1] ITU-T Recommendation G.694.1, Spectral grids for WDM 2156 applications: DWDM frequency grid, June 2002. 2158 [G.694.2] ITU-T Recommendation G.694.2, Spectral grids for WDM 2159 applications: CWDM wavelength grid, December 2003. 2161 [G.Sup39] ITU-T Series G Supplement 39, Optical system design and 2162 engineering considerations, February 2006. 2164 [G.Sup43] ITU-T Series G Supplement 43, Transport of IEEE 10G base-R 2165 in optical transport networks (OTN), November 2006. 2167 [Imajuku] W. Imajuku, Y. Sone, I. Nishioka, S. Seno, "Routing 2168 Extensions to Support Network Elements with Switching 2169 Constraint", work in progress: draft-imajuku-ccamp-rtg- 2170 switching-constraint. 2172 11. Contributors 2174 Snigdho Bardalai 2175 Fujitsu 2177 Email: Snigdho.Bardalai@us.fujitsu.com 2179 Diego Caviglia 2180 Ericsson 2181 Via A. Negrone 1/A 16153 2182 Genoa Italy 2184 Phone: +39 010 600 3736 2185 Email: diego.caviglia@(marconi.com, ericsson.com) 2187 Daniel King 2188 Old Dog Consulting 2189 UK 2191 Email: daniel@olddog.co.uk 2193 Itaru Nishioka 2194 NEC Corp. 2195 1753 Simonumabe, Nakahara-ku 2196 Kawasaki, Kanagawa 211-8666 2197 Japan 2199 Phone: +81 44 396 3287 2200 Email: i-nishioka@cb.jp.nec.com 2202 Lyndon Ong 2203 Ciena 2205 Email: Lyong@Ciena.com 2207 Pierre Peloso 2208 Alcatel-Lucent 2209 Route de Villejust, 91620 Nozay 2210 France 2212 Email: pierre.peloso@alcatel-lucent.fr 2214 Jonathan Sadler 2215 Tellabs 2216 Email: Jonathan.Sadler@tellabs.com 2218 Dirk Schroetter 2219 Cisco 2220 Email: dschroet@cisco.com 2222 Jonas Martensson 2223 Acreo 2224 Electrum 236 2225 16440 Kista, Sweden 2226 Email:Jonas.Martensson@acreo.se 2228 Author's Addresses 2230 Greg M. Bernstein (ed.) 2231 Grotto Networking 2232 Fremont California, USA 2234 Phone: (510) 573-2237 2235 Email: gregb@grotto-networking.com 2237 Young Lee (ed.) 2238 Huawei Technologies 2239 1700 Alma Drive, Suite 100 2240 Plano, TX 75075 2241 USA 2243 Phone: (972) 509-5599 (x2240) 2244 Email: ylee@huawei.com 2246 Wataru Imajuku 2247 NTT Network Innovation Labs 2248 1-1 Hikari-no-oka, Yokosuka, Kanagawa 2249 Japan 2251 Phone: +81-(46) 859-4315 2252 Email: imajuku.wataru@lab.ntt.co.jp 2254 Intellectual Property Statement 2256 The IETF Trust takes no position regarding the validity or scope of 2257 any Intellectual Property Rights or other rights that might be 2258 claimed to pertain to the implementation or use of the technology 2259 described in any IETF Document or the extent to which any license 2260 under such rights might or might not be available; nor does it 2261 represent that it has made any independent effort to identify any 2262 such rights. 2264 Copies of Intellectual Property disclosures made to the IETF 2265 Secretariat and any assurances of licenses to be made available, or 2266 the result of an attempt made to obtain a general license or 2267 permission for the use of such proprietary rights by implementers or 2268 users of this specification can be obtained from the IETF on-line IPR 2269 repository at http://www.ietf.org/ipr 2271 The IETF invites any interested party to bring to its attention any 2272 copyrights, patents or patent applications, or other proprietary 2273 rights that may cover technology that may be required to implement 2274 any standard or specification contained in an IETF Document. Please 2275 address the information to the IETF at ietf-ipr@ietf.org. 2277 Disclaimer of Validity 2279 All IETF Documents and the information contained therein are provided 2280 on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 2281 REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE 2282 IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL 2283 WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY 2284 WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE 2285 ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS 2286 FOR A PARTICULAR PURPOSE. 2288 Acknowledgment 2290 Funding for the RFC Editor function is currently provided by the 2291 Internet Society. 2293 12. Appendix A Revision History 2295 This appendix to be removed before publication as an RFC. 2297 A.1 Changes from 00 2299 o Added new first level section on modeling examples and control 2300 plane use cases. 2302 o Added new third level section on wavelength converter pool 2303 modeling 2305 o Editorial clean up of English and updated references. 2307 A.2 Changes from 01 2309 Fixed error in wavelength converter pool example. 2311 A.3 Changes from 02 2313 Updated the abstract to emphasize the focus of this draft and 2314 differentiate it from WSON impairment [WSON-Imp] and WSON 2315 compatibility [WSON-Compat] drafts. 2317 Added references to [WSON-Imp] and [WSON-Compat]. 2319 Updated the introduction to explain the relationship between this 2320 document and the [WSON-Imp] and [WSON-Compat] documents. 2322 In section 3.1 removed discussion of optical impairments in fibers. 2324 Merged section 3.2.2 and section 3.2.3. Deferred much of the 2325 discussion of signal types and standards to [WSON-Compat]. 2327 In section 3.4 on Wavelength converters removed paragraphs dealing 2328 with signal compatibility discussion as this is addressed in [WSON- 2329 Compat]. 2331 In section 6.1 removed discussion of signaling extensions to deal 2332 with different WSON signal types. This is deferred to [WSON-Compat]. 2334 In section 6 removed discussion of "Need for Wavelength Specific 2335 Maximum Bandwidth Information". 2337 In section 6 removed discussion of "Relationship to link bundling and 2338 layering". 2340 In section 6 removed discussion of "Computation Architecture 2341 Implications" as this material was redundant with text that occurs 2342 earlier in the document. 2344 In section 6 removed discussion of "Scaling Implications" as this 2345 material was redundant with text that occurs earlier in the document. 2347 A.4 Changes from 03 2349 In Section 3.3.1 added 4-degree ROADM example and its connectivity 2350 matrix. 2352 A.5 Changes from 04 2354 Added and enhanced sections on signal type and network element 2355 compatibility. 2357 Merged section 3.2.1 into section 3.2. 2359 Created new section 3.3 on Optical signals with material from [WSON- 2360 Compat]. 2362 Created new section 3.5 on Electro-Optical systems with material from 2363 [WSON-Compat]. 2365 Created new section 3.7 on Characterizing Electro-Optical Network 2366 Elements with material from [WSON-Compat]. 2368 Created new section 5.5 on Electro-Optical Networking Scenarios with 2369 material from [WSON-Compat]. 2371 Created new section 6.1.2 on WSON Signals and Network Element 2372 Processing with material from [WSON-Compat]. 2374 Created new section 6.3.2. Electro-Optical Related PCEP Extensions 2375 with material from [WSON-Compat]. 2377 A.6 Changes from 05 2379 Removal of Section 1.2; Removal of section on lightpath temporal 2380 characteristics; Removal of details on wavelength assignment 2381 algorithms; Removal of redundant summary in section 6.