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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Qilei Wang 3 Internet-Draft Xihua Fu 4 Intended status: Standards Track ZTE Corporation 5 Expires: September 12, 2012 Mar 11, 2012 7 Framework for GMPLS Control of Flexible Grid Network 8 draft-wang-ccamp-gmpls-flexigrid-framework-01.txt 10 Abstract 12 This document provides a framework for applying Generalized Multi- 13 Protocol Label Switching (GMPLS) and the Path Computation Element 14 (PCE) architecture to control the flexible grid network base on the 15 Wavelength Switched Optical Networks (WSONs). GMPLS control of WSON 16 which is addressed in RFC6163 is out of the scope of this document. 18 This document focuses on the topological elements changes and new 19 path selection constraints that flexible grid technology takes. 20 Impairments related technology is not covered in this document. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on September 12, 2012. 39 Copyright Notice 41 Copyright (c) 2012 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 1.1. Conventions used in this document . . . . . . . . . . . . 3 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 3. Flexible Grid Networks . . . . . . . . . . . . . . . . . . . . 4 60 3.1. Flexible Grid Network . . . . . . . . . . . . . . . . . . 4 61 3.2. WDM Links . . . . . . . . . . . . . . . . . . . . . . . . 5 62 3.3. Optical Transmitters and Receivers . . . . . . . . . . . . 5 63 3.4. Optical Signals in Flexible Grid Network . . . . . . . . . 6 64 3.4.1. Optical Tributary Signals . . . . . . . . . . . . . . 7 65 3.4.2. WSON Signal Characteristics . . . . . . . . . . . . . 7 66 3.5. ROADMs, OXCs, Splitters, Combiners, and FOADMs . . . . . . 7 67 3.5.1. Reconfigurable Optical Add/Drop Multiplexers, OXCs 68 and FOADM . . . . . . . . . . . . . . . . . . . . . . 8 69 3.5.2. Splitters and Combiners . . . . . . . . . . . . . . . 9 70 3.6. Electro-Optical Systems . . . . . . . . . . . . . . . . . 9 71 4. Routing and wavelength Assignment in flexible grid network . . 10 72 5. GMPLS and PCE Control . . . . . . . . . . . . . . . . . . . . 11 73 5.1. Extension to GMPLS Signaling . . . . . . . . . . . . . . . 11 74 5.2. Extension to GMPLS Routing . . . . . . . . . . . . . . . . 11 75 5.2.1. Available Wavelength Range . . . . . . . . . . . . . . 12 76 5.2.2. Port Label Restriction . . . . . . . . . . . . . . . . 12 77 5.3. Optical Path Computation and Implications for PCE . . . . 13 78 5.3.1. Optical Path Constraints and Electro-Optical 79 Element Signal Compatibility . . . . . . . . . . . . . 13 80 5.3.2. Discovery of RWA-Capable PCEs . . . . . . . . . . . . 14 81 5.3.3. Use of GCO . . . . . . . . . . . . . . . . . . . . . . 14 82 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 83 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 84 7.1. Normative References . . . . . . . . . . . . . . . . . . . 14 85 7.2. Informative References . . . . . . . . . . . . . . . . . . 14 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 88 1. Introduction 90 Flexible grid is a new DWDM application which is defined in the 91 newest version of [G.694.1]. Compared to traditional fixed grid 92 network, a flexible grid network can select its data channels with 93 arbitrary slot width, and mainly be used to setup path with higher 94 bitrates (e.g., 100G or 400G or higher). whereas traditional fixed 95 grid DWDM technology always uses fixed slot width and is mainly used 96 to setup path with lower bitrates signals. Flexible grid network is 97 also a WDM-based optical network in which switching is performed 98 selectively based on the center wavelength of optical channels ,which 99 means flexible grid channels can be represented as a lambda capable 100 switching LSP by center wavelength and slot width from the control 101 plane perspective. 103 Wavelength Switched Optical Network (WSON) which is addressed in 104 [RFC6163] is the application of Generalized Multi-Protocol Label 105 Switching (GMPLS) [RFC3945] operation to traditional fixed grid WDM 106 network. As flexible grid network is a new WDM network which evolves 107 from traditional fixed grid network, GMPLS also can be used to 108 operate flexible grid network. Similar to fixed grid network, 109 flexible grid network is also constructed from subsystems that 110 include Wavelength Division Multiplexing (WDM) links, tunable 111 transmitters and receivers, Reconfigurable Optical Add/Drop 112 Multiplexers (ROADMs), wavelength converters, and electro-optical 113 network elements, which have flexible grid characteristics. WSON 114 specific descriptions are addressed in [RFC6163] and are out of the 115 scope of this document. People who are interested in this document 116 are supposed to be familiar with [RFC6163]. 118 This document provides a framework for applying the GMPLS 119 architecture and protocols [RFC3945] and the PCE architecture 120 [RFC4655] to the control and operation of flexible grid networks. In 121 order to help GMPLS and PCE use for flexible grid network, this 122 document first focuses on the subsystems and characteristics 123 information that flexible grid network brings and then modeled the 124 characteristics information by GMPLS and PCE. This work will help 125 facilitate the development of protocol solution models and protocol 126 extensions within the GMPLS and PCE protocol families. 128 1.1. Conventions used in this document 130 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 131 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 132 document are to be interpreted as described in [RFC2119]. 134 2. Terminology 136 o Flexible Grid: a new WDM technology different from traditional 137 fixed grid DWDM technology defined with the aim of allowing 138 flexible optical spectrum management, in which the Slot Width of 139 the wavelength ranges allocated to different channels are flexible 140 (variable sized). 142 o Wavelength Range: [RFC6163] gives a description of this 143 terminology.Wavelength range given a mapping between labels and 144 the ITU-T grids, each range could be expressed in terms of a 145 tuple, (lambda1, lambda2) or (freq1, freq2), where the lambdas or 146 frequencies can be represented by 32-bit integers. 148 o Frequency slot: The definition in [G.694.1] is shown here. The 149 frequency range allocated to a channel and unavailable to other 150 channels within a flexible grid. A frequency slot is defined by 151 its nominal central frequency and its slot width. 153 o Slot width: The full width of a frequency slot in a flexible grid. 155 3. Flexible Grid Networks 157 Wavelength Switched Optical Network (WSON) related documents cover 158 the constraints information that needs to be considered in the 159 process of path computation. Emergence of flexible grid DWDM 160 technology raises some new characteristics and these new 161 characteristics should be modeled by GMPLS and PCE from the 162 perspective of contral plane in order to help path computation. This 163 document mainly focus on the flexible grid subsystems' 164 characteristics information and constraints information that impact 165 the flexible grid path selection process (i.e. wavelength selection). 166 Subsequent sections review and model flexible grid characteristics 167 that need to be emphasized by control plane and these sections follow 168 the sequence of the section addressed in [RFC6163]. 170 3.1. Flexible Grid Network 172 As described in the newest version of [G.694.1], flexible DWDM grid 173 allows frequency slots have a nominal central frequency (in THz) 174 defined by: 193.1 + n x 0.00625 where n is a positive or negative 175 integer including 0 and 0.00625 is the nominal central frequency 176 granularity in THz and a slot width defined by: 12.5 x m where m is a 177 positive integerand 12.5 is the slot width granularity in GHz. Any 178 combination of frequency slots is allowed as long as no two frequency 179 slots overlap. 181 3.2. WDM Links 183 According to the review of the newest version of [G.694.1], the 184 nominal central frequencies for the flexible grid network are defined 185 with a granularity of 6.25 GHz and the frequency slot widths are 186 defined as a multiple of 12.5 GHz. A label representation which 187 includes the information of central frequency and slot width is 188 needed to provides a common label format to be used in signaling 189 optical paths. The flexible grid labels can also be used to describe 190 WDM links, ROADM ports, and wavelength converters for the purposes of 191 path selection. 193 As described in section 3.1 of [RFC 6163], putting WDM over different 194 types of fiber require significant engineering and a fairly limited 195 range of wavelengths. Parameters that include wavelength range and 196 channel spacing is needed to perform basic, impairment-unaware 197 modeling of a WDM link. 199 o Wavelength range: wavelength range can be used to give a mapping 200 between labels and the flexible grid and each range could be 201 expressed in terms of a tuple,(lambda1, lambda2) or (freq1, 202 freq2). Maybe new label representation is needed to describe 203 wavelength range. 205 o Channel Spacing: since flexible grid can provide a granularity of 206 6.25GHz, this new channel spacing value needs to be added. 208 In addition to the wavelength range and channel spacing, indication 209 SHOULD also be added to indicate the link support flexible grid DWDM 210 technology. 212 As indicated in [RFC6163], this information is relatively statically 213 for a particular link as changes to these properties generally 214 require hardware upgrades. Such information may be used locally 215 during wavelength assignment via signaling. 217 3.3. Optical Transmitters and Receivers 219 Similar to WSON, flexible grid WDM optical systems make use of 220 coupled optical transmitters and receivers to setup LSC LSP. In the 221 case of an optical network without wavelength converters, an optical 222 path needs to be routed from source transmitter to sink receiver and 223 must use a single wavelength. Flexible grid brings some new 224 characteristics to transmitters and receivers compare to traditional 225 fixed grid characteristics like "Tunable", "Tuning range", "Tuning 226 time" and "Spectral characteristics and stability" which are 227 addressed in [RFC6163] for fixed grid. This section examines the new 228 characteristics that would impact optical transmitters and receivers 229 in the process of control plane path computation. Modeling 230 parameters for flexible grid optical transmitters and receivers from 231 the control plane perspective are: 233 o Tuning range: As described in [RFC6163], this is the frequency or 234 wavelength range over which the optics can be tuned. (lambda1, 235 lambda2) or (freq1, freq2) can be used to represent the wavelength 236 range, where lambda1 and lambda2 or freq1 and freq2 are the labels 237 representing the lower and upper bounds in wavelength. As nominal 238 central frequencies can't be figured out before the path setup in 239 flexible grid network and flexible grid label may be different 240 from fixed grid label, "Tuning range" may be encode with some 241 different format from traditional fixed grid technology. 243 o Slot width: this parameter indicates slot width needed by a 244 transmitter or receiver and SHOULD be considered in the process of 245 path computation. 247 When an end-to-end LSC LSP needs be setup, operator first sends a 248 path setup command which convey some characteristics information of 249 the LSP, such as bitrates, to the source node. Path setup request is 250 sent to path computation element to computes an end-to-end LSC LSP 251 with specific slot width information, which bases on the bitrates and 252 modulation format that transceiver and receiver support. 254 3.4. Optical Signals in Flexible Grid Network 256 Similar to the fixed grid swithing (e.g., WSON), the fundamental unit 257 of switching in flexible grid is also a "wavelength". The 258 transmitters and receivers in these networks will deal with one 259 wavelength at a time, while the switching systems themselves can deal 260 with multiple wavelengths at a time. Key non-impairment-related 261 parameters which are listed in [RFC6163] are shown below: 263 o (a) Minimum channel spacing (GHz) 265 o (b) Minimum and maximum central frequency 267 o (c) Bitrates/Line coding (modulation) of optical tributary signals 269 As described in [RFC6163], (a) and (b) are considered properties of 270 the link and restrictions on the GMPLS Labels while (c) is a property 271 of the "signal". For the purposes of modeling the flexible grid, new 272 parameters which are related to the properities of the link and 273 restrictions and property of "signal" SHOULD be considered: 275 o (d) Minimum and Maximum Slot Width 277 o (e) Slot Width 279 (d) is considered properties of the link and restrictions on the 280 GMPLS Labels, and description can be found in the following section. 281 (e) is a property of the "signal" and this property is determined by 282 the transmitter and may be changed if signal traverse an OEO. 284 3.4.1. Optical Tributary Signals 286 In [RFC6163], "optical tributary signal classes" are characterized by 287 a modulation format and bitrates range and both of them are key 288 parameters in characterizing the optical tributary signal. Note 289 that, with advances in technology, optical tributary signal classes 290 that support flexible grid would be added. 292 For optical tributary signals in flexible grid, bitrates range and 293 modulation format are still two key parameters, as a single 294 wavelength with central frequency and slot width used by a signal 295 sent from transmitter can be deduced from these two parameters base 296 on the available wavelength and slot width range from the source to 297 the destination. 299 3.4.2. WSON Signal Characteristics 301 Description about WSON signal characteristics in [RFC6163] also can 302 be applied to this document. Fundamental unit of switching in 303 flexible grid network is also "wavelength". WSON signal 304 characteristics like optical tributary signal class (modulation 305 format), forward error correction (FEC), central frequency 306 (wavelength), bitrates and general protocol identifier (G-PID) are 307 still used in flexible grid network in the process of path 308 computation and some more modulation formats and FECs may be added to 309 describe flexible grid network signal characteristics. 311 Except the parameter that have been included in [RFC6163], the 312 parameter slot width is also needed here to specify the slot width 313 that signal occupies. 315 3.5. ROADMs, OXCs, Splitters, Combiners, and FOADMs 317 This section mainly focuses on optical devices such as ROADMs, 318 Optical Cross-Connects (OXCs), splitters, combiners, and Fixed 319 Optical Add/Drop Multiplexers (FOADMs) which can be used in flexible 320 grid network and examines their parameters of these devices that can 321 be used in the process of control plane path computation. 323 3.5.1. Reconfigurable Optical Add/Drop Multiplexers, OXCs and FOADM 325 Tributary Side: E5 I5 E6 I6 326 O | O | 327 | | | | 328 | O | O 329 +-----------------------+ 330 |+-----+ +-----+| 331 Line side-1 --->||Split| |WSS-2||---> Line side-2 332 Input (I1) |+-----+ +-----+| Output (E2) 333 Line side-1 <---||WSS-1| |Split||<--- Line side-2 334 Output (E1) |+-----+ +-----+| Input (I2) 335 | ROADM | 336 |+-----+ +-----+| 337 Line side-3 --->||Split| |WSS-4||---> Line side-4 338 Input (I3) |+-----+ +-----+| Output (E4) 339 Line side-3 <---||WSS-3| |Split||<--- Line side-4 340 Output (E3) |+-----+ +-----+| Input (I4) 341 +-----------------------+ 342 | O | O 343 | | | | 344 O | O | 345 Tributary Side: E7 I7 E8 I8 347 Figure 1: ROADM 349 A picture is shown here to facilitate the description of ROADM. 350 ROADM is composed of WSSes (wavelength selective switch) and 351 splitters which are used massively in current WDM network. WSS can 352 be used to select the wavelength on the line side output port and 353 splitter can be used on the line side input port to split the income 354 wavelength. 356 Switched connectivity matrix is needed to show whether a wavelength 357 on input port can be connected to an output port internal. 359 Besides the switched connectivity matrix which is applied to line 360 side port and tributary side port included in [RFC6163], new 361 wavelength restriction of the line side port on a ROADM which are 362 brought by flexible grid are considered below: 364 o (a) Available wavelength range: 366 This parameter indicates the available wavelength that can be 367 allocated to a LSP. (lambda1, lambda2) or (freq1, freq2) can be 368 used to represent the available wavelength range. 370 o (b) Maximum/Minimum slot width that a port support 372 This is an inherent attribution of the network subsystems, like 373 WSS, and can be treated as port label restriction. Requirements 374 and descriptions about the restrictions information can be found 375 in [draft-wangl-ccamp-ospf-ext-constraint-flexi-grid]. For 376 flexible grid subsystems' ports, the possible values of slot width 377 are within the range [Minimum Slot Width, Maximum Slot Width] and 378 with the slot width granularity of 2 * C.S. (Channel Spacing). 379 The combination of C.S. and [Minimum Slot Width, Maximum Slot 380 Width] can represent any slot width that ROADM support. 382 o (c) Wavelength Range allocation 384 The whole wavelength that ROADM support can be partitioned into 385 several wavelength ranges, and one wavelength range can only be 386 used for paths setup with the specific bit rate and/or modulation 387 format. The advertisement of this restrictions information will 388 help reduce fragments in flexible grid network. Requirements 389 related description can be found in 390 [draft-wang-ccamp-flexible-grid-wavelength-range-ospf-te]. This 391 is an optional requirement. 393 These restrictions information can also be applied to fixed optical 394 Add/Drop Multiplexers. 396 3.5.2. Splitters and Combiners 398 Nothing is new except switched connectivity matrix and this has been 399 addressed in [RFC6163]. 401 3.6. Electro-Optical Systems 403 Some words can be found in [RFC6163]. OEO switches, wavelength 404 converters, and regenerators all share a similar property: they can 405 be more or less "transparent" to an "optical signal" depending on 406 their functionality and/or implementation. Properties can be applied 407 to flexible grid, and these properties can satisfy path computation 408 without taking any new characteristics into consideration. Modeling 409 of OEO switches, wavelength converters and regenerators can also be 410 applied to flexible grid. 412 Regenerator can be used to restore signal quality. Bitrates range 413 and modulation formats that the regenerator support need to be taken 414 into consideration to help path computation, whereas slot width do 415 not (May be someone will talk about slot width). If one regenerator 416 is designed to handle signal with specific bitrates and modulation 417 formats, then it would support the corresponding slot width because 418 slot width can be derived by modulation format and bitrates. Even if 419 the slot width is changed by the electro-optical systems due to the 420 change of modulation format, the slot width that has already changed 421 may not be explicitly specified because bitrates and modulation 422 format are explicitly specified. 424 4. Routing and wavelength Assignment in flexible grid network 426 This section briefly describes the constraints information of routing 427 and wavelength assignment in the flexible grid network. Similar to 428 WSON, the input to basic RWA in flexible grid network are the 429 requested optical path's source and destination, the network 430 topology, the locations and capabilities of any wavelength 431 converters, the wavelengths available on each optical link and port 432 label constraints information such as slot width range that a port 433 support and wavelength range partition information by bitrates and/or 434 modulation formats. The output that provided by RWA in flexible grid 435 network are an explicit route through ROADMs, a wavelength for 436 optical transmitter, the slot width that this wavelength occupies, 437 and a set of locations (generally associated with ROADMs or switches) 438 where wavelength conversion is to occur and the new wavelength to be 439 used on each component link after that point in the route.Similar to 440 WSON, an optical flexible grid path that from source to destination 441 also must use a single wavelength that is available along that path 442 without "colliding" with a wavelength used by any other optical path 443 that may share an optical fiber. 445 In [RFC6163], three different ways of performing RWA in conjunction 446 with the control plane are shown here: 448 1) Combined RWA 450 2) Separated R and WA (R + WA) 452 3) Routing and Distributed WA (R + DWA) 454 These ways can also be applied to flexible grid control plane path 455 computation. Related description about these three architectures can 456 be found in section 4.1 of [RFC6163]. 458 5. GMPLS and PCE Control 460 Flexible grid brings some new characteristics to WDM network, and 461 consequently WSON would add some extensions or change in order to 462 control the flexible grid network. Extensions to GMPLS signaling, 463 routing and PCE are described in this section. 465 5.1. Extension to GMPLS Signaling 467 Support for WSON signaling exists in [RFC3471], [RFC4328] and 468 [draft-ietf-ccamp-wson-signaling]. However, a number of practical 469 issues arise in the identification of wavelengths and signals in 470 wavelength assignment in flexible grid. 472 A mapping between label and wavelength is needed to simplify the 473 characterization of WDM links and WSON devices. The mapping like the 474 one described in [draft-farrkingel-ccamp-flexigrid-lambda-label] 475 provides label and wavelength mapping for communication between PCE 476 and WSON PCCs. Different LSP may occupy different slot width if 477 paths have different bitrates and modulation format in flexible grid 478 network. So in the flexible grid network, not only central frequency 479 is needed, but also slot width SHOULD be included to identify a 480 channel in the process of path setup in flexible grid network. 482 GMPLS Signaling should be able to convey the central frequency and 483 slot width information that a LSC LSP occupies. If the slot width is 484 changed due to the change of modulation format, signaling should also 485 be able to express this. Except methods that are specified in 486 [draft-farrkingel-ccamp-flexigrid-lambda-label], 487 [draft-hussain-ccamp-super-channel-label] and 488 [draft-zhang-ccamp-flexible-grid-rsvp-te-ext] also provide methods to 489 carry central frequency and slot width information in the process of 490 signaling. 492 Note: extension to GMPLS signaling SHOULD be compatible with current 493 signaling protocol. 495 5.2. Extension to GMPLS Routing 497 The following subsystem's properties are needed by IGP to minimally 498 characterize WSON, also these properties are needed to characterize 499 flexible grid control plane. This section addresses the constraints 500 information needed to model flexible grid from the control plane 501 perspective base on the Wavelength Switched Optical Network (WSON). 503 1) WDM link properties (allowed wavelengths) 505 2) Optical transmitters (wavelength range) 507 3) ROADM/FOADM properties (connectivity matrix, port wavelength 508 restrictions) 510 4) Wavelength converter properties (per network element, may change 511 if a common limited shared pool is used) 513 Here 1, 2 and 3 are re-considered in the flexible grid network. 515 5.2.1. Available Wavelength Range 517 Wavelengths available on WDM link and port of optical transmitters 518 are advertised through routing protocol, the wavelengths available 519 information can be used by path computation element to compute a 520 suitable end-to-end LSP. As different flexible grid channels always 521 have different slot widths and channels' central frequency position 522 and slot width can't be decided in advance, so mapping between label 523 and wavelength may not be able to use the representation similar to 524 [RFC6205] to represent every channel. Maybe new label formats and 525 representation of wavelength available are needed in routing protocol 526 to transfer IGP information between nodes and PCEs. Extensions to 527 label set field SHOULD be able to represent the wavelength available 528 validly in flexible grid network. Allowed wavelengths on WDM link 529 and wavelength range on optical transmitters neede to adapt to this 530 change.[draft-dhillon-ccamp-super-channel-ospfte-ext], 531 [draft-wangl-ccamp-ospf-ext-constraint-flexi-grid] and 532 [draft-zhang-ccamp-flexible-grid-ospf-ext] give some different 533 methods to represent the available wavelengths. 535 5.2.2. Port Label Restriction 537 Some new ROADM/FOADM properties brought by flexible grid need to be 538 advertised by routing protocol in order to help path computation. In 539 the section 3, properties of ROADM/FOADM are described as the port 540 label restrictions information. 542 The first one, maximum/minimum slot width supported on one port need 543 to be advertised. This slot width constraint information of a port 544 (i.e., available slot width range of a WSS) SHOULD be known by path 545 computation element in order to compute a suitable path. According 546 to [draft-wangl-ccamp-ospf-ext-constraint-flexi-grid], combination of 547 C.S. and [Minimum Slot Width, Maximum Slot Width] can represent any 548 slot width that ROADM support. LMP can be run between two neighbor 549 nodes to negotiate these attributes and related extension can be 550 found in [draft-li-ccamp-grid-property-lmp]. This is optional 551 because routing protocol can also be used to deal with it. 553 The second one, wavelength range allocation information of ROADM/ 554 FOADM needs to be advertised through routing protocol. Grouping of 555 wavelength of the same bitrates and/or modulation formats would help 556 reduce fragments. Channels in the same wavelength range with the 557 same bitrates looks almost like fixed grid technology, and they won't 558 generate much fragment in the path setup and release because every 559 channel use the same slot width. Requirements of wavelength range 560 allocation and protocol extensions can be found in 561 [draft-wang-ccamp-flexible-grid-wavelength-range-ospf-te]. 563 5.3. Optical Path Computation and Implications for PCE 565 Extensions to PCEP can be found in [draft-lee-pce-wson-rwa-ext] base 566 on Wavelength Switched Optical Network. Emergence of flexible grid 567 brings some extension to current draft. PCEP SHOULD be able to 568 support flexible grid path computation. 570 5.3.1. Optical Path Constraints and Electro-Optical Element Signal 571 Compatibility 573 Flexible grid may not change the computation architectures of WSON, 574 but new constraints information SHOULD be taken into consideration in 575 the process of path computation. According to the description in 576 [RFC6163], when requesting a path computation to PCE, the PCC should 577 be able to indicate: 579 1) The G-PID type of an LSP 581 2) The signal attributes at the transmitter and receiver. 583 And the PCE should be able to respond to the PCC with the following: 585 1) The conformity of the requested optical characteristics 586 associated with the resulting LSP with the source, sink, and NE 587 along the LSP. 589 2) Additional LSP attributes modified along the path. 591 3) Slot width of the LSP. This should be respond to the PCC as 592 flexible grid channels always have different slot widths. Slot 593 width information may be contained in the wavelength object which 594 is carried in PCRep message from PCE to PCC. 596 5.3.2. Discovery of RWA-Capable PCEs 598 Not all PCEs within a domain would necessarily need the capability of 599 flexible grid path computation. Therefore, it would be useful to 600 indicate that a PCE has the ability to deal with flexible grid via 601 the discovery mechanisms being established for PCE discovery in 602 [RFC5088]. Extensions to [RFC5088] are needed to achieve this goal. 604 5.3.3. Use of GCO 606 Though GCO is able to reduce the fragment of the wavelength or 607 spectrum, it is hard to be implemented in the network, because GCO 608 would involve massive LSPs and distrub current service. As fragment 609 can be reduced through early wavelength or spectrum allocation 610 planning, GCO maybe avoided. 612 6. Security Considerations 614 TBD 616 7. References 618 7.1. Normative References 620 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 621 Requirement Levels", BCP 14, RFC 2119, March 1997. 623 [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching 624 (GMPLS) Architecture", RFC 3945, October 2004. 626 7.2. Informative References 628 [G.694.1 v1] 629 International Telecommunications Union, "Draft revised 630 G.694.1 version 1.3". 632 [flexible-grid-ospf-ext] 633 Fatai Zhang, Xiaobing Zi, Ramon Casellas, O. Gonzalez de 634 Dios, and D. Ceccarelli, "GMPLS OSPF-TE Extensions in 635 support of Flexible-Grid in DWDM Networks", 636 draft-zhang-ccamp-flexible-grid-ospf-ext-00.txt . 638 [flexible-grid-requirements] 639 Fatai Zhang, Xiaobing Zi, O. Gonzalez de Dios, and Ramon 640 Casellas, "Requirements for GMPLS Control of Flexible 641 Grids", 642 draft-zhang-ccamp-flexible-grid-requirements-01.txt . 644 [flexible-grid-rsvp-te] 645 Fatai Zhang, O. Gonzalez de Dios, and D. Ceccarelli, 646 "RSVP-TE Signaling Extensions in support of Flexible 647 Grid", 648 draft-zhang-ccamp-flexible-grid-rsvp-te-ext-00.txt . 650 [flexigrid-lambda-label] 651 D. King, A. Farrel, Y. Li, F. Zhang, and R. Casellas, 652 "Generalized Labels for the Flexi-Grid in Lambda-Switch- 653 Capable (LSC) Label Switching Routers", 654 draft-farrkingel-ccamp-flexigrid-lambda-label-01.txt . 656 [ospf-ext-constraint-flexi-grid] 657 L Wang, Y Li, "OSPF Extensions for Routing Constraint 658 Encoding in Flexible-Grid Networks", 659 draft-wangl-ccamp-ospf-ext-constraint-flexi-grid-00.txt . 661 [super-channel-label] 662 Iftekhar Hussain, Abinder Dhillon, Zhong Pan, Marco Sosa 663 and Bert Basch, Steve Liu, Andrew G. Malis, "Generalized 664 Label for Super-Channel Assignment on Flexible Grid", 665 draft-hussain-ccamp-super-channel-label-02.txt . 667 [super-channel-ospfte] 668 Abinder Dhillon, Iftekhar Hussain, Rajan Rao, Marco Sosa, 669 "OSPFTE extension to support GMPLS for Flex Grid", 670 draft-dhillon-ccamp-super-channel-ospfte-ext-02.txt . 672 Authors' Addresses 674 Qilei Wang 675 ZTE Corporation 677 Email: wang.qilei@zte.com.cn 679 Xihua Fu 680 ZTE Corporation 681 ZTE Plaza, No.10, Tangyan South Road, Gaoxin District 682 Xi'an 683 P.R.China 685 Email: fu.xihua@zte.com.cn