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Casellas, Ed. 5 Expires: March 2, 2016 CTTC 6 August 30, 2015 8 Framework and Requirements for GMPLS-based control of Flexi-grid DWDM 9 networks 10 draft-ietf-ccamp-flexi-grid-fwk-07 12 Abstract 14 To allow efficient allocation of optical spectral bandwidth for high 15 bit-rate systems, the International Telecommunication Union 16 Telecommunication Standardization Sector (ITU-T) has extended its 17 Recommendations G.694.1 and G.872 to include a new dense wavelength 18 division multiplexing (DWDM) grid by defining a set of nominal 19 central frequencies, channel spacings and the concept of "frequency 20 slot". In such an environment, a data plane connection is switched 21 based on allocated, variable-sized frequency ranges within the 22 optical spectrum creating what is known as a flexible grid (flexi- 23 grid). 25 Given the specific characteristics of flexi-grid optical networks and 26 their associated technology, this document defines a framework and 27 the associated control plane requirements for the application of the 28 existing GMPLS architecture and control plane protocols to the 29 control of flexi-grid DWDM networks. The actual extensions to the 30 GMPLS protocols will be defined in companion documents. 32 Status of This Memo 34 This Internet-Draft is submitted in full conformance with the 35 provisions of BCP 78 and BCP 79. 37 Internet-Drafts are working documents of the Internet Engineering 38 Task Force (IETF). Note that other groups may also distribute 39 working documents as Internet-Drafts. The list of current Internet- 40 Drafts is at http://datatracker.ietf.org/drafts/current/. 42 Internet-Drafts are draft documents valid for a maximum of six months 43 and may be updated, replaced, or obsoleted by other documents at any 44 time. It is inappropriate to use Internet-Drafts as reference 45 material or to cite them other than as "work in progress." 47 This Internet-Draft will expire on March 2, 2016. 49 Copyright Notice 51 Copyright (c) 2015 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (http://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the Simplified BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 67 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 68 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 69 2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4 70 3. Overview of Flexi-grid Networks . . . . . . . . . . . . . . . 5 71 3.1. Flexi-grid in the Context of OTN . . . . . . . . . . . . 5 72 3.2. Flexi-grid Terminology . . . . . . . . . . . . . . . . . 6 73 3.2.1. Frequency Slots . . . . . . . . . . . . . . . . . . . 6 74 3.2.2. Media Layer Elements . . . . . . . . . . . . . . . . 8 75 3.2.3. Media Channels . . . . . . . . . . . . . . . . . . . 8 76 3.2.4. Optical Tributary Signals . . . . . . . . . . . . . . 9 77 3.2.5. Composite Media Channels . . . . . . . . . . . . . . 9 78 3.3. Hierarchy in the Media Layer . . . . . . . . . . . . . . 10 79 3.4. Flexi-grid Layered Network Model . . . . . . . . . . . . 10 80 3.4.1. DWDM Flexi-grid Enabled Network Element Models . . . 12 81 4. GMPLS Applicability . . . . . . . . . . . . . . . . . . . . . 12 82 4.1. General Considerations . . . . . . . . . . . . . . . . . 12 83 4.2. Consideration of TE Links . . . . . . . . . . . . . . . . 13 84 4.3. Consideration of LSPs in Flexi-grid . . . . . . . . . . . 15 85 4.4. Control Plane Modeling of Network Elements . . . . . . . 20 86 4.5. Media Layer Resource Allocation Considerations . . . . . 20 87 4.6. Neighbor Discovery and Link Property Correlation . . . . 24 88 4.7. Path Computation / Routing and Spectrum Assignment (RSA) 25 89 4.7.1. Architectural Approaches to RSA . . . . . . . . . . . 25 90 4.8. Routing and Topology Dissemination . . . . . . . . . . . 26 91 4.8.1. Available Frequency Ranges/Slots of DWDM Links . . . 27 92 4.8.2. Available Slot Width Ranges of DWDM Links . . . . . . 27 93 4.8.3. Spectrum Management . . . . . . . . . . . . . . . . . 27 94 4.8.4. Information Model . . . . . . . . . . . . . . . . . . 28 95 5. Control Plane Requirements . . . . . . . . . . . . . . . . . 29 96 5.1. Support for Media Channels . . . . . . . . . . . . . . . 29 97 5.1.1. Signaling . . . . . . . . . . . . . . . . . . . . . . 30 98 5.1.2. Routing . . . . . . . . . . . . . . . . . . . . . . . 30 99 5.2. Support for Media Channel Resizing . . . . . . . . . . . 31 100 5.3. Support for Logical Associations of Multiple Media 101 Channels . . . . . . . . . . . . . . . . . . . . . . . . 31 102 5.4. Support for Composite Media Channels . . . . . . . . . . 31 103 5.5. Support for Neighbor Discovery and Link Property 104 Correlation . . . . . . . . . . . . . . . . . . . . . . . 32 105 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 106 7. Security Considerations . . . . . . . . . . . . . . . . . . . 32 107 8. Manageability Considerations . . . . . . . . . . . . . . . . 33 108 9. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 109 10. Contributing Authors . . . . . . . . . . . . . . . . . . . . 34 110 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37 111 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 37 112 12.1. Normative References . . . . . . . . . . . . . . . . . . 37 113 12.2. Informative References . . . . . . . . . . . . . . . . . 38 114 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 40 116 1. Introduction 118 The term "Flexible grid" (flexi-grid for short) as defined by the 119 International Telecommunication Union Telecommunication 120 Standardization Sector (ITU-T) Study Group 15 in the latest version 121 of [G.694.1], refers to the updated set of nominal central 122 frequencies (a frequency grid), channel spacing and optical spectrum 123 management/allocation considerations that have been defined in order 124 to allow an efficient and flexible allocation and configuration of 125 optical spectral bandwidth for high bit-rate systems. 127 A key concept of flexi-grid is the "frequency slot"; a variable-sized 128 optical frequency range that can be allocated to a data connection. 129 As detailed later in the document, a frequency slot is characterized 130 by its nominal central frequency and its slot width which, as per 131 [G.694.1], is constrained to be a multiple of a given slot width 132 granularity. 134 Compared to a traditional fixed grid network, which uses fixed size 135 optical spectrum frequency ranges or frequency slots with typical 136 channel separations of 50 GHz, a flexible grid network can select its 137 media channels with a more flexible choice of slot widths, allocating 138 as much optical spectrum as required. 140 From a networking perspective, a flexible grid network is assumed to 141 be a layered network [G.872][G.800] in which the media layer is the 142 server layer and the optical signal layer is the client layer. In 143 the media layer, switching is based on a frequency slot, and the size 144 of a media channel is given by the properties of the associated 145 frequency slot. In this layered network, a media channel can 146 transport more than one Optical Tributary Signals (OTSi), as defined 147 later in this document. 149 A Wavelength Switched Optical Network (WSON), addressed in [RFC6163], 150 is a term commonly used to refer to the application/deployment of a 151 GMPLS-based control plane for the control (provisioning/recovery, 152 etc.) of a fixed grid wavelength division multiplexing (WDM) network 153 in which media (spectrum) and signal are jointly considered. 155 This document defines the framework for a GMPLS-based control of 156 flexi-grid enabled dense wavelength division multiplexing (DWDM) 157 networks (in the scope defined by ITU-T layered Optical Transport 158 Networks [G.872]), as well as a set of associated control plane 159 requirements. An important design consideration relates to the 160 decoupling of the management of the optical spectrum resource and the 161 client signals to be transported. 163 2. Terminology 165 Further terminology specific to flexi-grid networks can be found in 166 Section 3.2. 168 2.1. Requirements Language 170 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 171 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 172 document are to be interpreted as described in [RFC2119]. 174 While [RFC2119] describes interpretations of these key words in terms 175 of protocol specifications and implementations, they are used in this 176 document to describe design requirements for protocol extensions. 178 2.2. Abbreviations 180 FS: Frequency Slot 182 FSC: Fiber-Switch Capable 184 LSR: Label Switching Router 186 NCF: Nominal Central Frequency 188 OCh: Optical Channel 190 OCh-P: Optical Channel Payload 192 OTN: Optical Transport Network 193 OTSi: Optical Tributary Signal 195 OTSiG: OTSi Group is a set of OTSi 197 OCC: Optical Channel Carrier 199 PCE: Path Computation Element 201 ROADM: Reconfigurable Optical Add-Drop Multiplexer 203 SSON: Spectrum-Switched Optical Network 205 SWG: Slot Width Granularity 207 3. Overview of Flexi-grid Networks 209 3.1. Flexi-grid in the Context of OTN 211 [G.872] describes, from a network level, the functional architecture 212 of an OTN. It is decomposed into independent layer networks with 213 client/layer relationships among them. A simplified view of the OTN 214 layers is shown in Figure 1. 216 +----------------+ 217 | Digital Layer | 218 +----------------+ 219 | Signal Layer | 220 +----------------+ 221 | Media Layer | 222 +----------------+ 224 Figure 1: Generic OTN Overview 226 In the OTN layering context, the media layer is the server layer of 227 the optical signal layer. The optical signal is guided to its 228 destination by the media layer by means of a network media channel. 229 In the media layer, switching is based on a frequency slot. 231 In this scope, this document uses the term flexi-grid enabled DWDM 232 network to refer to a network in which switching is based on 233 frequency slots defined using the flexible grid, and covers mainly 234 the Media Layer as well as the required adaptations from the Signal 235 layer. The present document is thus focused on the control and 236 management of the media layer. 238 3.2. Flexi-grid Terminology 240 This section presents the definition of the terms used in flexi-grid 241 networks. More detail about these terms can be found in the ITU-T 242 Recommendations [G.694.1], [G.872]), [G.870], [G.8080], and 243 [G.959.1-2013]. 245 Where appropriate, this documents also uses terminology and 246 lexicography from [RFC4397]. 248 3.2.1. Frequency Slots 250 This subsection is focused on the frequency slot and related terms. 252 o Frequency Slot [G.694.1]: The frequency range allocated to a slot 253 within the flexible grid and unavailable to other slots. A 254 frequency slot is defined by its nominal central frequency and its 255 slot width. 257 o Nominal Central Frequency: Each of the allowed frequencies as per 258 the definition of flexible DWDM grid in [G.694.1]. The set of 259 nominal central frequencies can be built using the following 260 expression 262 f = 193.1 THz + n x 0.00625 THz 264 where 193.1 THz is ITU-T "anchor frequency" for transmission over 265 the C band, and n is a positive or negative integer including 0. 267 -5 -4 -3 -2 -1 0 1 2 3 4 5 <- values of n 268 ...+--+--+--+--+--+--+--+--+--+--+- 269 ^ 270 193.1 THz <- anchor frequency 272 Figure 2: Anchor Frequency and Set of Nominal Central Frequencies 274 o Nominal Central Frequency Granularity: This is the spacing between 275 allowed nominal central frequencies and it is set to 6.25 GHz 276 [G.694.1]. 278 o Slot Width Granularity (SWG): 12.5 GHz, as defined in [G.694.1]. 280 o Slot Width: The slot width determines the "amount" of optical 281 spectrum regardless of its actual "position" in the frequency 282 axis. A slot width is constrained to be m x SWG (that is, m x 283 12.5 GHz), where m is an integer greater than or equal to 1. 285 Frequency Slot 1 Frequency Slot 2 286 ------------- ------------------- 287 | | | | 288 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 289 ...--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--... 290 ------------- ------------------- 291 ^ ^ 292 Slot NCF = 193.1THz Slot NCF = 193.14375 THz 293 Slot width = 25 GHz Slot width = 37.5 GHz 294 n=0, m=2 n=7, m=3 296 Figure 3: Example Frequency Slots 298 * The symbol '+' represents the allowed nominal central 299 frequencies 301 * The '--' represents the nominal central frequency granularity 302 in units of 6.25 GHz 304 * The '^' represents the slot nominal central frequency 306 * The number on the top of the '+' symbol represents the 'n' in 307 the frequency calculation formula. 309 * The nominal central frequency is 193.1 THz when n equals to 310 zero. 312 o Effective Frequency Slot [G.870]: The effective frequency slot of 313 a media channel is that part of the frequency slots of the filters 314 along the media channel that is common to all of the filters' 315 frequency slots. Note that both the Frequency Slot and Effective 316 Frequency Slot are local terms. 318 o Figure 4 shows the effect of combining two filters along a 319 channel. The combination of frequency slot 1 and frequency slot 2 320 applied to the media channel is effective frequency slot shown. 322 Frequency Slot 1 323 ------------- 324 | | 325 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 326 ..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--... 328 Frequency Slot 2 329 ------------------- 330 | | 331 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 332 ..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--... 334 =============================================== 335 Effective Frequency Slot 336 ------------- 337 | | 338 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 339 ..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--... 341 Figure 4: Effective Frequency Slot 343 3.2.2. Media Layer Elements 345 o Media Element: A media element directs an optical signal or 346 affects the properties of an optical signal. It does not modify 347 the properties of the information that has been modulated to 348 produce the optical signal [G.870]. Examples of media elements 349 include fibers, amplifiers, filters, and switching matrices. 351 o Media Channel Matrixes: The media channel matrix provides flexible 352 connectivity for the media channels. That is, it represents a 353 point of flexibility where relationships between the media ports 354 at the edge of a media channel matrix may be created and broken. 355 The relationship between these ports is called a matrix channel. 356 (Network) Media Channels are switched in a Media Channel Matrix. 358 3.2.3. Media Channels 360 This section defines concepts such as (Network) Media Channel; the 361 mapping to GMPLS constructs (i.e., LSP) is detailed in Section 4. 363 o Media Channel: A media association that represents both the 364 topology (i.e., path through the media) and the resource 365 (frequency slot) that it occupies. As a topological construct, it 366 represents a frequency slot (an effective frequency slot) 367 supported by a concatenation of media elements (fibers, 368 amplifiers, filters, switching matrices...). This term is used to 369 identify the end-to-end physical layer entity with its 370 corresponding (one or more) frequency slots local at each link 371 filters. 373 o Network Media Channel: [G.870] defines the Network Media Channel 374 as a media channel that transports a single OTSi, defined next. 376 3.2.4. Optical Tributary Signals 378 o Optical Tributary Signal (OTSi) [G.959.1-2013]: The optical signal 379 that is placed within a network media channel for transport across 380 the optical network. This may consist of a single modulated 381 optical carrier or a group of modulated optical carriers or 382 subcarriers. To provide a connection between the OTSi source and 383 the OTSi sink the optical signal must be assigned to a network 384 media channel. 386 o OTSi Group (OTSiG): The set of OTSi that are carried by a group of 387 network media channels. Each OTSi is carried by one network media 388 channel. From a management perspective it SHOULD be possible to 389 manage both the OTSiG and a group of Network Media Channels as 390 single entities. 392 3.2.5. Composite Media Channels 394 o It is possible to construct an end-to-end media channel as a 395 composite of more than one network media channels. A composite 396 media channel carries a group of OTSi (i.e., OTSiG). Each OTSi is 397 carried by one network media channel. This group of OTSi are 398 carried over a single fibre. 400 o In this case, the effective frequency slots may be contiguous 401 (i.e., there is no spectrum between them that can be used for 402 other media channels) or non-contiguous. 404 o It is not currently envisaged that such composite media channels 405 may be constructed from slots carried on different fibers whether 406 those fibers traverse the same hop-by-hop path through the network 407 or not. 409 o Furthermore, it is not considered likely that a media channel may 410 be constructed from a different variation of slot composition on 411 each hop. That is, the slot composition (i.e., the group of OTSi 412 carried by the composite media channel) must be the same from one 413 end to the other of the media channel even if the specific slot 414 for each OTSi and the spacing among slots may vary hop by hop. 416 o How the signal is carried across such groups of network media 417 channels is out of scope for this document. 419 3.3. Hierarchy in the Media Layer 421 In summary, the concept of frequency slot is a logical abstraction 422 that represents a frequency range, while the media layer represents 423 the underlying media support. Media Channels are media associations, 424 characterized by their (effective) frequency slot, respectively; and 425 media channels are switched in media channel matrixes. From the 426 control and management perspective, a media channel can be logically 427 split into network media channels. 429 In Figure 5, a media channel has been configured and dimensioned to 430 support two network media channels, each of them carrying one OTSi. 432 Media Channel Frequency Slot 433 +-------------------------------X------------------------------+ 434 | | 435 | Frequency Slot Frequency Slot | 436 | +-----------X-----------+ +----------X-----------+ | 437 | | OTSi | | OTSi | | 438 | | o | | o | | 439 | | | | | | | | 440 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 441 --+---+---+---+---+---+---+---+---+---+---+---+--+---+---+---+---+-- 443 <- Network Media Channel-> <- Network Media Channel-> 445 <------------------------ Media Channel -----------------------> 447 X - Frequency Slot Central Frequency 449 o - Signal Central Frequency 451 Figure 5: Example of Media Channel / Network Media Channels and 452 Associated Frequency Slots 454 3.4. Flexi-grid Layered Network Model 456 In the OTN layered network, the network media channel transports a 457 single OTSi (see Figure 6) 458 | OTSi | 459 O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O 460 | | 461 | Channel Port Network Media Channel Channel Port | 462 O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O 463 | | 464 +--------+ +-----------+ +--------+ 465 | \ (1) | | (1) | | (1) / | 466 | \----|-----------------|-----------|-------------------|-----/ | 467 +--------+ Link Channel +-----------+ Link Channel +--------+ 468 Media Channel Media Channel Media Channel 469 Matrix Matrix Matrix 471 The symbol (1) indicates a Matrix Channel 473 Figure 6: Simplified Layered Network Model 475 Note that a particular example of OTSi is the OCh-P. Figure 7 shows 476 this specific example as defined in G.805 [G.805]. 478 OCh AP Trail (OCh) OCh AP 479 O- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O 480 | | 481 --- OCh-P OCh-P --- 482 \ / source sink \ / 483 + + 484 | OCh-P OCh-P Network Connection OCh-P | 485 O TCP - - - - - - - - - - - - - - - - - - - - - - - - - - -TCP O 486 | | 487 |Channel Port Network Media Channel Channel Port | 488 O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O 489 | | 490 +--------+ +-----------+ +---------+ 491 | \ (1) | OCh-P LC | (1) | OCh-P LC | (1) / | 492 | \----|-----------------|-----------|-----------------|------/ | 493 +--------+ Link Channel +-----------+ Link Channel +---------+ 494 Media Channel Media Channel Media Channel 495 Matrix Matrix Matrix 497 The symbol (1) indicates a Matrix Channel 499 Figure 7: Layered Network Model According to G.805 501 3.4.1. DWDM Flexi-grid Enabled Network Element Models 503 A flexible grid network is constructed from subsystems that include 504 WDM links, tunable transmitters, and receivers, (i.e, media elements 505 including media layer switching elements that are media matrices) as 506 well as electro-optical network elements. This is just the same as 507 in a fixed grid network except that each element has flexible grid 508 characteristics. 510 As stated in Clause 7 of [G.694.1] the flexible DWDM grid has a 511 nominal central frequency granularity of 6.25 GHz and a slot width 512 granularity of 12.5 GHz. However, devices or applications that make 513 use of the flexible grid might not be capable of supporting every 514 possible slot width or position. In other words, applications may be 515 defined where only a subset of the possible slot widths and positions 516 are required to be supported. For example, an application could be 517 defined where the nominal central frequency granularity is 12.5 GHz 518 (by only requiring values of n that are even) and that only requires 519 slot widths as a multiple of 25 GHz (by only requiring values of m 520 that are even). 522 4. GMPLS Applicability 524 The goal of this section is to provide an insight into the 525 application of GMPLS as a control mechanism in flexi-grid networks. 526 Specific control plane requirements for the support of flexi-grid 527 networks are covered in Section 5. This framework is aimed at 528 controlling the media layer within the OTN hierarchy, and controlling 529 the required adaptations of the signal layer. This document also 530 defines the term Spectrum-Switched Optical Network (SSON) to refer to 531 a Flexi-grid enabled DWDM network that is controlled by a GMPLS/PCE 532 control plane. 534 This section provides a mapping of the ITU-T G.872 architectural 535 aspects to GMPLS/Control plane terms, and considers the relationship 536 between the architectural concept/construct of media channel and its 537 control plane representations (e.g., as a TE link, as defined in 538 [RFC3945]). 540 4.1. General Considerations 542 The GMPLS control of the media layer deals with the establishment of 543 media channels that are switched in media channel matrices. GMPLS 544 labels are used to locally represent the media channel and its 545 associated frequency slot. Network media channels are considered a 546 particular case of media channels when the end points are 547 transceivers (that is, source and destination of an OTSi). 549 4.2. Consideration of TE Links 551 From a theoretical / abstract point of view, a fiber can be modeled 552 as having a frequency slot that ranges from minus infinity to plus 553 infinity. This representation helps understand the relationship 554 between frequency slots and ranges. 556 The frequency slot is a local concept that applies within a component 557 or element. When applied to a media channel, we are referring to its 558 effective frequency slot as defined in [G.872]. 560 The association sequence of the three components (i.e., a filter, a 561 fiber, and a filter), is a media channel in its most basic form. 562 From the control plane perspective this may modeled as a (physical) 563 TE-link with a contiguous optical spectrum. This can be represented 564 by saying that the portion of spectrum available at time t0 depends 565 on which filters are placed at the ends of the fiber and how they 566 have been configured. Once filters are placed we have a one-hop 567 media channel. In practical terms, associating a fiber with the 568 terminating filters determines the usable optical spectrum. 570 ---------------+ +-----------------+ 571 | | 572 +--------+ +--------+ 573 | | | | +--------- 574 ---o| =============================== o--| 575 | | Fiber | | | --\ /-- 576 ---o| | | o--| \/ 577 | | | | | /\ 578 ---o| =============================== o--| --/ \-- 579 | Filter | | Filter | | 580 | | | | +--------- 581 +--------+ +--------+ 582 | | 583 |------- Basic Media Channel ---------| 584 ---------------+ +-----------------+ 586 --------+ +-------- 587 |--------------------------------------| 588 LSR | TE link | LSR 589 |--------------------------------------| 590 +--------+ +-------- 592 Figure 8: (Basic) Media Channel and TE Link 594 Additionally, when a cross-connect for a specific frequency slot is 595 considered, the resulting media support of joining basic media 596 channels is still a media channel, i.e., a longer association 597 sequence of media elements and its effective frequency slot. In 598 other words, It is possible to "concatenate" several media channels 599 (e.g., patch on intermediate nodes) to create a single media channel. 601 The architectural construct resulting of the association sequence of 602 basic media channels and media layer matrix cross-connects can be 603 represented as (i.e., corresponds to) a Label Switched Path (LSP) 604 from a control plane perspective. 606 ----------+ +------------------------------+ +--------- 607 | | | | 608 +------+ +------+ +------+ +------+ 609 | | | | +----------+ | | | | 610 --o| ========= o--| |--o ========= o-- 611 | | Fiber | | | --\ /-- | | | Fiber | | 612 --o| | | o--| \/ |--o | | o-- 613 | | | | | /\ | | | | | 614 --o| ========= o--***********|--o ========= o-- 615 |Filter| |Filter| | | |Filter| |Filter| 616 | | | | | | | | 617 +------+ +------+ +------+ +------+ 618 | | | | 619 <- Basic Media -> <- Matrix -> <- Basic Media-> 620 |Channel| Channel |Channel| 621 ----------+ +------------------------------+ +--------- 623 <-------------------- Media Channel ----------------> 625 ------+ +---------------+ +------ 626 |------------------| |------------------| 627 LSR | TE link | LSR | TE link | LSR 628 |------------------| |------------------| 629 ------+ +---------------+ +------ 631 Figure 9: Extended Media Channel 633 Furthermore, if appropriate, the media channel can also be 634 represented as a TE link or Forwarding Adjacency (FA) [RFC4206], 635 augmenting the control plane network model. 637 ----------+ +------------------------------+ +--------- 638 | | | | 639 +------+ +------+ +------+ +------+ 640 | | | | +----------+ | | | | 641 --o| ========= o--| |--o ========= o-- 642 | | Fiber | | | --\ /-- | | | Fiber | | 643 --o| | | o--| \/ |--o | | o-- 644 | | | | | /\ | | | | | 645 --o| ========= o--***********|--o ========= o-- 646 |Filter| |Filter| | | |Filter| |Filter| 647 | | | | | | | | 648 +------+ +------+ +------+ +------+ 649 | | | | 650 ----------+ +------------------------------+ +--------- 652 <------------------------ Media Channel -----------> 654 ------+ +----- 655 |------------------------------------------------------| 656 LSR | TE link | LSR 657 |------------------------------------------------------| 658 ------+ +----- 660 Figure 10: Extended Media Channel / TE Link / FA 662 4.3. Consideration of LSPs in Flexi-grid 664 The flexi-grid LSP is a control plane representation of a media 665 channel. Since network media channels are media channels, an LSP may 666 also be the control plane representation of a network media channel 667 (without considering the adaptation functions). From a control plane 668 perspective, the main difference (regardless of the actual effective 669 frequency slot which may be dimensioned arbitrarily) is that the LSP 670 that represents a network media channel also includes the endpoints 671 (transceivers), including the cross-connects at the ingress and 672 egress nodes. The ports towards the client can still be represented 673 as interfaces from the control plane perspective. 675 Figure 11 shows an LSP routed between 3 nodes. The LSP is terminated 676 before the optical matrix of the ingress and egress nodes and can 677 represent a media channel. This case does not (and cannot) represent 678 a network media channel because it does not include (and cannot 679 include) the transceivers. 681 ---------+ +--------------------------------+ +-------- 682 | | | | 683 +------+ +------+ +------+ +------+ 684 | | | | +----------+ | | | | 685 -o| ========= o---| |---o ========= o- 686 | | Fiber | | | --\ /-- | | | Fiber | | 687 -o|>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>o- 688 | | | | | /\ | | | | | 689 -o| ========= o---***********|---o ========= o- 690 |Filter| |Filter| | | |Filter| |Filter| 691 | | | | | | | | 692 +------+ +------+ +------+ +------+ 693 | | | | 694 ---------+ +--------------------------------+ +-------- 696 >>>>>>>>>>>>>>>>>>>>>>>>>>>> LSP >>>>>>>>>>>>>>>>>>>>>>>> 697 -----+ +---------------+ +----- 698 |------------------| |----------------| 699 LSR | TE link | LSR | TE link | LSR 700 |------------------| |----------------| 701 -----+ +---------------+ +----- 703 Figure 11: Flex-grid LSP Representing a Media Channel that Starts at 704 the Filter of the Outgoing Interface of the Ingress LSR and ends at 705 the Filter of the Incoming Interface of the Egress LSR 707 In Figure 12 a Network Media Channel is represented as terminated at 708 the network side of the transceivers. This is commonly named an 709 OTSi-trail connection. 711 |--------------------- Network Media Channel ----------------------| 713 +----------------------+ +----------------------+ 714 | | | 715 +------+ +------+ +------+ +------+ 716 | | +----+ | | | | +----+ | |OTSi 717 OTSi| o-| |-o | +-----+ | o-| |-o |sink 718 src | | | | | ===+-+ +-+==| | | | | O---|R 719 T|***o******o******************************************************** 720 | | |\ /| | | | | | | | |\ /| | | 721 | o-| \/ |-o ===| | | |==| o-| \/ |-o | 722 | | | /\ | | | +-+ +-+ | | | /\ | | | 723 | o-|/ \|-o | | \/ | | o-|/ \|-o | 724 |Filter| | | |Filter| | /\ | |Filter| | | |Filter| 725 +------+ | | +------+ +-----+ +------+ | | +------+ 726 | | | | | | | | 727 +----------------------+ +----------------------+ 728 LSP 729 <-------------------------------------------------------------------> 731 LSP 732 <------------------------------------------------------------------> 733 +-----+ +--------+ +-----+ 734 o--- | |-------------------| |----------------| |---o 735 | LSR | TE link | LSR | TE link | LSR | 736 | |-------------------| |----------------| | 737 +-----+ +--------+ +-----+ 739 Figure 12: LSP Representing a Network Media Channel (OTSi Trail) 741 In a third case, a Network Media Channel is terminated on the Filter 742 ports of the Ingress and Egress nodes. This is named in G.872 as 743 OTSi Network Connection. As can be seen from the figures, there is 744 no difference from a GMPLS modelling perspective between these cases, 745 but they are shown as distinct examples to highlight the differences 746 in the data plane. 748 |--------------------- Network Media Channel --------------------| 750 +------------------------+ +------------------------+ 751 +------+ +------+ +------+ +------+ 752 | | +----+ | | | | +----+ | | 753 | o-| |-o | +------+ | o-| |-o | 754 | | | | | =====+-+ +-+=====| | | | | | 755 T-o******o********************************************************O-R 756 | | |\ /| | | | | | | | |\ /| | | 757 | o-| \/ |-o =====| | | |=====| o-| \/ |-o | 758 | | | /\ | | | +-+ +-+ | | | /\ | | | 759 | o-|/ \|-o | | \/ | | o-|/ \|-o | 760 |Filter| | | |Filter| | /\ | |Filter| | | |Filter| 761 +------+ | | +------+ +------+ +------+ | | +------+ 762 | | | | | | | | 763 +----------------------+ +----------------------+ 764 <-----------------------------------------------------------------> 765 LSP 767 LSP 768 <--------------------------------------------------------------> 769 +-----+ +--------+ +-----+ 770 o--| |--------------------| |-------------------| |--o 771 | LSR | TE link | LSR | TE link | LSR | 772 | |--------------------| |-------------------| | 773 +-----+ +--------+ +-----+ 775 Figure 13: LSP Representing a Network Media Channel (OTSi Network 776 Connection) 778 Applying the notion of hierarchy at the media layer, by using the LSP 779 as an FA (i.e., by using hierarchical LSPs), the media channel 780 created can support multiple (sub-)media channels. 782 +--------------+ +--------------+ 783 | Media Channel| TE | Media Channel| Virtual TE 784 | | link | | link 785 | Matrix |o- - - - - - - - - - o| Matrix |o- - - - - - 786 +--------------+ +--------------+ 787 | +---------+ | 788 | | Media | | 789 |o----| Channel |-----o| 790 | | 791 | Matrix | 792 +---------+ 794 Figure 14: Topology View with TE Link / FA 796 Note that there is only one media layer switch matrix (one 797 implementation is a FlexGrid ROADM) in SSON, while a signal layer LSP 798 (Network Media Channel) is established mainly for the purpose of 799 management and control of individual optical signals. Signal layer 800 LSPs with the same attributes (such as source and destination) can be 801 grouped into one media-layer LSP (media channel): this has advantages 802 in spectral efficiency (reduce guard band between adjacent OChs in 803 one FSC channel) and LSP management. However, assuming some network 804 elements perform signal layer switching in an SSON, there must be 805 enough guard band between adjacent OTSis in any media channel to 806 compensate for the filter concatenation effects and other effects 807 caused by signal layer switching elements. In such a situation, the 808 separation of the signal layer from the media layer does not bring 809 any benefit in spectral efficiency or in other aspects, but makes the 810 network switch and control more complex. If two OTSis must be 811 switched to different ports, it is better to carry them by diferent 812 FSC channels, and the media layer switch is enough in this scenario. 814 As discussed in Section 3.2.5, a media channel may be constructed 815 from a compsite of network media channels. This may be achieved in 816 two ways using LSPs. These mechanisms may be compared to the 817 techniques used in GMPLS to support inverse multiplexing in Time 818 Division Multiplexing (TDM) networks and in OTN [RFC4606], [RFC6344], 819 and [RFC7139]. 821 o In the first case, a single LSP may be established in the control 822 plane. The signaling messages include information for all of the 823 component network media channels that make up the composite media 824 channel. 826 o In the second case, each component network media channel is 827 established using a separate control plane LSP, and these LSPs are 828 associated within the control plane so that the end points may see 829 them as a single media channel. 831 4.4. Control Plane Modeling of Network Elements 833 Optical transmitters and receivers may have different tunability 834 constraints, and media channel matrixes may have switching 835 restrictions. Additionally, a key feature of their implementation is 836 their highly asymmetric switching capability which is described in 837 detail in [RFC6163]. Media matrices include line side ports that are 838 connected to DWDM links, and tributary side input/output ports that 839 can be connected to transmitters/receivers. 841 A set of common constraints can be defined: 843 o Slot widths: The minimum and maximum slot width. 845 o Granularity: The optical hardware may not be able to select 846 parameters with the lowest granularity (e.g., 6.25 GHz for nominal 847 central frequencies or 12.5 GHz for slot width granularity). 849 o Available frequency ranges: The set or union of frequency ranges 850 that have not been allocated (i.e., are available). The relative 851 grouping and distribution of available frequency ranges in a fiber 852 is usually referred to as "fragmentation". 854 o Available slot width ranges: The set or union of slot width ranges 855 supported by media matrices. It includes the following 856 information. 858 * Slot width threshold: The minimum and maximum Slot Width 859 supported by the media matrix. For example, the slot width 860 could be from 50GHz to 200GHz. 862 * Step granularity: The minimum step by which the optical filter 863 bandwidth of the media matrix can be increased or decreased. 864 This parameter is typically equal to slot width granularity 865 (i.e., 12.5GHz) or integer multiples of 12.5GHz. 867 4.5. Media Layer Resource Allocation Considerations 869 A media channel has an associated effective frequency slot. From the 870 perspective of network control and management, this effective slot is 871 seen as the "usable" end-to-end frequency slot. The establishment of 872 an LSP is related to the establishment of the media channel and the 873 configuration of the effective frequency slot. 875 A "service request" is characterized (at a minimum) by its required 876 effective slot width. This does not preclude that the request may 877 add additional constraints such as also imposing the nominal central 878 frequency. A given effective frequency slot may be requested for the 879 media channel in the control plane LSP setup messages, and a specific 880 frequency slot can be requested on any specific hop of the LSP setup. 881 Regardless of the actual encoding, the LSP setup message specifies a 882 minimum effective frequency slot width that needs to be fulfilled in 883 order to successful establish the requsted LSP. 885 An effective frequency slot must equally be described in terms of a 886 central nominal frequency and its slot width (in terms of usable 887 spectrum of the effective frequency slot). That is, it must be 888 possible to determine the end-to-end values of the n and m 889 parameters. We refer to this by saying that the "effective frequency 890 slot of the media channel/LSP must be valid". 892 In GMPLS the requested effective frequency slot is represented to the 893 TSpec present in the RSVP-TE Path message, and the effective 894 frequency slot is mapped to the FlowSpec carried in the RSVP-TE Resv 895 message. 897 In GMPLS-controlled systems, the switched element corresponds to the 898 'label'. In flexi-grid where the switched element is a frequency 899 slot, the label represents a frequency slot. In consequence, the 900 label in flexi-grid conveys the necessary information to obtain the 901 frequency slot characteristics (i.e, central frequency and slot 902 width: the n and m parameters). The frequency slot is locally 903 identified by the label. 905 The local frequency slot may change at each hop, given hardware 906 constraints and capabilities (e.g., a given node might not support 907 the finest granularity). This means that the values of n and m may 908 change at each hop. As long as a given downstream node allocates 909 enough optical spectrum, m can be different along the path. This 910 covers the issue where media matrices can have different slot width 911 granularities. Such variations in the local value of m will appear 912 in the allocated label that encodes the frequency slot as well as the 913 in the FlowSpec that describes the flow. 915 Different operational modes can be considered. For Routing and 916 Spectrum Assignment (RSA) with explicit label control, and for 917 Routing and Distributed Spectrum Assignment (R+DSA), the GMPLS 918 signaling procedures are similar to those described in section 4.1.3 919 of [RFC6163] for Routing and Wavelength Assignment (RWA) and for 920 Routing and Distributed Wavelength Assignment (R+DWA). The main 921 difference is that the label set specifies the available nominal 922 central frequencies that meet the slot width requirements of the LSP. 924 The intermediate nodes use the control plane to collect the 925 acceptable central frequencies that meet the slot width requirement 926 hop by hop. The tail-end node also needs to know the slot width of 927 an LSP to assign the proper frequency resource. Except for 928 identifying the resource (i.e., fixed wavelength for WSON, and 929 frequency resource for flexible grids), the other signaling 930 requirements (e.g., unidirectional or bidirectional, with or without 931 converters) are the same as for WSON as described in section 6.1 of 932 [RFC6163]. 934 Regarding how a GMPLS control plane can assign n and m hop-by-hop 935 along the path of an LSP, different cases can apply: 937 a. n and m can both change. It is the effective frequency slot that 938 matters, it needs to remain valid along the path. 940 b. m can change, but n needs to remain the same along the path. 941 This ensures that the nominal central frequency stays the same, 942 but the width of the slot can vary along the path. Again, the 943 important thing is that the effective frequency slot remains 944 valid and satisfies the requested parameters along the whole path 945 of the LSP. 947 c. n and m need to be unchanging along the path. This ensures that 948 the frequency slot is well-known end-to-end, and is a simple way 949 to ensure that the effective frequency slot remains valid for the 950 whole LSP. 952 d. n can change, but m needs to remain the same along the path. 953 This ensures that the effective frequency slot remains valid, but 954 allows the frequency slot to be moved within the spectrum from 955 hop to hop. 957 The selection of a path that ensures n and m continuity can be 958 delegated to a dedicated entity such as a Path Computation Element 959 (PCE). Any constraint (including frequency slot and width 960 granularities) can be taken into account during path computation. 961 Alternatively, A PCE can compute a path leaving the actual frequency 962 slot assignment to be done, for example, with a distributed 963 (signaling) procedure: 965 o Each downstream node ensures that m is >= requested_m. 967 o A downstream node cannot foresee what an upstream node will 968 allocate. A way to ensure that the effective frequency slot is 969 valid along the length of the LSP is to ensure that the same value 970 of n is allocated at each hop. By forcing the same value of n we 971 avoid cases where the effective frequency slot of the media 972 channel is invalid (that is, the resulting frequency slot cannot 973 be described by its n and m parameters). 975 o This may be too restrictive, since a node (or even a centralized/ 976 combined RSA entity) may be able to ensure that the resulting end- 977 to-end effective frequency slot is valid even if n varies locally. 978 That means, the effective frequency slot that characterizes the 979 media channel from end to end is consistent and is determined by 980 its n and m values, but that the effective frequency slot and 981 those values are logical (i.e., do not map direct to the 982 physically assigned spectrum) in the sense that they are the 983 result of the intersection of locally-assigned frequency slots 984 applicable at local components (such as filters) each of which may 985 have assigned different frequency slots. 987 For Figure 15 the effective slot is made valid by ensuring that the 988 minimum m is greater than the requested m. The effective slot 989 (intersection) is the lowest m (bottleneck). 991 For Figure 16 the effective slot is made valid by ensuring that it is 992 valid at each hop in the upstream direction. The intersection needs 993 to be computed because invalid slots could result otherwise. 995 C B A 996 |Path(m_req) | ^ | 997 |---------> | # | 998 | | # ^ 999 -^--------------^----------------#----------------#-- 1000 Effective # # # # 1001 FS n, m # . . . . . . .#. . . . . . . . # . . . . . . . .# <-fixed 1002 # # # # n 1003 -v--------------v----------------#----------------#--- 1004 | | # v 1005 | | # Resv | 1006 | | v <------ | 1007 | | |FlowSpec(n, m_a)| 1008 | | <--------| | 1009 | | FlowSpec (n, | 1010 <--------| min(m_a, m_b)) 1011 FlowSpec (n, | 1012 min(m_a, m_b, m_c)) 1014 m_a, m_b, m_c: Selected frequency slot widths 1016 Figure 15: Distributed Allocation with Different m and Same n 1017 C B A 1018 |Path(m_req) ^ | | 1019 |---------> # | | 1020 | # ^ ^ 1021 -^-------------#----------------#-----------------#-------- 1022 Effective # # # # 1023 FS n, m # # # # 1024 # # # # 1025 -v-------------v----------------#-----------------#-------- 1026 | | # v 1027 | | # Resv | 1028 | | v <------ | 1029 | | |FlowSpec(n_a, m_a) 1030 | | <--------| | 1031 | | FlowSpec (FSb [intersect] FSa) 1032 <--------| 1033 FlowSpec ([intersect] FSa,FSb,FSc) 1035 n_a: Selected nominal central frequencyfr by node A 1036 m_a: Selected frequency slot widths by node A 1037 FSa, FSb, FSc: Frequency slot at each hop A, B, C 1039 Figure 16: Distributed Allocation with Different m and Different n 1041 Note, when a media channel is bound to one OTSi (i.e., is a network 1042 media channel), the effective FS must be the one of the OTSi. The 1043 media channel setup by the LSP may contain the effective FS of the 1044 network media channel effective FS. This is an endpoint property: 1045 the egress and ingress have to constrain the Effective FS to be the 1046 OTSi Effective FS. 1048 4.6. Neighbor Discovery and Link Property Correlation 1050 There are potential interworking problems between fixed-grid DWDM and 1051 flexi-grid DWDM nodes. Additionally, even two flexi-grid nodes may 1052 have different grid properties, leading to link property conflict 1053 with resulting limited interworking. 1055 Devices or applications that make use of the flexi-grid might not be 1056 able to support every possible slot width. In other words, different 1057 applications may be defined where each supports a different grid 1058 granularity. In this case the link between two optical nodes with 1059 different grid granularities must be configured to align with the 1060 larger of both granularities. Furthermore, different nodes may have 1061 different slot-width tuning ranges. 1063 In summary, in a DWDM Link between two nodes, at least the following 1064 properties need to be negotiated: 1066 o Grid capability (channel spacing) - Between fixed-grid and flexi- 1067 grid nodes. 1069 o Grid granularity - Between two flexi-grid nodes. 1071 o Slot width tuning range - Between two flexi-grid nodes. 1073 4.7. Path Computation / Routing and Spectrum Assignment (RSA) 1075 In WSON, if there is no (available) wavelength converter in an 1076 optical network, an LSP is subject to the "wavelength continuity 1077 constraint" (see section 4 of [RFC6163]). Similarly in flexi-grid, 1078 if the capability to shift or convert an allocated frequency slot is 1079 absent, the LSP is subject to the "Spectrum Continuity Constraint". 1081 Because of the limited availability of wavelength/spectrum converters 1082 (in what is called a "sparse translucent optical network") the 1083 wavelength/spectrum continuity constraint always has to be 1084 considered. When available, information regarding spectrum 1085 conversion capabilities at the optical nodes may be used by RSA 1086 mechanisms. 1088 The RSA process determines a route and frequency slot for an LSP. 1089 Hence, when a route is computed the spectrum assignment process (SA) 1090 determines the central frequency and slot width based on the slot 1091 width and available central frequencies information of the 1092 transmitter and receiver, and utilizing the available frequency 1093 ranges information and available slot width ranges of the links that 1094 the route traverses. 1096 4.7.1. Architectural Approaches to RSA 1098 Similar to RWA for fixed grids [RFC6163], different ways of 1099 performing RSA in conjunction with the control plane can be 1100 considered. The approaches included in this document are provided 1101 for reference purposes only: other possible options could also be 1102 deployed. 1104 Note that all of these models allow the concept of a composite media 1105 channel supported by a single control plane LSP or by a set of 1106 associated LSPs. 1108 4.7.1.1. Combined RSA (R&SA) 1110 In this case, a computation entity performs both routing and 1111 frequency slot assignment. The computation entity needs access to 1112 detailed network information, e.g., the connectivity topology of the 1113 nodes and links, the available frequency ranges on each link, the 1114 node capabilities, etc. 1116 The computation entity could reside on a dedicated PCE server, in the 1117 provisioning application that requests the service, or on the ingress 1118 node. 1120 4.7.1.2. Separated RSA (R+SA) 1122 In this case, routing computation and frequency slot assignment are 1123 performed by different entities. The first entity computes the 1124 routes and provides them to the second entity. The second entity 1125 assigns the frequency slot. 1127 The first entity needs the connectivity topology to compute the 1128 proper routes. The second entity needs information about the 1129 available frequency ranges of the links and the capabilities of the 1130 nodes in order to assign the spectrum. 1132 4.7.1.3. Routing and Distributed SA (R+DSA) 1134 In this case an entity computes the route, but the frequency slot 1135 assignment is performed hop-by-hop in a distributed way along the 1136 route. The available central frequencies which meet the spectrum 1137 continuity constraint need to be collected hop-by-hop along the 1138 route. This procedure can be implemented by the GMPLS signaling 1139 protocol. 1141 4.8. Routing and Topology Dissemination 1143 In the case of the combined RSA architecture, the computation entity 1144 needs the detailed network information, i.e., connectivity topology, 1145 node capabilities, and available frequency ranges of the links. 1146 Route computation is performed based on the connectivity topology and 1147 node capabilities, while spectrum assignment is performed based on 1148 the available frequency ranges of the links. The computation entity 1149 may get the detailed network information via the GMPLS routing 1150 protocol. 1152 For WSON, the connectivity topology and node capabilities can be 1153 advertised by the GMPLS routing protocol (refer to section 6.2 of 1154 [RFC6163]. Except for wavelength-specific availability information, 1155 the information for flexi-grid is the same as for WSON and can 1156 equally be distributed by the GMPLS routing protocol. 1158 This section analyses the necessary changes on link information 1159 brought by flexible grids. 1161 4.8.1. Available Frequency Ranges/Slots of DWDM Links 1163 In the case of flexible grids, channel central frequencies span from 1164 193.1 THz towards both ends of the C band spectrum with 6.25 GHz 1165 granularity. Different LSPs could make use of different slot widths 1166 on the same link. Hence, the available frequency ranges need to be 1167 advertised. 1169 4.8.2. Available Slot Width Ranges of DWDM Links 1171 The available slot width ranges need to be advertised in combination 1172 with the available frequency ranges, in order that the computing 1173 entity can verify whether an LSP with a given slot width can be set 1174 up or not. This is constrained by the available slot width ranges of 1175 the media matrix. Depending on the availability of the slot width 1176 ranges, it is possible to allocate more spectrum than strictly needed 1177 by the LSP. 1179 4.8.3. Spectrum Management 1181 The total available spectrum on a fiber can be described as a 1182 resource that can be partitioned. For example, a part of the 1183 spectrum could be assigned to a third party to manage, or parts of 1184 the spectrum could be assigned by the operator for different classes 1185 of traffic. This partitioning creates the impression that spectrum 1186 is a hierarchy in view of Management and Control Plane: each 1187 partition could be itself be partitioned. However, the hierarchy is 1188 created purely within a management system: it defines a hierarchy of 1189 access or management rights, but there is no corresponding resource 1190 hierarchy within the fiber. 1192 The end of fiber is a link end and presents a fiber port which 1193 represents all of spectrum available on the fiber. Each spectrum 1194 allocation appears as Link Channel Port (i.e., frequency slot port) 1195 within fiber. Thus, while there is a hierarchy of ownership (the 1196 Link Channel Port and corresponding LSP are located on a fiber and so 1197 associated with a fiber port) there is no continued nesting hierarchy 1198 of frequency slots within larger frequency slots. In its way, this 1199 mirrors the fixed grid behavior where a wavelength is associated with 1200 a port/fiber, but cannot be subdivided even though it is a partition 1201 of the total spectrum available on the fiber. 1203 4.8.4. Information Model 1205 This section defines an information model to describe the data that 1206 represents the capabilities and resources available in an flexi-grid 1207 network. It is not a data model and is not intended to limit any 1208 protocol solution such as an encoding for an IGP. For example, 1209 information required for routing/path selection may be the set of 1210 available nominal central frequencies from which a frequency slot of 1211 the required width can be allocated. A convenient encoding for this 1212 information is for further study in an IGP encoding document. 1214 Fixed DWDM grids can also be described via suitable choices of slots 1215 in a flexible DWDM grid. However, devices or applications that make 1216 use of the flexible grid may not be capable of supporting every 1217 possible slot width or central frequency position. Thus, the 1218 information model needs to enable: 1220 exchange of information to enable RSA in a flexi-grid network 1222 representation of a fixed grid device participating in a flexi- 1223 grid network 1225 full interworking of fixed and flexible grid devices within the 1226 same network 1228 interworking of flexgrid devices with different capabilities. 1230 The information model is represented using Routing Backus-Naur Format 1231 (RBNF) as defined in [RFC5511]. 1233 ::= 1234 1235 1236 1238 where 1240 ::= 1241 [] 1243 ::= 1244 ( ) | 1245 1247 and 1249 ::= 1250 [] 1251 -- Subset of supported n values given by p x n + q 1252 -- where p is a positive integer 1253 -- and q (offset) belongs to 0,..,p-1. 1255 and 1257 ::= 1258 1259 1260 -- given by j x 12.5GHz, with j a positive integer 1261 1262 -- given by k x 12.5GHz, with k a positive integer (k >= j) 1264 Figure 17: Routing Information Model 1266 5. Control Plane Requirements 1268 The control of a flexi-grid networks places additional requirements 1269 on the GMPLS protocols. This section summarizes those requirements 1270 for signaling and routing. 1272 5.1. Support for Media Channels 1274 The control plane SHALL be able to support Media Channels, 1275 characterized by a single frequency slot. The representation of the 1276 Media Channel in the GMPLS control plane is the so-called flexi-grid 1277 LSP. Since network media channels are media channels, an LSP may 1278 also be the control plane representation of a network media channel. 1280 Consequently, the control plane will also be able to support Network 1281 Media Channels. 1283 5.1.1. Signaling 1285 The signaling procedure SHALL be able to configure the nominal 1286 central frequency (n) of a flexi-grid LSP. 1288 The signaling procedure SHALL allow a flexible range of values for 1289 the frequency slot width (m) parameter. Specifically, the control 1290 plane SHALL allow setting up a media channel with frequency slot 1291 width (m) ranging from a minimum of m=1 (12.5GHz) to a maximum of the 1292 entire C-band (the wavelength range 1530 nm to 1565 nm, which 1293 corresponds to the amplification range of erbium doped fiber 1294 amplifiers) with a slot width granularity of 12.5GHz. 1296 The signaling procedure SHALL be able to configure the minimum width 1297 (m) of a flexi-grid LSP. In addition, the signaling procedure SHALL 1298 be able to configure local frequency slots. 1300 The control plane architecture SHOULD allow for the support of L-band 1301 (the wavelength range 1565 nm to 1625 nm) and S-band (the wavelength 1302 range 1460 nm to 1530 nm). 1304 The signalling process SHALL be able to collect the local frequency 1305 slot assigned at each link along the path. 1307 The signaling procedures SHALL support all of the RSA architectural 1308 models (R&SA, R+SA, and R+DSA) within a single set of protocol 1309 objects although some objects may only be applicable within one of 1310 the models. 1312 5.1.2. Routing 1314 The routing protocol will support all functions as described in 1315 [RFC4202] and extend them to a flexi-grid data plane. 1317 The routing protocol SHALL distribute sufficient information to 1318 compute paths to enable the signaling procedure to establish LSPs as 1319 described in the previous sections. This includes, at a minimum the 1320 data described by the Information Model in Figure 17. 1322 The routing protocol SHALL update its advertisements of available 1323 resources and capabilities as the usage of resources in the network 1324 varies with the establishment or tear-down of LSPs. These updates 1325 SHOULD be amenable to damping and thresholds as in other traffic 1326 engineering routing advertisements. 1328 The routing protocol SHALL support all of the RSA architectural 1329 models (R&SA, R+SA, and R+DSA) without any configuration or change of 1330 behavior. Thus, the routing protocols SHALL be agnostic to the 1331 computation and signaling model that is in use. 1333 5.2. Support for Media Channel Resizing 1335 The signaling procedures SHALL allow resizing (grow or shrink) the 1336 frequency slot width of a media channel/network media channel. The 1337 resizing MAY imply resizing the local frequency slots along the path 1338 of the flexi-grid LSP. 1340 The routing protocol SHALL update its advertisements of available 1341 resources and capabilities as the usage of resources in the network 1342 varies with the resizing of LSP. These updates SHOULD be amenable to 1343 damping and thresholds as in other traffic engineering routing 1344 advertisements. 1346 5.3. Support for Logical Associations of Multiple Media Channels 1348 A set of media channels can be used to transport signals that have a 1349 logical association between them. The control plane architecture 1350 SHOULD allow multiple media channels to be logically associated. The 1351 control plane SHOULD allow the co-routing of a set of media channels 1352 that are logically associated. 1354 5.4. Support for Composite Media Channels 1356 As described in Section 3.2.5 and Section 4.3, a media channel may be 1357 composed of multiple network media channels. 1359 The signaling procedures SHOULD include support for signaling a 1360 single control plane LSP that includes information about multiple 1361 network media channels that will comprise the single compound media 1362 channel. 1364 The signaling procedures SHOULD include a mechanism to associate 1365 separately signaled control plane LSPs so that the end points may 1366 correlate them into a single compound media channel. 1368 The signaling procedures MAY include a mechanism to dynamically vary 1369 the composition of a composite media channel by allowing network 1370 media channels to be added to or removed from the whole. 1372 The routing protocols MUST provide sufficient information for the 1373 computation of paths and slots for composite media channels using any 1374 of the three RSA architectural models (R&SA, R+SA, and R+DSA). 1376 5.5. Support for Neighbor Discovery and Link Property Correlation 1378 The control plane MAY include support for neighbor discovery such 1379 that an flexi-grid network can be constructed in a "plug-and-play" 1380 manner. Note, however, that in common operational practice 1381 validation processes are used rather than automatic discovery. 1383 The control plane SHOULD allow the nodes at opposite ends of a link 1384 to correlate the properties that they will apply to the link. Such 1385 correlation SHOULD include at least the identities of the node and 1386 the identities they apply to the link. Other properties such as the 1387 link characteristics described for the routing information model in 1388 Figure 17 SHOULD also be correlated. 1390 Such neighbor discovery and link property correlation, if provided, 1391 MUST be able to operate in both an out-of-band and an out-of-fiber 1392 control channel. 1394 6. IANA Considerations 1396 This framework document makes no requests for IANA action. 1398 7. Security Considerations 1400 The control plane and data plane aspects of a flexi-grid system are 1401 fundamentally the same as a fixed grid system and there is no 1402 substantial reason to expect the security considerations to be any 1403 different. 1405 A good overview of the security considerations for a GMPLS-based 1406 control plane can be found in [RFC5920]. 1408 [RFC6163] includes a section describing security considerations for 1409 WSON, and it is reasonable to infer that these considerations apply 1410 and may be exacerbated in a flexi-grid SSON system. In particular, 1411 the detailed and granular information describing a flexi- grid 1412 network and the capabilities of nodes in that network could put 1413 stress on the routing protocol or the out-of-band control channel 1414 used by the protocol. An attacker might be able to cause small 1415 variations in the use of the network or the available resources 1416 (perhaps by modifying the environment of a fiber) and so trigger the 1417 routing protocol to make new flooding announcements. This situation 1418 is explicitly mitigated in the requirements for the routing protocol 1419 extensions where it is noted that the protocol must include damping 1420 and configurable thresholds as already exist in the core GMPLS 1421 routing protocols. 1423 8. Manageability Considerations 1425 GMPLS systems already contain a number of management tools. 1427 o MIB modules exist to model the control plane protocols and the 1428 network elements [RFC4802], [RFC4803], and there is early work to 1429 provide similar access through YANG. The features described in 1430 these models are currently designed to represent fixed-label 1431 technologies such as optical networks using the fixed grid: 1432 extensions may be needed in order to represent bandwidth, 1433 frequency slots, and effective frequency slots in flexi- grid 1434 networks. 1436 o There are protocol extensions within GMPLS signaling to allow 1437 control plane systems to report the presence of faults that affect 1438 LSPs [RFC4783], although it must be carefully noted that these 1439 mechanisms do not constitute an alarm mechanism that could be used 1440 to rapidly propagate information about faults in a way that would 1441 allow the data plane to perform protection switching. These 1442 mechanisms could easily be enhanced with the addition of 1443 technology-specific reasons codes if any are needed. 1445 o The GMPLS protocols, themselves, already include fault detection 1446 and recovery mechanisms (such as the PathErr and Notify messages 1447 in RSVP-TE signaling as used by GMPLS [RFC3473]. It is not 1448 anticipated that these mechanisms will need enhancement to support 1449 flexi-grid although additional reason codes may be needed to 1450 describe technology-specific error cases. 1452 o [RFC7260] describes a framework for the control and configuration 1453 of data plane Operations, Administration, and Management (OAM). 1454 It would not be appropriate for the IETF to define or describe 1455 data plane OAM for optical systems, but the framework described in 1456 RFC 7260 could be used (with minor protocol extensions) to enable 1457 data plane OAM that has been defined by the originators of the 1458 flexi-grid data plane technology (the ITU-T). 1460 o The Link Management Protocol [RFC4204] is designed to allow the 1461 two ends of a network link to coordinate and confirm the 1462 configuration and capabilities that they will apply to the link. 1463 This protocol is particularly applicable to optical links where 1464 the characteristics of the network devices may considerably affect 1465 how the link is used and where misconfiguration of mis-fibering 1466 could make physical interoperability impossible. LMP could easily 1467 be extended to collect and report information between the end 1468 points of links in a flexi-grid network. 1470 9. Authors 1472 Fatai Zhang 1473 Huawei 1474 Huawei Base, Longgang District, Chine 1475 zhangfatai@huawei.com 1477 Xihua Fu 1478 ZTE 1479 ZTE Plaza,No.10,Tangyan South Road, Gaoxin District, China 1480 fu.xihua@zte.com.cn 1482 Daniele Ceccarelli 1483 Ericsson 1484 Via Calda 5, Genova, Italy 1485 daniele.ceccarelli@ericsson.com 1487 Iftekhar Hussain 1488 Infinera 1489 140 Caspian Ct, Sunnyvale, 94089, USA 1490 ihussain@infinera.com 1492 10. Contributing Authors 1494 Adrian Farrel 1495 Old Dog Consulting 1496 adrian@olddog.co.uk 1498 Daniel King 1499 Old Dog Consulting 1500 daniel@olddog.co.uk 1502 Xian Zhang 1503 Huawei 1504 zhang.xian@huawei.com 1506 Cyril Margaria 1507 Juniper Networks 1508 cmargaria@juniper.net 1509 Qilei Wang 1510 ZTE 1511 Ruanjian Avenue, Nanjing, China 1512 wang.qilei@zte.com.cn 1514 Malcolm Betts 1515 ZTE 1516 malcolm.betts@zte.com.cn 1518 Sergio Belotti 1519 Alcatel Lucent 1520 Optics CTO 1521 Via Trento 30 20059 Vimercate (Milano) Italy 1522 +39 039 6863033 1523 sergio.belotti@alcatel-lucent.com 1525 Yao Li 1526 Nanjing University 1527 wsliguotou@hotmail.com 1529 Fei Zhang 1530 Huawei 1531 zhangfei7@huawei.com 1533 Lei Wang 1534 wang.lei@bupt.edu.cn 1536 Guoying Zhang 1537 China Academy of Telecom Research 1538 No.52 Huayuan Bei Road, Beijing, China 1539 zhangguoying@ritt.cn 1541 Takehiro Tsuritani 1542 KDDI R&D Laboratories Inc. 1543 2-1-15 Ohara, Fujimino, Saitama, Japan 1544 tsuri@kddilabs.jp 1546 Lei Liu 1547 U.C. Davis, USA 1548 leiliu@ucdavis.edu 1549 Eve Varma 1550 Alcatel-Lucent 1551 +1 732 239 7656 1552 eve.varma@alcatel-lucent.com 1554 Young Lee 1555 Huawei 1557 Jianrui Han 1558 Huawei 1560 Sharfuddin Syed 1561 Infinera 1563 Rajan Rao 1564 Infinera 1566 Marco Sosa 1567 Infinera 1569 Biao Lu 1570 Infinera 1572 Abinder Dhillon 1573 Infinera 1575 Felipe Jimenez Arribas 1576 Telefonica I+D 1578 Andrew G. Malis 1579 Huawei 1580 agmalis@gmail.com 1582 Huub van Helvoort 1583 Hai Gaoming BV 1584 The Neterlands 1585 huubatwork@gmail.com 1587 11. Acknowledgments 1589 The authors would like to thank Pete Anslow for his insights and 1590 clarifications, and to Matt Hartley and Jonas Maertensson for their 1591 reviews. 1593 This work was supported in part by the FP-7 IDEALIST project under 1594 grant agreement number 317999. 1596 12. References 1598 12.1. Normative References 1600 [G.694.1] International Telecomunications Union, "ITU-T 1601 Recommendation G.694.1, Spectral grids for WDM 1602 applications: DWDM frequency grid", November 2012. 1604 [G.800] International Telecomunications Union, "ITU-T 1605 Recommendation G.800, Unified functional architecture of 1606 transport networks.", February 2012. 1608 [G.805] International Telecomunications Union, "ITU-T 1609 Recommendation G.805, Generic functional architecture of 1610 transport networks.", March 2000. 1612 [G.8080] International Telecomunications Union, "ITU-T 1613 Recommendation G.8080/Y.1304, Architecture for the 1614 automatically switched optical network", 2012. 1616 [G.870] International Telecomunications Union, "ITU-T 1617 Recommendation G.870/Y.1352, Terms and definitions for 1618 optical transport networks", November 2012. 1620 [G.872] International Telecomunications Union, "ITU-T 1621 Recommendation G.872, Architecture of optical transport 1622 networks, draft v0.16 2012/09 (for discussion)", 2012. 1624 [G.959.1-2013] 1625 International Telecomunications Union, "Update of ITU-T 1626 Recommendation G.959.1, Optical transport network physical 1627 layer interfaces", 2013. 1629 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1630 Requirement Levels", BCP 14, RFC 2119, 1631 DOI 10.17487/RFC2119, March 1997, 1632 . 1634 [RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label 1635 Switching (GMPLS) Architecture", RFC 3945, 1636 DOI 10.17487/RFC3945, October 2004, 1637 . 1639 [RFC4202] Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions 1640 in Support of Generalized Multi-Protocol Label Switching 1641 (GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005, 1642 . 1644 [RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP) 1645 Hierarchy with Generalized Multi-Protocol Label Switching 1646 (GMPLS) Traffic Engineering (TE)", RFC 4206, 1647 DOI 10.17487/RFC4206, October 2005, 1648 . 1650 [RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax 1651 Used to Form Encoding Rules in Various Routing Protocol 1652 Specifications", RFC 5511, DOI 10.17487/RFC5511, April 1653 2009, . 1655 12.2. Informative References 1657 [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label 1658 Switching (GMPLS) Signaling Resource ReserVation Protocol- 1659 Traffic Engineering (RSVP-TE) Extensions", RFC 3473, 1660 DOI 10.17487/RFC3473, January 2003, 1661 . 1663 [RFC4204] Lang, J., Ed., "Link Management Protocol (LMP)", RFC 4204, 1664 DOI 10.17487/RFC4204, October 2005, 1665 . 1667 [RFC4397] Bryskin, I. and A. Farrel, "A Lexicography for the 1668 Interpretation of Generalized Multiprotocol Label 1669 Switching (GMPLS) Terminology within the Context of the 1670 ITU-T's Automatically Switched Optical Network (ASON) 1671 Architecture", RFC 4397, DOI 10.17487/RFC4397, February 1672 2006, . 1674 [RFC4606] Mannie, E. and D. Papadimitriou, "Generalized Multi- 1675 Protocol Label Switching (GMPLS) Extensions for 1676 Synchronous Optical Network (SONET) and Synchronous 1677 Digital Hierarchy (SDH) Control", RFC 4606, 1678 DOI 10.17487/RFC4606, August 2006, 1679 . 1681 [RFC4783] Berger, L., Ed., "GMPLS - Communication of Alarm 1682 Information", RFC 4783, DOI 10.17487/RFC4783, December 1683 2006, . 1685 [RFC4802] Nadeau, T., Ed., Farrel, A., and , "Generalized 1686 Multiprotocol Label Switching (GMPLS) Traffic Engineering 1687 Management Information Base", RFC 4802, 1688 DOI 10.17487/RFC4802, February 2007, 1689 . 1691 [RFC4803] Nadeau, T., Ed. and A. Farrel, Ed., "Generalized 1692 Multiprotocol Label Switching (GMPLS) Label Switching 1693 Router (LSR) Management Information Base", RFC 4803, 1694 DOI 10.17487/RFC4803, February 2007, 1695 . 1697 [RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS 1698 Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010, 1699 . 1701 [RFC6163] Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku, 1702 "Framework for GMPLS and Path Computation Element (PCE) 1703 Control of Wavelength Switched Optical Networks (WSONs)", 1704 RFC 6163, DOI 10.17487/RFC6163, April 2011, 1705 . 1707 [RFC6344] Bernstein, G., Ed., Caviglia, D., Rabbat, R., and H. van 1708 Helvoort, "Operating Virtual Concatenation (VCAT) and the 1709 Link Capacity Adjustment Scheme (LCAS) with Generalized 1710 Multi-Protocol Label Switching (GMPLS)", RFC 6344, 1711 DOI 10.17487/RFC6344, August 2011, 1712 . 1714 [RFC7139] Zhang, F., Ed., Zhang, G., Belotti, S., Ceccarelli, D., 1715 and K. Pithewan, "GMPLS Signaling Extensions for Control 1716 of Evolving G.709 Optical Transport Networks", RFC 7139, 1717 DOI 10.17487/RFC7139, March 2014, 1718 . 1720 [RFC7260] Takacs, A., Fedyk, D., and J. He, "GMPLS RSVP-TE 1721 Extensions for Operations, Administration, and Maintenance 1722 (OAM) Configuration", RFC 7260, DOI 10.17487/RFC7260, June 1723 2014, . 1725 Authors' Addresses 1727 Oscar Gonzalez de Dios (editor) 1728 Telefonica I+D 1729 Don Ramon de la Cruz 82-84 1730 Madrid 28045 1731 Spain 1733 Phone: +34913128832 1734 Email: oscar.gonzalezdedios@telefonica.com 1736 Ramon Casellas (editor) 1737 CTTC 1738 Av. Carl Friedrich Gauss n.7 1739 Castelldefels Barcelona 1740 Spain 1742 Phone: +34 93 645 29 00 1743 Email: ramon.casellas@cttc.es