idnits 2.17.1 draft-ietf-ccamp-flexi-grid-fwk-04.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (May 18, 2015) is 3263 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 CCAMP Working Group O. Gonzalez de Dios, Ed. 3 Internet-Draft Telefonica I+D 4 Intended status: Informational R. Casellas, Ed. 5 Expires: November 19, 2015 CTTC 6 F. Zhang 7 Huawei 8 X. Fu 9 ZTE 10 D. Ceccarelli 11 Ericsson 12 I. Hussain 13 Infinera 14 May 18, 2015 16 Framework and Requirements for GMPLS-based control of Flexi-grid DWDM 17 networks 18 draft-ietf-ccamp-flexi-grid-fwk-04 20 Abstract 22 To allow efficient allocation of optical spectral bandwidth for high 23 bit-rate systems, the International Telecommunication Union 24 Telecommunication Standardization Sector (ITU-T) has extended its 25 Recommendations G.694.1 and G.872 to include a new dense wavelength 26 division multiplexing (DWDM) grid by defining a set of nominal 27 central frequencies, channel spacings and the concept of "frequency 28 slot". In such an environment, a data plane connection is switched 29 based on allocated, variable-sized frequency ranges within the 30 optical spectrum creating what is known as a flexible grid (flexi- 31 grid). 33 This document defines a framework and the associated control plane 34 requirements for the GMPLS-based control of flexi-grid DWDM networks. 36 Status of This Memo 38 This Internet-Draft is submitted in full conformance with the 39 provisions of BCP 78 and BCP 79. 41 Internet-Drafts are working documents of the Internet Engineering 42 Task Force (IETF). Note that other groups may also distribute 43 working documents as Internet-Drafts. The list of current Internet- 44 Drafts is at http://datatracker.ietf.org/drafts/current/. 46 Internet-Drafts are draft documents valid for a maximum of six months 47 and may be updated, replaced, or obsoleted by other documents at any 48 time. It is inappropriate to use Internet-Drafts as reference 49 material or to cite them other than as "work in progress." 51 This Internet-Draft will expire on November 19, 2015. 53 Copyright Notice 55 Copyright (c) 2015 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents 60 (http://trustee.ietf.org/license-info) in effect on the date of 61 publication of this document. Please review these documents 62 carefully, as they describe your rights and restrictions with respect 63 to this document. Code Components extracted from this document must 64 include Simplified BSD License text as described in Section 4.e of 65 the Trust Legal Provisions and are provided without warranty as 66 described in the Simplified BSD License. 68 Table of Contents 70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 71 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 72 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 73 2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4 74 3. Overview of Flexi-grid Networks . . . . . . . . . . . . . . . 5 75 3.1. Flexi-grid in the Context of OTN . . . . . . . . . . . . 5 76 3.2. Flexi-grid Terminology . . . . . . . . . . . . . . . . . 6 77 3.2.1. Frequency Slots . . . . . . . . . . . . . . . . . . . 6 78 3.2.2. Media Layer Elements . . . . . . . . . . . . . . . . 8 79 3.2.3. Media Channels . . . . . . . . . . . . . . . . . . . 8 80 3.2.4. Optical Tributary Signals . . . . . . . . . . . . . . 9 81 3.2.5. Composite Media Channels . . . . . . . . . . . . . . 9 82 3.3. Hierarchy in the Media Layer . . . . . . . . . . . . . . 10 83 3.4. Flexi-grid Layered Network Model . . . . . . . . . . . . 10 84 3.4.1. DWDM Flexi-grid Enabled Network Element Models . . . 12 85 4. GMPLS Applicability . . . . . . . . . . . . . . . . . . . . . 12 86 4.1. General Considerations . . . . . . . . . . . . . . . . . 12 87 4.2. Consideration of TE Links . . . . . . . . . . . . . . . . 13 88 4.3. Consideration of LSPs in Flexi-grid . . . . . . . . . . . 15 89 4.4. Control Plane Modeling of Network Elements . . . . . . . 20 90 4.5. Media Layer Resource Allocation Considerations . . . . . 20 91 4.6. Neighbor Discovery and Link Property Correlation . . . . 24 92 4.7. Path Computation / Routing and Spectrum Assignment (RSA) 25 93 4.7.1. Architectural Approaches to RSA . . . . . . . . . . . 25 94 4.8. Routing and Topology Dissemination . . . . . . . . . . . 26 95 4.8.1. Available Frequency Ranges/Slots of DWDM Links . . . 27 96 4.8.2. Available Slot Width Ranges of DWDM Links . . . . . . 27 97 4.8.3. Spectrum Management . . . . . . . . . . . . . . . . . 27 98 4.8.4. Information Model . . . . . . . . . . . . . . . . . . 27 99 5. Control Plane Requirements . . . . . . . . . . . . . . . . . 29 100 5.1. Support for Media Channels . . . . . . . . . . . . . . . 29 101 5.1.1. Signaling . . . . . . . . . . . . . . . . . . . . . . 30 102 5.1.2. Routing . . . . . . . . . . . . . . . . . . . . . . . 30 103 5.2. Support for Media Channel Resizing . . . . . . . . . . . 31 104 5.3. Support for Logical Associations of Multiple Media 105 Channels . . . . . . . . . . . . . . . . . . . . . . . . 31 106 5.4. Support for Composite Media Channels . . . . . . . . . . 31 107 5.5. Support for Neighbor Discovery and Link Property 108 Correlation . . . . . . . . . . . . . . . . . . . . . . . 31 109 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 110 7. Security Considerations . . . . . . . . . . . . . . . . . . . 32 111 8. Manageability Considerations . . . . . . . . . . . . . . . . 32 112 9. Contributing Authors . . . . . . . . . . . . . . . . . . . . 33 113 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36 114 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 36 115 11.1. Normative References . . . . . . . . . . . . . . . . . . 36 116 11.2. Informative References . . . . . . . . . . . . . . . . . 37 117 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38 119 1. Introduction 121 The term "Flexible grid" (flexi-grid for short) as defined by the 122 International Telecommunication Union Telecommunication 123 Standardization Sector (ITU-T) Study Group 15 in the latest version 124 of [G.694.1], refers to the updated set of nominal central 125 frequencies (a frequency grid), channel spacing and optical spectrum 126 management/allocation considerations that have been defined in order 127 to allow an efficient and flexible allocation and configuration of 128 optical spectral bandwidth for high bit-rate systems. 130 A key concept of flexi-grid is the "frequency slot"; a variable-sized 131 optical frequency range that can be allocated to a data connection. 132 As detailed later in the document, a frequency slot is characterized 133 by its nominal central frequency and its slot width which, as per 134 [G.694.1], is constrained to be a multiple of a given slot width 135 granularity. 137 Compared to a traditional fixed grid network, which uses fixed size 138 optical spectrum frequency ranges or frequency slots with typical 139 channel separations of 50 GHz, a flexible grid network can select its 140 media channels with a more flexible choice of slot widths, allocating 141 as much optical spectrum as required. 143 From a networking perspective, a flexible grid network is assumed to 144 be a layered network [G.872][G.800] in which the media layer is the 145 server layer and the optical signal layer is the client layer. In 146 the media layer, switching is based on a frequency slot, and the size 147 of a media channel is given by the properties of the associated 148 frequency slot. In this layered network, a media channel can 149 transport more than one Optical Tributary Signals (OTSi), as defined 150 later in this document. 152 A Wavelength Switched Optical Network (WSON), addressed in [RFC6163], 153 is a term commonly used to refer to the application/deployment of a 154 GMPLS-based control plane for the control (provisioning/recovery, 155 etc.) of a fixed grid wavelength division multiplexing (WDM) network 156 in which media (spectrum) and signal are jointly considered. 158 This document defines the framework for a GMPLS-based control of 159 flexi-grid enabled dense wavelength division multiplexing (DWDM) 160 networks (in the scope defined by ITU-T layered Optical Transport 161 Networks [G.872]), as well as a set of associated control plane 162 requirements. An important design consideration relates to the 163 decoupling of the management of the optical spectrum resource and the 164 client signals to be transported. 166 2. Terminology 168 Further terminology specific to flexi-grid networks can be found in 169 Section 3.2. 171 2.1. Requirements Language 173 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 174 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 175 document are to be interpreted as described in [RFC2119]. 177 2.2. Abbreviations 179 EFS: Effective Frequency Slot 181 FS: Frequency Slot 183 FSC: Fiber-Switch Capable 185 LSR: Label Switching Router 187 NCF: Nominal Central Frequency 189 OCh: Optical Channel 190 OCh-P: Optical Channel Payload 192 OTN: Optical Transport Network 194 OTSi: Optical Tributary Signal 196 OTSiG: OTSi Group is a set of OTSi 198 OCC: Optical Channel Carrier 200 PCE: Path Computation Element 202 ROADM: Reconfigurable Optical Add-Drop Multiplexer 204 SSON: Spectrum-Switched Optical Network 206 SWG: Slot Width Granularity 208 3. Overview of Flexi-grid Networks 210 3.1. Flexi-grid in the Context of OTN 212 [G.872] describes, from a network level, the functional architecture 213 of an OTN. It is decomposed into independent layer networks with 214 client/layer relationships among them. A simplified view of the OTN 215 layers is shown in Figure 1. 217 +----------------+ 218 | Digital Layer | 219 +----------------+ 220 | Signal Layer | 221 +----------------+ 222 | Media Layer | 223 +----------------+ 225 Figure 1: Generic OTN Overview 227 In the OTN layering context, the media layer is the server layer of 228 the optical signal layer. The optical signal is guided to its 229 destination by the media layer by means of a network media channel. 230 In the media layer, switching is based on a frequency slot. 232 In this scope, this document uses the term flexi-grid enabled DWDM 233 network to refer to a network in which switching is based on 234 frequency slots defined using the flexible grid, and covers mainly 235 the Media Layer as well as the required adaptations from the Signal 236 layer. The present document is thus focused on the control and 237 management of the media layer. 239 3.2. Flexi-grid Terminology 241 This section presents the definition of the terms used in flexi-grid 242 networks. More detail about these terms can be found in the ITU-T 243 Recommendations [G.694.1], [G.872]), [G.870], [G.8080], and 244 [G.959.1-2013]. 246 Where appropriate, this documents also uses terminology and 247 lexicography from [RFC4397]. 249 3.2.1. Frequency Slots 251 This subsection is focused on the frequency slot and related terms. 253 o Frequency Slot [G.694.1]: The frequency range allocated to a slot 254 within the flexible grid and unavailable to other slots. A 255 frequency slot is defined by its nominal central frequency and its 256 slot width. 258 o Nominal Central Frequency: Each of the allowed frequencies as per 259 the definition of flexible DWDM grid in [G.694.1]. The set of 260 nominal central frequencies can be built using the following 261 expression 263 f = 193.1 THz + n x 0.00625 THz 265 where 193.1 THz is ITU-T "anchor frequency" for transmission over 266 the C band, and n is a positive or negative integer including 0. 268 -5 -4 -3 -2 -1 0 1 2 3 4 5 <- values of n 269 ...+--+--+--+--+--+--+--+--+--+--+- 270 ^ 271 193.1 THz <- anchor frequency 273 Figure 2: Anchor Frequency and Set of Nominal Central Frequencies 275 o Nominal Central Frequency Granularity: This is the spacing between 276 allowed nominal central frequencies and it is set to 6.25 GHz 277 [G.694.1]. 279 o Slot Width Granularity (SWG): 12.5 GHz, as defined in [G.694.1]. 281 o Slot Width: The slot width determines the "amount" of optical 282 spectrum regardless of its actual "position" in the frequency 283 axis. A slot width is constrained to be m x SWG (that is, m x 284 12.5 GHz), where m is an integer greater than or equal to 1. 286 Frequency Slot 1 Frequency Slot 2 287 ------------- ------------------- 288 | | | | 289 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 290 ...--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--... 291 ------------- ------------------- 292 ^ ^ 293 Central F = 193.1THz Central F = 193.14375 THz 294 Slot width = 25 GHz Slot width = 37.5 GHz 296 Figure 3: Example Frequency Slots 298 * The symbol '+' represents the allowed nominal central 299 frequencies 301 * The '--' represents the nominal central frequency granularity 303 * The '^' represents the slot nominal central frequency 305 * The number on the top of the '+' symbol represents the 'n' in 306 the frequency calculation formula. 308 * The nominal central frequency is 193.1 THz when n equals to 309 zero. 311 o Effective Frequency Slot [G.870]: The effective frequency slot of 312 a media channel is that part of the frequency slots of the filters 313 along the media channel that is common to all of the filters' 314 frequency slots. Note that both the Frequency Slot and Effective 315 Frequency Slot are local terms. 317 Frequency Slot 1 318 ------------- 319 | | 320 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 321 ..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--... 323 Frequency Slot 2 324 ------------------- 325 | | 326 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 327 ..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--... 329 =============================================== 330 Effective Frequency Slot 331 ------------- 332 | | 333 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 334 ..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--... 336 Figure 4: Effective Frequency Slot 338 3.2.2. Media Layer Elements 340 o Media Element: A media element directs an optical signal or 341 affects the properties of an optical signal. It does not modify 342 the properties of the information that has been modulated to 343 produce the optical signal [G.870]. Examples of media elements 344 include fibers, amplifiers, filters, and switching matrices. 346 o Media Channel Matrixes: The media channel matrix provides flexible 347 connectivity for the media channels. That is, it represents a 348 point of flexibility where relationships between the media ports 349 at the edge of a media channel matrix may be created and broken. 350 The relationship between these ports is called a matrix channel. 351 (Network) Media Channels are switched in a Media Channel Matrix. 353 3.2.3. Media Channels 355 This section defines concepts such as (Network) Media Channel; the 356 mapping to GMPLS constructs (i.e., LSP) is detailed in Section 4. 358 o Media Channel: A media association that represents both the 359 topology (i.e., path through the media) and the resource 360 (frequency slot) that it occupies. As a topological construct, it 361 represents a frequency slot (an effective frequency slot) 362 supported by a concatenation of media elements (fibers, 363 amplifiers, filters, switching matrices...). This term is used to 364 identify the end-to-end physical layer entity with its 365 corresponding (one or more) frequency slots local at each link 366 filters. 368 o Network Media Channel: [G.870] defines the Network Media Channel 369 as a media channel that transports a single OTSi, defined next. 371 3.2.4. Optical Tributary Signals 373 o Optical Tributary Signal (OTSi) [G.959.1-2013]: The optical signal 374 that is placed within a network media channel for transport across 375 the optical network. This may consist of a single modulated 376 optical carrier or a group of modulated optical carriers or 377 subcarriers. To provide a connection between the OTSi source and 378 the OTSi sink the optical signal must be assigned to a network 379 media channel. 381 o OTSi Group (OTSiG): The set of OTSi that are carried by a group of 382 network media channels. Each OTSi is carried by one network media 383 channel. From a management perspective it SHOULD be possible to 384 manage both the OTSiG and a group of Network Media Channels as 385 single entities. 387 3.2.5. Composite Media Channels 389 o It is possible to construct an end-to-end media channel as a 390 composite of more than one network media channels. A composite 391 media channel carries a group of OTSi (i.e., OTSiG). Each OTSi is 392 carried by one network media channel. This group of OTSi are 393 carried over a single fibre. 395 o In this case, the effective frequency slots may be contiguous 396 (i.e., there is no spectrum between them that can be used for 397 other media channels) or non-contiguous. 399 o It is not currently envisaged that such composite media channels 400 may be constructed from slots carried on different fibers whether 401 those fibers traverse the same hop-by-hop path through the network 402 or not. 404 o Furthermore, it is not considered likely that a media channel may 405 be constructed from a different variation of slot composition on 406 each hop. That is, the slot composition must be the same from one 407 end to the other of the media channel even if the specific slots 408 and their spacing may vary hop by hop. 410 o How the signal is carried across such groups of network media 411 channels is out of scope for this document. 413 3.3. Hierarchy in the Media Layer 415 In summary, the concept of frequency slot is a logical abstraction 416 that represents a frequency range, while the media layer represents 417 the underlying media support. Media Channels are media associations, 418 characterized by their (effective) frequency slot, respectively; and 419 media channels are switched in media channel matrixes. From the 420 control and management perspective, a media channel can be logically 421 split into network media channels. 423 In Figure 5, a media channel has been configured and dimensioned to 424 support two network media channels, each of them carrying one OTSi. 426 Media Channel Frequency Slot 427 +-------------------------------X------------------------------+ 428 | | 429 | Frequency Slot Frequency Slot | 430 | +------------X----------+ +----------X-----------+ | 431 | | OTSi | | OTSi | | 432 | | o | | o | | 433 | | | | | | | | 434 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 435 --+---+---+---+---+---+---+---+---+---+---+---+--+---+---+---+---+-- 437 <- Network Media Channel-> <- Network Media Channel-> 439 <------------------------ Media Channel -----------------------> 441 X - Frequency Slot Central Frequency 443 o - Signal Central Frequency 445 Figure 5: Example of Media Channel / Network Media Channels and 446 Associated Frequency Slots 448 3.4. Flexi-grid Layered Network Model 450 In the OTN layered network, the network media channel transports a 451 single OTSi (see Figure 6) 452 | OTSi | 453 O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O 454 | | 455 | Channel Port Network Media Channel Channel Port | 456 O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O 457 | | 458 +--------+ +-----------+ +--------+ 459 | \ (1) | | (1) | | (1) / | 460 | \----|-----------------|-----------|-------------------|-----/ | 461 +--------+ Link Channel +-----------+ Link Channel +--------+ 462 Media Channel Media Channel Media Channel 463 Matrix Matrix Matrix 465 The symbol (1) indicates a Matrix Channel 467 Figure 6: Simplified Layered Network Model 469 Note that a particular example of OTSi is the OCh-P. Figure 7 shows 470 this specific example as defined in G.805 [G.805]. 472 OCh AP Trail (OCh) OCh AP 473 O- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O 474 | | 475 --- OCh-P OCh-P --- 476 \ / source sink \ / 477 + + 478 | OCh-P OCh-P Network Connection OCh-P | 479 O TCP - - - - - - - - - - - - - - - - - - - - - - - - - - -TCP O 480 | | 481 |Channel Port Network Media Channel Channel Port | 482 O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O 483 | | 484 +--------+ +-----------+ +---------+ 485 | \ (1) | OCh-P LC | (1) | OCh-P LC | (1) / | 486 | \----|-----------------|-----------|-----------------|------/ | 487 +--------+ Link Channel +-----------+ Link Channel +---------+ 488 Media Channel Media Channel Media Channel 489 Matrix Matrix Matrix 491 The symbol (1) indicates a Matrix Channel 493 Figure 7: Layered Network Model According to G.805 495 3.4.1. DWDM Flexi-grid Enabled Network Element Models 497 A flexible grid network is constructed from subsystems that include 498 WDM links, tunable transmitters, and receivers, (i.e, media elements 499 including media layer switching elements that are media matrices) as 500 well as electro-optical network elements. This is just the same as 501 in a fixed grid network except that each element has flexible grid 502 characteristics. 504 As stated in Clause 7 of [G.694.1] the flexible DWDM grid has a 505 nominal central frequency granularity of 6.25 GHz and a slot width 506 granularity of 12.5 GHz. However, devices or applications that make 507 use of the flexible grid might not be capable of supporting every 508 possible slot width or position. In other words, applications may be 509 defined where only a subset of the possible slot widths and positions 510 are required to be supported. For example, an application could be 511 defined where the nominal central frequency granularity is 12.5 GHz 512 (by only requiring values of n that are even) and that only requires 513 slot widths as a multiple of 25 GHz (by only requiring values of m 514 that are even). 516 4. GMPLS Applicability 518 The goal of this section is to provide an insight into the 519 application of GMPLS as a control mechanism in flexi-grid networks. 520 Specific control plane requirements for the support of flexi-grid 521 networks are covered in Section 5. This framework is aimed at 522 controlling the media layer within the OTN hierarchy, and controlling 523 the required adaptations of the signal layer. This document also 524 defines the term Spectrum-Switched Optical Network (SSON) to refer to 525 a Flexi-grid enabled DWDM network that is controlled by a GMPLS/PCE 526 control plane. 528 This section provides a mapping of the ITU-T G.872 architectural 529 aspects to GMPLS/Control plane terms, and considers the relationship 530 between the architectural concept/construct of media channel and its 531 control plane representations (e.g., as a TE link). 533 4.1. General Considerations 535 The GMPLS control of the media layer deals with the establishment of 536 media channels that are switched in media channel matrices. GMPLS 537 labels are used to locally represent the media channel and its 538 associated frequency slot. Network media channels are considered a 539 particular case of media channels when the end points are 540 transceivers (that is, source and destination of an OTSi). 542 4.2. Consideration of TE Links 544 From a theoretical / abstract point of view, a fiber can be modeled 545 as having a frequency slot that ranges from minus infinity to plus 546 infinity. This representation helps understand the relationship 547 between frequency slots and ranges. 549 The frequency slot is a local concept that applies within a component 550 or element. When applied to a media channel, we are referring to its 551 effective frequency slot as defined in [G.872]. 553 The association sequence of the three components (i.e., a filter, a 554 fiber, and a filter), is a media channel in its most basic form. 555 From the control plane perspective this may modeled as a (physical) 556 TE-link with a contiguous optical spectrum. This can be represented 557 by saying that the portion of spectrum available at time t0 depends 558 on which filters are placed at the ends of the fiber and how they 559 have been configured. Once filters are placed we have a one-hop 560 media channel. In practical terms, associating a fiber with the 561 terminating filters determines the usable optical spectrum. 563 ---------------+ +-----------------+ 564 | | 565 +--------+ +--------+ 566 | | | | +--------- 567 ---o| =============================== o--| 568 | | Fiber | | | --\ /-- 569 ---o| | | o--| \/ 570 | | | | | /\ 571 ---o| =============================== o--| --/ \-- 572 | Filter | | Filter | | 573 | | | | +--------- 574 +--------+ +--------+ 575 | | 576 |------- Basic Media Channel ---------| 577 ---------------+ +-----------------+ 579 --------+ +-------- 580 |--------------------------------------| 581 LSR | TE link | LSR 582 |--------------------------------------| 583 +--------+ +-------- 585 Figure 8: (Basic) Media Channel and TE Link 587 Additionally, when a cross-connect for a specific frequency slot is 588 considered, the resulting media support of joining basic media 589 channels is still a media channel, i.e., a longer association 590 sequence of media elements and its effective frequency slot. In 591 other words, It is possible to "concatenate" several media channels 592 (e.g., patch on intermediate nodes) to create a single media channel. 594 The architectural construct resulting of the association sequence of 595 basic media channels and media layer matrix cross-connects can be 596 represented as (i.e., corresponds to) a Label Switched Path (LSP) 597 from a control plane perspective. 599 ----------+ +------------------------------+ +--------- 600 | | | | 601 +------+ +------+ +------+ +------+ 602 | | | | +----------+ | | | | 603 --o| ========= o--| |--o ========= o-- 604 | | Fiber | | | --\ /-- | | | Fiber | | 605 --o| | | o--| \/ |--o | | o-- 606 | | | | | /\ | | | | | 607 --o| ========= o--***********|--o ========= o-- 608 |Filter| |Filter| | | |Filter| |Filter| 609 | | | | | | | | 610 +------+ +------+ +------+ +------+ 611 | | | | 612 <- Basic Media -> <- Matrix -> <- Basic Media-> 613 |Channel| Channel |Channel| 614 ----------+ +------------------------------+ +--------- 616 <-------------------- Media Channel ----------------> 618 ------+ +---------------+ +------ 619 |------------------| |------------------| 620 LSR | TE link | LSR | TE link | LSR 621 |------------------| |------------------| 622 ------+ +---------------+ +------ 624 Figure 9: Extended Media Channel 626 Furthermore, if appropriate, the media channel can also be 627 represented as a TE link or Forwarding Adjacency (FA) [RFC4206], 628 augmenting the control plane network model. 630 ----------+ +------------------------------+ +--------- 631 | | | | 632 +------+ +------+ +------+ +------+ 633 | | | | +----------+ | | | | 634 --o| ========= o--| |--o ========= o-- 635 | | Fiber | | | --\ /-- | | | Fiber | | 636 --o| | | o--| \/ |--o | | o-- 637 | | | | | /\ | | | | | 638 --o| ========= o--***********|--o ========= o-- 639 |Filter| |Filter| | | |Filter| |Filter| 640 | | | | | | | | 641 +------+ +------+ +------+ +------+ 642 | | | | 643 ----------+ +------------------------------+ +--------- 645 <------------------------ Media Channel -----------> 647 ------+ +----- 648 |------------------------------------------------------| 649 LSR | TE link | LSR 650 |------------------------------------------------------| 651 ------+ +----- 653 Figure 10: Extended Media Channel / TE Link / FA 655 4.3. Consideration of LSPs in Flexi-grid 657 The flexi-grid LSP is a control plane representation of a media 658 channel. Since network media channels are media channels, an LSP may 659 also be the control plane representation of a network media channel 660 (without considering the adaptation functions). From a control plane 661 perspective, the main difference (regardless of the actual effective 662 frequency slot which may be dimensioned arbitrarily) is that the LSP 663 that represents a network media channel also includes the endpoints 664 (transceivers), including the cross-connects at the ingress and 665 egress nodes. The ports towards the client can still be represented 666 as interfaces from the control plane perspective. 668 Figure 11 shows an LSP routed between 3 nodes. The LSP is terminated 669 before the optical matrix of the ingress and egress nodes and can 670 represent a media channel. This case does not (and cannot) represent 671 a network media channel because it does not include (and cannot 672 include) the transceivers. 674 ---------+ +--------------------------------+ +-------- 675 | | | | 676 +------+ +------+ +------+ +------+ 677 | | | | +----------+ | | | | 678 -o| ========= o---| |---o ========= o- 679 | | Fiber | | | --\ /-- | | | Fiber | | 680 -o|>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>o- 681 | | | | | /\ | | | | | 682 -o| ========= o---***********|---o ========= o- 683 |Filter| |Filter| | | |Filter| |Filter| 684 | | | | | | | | 685 +------+ +------+ +------+ +------+ 686 | | | | 687 ---------+ +--------------------------------+ +-------- 689 >>>>>>>>>>>>>>>>>>>>>>>>>>>> LSP >>>>>>>>>>>>>>>>>>>>>>>> 690 -----+ +---------------+ +----- 691 |------------------| |----------------| 692 LSR | TE link | LSR | TE link | LSR 693 |------------------| |----------------| 694 -----+ +---------------+ +----- 696 Figure 11: Flex-grid LSP Representing a Media Channel that Starts at 697 the Filter of the Outgoing Interface of the Ingress LSR and ends at 698 the Filter of the Incoming Interface of the Egress LSR 700 In Figure 12 a Network Media Channel is represented as terminated at 701 the network side of the trnaponders. This is commonly names as OTSi- 702 trail connection. 704 |--------------------- Network Media Channel ----------------------| 706 +----------------------+ +----------------------+ 707 | | | 708 +------+ +------+ +------+ +------+ 709 | | +----+ | | | | +----+ | |OTSi 710 OTSi| o-| |-o | +-----+ | o-| |-o |sink 711 src | | | | | ===+-+ +-+==| | | | | O---|R 712 T|***o******o******************************************************** 713 | | |\ /| | | | | | | | |\ /| | | 714 | o-| \/ |-o ===| | | |==| o-| \/ |-o | 715 | | | /\ | | | +-+ +-+ | | | /\ | | | 716 | o-|/ \|-o | | \/ | | o-|/ \|-o | 717 |Filter| | | |Filter| | /\ | |Filter| | | |Filter| 718 +------+ | | +------+ +-----+ +------+ | | +------+ 719 | | | | | | | | 720 +----------------------+ +----------------------+ 721 LSP 722 <-------------------------------------------------------------------> 724 LSP 725 <------------------------------------------------------------------> 726 +-----+ +--------+ +-----+ 727 o--- | |-------------------| |----------------| |---o 728 | LSR | TE link | LSR | TE link | LSR | 729 | |-------------------| |----------------| | 730 +-----+ +--------+ +-----+ 732 Figure 12: LSP Representing a Network Media Channel (OTSi Trail) 734 In a third case, a Network Media Channel is terminated on the Filter 735 ports of the Ingress and Egress nodes. This is named in G.872 as 736 OTSi Network Connection. As can be seen from the figures, there is 737 no difference from a GMPLS modelling perspective between these cases, 738 but they are shown as distinct examples to highlight the differences 739 in the data plane. 741 |--------------------- Network Media Channel --------------------| 743 +------------------------+ +------------------------+ 744 +------+ +------+ +------+ +------+ 745 | | +----+ | | | | +----+ | | 746 | o-| |-o | +------+ | o-| |-o | 747 | | | | | =====+-+ +-+=====| | | | | | 748 T-o******o********************************************************O-R 749 | | |\ /| | | | | | | | |\ /| | | 750 | o-| \/ |-o =====| | | |=====| o-| \/ |-o | 751 | | | /\ | | | +-+ +-+ | | | /\ | | | 752 | o-|/ \|-o | | \/ | | o-|/ \|-o | 753 |Filter| | | |Filter| | /\ | |Filter| | | |Filter| 754 +------+ | | +------+ +------+ +------+ | | +------+ 755 | | | | | | | | 756 +----------------------+ +----------------------+ 757 <-----------------------------------------------------------------> 758 LSP 760 LSP 761 <--------------------------------------------------------------> 762 +-----+ +--------+ +-----+ 763 o--| |--------------------| |-------------------| |--o 764 | LSR | TE link | LSR | TE link | LSR | 765 | |--------------------| |-------------------| | 766 +-----+ +--------+ +-----+ 768 Figure 13: LSP Representing a Network Media Channel (OTSi Network 769 Connection) 771 Applying the notion of hierarchy at the media layer, by using the LSP 772 as an FA (i.e., by using hierarchical LSPs), the media channel 773 created can support multiple (sub-)media channels. 775 +--------------+ +--------------+ 776 | Media Channel| TE | Media Channel| Virtual TE 777 | | link | | link 778 | Matrix |o- - - - - - - - - - o| Matrix |o- - - - - - 779 +--------------+ +--------------+ 780 | +---------+ | 781 | | Media | | 782 |o----| Channel |-----o| 783 | | 784 | Matrix | 785 +---------+ 787 Figure 14: Topology View with TE Link / FA 789 Note that there is only one media layer switch matrix (one 790 implementation is a FlexGrid ROADM) in SSON, while a signal layer LSP 791 (Network Media Channel) is established mainly for the purpose of 792 management and control of individual optical signals. Signal layer 793 LSPs with the same attributes (such as source and destination) can be 794 grouped into one media-layer LSP (media channel): this has advantages 795 in spectral efficiency (reduce guard band between adjacent OChs in 796 one FSC channel) and LSP management. However, assuming some network 797 elements perform signal layer switching in an SSON, there must be 798 enough guard band between adjacent OTSis in any media channel to 799 compensate for the filter concatenation effects and other effects 800 caused by signal layer switching elements. In such a situation, the 801 separation of the signal layer from the media layer does not bring 802 any benefit in spectral efficiency or in other aspects, but makes the 803 network switch and control more complex. If two OTSis must be 804 switched to different ports, it is better to carry them by diferent 805 FSC channels, and the media layer switch is enough in this scenario. 807 As discussed in Section 3.2.5, a media channel may be constructed 808 from a compsite of network media channels. This may be achieved in 809 two ways using LSPs. These mechanisms may be compared to the 810 techniques used in GMPLS to support inverse multiplexing in Time 811 Division Multiplexing (TDM) networks and in OTN [RFC4606], [RFC6344], 812 and [RFC7139]. 814 o In the first case, a single LSP may be established in the control 815 plane. The signaling messages include information for all of the 816 component network media channels that make up the composite media 817 channel. 819 o In the second case, each component network media channel is 820 established using a separate control plane LSP, and these LSPs are 821 associated within the control plane so that the end points may see 822 them as a single media channel. 824 4.4. Control Plane Modeling of Network Elements 826 Optical transmitters and receivers may have different tunability 827 constraints, and media channel matrixes may have switching 828 restrictions. Additionally, a key feature of their implementation is 829 their highly asymmetric switching capability which is described in 830 detail in [RFC6163]. Media matrices include line side ports that are 831 connected to DWDM links, and tributary side input/output ports that 832 can be connected to transmitters/receivers. 834 A set of common constraints can be defined: 836 o Slot widths: The minimum and maximum slot width. 838 o Granularity: The optical hardware may not be able to select 839 parameters with the lowest granularity (e.g., 6.25 GHz for nominal 840 central frequencies or 12.5 GHz for slot width granularity). 842 o Available frequency ranges: The set or union of frequency ranges 843 that have not been allocated (i.e., are available). The relative 844 grouping and distribution of available frequency ranges in a fiber 845 is usually referred to as "fragmentation". 847 o Available slot width ranges: The set or union of slot width ranges 848 supported by media matrices. It includes the following 849 information. 851 * Slot width threshold: The minimum and maximum Slot Width 852 supported by the media matrix. For example, the slot width 853 could be from 50GHz to 200GHz. 855 * Step granularity: The minimum step by which the optical filter 856 bandwidth of the media matrix can be increased or decreased. 857 This parameter is typically equal to slot width granularity 858 (i.e., 12.5GHz) or integer multiples of 12.5GHz. 860 4.5. Media Layer Resource Allocation Considerations 862 A media channel has an associated effective frequency slot. From the 863 perspective of network control and management, this effective slot is 864 seen as the "usable" end-to-end frequency slot. The establishment of 865 an LSP is related to the establishment of the media channel and the 866 configuration of the effective frequency slot. 868 A "service request" is characterized (at a minimum) by its required 869 effective frequency slot width. This does not preclude that the 870 request may add additional constraints such as also imposing the 871 nominal central frequency. A given effective frequency slot may be 872 requested for the media channel in the control plane LSP setup 873 messages, and a specific frequency slot can be requeste on any 874 specific hop of the LSP setup. Regardless of the actual encoding, 875 the LSP setup message specifies a minimum frequency slot width that 876 needs to be fulfilled in order to successful establish the requsted 877 LSP. 879 An effective frequency slot must equally be described in terms of a 880 central nominal frequency and its slot width (in terms of usable 881 spectrum of the effective frequency slot). That is, it must be 882 possible to determine the end-to-end values of the n and m 883 parameters. We refer to this by saying that the "effective frequency 884 slot of the media channel/LSP must be valid". 886 In GMPLS the requested effective frequency slot is represented to the 887 TSpec present in the Path message, and the effective frequency slot 888 is mapped to the FlowSpec carried in the Resv message. 890 In GMPLS-controlled systems, the switched element corresponds to the 891 'label'. In flexi-grid where the switched element is a frequency 892 slot, the label represents a frequency slot. In consequence, the 893 label in flexi-grid conveys the necessary information to obtain the 894 frequency slot characteristics (i.e, central frequency and slot 895 width: the n and m parameters). The frequency slot is locally 896 identified by the label. 898 The local frequency slot may change at each hop, given hardware 899 constraints and capabilities (e.g., a given node might not support 900 the finest granularity). This means that the values of n and m may 901 change at each hop. As long as a given downstream node allocates 902 enough optical spectrum, m can be different along the path. This 903 covers the issue where media matrices can have different slot width 904 granularities. Such variations in the local value of m will appear 905 in the allocated label that encodes the frequency slot as well as the 906 in the FlowSpec that describes the flow. 908 Different operational modes can be considered. For Routing and 909 Spectrum Assignment (RSA) with explicit label control, and for 910 Routing and Distributed Spectrum Assignment (R+DSA), the GMPLS 911 signaling procedures are similar to those described in section 4.1.3 912 of [RFC6163] for Routing and Wavelength Assignment (RWA) and for 913 Routing and Distributed Wavelength Assignment (R+DWA). The main 914 difference is that the label set specifies the available nominal 915 central frequencies that meet the slot width requirements of the LSP. 917 The intermediate nodes use the control plane to collect the 918 acceptable central frequencies that meet the slot width requirement 919 hop by hop. The tail-end node also needs to know the slot width of 920 an LSP to assign the proper frequency resource. Except for 921 identifying the resource (i.e., fixed wavelength for WSON, and 922 frequency resource for flexible grids), the other signaling 923 requirements (e.g., unidirectional or bidirectional, with or without 924 converters) are the same as for WSON as described in section 6.1 of 925 [RFC6163]. 927 Regarding how a GMPLS control plane can assign n and m hop-by-hop 928 along the path of an LSP, different cases can apply: 930 a. n and m can both change. It is the effective frequency slot that 931 matters, it needs to remain valid along the path. 933 b. m can change, but n needs to remain the same along the path. 934 This ensures that the nominal central frequency stays the same, 935 but the width of the slot can vary along the path. Again, the 936 important thing is that the effective frequency slot remains 937 valid and satisfies the requested parameters along the whole path 938 of the LSP. 940 c. n and m need to be unchanging along the path. This ensures that 941 the frequency slot is well-known end-to-end, and is a simple way 942 to ensure that the effective frequency slot remains valid for the 943 whole LSP. 945 d. n can change, but m needs to remain the same along the path. 946 This ensures that the effective frequency slot remains valid, but 947 allows the frequency slot to be moved within the spectrum from 948 hop to hop. 950 The selection of a path that ensures n and m continuity can be 951 delegated to a dedicated entity such as a Path Computation Element 952 (PCE). Any constraint (including frequency slot and width 953 granularities) can be taken into account during path computation. 954 Alternatively, A PCE can compute a path leaving the actual frequency 955 slot assignment to be done, for example, with a distributed 956 (signaling) procedure: 958 o Each downstream node ensures that m is >= requested_m. 960 o A downstream node cannot foresee what an upstream node will 961 allocate. A way to ensure that the effective frequency slot is 962 valid along the length of the LSP is to ensure that the same value 963 of n is allocated at each hop. By forcing the same value of n we 964 avoid cases where the effective frequency slot of the media 965 channel is invalid (that is, the resulting frequency slot cannot 966 be described by its n and m parameters). 968 o This may be too restrictive, since a node (or even a centralized/ 969 combined RSA entity) may be able to ensure that the resulting end- 970 to-end effective frequency slot is valid even if n varies locally. 971 That means, the effective frequency slot that characterizes the 972 media channel from end to end is consistent and is determined by 973 its n and m values, but that the effective frequency slot and 974 those values are logical (i.e., do not map direct to the 975 physically assigned spectrum) in the sense that they are the 976 result of the intersection of locally-assigned frequency slots 977 applicable at local components (such as filters) each of which may 978 have assigned different frequency slots. 980 For Figure 15 the effective slot is made valid by ensuring that the 981 minimum m is greater than the requested m. The effective slot 982 (intersection) is the lowest m (bottleneck). 984 For Figure 16 the effective slot is made valid by ensuring that it is 985 valid at each hop in the upstream direction. The intersection needs 986 to be computed because invalid slots could result otherwise. 988 |Path(m_req) | ^ | 989 |---------> | # | 990 | | # ^ 991 -^--------------^----------------#----------------#-- 992 Effective # # # # 993 FS n, m # . . . . . . .#. . . . . . . . # . . . . . . . .# <-fixed 994 # # # # n 995 -v--------------v----------------#----------------#--- 996 | | # v 997 | | # Resv | 998 | | v <------ | 999 | | |FlowSpec(n, m_a)| 1000 | | <--------| | 1001 | | FlowSpec (n, | 1002 <--------| min(m_a, m_b)) 1003 FlowSpec (n, | 1004 min(m_a, m_b, m_c)) 1006 Figure 15: Distributed Allocation with Different m and Same n 1007 |Path(m_req) ^ | 1008 |---------> # | | 1009 | # ^ ^ 1010 -^-------------#----------------#-----------------#-------- 1011 Effective # # # # 1012 FS n, m # # # # 1013 # # # # 1014 -v-------------v----------------#-----------------#-------- 1015 | | # v 1016 | | # Resv | 1017 | | v <------ | 1018 | | |FlowSpec(n_a, m_a) 1019 | | <--------| | 1020 | | FlowSpec (FSb [intersect] FSa) 1021 <--------| 1022 FlowSpec ([intersect] FSa,FSb,FSc) 1024 Figure 16: Distributed Allocation with Different m and Different n 1026 Note, when a media channel is bound to one OTSi (i.e., is a network 1027 media channel), the EFS must be the one of the OTSi. The media 1028 channel setup by the LSP may contains the EFS of the network media 1029 channel EFS. This is an endpoint property: the egress and ingress 1030 have to constrain the EFS to be the OTSi EFS. 1032 4.6. Neighbor Discovery and Link Property Correlation 1034 There are potential interworking problems between fixed-grid DWDM and 1035 flexi-grid DWDM nodes. Additionally, even two flexi-grid nodes may 1036 have different grid properties, leading to link property conflict 1037 with resulting limited interworking. 1039 Devices or applications that make use of the flexi-grid might not be 1040 able to support every possible slot width. In other words, different 1041 applications may be defined where each supports a different grid 1042 granularity. Consider a node with an application where the nominal 1043 central frequency granularity is 12.5 GHz and where slot widths are 1044 multiples of 25 GHz. In this case the link between two optical nodes 1045 with different grid granularities must be configured to align with 1046 the larger of both granularities. Furthermore, different nodes may 1047 have different slot-width tuning ranges. 1049 In summary, in a DWDM Link between two nodes, at least the following 1050 properties need to be negotiated: 1052 o Grid capability (channel spacing) - Between fixed-grid and flexi- 1053 grid nodes. 1055 o Grid granularity - Between two flexi-grid nodes. 1057 o Slot width tuning range - Between two flexi-grid nodes. 1059 4.7. Path Computation / Routing and Spectrum Assignment (RSA) 1061 In WSON, if there is no (available) wavelength converter in an 1062 optical network, an LSP is subject to the "wavelength continuity 1063 constraint" (see section 4 of [RFC6163]). Similarly in flexi-grid, 1064 if the capability to shift or convert an allocated frequency slot is 1065 absent, the LSP is subject to the "Spectrum Continuity Constraint". 1067 Because of the limited availability of wavelength/spectrum converters 1068 (in what is called a "sparse translucent optical network") the 1069 wavelength/spectrum continuity constraint always has to be 1070 considered. When available, information regarding spectrum 1071 conversion capabilities at the optical nodes may be used by RSA 1072 mechanisms. 1074 The RSA process determines a route and frequency slot for an LSP. 1075 Hence, when a route is computed the spectrum assignment process (SA) 1076 determines the central frequency and slot width based on the slot 1077 width and available central frequencies information of the 1078 transmitter and receiver, and utilizing the available frequency 1079 ranges information and available slot width ranges of the links that 1080 the route traverses. 1082 4.7.1. Architectural Approaches to RSA 1084 Similar to RWA for fixed grids [RFC6163], different ways of 1085 performing RSA in conjunction with the control plane can be 1086 considered. The approaches included in this document are provided 1087 for reference purposes only: other possible options could also be 1088 deployed. 1090 Note that all of these models allow the concept of a composite media 1091 channel supported by a single control plane LSP or by a set of 1092 associated LSPs. 1094 4.7.1.1. Combined RSA (R&SA) 1096 In this case, a computation entity performs both routing and 1097 frequency slot assignment. The computation entity needs access to 1098 detailed network information, e.g., the connectivity topology of the 1099 nodes and links, the available frequency ranges on each link, the 1100 node capabilities, etc. 1102 The computation entity could reside on a dedicated PCE server, in the 1103 provisioning application that requests the service, or on the ingress 1104 node. 1106 4.7.1.2. Separated RSA (R+SA) 1108 In this case, routing computation and frequency slot assignment are 1109 performed by different entities. The first entity computes the 1110 routes and provides them to the second entity. The second entity 1111 assigns the frequency slot. 1113 The first entity needs the connectivity topology to compute the 1114 proper routes. The second entity needs information about the 1115 available frequency ranges of the links and the capabilities of the 1116 nodes in order to assign the spectrum. 1118 4.7.1.3. Routing and Distributed SA (R+DSA) 1120 In this case an entity computes the route, but the frequency slot 1121 assignment is performed hop-by-hop in a distributed way along the 1122 route. The available central frequencies which meet the spectrum 1123 continuity constraint need to be collected hop-by-hop along the 1124 route. This procedure can be implemented by the GMPLS signaling 1125 protocol. 1127 4.8. Routing and Topology Dissemination 1129 In the case of the combined RSA architecture, the computation entity 1130 needs the detailed network information, i.e., connectivity topology, 1131 node capabilities, and available frequency ranges of the links. 1132 Route computation is performed based on the connectivity topology and 1133 node capabilities, while spectrum assignment is performed based on 1134 the available frequency ranges of the links. The computation entity 1135 may get the detailed network information via the GMPLS routing 1136 protocol. 1138 For WSON, the connectivity topology and node capabilities can be 1139 advertised by the GMPLS routing protocol (refer to section 6.2 of 1140 [RFC6163]. Except for wavelength-specific availability information, 1141 the information for flexi-grid is the same as for WSON and can 1142 equally be distributed by the GMPLS routing protocol. 1144 This section analyses the necessary changes on link information 1145 brought by flexible grids. 1147 4.8.1. Available Frequency Ranges/Slots of DWDM Links 1149 In the case of flexible grids, channel central frequencies span from 1150 193.1 THz towards both ends of the C band spectrum with 6.25 GHz 1151 granularity. Different LSPs could make use of different slot widths 1152 on the same link. Hence, the available frequency ranges need to be 1153 advertised. 1155 4.8.2. Available Slot Width Ranges of DWDM Links 1157 The available slot width ranges need to be advertised in combination 1158 with the available frequency ranges, in order that the computing 1159 entity can verify whether an LSP with a given slot width can be set 1160 up or not. This is constrained by the available slot width ranges of 1161 the media matrix. Depending on the availability of the slot width 1162 ranges, it is possible to allocate more spectrum than strictly needed 1163 by the LSP. 1165 4.8.3. Spectrum Management 1167 The total available spectrum on a fiber can be described as a 1168 resource that can be partitioned. For example, a part of the 1169 spectrum could be assigned to a third party to manage, or parts of 1170 the spectrum could be assigned by the operator for different classes 1171 of traffic. This partitioning creates the impression that spectrum 1172 is a hierarchy in view of Management and Control Plane: each 1173 partition could be itself be partitioned. However, the hierarchy is 1174 created purely within a management system: it defines a hierarchy of 1175 access or management rights, but there is no corresponding resource 1176 hierarchy within the fiber. 1178 The end of fiber is a link end and presents a fiber port which 1179 represents all of spectrum available on the fiber. Each spectrum 1180 allocation appears as Link Channel Port (i.e., frequency slot port) 1181 within fiber. Thus, while there is a hierarchy of ownership (the 1182 Link Channel Port and corresponding LSP are located on a fiber and so 1183 associated with a fiber port) there is no continued nesting hierarchy 1184 of frequency slots within larger frequency slots. In its way, this 1185 mirrors the fixed grid behavior where a wavelength is associated with 1186 a port/fiber, but cannot be subdivided even though it is a partition 1187 of the total spectrum available on the fiber. 1189 4.8.4. Information Model 1191 This section defines an information model to describe the data that 1192 represents the capabilities and resources available in an flexi-grid 1193 network. It is not a data model and is not intended to limit any 1194 protocol solution such as an encoding for an IGP. For example, 1195 information required for routing/path selection may be the set of 1196 available nominal central frequencies from which a frequency slot of 1197 the required width can be allocated. A convenient encoding for this 1198 information is for further study in an IGP encoding document. 1200 Fixed DWDM grids can also be described via suitable choices of slots 1201 in a flexible DWDM grid. However, devices or applications that make 1202 use of the flexible grid may not be capable of supporting every 1203 possible slot width or central frequency position. Thus, the 1204 information model needs to enable: 1206 exchange of information to enable RSA in a flexi-grid network 1208 representation of a fixed grid device participating in a flexi- 1209 grid network 1211 full interworking of fixed and flexible grid devices within the 1212 same network 1214 interworking of flexgrid devices with different capabilities. 1216 The information model is represented using Routing Backus-Naur Format 1217 (RBNF) as defined in [RFC5511]. 1219 ::= 1220 1221 1222 1223 1224 1226 ::= 1227 [] 1229 ::= 1230 ( ) | 1231 1233 ::= (2^n) x 6.25GHz 1234 where n is a non negative integer, giving rise to granularities 1235 such as 6.25GHz, 12.5GHz, 25GHz, 50GHz, and 100GHz 1237 ::= (2^m) x 12.5GHz 1238 where m is positive integer 1240 ::= j x 12.5GHz, 1241 j is a positive integer 1243 ::= k x 12.5GHz, 1244 k is a positive integer (k >= j) 1246 Figure 17: Routing Information Model 1248 5. Control Plane Requirements 1250 The control of a flexi-grid networks places additional requirements 1251 on the GMPLS protocols. This section summarizes those requirements 1252 for signaling and routing. 1254 5.1. Support for Media Channels 1256 The control plane SHALL be able to support Media Channels, 1257 characterized by a single frequency slot. The representation of the 1258 Media Channel in the GMPLS control plane is the so-called flexi-grid 1259 LSP. Since network media channels are media channels, an LSP may 1260 also be the control plane representation of a network media channel. 1261 Consequently, the control plane will also be able to support Network 1262 Media Channels. 1264 5.1.1. Signaling 1266 The signaling procedure SHALL be able to configure the nominal 1267 central frequency (n) of a flexi-grid LSP. 1269 The signaling procedure SHALL allow a flexible range of values for 1270 the frequency slot width (m) parameter. Specifically, the control 1271 plane SHALL allow setting up a media channel with frequency slot 1272 width (m) ranging from a minimum of m=1 (12.5GHz) to a maximum of the 1273 entire C-band with a slot width granularity of 12.5GHz. 1275 The signaling procedure SHALL be able to configure the minimum width 1276 (m) of a flexi-grid LSP. In addition, the signaling procedure SHALL 1277 be able to configure local frequency slots. 1279 The control plane architecture SHOULD allow for the support of L-band 1280 and S-band. 1282 The signalling process SHALL be able to collect the local frequency 1283 slot assigned at each link along the path. 1285 The signaling procedures SHALL support all of the RSA architectural 1286 models (R&SA, R+SA, and R+DSA) within a single set of protocol 1287 objects although some objects may only be applicable within one of 1288 the models. 1290 5.1.2. Routing 1292 The routing protocol will support all functions as described in 1293 [RFC4202] and extend them to a flexi-grid data plane. 1295 The routing protocol SHALL distribute sufficient information to 1296 compute paths to enable the signaling procedure to establish LSPs as 1297 described in the previous sections. This includes, at a minimum the 1298 data described by the Information Model in Figure 17. 1300 The routing protocol SHALL update its advertisements of available 1301 resources and capabilities as the usage of resources in the network 1302 varies with the establishment or tear-down of LSPs. These updates 1303 SHOULD be amenable to damping and thresholds as in other traffic 1304 engineering routing advertisements. 1306 The routing protocol SHALL support all of the RSA architectural 1307 models (R&SA, R+SA, and R+DSA) without any configuration or change of 1308 behavior. Thus, the routing protocols SHALL be agnostic to the 1309 computation and signaling model that is in use. 1311 5.2. Support for Media Channel Resizing 1313 The signaling procedures SHALL allow resizing (grow or shrink) the 1314 frequency slot width of a media channel/network media channel. The 1315 resizing MAY imply resizing the local frequency slots along the path 1316 of the flexi-grid LSP. 1318 The routing protocol SHALL update its advertisements of available 1319 resources and capabilities as the usage of resources in the network 1320 varies with the resizing of LSP. These updates SHOULD be amenable to 1321 damping and thresholds as in other traffic engineering routing 1322 advertisements. 1324 5.3. Support for Logical Associations of Multiple Media Channels 1326 A set of media channels can be used to transport signals that have a 1327 logical association between them. The control plane architecture 1328 SHOULD allow multiple media channels to be logically associated. The 1329 control plane SHOULD allow the co-routing of a set of media channels 1330 that are logically associated. 1332 5.4. Support for Composite Media Channels 1334 As described in Section 3.2.5 and Section 4.3, a media channel may be 1335 composed of multiple network media channels. 1337 The signaling procedures SHOULD include support for signaling a 1338 single control plane LSP that includes information about multiple 1339 network media channels that will comprise the single compound media 1340 channel. 1342 The signaling procedures SHOULD include a mechanism to associate 1343 separately signaled control plane LSPs so that the end points may 1344 correlate them into a single compound media channel. 1346 The signaling procedures MAY include a mechanism to dynamically vary 1347 the composition of a composite media channel by allowing network 1348 media channels to be added to or removed from the whole. 1350 The routing protocols MUST provide sufficient information for the 1351 computation of paths and slots for composite media channels using any 1352 of the three RSA architectural models (R&SA, R+SA, and R+DSA). 1354 5.5. Support for Neighbor Discovery and Link Property Correlation 1356 The control plane MAY include support for neighbor discovery such 1357 that an flexi-grid network can be constructed in a "plug-and-play" 1358 manner. 1360 The control plane SHOULD allow the nodes at opposite ends of a link 1361 to correlate the properties that they will apply to the link. Such 1362 correlation SHOULD include at least the identities of the node and 1363 the identities they apply to the link. Other properties such as the 1364 link characteristics described for the routing information model in 1365 Figure 17 SHOULD also be correlated. 1367 Such neighbor discovery and link property correlation, if provided, 1368 MUST be able to operate in both an out-of-band and an out-of-fiber 1369 control channel. 1371 6. IANA Considerations 1373 This framework document makes no requests for IANA action. 1375 7. Security Considerations 1377 The control plane and data plane aspects of a flexi-grid system are 1378 fundamentally the same as a fixed grid system and there is no 1379 substantial reason to expect the security considerations to be any 1380 different. 1382 A good overview of the security considerations for a GMPLS-based 1383 control plane can be found in [RFC5920]. 1385 [RFC6163] includes a section describing security considerations for 1386 WSON, and it is reasonable to infer that these considerations apply 1387 and may be exacerbated in a flexi-grid SSON system. In particular, 1388 the detailed and granular information describing a flexi- grid 1389 network and the capabilities of nodes in that network could put 1390 stress on the routing protocol or the out-of-band control channel 1391 used by the protocol. An attacker might be able to cause small 1392 variations in the use of the network or the available resources 1393 (perhaps by modifying the environment of a fiber) and so trigger the 1394 routing protocol to make new flooding announcements. This situation 1395 is explicitly mitigated in the requirements for the routing protocol 1396 extensions where it is noted that the protocol must include damping 1397 and configurable thresholds as already exist in the core GMPLS 1398 routing protocols. 1400 8. Manageability Considerations 1402 GMPLS systems already contain a number of management tools. 1404 o MIB modules exist to model the control plane protocols and the 1405 network elements [RFC4802], [RFC4803], and there is early work to 1406 provide similar access through YANG. The features described in 1407 these models are currently designed to represent fixed-label 1408 technologies such as optical networks using the fixed grid: 1409 extensions may be needed in order to represent bandwidth, 1410 frequency slots, and effective frequency slots in flexi- grid 1411 networks. 1413 o There are protocol extensions within GMPLS signaling to allow 1414 control plane systems to report the presence of faults that affect 1415 LSPs [RFC4783], although it must be carefully noted that these 1416 mechanisms do not constitute an alarm mechanism that could be used 1417 to rapidly propagate information about faults in a way that would 1418 allow the data plane to perform protection switching. These 1419 mechanisms could easily be enhanced with the addition of 1420 technology-specific reasons codes if any are needed. 1422 o The GMPLS protocols, themselves, already include fault detection 1423 and recovery mechanisms (such as the PathErr and Notify messages 1424 in RSVP-TE signaling as used by GMPLS [RFC3473]. It is not 1425 anticipated that these mechanisms will need enhancement to support 1426 flexi-grid although additional reason codes may be needed to 1427 describe technology-specific error cases. 1429 o [RFC7260] describes a framework for the control and configuration 1430 of data plane Operations, Administration, and Management (OAM). 1431 It would not be appropriate for the IETF to define or describe 1432 data plane OAM for optical systems, but the framework described in 1433 RFC 7260 could be used (with minor protocol extensions) to enable 1434 data plane OAM that has been defined by the originators of the 1435 flexi-grid data plane technology (the ITU-T). 1437 o The Link Management Protocol [RFC4204] is designed to allow the 1438 two ends of a network link to coordinate and confirm the 1439 configuration and capabilities that they will apply to the link. 1440 This protocol is particularly applicable to optical links where 1441 the characteristics of the network devices may considerably affect 1442 how the link is used and where misconfiguration of mis-fibering 1443 could make physical interoperability impossible. LMP could easily 1444 be extended to collect and report information between the end 1445 points of links in a flexi-grid network. 1447 9. Contributing Authors 1449 Adrian Farrel 1450 Old Dog Consulting 1451 adrian@olddog.co.uk 1453 Daniel King 1454 Old Dog Consulting 1455 daniel@olddog.co.uk 1457 Xian Zhang 1458 Huawei 1459 zhang.xian@huawei.com 1461 Cyril Margaria 1462 Juniper Networks 1463 cmargaria@juniper.net 1465 Qilei Wang 1466 ZTE 1467 Ruanjian Avenue, Nanjing, China 1468 wang.qilei@zte.com.cn 1470 Malcolm Betts 1471 ZTE 1472 malcolm.betts@zte.com.cn 1474 Sergio Belotti 1475 Alcatel Lucent 1476 Optics CTO 1477 Via Trento 30 20059 Vimercate (Milano) Italy 1478 +39 039 6863033 1479 sergio.belotti@alcatel-lucent.com 1481 Yao Li 1482 Nanjing University 1483 wsliguotou@hotmail.com 1485 Fei Zhang 1486 Huawei 1487 zhangfei7@huawei.com 1489 Lei Wang 1490 wang.lei@bupt.edu.cn 1492 Guoying Zhang 1493 China Academy of Telecom Research 1494 No.52 Huayuan Bei Road, Beijing, China 1495 zhangguoying@ritt.cn 1497 Takehiro Tsuritani 1498 KDDI R&D Laboratories Inc. 1499 2-1-15 Ohara, Fujimino, Saitama, Japan 1500 tsuri@kddilabs.jp 1502 Lei Liu 1503 U.C. Davis, USA 1504 leiliu@ucdavis.edu 1506 Eve Varma 1507 Alcatel-Lucent 1508 +1 732 239 7656 1509 eve.varma@alcatel-lucent.com 1511 Young Lee 1512 Huawei 1514 Jianrui Han 1515 Huawei 1517 Sharfuddin Syed 1518 Infinera 1520 Rajan Rao 1521 Infinera 1523 Marco Sosa 1524 Infinera 1526 Biao Lu 1527 Infinera 1529 Abinder Dhillon 1530 Infinera 1531 Felipe Jimenez Arribas 1532 Telefonica I+D 1534 Andrew G. Malis 1535 Huawei 1536 agmalis@gmail.com 1538 Huub van Helvoort 1539 Hai Gaoming BV 1540 The Neterlands 1541 huubatwork@gmail.com 1543 10. Acknowledgments 1545 The authors would like to thank Pete Anslow for his insights and 1546 clarifications. 1548 This work was supported in part by the FP-7 IDEALIST project under 1549 grant agreement number 317999. 1551 11. References 1553 11.1. Normative References 1555 [G.694.1] International Telecomunications Union, "ITU-T 1556 Recommendation G.694.1, Spectral grids for WDM 1557 applications: DWDM frequency grid", November 2012. 1559 [G.800] International Telecomunications Union, "ITU-T 1560 Recommendation G.800, Unified functional architecture of 1561 transport networks.", February 2012. 1563 [G.805] International Telecomunications Union, "ITU-T 1564 Recommendation G.805, Generic functional architecture of 1565 transport networks.", March 2000. 1567 [G.8080] International Telecomunications Union, "ITU-T 1568 Recommendation G.8080/Y.1304, Architecture for the 1569 automatically switched optical network", 2012. 1571 [G.870] International Telecomunications Union, "ITU-T 1572 Recommendation G.870/Y.1352, Terms and definitions for 1573 optical transport networks", November 2012. 1575 [G.872] International Telecomunications Union, "ITU-T 1576 Recommendation G.872, Architecture of optical transport 1577 networks, draft v0.16 2012/09 (for discussion)", 2012. 1579 [G.959.1-2013] 1580 International Telecomunications Union, "Update of ITU-T 1581 Recommendation G.959.1, Optical transport network physical 1582 layer interfaces (to appear in July 2013)", 2013. 1584 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1585 Requirement Levels", BCP 14, RFC 2119, March 1997. 1587 [RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in 1588 Support of Generalized Multi-Protocol Label Switching 1589 (GMPLS)", RFC 4202, October 2005. 1591 [RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP) 1592 Hierarchy with Generalized Multi-Protocol Label Switching 1593 (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005. 1595 [RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax 1596 Used to Form Encoding Rules in Various Routing Protocol 1597 Specifications", RFC 5511, April 2009. 1599 11.2. Informative References 1601 [RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching 1602 (GMPLS) Signaling Resource ReserVation Protocol-Traffic 1603 Engineering (RSVP-TE) Extensions", RFC 3473, January 2003. 1605 [RFC4204] Lang, J., "Link Management Protocol (LMP)", RFC 4204, 1606 October 2005. 1608 [RFC4397] Bryskin, I. and A. Farrel, "A Lexicography for the 1609 Interpretation of Generalized Multiprotocol Label 1610 Switching (GMPLS) Terminology within the Context of the 1611 ITU-T's Automatically Switched Optical Network (ASON) 1612 Architecture", RFC 4397, February 2006. 1614 [RFC4606] Mannie, E. and D. Papadimitriou, "Generalized Multi- 1615 Protocol Label Switching (GMPLS) Extensions for 1616 Synchronous Optical Network (SONET) and Synchronous 1617 Digital Hierarchy (SDH) Control", RFC 4606, August 2006. 1619 [RFC4783] Berger, L., "GMPLS - Communication of Alarm Information", 1620 RFC 4783, December 2006. 1622 [RFC4802] Nadeau, T. and A. Farrel, "Generalized Multiprotocol Label 1623 Switching (GMPLS) Traffic Engineering Management 1624 Information Base", RFC 4802, February 2007. 1626 [RFC4803] Nadeau, T. and A. Farrel, "Generalized Multiprotocol Label 1627 Switching (GMPLS) Label Switching Router (LSR) Management 1628 Information Base", RFC 4803, February 2007. 1630 [RFC5920] Fang, L., "Security Framework for MPLS and GMPLS 1631 Networks", RFC 5920, July 2010. 1633 [RFC6163] Lee, Y., Bernstein, G., and W. Imajuku, "Framework for 1634 GMPLS and Path Computation Element (PCE) Control of 1635 Wavelength Switched Optical Networks (WSONs)", RFC 6163, 1636 April 2011. 1638 [RFC6344] Bernstein, G., Caviglia, D., Rabbat, R., and H. van 1639 Helvoort, "Operating Virtual Concatenation (VCAT) and the 1640 Link Capacity Adjustment Scheme (LCAS) with Generalized 1641 Multi-Protocol Label Switching (GMPLS)", RFC 6344, August 1642 2011. 1644 [RFC7139] Zhang, F., Zhang, G., Belotti, S., Ceccarelli, D., and K. 1645 Pithewan, "GMPLS Signaling Extensions for Control of 1646 Evolving G.709 Optical Transport Networks", RFC 7139, 1647 March 2014. 1649 [RFC7260] Takacs, A., Fedyk, D., and J. He, "GMPLS RSVP-TE 1650 Extensions for Operations, Administration, and Maintenance 1651 (OAM) Configuration", RFC 7260, June 2014. 1653 Authors' Addresses 1655 Oscar Gonzalez de Dios (editor) 1656 Telefonica I+D 1657 Don Ramon de la Cruz 82-84 1658 Madrid 28045 1659 Spain 1661 Phone: +34913128832 1662 Email: oscar.gonzalezdedios@telefonica.com 1663 Ramon Casellas (editor) 1664 CTTC 1665 Av. Carl Friedrich Gauss n.7 1666 Castelldefels Barcelona 1667 Spain 1669 Phone: +34 93 645 29 00 1670 Email: ramon.casellas@cttc.es 1672 Fatai Zhang 1673 Huawei 1674 Huawei Base, Bantian, Longgang District 1675 Shenzhen 518129 1676 China 1678 Phone: +86-755-28972912 1679 Email: zhangfatai@huawei.com 1681 Xihua Fu 1682 ZTE 1683 ZTE Plaza,No.10,Tangyan South Road, Gaoxin District 1684 Xi'An 1685 China 1687 Email: fu.xihua@zte.com.cn 1689 Daniele Ceccarelli 1690 Ericsson 1691 Via Calda 5 1692 Genova 1693 Italy 1695 Phone: +39 010 600 2512 1696 Email: daniele.ceccarelli@ericsson.com 1698 Iftekhar Hussain 1699 Infinera 1700 140 Caspian Ct. 1701 Sunnyvale 94089 1702 USA 1704 Phone: 408-572-5233 1705 Email: ihussain@infinera.com