Network Working Group O. Gonzalez de Dios, Ed. Internet-Draft Telefonica I+D Intended status: Standards Track R. Casellas, Ed. Expires: January 7, 2013 CTTC F. Zhang Huawei X. Fu ZTE D. Ceccarelli Ericsson I. Hussain Infinera July 6, 2012 Framework for GMPLS based control of Flexi-grid DWDM networks draft-ogrcetal-ccamp-flexi-grid-fwk-00 Abstract This document defines a framework and the associated control plane requirements for the GMPLS based control of flexi-grid DWDM networks. To allow efficient allocation of optical spectral bandwidth for high bit-rate systems, the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is extending the standard [G.694.1] to include the concept of flexible grid: a new DWDM grid has been developed within the ITU-T Study Group 15, by defining a set of nominal central frequencies, smaller channel spacings and the concept of "frequency slot". In such environment, a data plane connection is switched based on the allocated, variable- width optical spectrum frequency slot. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 7, 2013. Gonzalez de Dios, et al. Expires January 7, 2013 [Page 1] Internet-Draft GMPLS Flexi-grid Framework July 2012 Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Gonzalez de Dios, et al. Expires January 7, 2013 [Page 2] Internet-Draft GMPLS Flexi-grid Framework July 2012 Table of Contents 1. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. DWDM flexi-grid enabled network element models . . . . . . . . 11 5.1. Switched Resources and Labels . . . . . . . . . . . . . . 11 5.2. Physical links . . . . . . . . . . . . . . . . . . . . . . 12 5.3. Transceivers . . . . . . . . . . . . . . . . . . . . . . . 12 5.4. ROADMs . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6. Layered Network Model . . . . . . . . . . . . . . . . . . . . 14 7. Topology view in Control Plane . . . . . . . . . . . . . . . . 15 8. Control Plane Requirements . . . . . . . . . . . . . . . . . . 15 8.1. Neighbor Discovery and Link Property Correlation . . . . . 16 8.2. Path Computation / Routing and Spectrum Assignment (RSA) . . . . . . . . . . . . . . . . . . . . . . . . . . 16 8.2.1. Architectural Approaches to RSA . . . . . . . . . . . 17 8.3. Routing / Topology dissemination . . . . . . . . . . . . . 17 8.3.1. Available Frequency Ranges/slots of DWDM Links . . . . 18 8.3.2. Available Slot Width Ranges of DWDM Links . . . . . . 18 8.3.3. Tunable Optical Transmitters and Receivers . . . . . . 18 8.3.4. Hierarchical Spectrum Management . . . . . . . . . . . 18 8.3.5. Information Model . . . . . . . . . . . . . . . . . . 19 8.4. Signaling requirements . . . . . . . . . . . . . . . . . . 20 8.4.1. Slot Width Requirement . . . . . . . . . . . . . . . . 20 8.4.2. Frequency Slot Representation . . . . . . . . . . . . 20 8.4.3. Relationship with MRN/MLN . . . . . . . . . . . . . . 20 9. Control Plane Procedures . . . . . . . . . . . . . . . . . . . 20 10. Backwards (fixed-grid) compatibility, and WSON interworking . 21 11. Misc & Summary of open Issues [To be removed at later versions] . . . . . . . . . . . . . . . . . . . . . . . . . . 22 12. Security Considerations . . . . . . . . . . . . . . . . . . . 23 13. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 23 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25 15.1. Normative References . . . . . . . . . . . . . . . . . . . 25 15.2. Informative References . . . . . . . . . . . . . . . . . . 26 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26 Gonzalez de Dios, et al. Expires January 7, 2013 [Page 3] Internet-Draft GMPLS Flexi-grid Framework July 2012 1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Introduction The term "Flexible grid" (flexi-grid for short) as defined by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) study group 15 in the latest version of [G.694.1], refers to the updated set of nominal central frequencies (a frequency grid), channel spacings and optical spectrum management/allocation considerations that have been defined in order to allow an efficient and flexible allocation and configuration of optical spectral bandwidth for high bit-rate systems. A key concept of flexi-grid is the "frequency slot"; a variable-sized optical frequency range that can be allocated to a data connection. As detailed later in the document, a frequency slot is characterized by its nominal central frequency, selected from the set of reference frequencies, and its slot width which, as per [G.694.1], is constrained to be a multiple of a given slot width granularity. Compared to a traditional fixed grid network, which uses fixed size optical spectrum frequency ranges or "frequency slots" with typical channel separations of 100 or 50 GHz, a flexible grid network can select its data channels with with a more flexible choice of slot widths, allocating as much optical spectrum as required, and allowing higher bitrates (e.g., 100G or 400G or higher). From a networking perspective, a flexible grid network is assumed to be a layered network [G.872][G.805], extending the OTN architecture and interfaces [G.709], in which the flexi-grid layer (also referred to as the media layer) is the server layer and the OCh Layer (also referred to as the signal layer) is the client layer. In the media layer, switching is based on a frequency slot, and the size of a media channel is given by the properties of the associated frequency slot. In this layered network, the media channel itself can be dimensioned to contain one or more Optical Channels. As described in [RFC3945], GMPLS extends MPLS from supporting only Packet Switching Capable (PSC) interfaces and switching to also support four new classes of interfaces and switching that include Lambda Switch Capable (LSC). A Wavelength Switched Optical Network (WSON), addressed in [RFC6163], Gonzalez de Dios, et al. Expires January 7, 2013 [Page 4] Internet-Draft GMPLS Flexi-grid Framework July 2012 is a term commonly used to refer to the application/deployment of a Generalized Multi-Protocol Label Switching (GMPLS)-based control plane for the control (provisioning/recovery, etc) of a fixed grid WDM network. [editors' note: we need to think of the relationship of WSON and OCh switching. Are they equivalent? WSON includes regeneration, OCh does not? decoupling of lambda/OCh/OCC] This document defines the framework for a GMPLS-based control of flexi-grid enabled DWDM networks (in the scope defined by ITU-T layered Optical Transport Networks [G.872], as well as a set of associated control plane requirements. An important design consideration relates to the decoupling of the management of the optical spectrum resource and the client signals to be transported. [Editor's note: a point was raised during the meeting that WSON has not made separation between Och and Lambda (spectrum and signal are bundled). This needs to be confirmed.] A direct consequence of this "separation of concerns" is that, although not in scope of the present document, single-carrier / multi-carrier and related modulation formats, etc. could be supported. [Editor's note: the concept of frequency slot channel supporting multiple OCHs is defined in an ITU contribution. It is not a standard document yet.] [Editors' note: this document will track changes and evolutions of [G.694.1] [G.872] documents until their final publication. This document is not expected to become RFC until then. Likewise, as agreed during IETF83, the consideration of the concepts of Super- channel (a collection of one or more frequency slots to be treated as unified entity for management and control plane) and consequently Contiguous Spectrum Super-channel (a super-channel with a single frequency slot) and Split-Spectrum super-channel (a super-channel with multiple frequency slots) is postponed until the ITU-T data plane includes such physical layer entities, e.g., an ITU-T contribution exists] 3. Acronyms FS: Frequency Slot FSCh: Frequency Slot Channel NCF: Nominal Central Frequency OCG: Optical Carrier Group OCh: Optical Channel OCC: Optical Channel Carrier Gonzalez de Dios, et al. Expires January 7, 2013 [Page 5] Internet-Draft GMPLS Flexi-grid Framework July 2012 OTUk: Optical channel Transport Unit level k ODUk: Optical channel Data Unit Level k ODUj: Optical channel Data Unit Level j SWG: Slot Width Granularity 4. Terminology The following is a list of terms (see [G.694.1] and [G.872]) reproduced here for completeness. [Editors' note: regarding wavebands, we agreed NOT to use the term in flexigrid. The term has been used inconsistently in fixed-grid networks and overlaps with the definition of frequency slot. If need be, a question will be sent to ITU-T asking for clarification regarding wavebands.] [Editors' note: *important* these terms are not yet final and they may change / be replaced or obsoleted at any time.] o Optical Channel Slot (definition in the scope of a fixed grid DWDM network, to be adapted to a flexi-grid). The optical spectrum frequency range (portion of optical spectrum) allocated / occupied by a single optical channel. Each optical channel signal has a defined carrier central frequency and required frequency slot width (the supported optical channel signal bandwidth plus source stability). Optical Channel slots within an optical multiplex section may be allocated (in-service) or may be unallocated (out- of-service). An in-service Optical Channel Slot may be carrying an Optical Channel Signal or not. Optical Channel Slots are switched in an Optical Channel Matrix. o Nominal Central Frequency Granularity: 6.25 GHz (note: sometimes referred to as 0.00625 THz). o Nominal Central Frequency: each of the allowed frequences as per the definition of flexible DWDM grid in [G.694.1]. The set of nominal central frequencies can be built using the following expression f = 193.1 THz + n x 0.00625 THz, where 193.1 THz is ITU-T ''anchor frequency'' for transmission over the C band, n is a positive or negative integer including 0. -5 -4 -3 -2 -1 0 1 2 3 4 5 <- values of n ...+--+--+--+--+--+--+--+--+--+--+- ^ 193.1 THz <- anchor frequency Gonzalez de Dios, et al. Expires January 7, 2013 [Page 6] Internet-Draft GMPLS Flexi-grid Framework July 2012 Figure 1. Anchor frequency and set of nominal central frequencies o Slot Width Granularity: 12.5 GHz, as defined in [G.694.1]. o Slot Width: The slot width determines the "amount" of optical spectrum regardless of its actual "position" in the frequency axis. A slot width is constrained to be m x SWG (that is, m x 12.5 GHz), where m is an integer greater than or equal to 1. o Frequency Slot: The frequency range allocated to a slot within the flexible grid. A frequency slot is defined by its nominal central frequency and its slot width. Assuming a fixed and known central nominal frequency granularity, and assuming a fixed and known slot width granularity, a frequency slot is fully characterized by the values of 'n' and 'm'. Note that an equivalent characterization of a frequency slot is given by the start and end frequencies (i.e., a frequency range) which can, in turn, be defined by their respective values of 'n'. Note that a bidirectional optical transmission section layer network connection may be supported by one optical fiber for both directions (single fiber), or each direction of the connection may be supported by different fibers (pair of fibers). Since a frequency slot is a unidirectional entity (the same nominal central frequency cannot be used in two directions of transmission), the single fiber case is carried out by a pair of unidirectional frequency slots on the same fiber, and the pair of fibers case may have frequency slots that use the same nominal central frequencies. Frequency Slot 1 Frequency Slot 2 ------------- ------------------- | | | | -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 ..--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--... ------------- ------------------- ^ ^ Central F = 193.1THz Central F = 193.14375 THz Slot width = 25 GHz Slot width = 37.5 GHz Figure 2. Example Frequency slots The symbol '+' represents the allowed nominal central frequencies, the '--' represents the nominal central frequency granularity, and the '^' represents the slot nominal central frequency. The number on the top of the '+' symbol represents the 'n' in the frequency calculation formula. The nominal central frequency is 193.1 THz when n equals zero. Note that over a single frequency slot, one Gonzalez de Dios, et al. Expires January 7, 2013 [Page 7] Internet-Draft GMPLS Flexi-grid Framework July 2012 or multiple Optical Channels may be transported. o Fiber Frequency Slot: the total allocable spectrum on a fiber (n=0 and m= infinity?). [Editors' note/CM: is this useful? is the spectrum bounded/symmetric w.r.t anchor frequency?] o Frequency Slot Channel: a topological construct that represents a piece of spectrum supported by a concatenation of media elements (fiber, amplifiers, filters..). This term is used to identify the end-to-end physical layer entity with its corresponding (one or more) frequency slots local at each link. [Editors' note: * MB: a frequency slot is a local (i.e., to the link) concept, while a frequency slot channel has an end to end meaning. * IH: the FSCh is the CTP layer that is defining the frequency slot connection matrix. * CM: the CTP is the Frequency Slot and the Frequency Slot Channel the trail, the OCh being on top of the Channel. * ITU-T mailing list defines Common Frequency Slot which may replace Frequency Slot Channel (?). ] o Common Frequency Slot: the optical frequency range that is common to all of the devices in a particular path through the optical network. It is a logical construct derived from the frequency slots allocated to each device in the path (intersection). As an example, if there are two devices having slots with the same n but different m, then the common frequency slot has the smaller of the two m values. [Editors' note: this definition overlaps with Effective Frequency Slot] [Editors' note: clarify what happens when the resulting slot cannot be characterized with n and m, see Figure. Are we assuming that the same "n" applies?]. Gonzalez de Dios, et al. Expires January 7, 2013 [Page 8] Internet-Draft GMPLS Flexi-grid Framework July 2012 Frequency Slot 1 ------------- | | -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 ..--+--+--X--+--+--+--+--+--+--+--+--+--+--+--+--+--... Frequency Slot 2 ------------------- | | -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 ..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--... =============================================== Common Common Frequency Slot (valid?, CF?) ---------- | | -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 ..--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--... Figure 4. Common Frequency Slot o [Note: Following terminology is copied from ITU-T WP3 Q12 interim meeting [WD12R2]]. o [Editors' note: if we accept that a frequency slot can support one or more optical channel signals do we need the following two definitions?). o Single-Channel Frequency Slot: a frequency slot associated with a single optical channel signal ((that carries a single OCh payload). o Multi-Channel Frequency Slot: a frequency slot associated with multiple optical channel signals (i.e. multiple OChs). Note that if there are multiple optical signals within frequency slot, then each signal still has its own central frequency. That is, the term "central frequency" applies to an Optical signal and the term "nominal central frequency" applies to a frequency slot. In other words, the Frequency Slot central frequency is independent of the signals central frequencies. Gonzalez de Dios, et al. Expires January 7, 2013 [Page 9] Internet-Draft GMPLS Flexi-grid Framework July 2012 Frequency Slot -----------------------------------+ | Optical Optical | | Channel Channel | | Signal Signal | | +-----+ +-----------+ | | | | | | | | | o | | o | | -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 ... +--+--+--+--+--X--+--+--+--+--+--+-+--... ^ +-- Frequency Slot Central Frequency o - signal central frequency Figure 3. Frequency slot with 2 Optical channel signals o Network Channel (NCh): An end-to-end path through an optical network from a port on an OCh termination source to a port on an OCh termination sink (i.e. one OEO to another OEO). It is constructed from a concatenation of link channels and subnetwork channels. o Link Channel (LCh): A partial path through an optical network that provides a fixed relationship between the ports on a "subnetwork" or "access group" and the ports on another "subnetwork" or "access group". [Note: the terms subnetwork and access group are defined in G.805]. o Subnetwork Channel (SNCh): A path through an optical subnetwork that provides a relationship across a subnetwork. It is formed by the association of "ports" on the boundary of the subnetwork. o Matrix Channel (MCh): A path through an optical matrix that provides a relationship across a matrix. It is formed by the association of "ports" on the boundary of the matrix. o Effective Frequency Slot: An attribute of a channel which identifies that part of the frequency slots allocated to the devices along the channel that is common to all The following terms are defined in the scope of a GMPLS control plane. [Editors' note: the following ones were *not* agreed during IETF83 but are put here to be discussed.] Gonzalez de Dios, et al. Expires January 7, 2013 [Page 10] Internet-Draft GMPLS Flexi-grid Framework July 2012 o SSON: Spectrum-Switched Optical Network. An optical network in which a data plane connection is switched based on an optical spectrum frequency slot of a variable slot width, rather than based on a fixed grid and fixed slot width. Please note that a Wavelength Switched Optical Network (WSON) can be seen as a particular case of SSON in which all slot widths are equal and depend on the used channel spacing. o Flexi-LSP: a control plane construct that represents a data plane connection in which the switching involves a frequency slot. Different Flexi-LSPs may have different slot widths. The term flexi-LSP is used when needed to differentiate from regular WSON LSP in which switching is based on a nominal wavelength. o RSA: Routing and Spectrum Assignment. As opposed to the typical Routing and Wavelength Assignment (RWA) problem of traditional WDM networks, the flexibility in SSON leads to spectral contiguous constraint, which means that when assigning the spectral resources to single connections, the resources assigned to them must be contiguous over the entire connections in the spectrum domain. 5. DWDM flexi-grid enabled network element models Similar to fixed grid networks, a flexible grid network is also constructed from subsystems that include Wavelength Division Multiplexing (WDM) links, tunable transmitters and receivers, Reconfigurable Optical Add/Drop Multiplexers (ROADMs), wavelength converters, and electro-optical network elements, all of them with flexible grid characteristics. As stated in [G.694.1] the flexible DWDM grid defined in Clause 7 has a nominal central frequency granularity of 6.25 GHz and a slot width granularity of 12.5 GHz. However, devices or applications that make use of the flexible grid may not be capable of supporting every possible slot width or position. In other words, applications may be defined where only a subset of the possible slot widths and positions are required to be supported. For example, an application could be defined where the nominal central frequency granularity is 12.5 GHz (by only requiring values of n that are even) and that only requires slot widths as a multiple of 25 GHz (by only requiring values of m that are even). 5.1. Switched Resources and Labels As per [G.872] [Editor's note/CM: we need to better distinguish between G.872 and contributions, it would help to see what is agreed and what is still open, the list below contains items as per MB/XF Gonzalez de Dios, et al. Expires January 7, 2013 [Page 11] Internet-Draft GMPLS Flexi-grid Framework July 2012 slides]: o OCh Slots are switched in an Optical Channel Matrix. o The (link) physical layer entity, as defined by ITU-T is the Frequency Slot. o A frequency slot channel may be switched in a Frequency Slot Matrix [ITU-T contribution draft]. o The frequency slot matrix connection cannot modify the center frequency or increase the bandwidth of the frequency slots present at its ports [Editors' note: this text comes from G.872 updated. This seems to constrain / limit to only a transparent segment? the "m" must be the same end to end while "n" can be change by the equivalent of a wavelength converter, but WC are not defined. Currently, we only consider the case that the frequency slot matrix connection cannot modify the center frequency or the bandwidth of the frequency slots present at its ports. The use cases of dynamically modifying the center frequency or the bandwidth of the frequency slots are for further study after the clear definition by ITU-T]. o [Editors' note: we are not discarding O/E/O. If defined in a ITU-T network reference model with trail/terminations, considering optical channels i.e. with well-defined interfaces, reference points, and architectures. The implications of O/E/O will be also addressed once we have another context that includes them. In OTN from an OCh point of view end to end means from transponder to transponder, so if there is a 3R from ingress to egress there are 2 OCh which can have different 'n' and 'm']. 5.2. Physical links 5.3. Transceivers Optical transmitters/receivers may have different restrictions on the following properties: o Available central frequencies: The set of central frequencies which can be used by an optical transmitter/receiver. o Slot width: The slot width needed by a transmitter/receiver. The slot width is dependent on bit rate and modulation format. For one specific transmitter, the bit rate and modulation format may be tunable, so slot width would be determined by the modulation format used at a given bit rate. Gonzalez de Dios, et al. Expires January 7, 2013 [Page 12] Internet-Draft GMPLS Flexi-grid Framework July 2012 o The minimum and maximum slot width. o The step granularity: the optical hardare may not be able to select parameters with the lowest granulairy (e.g. 6.25 GHz for nominal central frequencies or 12.5 GHz for slot width granularity). 5.4. ROADMs Tributary Side: E5 I5 E6 I6 O | O | | | | | | O | O +-----------------------+ |+-----+ +-----+| Line side-1 --->||Split| |WSS-2||---> Line side-2 Input (I1) |+-----+ +-----+| Output (E2) Line side-1 <---||WSS-1| |Split||<--- Line side-2 Output (E1) |+-----+ +-----+| Input (I2) | ROADM | |+-----+ +-----+| Line side-3 --->||Split| |WSS-4||---> Line side-4 Input (I3) |+-----+ +-----+| Output (E4) Line side-3 <---||WSS-3| |Split||<--- Line side-4 Output (E3) |+-----+ +-----+| Input (I4) +-----------------------+ | O | O | | | | O | O | Tributary Side: E7 I7 E8 I8 Figure 5. Simplified ROADM model with Line Sides and Tributaries [Editor's note: different ROADM configuration such as C/CD/CDC will be added later.] A Frequency slot matrix may have switching restrictions, for example , when it is realized using flexi-grid enabled ROADMs. A key feature of ROADMs is their highly asymmetric switching capability which is described in [RFC6163] in detail. The ports on ROADM include line side ports which are connected to DWDM links and tributary side input/output ports which can be connected to transmitters/receivers. The capability of ports on ROADM, which are characterized as follows: o Available frequency ranges: the set or union of frequency ranges that are not allocated (i.e. available). The relative grouping and distribution of available frequency ranges in a fiber is Gonzalez de Dios, et al. Expires January 7, 2013 [Page 13] Internet-Draft GMPLS Flexi-grid Framework July 2012 usually referred to as ''fragmentation''. o Available slot width ranges: the set or union of slot width ranges supported by ROADM. It includes the following information. * Slot width threshold: the minimum and maximum Slot Width supported by ROADM. For example, the slot width can be from 50GHz to 200GHz. * Step granularity: the minimum step by which the optical filter bandwidth of ROADM can be increased or decreased. This parameter is typically equal to slot width granularity (i.e. 12.5GHz) or integer multiples of 12.5GHz. 6. Layered Network Model [Editors' note: OTN hierarchy is not fully covered. It is important to understand, where the FSC sits in the OTN hierarchy. This is also important from control plane perspective as this layer becomes the connection end points of optical layer service]. OCh / flexi-grid layered model. AP Trail (OCh) AP O- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O TCP Link Connection (OCh) TCP o------------o-------------------------------------------o---------o Subnetwork Subnetwork Connection Connection | Media Path | AP O- - - - - - - - - - - - - - - - - - - - - -O AP | | | Link (Fiber) | TCP o---------------o-----------o---------------o Subnet. channel Link channel Subnet. chan (freq slot) (freq slot) (freq slot) Figure 6. Layered Network Model G.805 [Editors' note: we are replicating the figure here for reference, until the ITU-T document is official. The media path is a piece of spectrum that has been allocated to a path between two ports of a media device. [Editors'note/CM/IH: it seems the media path is equivalent to the FSC (freq.slot channel is between the AP?. Why use a new term media path?] Gonzalez de Dios, et al. Expires January 7, 2013 [Page 14] Internet-Draft GMPLS Flexi-grid Framework July 2012 7. Topology view in Control Plane [Note: the frequency slot matrix connection may interconnect one or more frequency slot channels which in turn may carry one or more Och signals.] +--------------+ +--------------+ | Signal (OCh) | TE | Signal (OCh) | Virtual TE | | link | | link | Matrix |o- - - - - - - - - - - - - o| Matrix |o- - - - - - | | | | +--------------+ +--------------+ | +---------+ | | |Freq Slot| | |o------| Matrix |---------o| | | +---------+ Figure 7. MRN/MLN topology view with TE link / FA 8. Control Plane Requirements [Editor's note: The considered topology view is a layered network, in which the media layer corresponds to the server layer (flexigrid) and the signal layer corresponds to the client layer (Och). This data plane modeling considers the flexigrid and the OCh as separate layers, especially considering both the single and multi-channel frequency slots. However, this has implications on the interop/ interworking with WSON and OCh switching. We need to manage a MRN for OCh and stitching for WSON? In other words, a key part of the fwk is to define how can we have MRN/MLN hierarchical relationship with Och/FS and yet stitching 1:1 between WSON and SSON? In this line: how does OCh switching and WSON relate, actually?] [Editor's note: formal requirements such as noted in the comments will be added in a later version of the document]. Hierarchy spectrum management decouples media and signal, but from the point of view of the control plane, such separation of concerns implies the management of a MRN/MLN network. So Control Plane needs to differentiate signal LSP and media LSP. It should also need to support Hierarchy-LSP [RFC4206] The central frequency of each hop should be same along end-to-end media or signal LSP because of Spectrum Continuity Constraint. Otherwise some nodes need to convert the central frequency along media or signal LSP. Gonzalez de Dios, et al. Expires January 7, 2013 [Page 15] Internet-Draft GMPLS Flexi-grid Framework July 2012 8.1. Neighbor Discovery and Link Property Correlation [Editors' note: text from draft-li-ccamp-grid-property-lmp-01] During the practical deployment procedure, fixed-grid optical nodes will be gradually replaced by flexible nodes. This will lead to an interworking problem between fixed-grid DWDM and flexible-grid DWDM nodes. Additionally, even two flexible-grid optical nodes may have different grid properties, leading to link property conflict. Devices or applications that make use of the flexible-grid may not be able to support every possible slot width. In other words, applications may be defined where different grid granularity can be supported. Taking node F as an example, an application could be defined where the nominal central frequency granularity is 12.5 GHz requiring slot widths being multiple of 25 GHz. Therefore the link between two optical nodes with different grid granularity must be configured to align with the larger of both granularities. Besides, different nodes may have different slot width tuning ranges. In summary, in a DWDM Link between two nodes, at least the following properties should be negotiated: Grid capability (channel spacing) - Between fixed-grid and flexible-grid nodes. Grid granularity - Between two flexible-grid nodes. Slot width tuning range - Between two flexible-grid nodes. 8.2. Path Computation / Routing and Spectrum Assignment (RSA) Much like in WSON, in which if there is no (available) wavelength converters in an optical network, an LSP is subject to the ''wavelength continuity constraint'' (see section 4 of [RFC6163]), if the capability of shifting or converting an allocated frequency slot, the LSP is subject to the Optical ''Spectrum Continuity Constraint''. Because of the limited availability of wavelength/spectrum converters (sparse translucent optical network) the wavelength/spectrum continuity constraint should always be considered. When available, information regarding spectrum conversion capabilities at the optical nodes may be used by RSA mechanisms. The RSA process determines a route and frequency slot for a LSP. Hence, when a route is computed the spectrum assignment process (SA) should determine the central frequency and slot width based on the slot width and available central frequencies information of the Gonzalez de Dios, et al. Expires January 7, 2013 [Page 16] Internet-Draft GMPLS Flexi-grid Framework July 2012 transmitter and receiver, and the available frequency ranges information and available slot width ranges of the links that the route traverses. 8.2.1. Architectural Approaches to RSA Similar to RWA for fixed grids, different ways of performing RSA in conjunction with the control plane can be considered. The approaches included in this document are provided for reference purposes only; other possible options could also be deployed. 8.2.1.1. Combined RSA (R&SA) In this case, a computation entity performs both routing and frequency slot assignment. The computation entity should have the detailed network information, e.g. connectivity topology constructed by nodes/links information, available frequency ranges on each link, node capabilities, etc. The computation entity could reside either on a PCE or the ingress node. 8.2.1.2. Separated RSA (R+SA) In this case, routing computation and frequency slot assignment are performed by different entities. The first entity computes the routes and provides them to the second entity; the second entity assigns the frequency slot. The first entity should get the connectivity topology to compute the proper routes; the second entity should get the available frequency ranges of the links and nodes' capabilities information to assign the spectrum. 8.2.1.3. Routing and Distributed SA (R+DSA) In this case, one entity computes the route but the frequency slot assignment is performed hop-by-hop in a distributed way along the route. The available central frequencies which meet the spectrum continuity constraint should be collected hop by hop along the route. This procedure can be implemented by the GMPLS signaling protocol. 8.3. Routing / Topology dissemination In the case of combined RSA architecture, the computation entity needs to get the detailed network information, i.e. connectivity topology, node capabilities and available frequency ranges of the links. Route computation is performed based on the connectivity Gonzalez de Dios, et al. Expires January 7, 2013 [Page 17] Internet-Draft GMPLS Flexi-grid Framework July 2012 topology and node capabilities; spectrum assignment is performed based on the available frequency ranges of the links. The computation entity may get the detailed network information by the GMPLS routing protocol. Compared with [RFC6163], except wavelength- specific availability information, the connectivity topology and node capabilities are the same as WSON, which can be advertised by GMPLS routing protocol (refer to section 6.2 of [RFC6163]. This section analyses the necessary changes on link information brought by flexible grids. 8.3.1. Available Frequency Ranges/slots of DWDM Links In the case of flexible grids, channel central frequencies span from 193.1 THz towards both ends of the C band spectrum with 6.25 GHz granularity. Different LSPs could make use of different slot widths on the same link. Hence, the available frequency ranges should be advertised. 8.3.2. Available Slot Width Ranges of DWDM Links The available slot width ranges needs to be advertised, in combination with the Available frequency ranges, in order to verify whether a LSP with a given slot width can be set up or not; this is is constrained by the available slot width ranges of the flexi-grid enabled ROADMs (the flexi-grid Frequency slot matrix). Depending on the availability of the slot width ranges, it is possible to allocate more spectrum than strictly needed by the LSP. 8.3.3. Tunable Optical Transmitters and Receivers The slot width of a LSP is determined by the transmitter and receiver that could be mapped to ADD/DROP interfaces in WSON. Moreover their central frequency could be fixed or tunable, hence, both the slot width of an ADD/DROP interface and the available central frequencies should be advertised. 8.3.4. Hierarchical Spectrum Management [Editors' note: the part on the hierarchy of the optical spectrum could be confusing, we can discuss it]. The total available spectrum on a fiber could be described as a resource that can be divided by a media device into a set of Frequency Slots. In terms of managing spectrum, it is necessary to be able to speak about different granularities of managed spectrum. For example, a part of the spectrum could be assigned to a third party to manage. This need to partition creates the impression that spectrum is a hierarchy in view of Management and Control Plane. The hierarchy is created within a management system, and it is an access right hierarchy only. It is a Gonzalez de Dios, et al. Expires January 7, 2013 [Page 18] Internet-Draft GMPLS Flexi-grid Framework July 2012 management hierarchy without any actual resource hierarchy within fiber. The end of fiber is a link end and presents a fiber port which represents all of spectrum available on the fiber. Each spectrum allocation appears as Link Channel Port (i.e., frequency slot port) within fiber. 8.3.5. Information Model Fixed DM grids can also be described via suitable choices of slots in a flexible DWDM grid. However, devices or applications that make use of the flexible grid may not be capable of supporting every possible slot width or central frequency position. Following is the definition of information model, not intended to limit any IGP encoding implementation. For example, information required for routing/path selection may be the set of available nominal central frequencies from which a frequency slot of the required width can be allocated. A convenient encoding for this information (may be as a frequency slot or sets of contiguous slices) is further study in IGP encoding document. [Editor's note: to be discussed] ::= ::= [< Available Frequency Range-List>] ::= | ::= n x 6.25GHz, where n is positive integer, such as 6.25GHz, 12.5GHz, 25GHz, 50GHz or 100GHz ::= m x 12.5GHz, where m is positive integer ::= j x 12.5GHz, j is a positive integer ::= k x 12.5GHz, k is a positive integer (k >= j) Gonzalez de Dios, et al. Expires January 7, 2013 [Page 19] Internet-Draft GMPLS Flexi-grid Framework July 2012 Figure 8. Routing Information model 8.4. Signaling requirements Note on explicit label control Compared with [RFC6163], except identifying the resource (i.e., fixed wavelength for WSON and frequency resource for flexible grids), the other signaling requirements (e.g., unidirectional or bidirectional, with or without converters) are the same as WSON described in the section 6.1 of [RFC6163]. In the case of routing and distributed SA, GMPLS signaling can be used to allocate the frequency slot to a LSP. For R+DSA, the GMPLS signaling procedure is similar to the one described in section 4.1.3 of [RFC6163] except that the label set should specify the available nominal central frequencies that meet the slot width requirement of the LSP. 8.4.1. Slot Width Requirement [Editors' note: the signaling requirements need to be discussed. This is just preliminary text]. In order to allocate a proper frequency slot for a LSP, the signaling should specify its slot width requirement. The intermediate nodes can collect the acceptable central frequencies that meet the slot width requirement hop by hop. The tail-end node also needs to know the slot width of a LSP to assign the proper frequency resource. Hence, the slot width requirement should be specified in the signaling message when a LSP is being set up. [Note: other methods may not need to collect availability] 8.4.2. Frequency Slot Representation The frequency slot can be determined by the central frequency (n value) and slot width (m value). Such parameters should be able to be specified by the signaling protocol. 8.4.3. Relationship with MRN/MLN 8.4.3.1. OCh Layer 8.4.3.2. Media (frequency slot) layer 9. Control Plane Procedures Resizing existing LSP(s) without deletion: refers to increase or Gonzalez de Dios, et al. Expires January 7, 2013 [Page 20] Internet-Draft GMPLS Flexi-grid Framework July 2012 decrease of slot width value 'm' without changing the value of 'n' [Editor's note: Restoration / Resizing a single LSP without deletion as well as timing constraints. As per ITU-T clarification on service affecting or non-service affecting (i.e., hitless) restoration, at present no hitless resizing protocol has been defined for OCh. Hitless resizing is defined for an ODU entity only.] 10. Backwards (fixed-grid) compatibility, and WSON interworking o SSON as evolution of WSON, same LSC, different Swcap? o Potential problems with having the same swcap but the label format changes w.r.t. wson o A new SwCap may need to be defined, LSC swcap already defined ISCD which can not be modified o Role of LSP encoding type? o Notion of hierarchy? There is no notion of hierarchy between WSON and flexi-grid / SSON - only interop / interwork. Arguments for LSC switching capability [QW] A LSP for an optical signal which has a bandwidth of 50GHz passes through both a fixed grid network and a flexible grid network. We assume that no OEOs exist in the LSP, so both the fixed grid path and flexible grid path occupy 50GHz. From the perspective of data plane, there is no change of the signal and no multiplexing when the fixed grid path interconnects with flexible grid path. From this scenario we can conclude that both fixed grid network path and flexible grid network path belong to the same layer. No notion of hierarchy exists between them. [QW] stitching LSP which is described in [RFC5150] can be applied in one layer. LSP hierarchy allows more than one LSP to be mapped to an H-LSP, but in case of S-LSP, at most one LSP may be associated with an S-LSP. This is similar to the scenario of interconnection between fixed grid LSP and flexible grid LSP. Similar to an H-LSP, an S-LSP could be managed and advertised, although it is not required, as a TE link, either in the same TE domain as it was provisioned or a different one. Path setup procedure of stitching LSP can be applied in the scenario of interconnection between fixed grid path and flexible grid path. Gonzalez de Dios, et al. Expires January 7, 2013 [Page 21] Internet-Draft GMPLS Flexi-grid Framework July 2012 e2e LSP +++++++++++++++++++++++++++++++++++> (LSP1-2) LSP segment (flexi-LSP) ====================> (LSP-AB) C --- E --- G /|\ | / |\ / | \ | / | \ R1 ---- A \ | \ | / | / B --- R2 \| \ |/ |/ D --- F --- H fixed grid --A-- flexi-grid --B-- fixed grid Figure 9. LSP Stitching [RFC5150] and relationship with fixed-flexi 11. Misc & Summary of open Issues [To be removed at later versions] o Will reuse a lot of work / procedures / encodings defined in the context of WSON o At data rates of GBps / TBps, encoding bandwidths with bytes per second unit and IEEE 32-bit floating may be problematic / non scalable. o Bandwidth fields not relevant since there is not a 1-to-1 mapping between bps and Hz, since it depends on the modulation format, fec, either there is an agreement on assuming best / worst case modulations and spectral efficiency. o Label I: "m" is inherent part of the label, part of the switching, allows encode the "lightpath" in a ERO using Explicit Label Control, Still maintains that feature a cross-connect is defined by the tuple (port-in, label-in, port-out, label-out), allows a kind-of "best effort LSP" o Label II: "m" is not part of the label but of the TSPEC, neds to be in the TSPEC to decouple client signal traffic specification and management of the optical spectrum, having in both places is redundant and open to incoherences, extra error checking. o Label III: both, It reflects both the concept of resource request allocation / reservation and the concept of being inherent part of the switching. Gonzalez de Dios, et al. Expires January 7, 2013 [Page 22] Internet-Draft GMPLS Flexi-grid Framework July 2012 12. Security Considerations TBD 13. Contributing Authors Qilei Wang ZTE Ruanjian Avenue, Nanjing, China wang.qilei@zte.com.cn Malcolm Betts ZTE malcolm.betts@zte.com.cn Sergio Belotti Alcatel Lucent Optics CTO Via Trento 30 20059 Vimercate (Milano) Italy +39 039 6863033 sergio.belotti@alcatel-lucent.com Cyril Margaria Nokia Siemens Networks St Martin Strasse 76, Munich, 81541, Germany +49 89 5159 16934 cyril.margaria@nsn.com Xian Zhang Huawei zhang.xian@huawei.com Yao Li ZTE Zijinghua Road, Nanjing, China li.yao3@zte.com.cn Fei Zhang ZTE Zijinghua Road, Nanjing, China zhang.fei3@zte.com.cn Lei Wang ZTE East Huayuan Road, Haidian district, Beijing, China wang.lei131@zte.com.cn Gonzalez de Dios, et al. Expires January 7, 2013 [Page 23] Internet-Draft GMPLS Flexi-grid Framework July 2012 Guoying Zhang China Academy of Telecom Research No.52 Huayuan Bei Road, Beijing, China zhangguoying@ritt.cn Takehiro Tsuritani KDDI R&D Laboratories Inc. 2-1-15 Ohara, Fujimino, Saitama, Japan tsuri@kddilabs.jp Lei Liu KDDI R&D Laboratories Inc. 2-1-15 Ohara, Fujimino, Saitama, Japan le-liu@kddilabs.jp Eve Varma Alcatel-Lucent +1 732 239 7656 eve.varma@alcatel-lucent.com Young Lee Huawei Jianrui Han Huawei Sharfuddin Syed Infinera Rajan Rao Infinera Marco Sosa Infinera Biao Lu Infinera Abinder Dhillon Infinera Felipe Jimenez Arribas Telefonica I+D Andrew G. Malis Verizon Gonzalez de Dios, et al. Expires January 7, 2013 [Page 24] Internet-Draft GMPLS Flexi-grid Framework July 2012 Adrian Farrel Old Dog Consulting Daniel King Old Dog Consulting 14. Acknowledgments The authors would like to thank Pete Anslow for his insights and clarifications. 15. References 15.1. Normative References [G.709] International Telecomunications Union, "ITU-T Recommendation G.709: Interfaces for the Optical Transport Network (OTN).", March 2009. [G.805] International Telecomunications Union, "ITU-T Recommendation G.805: Generic functional architecture of transport networks.", March 2000. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004. [RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP) Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005. [RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel, "Label Switched Path Stitching with Generalized Multiprotocol Label Switching Traffic Engineering (GMPLS TE)", RFC 5150, February 2008. [RFC6163] Lee, Y., Bernstein, G., and W. Imajuku, "Framework for GMPLS and Path Computation Element (PCE) Control of Wavelength Switched Optical Networks (WSONs)", RFC 6163, April 2011. Gonzalez de Dios, et al. Expires January 7, 2013 [Page 25] Internet-Draft GMPLS Flexi-grid Framework July 2012 15.2. Informative References [G.694.1] International Telecomunications Union, "ITU-T Recommendation G.694.1, Spectral grids for WDM applications: DWDM frequency grid, draft v1.6 2011/12", 2011. [G.872] International Telecomunications Union, "ITU-T Recommendation G.872, Architecture of optical transport networks, draft v0.12 2012/03 (for discussion)", 2012. [WD12R2] International Telecomunications Union, WD12R2, Q12-SG15, ZTE, Ciena WP3, "Proposed media layer terminology for G.872", 05 2012. Authors' Addresses Oscar Gonzalez de Dios (editor) Telefonica I+D Don Ramon de la Cruz 82-84 Madrid, 28045 Spain Phone: +34913128832 Email: ogondio@tid.es Ramon Casellas (editor) CTTC Av. Carl Friedrich Gauss n.7 Castelldefels, Barcelona Spain Phone: +34 93 645 29 00 Email: ramon.casellas@cttc.es Fatai Zhang Huawei Huawei Base, Bantian, Longgang District Shenzhen, 518129 China Phone: +86-755-28972912 Email: zhangfatai@huawei.com Gonzalez de Dios, et al. Expires January 7, 2013 [Page 26] Internet-Draft GMPLS Flexi-grid Framework July 2012 Xihua Fu ZTE Ruanjian Avenue Nanjing, China Email: fu.xihua@zte.com.cn Daniele Ceccarelli Ericsson Via Calda 5 Genova, Italy Phone: +39 010 600 2512 Email: daniele.ceccarelli@ericsson.com Iftekhar Hussain Infinera 140 Caspian Ct. Sunnyvale, 94089 USA Phone: 408-572-5233 Email: ihussain@infinera.com Gonzalez de Dios, et al. Expires January 7, 2013 [Page 27]