Network Working Group Qilei Wang Internet-Draft Xihua Fu Intended status: Standards Track ZTE Corporation Expires: September 1, 2012 Feb 29, 2012 Framework for GMPLS Control of Flexible Grid Network draft-wang-ccamp-gmpls-flexigrid-framework-00.txt Abstract This document provides a framework for applying Generalized Multi- Protocol Label Switching (GMPLS) and the Path Computation Element (PCE) architecture to control the flexible grid network base on the Wavelength Switched Optical Networks (WSONs). GMPLS control of WSON which is addressed in RFC6163 is out of the scope of this document. This document focuses on the topological elements changes and new path selection constraints that flexible grid technology takes. Impairments related technology is not covered in this document. 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 September 1, 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 Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 1] Internet-Draft flexible grid Feb 2012 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Flexible Grid Networks . . . . . . . . . . . . . . . . . . . . 4 3.1. WDM Links . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. Optical Transmitters and Receivers . . . . . . . . . . . . 5 3.3. Optical Signals in Flexible Grid Network . . . . . . . . . 5 3.3.1. Optical Tributary Signals . . . . . . . . . . . . . . 6 3.3.2. WSON Signal Characteristics . . . . . . . . . . . . . 6 3.4. ROADMs, OXCs, Splitters, Combiners, and FOADMs . . . . . . 6 3.4.1. Reconfigurable Optical Add/Drop Multiplexers, OXCs and FOADM . . . . . . . . . . . . . . . . . . . . . . 7 3.4.2. Splitters and Combiners . . . . . . . . . . . . . . . 7 3.5. Electro-Optical Systems . . . . . . . . . . . . . . . . . 7 4. Routing and wavelength Assignment in flexible grid network . . 8 5. GMPLS and PCE Control . . . . . . . . . . . . . . . . . . . . 8 5.1. Extension to GMPLS Signaling . . . . . . . . . . . . . . . 9 5.2. Extension to GMPLS Routing . . . . . . . . . . . . . . . . 9 5.3. Optical Path Computation and Implications for PCE . . . . 11 5.3.1. Optical Path Constraints and Electro-Optical Element Signal Compatibility . . . . . . . . . . . . . 11 5.3.2. Discovery of RWA-Capable PCEs . . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.1. Normative References . . . . . . . . . . . . . . . . . . . 11 7.2. Informative References . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 2] Internet-Draft flexible grid Feb 2012 1. Introduction Flexible grid is a new DWDM application which is defined in the newest version of [G.694.1]. A flexible grid network can select its data channels with arbitrary slot width, and mainly be used to setup path with higher bitrates. This is different from traditional fixed grid DWDM technology, which uses fixed slot width. Flexible grid network is a WDM-based optical network in which switching is performed selectively based on the center wavelength of an optical signal as well as WSON, and flexible grid network can be 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 which are used in WSON, whereas these subsystems have flexible grid characteristics. Wavelength Switched Optical Network (WSON) is the application of Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] operation to traditional fixed grid WDM network. As described in the previous section, flexible grid network is a new WDM network which introduces some new characteristics, so GMPLS also can be used to operate flexible grid network. WSON specific descriptions are out of the scope of this document. This document provides a framework for applying the GMPLS architecture and protocols [RFC3945] and the PCE architecture [RFC4655] to the control and operation of flexible grid networks. In order to help GMPLS and PCE use for flexible grid network, this document first focuses on the subsystems and new characteristics information that flexible grid network brings and then modeled the characteristics information by GMPLS and PCE. This work will help facilitate the development of protocol solution models and protocol extensions within the GMPLS and PCE protocol families. 1.1. Conventions used in this document 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. Terminology o Flexible Grid: a new WDM technology different from traditional fixed grid DWDM technology defined with the aim of allowing flexible optical spectrum management, in which the Slot Width of the wavelength ranges allocated to different channels are flexible (variable sized). Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 3] Internet-Draft flexible grid Feb 2012 o Wavelength Range: [RFC6163] gives a description of this terminology.Wavelength range given a mapping between labels and the ITU-T grids, each range could be expressed in terms of a tuple, (lambda1, lambda2) or (freq1, freq2), where the lambdas or frequencies can be represented by 32-bit integers. o Frequency slot: The definition in [G.694.1] is shown here. The frequency range allocated to a channel and unavailable to other channels within a flexible grid. A frequency slot is defined by its nominal central frequency and its slot width. o Slot width: The full width of a frequency slot in a flexible grid. 3. Flexible Grid Networks Wavelength Switched Optical Network (WSON) related documents cover the constraints information that needs to be considered by Path Computation Element (PCE). Emergence of flexible grid DWDM technology raises some new features that would be considered in the process of path computation. This section examines the flexible grid subsystems' new features and mainly focuses on the new features or constraints information that impact the flexible grid path selection process (i.e. wavelength selection). The subsequent sections which follow the sequence of the section addressed in [RFC6163] review and model some new features that need to be emphasized by control plane. 3.1. WDM Links According to the newest version of [G.694.1], the nominal central frequencies for the flexible grid network are defined with a granularity of 6.25 GHz and the frequency slot widths are defined as a multiple of 12.5 GHz. As described in section 3.1 of [RFC 6163], parameters that include wavelength range and channel spacing is needed to perform basic, impairment-unaware modeling of a WDM link. Wavelength range can be used to give a mapping between labels and the ITU-T grids and each range could be expressed in terms of a tuple, (lambda1, lambda2) or (freq1, freq2). Wavelength range is also needed in flexible grid network, but some changes are required when consider the flexible feature. Channel spacing is also needed, but new channel spacing needs to be added to this field base on WSON when used in flexible grid network. In addition to the wavelength range and channel spacing, indication SHOULD also be added to indicate the link support flexible grid DWDM technology. Similar to WSON, this information is relatively statically for a particular link. Such information may be used locally during wavelength assignment via signaling. Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 4] Internet-Draft flexible grid Feb 2012 3.2. Optical Transmitters and Receivers WDM optical systems make use of optical transmitters and receivers utilizing different wavelengths (frequencies). Flexible grid brings some new features to transmitters and receivers compare to traditional fixed grid technology. Besides characteristics like "Tunable", "Tuning range", "Tuning time" and "Spectral characteristics and stability" which are addressed in [RFC6163], some new features could also impact optical transmitters and receivers in the process of control plane path computation. Before model the new features from control plane perspective, focus SHOULD be paid to the old modeling parameters (here we mainly focus on "Tuning range"), because flexible grid may bring changes to these parameters. "Tuning range" may be encode by some different format from traditional fixed grid technology, as nominal central frequencies can't be figured out before the path setup in flexible grid network. New features that would impact optical transmitters and receivers in the process of control plane path computation are listed below: Slot width: main difference between flexible grid and traditional fixed grid is flexible grid network can select its data channels with arbitrary slot width compare to fixed slot width in traditional fixed grid network. This parameter indicates slot width needed by a transmitter or receiver and SHOULD be considered in the process of path computation. 3.3. Optical Signals in Flexible Grid Network The fundamental unit of switching in WSONs is intuitively that of a "wavelength". The transmitters and receivers in these networks will deal with one wavelength at a time, while the switching systems themselves can deal with multiple wavelengths at a time. Key non- impairment-related parameters which are listed in [RFC6163] are shown below: o (a) Minimum channel spacing (GHz) o (b) Minimum and maximum central frequency o (c) Bitrates/Line coding (modulation) of optical tributary signals For the purposes of modeling the WSON in the control plane, new parameters that SHOULD be considered are shown here: Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 5] Internet-Draft flexible grid Feb 2012 o (d) Minimum and Maximum Slot Width o (e) Slot Width (d) is considered properties of the link and restrictions on the GMPLS Labels and (e) is a property of the "signal". 3.3.1. Optical Tributary Signals In [RFC6163], "optical tributary signal classes" are characterized by a modulation format and bitrates range and both of them are key parameters in characterizing the optical tributary signal. Note that, with advances in technology, more optical tributary signal classes would be added in flexible grid network. Currently no more parameters are needed to depict flexible grid network in the process of path computation. New parameter "slot width" is needed here, and SHOULD be specified in the signaling process of flexible grid path, because paths in flexible grid network often with variable slot width. 3.3.2. WSON Signal Characteristics Description about WSON signal characteristics in [RFC6163] also can be applied to this document. Fundamental unit of switching in flexible grid network is also "wavelength". WSON signal characteristics like optical tributary signal class (modulation format), forward error correction (FEC), central frequency (wavelength), bitrates and general protocol identifier (G-PID) are still used in flexible grid network in the process of path computation and some more modulation formats and FECs may be added to describe flexible grid network signal characteristics. Except the parameter that have been included in [RFC6163], the parameter (i.e., slot width) described in the previous section is also needed here, WSON signal would convey this value in the process of path computation in order to select a suitable path. 3.4. ROADMs, OXCs, Splitters, Combiners, and FOADMs This section mainly focuses on optical devices such as ROADMs, Optical Cross-Connects (OXCs), splitters, combiners, and Fixed Optical Add/Drop Multiplexers (FOADMs) which can be used in flexible grid network and examines their parameters of these devices that can be used in the process of control plane path computation. Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 6] Internet-Draft flexible grid Feb 2012 3.4.1. Reconfigurable Optical Add/Drop Multiplexers, OXCs and FOADM Switched connectivity matrix is needed here to show whether a wavelength on input port can be connected to an output port. Besides switched connectivity matrix and wavelength restrictions included in [RFC6163], new wavelength restriction of a port on a ROADM which are brought by flexible grid SHOULD be considered. A port on a ROADM could have following wavelength restrictions in flexible grid: o (a) Maximum/Minimum slot width that a port support Requirements and descriptions about the restrictions information can be found in [draft-wangl-ccamp-ospf-ext-constraint-flexi-grid]. o (b) Wavelength ranges partition information according to bitrates and/or modulation format This restrictions information will help reduce fragments in flexible grid network. Requirements related description can be found in [draft-wang-ccamp-flexible-grid-wavelength-range-ospf-te]. These restrictions information can also be applied to fixed optical Add/Drop Multiplexers. 3.4.2. Splitters and Combiners Nothing is new except switched connectivity matrix and this has been addressed in [RFC6163]. 3.5. Electro-Optical Systems OEO switches, wavelength converters, and regenerators all share a similar property: they can be more or less "transparent" to an "optical signal" depending on their functionality and/or implementation. Properties that are described in [RFC6163] can be applied to flexible grid, and these properties can satisfy path computation without taking ant new features into consideration. Modeling of OEO switches, wavelength converters and regenerators can also be applied to flexible grid. Regenerator can be used to restore signal quality. Bitrates range and modulation formats that the regenerator support need to be used to help path computation, whereas slot width do not (May be someone Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 7] Internet-Draft flexible grid Feb 2012 will talk about slot width). If one regenerator is designed to handle signal with specific bitrates and modulation formats, then it would support the corresponding slot width because slot width can be derived by modulation format and bitrates. Even if the slot width is changed by the electro-optical systems due to the change of modulation format, the slot width that has already changed may not be explicitly specified because bitrates and modulation format are explicitly specified. 4. Routing and wavelength Assignment in flexible grid network This section briefly describes the constraints information of routing and wavelength assignment in the flexible grid network. The input to basic RWA in flexible grid network are the requested optical path's source and destination, the network topology, the locations and capabilities of any wavelength converters, the wavelengths available on each optical link and port label constraints information such as slot width range that a port support and wavelength range partition information by bitrates and/or modulation formats. The output that provided by RWA in flexible grid network are an explicit route through ROADMs, a wavelength for optical transmitter, the slot width that this wavelength occupies, and a set of locations (generally associated with ROADMs or switches) where wavelength conversion is to occur and the new wavelength to be used on each component link after that point in the route. In [RFC6163], three different ways of performing RWA in conjunction with the control plane are shown here: 1) Combined RWA 2) Separated R and WA (R + WA) 3) Routing and Distributed WA (R + DWA) These ways can also be applied to flexible grid control plane path computation. Related description about these three architectures can be found in [RFC6163]. 5. GMPLS and PCE Control Flexible grid brings some new features to WDM network, and consequently WSON would add some extensions or change in order to adapt to control of flexible grid. Extensions to GMPLS signaling, routing and PCE are described in this section. Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 8] Internet-Draft flexible grid Feb 2012 5.1. Extension to GMPLS Signaling Support for WSON signaling exists in [RFC3471], [RFC4328] and [draft-ietf-ccamp-wson-signaling]. However, a number of practical issues arise in the identification of wavelengths and signals in wavelength assignment in flexible grid. A mapping between label and wavelength is needed to simplify the characterization of WDM links and WSON devices. The mapping like the one described in [draft-farrkingel-ccamp-flexigrid-lambda-label] provides label and wavelength mapping for communication between PCE and WSON PCCs. Different LSP may occupy different slot width if paths have different bitrates and modulation format in flexible grid network. So in the flexible grid network, not only central frequency is needed, but also slot width SHOULD be included to identify a channel in the process of path computation in flexible grid network. GMPLS Signaling should be able to convey the central frequency and slot width information in the process of path request of a LSC LSP. If the slot width is changed due to the change of modulation format, signaling should also be able to express this. Except methods that are specified in [draft-farrkingel-ccamp-flexigrid-lambda-label], [draft-hussain-ccamp-super-channel-label] and [draft-zhang-ccamp-flexible-grid-rsvp-te-ext] also provide methods to carry central frequency and slot width information in the process of signaling. Note: extension to GMPLS signaling SHOULD be compatible with current signaling protocol. 5.2. Extension to GMPLS Routing The following subsystem's properties are needed by IGP to minimally characterize WSON, also these properties are needed to characterize flexible grid control plane. This section addresses the constraints information needed to model flexible grid from the control plane perspective base on the Wavelength Switched Optical Network (WSON). 1) 1. WDM link properties (allowed wavelengths) 2) 2. Optical transmitters (wavelength range) 3) 3. ROADM/FOADM properties (connectivity matrix, port wavelength restrictions) Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 9] Internet-Draft flexible grid Feb 2012 4) 4. Wavelength converter properties (per network element, may change if a common limited shared pool is used) Here 1, 2 and 3 are re-considered in the flexible grid network. Firstly, wavelengths available on WDM link and port of optical transmitters are advertised through routing protocol, the wavelength available information can be used by path computation element to compute a suitable end-to-end LSP. As different flexible grid channels always have different slot widths and channels' central frequency position and slot width can't be decided in advance, so mapping between label and wavelength may not be able to use the representation similar to [RFC6205] to represent every channel. New label formats and representation of wavelength available are needed in routing protocol to transfer IGP information between nodes and PCEs. Extensions to label set field SHOULD be able to represent the wavelength available validly in flexible grid network. Allowed wavelengths on WDM link and wavelength range on optical transmitters would adapt to this change.[draft-dhillon-ccamp-super-channel-ospfte-ext], [draft-wangl-ccamp-ospf-ext-constraint-flexi-grid] and [draft-zhang-ccamp-flexible-grid-ospf-ext] give some different methods to represent the available wavelengths. Secondly, some new ROADM/FOADM properties brought by flexible grid need to be advertised by routing protocol in order to help path computation. In the section 3, properties of ROADM/FOADM are described. The first one, maximum/minimum slot width supported on one port need to be advertised. This slot width constraint information of a port (i.e., slot width constraint information of a WSS) SHOULD be known by path computation element in order to compute a suitable path. Ports on a link may support different grid granularities and slot widths. LMP can be run between two neighbor nodes to negotiate these attributes and related extension can be found in [draft-li-ccamp-grid-property-lmp]. This is optional because routing protocol can also be used to deal with it. The second one, wavelength range allocation information of ROADM/FOADM needs to be advertised through routing protocol. Grouping of wavelength of the same bitrates and/or modulation formats would help reduce fragments. Channels in the same wavelength range with the same bitrates looks almost like fixed grid technology, and they won't generate much fragment in the path setup and release because every channel use the same slot width. Requirements of wavelength range allocation and protocol extensions can be found in [draft-wang-ccamp-flexible-grid-wavelength-range-ospf-te]. Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 10] Internet-Draft flexible grid Feb 2012 5.3. Optical Path Computation and Implications for PCE Extensions to PCEP can be found in [draft-lee-pce-wson-rwa-ext] base on Wavelength Switched Optical Network. Emergence of flexible grid brings some extension to current draft. PCEP SHOULD be able to support flexible grid path computation. 5.3.1. Optical Path Constraints and Electro-Optical Element Signal Compatibility Flexible grid may not change the computation architectures of WSON, but new constraints information is needed in the process of path computation. When requesting a path computation to PCE, the PCC should be able to indicate the G-PID type of an LSP, the signal attributes at the transmitter and receiver. As no new attribute need to be considered, no implication is indicated here. And the PCE should be able to respond to the PCC with the following except the conformity of the requested optical characteristics associated with the resulting LSP with the source, sink, and NE along the LSP and additional LSP attributes modified along the path: ~ Slot width of the path should be respond to the PCC as flexible grid channels may have different slot widths. 5.3.2. Discovery of RWA-Capable PCEs > Not all PCEs within a domain would necessarily need the capability of flexible grid path computation. Therefore, it would be useful to indicate that a PCE has the ability to deal with flexible grid via the discovery mechanisms being established for PCE discovery in [RFC5088]. Extensions to [RFC5088] are needed to achieve this goal. 6. Security Considerations TBD 7. References 7.1. Normative References [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. Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 11] Internet-Draft flexible grid Feb 2012 7.2. Informative References [G.694.1 v1] International Telecommunications Union, "Draft revised G.694.1 version 1.3". [flexible-grid-ospf-ext] Fatai Zhang, Xiaobing Zi, Ramon Casellas, O. Gonzalez de Dios, and D. Ceccarelli, "GMPLS OSPF-TE Extensions in support of Flexible-Grid in DWDM Networks", draft-zhang-ccamp-flexible-grid-ospf-ext-00.txt . [flexible-grid-requirements] Fatai Zhang, Xiaobing Zi, O. Gonzalez de Dios, and Ramon Casellas, "Requirements for GMPLS Control of Flexible Grids", draft-zhang-ccamp-flexible-grid-requirements-01.txt . [flexible-grid-rsvp-te] Fatai Zhang, O. Gonzalez de Dios, and D. Ceccarelli, "RSVP-TE Signaling Extensions in support of Flexible Grid", draft-zhang-ccamp-flexible-grid-rsvp-te-ext-00.txt . [flexigrid-lambda-label] D. King, A. Farrel, Y. Li, F. Zhang, and R. Casellas, "Generalized Labels for the Flexi-Grid in Lambda-Switch- Capable (LSC) Label Switching Routers", draft-farrkingel-ccamp-flexigrid-lambda-label-01.txt . [ospf-ext-constraint-flexi-grid] L Wang, Y Li, "OSPF Extensions for Routing Constraint Encoding in Flexible-Grid Networks", draft-wangl-ccamp-ospf-ext-constraint-flexi-grid-00.txt . [super-channel-label] Iftekhar Hussain, Abinder Dhillon, Zhong Pan, Marco Sosa and Bert Basch, Steve Liu, Andrew G. Malis, "Generalized Label for Super-Channel Assignment on Flexible Grid", draft-hussain-ccamp-super-channel-label-02.txt . [super-channel-ospfte] Abinder Dhillon, Iftekhar Hussain, Rajan Rao, Marco Sosa, "OSPFTE extension to support GMPLS for Flex Grid", draft-dhillon-ccamp-super-channel-ospfte-ext-02.txt . Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 12] Internet-Draft flexible grid Feb 2012 Authors' Addresses Qilei Wang ZTE Corporation Email: wang.qilei@zte.com.cn Xihua Fu ZTE Corporation ZTE Plaza, No.10, Tangyan South Road, Gaoxin District Xi'an P.R.China Email: fu.xihua@zte.com.cn Qilei Wang & Xihua Fu Expires September 1, 2012 [Page 13]