Network Working Group Fatai Zhang Internet-Draft Xiaobing Zi Intended status: Standards Track Huawei O. Gonzalez de Dios Telefonica Expires: April 11, 2012 October 11, 2011 Requirements for GMPLS Control of Flexible Grids draft-zhang-ccamp-flexible-grid-requirements-00.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 15, 2012. Abstract A new flexible grid of DWDM is being developed within the ITU-T Study Group 15 to allow spectrum allocation much more efficient. This memo describes the requirements of GMPLS control of flexible grid DWDM network. Zhang Expires 2012 [Page 1] draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011 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 RFC-2119 [RFC2119]. Table of Contents 1. Introduction ................................................ 2 2. Characteristics of Flexible Grid............................. 3 2.1. Central Frequency....................................... 3 2.2. Slot Width ............................................. 4 3. Impact on WSON .............................................. 4 3.1. Fiber Links ............................................ 4 3.2. Optical Transmitters and Receivers ..................... 5 4. Routing and Spectrum Assignment.............................. 5 4.1. Architecture Approaches to RSA ......................... 6 4.1.1. Combined RSA (R&SA)................................ 6 4.1.2. Separated RSA (R+SA)............................... 7 4.1.3. Routing and Distributed SA (R+DSA) ................ 7 5. Requirements of GMPLS Control................................ 7 5.1. Routing ................................................ 7 5.1.1. Available Central Frequency of DWDM Links.......... 8 5.1.2. Tunable Optical Transmitters and Receivers......... 8 5.2. Signaling .............................................. 8 5.2.1. Slot Width Requirement............................. 8 5.2.2. Frequency Slot Representation ..................... 9 5.3. PCE .................................................... 9 5.3.1. RSA Computation Type............................... 9 5.3.2. RSA path re-optimization request/reply ............ 9 5.3.3. Frequency Constraints.............................. 10 6. Security Considerations...................................... 10 7. References .................................................. 10 7.1. Normative References.................................... 10 7.2. Informative References.................................. 11 8. Authors' Addresses .......................................... 12 1. Introduction In WDM applications, each wavelength needs to occupy a range of frequency on a fiber. [G.694.1v1] defines the DWDM frequency grids for WDM applications. A frequency grid is a reference set of frequencies used to denote allowed nominal central frequencies that may be used for defining applications. The channel spacing, i.e. the Zhang Expires 2012 [Page 2] draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011 frequency spacing between two allowed nominal central frequencies could be 12.5 GHz, 25 GHz, 50 GHz, 100 GHz and integer multiples of 100 GHz as defined in [G.694.1v1]. The channel spacing of the channels on a fiber is fixed. The speed of the optical signal becomes higher and higher with the advancement of the optical technology. In the near future, high- speed signal (beyond 100 Gbps or 400Gbps) will be deployed in the optical network. Those signals may not be accommodated in the channel spacing specified in [G.694.1v1]. On the other hand, the frequency bandwidth requirements of the optical signals with different rate speed may be different. When the optical signals with different rate speed are mixed to be transmitted on a fiber, the frequency allocation needs to be more flexible to promote the frequency efficiency. [G.FLEXIGRID], an updated version of [G.694.1v1] will be consented in December 2011 in support of flexible grids. The terms "frequency slot (The frequency range allocated to a specific channel and unavailable to other channels within a flexible grid)" and "slot width" (the full width of a frequency slot in a flexible grid) are introduced to define flexible grid. A channel is represented as a wavelength LSP in the control plane, it means a wavelength LSP should occupy a frequency slot on each fiber it traverses. In the case of flexible grid, the different wavelength LSPs may have different slot width on a fiber, i.e. the slot width is flexible on a fiber. WSON related documents are being developed currently and those documents focus on the GMPLS control of the fixed grids. This document describes the new characteristics of flexible grid and analysis the requirements of GMPLS control of flexible grid. 2. Characteristics of Flexible Grid Per [G.FLEXIGRID], flexible grid is defined for the DWDM system. Compared with the fixed grids (i.e. traditional DWDM), flexible grid has a smaller granularity for the central frequency and the slot width of the wavelength LSPs is more flexible on a fiber. 2.1. Central Frequency According to the definition of flexible DWDM grid in [G.FLEXIGRID], the step granularity for the central frequency of flexible grid is 6.25 GHz. The allowed nominal central frequency is calculated as such in the case of flexible grid: Zhang Expires 2012 [Page 3] draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011 Central Frequency = 193.1 THz + n * 0.00625 THz Where n is a positive or negative integer including 0. 2.2. Slot Width A slot width defined by: 12.5 GHz * m where m is a positive integer. On a fiber, the slot width of different wavelength LSPs may be different. 3. Impact on WSON Wavelength Switched Optical Networks (WSONs) are 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. WSON framework is described in [RFC 6163]. The introduced flexible grid brings some changes on WSON. 3.1. Fiber Links The flexible grid has a granularity of 6.25 GHz for the central frequency and a multiple of 12.5 GHz for the slot width. The fiber link for flexible grid can be modeled as shown in figure 1. -9 -8 -7 -6 -5 -4 3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 ...+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--... ^ 193.1THz Figure 1 Fiber link model for flexible grid The symbol '+' represents the allowed nominal central frequency. The symbol "--" represents a 6.25 GHz frequency unit. Each frequency slot must occupy an even multiple of the 6.25 GHz frequency units, i.e. a multiple of 12.5 GHz frequency range. The number on the top of the line represents the 'n' in the frequency calculation formula. The nominal central frequency is 193.1 THz when n equals zero. Hence, the following information is needed as parameters to perform basic, impairment-unaware modeling of a flexible grid link: o Available central frequencies: The set of central frequencies which are available on this link. Zhang Expires 2012 [Page 4] draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011 3.2. Optical Transmitters and Receivers Optical transmitter is the wavelength source and optical receiver is the wavelength sink of the WDM system. In each direction, the wavelength used by the transmitter and receiver along a path shall be consistent if there is no wavelength converter in the path. In the case of flexible grids, the central frequency utilized by a transmitter or receiver may be fixed or tunable. The slot width needed by different transmitters or receivers may be different. Hence, the changes introduced by flexible grid of fundamental modeling parameters for optical transmitters and receivers from the control plane perspective are: o Available central frequencies: The set of central frequencies which can be used by an optical transmitter or receiver. o Slot width: The slot width needed by a transmitter or receiver. 4. Routing and Spectrum Assignment A wavelength LSP should occupy a frequency slot, i.e. a range of frequency. The route computation and frequency slot assignment could be called RSA (Routing and Spectrum Assignment). Similar to fixed grids network, if there is no wavelength converter in an optical network, there is "wavelength continuity constraint" for a flexible grid wavelength LSP which is described as section 4 of [RFC 6163]. Because of the high cost of the wavelength converters, an optical network is generally deployed with limited or without wavelength converters. Hence, the wavelength continuity constraint should be considered without wavelength converters during the RSA process. The RSA should determine a route and frequency slot for a wavelength LSP. The frequency slot can be deduced from the two parameters which are central frequency and slot width as follows: Lowest frequency = (central frequency) - (slot width)/2; Highest frequency = (central frequency) + (slot width)/2. Hence, after a route is determined, the SA process should determine the central frequency for a wavelength LSP based on the slot width and available central frequency information of the links that the route traverses. Zhang Expires 2012 [Page 5] draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011 Figure 2 shows two wavelength LSPs that traverse a link. Frequency Slot 1 Frequency Slot 2 ------------- ------------------- | | | | -9 -8 -7 -6 -5 -4 -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 Two Wavelength LSPs traverse a Link The two wavelengths shown in figure 2 have the following meaning: Wavelength LSP 1: central frequency = 193.1 THz, slot width = 25 GHz. It means the frequency slot [193.0875 THz, 193.1125 THz] is assigned to this wavelength LSP. Wavelength LSP 2: central frequency = 193.14375 THz, slot width = 37.5 GHz. It means the frequency slot [193.125 THz, 193.1625 THz] is assigned to this wavelength LSP. Note that the frequency slots of two wavelength LSPs on a fiber should not overlap with each other. 4.1. Architecture Approaches to RSA Similar to RWA for fixed grids, three different ways of performing RSA in conjunction with the control plane are considered. The approaches are provided for reference purposes only, and other approaches are possible. 4.1.1. Combined RSA (R&SA) In this case, a centralized entity performs the routing and frequency slot assignment. The centralized entity should have the detailed network information, e.g. network topology, available frequency resource on each link, node capability, etc. The centralized computation entity could be placed on the following two places: o PCE: PCE get the detailed network information and implement the RSA algorithm for RSA requests from the PCCs. Zhang Expires 2012 [Page 6] draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011 o Ingress node: Ingress node gets the detailed network information through routing protocol and implements the RSA algorithm when a wavelength LSP request is received. 4.1.2. 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 determines the route and assigns the frequency slot. The first entity should get the network topology information to compute the proper routes; the second entity should get the available frequency resource information and nodes capabilities to assign the spectrum. 4.1.3. Routing and Distributed SA (R+DSA) In this case, one entity computes the route and the frequency slot assignment is performed hop-by-hop in a distributed way along the route. The available central frequencies which meet the wavelength continuity constraint should be collected hop by hop along the route. This procedure can be implemented by GMPLS signaling protocol. The GMPLS signaling procedure is similar to the procedure which is described in section 4.1.3 of [RFC 6163] except that the label set should specify the available central frequency that meet the slot width requirement of the wavelength LSP, i.e. the frequency slot which is determined by the central frequency and slot width should not overlap with the existing wavelength LSPs. 5. Requirements of GMPLS Control According to the different architecture approaches to RSA, it brings some additional requirements of GMPLS control. 5.1. Routing In the case of combined RSA architecture, the computation entity needs to get the detailed network information, i.e. network topology, available frequency resources and node capabilities. This can be done by the GMPLS routing protocol. Compared with [RFC6163], except wavelength-specific availability information, the network topology and node capabilities are the same as WSON which can be advertised by GMPLS routing protocol (refer to Zhang Expires 2012 [Page 7] draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011 section 6.2 of [RFC6163]. This section analysis the changes of link information brought by flexible grids. 5.1.1. Available Central Frequency of DWDM Links In the case of flexible grids, the central frequency steps from 193.1 THz towards the two sides with 6.25 GHz granularity (See Figure 1). Different wavelength LSPs could occupy the frequency slots with different slot width. Hence, the available central frequency should be advertised, but the slot width is not required to be advertised for a DWDM link. 5.1.2. Tunable Optical Transmitters and Receivers The slot width of a wavelength LSP is determined by the transmitter and receiver. The transmitters and receivers could be mapped to ADD/DROP interfaces in WSON. Hence, the slot width of an ADD/DROP interface should be advertised. The central frequency of a transmitter or receiver could be fixed or tunable. Hence, the available central frequencies should be advertised. 5.2. Signaling 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 wavelength LSP. This brings the following changes to the GMPLS signaling. 5.2.1. Slot Width Requirement In order to allocate a proper frequency slot for a wavelength LSP, the signaling should specify the slot width requirement of a wavelength LSP. Then the intermediate nodes can collect the acceptable central frequencies that meet the slot width requirement hop by hop. The tail node also needs to know the slot width of a wavelength LSP to assign the proper frequency resource. Hence, the slot width requirement should be specified in the signaling message when a wavelength LSP is being set up. Zhang Expires 2012 [Page 8] draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011 5.2.2. Frequency Slot Representation The frequency slot can be determined by the two parameters, which are central frequency and slot width as described in section 4. Hence, the frequency slot can be represented as a combination of [central frequency, slot width]. The signaling messages should be able to specify the accurate frequency slot which is assigned to a wavelength LSP, i.e. the signaling messages should be able to specify the central frequency and slot width of a wavelength LSP. 5.3. PCE [WSON-PCE] describes the architecture and requirements of PCE for WSON. In the case of flexible grid, RSA instead of RWA is used for routing and frequency slot assignment. Hence PCE should implement RSA for flexible grids. The architecture and requirements of PCE for flexible grids are similar to what is described in [WSON-PCE]. This section describes the changes brought by flexible grids. 5.3.1. RSA Computation Type The PCReq message must be able to specify the computation type of the request: o Combined RSA: Both of the route and frequency slot should be provided by PCE. o Routing Only: Only the route is requested to be provided by PCE. The PCRep Message must be able to specify the route, frequency slot assigned to the route. In the case where a valid path is not found, the PCRep Message must be able to specify why the path is not found (e.g., no route, spectrum not found, etc.) 5.3.2. RSA path re-optimization request/reply For a re-optimization request, the PCReq Message must provide the path to be re-optimized and include the following options: o Re-optimize the path keeping the same frequency slot. o Re-optimize spectrum keeping the same path. o Re-optimize allowing both frequency slot and the path to change. Zhang Expires 2012 [Page 9] draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011 The corresponding PCRep Message for the re-optimized request must provide the Re-optimized path and frequency slot. In case that the path is not found, the PCRep Message must include why the path is not found (e.g., no route, frequency slot not found, both route and frequency slot not found, etc.) 5.3.3. Frequency Constraints PCE for flexible grids should consider the following constraints brought by the transmitters and receivers: o Available central frequencies: The set of central frequency that can be used by an optical transmitter or receiver. o Slot width: The slot width needed by a transmitter or receiver. This constraint may be provided by requester (PCC) in PCReq or the PCE's TEDB which stores the ability of the origination laser transmitter. PCC may also specify the frequency constraints for policy reasons. In this case, the constraints should be specified in the PCReq message. PCE compute the route and assign the frequency slot to meet the constraints specified in the PCReq message. Then return the result to the PCC. 6. Security Considerations This document does not introduce any further security issues other than those described in [RFC6163] and [RFC5920]. 7. References 7.1. Normative References [RFC2119] S. Bradner, "Key words for use in RFCs to indicate requirements levels", RFC 2119, March 1997. [WSON-PCE] Y. Lee, G. Bernstein, Jonas Martensson, T. Takeda and T. Tsuritani, "PCEP Requirements for WSON Routing and Wavelength Assignment", draft-ietf-pce-wson-routing- wavelength-05, July 2011. Zhang Expires 2012 [Page 10] draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011 [RFC6163] Y. Lee, G. Bernstein and W. Imajuku, "Framework for GMPLS and Path Computation Element (PCE) Control of Wavelength Switched Optical Networks (WSONs)", RFC 6163, April 2011. [G.FLEXIGRID] Draft revised G.694.1 version 1.3, Unpublished ITU-T Study Group 15, Question 6. 7.2. Informative References [G.694.1v1] ITU-T Recommendation G.694.1, Spectral grids for WDM applications: DWDM frequency grid, June 2002. [RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks", RFC 5920, July 2010. Zhang Expires 2012 [Page 11] draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011 8. Authors' Addresses Fatai Zhang Huawei Technologies F3-5-B R&D Center, Huawei Base Bantian, Longgang District Shenzhen 518129 P.R.China Phone: +86-755-28972912 Email: zhangfatai@huawei.com Oscar Gonzalez de Dios Telefonica Investigacion y Desarrollo Emilio Vargas 6 Madrid, 28045 Spain Phone: +34 913374013 Email: ogondio@tid.es Xiaobing Zi Huawei Technologies F3-5-B R&D Center, Huawei Base Bantian, Longgang District Shenzhen 518129 P.R.China Phone: +86-755-28973229 Email: zixiaobing@huawei.com Intellectual Property The IETF Trust takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in any IETF Document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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