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GMPLS OSPF-TE Extensions in support of Flexible Grid DWDM Networks

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors Fatai Zhang , Xian Zhang , Ramon Casellas , Oscar Gonzalez de Dios , Daniele Ceccarelli
Last updated 2013-06-28
Replaced by draft-ietf-ccamp-flexible-grid-ospf-ext, draft-ietf-ccamp-flexible-grid-ospf-ext, draft-ietf-ccamp-flexible-grid-ospf-ext, RFC 8363
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Network Working Group                                        Fatai Zhang 
Internet-Draft                                                Xian Zhang 
Intended status: Informational                                    Huawei 
                                                          Ramon Casellas 
                                                     O. Gonzalez de Dios 
                                                           D. Ceccarelli 
Expires: December 28, 2013                                 June 29, 2013 
  GMPLS OSPF-TE Extensions in support of Flexible Grid DWDM Networks  


   This memo describes the OSPF-TE extensions in support of GMPLS 
   control of networks that include devices that use the new flexible 
   optical grid. 

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   
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  This Internet-Draft will expire on December 28, 2013. 

Copyright Notice 
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   Copyright (c) 2013 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 
   ( in effect on the date of 
   publication of this document.  Please review these documents 
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   warranty as described in the Simplified BSD License. 

Table of Contents 

   1. Introduction ................................................ 2 
   2. Terminology ................................................. 3 
      2.1. Conventions Used in this Document .......................3 
   3. Requirements for Flexi-grid Routing ..........................3 
      3.1. Available Frequency Ranges.............................. 4 
      3.2. Application Compliance Considerations ...................5 
      3.3. Comparison with Fixed-grid DWDM Links ...................5 
   4. Extensions .................................................. 6 
      4.1. Available Labels Set Sub-TLV............................ 6 
         4.1.1. Inclusive/Exclusive Label Range ....................7 
         4.1.2. Inclusive/Exclusive Label Lists ....................7 
         4.1.3. Bitmap ............................................ 7 
      4.2. Extensions to Port Label Restriction sub-TLV ............7 
      4.3. Examples for Available Label Set Sub-TLV ................8 
   5. IANA Considerations ......................................... 9 
   6. Security Considerations...................................... 9 
   7. References ................................................. 10 
      7.1. Normative References................................... 10 
      7.2. Informative References................................. 10 
   8. Authors' Addresses ..........................................11 
   9. Contributors' Addresses..................................... 11 

    1. Introduction 

   [G.694.1] defines the Dense Wavelength Division Multiplexing (DWDM) 
   frequency grids for Wavelength Division Multiplexing (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 is the frequency 
   spacing between two allowed nominal central frequencies. All of the 
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   wavelengths on a fiber should use different central frequencies and 
   occupy a fixed bandwidth of frequency. 

   Fixed grid channel spacing is selected from 12.5 GHz, 25 GHz, 50 GHz, 
   100 GHz and integer multiples of 100 GHz.  But [G.694.1] also 
   defines "flexible grids", also known as "flexi-grid".  The terms 
   "frequency slot" (i.e., the frequency range allocated to a specific 
   channel and unavailable to other channels within a flexible grid) 
   and "slot width" (i.e., the full width of a frequency slot in a 
   flexible grid) are used to define a flexible grid. 

   [FLEX-FWK] defines a framework and the associated control plane 
   requirements for the GMPLS based control of flexi-grid DWDM networks. 

   [RFC6163] provides a framework for GMPLS and Path Computation 
   Element (PCE) control of Wavelength Switched Optical Networks 
   (WSONs), and [WSON-OSPF] defines the requirements and OSPF-TE 
   extensions in support of GMPLS control of a WSON. 

   [FLEX-SIG] describes requirements and protocol extensions for 
   signaling to set up LSPs in networks that support the flexi-grid, 
   and this document complements [FLEX-SIG] by describing the 
   requirement and extensions for OSPF-TE routing in a flexi-grid 

2. Terminology  

   For terminology related to flexi-grid, please consult [FLEX-FWK] and 

2.1. Conventions Used in this Document 

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   document are to be interpreted as described in RFC-2119 [RFC2119]. 

   3. Requirements for Flexi-grid Routing  

   The architecture for establishing LSPs in a Spectrum Switched 
   optical Network (SSON) is described in [FLEX-FWK].  

   An flexi-LSP occupies a specific frequency slot, i.e. a range of 
   frequencies.  The process of computing a route and the allocation of 
   a frequency slot is referred to as RSA (Routing and Spectrum 
   Assignment).  [FLEX-FWK] describes three types of architectural 
   approaches to RSA: combined RSA; separated RSA; and distributed SA.  
   The first two approaches among them could be called "centralized SA" 
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   because both routing and spectrum (frequency slot) assignment are 
   performed by centralized entity before the signaling procedure. 

   In the case of centralized SA, the assigned frequency slot is 
   specified in the Path message during LSP setup.  In the case of 
   distributed SA, the slot width of the flexi-grid LSP is specified in 
   the Path message, allowing the involved network elements to select 
   the frequency slot to be used. 

   If the capability of switching or converting the whole optical 
   spectrum allocated to an optical spectrum LSP is not available at 
   nodes along the path of the LSP, the LSP is subject to the Optical 
   "Spectrum Continuity Constraint", as described in [FLEX-FWK]. 

   The remainder of this section states the additional extensions on 
   the routing protocols in a flexi-grid network.  That is, the 
   additional information that must be collected and passed between 
   nodes in the network by the routing protocols in order to enable 
   correct path computation and signaling in support of LSPs within the 

3.1. Available Frequency Ranges  

   In the case of flexi-grids, the central frequency steps from 193.1 
   THz with 6.25 GHz granularity. The calculation method of central 
   frequency and the frequency slot width of flexi-LSP are defined in 

   On a DWDM link, the frequency slots must not overlap with each other.  
   However, the border frequencies of two frequency slots may be the 
   same frequency, i.e., the highest frequency of a frequency slot may 
   be the lowest frequency of the next frequency slot.  

                         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 = 193.1375 THz 
                     Slot width = 25 GHz    Slot width = 50 GHz 
                 Figure 1 - Two Frequency Slots on a Link 

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   Figure 1 shows two adjacent frequency slots on a link.  The highest 
   frequency of frequency slot 1 denoted by n=2 is the lowest frequency 
   of slot 2.  In this example, it means that the frequency range from 
   n=-2 to n=10 is occupied and is unavailable to other flexi-LSPs.  

   Hence, in order to clearly show which LSPs can be supported and what 
   frequency slots are unavailable, the available frequency ranges 
   should be advertised by the routing protocol for the flexi-grid DWDM 
   links.  A set of non-overlapping available frequency ranges should 
   be disseminated in order to allow efficient resource management of 
   flexi-grid DWDM links and RSA procedures which are described in 
   section 5.7 of [FLEX-FWK]. 

3.2. Application Compliance Considerations 

   As described in [G.694.1], devices or applications that make use of 
   the flexi-grid may not be capable of supporting every possible slot 
   width or position (i.e., central frequency).  In other words, 
   applications or implementations may be defined where only a subset 
   of the possible slot widths and positions are required to be 

   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).  

   Hence, in order to support all possible applications and 
   implementations the following information should be advertised for a 
   flexi-grid DWDM link:  

   o Central frequency granularity: a multiplier of 6.25 GHz. 

   o Slot width granularity: a multiplier of 12.5 GHz. 

   o Slot width range: two multipliers of 12.5GHz, each indicate the 
      minimal and maximal slot width supported by a port respectively.  

   The combination of slot width range and slot width granularity can 
   be used to determine the slot widths set supported by a port.  

3.3. Comparison with Fixed-grid DWDM Links  

   In the case of fixed-grid DWDM links, each wavelength has a pre-
   defined central frequency and each wavelength has the same frequency 
   range (i.e., there is a uniform channel spacing). Hence all the 
   wavelengths on a DWDM link can be identified uniquely simply by 
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   giving it an identifier (such as the central wavelength [RFC6205]), 
   and the status of the wavelengths (available or not) can be 
   advertised through a routing protocol. 

   Figure 2 shows a link that supports a fixed-grid with 50 GHz channel 
   spacing.  The central frequencies of the wavelengths are pre-defined 
   by values of 'n' and each wavelength occupies a fixed 50 GHz 
   frequency range as described in [G.694.1].  

        W(-2)  |    W(-1)  |    W(0)   |    W(1)   |     W(2)  | 
         |   50 GHz  |  50 GHz   |  50 GHz   |   50 GHz  |  
       n=-2        n=-1        n=0         n=1         n=2               
                    Central F = 193.1THz     
      Figure 2 - A Link Supports Fixed Wavelengths with 50 GHz Channel 
   Unlike the fixed-grid DWDM links, on a flexi-grid DWDM link the slot 
   width of the frequency slot are flexible as described in section 2.1. 
   That is, the value of m in the formula is uncertain before a 
   frequency slot is actually allocated.  For this reason, the 
   available frequency slot/ranges need to be advertised for a flexi-
   grid DWDM link instead of the specific "wavelengths" that are 
   sufficient for a fixed-grid link. 

4. Extensions 

   As described in [FLEX-FWK], the network connectivity topology 
   constructed by the links/nodes and node capabilities are the same as 
   for WSON, and can be advertised by the GMPLS routing protocols 
   (refer to section 6.2 of [RFC6163]).  In the flexi-grid case, the 
   available frequency ranges instead of the specific "wavelengths" are 
   advertised for the link.  This section defines the GMPLS OSPF-TE 
   extensions in support of advertising the available frequency ranges 
   for flexi-grid DWDM links. 

4.1. Available Labels Set Sub-TLV  

   As described in section 3.1, the available frequency ranges other 
   than the available frequency slots should be advertised for the 
   flexi-grid DWDM links.  The label encoding defined in [FLEX-LBL] is 

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   used to encode the label field in Available Labels Set sub-TLV [GEN-

4.1.1. Inclusive/Exclusive Label Range 

   The inclusive/exclusive label ranges format of the Available Labels 
   Set sub-TLV defined in [GEN-ENCODE] can be used for specifying the 
   frequency ranges of the flexi-grid DWDM links. 

   Note that multiple Available Labels Set sub-TLVs may be needed if 
   there are multiple discontinuous frequency ranges on a link. 

4.1.2. Inclusive/Exclusive Label Lists 

   The inclusive/exclusive label lists format of Available Labels Set 
   sub-TLV defined in [GEN-ENCODE] can be used for specifying the 
   available central frequencies of flexi-grid DWDM links.  

4.1.3. Bitmap 

   The bitmap format of Available Labels Set sub-TLV defined in [GEN-
   ENCODE] can be used for specifying the available central frequencies 
   of the flexi-grid DWDM links.  

   Each bit in the bit map represents a particular central frequency 
   with a value of 1/0 indicating whether the central frequency is in 
   the set or not.  Bit position zero represents the lowest central 
   frequency and corresponds to the base label, while each succeeding 
   bit position represents the next central frequency logically above 
   the previous.  

4.2. Extensions to Port Label Restriction sub-TLV 

   As described in Section 3.2, a port that supports flexi-grid may 
   support only a restricted subset of the full flexible grid.  The 
   Port Label Restriction sub-TLV is defined in [GEN-ENCODE] and [GEN-
   OSPF].  It can be used to describe the label restrictions on a port.  
   A new restriction type, the flexi-grid Restriction Type, is defined 
   here to specify the restrictions on a port to support flexi-grid. 

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     0                   1                   2                   3 
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
    | MatrixID      | RstType = TBA |            Reserved           | 
    |     C.F.G     |    S.W.G      |   Min Width   |   Max Width   | 
   MatrixID (8 bits): As defined in [GEN-ENCODE]. 

   RstType (Restriction Type, 8 bits): Takes the value (TBD) to 
   indicate the restrictions on a port to support flexi-grid. 
   C.F.G (Central Frequency Granularity, 8 bits): A positive integer.  
   Its value indicates the multiple of 6.25 GHz in terms of central 
   frequency granularity. 

   S.W.G (Slot Width Granularity, 8 bits): A positive integer.  Its 
   value indicates the multiple of 12.5 GHz in terms of slot width 

   Min Width (8 bits): A positive integer.  Its value indicates the 
   multiple of 12.5 GHz in terms of the supported minimal slot width. 

   Max Width (8 bits): A positive integer.  Its value indicates the 
   multiple of 12.5 GHz in terms of the supported maximal slot width. 

4.3. Examples for Available Label Set Sub-TLV 

   Figure 3 shows an example of available frequency range of a flexi-
   grid DWDM link.  

      -9 -8 -7 -6 -5 -4 -3 -2 -1 0  1  2  3  4  5  6  7  8  9 10  11     
                           |--Available Frequency Range--| 
                      Figure 3 - Flexi-grid DWDM Link 
   The symbol '+' represents the allowed nominal central frequency. The 
   symbol "--" represents a 6.25 GHz frequency unit.  The number on the 
   top of the line represents the 'n' in the frequency calculation 
   formula (193.1 + n * 0.00625).  The nominal central frequency is 
   193.1 THz when n equals zero. 

   Assume that the central frequency granularity is 6.25GHz, the label 
   set can be encoded as follows: 
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   Inclusive Label Range:  

   o  Start Slot = -2;  
   o  End Slot = 8.  
   The available central frequencies (-1, 0, 1, 2, 3, 4, 5, 6, 7) can 
   be deduced by the Inclusive Label Range, because the Central 
   Frequency Granularity is 6.25 GHz.  

   Inclusive Label Lists:  

   o  List Entry 1 = slot -1;  
   o  List Entry 2 = slot 0;  
   o  List Entry 3 = slot 1;  
   o  List Entry 4 = slot 2;  
   o  List Entry 5 = slot 3;  
   o  List Entry 6 = slot 4;  
   o  List Entry 7 = slot 5;  
   o  List Entry 8 = slot 6;  
   o  List Entry 9 = slot 7.  

   o  Base Slot = -1;  
   o  Bitmap = 111111111(padded out to a full multiple of 32 bits)  
    5. IANA Considerations 

   [GEN-OSPF] defines the Port label Restriction sub-TLV of OSPF TE 
   Link TLV.  It also creates a registry of values of the Restriction 
   Type field of that sub-TLV 

   IANA is requested to assign a new value from that registry as 

   Value    Meaning                    Reference 

   TBD      Flexi-grid restriction     [This.I-D] 

    6. Security Considerations 

   This document does not introduce any further security issues other 
   than those discussed in [RFC3630], [RFC4203]. 

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    7. References 

7.1. Normative References 

   [RFC2119] S. Bradner, "Key words for use in RFCs to indicate 
             requirements levels", RFC 2119, March 1997.  

   [G.694.1] ITU-T Recommendation G.694.1 (revision 2), "Spectral grids 
             for WDM applications: DWDM frequency grid", February 2012. 

   [GEN-ENCODE] Bernstein, G., Lee, Y., Li, D., and W. Imajuku, 
             "General Network Element Constraint Encoding for GMPLS 
             Controlled Networks", draft-ietf-ccamp-general-constraint-
             encode, work in progress. 

   [GEN-OSPF] Fatai Zhang, Y. Lee, Jianrui Han, G. Bernstein and Yunbin 
             Xu, " OSPF-TE Extensions for General Network Element 
             Constraints ", draft-ietf-ccamp-gmpls-general-constraints-
             ospf-te, work in progress. 

   [RFC6205] T. Otani and D. Li, "Generalized Labels for Lambda-Switch-
             Capable (LSC) Label Switching Routers", RFC 6205, March 

   [FLEX-LBL] King, D., Farrel, A. and Y. Li, "Generalized Labels for 
             the Flexi-Grid in Lambda Switch Capable (LSC) Label 
             Switching Routers", draft-farrkingel-ccamp-flexigrid-
             lambda-label, work in progress. 

7.2. Informative References 

   [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. 

   [FLEX-SIG] F.Zhang et al, "RSVP-TE Signaling Extensions in support 
             of Flexible-grid", draft-zhang-ccamp-flexible-grid-rsvp-
             te-ext, work in progress. 

   [FLEX-FWK] Gonzalez de Dios, O,, Casellas R., Zhang, F., Fu, X., 
             Ceccarelli, D., and I. Hussain, "Framework and 
             Requirements for GMPLS based control of Flexi-grid DWDM 
             networks', draft-ogrcetal-cammp-flexi-grid-fwk, work in 

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   [WSON-OSPF] Y. Lee and G. Bernstein, "GMPLS OSPF Enhancement for 
             Signal and Network Element Compatibility for Wavelength 
             Switched Optical Networks ", draft-ietf-ccamp-wson-signal-
             compatibility-ospf, work in progress.  

   8. Authors' Addresses 

   Fatai Zhang 
   Huawei Technologies 
   Xian Zhang  
   Huawei Technologies  
   Ramon Casellas, Ph.D. 
   Phone: +34 936452916 
   Oscar Gonzalez de Dios 
   Telefonica Investigacion y Desarrollo 
   Emilio Vargas 6 
   Madrid,   28045 
   Phone: +34 913374013 
   Daniele Ceccarelli 
   Via A. Negrone 1/A 
   Genova - Sestri Ponente 
9. Contributors' Addresses 

   Adrian Farrel 
   Old Dog Consulting 
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