GMPLS OSPF-TE Extensions in support of Flexible-Grid in DWDM Networks
draft-zhang-ccamp-flexible-grid-ospf-ext-00

Network Working Group                                       Fatai Zhang 
Internet-Draft                                              Xiaobing Zi 
Intended status: Standards Track                                 Huawei 
                                                         Ramon Casellas 
                                                                   CTTC 
                                                    O. Gonzalez de Dios 
                                                             Telefonica 
                                                          D. Ceccarelli 
                                                               Ericsson 
Expires: April 24, 2012                                October 24, 2011 
                                      

                                    
  GMPLS OSPF-TE Extensions in support of Flexible-Grid in DWDM Networks  
                                      
              draft-zhang-ccamp-flexible-grid-ospf-ext-00.txt 

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Abstract 

   This memo describes the OSPF-TE extensions in support of GMPLS 
   control for flexible-grid in DWDM networks. 

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. Terminology .................................................. 3 
   3. Requirements for Flexible-grid Routing ....................... 3 
      3.1. Available Frequency Ranges on the Flexible-Grid DWDM Links3 
      3.2. Comparison with Fixed-grid DWDM Links ................... 5 
   4. Extensions ................................................... 5 
      4.1. Available Labels Set sub-TLV ............................ 6 
      4.2. Examples ................................................ 7 
   5. IANA Considerations .......................................... 8 
   6. Security Considerations ...................................... 8 
   7. References ................................................... 8 
   8. Authors' Addresses .......................................... 10 
    
    

1. Introduction 

   [G.694.1v1] defines the Dense Wavelength Division Multiplexing (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 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]. All of the 
   wavelengths on a fiber should use different central frequencies and 
   occupy a fixed bandwidth of frequency.  

   [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 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 
   address flexible-grids. A channel is represented as a LSC (Lambda 
 
 
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   Switching Capable) LSP in the control plane, i.e. a LSC LSP should 
   occupy a frequency slot on each fiber it traverses. In the case of 
   flexible-grid, different LSC LSPs may have different slot width on a 
   fiber, i.e. the slot width is flexible on a fiber.  

   [WSON-OSPF] defines the OSPF-TE extensions for WSON networks, which 
   focuses on the fixed grids of DWDM. [GEN-OSPF] defines OSPF-TE 
   extensions in support of the general network element constraints   
   under the control of GMPLS. This document describes the additional 
   requirements and extensions of routing protocol brought by flexible-
   grid.  

   This document uses the fiber link model which is shown in [FLEXIBLE-
   REQ] to describe the requirement and extensions for routing. The 
   flexible-grid related terminologies can also refer to [FLEXIBLE-REQ].   

2. Terminology  

   Flexible Grid: See [FLEXIBLE-REQ]. 

   Frequency Slot Width: See [FLEXIBLE-REQ]. 

   Frequency Range: See [FLEXIBLE-REQ]. 

   SSON: Spectrum-Switched Optical Networks; See [FLEXIBLE-REQ]. 

   LSC SS-LSP or flexi-LSP (Lambda Switch Capable Spectrum-Switched 
   Label Switched Path): a control plane construct that represents a 
   data plane connection in which the switching involves a frequency 
   slot of a variable (flexible) slot width. The mapped client signal 
   is transported over the slot width, using spectrum efficient 
   modulations such as Coherent Optical Orthogonal Frequency Division 
   Multiplexing (CO-OFDM).  

3. Requirements for Flexible-grid Routing  

   As described in [FLEXIBLE-REQ], the main changes for routing brought 
   by flexible-grid are related to the DWDM links.  

3.1. Available Frequency Ranges on the Flexible-Grid DWDM Links  

   In the case of flexible-grids, the central frequency steps from 
   193.1 THz with 6.25 GHz granularity. The central frequency is 
   calculated as follows:  

   Central Frequency = 193.1 THz + n * 0.00625 THz  

 
 
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   Where n is a positive or negative integer including 0.  

   Different LSC LSPs could occupy frequency slots with different slot 
   width. The frequency slot width of a LSC LSP is defined as follows:  

              Slot width = 0.0125 THz * m  

   Where m is a positive integer.  

   The frequency slot of a LSP can be determined by the slot width and 
   central frequency as follows.  

   Lowest frequency = (central frequency) - (slot width)/2 

                    = (193.1 + n * 0.00625) - (0.0125 * m)/2 

                    = (193.1 + (n - m) * 0.00625) THz; 

   Highest frequency = (central frequency) + (slot width)/2  

                    = (193.1 + n * 0.00625) + (0.0125 * m)/2 

                    = (193.1 + (n + m) * 0.00625) THz; 

   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 
    
   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 

 
 
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   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 LSC LSPs.  

   Hence, the available frequency ranges should be advertised for the 
   flexible-grid DWDM links. A set of non-overlapping available 
   frequency ranges SHOULD be disseminated in order to allow efficient 
   resource management of Flexible-grid DWDM links and RSA procedures 
   which are described in section 4 of [FLEXIBLE-REQ]. 

3.2. Comparison with Fixed-grid DWDM Links  

   In case of fixed-grid DWDM links, each wavelength has a pre-defined 
   central frequency and all the wavelengths occupy the same frequency 
   range (channel spacing). Hence all the wavelengths in the DWDM links 
   can be identified uniquely and the status (available or not) of the 
   wavelengths can be advertised through routing protocol.  

        W(-2)  |    W(-1)  |    W(0)   |    W(1)   |     W(2)  | 
   ...---------+-----------+-----------+-----------+-----------+----... 
   50 GHz  |   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 
                                 Spacing 
    
   Figure 2 shows a link that supports fixed-grid with 50 GHz channel 
   spacing. The central frequencies of the wavelengths are pre-defined 
   by 'n' and each wavelength occupies a fixed 50 GHz frequency range 
   as described in [G.694.1v1].  

   Different from the fixed-grid DWDM links, the slot width of the 
   wavelengths are flexible on a flexible-grid DWDM link as described 
   in section 2.1, i.e., the value of m in the formula is uncertain 
   before a frequency slot is allocated. So, the available frequency 
   ranges instead of the specific "wavelengths" should be advertised 
   for a flexible-grid DWDM link. 

4. Extensions  

   As described in [FLEXIBLE-REQ], the network connectivity topology 
   constructed by the links/nodes and node capabilities are the same as 
 
 
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   WSON which can be advertised by GMPLS routing protocol (refer to 
   section 6.2 of [RFC6163].  In case of flexible-grid, the available 
   frequency ranges instead of the specific ''wavelengths'' should be 
   advertised for the link, which is different from the fixed grid DWDM. 
   This section defines the GMPLS OSPF-TE extensions in support of 
   advertising the available frequency ranges for the flexible-grid 
   DWDM links.  

4.1. Available Labels Set sub-TLV  

   As described in section 2.1, the available frequency ranges other 
   than the available frequency slots should be advertised for the 
   flexible-grid DWDM links. The Available Labels Set sub-TLV defined 
   in [GEN-OSPF] can be re-used to advertise the available frequency 
   ranges for the flexible-grid DWDM links.  

   To make the encoding efficiently, the inclusive/exclusive label 
   ranges format of Available Labels Set sub-TLV defined in [GEN-OSPF] 
   can be used for specifying the frequency ranges of the flexible-grid 
   DWDM links.  

    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 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |2 or 3 | Num Labels(not used)  |             Length            | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                    Start Label                                | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                     End Label                                 | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
   Note that it needs multiple Available Labels Set sub-TLVs if there 
   are multiple discontinuous frequency ranges on a link. 

   The fields of Start Label and End Label specify the lowest frequency 
   and highest frequency of a frequency range. The label format defined 
   in [FLEXIBLE-SIG] shown below can be used to encode the Start Label 
   and End Label:  

    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 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |Grid | C.S.  |    Identifier   |                n              | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 

 
 
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   In case of Grid=1 (ITU-T DWDM), a new value of C.S. is defined for 
   flexible 6.25 GHz grid.  

   If the C.S. is 6.25 GHz in an Available Labels Set sub-TLV, it means 
   that the corresponding link supports flexible-grid and the Start 
   Label/End Label specifies the frequency range of the link.  

   [Editors' Note: the other formats of Label set (e.g., 
   Inclusive/Exclusive Label Lists and Bitmap Label Set) can also be 
   used to specify the frequency ranges for the flexible-grid DWDM 
   links.] 

4.2. Examples  

   Figure 3 shows an example of a flexible-grid DWDM link which is 
   traversed by two LSC LSPs.  

                         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 3 - Two Frequency Slots on a Link  
                                      
   The available frequency resource of the link could be advertised as 
   follows:  

   <Available Labels> sub-TLV: 

   o Exclusive Range 1: [Start label = 193.1 + (-2)*0.00625,  

                          End Label = 193.1 + 2*0.00625] 

   o Exclusive Range 2: [Start label = 193.1 + 4*0.00625,  

                          End Label = 193.1 + 10*0.00625] 

   It is noted that the central frequency denoted by n=3 is available 
   for a LSC LSP with 12.5 GHz slot width request but unavailable for a 
   LSC LSP with a wider slot width request.  

 
 
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   o If a LSC LSP which requires a 12.5 GHz width frequency slot is 
      requested on this link, the central frequency denoted by n=3 is 
      available because the corresponding frequency slot [n=2, n=4] dose 
      not overlap the existing LSPs (the unavailable frequency ranges is 
      [n=-2, n=2] and [n=4, n=10]).  

   o If a LSC LSP which requires a 25 GHz width frequency slot is 
      requested on this link, the central frequency denoted by n=3 is 
      unavailable because the corresponding frequency slot [n=1, n=5] 
      overlaps the unavailable central frequencies (the unavailable 
      frequency ranges is [n=-2, n=2] and [n=4, n=10]).  

5. IANA Considerations 

   TBD. 

6. Security Considerations 

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

7. References 

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

   [G.694.1v1] ITU-T Recommendation G.694.1, Spectral grids for WDM 
             applications: DWDM frequency grid, June 2002. 

   [G.FLEXIGRID] Draft revised G.694.1 version 1.3, Unpublished ITU-T 
             Study Group 15, Question 6. 

   [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. 

   [WSON-SIG] G. Bernstein, Sugang Xu, Y. Lee, G. Martinelli and 
             Hiroaki Harai, "Signaling Extensions for Wavelength 
             Switched Optical Networks", draft-ietf-ccamp-wson-
             signaling-02, September 2011. 

   [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-06, September 2011. 

 
 
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   [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-02, September 2011. 

   [RFC6163] Y. Lee, G. Bernstein and W. Imajuku, "Framework for GMPLS 
             and Path Computation Element (PCE) Control of Wavelength 
             Switched Optical Networks (WSONs)t", RFC 6163, April 2011. 

   [RFC6205] T. Otani and D. Li, "Generalized Labels for Lambda-Switch-
             Capable (LSC) Label Switching Routers", RFC 6205, March 
             2011. 

   [FLEXIBLE-REQ] F.Zhang et al, "Requirements for GMPLS Control of 
             Flexible-grids",draft-zhang-ccamp-flexible-grid-
             requirements, in progress. 

   [FLEXIBLE-SIG] F.Zhang et al, " RSVP-TE Signaling Extensions in 
             support of Flexible-grid",draft-zhang-ccamp-flexible-grid-
             rsvp-te-ext-00, in progress. 

 
 
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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 
    
    
   Ramon Casellas, Ph.D. 
   CTTC 
   Spain 
   Phone: +34 936452916 
   Email: ramon.casellas@cttc.es 
    
    
   Oscar Gonzalez de Dios 
   Telefonica Investigacion y Desarrollo 
   Emilio Vargas 6 
   Madrid,   28045 
   Spain 
   Phone: +34 913374013 
   Email: ogondio@tid.es 
    
    
   Daniele Ceccarelli 
   Ericsson 
   Via A. Negrone 1/A 
   Genova - Sestri Ponente 
   Italy 
   Email: daniele.ceccarelli@ericsson.com 
    
    
   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 
    
    
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