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


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
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   This Internet-Draft will expire on April 24, 2012.









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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


Intellectual Property




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