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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   The list of Internet-Draft Shadow Directories can be accessed at

  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
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   ( in effect on the date of
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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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