Link Management Protocol Extensions for Grid Property Negotiation
draft-li-ccamp-grid-property-lmp-01

Network Working Group                                              Y. Li
Internet-Draft                                                       ZTE
Intended status: Standards Track                             R. Casellas
Expires: September 9, 2012                                          CTTC
                                                                 Y. Wang
                                                                    CATR
                                                           March 8, 2012

   Link Management Protocol Extensions for Grid Property Negotiation
                  draft-li-ccamp-grid-property-lmp-01

Abstract

   The recent updated version of ITU-T [G.694.1] has introduced the
   flexible-grid DWDM technique, which provides a new tool that
   operators can implement to provide a higher degree of network
   optimization than is possible with fixed-grid systems.  This document
   describes the extensions to the Link Management Protocol (LMP) to
   negotiate link grid property between the adjacent DWDM nodes before
   the link is brought up.

Status of this Memo

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   This Internet-Draft will expire on September 9, 2012.

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   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Conventions Used in This Document  . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Flexi-fixed Grid Nodes Interworking  . . . . . . . . . . .  4
     3.2.  Flexible-Grid Capability Negotiation . . . . . . . . . . .  5
     3.3.  Problem Summary  . . . . . . . . . . . . . . . . . . . . .  6
   4.  LMP extensions . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Grid Property Subobject  . . . . . . . . . . . . . . . . .  6
   5.  Messages Exchange Procedure  . . . . . . . . . . . . . . . . .  8
     5.1.  Flexi-fixed Grid Nodes Messages Exchange . . . . . . . . .  8
     5.2.  Flexible Nodes Messages Exchange . . . . . . . . . . . . .  9
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1.  Normative references . . . . . . . . . . . . . . . . . . . 10
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11

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1.  Introduction

   The recent updated version of ITU-T [G.694.1] has introduced the
   flexible-grid DWDM technique, which provides a new tool that
   operators can implement to provide a higher degree of network
   optimization than is possible with fixed-grid systems.  A flexible-
   grid network supports allocating an arbitrary spectral slot to a
   channel.  Mixed bitrate transmission systems can allocate their
   channels with different spectral bandwidths/slot widths so that they
   can be optimized for the bandwidth requirements of the particular
   bitrate and modulation scheme of the individual channels.  This
   technique is regarded to be a promising way to improve the spectrum
   utilization efficiency and fundamentally reduce the cost of the core
   network.

   During the practical deployment procedure, fixed-grid optical nodes
   will be gradually replaced by flexible nodes.  This will lead to an
   interworking problem between fixed-grid DWDM and flexible-grid DWDM
   nodes.  Additionally, even two flexible-grid optical nodes may have
   different grid properties, leading to link property conflict.
   Therefore, this document describes the extensions to the Link
   Management Protocol (LMP) to negotiate a link grid property between
   two adjacent DWDM nodes before the link is brought up.

1.1.  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].

2.  Terminology

   For the flexible DWDM grid, the allowed frequency slots have a
   nominal central frequency (in THz) defined by:

   193.1 + n * 0.00625

   where n is a positive or negative integer including 0 and 0.00625 is
   the nominal central frequency granularity in THz

   and a slot width defined by:

   12.5 * m

   where m is a positive integer and 12.5 is the slot width granularity
   in GHz.  Any combination of frequency slots is allowed as long as no
   two slots overlap.

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   In this contribution, some other definitions are listed below:

   Grid granularity: Grid granularity includes two elements: nominal
   central frequency granularity and slot width granularity.  The value
   of slot width granularity is always configured to be twice of the
   central frequency granularity, so that the spectral resources can be
   allocated without leaving any gaps.  Therefore, when grid granularity
   appears alone, we just refer to the nominal central frequency
   granularity.

   Tuning range: In this draft we just refer to the tuning range of the
   spectral bandwidth or slot width.

   Channel spacing: In traditional fixed-grid network, the adjacent
   channel spacing is constant.  While for the flexible-grid network,
   the adjacent channel spacing is determined by the two central
   frequencies.

3.  Problem Statement

3.1.  Flexi-fixed Grid Nodes Interworking

        +---+         +---+         +---+         +---+        +---+
        | A |---------| B |=========| C |=========| D +--------+ E |
        +---+         +---+         +---+         +---+        +---+

                                 Figure 1

              ^               ^               ^               ^
      ------->|<----50GHz---->|<----50GHz---->|<----50GHz---->|<------
        ..... |               |               |               | .....
      +-------+-------+-------+-------+-------+--------+------+-------+-
   n=-2              -1               0                1              2
                   Fixed channel spacing of 50 GHz (Node C)

              ^               ^               ^               ^
              |               |               |               |
      --------+---------------+---------------+---------------+---------
        ..... |  n=-8, m=4    |   n=0, m=4    |   n=8, m=4    | .....
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   n=-16 -14 -12 -10 -8  -6  -4  -2   0   2   4   6   8   10  12  14  16
                                                                    |_|
                           Flexi-grid (Nodes B,D)               6.25 GHz
                    Central frequency granularity=6.25 GHz
                    Slot width granularity=12.5 GHz

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                                 Figure 2

   Figure 1 shows an example of interworking between flexible and fixed-
   grid nodes.  Nodes A, B, D, E support flexible-grid.  All these nodes
   can support frequency slots with a central frequency granularity of
   6.25 GHz and slot width granularity of 12.5 GHz.  Given the
   flexibility in flexible-grid nodes, it is possible to configure the
   nodes in such a way that the central frequencies and slot width
   parameters are backwards compatible with the fixed DWDM grids
   (adjacent flexible frequency slots with channel spacing of 8*6.25 and
   slot width of 4*12.5 GHz is equivalent to fixed DWDM grids with
   channel spacing of 50 GHz).

   As node C can only support the fixed-grid DWDM property with channel
   spacing of 50 GHz, to establish a LSP through node B,C,D, the links
   between B to C and C to D must set to align with the fixed-grid
   values.  This link grid property must be negotiated before
   establishing the LSP.

3.2.  Flexible-Grid Capability Negotiation

                           +---+            +---+
                           | F +------------| G |
                           +---+            +---+

              +------------------+-------------+-----------+
              |    Unit (GHz)    |    Node F   |   Node G  |
              +------------------+-------------+-----------+
              | Grid granularity | 6.25 (12.5) | 12.5 (25) |
              +------------------+-------------+-----------+
              |   Tuning range   | [12.5, 100] | [25, 200] |
              +------------------+-------------+-----------+

                                 Figure 3

   The updated version of ITU-T [G.694.1] has defined the flexible-grid
   with a nominal central frequency granularity of 6.25 GHz and a slot
   width granularity of 12.5 GHz.  However, devices or applications that
   make use of the flexible-grid may not be able to support every
   possible slot width.  In other words, applications may be defined
   where different grid granularity can be supported.  Taking node F as
   an example, an application could be defined where the nominal central
   frequency granularity is 12.5 GHz requiring slot widths being
   multiple of 25 GHz .  Therefore the link between two optical nodes
   with different grid granularity must be configured to align with the
   larger of both granularities.  Besides, different nodes may have
   different slot width tuning ranges.  For example, in figure 3, node F
   can only support slot width with tuning change from 12.5 to 100 GHz,

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   while node G supports tuning range from 25 GHz to 200 GHz.  The link
   property of slot width tuning range for the link between F and G
   should be chosen as the range intersection, resulting in a range from
   25 GHz to 100 GHz.

3.3.  Problem Summary

   In summary, in a DWDM Link between two nodes, the following
   properties can be negotiated:

   o  Grid capability (channel spacing) --- Between fixed-grid and
      flexible-grid nodes.

   o  Grid granularity --- Between two flexible-grid nodes.

   o  Slot width tuning range--- Between two flexible-grid nodes.

4.  LMP extensions

4.1.   Grid Property Subobject

   According to [RFC4204], the LinkSummary message is used to verify the
   consistency of the link property on both sides of the link before it
   is brought up.  The LinkSummary message contains negotiable and non-
   negotiable DATA_LINK objects, carrying a series of variable-length
   data items called subobjects, which illustrate the detailed link
   properties.  The subobjects are defined in Section 12.12.1 in
   [RFC4204].

   To solve the problems stated in section 3, this draft extends the LMP
   protocol by introducing a new DATA_LINK subobject called "Grid
   property", allowing the grid property correlation between adjacent
   nodes.  The encoding format of this new subobject is as follows:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Length    |            Reserved           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Grid |  C.S. |     Reserved    |      Min      |      Max      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type=TBD, Grid property type.

   Grid:

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   The value is used to represent which grid the node/interface
   supports.  Values defined in [RFC6205] identify DWDM [G.694.1] and
   CWDM [G.694.2].  The value defined in
   [I-D.farrkingel-ccamp-flexigrid-lambda-label] identifies flexible
   DWDM.

   +---------------+-------+
   | Grid          | Value |
   +---------------+-------+
   | Reserved      |   0   |
   +---------------+-------+
   | ITU-T DWDM    |   1   |
   +---------------+-------+
   | ITU-T CWDM    |   2   |
   +---------------+-------+
   | Flexible DWDM |   3   |
   +---------------+-------+
   | Future use    |  4-7  |
   +---------------+-------+

   C.S.:

   For a fixed-grid node/interface, the C.S. value is used to represent
   the channel spacing, as the spacing between adjacent channels is
   constant.  For a flexible-grid node/interface, this field should be
   used to represent the central frequency granularity.

   +------------+-------+
   | C.S. (GHz) | Value |
   +------------+-------+
   | Reserved   |   0   |
   +------------+-------+
   | 100        |   1   |
   +------------+-------+
   | 50         |   2   |
   +------------+-------+
   | 25         |   3   |
   +------------+-------+
   | 12.5       |   4   |
   +------------+-------+
   | 6.25       |   5   |
   +------------+-------+
   | Future use |  6-15 |
   +------------+-------+

   Min & Max:

   The slot width tuning range the interface supports (indicated by the

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   m value defined in section 2).  For example, for slot width tuning
   range from 25 GHz to 100 GHz (with regarding to a node with slot
   width granularity of 12.5 GHz ), the values of Min and Max should be
   2 and 8 respectively.  For fixed-grid nodes, these two fields are
   meaningless and should be set to zeros.

5.  Messages Exchange Procedure

5.1.  Flexi-fixed Grid Nodes Messages Exchange

   To demonstrate the procedure of grid property correlation, the model
   shown in Figure 1 is reused.  Node B starts sending messages.
   o  After inspecting its own node/interface property, node B sends
      node C a LinkSummary message including the MESSAGE ID, TE_LINK ID
      and DATA_LINK objects.  The setting and negotiating of MESSAGE ID
      and TE_link ID can be referenced to [RFC4204].  As node B supports
      flexible-grid property, the Grid and C.S. values in the grid
      property subobject are set to be 3 and 5 respectively.  The slot
      width tuning range is from 12.5 GHz to 200 GHz.  Meanwhile, the N
      bit of the DATA_LINK object is set to 1, indicating that the
      property is negotiable.

   o  When node C receives the LinkSummary message from B, it checks the
      Grid, C.S., Min and Max values in the grid property subobject.
      Node C can only support fixed-grid DWDM and realizes that the
      flexible-grid property is not acceptable for the link.  Since the
      receiving N bit in the DATA_LINK object is set, indicating that
      the Grid property of B is negotiable, node C responds to B with a
      LinkSummaryNack containing a new Error_code object and state that
      the property needs further negotiation.  Meanwhile, an accepted
      grid property subobject (Grid=2, C.S.=2, fixed DWDM with channel
      spacing of 50 GHz) is carried in LinkSummaryNack message.  At this
      moment, the N bit in the DATA_LINK object is set to 0, indicating
      that the grid property subobject is non-negotiable.

   o  As the channel spacing and slot width of node B can be configured
      to be any integral multiples of 6.25 GHz and 12.5 GHz
      respectively, node B supports the fixed DWDM values announced by
      node C. Consequently, node B will resend the LinkSummary message
      carrying the grid property subobject with values of Grid=2 and
      C.S.=2.

   o  Once received the LinkSummary message from node B, node C replies
      with a LinkSummaryACK message.  After the message exchange, the
      link between node B and C is brought up with a fixed channel
      spacing of 50 GHz.

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   In the above mentioned grid property correlation scenario, the node
   supporting a flexible-grid is the one that starts sending LMP
   messages.  The procedure where the initiator is the fixed-grid node
   is as follows:

   o  After inspecting its own interface property, Node C sends B a
      LinkSummary message containing a grid property subobject with
      Grid=2, C.S.=2.  The N bit in the DATA_LINK object is set to 0,
      indicating that it is non-negotiable.

   o  As the channel spacing and slot width of node B can be configured
      to be any integral multiples of 6.25 GHz and 12.5 GHz
      respectively, node B is able to support the fixed DWDM parameters.
      Then, node B will make appropriate configuration and reply node C
      the LinkSummaryACK message.

   o  After the message exchange, the link between node B and C is
      brought up with a fixed channel spacing of 50 GHz.

5.2.  Flexible Nodes Messages Exchange

   To demonstrate the procedure of grid property correlation between to
   flexi-grid capable nodes, the model shown in figure 3 is reused.  The
   procedure of grid property correlation (negotiating the grid
   granularity and slot width tuning range) is similar to the scenarios
   mentioned above.

   o  The Grid, C.S., Min and Max values in the grid property subobject
      sent from node F to G are set to be 3,5,1,8 respectively.
      Meanwhile, the N bit of the DATA_LINK object is set to 1,
      indicating that the grid property is negotiable.

   o  When node G has received the LinkSummary message from F, it will
      analyze the Grid, C.S., Min and Max values in the Grid property
      subobject.  But node G can only support grid granularity of 12.5
      GHz and a slotwdith tuning range from 25 GHz to 200 GHz.
      Considering the property of node F, node G then will respond F a
      LinkSummaryNack containing a new Error_code object and state that
      the property need further negotiation.  Meanwhile, an accepted
      grid property subobject (Grid=3, C.S.=4, Min=1, Max=4, the slot
      width tuning range is set to the intersection of Node F and G) is
      carried in LinkSummaryNack message.  Meanwhile, the N bit in the
      DATA_LINK object is set to 1, indicating that the grid property
      subobject is non-negotiable.

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   o  As the channel spacing and slot width of node F can be configured
      to be any integral multiples of 6.25 GHz and 12.5 GHz
      respectively, node F can support the lager granularity.  The
      suggested slot width tuning range is acceptable for node F. In
      consequence, node F will resend the LinkSummary message carrying
      the grid subobject with values of Grid=3, C.S.=4, Min=1 and Max=4.

   o  Once received the LinkSummary message from node F, node G replies
      with a LinkSummaryACK message.  After the message exchange, the
      link between node F and G is brought up supporting central
      frequency granularity of 12.5 GHz and slot width tuning range from
      25 GHz to 100 GHz.

   From the perspective of the control plane, once the links have been
   brought up, wavelength constraint information can be advertised and
   the wavelength label can be assigned hop-by-hop when establishing a
   LSP based on the link grid property.

6.  IANA Considerations

   TBD

7.  Security Considerations

   TBD

8.  References

8.1.  Normative references

   [G.694.1]  International Telecommunications Union, "Spectral grids
              for WDM applications: DWDM frequency grid", Recommendation
              G.694.1, June 2002 .

   [G.694.2]  International Telecommunications Union, "Spectral grids
              for WDM applications: CWDM wavelength grid",
              Recommendation G.694.2, December 2003 .

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4204]  Lang, J., "Link Management Protocol (LMP)", RFC 4204,
              October 2005.

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

8.2.  Informative References

   [I-D.farrkingel-ccamp-flexigrid-lambda-label]
              King, D., Farrel, A., Li, Y., Zhang, F., and R. Casellas,
              "Generalized Labels for the Flexi-Grid in Lambda-Switch-
              Capable (LSC) Label Switching Routers",
              draft-farrkingel-ccamp-flexigrid-lambda-label-01 (work in
              progress), October 2011.

Authors' Addresses

   Yao Li
   ZTE

   Email: li.yao3@zte.com.cn

   Ramon Casellas
   CTTC

   Email: ramon.casellas@cttc.es

   Yu Wang
   China Academy of Telecom Research, MIIT
   No.52 Huayuan Beilu, Haidian District,Beijing,P.R. China, 100083

   Email: wangyu@mail.ritt.com.cn

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