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Network Working Group                                              Y. Li
Internet-Draft                                                  F. Zhang
Intended status: Standards Track                                     ZTE
Expires: January 5, 2012                                     R. Casellas
                                                                    CTTC
                                                            July 4, 2011


   Flexible Grid Label Format in Wavelength Switched Optical Network
                 draft-li-ccamp-flexible-grid-label-00

Abstract

   Flexible grid is regarded as an efficient way to improve the network
   capacity utilization.  Mixed bit rate transmission systems can
   allocate their channel with different spectral bandwidths so that
   they can be optimized for the bandwidth requirements of the
   particular bit rate and modulation scheme of the individual channels.
   To support the flexible grid technique, this document extends the
   wavelength label to accommodate this new specification.  It is
   demonstrated that the extended label format is compatible to the
   rigid one and can be used in the routing and signaling procedure in
   the Wavelength Switched Optical Network (WSON).

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 5, 2012.

Copyright Notice

   Copyright (c) 2011 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



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Label format . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Label values . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Flexible Label . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Flexible label applications  . . . . . . . . . . . . . . . . .  7
     4.1.  Application for Routing  . . . . . . . . . . . . . . . . .  7
     4.2.  Applications for Signaling . . . . . . . . . . . . . . . .  8
     4.3.  Applications for PCE . . . . . . . . . . . . . . . . . . .  8
   5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     8.1.  Normative references . . . . . . . . . . . . . . . . . . .  9
     8.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
























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1.  Introduction

   Dense Wavelength Division Multiplexing (DWDM) optical network is
   widely deployed by telecom operators to carry their data service.
   With the continuing exponential growth of internet traffic, more
   efficient utilization of optical network bandwidth for extremely high
   data rates is required.  Although multi-level modulation formats and
   advanced photonics techniques have enabled 100 G/s transmission
   within a 50 GHz DWDM fixed gird (or channel spacing), much higher
   speed traffic, such as 400 Gbit/s and 1 Tbit/s signals are not
   expected to adapt such a narrow channel.  So a wider fixed grid like
   100 GHz spacing is required to enable these new transmission formats
   without inter-channel crosstalk.  However, the total available
   spectrum resource of the specific band is limited (about 4.4 THz in C
   band).  If a wider grid is chosen, the fewer wavelengths can be
   allocated to carry the data.  Not to mention that some low bitrate
   signals will occupy too much spectral bandwidth so that the total
   utilization efficiency of the spectrum resource is relatively low.

   The recent revision of ITU-T Recommendation [G.694.1] has decided to
   introduce the flexible grid DWDM technique which provide a new tool
   that operators can implement to provide a higher degree of network
   optimization than fixed grid systems.  Flexible grid network is
   composed of arbitrarily assigned spectral slices.  That means in such
   networks the adjacent channel spacing and assigned spectral bandwidth
   per wavelength are variable.  Mixed bitrate transmission systems can
   allocate their channel with different spectral bandwidths so that
   they can be optimized for the bandwidth requirements of the
   particular bit rate and modulation scheme of the individual channels.
   This technique is regarded to be a promising way to improve the
   network utilization efficiency and fundamentally reduce the cost of
   the IP core network.

   Based on the DWDM technique, Wavelength Switched Optical Network
   (WSON) uses the control plane to dynamically provide Label Switched
   Paths (LSPs) for the requested end to end connections.  The label
   switching is performed selectively on wavelength label representing
   the center wavelength/frequency of the optical signal.  To support
   the flexible grid technique, this document extends the wavelength
   label defined in [RFC6205] to accommodate the new specification.  It
   is proved that the extended label format is compatible to the rigid
   one and can be used in the routing and signaling procedure in WSON
   and generic GMPLS network.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",



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   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].


3.  Label format

3.1.  Label values

   The wavelength label format is defined in [RFC6205] and the
   corresponding wavelength or frequency value is referred to ITU-T
   Recommendations [G.694.1] and [G.694.2] for DWDM and CWDM grid
   respectively.  The ITU-T fixed grid is based on nominal center
   frequency/wavelength.

   For DWDM system, the nominal center frequency is calculated as:

   Frequency (THz)=193.1 THz+n* channel spacing

   In the context of rigid grid, the channel spacing of DWDM can support
   12.5 GHz, 25 GHz, 50 GHz, or 100 GHz.  However, once chosen, the
   adjacent channel spacing of the wavelengths is fixed.  As mentioned
   in the section 1, 50 GHz channel spacing is most commonly used.

   The recent revision of [G.694.1] has defined suggested values for the
   flexible DWDM grid.  The concept of "frequency slot" is introduced to
   describe the frequency range allocated to a channel.  A frequency
   slot is defined by its nominal central frequency and its required
   slot width values.

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

   Frequency (THz)=193.1 THz + n * 0.00625

   and a slot width (the same meaning as the spectral bandwidth) defined
   by:

   12.5 GHz * m

   where m is a positive integer.

   The nominal center frequency representations of the fixed grid and
   flexible grid types are similar except that the latter has a more
   precise channel spacing granularity (6.25 GHz).  Meanwhile the
   adjacent channel spacing (the spacing of the adjacent nominal center
   frequency) is implied to be (n1-n2) * 6.25 GHz, where n1 and n2
   represent the n number defined above for the nominal center frequency
   of the adjacent frequency slots respectively (n is an integer



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   including positive, negative integer and 0).  The slot width assigned
   to a frequency slot is arbitrary times of the slot width granularity.
   It was agreed on flexible grids with a granularity of 6.25 GHz for
   the central frequency and slot width of a multiple of 12.5 GHz.  The
   slot width granularity is twice the channel spacing granularity, so
   that by carefully choosing n and m, the spectral resources can be
   allocated without leaving any gaps between slots.  Therefore, in
   contrast to the rigid label, the new flexible label should have a
   capability to indicating the slot width allocation.

   Note that in this document, the concepts "slot width" and "frequency
   slot" are similar to "spectral bandwidth" and "wavelength channel"
   respectively.

3.2.  Flexible Label

   To accommodate the new feature mentioned above, the wavelength label
   supporting flexible grid is illustrated 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Grid | C.S.  |    Identifier   |              n                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |               Additional slot width parameters                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Additional slot width parameters:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    m    |                      Reserved                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Grid:

   One new Grid type called "Flexible DWDM" is defined.

   +---------------+-------+
   | Grid          | Value |
   +---------------+-------+
   | Reserved      |   0   |
   +---------------+-------+
   | ITU-T DWDM    |   1   |
   +---------------+-------+
   | ITU-T CWDM    |   2   |
   +---------------+-------+



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   +---------------+-------+
   | Flexible DWDM |   3   |
   +---------------+-------+
   | Future use    |  4-7  |
   +---------------+-------+

   C.S.:

   For Grid=1 and 2, C.S. is referred to DWDM and CWDM channel spacing
   [RFC6205], which indicates that the adjacent channel spacing is
   constant.  In this situation, the spectral bandwidth value allocated
   to every single channel is equal to value of the channel spacing.

   For Grid=3, C.S. is referred to channel spacing granularity,
   accordingly the slot width granularity is twice of the C.S..  Minimum
   channel spacing granularity of 6.25 GHz with a slot width granularity
   of 12.5 GHz is supported.

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

   Identifier:

   The identifier field in the flexible label format is left unmodified
   compared with [RFC6205].  It is defined to distinguish which
   transmitter is used to carry the lambda.  This identifier only has a
   local significance that should be indicated in the signaling message
   for LSP establishment.  For routing information flooding, this filed
   is meaningless and should be ignored on receipt.

   n:

   This field is used to compute the nominal center frequency/wavelength



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   of the channel mentioned above.  Together with the channel spacing
   granularity (C.S.), the spacing of the adjacent channel is (n1-n2) *
   6.25 GHz in flexible grid network (see definition of n1 and n2 in
   section 3.1).

   Additional slot width parameters.

   The slot width parameters field is mandatory only when Grid is set to
   3 for flexible grid condition.  These 5 bits field are used to
   represent how many slot width granularity the label has occupied.  As
   the granularity is defined to be twice of the channel spacing
   granularity, so the slot width is calculated to be m * 2 * C.S..


4.  Flexible label applications

   This section illustrated the routing, signaling, PCE application of
   the extended flexible grid label.

4.1.  Application for Routing

   Flexible grid is regarded as an enabler for another kind of networks,
   requiring network elements, or nodes, that go past beyond the
   functional requirements of OXCs or ROADMs, in the sense that they do
   switching based on a frequency range.  This means that a new swithing
   type called e.g.  "Spectrum Selective Switching" in Interface
   Switching Capability Descriptor (ISCD) SHOULD be defined.  However
   this is beyond the scope of this document and will be studied in the
   routing draft.

   In addition to the topology information, wavelength constraints
   information like Port Label Restrictions, Shared Backup Labels,
   Resource Pool Wavelength Constrains, Resource Block Available
   Wavelengths detailed in [I-D.ietf-ccamp-rwa-info] should be flooded
   in the network through routing protocol like OSPF-TE.  All the
   information is described by the label set object.  The general label
   set is described in [RFC3471] and specific wavelength label set in
   [I-D.ietf-ccamp-general-constraint-encode] .  There are 5 ways to
   represent the wavelength label set

   1.  Inclusive list
   2.  Exclusive list
   3.  Inclusive range
   4.  Exclusive range
   5.  Bitmap set

   For flexible grid optical network, the label set should be more
   actually to represent the spectral resources constraints.  For type 1



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   and 2, flexible label with different slot width is acceptable to put
   into the list.  For type 3 and 4, start label and end label with
   minimal slot width (while it is not mandatory) is RECOMMENDED.  For
   type 5, the base label/frequency slot is REQUIRED to have a minimum
   slot width (m=1).  As there MAY exist some situations that the unused
   bandwidth between two occupied bandwidth is odd times of the channel
   spacing granularity (not integral times of the slot with
   granularity), two bits are needed to represent a single slot.  It can
   be seen that these 5 types of representations can be easily inherited
   by incorporating the new flexible label into the object.  Note that
   in the procedure of wavelength constraints flooding, any combination
   of the 5 types of label sets is feasible.

4.2.  Applications for Signaling

   In flexibel grid network, flexible label representing frequency
   "slots" or "ranges" rather than individual wavelengths is requested
   to establish the LSP.  The extensions to the Genralized Label Request
   object and TSPEC object are needed, this will be studied in the
   future.

   To establish a label switched path, an available wavelength label
   satisfying the wavelength continuity constraints is reserved with
   signaling protocol like RSVP-TE.  For the flexible grid DWDM network,
   this procedure should be modified to assign available spectral
   resources.  In other words, the label is not only assigning the
   nominal center frequency of wavelength but also the slot width for
   the LSP.  The slot width is definitely clarified through the field m
   in the label.  Nevertheless in the procedure, wavelength continuity
   constraint is unchanged.

4.3.  Applications for PCE

   [RFC6163] describes a Path Computation Element (PCE) can be used to
   performing routing and wavelength assignment in WSON.  [RFC5440]
   details the path computation element communication protocol messages
   for this purpose.  According to the modulation format, FEC type,
   client
   bitrates[I-D.ietf-ccamp-rwa-info][I-D.ietf-ccamp-rwa-wson-encode],
   and physical impairment, the required frequency slot indicated by
   flexible label should be calculated out by the PCE to carry the
   client signal.









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5.  Acknowledgements


6.  IANA Considerations

   A future revision of this document will present requests to IANA for
   codepoint allocation.


7.  Security Considerations


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.

   [RFC3471]  Berger, L., "Generalized Multi-Protocol Label Switching
              (GMPLS) Signaling Functional Description", RFC 3471,
              January 2003.

   [RFC5440]  Vasseur, JP. and JL. Le Roux, "Path Computation Element
              (PCE) Communication Protocol (PCEP)", RFC 5440,
              March 2009.

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

   [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.ietf-ccamp-general-constraint-encode]
              Bernstein, G., Lee, Y., Li, D., and W. Imajuku, "General



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              Network Element Constraint Encoding for GMPLS Controlled
              Networks", draft-ietf-ccamp-general-constraint-encode-05
              (work in progress), May 2011.

   [I-D.ietf-ccamp-rwa-info]
              Bernstein, G., Lee, Y., Li, D., and W. Imajuku, "Routing
              and Wavelength Assignment Information Model for Wavelength
              Switched Optical Networks", draft-ietf-ccamp-rwa-info-11
              (work in progress), March 2011.

   [I-D.ietf-ccamp-rwa-wson-encode]
              Bernstein, G., Lee, Y., Li, D., Imajuku, W., and J. Han,
              "Routing and Wavelength Assignment Information Encoding
              for Wavelength Switched Optical Networks",
              draft-ietf-ccamp-rwa-wson-encode-11 (work in progress),
              March 2011.


Authors' Addresses

   Yao Li
   ZTE
   P.R.China

   Phone: +86 025 52871109
   Email: li.yao3@zte.com.cn


   Zhang Fei
   ZTE
   P.R.China

   Phone: +86 025 52871109
   Email: zhang.fei3@zte.com.cn


   Ramon Casellas
   CTTC
   Spain

   Phone: +34 936452916
   Email: ramon.casellas@cttc.es









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