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+Internet Engineering Task Force (IETF)                     T. Otani, Ed.
+Request for Comments: 6205                                          KDDI
+Updates: 3471                                                 D. Li, Ed.
+Category: Standards Track                                         Huawei
+ISSN: 2070-1721                                               March 2011
+
+
+           Generalized Labels for Lambda-Switch-Capable (LSC)
+                        Label Switching Routers
+
+Abstract
+
+   Technology in the optical domain is constantly evolving, and, as a
+   consequence, new equipment providing lambda switching capability has
+   been developed and is currently being deployed.
+
+   Generalized MPLS (GMPLS) is a family of protocols that can be used to
+   operate networks built from a range of technologies including
+   wavelength (or lambda) switching.  For this purpose, GMPLS defined a
+   wavelength label as only having significance between two neighbors.
+   Global wavelength semantics are not considered.
+
+   In order to facilitate interoperability in a network composed of next
+   generation lambda-switch-capable equipment, this document defines a
+   standard lambda label format that is compliant with the Dense
+   Wavelength Division Multiplexing (DWDM) and Coarse Wavelength
+   Division Multiplexing (CWDM) grids defined by the International
+   Telecommunication Union Telecommunication Standardization Sector.
+   The label format defined in this document can be used in GMPLS
+   signaling and routing protocols.
+
+Status of This Memo
+
+   This is an Internet Standards Track document.
+
+   This document is a product of the Internet Engineering Task Force
+   (IETF).  It represents the consensus of the IETF community.  It has
+   received public review and has been approved for publication by the
+   Internet Engineering Steering Group (IESG).  Further information on
+   Internet Standards is available in Section 2 of RFC 5741.
+
+   Information about the current status of this document, any errata,
+   and how to provide feedback on it may be obtained at
+   http://www.rfc-editor.org/info/rfc6205.
+
+
+
+
+
+
+
+Otani & Li                   Standards Track                    [Page 1]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+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
+   (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
+   to this document.  Code Components extracted from this document must
+   include Simplified BSD License text as described in Section 4.e of
+   the Trust Legal Provisions and are provided without warranty as
+   described in the Simplified BSD License.
+
+   This document may contain material from IETF Documents or IETF
+   Contributions published or made publicly available before November
+   10, 2008.  The person(s) controlling the copyright in some of this
+   material may not have granted the IETF Trust the right to allow
+   modifications of such material outside the IETF Standards Process.
+   Without obtaining an adequate license from the person(s) controlling
+   the copyright in such materials, this document may not be modified
+   outside the IETF Standards Process, and derivative works of it may
+   not be created outside the IETF Standards Process, except to format
+   it for publication as an RFC or to translate it into languages other
+   than English.
+
+1.  Introduction
+
+   As described in [RFC3945], GMPLS extends MPLS from supporting only
+   Packet Switching Capable (PSC) interfaces and switching to also
+   supporting four new classes of interfaces and switching:
+
+   o Layer-2 Switch Capable (L2SC)
+
+   o Time-Division Multiplex (TDM) Capable
+
+   o Lambda Switch Capable (LSC)
+
+   o Fiber Switch Capable (FSC)
+
+   A functional description of the extensions to MPLS signaling needed
+   to support new classes of interfaces and switching is provided in
+   [RFC3471].
+
+   This document presents details that are specific to the use of GMPLS
+   with LSC equipment.  Technologies such as Reconfigurable Optical
+   Add/Drop Multiplex (ROADM) and Wavelength Cross-Connect (WXC) operate
+
+
+
+Otani & Li                   Standards Track                    [Page 2]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+   at the wavelength switching level.  [RFC3471] states that wavelength
+   labels "only have significance between two neighbors" (Section
+   3.2.1.1); global wavelength semantics are not considered.  In order
+   to facilitate interoperability in a network composed of LSC
+   equipment, this document defines a standard lambda label format,
+   which is compliant with both the Dense Wavelength Division
+   Multiplexing (DWDM) grid [G.694.1] and the Coarse Wavelength Division
+   Multiplexing (CWDM) grid [G.694.2].
+
+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 [RFC2119].
+
+2.  Assumed Network Model and Related Problem Statement
+
+   Figure 1 depicts an all-optical switched network consisting of
+   different vendors' optical network domains.  Vendor A's network
+   consists of ROADM or WXC, and Vendor B's network consists of a number
+   of Photonic Cross-Connects (PXCs) and DWDM multiplexers and
+   demultiplexers.  Otherwise, both vendors' networks might be based on
+   the same technology.
+
+   In this case, the use of standardized wavelength label information is
+   quite significant to establish a wavelength-based Label Switched Path
+   (LSP).  It is also an important constraint when calculating the
+   Constrained Shortest Path First (CSPF) for use by Generalized Multi-
+   Protocol Label Switching (GMPLS) Resource ReserVation Protocol -
+   Traffic Engineering (RSVP-TE) signaling [RFC3473].  The way the CSPF
+   is performed is outside the scope of this document.
+
+   Needless to say, an LSP must be appropriately provisioned between a
+   selected pair of ports not only within Domain A but also over
+   multiple domains satisfying wavelength constraints.
+
+   Figure 2 illustrates the interconnection between Domain A and Domain
+   B in detail.
+
+
+
+
+
+
+
+
+
+
+
+
+
+Otani & Li                   Standards Track                    [Page 3]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+                                  |
+      Domain A (or Vendor A)      |      Domain B (or Vendor B)
+                                  |
+     Node-1            Node-2     |         Node-6            Node-7
+   +--------+        +--------+   |      +-------+ +-+     +-+ +-------+
+   | ROADM  |        | ROADM  +---|------+  PXC  +-+D|     |D+-+  PXC  |
+   | or WXC +========+ or WXC +---|------+       +-+W+=====+W+-+       |
+   | (LSC)  |        | (LSC)  +---|------+ (LSC) +-+D|     |D+-+ (LSC) |
+   +--------+        +--------+   |      |       +-|M|     |M+-+       |
+       ||                ||       |      +++++++++ +-+     +-+ +++++++++
+       ||     Node-3     ||       |       |||||||               |||||||
+       ||   +--------+   ||       |      +++++++++             +++++++++
+       ||===|  WXC   +===||       |      | DWDM  |             | DWDM  |
+            | (LSC)  |            |      +--++---+             +--++---+
+       ||===+        +===||       |         ||                    ||
+       ||   +--------+   ||       |      +--++---+             +--++---+
+       ||                ||       |      | DWDM  |             | DWDM  |
+   +--------+        +--------+   |      +++++++++             +++++++++
+   | ROADM  |        | ROADM  |   |       |||||||               |||||||
+   | or WXC +========+ or WXC +=+ |  +-+ +++++++++ +-+     +-+ +++++++++
+   | (LSC)  |        | (LSC)  | | |  |D|-|  PXC  +-+D|     |D+-+  PXC  |
+   +--------+        +--------+ +=|==+W|-|       +-+W+=====+W+-+       |
+     Node-4            Node-5     |  |D|-| (LSC) +-+D|     |D+-+ (LSC) |
+                                  |  |M|-|       +-+M|     |M+-+       |
+                                  |  +-+ +-------+ +-+     +-+ +-------+
+                                  |        Node-8             Node-9
+
+      Figure 1.  Wavelength-Based Network Model
+
+
+
+
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+Otani & Li                   Standards Track                    [Page 4]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+   +-------------------------------------------------------------+
+   |          Domain A             |        Domain B             |
+   |                               |                             |
+   |           +---+     lambda 1  |         +---+               |
+   |           |   |---------------|---------|   |               |
+   |       WDM | N |     lambda 2  |         | N | WDM           |
+   |      =====| O |---------------|---------| O |=====          |
+   |  O        | D |        .      |         | D |        O      |
+   |  T    WDM | E |        .      |         | E | WDM    T      |
+   |  H   =====| 2 |     lambda n  |         | 6 |=====   H      |
+   |  E        |   |---------------|---------|   |        E      |
+   |  R        +---+               |         +---+        R      |
+   |                               |                             |
+   |  N        +---+               |         +---+        N      |
+   |  O        |   |               |         |   |        O      |
+   |  D    WDM | N |               |         | N | WDM    D      |
+   |  E   =====| O |      WDM      |         | O |=====   E      |
+   |  S        | D |=========================| D |        S      |
+   |       WDM | E |               |         | E | WDM           |
+   |      =====| 5 |               |         | 8 |=====          |
+   |           |   |               |         |   |               |
+   |           +---+               |         +---+               |
+   +-------------------------------------------------------------+
+
+      Figure 2.  Interconnecting Details between Two Domains
+
+   In the scenario of Figure 1, consider the setting up of a
+   bidirectional LSP from ingress switch (Node-1) to egress switch
+   (Node-9) using GMPLS RSVP-TE.  In order to satisfy wavelength
+   continuity constraints, a fixed wavelength (lambda 1) needs to be
+   used in Domain A and Domain B.  A Path message will be used for
+   signaling.  The Path message will contain an Upstream_Label object
+   and a Label_Set object, both containing the same value.  The
+   Label_Set object shall contain a single sub-channel that must be the
+   same as the Upstream_Label object.  The Path setup will continue
+   downstream to egress switch (Node-9) by configuring each lambda
+   switch based on the wavelength label.  If a node has a tunable
+   wavelength transponder, the tuning wavelength is considered a part of
+   the wavelength switching operation.
+
+   Not using a standardized label would add undue burden on the operator
+   to enforce policy as each manufacturer may decide on a different
+   representation; therefore, each domain may have its own label
+   formats.  Moreover, manual provisioning may lead to misconfiguration
+   if domain-specific labels are used.
+
+
+
+
+
+
+Otani & Li                   Standards Track                    [Page 5]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+   Therefore, a wavelength label should be standardized in order to
+   allow interoperability between multiple domains; otherwise,
+   appropriate existing labels are identified in support of wavelength
+   availability.  Containing identical wavelength information, the ITU-T
+   DWDM frequency grid specified in [G.694.1] and the CWDM wavelength
+   information in [G.694.2] are used by Label Switching Routers (LSRs)
+   and should be followed for wavelength labels.
+
+3.  Label-Related Formats
+
+   To deal with the widening scope of MPLS into the optical switching
+   and time division multiplexing domains, several new forms of "label"
+   have been defined in [RFC3471].  This section contains a definition
+   of a wavelength label based on [G.694.1] or [G.694.2] for use by LSC
+   LSRs.
+
+3.1.  Wavelength Labels
+
+   Section 3.2.1.1 of [RFC3471] defines wavelength labels: "values used
+   in this field only have significance between two neighbors, and the
+   receiver may need to convert the received value into a value that has
+   local significance".
+
+   We do not need to define a new type as the information stored is
+   either a port label or a wavelength label.  Only the wavelength label
+   needs to be defined.
+
+   LSC equipment uses multiple wavelengths controlled by a single
+   control channel.  In such a case, the label indicates the wavelength
+   to be used for the LSP.  This document defines a standardized
+   wavelength label format.  For examples of wavelength values, refer to
+   [G.694.1], which lists the frequencies from the ITU-T DWDM frequency
+   grid.  For CWDM technology, refer to the wavelength values defined in
+   [G.694.2].
+
+   Since the ITU-T DWDM grid is based on nominal central frequencies, we
+   need to indicate the appropriate table, the channel spacing in the
+   grid, and a value n that allows the calculation of the frequency.
+   That value can be positive or negative.
+
+   The frequency is calculated as such in [G.694.1]:
+
+        Frequency (THz) = 193.1 THz + n * channel spacing (THz)
+
+   Where "n" is a two's-complement integer (positive, negative, or 0)
+   and "channel spacing" is defined to be 0.0125, 0.025, 0.05, or 0.1
+   THz.  When wider channel spacing such as 0.2 THz is utilized, the
+   combination of narrower channel spacing and the value "n" can provide
+
+
+
+Otani & Li                   Standards Track                    [Page 6]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+   proper frequency with that channel spacing.  Channel spacing is not
+   utilized to indicate the LSR capability but only to specify a
+   frequency in signaling.
+
+   For other cases that use the ITU-T CWDM grid, the spacing between
+   different channels is defined as 20 nm, so we need to express the
+   wavelength value in nanometers (nm).  Examples of CWDM wavelengths in
+   nm are 1471, 1491, etc.
+
+   The wavelength is calculated as follows:
+
+        Wavelength (nm) = 1471 nm + n * 20 nm
+
+   Where "n" is a two's-complement integer (positive, negative, or 0).
+   The grids listed in [G.694.1] and [G.694.2] are not numbered and
+   change with the changing frequency spacing as technology advances, so
+   an index is not appropriate in this case.
+
+3.2.  DWDM Wavelength Label
+
+   For the case of lambda switching of DWDM, the information carried in
+   a wavelength label is:
+
+    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                |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   (1) Grid: 3 bits
+
+   The value for Grid is set to 1 for the ITU-T DWDM grid as defined in
+   [G.694.1].
+
+   +----------+---------+
+   |   Grid   |  Value  |
+   +----------+---------+
+   | Reserved |    0    |
+   +----------+---------+
+   |ITU-T DWDM|    1    |
+   +----------+---------+
+   |ITU-T CWDM|    2    |
+   +----------+---------+
+   |Future use|  3 - 7  |
+   +----------+---------+
+
+   (2) C.S. (channel spacing): 4 bits
+
+
+
+
+Otani & Li                   Standards Track                    [Page 7]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+   DWDM channel spacing is defined as follows.
+
+   +----------+---------+
+   |C.S. (GHz)|  Value  |
+   +----------+---------+
+   | Reserved |    0    |
+   +----------+---------+
+   |    100   |    1    |
+   +----------+---------+
+   |    50    |    2    |
+   +----------+---------+
+   |    25    |    3    |
+   +----------+---------+
+   |    12.5  |    4    |
+   +----------+---------+
+   |Future use|  5 - 15 |
+   +----------+---------+
+
+   (3) Identifier: 9 bits
+
+   The Identifier field in lambda label format is used to distinguish
+   different lasers (in one node) when they can transmit the same
+   frequency lambda.  The Identifier field is a per-node assigned and
+   scoped value.  This field MAY change on a per-hop basis.  In all
+   cases but one, a node MAY select any value, including zero (0), for
+   this field.  Once selected, the value MUST NOT change until the LSP
+   is torn down, and the value MUST be used in all LSP-related messages,
+   e.g., in Resv messages and label Record Route Object (RRO)
+   subobjects.  The sole special case occurs when this label format is
+   used in a label Explicit Route Object (ERO) subobject.  In this case,
+   the special value of zero (0) means that the referenced node MAY
+   assign any Identifier field value, including zero (0), when
+   establishing the corresponding LSP.  When a non-zero value is
+   assigned to the Identifier field in a label ERO subobject, the
+   referenced node MUST use the assigned value for the Identifier field
+   in the corresponding LSP-related messages.
+
+   (4) n: 16 bits
+
+   n is a two's-complement integer to take either a positive, negative,
+   or zero value.  This value is used to compute the frequency as shown
+   above.
+
+3.3.  CWDM Wavelength Label
+
+   For the case of lambda switching of CWDM, the information carried in
+   a wavelength label is:
+
+
+
+
+Otani & Li                   Standards Track                    [Page 8]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+    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              |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   The structure of the label in the case of CWDM is the same as that of
+   the DWDM case.
+
+   (1) Grid: 3 bits
+
+   The value for Grid is set to 2 for the ITU-T CWDM grid as defined in
+   [G.694.2].
+
+   +----------+---------+
+   |   Grid   |  Value  |
+   +----------+---------+
+   | Reserved |    0    |
+   +----------+---------+
+   |ITU-T DWDM|    1    |
+   +----------+---------+
+   |ITU-T CWDM|    2    |
+   +----------+---------+
+   |Future use|  3 - 7  |
+   +----------+---------+
+
+   (2) C.S. (channel spacing): 4 bits
+
+   CWDM channel spacing is defined as follows.
+
+   +----------+---------+
+   |C.S. (nm) |  Value  |
+   +----------+---------+
+   | Reserved |    0    |
+   +----------+---------+
+   |    20    |    1    |
+   +----------+---------+
+   |Future use|  2 - 15 |
+   +----------+---------+
+
+   (3) Identifier: 9 bits
+
+   The Identifier field in lambda label format is used to distinguish
+   different lasers (in one node) when they can transmit the same
+   frequency lambda.  The Identifier field is a per-node assigned and
+   scoped value.  This field MAY change on a per-hop basis.  In all
+   cases but one, a node MAY select any value, including zero (0), for
+   this field.  Once selected, the value MUST NOT change until the LSP
+
+
+
+Otani & Li                   Standards Track                    [Page 9]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+   is torn down, and the value MUST be used in all LSP-related messages,
+   e.g., in Resv messages and label RRO subobjects.  The sole special
+   case occurs when this label format is used in a label ERO subobject.
+   In this case, the special value of zero (0) means that the referenced
+   node MAY assign any Identifier field value, including zero (0), when
+   establishing the corresponding LSP.  When a non-zero value is
+   assigned to the Identifier field in a label ERO subobject, the
+   referenced node MUST use the assigned value for the Identifier field
+   in the corresponding LSP-related messages.
+
+   (4) n: 16 bits
+
+   n is a two's-complement integer.  This value is used to compute the
+   wavelength as shown above.
+
+4.  Security Considerations
+
+   This document introduces no new security considerations to [RFC3471]
+   and [RFC3473].  For a general discussion on MPLS and GMPLS-related
+   security issues, see the MPLS/GMPLS security framework [RFC5920].
+
+5.  IANA Considerations
+
+   IANA maintains the "Generalized Multi-Protocol Label Switching
+   (GMPLS) Signaling Parameters" registry.  IANA has added three new
+   subregistries to track the codepoints (Grid and C.S.)  used in the
+   DWDM and CWDM wavelength labels, which are described in the following
+   sections.
+
+5.1.  Grid Subregistry
+
+   Initial entries in this subregistry are as follows:
+
+   Value   Grid                         Reference
+   -----   -------------------------    ----------
+     0     Reserved                     [RFC6205]
+     1     ITU-T DWDM                   [RFC6205]
+     2     ITU-T CWDM                   [RFC6205]
+    3-7    Unassigned                   [RFC6205]
+
+   New values are assigned according to Standards Action.
+
+
+
+
+
+
+
+
+
+
+Otani & Li                   Standards Track                   [Page 10]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+5.2.  DWDM Channel Spacing Subregistry
+
+   Initial entries in this subregistry are as follows:
+
+   Value   Channel Spacing (GHz)        Reference
+   -----   -------------------------    ----------
+     0     Reserved                     [RFC6205]
+     1     100                          [RFC6205]
+     2     50                           [RFC6205]
+     3     25                           [RFC6205]
+     4     12.5                         [RFC6205]
+    5-15   Unassigned                   [RFC6205]
+
+   New values are assigned according to Standards Action.
+
+5.3.  CWDM Channel Spacing Subregistry
+
+   Initial entries in this subregistry are as follows:
+
+   Value   Channel Spacing (nm)         Reference
+   -----   -------------------------    ----------
+   0       Reserved                     [RFC6205]
+   1       20                           [RFC6205]
+   2-15    Unassigned                   [RFC6205]
+
+   New values are assigned according to Standards Action.
+
+6.  Acknowledgments
+
+   The authors would like to thank Adrian Farrel, Lou Berger, Lawrence
+   Mao, Zafar Ali, and Daniele Ceccarelli for the discussion and their
+   comments.
+
+7.  References
+
+7.1.  Normative References
+
+   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
+              Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+   [RFC3471]  Berger, L., Ed., "Generalized Multi-Protocol Label
+              Switching (GMPLS) Signaling Functional Description", RFC
+              3471, January 2003.
+
+   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
+              Switching (GMPLS) Signaling Resource ReserVation Protocol-
+              Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
+              January 2003.
+
+
+
+Otani & Li                   Standards Track                   [Page 11]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+   [RFC3945]  Mannie, E., Ed., "Generalized Multi-Protocol Label
+              Switching (GMPLS) Architecture", RFC 3945, October 2004.
+
+7.2.  Informative References
+
+   [G.694.1]  ITU-T Recommendation G.694.1, "Spectral grids for WDM
+              applications: DWDM frequency grid", June 2002.
+
+   [G.694.2]  ITU-T Recommendation G.694.2, "Spectral grids for WDM
+              applications: CWDM wavelength grid", December 2003.
+
+   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
+              Networks", RFC 5920, July 2010.
+
+
+
+
+
+
+
+
+
+
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+Otani & Li                   Standards Track                   [Page 12]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+Appendix A.  DWDM Example
+
+   Considering the network displayed in Figure 1, it is possible to show
+   an example of LSP setup using the lambda labels.
+
+   Node 1 receives the request for establishing an LSP from itself to
+   Node 9.  The ITU-T grid to be used is the DWDM one, the channel
+   spacing is 50 Ghz, and the wavelength to be used is 193,35 THz.
+
+   Node 1 signals the LSP via a Path message including a wavelength
+   label structured as defined in Section 3.2:
+
+    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                |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   Where:
+
+   Grid = 1 : ITU-T DWDM grid
+
+   C.S. = 2 : 50 GHz channel spacing
+
+   n    = 5 :
+
+        Frequency (THz) = 193.1 THz + n * channel spacing (THz)
+
+        193.35 (THz) = 193.1 (THz) + n* 0.05 (THz)
+
+        n = (193.35-193.1)/0.05 = 5
+
+Appendix B.  CWDM Example
+
+   The network displayed in Figure 1 can also be used to display an
+   example of signaling using the wavelength label in a CWDM
+   environment.
+
+   This time, the signaling of an LSP from Node 4 to Node 7 is
+   considered.  Such LSP exploits the CWDM ITU-T grid with a 20 nm
+   channel spacing and is established using a wavelength equal to 1331
+   nm.
+
+   Node 4 signals the LSP via a Path message including a wavelength
+   label structured as defined in Section 3.3:
+
+
+
+
+
+
+Otani & Li                   Standards Track                   [Page 13]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+    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                |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   Where:
+
+   Grid = 2 : ITU-T CWDM grid
+
+   C.S. = 1 : 20 nm channel spacing
+
+   n    = -7 :
+
+        Wavelength (nm) = 1471 nm + n * 20 nm
+
+        1331 (nm) = 1471 (nm) + n * 20 nm
+
+        n = (1331-1471)/20 = -7
+
+Authors' Addresses
+
+   Richard Rabbat
+   Google, Inc.
+   1600 Amphitheatre Parkway
+   Mountain View, CA 94043
+   USA
+   EMail: rabbat@alum.mit.edu
+
+
+   Sidney Shiba
+   EMail: sidney.shiba@att.net
+
+
+   Hongxiang Guo
+   EMail: hongxiang.guo@gmail.com
+
+   Keiji Miyazaki
+   Fujitsu Laboratories Ltd
+   4-1-1 Kotanaka Nakahara-ku,
+   Kawasaki Kanagawa, 211-8588
+   Japan
+   Phone: +81-44-754-2765
+   EMail: miyazaki.keiji@jp.fujitsu.com
+
+
+
+
+
+
+
+Otani & Li                   Standards Track                   [Page 14]
+
+RFC 6205             Generalized Labels for LSC LSRs          March 2011
+
+
+   Diego Caviglia
+   Ericsson
+   16153 Genova Cornigliano
+   Italy
+   Phone: +390106003736
+   EMail: diego.caviglia@ericsson.com
+
+
+   Takehiro Tsuritani
+   KDDI R&D Laboratories Inc.
+   2-1-15 Ohara Fujimino-shi
+   Saitama, 356-8502
+   Japan
+   Phone:  +81-49-278-7806
+   EMail:  tsuri@kddilabs.jp
+
+Editors' Addresses
+
+   Tomohiro Otani (editor)
+   KDDI Corporation
+   2-3-2 Nishishinjuku Shinjuku-ku
+   Tokyo, 163-8003
+   Japan
+   Phone:  +81-3-3347-6006
+   EMail:  tm-otani@kddi.com
+
+
+   Dan Li (editor)
+   Huawei Technologies
+   F3-5-B R&D Center, Huawei Base,
+   Shenzhen 518129
+   China
+   Phone: +86 755-289-70230
+   EMail: danli@huawei.com
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Otani & Li                   Standards Track                   [Page 15]
+