RFC6205

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.

Copyright Notice

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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

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].

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.

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.

                              |
  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

+-------------------------------------------------------------+ | 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.

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.

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.

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

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.

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

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.

CWDM Wavelength Label

For the case of lambda switching of CWDM, 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

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.

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.

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.

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.

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.

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.

Acknowledgments

The authors would like to thank Adrian Farrel, Lou Berger, Lawrence Mao, Zafar Ali, and Daniele Ceccarelli for the discussion and their comments.

References

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.

RFC3945 Mannie, E., Ed., "Generalized Multi-Protocol Label

          Switching (GMPLS) Architecture", RFC 3945, October 2004.

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.

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:

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: [email protected]

Sidney Shiba EMail: [email protected]

Hongxiang Guo EMail: [email protected]

Keiji Miyazaki Fujitsu Laboratories Ltd 4-1-1 Kotanaka Nakahara-ku, Kawasaki Kanagawa, 211-8588 Japan Phone: +81-44-754-2765 EMail: [email protected]

Diego Caviglia Ericsson 16153 Genova Cornigliano Italy Phone: +390106003736 EMail: [email protected]

Takehiro Tsuritani KDDI R&D Laboratories Inc. 2-1-15 Ohara Fujimino-shi Saitama, 356-8502 Japan Phone: +81-49-278-7806 EMail: [email protected]

Editors' Addresses

Tomohiro Otani (editor) KDDI Corporation 2-3-2 Nishishinjuku Shinjuku-ku Tokyo, 163-8003 Japan Phone: +81-3-3347-6006 EMail: [email protected]

Dan Li (editor) Huawei Technologies F3-5-B R&D Center, Huawei Base, Shenzhen 518129 China Phone: +86 755-289-70230 EMail: [email protected]