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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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
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.
|
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.
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
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
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:
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.
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.
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.
[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.
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: 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
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
|
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