Network Working Group D. King (Ed.)
Internet Draft A. Farrel (Ed.)
Updates: 3471, 6205 (if approved) Old Dog Consulting
Category: Standards Track Y. Li (Ed.)
Expires: 12 Spetember 2012 F. Zhang
ZTE
R. Casellas
CTTC
12 March 2012
Generalized Labels for the Flexi-Grid in
Lambda-Switch-Capable (LSC) Label Switching Routers
draft-farrkingel-ccamp-flexigrid-lambda-label-03.txt
Abstract
A new flexible wavelength grid ("flexi-grid") is being developed
within the ITU-T Study Group 15 to allow selection and switching of
individual lambdas chosen flexibly from a detailed, fine granularity
grid of available wavelengths. This document updates the definition
of GMPLS lambda labels to support the flexi-grid.
This document updates RFC 3471 and updates RFC 6205.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright Notice
Copyright (c) 2012 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
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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.
1. Introduction
As described in [RFC3945], GMPLS extends MPLS from supporting only
Packet Switching Capable (PSC) interfaces and switching to also
support four new classes of interfaces and switching that include
Lambda Switch Capable (LSC).
A functional description of the extensions to MPLS signaling needed
to support this new class of interface and switching is provided in
[RFC3471].
[RFC3471] states that wavelength labels "only have significance
between two neighbors" (Section 3.2.1.1); global wavelength semantics
are not considered. [RFC6205] 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]. The terms DWDM and CWDM are
defined in [G.671].
A flexible grid network selects its data channels as arbitrarily
assigned spectral slices. Mixed bitrate transmission systems can
allocate their channels with different spectral bandwidths so that
the channels can be optimized for the bandwidth requirements of the
particular bit rate and modulation scheme of the individual channels.
This technique is regarded as a promising way to improve the network
utilization efficiency and fundamentally reduce the cost of the core
network.
The "flexi-grid" is being developed within the ITU-T Study Group 15
to allow selection and switching of individual lambdas chosen
flexibly from a detailed, fine granularity grid of wavelengths with
arbitrary spectral bandwidth [G.FLEXIGRID]. This document updates
the definition of GMPLS lambda labels provided in [RFC6205] to
support the flexi-grid.
This document will not be put forward for publication as an RFC
before the ITU-T have completed technical development of
[G.FLEXIGRID], and the encoding specified in this document will also
be communicated to the ITU-T for comment before publication as an
RFC.
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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. Overview of Flexi-Grid
[G.FLEXIGRID] extends DWDM fixed grids as defined in [G.694.1] to
add support for flexible grids. The basis of the work is to allow
a data channel to be formed from an abstract grid anchored at
193.1 THz and selected on a channel spacing of 6.25 GHz with a
variable slot width measured in units of 12.5 GHz. Individual
allocations may be made on this basis from anywhere in the spectrum,
subject to allocations not overlapping.
[G.FLEXIGRID] provides clear guidance on the support of flexible grid
by implementations in Section 2 of Appendix I:
However, devices or applications that make use of the flexible
grid may not have to be capable of supporting every possible slot
width or position. In other words, applications may be defined
where only a subset of the possible slot widths and positions are
required to be supported.
For example, an application could be defined where the nominal
central frequency granularity is 12.5 GHz (by only requiring
values of n that are even) and that only requires slot widths as a
multiple of 25 GHz (by only requiring values of m that are even).
3. Fixed Grid Lambda Label Encoding
[RFC6205] defines an encoding for a global semantic for a DWDM label
based on four fields:
- Grid: used to select which grid the lambda is selected from.
Values defined in [RFC6205] identify DWDM [G.694.1] and CWDM
[G.694.2].
- C.S. (Channel Spacing): used to indicate the channel spacing.
[RFC6205] defines values to represent spacing of 100, 50, 25 and
12.5 GHz.
- Identifier: a local-scoped integer used to distinguish different
lasers (in one node) when they can transmit the same frequency
lambda.
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- n: a two's-complement integer to take either a positive, negative,
or zero value. This value is used to compute the frequency as
defined in [RFC6205] and based on [G.694.1]. The use of n is
repeated here for ease of reading.
Frequency (THz) = 193.1 THz + n * channel spacing (THz)
4. Flexi-Label Format and Values
4.1 Flexi-Label Encoding
This document defines a new generalized label encoding for use in
flexi-grid systems. As with all other GMPLS lambda labels, the use of
this label is known a priori. That is, since the interpretation of
all lambda labels is determined hop-by-hop, the use of this label
requires that all nodes on the path expect to use this label.
For convenience, however, the label is modeled on the fixed grid
label defined in [RFC6205] and briefly described in Section 3.
Figure 1 shows the format of the Flexi-Label. It is a 64 bit label.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| m | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 : The Flexi-Label Encoding
This document defines a new Grid value to supplement those in
[RFC6205]:
+----------+---------+
| Grid | Value |
+----------+---------+
|ITU-T Flex| 3 |
+----------+---------+
Within the fixed grid network, the C.S. value is used to represent
the channel spacing, as the spacing between adjacent channels is
constant. While, for flexible grid situation, this field should be
used to represent the channel spacing granularity/or central
frequency granularity.
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This document defines a new C.S. value to supplement those in
[RFC6205]:
+----------+---------+
| C.S(GHz) | Value |
+----------+---------+
| 6.25 | 5 |
+----------+---------+
The meaning of the Identifier field is maintained from [RFC6205] (see
also Section 3).
The meaning of n is maintained from [RFC6205] (see also Section 3).
The m field is used to identify the slot width according to the
formula given in [G.FLEXIGRID] as follows:
Slot Width (GHz) = 12.5 GHz * m
The practical range of values for m is from 1 to 8 for slot widths
ranging from 12.5 GHz to 100 GHz. Wider slot widths may be considered
with larger values of m.
The Reserved field MUST be set to zero on transmission and SHOULD be
ignored on receipt.
An implementation that wishes to use the flexi-grid MUST follow the
procedures of [RFC3473] and of [RFC3471] as updated by [RFC6205]. It
MUST set Grid to 3 and C.S. to 5. It MUST set Identifier to indicate
the local identifier of the laser in use as described in [RFC6205].
It MUST also set n according to the formula in Section 3 (inherited
unchanged from [RFC6205]). Finally,the implementation MUST set m as
described in the formula stated above.
5. Manageability Considerations
This document introduces no new elements for management. That is,
labels will continue to be used in the same way by the GMPLS
protocols and lambda labels have the same fields as previously
defined so any management tools defined to handle [RFC6205] labels
will be able to handle labels as specified in this document. However,
it is obvious that the management tools will have to interpret the
new values and meanings of label fields as defined in this document,
and management tools that may have been (unwisely) coded to expect
all lambda labels to be 32 bits, will need to be updated to handle
these 64 bit labels.
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6. Security Considerations
[RFC6205] notes that the definition of a new label encoding does not
introduces any new security considerations to [RFC3471] and
[RFC3473]. That statement applies equally to this document.
For a general discussion on MPLS and GMPLS-related security issues,
see the MPLS/GMPLS security framework [RFC5920].
7. IANA Considerations
IANA maintains the "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Parameters" registry that contains several
subregistries.
7.1. Grid Subregistry
IANA is requested to allocate a new entry in this subregistry as
follows:
Value Grid Reference
----- ------------------------- ----------
3 ITU-T Flex [This.I-D]
7.2. DWDM Channel Spacing Subregistry
IANA is requested to allocate a new entry in this subregistry as
follows:
Value Channel Spacing (GHz) Reference
----- ------------------------- ----------
5 6.25 [This.I-D]
8. Acknowledgments
Very many thanks to Lou Berger for discussions of labels of more than
32 bits.
Many thanks to Sergio Belotti, Pietro Vittorio Grandi and Fatai Zhang
for their support of this work.
The authors would like to thank Ben Niven-Jenkins for inspiring the
choice of filename for this document.
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9. References
9.1. 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.
[RFC6205] Otani, T., and Li, D., "Generalized Labels for Lambda-
Switch-Capable (LSC) Label Switching Routers", RFC 6205,
March 2011.
[G.FLEXIGRID] ITU-T Revised Recommendation G.694.1 (revision 2),
Consented for publication by ITU-T Study Group 15,
December 2011.
9.2. Informative References
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[G.671] ITU-T Recommendation G.671, "Transmission characteristics
of optical components and subsystems", 2009.
[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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Appendix A. Flexi-Grid Example
Considering the network displayed in Figure 2 (reproduced from
[RFC6205]) it is possible to show an example of LSP setup using the
lambda labels. The figure shows Reconfigurable Optical Add/Drop
Multiplexers (ROADMs) and Wavelength Cross-Connects (WXCs) that
operate at the wavelength switching level as well as PXCs
|
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 2 : Example Network
Node 1 receives the request for establishing an LSP from itself to
Node 9. The ITU-T grid to be used is the Flexi-Grid, the channel
spacing is 6.25 GHz, and the wavelength to be used is 193.05 THz.
The cslot width to be used is 50 GHz. Node 1 signals the LSP using a
Path message including a wavelength label structured 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| m | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Where:
Grid = 3 : ITU-T Flexi-Grid
C.S. = 5 : 6.25 GHz channel spacing
Identifier = local value indicating the laser in use
n = 24 :
Frequency (THz) = 193.1 THz + n * channel spacing (THz)
193.05 (THz) = 193.1 (THz) + n* 0.00625 (THz)
n = (193.05-193.1)/0.00625 = -8
m = 4 :
Slot Width (GHz) = 12.5 GHz * m
50 (GHz) = 12.5 (GHz) * m
m = 50 / 12.5 = 4
Authors' Addresses
Adrian Farrel
Old Dog Consulting
EMail: adrian@olddog.co.uk
Daniel King (Editor)
Old Dog Consulting
EMail: daniel@olddog.co.uk
Yao Li (Editor)
ZTE
EMail: li.yao3@zte.com.cn
Zhang Fei
ZTE
EMail: zhang.fei3@zte.com.cn
Ramon Casellas
CTTC
EMail: ramon.casellas@cttc.es
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