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: 22 April 2013 Nanjing University
F. Zhang
ZTE
R. Casellas
CTTC
22 October 2012
Generalized Labels for the Flexi-Grid in
Lambda-Switch-Capable (LSC) Label Switching Routers
draft-farrkingel-ccamp-flexigrid-lambda-label-04.txt
Abstract
GMPLS supports the description of optical switching by identifying
entries in fixed lists of switchable wavelengths (called grids)
through the encoding of lambda labels. New work within the ITU-T
Study Group 15 has defined a finer granularity grid, and the facility
to flexibly select different width amounts of spectrum from the grid.
This document defines a new GMPLS lambda label format to support this
flexi-grid.
This document updates RFC 3471 and RFC 6205 by introducing a new
label format.
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
Provisions Relating to IETF Documents
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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 pieces of the spectrum. 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" has been developed within the ITU-T Study Group 15
to allow selection and switching of pieces of the optical spectrum
chosen flexibly from a fine granularity grid of wavelengths with
variable spectral bandwidth [G.694.1]. This document updates the
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definition of GMPLS lambda labels provided in [RFC6205] to support
the flexi-grid.
This document will relies on [G.694.1] for the definition of the
optical data plane and does not make any updates to the work of the
ITU-T in that regard. The encoding specified in this document will
be communicated to the ITU-T for comment before publication as an
RFC.
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.694.1] 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.694.1] provides clear guidance on the support of flexible grid by
implementations in Section 2 of Appendix I:
The flexible DWDM grid defined in clause 7 has a nominal central
frequency granularity of 6.25 GHz and a slot width granularity of
12.5 GHz. 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).
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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.
- 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 * frequency granularity (THz)
where the nominal central frequency granularity for the flexible
grid is 0.00625 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 the other GMPLS lambda label formats
defined in [RFC3471] and [RFC6205], the use of this label format 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.
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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. For the flexible grid situation, this field is used to
represent the nominal central frequency granularity.
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.694.1] as follows:
Slot Width (GHz) = 12.5 GHz * m
The Reserved field MUST be set to zero on transmission and SHOULD be
ignored on receipt.
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An implementation that wishes to use the flexi-grid label encoding
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.
4.2. Considerations of Bandwidth
There is some overlap between the concept of bandwidth and label in
many GMPLS-based systems where a label indicates a physical switching
resource. This overlap is increased in a flexi-grid system where a
label value indicates the slot width and so affects the bandwidth
supported by an LSP. Thus the 'm' parameter is both a property of
the label (i.e., it helps define exactly what is switched) and of the
bandwidth.
In GMPLS signaling [RFC3473], bandwidth is requested in the TSpec
object and confirmed in the Flowspec object. The 'm' parameter is a
parameter of the GMPLS flexi-grid label as described above and is
also a parameter of the flexi-grid TSpec and Flowspec as described in
[FLEXRSVP].
5. Manageability Considerations
This document introduces no new elements for management. That is,
labels can continue to be used in the same way by the GMPLS protocols
and where those labels were treated as opaque quantities with local
or global significance, no change is needed to the management
systems.
However, this document introduces some changes to the nature of a
label that may require changes to management systems. Firstly,
systems that handle lambda labels as 32 bit quantities need to be
updated to process the 64 bit labels described in this document even
if the labels are treated as opaque quantities. Furthermore,
although management systems that can handle lambda labels as defined
in [RFC6205] can continue to process the fields defined in RFC 6205
as before, they have to handle new legal values of some of those
fields (Greid = 3 and C.S. = 5), and they have to be aware of the new
'm' field.
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6. Security Considerations
[RFC6205] notes that the definition of a new label encoding does not
introduce 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.
Special thanks to the Vancouver 2012 Pool Party for discussions and
rough consensus: Dieter Beller, Ramon Casellas, Daniele Ceccarelli,
Oscar Gonzalez de Dios, Iftekhar Hussain, Cyril Margaria, Lyndon Ong,
and Fatai Zhang.
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,
October 2011.
[G.694.1] ITU-T Recommendation G.694.1 (revision 2), "Spectral grids
for WDM applications: DWDM frequency grid", February 2012.
9.2. Informative References
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[G.671] ITU-T Recommendation G.671, "Transmission characteristics
of optical components and subsystems", 2009.
[G.694.2] ITU-T Recommendation G.694.2, "Spectral grids for WDM
applications: CWDM wavelength grid", December 2003.
[FLEXRSVP] Zhang, F., Gonzalez de Dios, O., and D. Ceccarelli,
"RSVP-TE Signaling Extensions in support of Flexible
Grid", draft-zhang-ccamp-flexible-grid-rsvp-te-ext, work
in progress.
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Appendix A. Flexi-Grid Example
Consider a fragment of an optical LSP between node A and node B using
the flexible grid. Suppose that the LSP on this hop is formed:
- using the ITU-T Flexi-Grid
- the nominal central freequency of the slot 193.05 THz
- the nominal central frequency granularity is 6.25 GHz
- the slot width is 50 GHz.
In this case the label representing the switchable quantity that is
the flexi-grid quantity is encoded as described in Section 4.1 with
the following parameter settings. The label can be used in signaling
or in management protocols to describe the LSP.
Grid = 3 : ITU-T Flexi-Grid
C.S. = 5 : 6.25 GHz nominal central frequency granularity
Identifier = local value indicating the laser in use
n = -8 :
Frequency (THz) = 193.1 THz + n * frequency granularity (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)
Nanjing University
EMail: wsliguotou@hotmail.com
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Zhang Fei
ZTE
EMail: zhang.fei3@zte.com.cn
Ramon Casellas
CTTC
EMail: ramon.casellas@cttc.es
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