Network Working Group Fatai Zhang
Internet-Draft Xian Zhang
Intended status: Informational Huawei
Ramon Casellas
CTTC
O. Gonzalez de Dios
Telefonica
D. Ceccarelli
Ericsson
Expires: May 12, 2014 November 12, 2013
GMPLS OSPF-TE Extensions in support of Flexible Grid
draft-zhang-ccamp-flexible-grid-ospf-ext-03.txt
Abstract
This memo describes the OSPF-TE extensions in support of GMPLS
control of networks that include devices that use the new flexible
optical grid.
Status of this Memo
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This Internet-Draft will expire on May 12, 2014.
Copyright Notice
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Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction ................................................ 2
2. Terminology ................................................. 3
2.1. Conventions Used in this Document .......................3
3. Requirements for Flexi-grid Routing ..........................3
3.1. Available Frequency Ranges.............................. 4
3.2. Application Compliance Considerations ...................5
3.3. Comparison with Fixed-grid DWDM Links ...................6
4. Extensions .................................................. 6
4.1. Available Labels Set Sub-TLV............................ 7
4.1.1. Inclusive/Exclusive Label Range ....................7
4.1.2. Inclusive/Exclusive Label Lists ....................7
4.1.3. Bitmap ............................................ 7
4.2. Extensions to Port Label Restriction sub-TLV ............7
4.3. Examples for Available Label Set Sub-TLV ................8
5. IANA Considerations ......................................... 9
6. Acknowledgments ............................................ 10
7. Security Considerations..................................... 10
8. References ................................................. 10
8.1. Normative References................................... 10
8.2. Informative References................................. 10
9. Authors' Addresses ..........................................12
10. Contributors' Addresses.................................... 12
1. Introduction
[G.694.1] defines the Dense Wavelength Division Multiplexing (DWDM)
frequency grids for Wavelength Division Multiplexing (WDM)
applications. A frequency grid is a reference set of frequencies
used to denote allowed nominal central frequencies that may be used
for defining applications. The channel spacing is the frequency
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spacing between two allowed nominal central frequencies. All of the
wavelengths on a fiber should use different central frequencies and
occupy a fixed bandwidth of frequency.
Fixed grid channel spacing is selected from 12.5 GHz, 25 GHz, 50 GHz,
100 GHz and integer multiples of 100 GHz. But [G.694.1] also
defines "flexible grids", also known as "flexi-grid". The terms
"frequency slot" (i.e., the frequency range allocated to a specific
channel and unavailable to other channels within a flexible grid)
and "slot width" (i.e., the full width of a frequency slot in a
flexible grid) are used to define a flexible grid.
[FLEX-FWK] defines a framework and the associated control plane
requirements for the GMPLS based control of flexi-grid DWDM networks.
[RFC6163] provides a framework for GMPLS and Path Computation
Element (PCE) control of Wavelength Switched Optical Networks
(WSONs), and [WSON-OSPF] defines the requirements and OSPF-TE
extensions in support of GMPLS control of a WSON.
[FLEX-SIG] describes requirements and protocol extensions for
signaling to set up LSPs in networks that support the flexi-grid,
and this document complements [FLEX-SIG] by describing the
requirement and extensions for OSPF-TE routing in a flexi-grid
network.
2. Terminology
For terminology related to flexi-grid, please consult [FLEX-FWK] and
[G.694.1].
2.1. 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 RFC-2119 [RFC2119].
3. Requirements for Flexi-grid Routing
The architecture for establishing LSPs in a Spectrum Switched
optical Network (SSON) is described in [FLEX-FWK].
An flexi-LSP occupies a specific frequency slot, i.e. a range of
frequencies. The process of computing a route and the allocation of
a frequency slot is referred to as RSA (Routing and Spectrum
Assignment). [FLEX-FWK] describes three types of architectural
approaches to RSA: combined RSA; separated RSA; and distributed SA.
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The first two approaches among them could be called "centralized SA"
because both routing and spectrum (frequency slot) assignment are
performed by centralized entity before the signaling procedure.
In the case of centralized SA, the assigned frequency slot is
specified in the Path message during LSP setup. In the case of
distributed SA, the slot width of the flexi-grid LSP is specified in
the Path message, allowing the involved network elements to select
the frequency slot to be used.
If the capability of switching or converting the whole optical
spectrum allocated to an optical spectrum LSP is not available at
nodes along the path of the LSP, the LSP is subject to the Optical
"Spectrum Continuity Constraint", as described in [FLEX-FWK].
The remainder of this section states the additional extensions on
the routing protocols in a flexi-grid network. That is, the
additional information that must be collected and passed between
nodes in the network by the routing protocols in order to enable
correct path computation and signaling in support of LSPs within the
network.
3.1. Available Frequency Ranges
In the case of flexi-grids, the central frequency steps from 193.1
THz with 6.25 GHz granularity. The calculation method of central
frequency and the frequency slot width of flexi-LSP are defined in
[G.694.1].
On a DWDM link, the frequency slots must not overlap with each other.
However, the border frequencies of two frequency slots may be the
same frequency, i.e., the highest frequency of a frequency slot may
be the lowest frequency of the next frequency slot.
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Frequency Slot 1 Frequency Slot 2
+-----------+-----------------------+
| | |
-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
...+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
------------ ------------------------
^ ^
Central F = 193.1THz Central F = 193.1375 THz
Slot width = 25 GHz Slot width = 50 GHz
Figure 1 - Two Frequency Slots on a Link
Figure 1 shows two adjacent frequency slots on a link. The highest
frequency of frequency slot 1 denoted by n=2 is the lowest frequency
of slot 2. In this example, it means that the frequency range from
n=-2 to n=10 is occupied and is unavailable to other flexi-LSPs.
Hence, in order to clearly show which LSPs can be supported and what
frequency slots are unavailable, the available frequency ranges
should be advertised by the routing protocol for the flexi-grid DWDM
links. A set of non-overlapping available frequency ranges should
be disseminated in order to allow efficient resource management of
flexi-grid DWDM links and RSA procedures which are described in
section 5.7 of [FLEX-FWK].
3.2. Application Compliance Considerations
As described in [G.694.1], devices or applications that make use of
the flexi-grid may not be capable of supporting every possible slot
width or position (i.e., central frequency). In other words,
applications or implementations 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).
Hence, in order to support all possible applications and
implementations the following information should be advertised for a
flexi-grid DWDM link:
o Central frequency granularity: a multiplier of 6.25 GHz.
o Slot width granularity: a multiplier of 12.5 GHz.
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o Slot width range: two multipliers of 12.5GHz, each indicate the
minimal and maximal slot width supported by a port respectively.
The combination of slot width range and slot width granularity can
be used to determine the slot widths set supported by a port.
3.3. Comparison with Fixed-grid DWDM Links
In the case of fixed-grid DWDM links, each wavelength has a pre-
defined central frequency and each wavelength has the same frequency
range (i.e., there is a uniform channel spacing). Hence all the
wavelengths on a DWDM link can be identified uniquely simply by
giving it an identifier (such as the central wavelength [RFC6205]),
and the status of the wavelengths (available or not) can be
advertised through a routing protocol.
Figure 2 shows a link that supports a fixed-grid with 50 GHz channel
spacing. The central frequencies of the wavelengths are pre-defined
by values of 'n' and each wavelength occupies a fixed 50 GHz
frequency range as described in [G.694.1].
W(-2) | W(-1) | W(0) | W(1) | W(2) |
...---------+-----------+-----------+-----------+-----------+----...
| 50 GHz | 50 GHz | 50 GHz | 50 GHz |
n=-2 n=-1 n=0 n=1 n=2
...---+-----------+-----------+-----------+-----------+----------...
^
Central F = 193.1THz
Figure 2 - A Link Supports Fixed Wavelengths with 50 GHz Channel
Spacing
Unlike the fixed-grid DWDM links, on a flexi-grid DWDM link the slot
width of the frequency slot are flexible as described in section 2.1.
That is, the value of m in the formula is uncertain before a
frequency slot is actually allocated. For this reason, the
available frequency slot/ranges need to be advertised for a flexi-
grid DWDM link instead of the specific "wavelengths" that are
sufficient for a fixed-grid link.
4. Extensions
As described in [FLEX-FWK], the network connectivity topology
constructed by the links/nodes and node capabilities are the same as
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for WSON, and can be advertised by the GMPLS routing protocols
(refer to section 6.2 of [RFC6163]). In the flexi-grid case, the
available frequency ranges instead of the specific "wavelengths" are
advertised for the link. This section defines the GMPLS OSPF-TE
extensions in support of advertising the available frequency ranges
for flexi-grid DWDM links.
4.1. Available Labels Set Sub-TLV
As described in section 3.1, the available frequency ranges other
than the available frequency slots should be advertised for the
flexi-grid DWDM links. The label encoding defined in [FLEX-LBL] is
used to encode the label field in Available Labels Set sub-TLV [GEN-
Encode].
4.1.1. Inclusive/Exclusive Label Range
The inclusive/exclusive label ranges format of the Available Labels
Set sub-TLV defined in [GEN-ENCODE] can be used for specifying the
frequency ranges of the flexi-grid DWDM links.
Note that multiple Available Labels Set sub-TLVs may be needed if
there are multiple discontinuous frequency ranges on a link.
4.1.2. Inclusive/Exclusive Label Lists
The inclusive/exclusive label lists format of Available Labels Set
sub-TLV defined in [GEN-ENCODE] can be used for specifying the
available central frequencies of flexi-grid DWDM links.
4.1.3. Bitmap
The bitmap format of Available Labels Set sub-TLV defined in [GEN-
ENCODE] can be used for specifying the available central frequencies
of the flexi-grid DWDM links.
Each bit in the bit map represents a particular central frequency
with a value of 1/0 indicating whether the central frequency is in
the set or not. Bit position zero represents the lowest central
frequency and corresponds to the base label, while each succeeding
bit position represents the next central frequency logically above
the previous.
4.2. Extensions to Port Label Restriction sub-TLV
As described in Section 3.2, a port that supports flexi-grid may
support only a restricted subset of the full flexible grid. The
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Port Label Restriction sub-TLV is defined in [GEN-ENCODE] and [GEN-
OSPF]. It can be used to describe the label restrictions on a port.
A new restriction type, the flexi-grid Restriction Type, is defined
here to specify the restrictions on a port to support flexi-grid.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MatrixID | RstType = TBA | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C.F.G | S.W.G | Min Width | Max Width |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
MatrixID (8 bits): As defined in [GEN-ENCODE].
RstType (Restriction Type, 8 bits): Takes the value (TBD) to
indicate the restrictions on a port to support flexi-grid.
C.F.G (Central Frequency Granularity, 8 bits): A positive integer.
Its value indicates the multiple of 6.25 GHz in terms of central
frequency granularity.
S.W.G (Slot Width Granularity, 8 bits): A positive integer. Its
value indicates the multiple of 12.5 GHz in terms of slot width
granularity.
Min Width (8 bits): A positive integer. Its value indicates the
multiple of 12.5 GHz in terms of the supported minimal slot width.
Max Width (8 bits): A positive integer. Its value indicates the
multiple of 12.5 GHz in terms of the supported maximal slot width.
4.3. Examples for Available Label Set Sub-TLV
Figure 3 shows an example of available frequency range of a flexi-
grid DWDM link.
-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
...+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
|--Available Frequency Range--|
Figure 3 - Flexi-grid DWDM Link
The symbol '+' represents the allowed nominal central frequency. The
symbol "--" represents a 6.25 GHz frequency unit. The number on the
top of the line represents the 'n' in the frequency calculation
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formula (193.1 + n * 0.00625). The nominal central frequency is
193.1 THz when n equals zero.
Assume that the central frequency granularity is 6.25GHz, the label
set can be encoded as follows:
Inclusive Label Range:
o Start Slot = -2;
o End Slot = 8.
The available central frequencies (-1, 0, 1, 2, 3, 4, 5, 6, 7) can
be deduced by the Inclusive Label Range, because the Central
Frequency Granularity is 6.25 GHz.
Inclusive Label Lists:
o List Entry 1 = slot -1;
o List Entry 2 = slot 0;
o List Entry 3 = slot 1;
o List Entry 4 = slot 2;
o List Entry 5 = slot 3;
o List Entry 6 = slot 4;
o List Entry 7 = slot 5;
o List Entry 8 = slot 6;
o List Entry 9 = slot 7.
Bitmap:
o Base Slot = -1;
o Bitmap = 111111111(padded out to a full multiple of 32 bits)
5. IANA Considerations
[GEN-OSPF] defines the Port label Restriction sub-TLV of OSPF TE
Link TLV. It also creates a registry of values of the Restriction
Type field of that sub-TLV
IANA is requested to assign a new value from that registry as
follows:
Value Meaning Reference
TBD Flexi-grid restriction [This.I-D]
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6. Acknowledgments
This work was supported in part by the FP-7 IDEALIST project under
grant agreement number 317999.
7. Security Considerations
This document does not introduce any further security issues other
than those discussed in [RFC3630], [RFC4203].
8. References
8.1. Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
[G.694.1] ITU-T Recommendation G.694.1 (revision 2), "Spectral grids
for WDM applications: DWDM frequency grid", February 2012.
[GEN-ENCODE] Bernstein, G., Lee, Y., Li, D., and W. Imajuku,
"General Network Element Constraint Encoding for GMPLS
Controlled Networks", draft-ietf-ccamp-general-constraint-
encode, work in progress.
[GEN-OSPF] Fatai Zhang, Y. Lee, Jianrui Han, G. Bernstein and Yunbin
Xu, " OSPF-TE Extensions for General Network Element
Constraints ", draft-ietf-ccamp-gmpls-general-constraints-
ospf-te, work in progress.
[RFC6205] T. Otani and D. Li, "Generalized Labels for Lambda-Switch-
Capable (LSC) Label Switching Routers", RFC 6205, March
2011.
[FLEX-LBL] King, D., Farrel, A. and Y. Li, "Generalized Labels for
the Flexi-Grid in Lambda Switch Capable (LSC) Label
Switching Routers", draft-farrkingel-ccamp-flexigrid-
lambda-label, work in progress.
8.2. Informative References
[RFC6163] Y. Lee, G. Bernstein and W. Imajuku, "Framework for GMPLS
and Path Computation Element (PCE) Control of Wavelength
Switched Optical Networks (WSONs)", RFC 6163, April 2011.
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[FLEX-SIG] F.Zhang et al, "RSVP-TE Signaling Extensions in support
of Flexible-grid", draft-zhang-ccamp-flexible-grid-rsvp-
te-ext, work in progress.
[FLEX-FWK] Gonzalez de Dios, O,, Casellas R., Zhang, F., Fu, X.,
Ceccarelli, D., and I. Hussain, "Framework and
Requirements for GMPLS based control of Flexi-grid DWDM
networks', draft-ogrcetal-cammp-flexi-grid-fwk, work in
progress.
[WSON-OSPF] Y. Lee and G. Bernstein, "GMPLS OSPF Enhancement for
Signal and Network Element Compatibility for Wavelength
Switched Optical Networks ", draft-ietf-ccamp-wson-signal-
compatibility-ospf, work in progress.
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9. Authors' Addresses
Fatai Zhang
Huawei Technologies
Email: zhangfatai@huawei.com
Xian Zhang
Huawei Technologies
Email: zhang.xian@huawei.com
Ramon Casellas, Ph.D.
CTTC
Spain
Phone: +34 936452916
Email: ramon.casellas@cttc.es
Oscar Gonzalez de Dios
Telefonica Investigacion y Desarrollo
Emilio Vargas 6
Madrid, 28045
Spain
Phone: +34 913374013
Email: ogondio@tid.es
Daniele Ceccarelli
Ericsson
Via A. Negrone 1/A
Genova - Sestri Ponente
Italy
Email: daniele.ceccarelli@ericsson.com
10. Contributors' Addresses
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
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