Network Working Group Fatai Zhang
Internet-Draft Xiaobing Zi
Intended status: Standards Track Huawei
Ramon Casellas
CTTC
O. Gonzalez de Dios
Telefonica
D. Ceccarelli
Ericsson
Expires: April 24, 2012 October 24, 2011
GMPLS OSPF-TE Extensions in support of Flexible-Grid in DWDM Networks
draft-zhang-ccamp-flexible-grid-ospf-ext-00.txt
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Abstract
This memo describes the OSPF-TE extensions in support of GMPLS
control for flexible-grid in DWDM networks.
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].
Table of Contents
1. Introduction ................................................. 2
2. Terminology .................................................. 3
3. Requirements for Flexible-grid Routing ....................... 3
3.1. Available Frequency Ranges on the Flexible-Grid DWDM Links3
3.2. Comparison with Fixed-grid DWDM Links ................... 5
4. Extensions ................................................... 5
4.1. Available Labels Set sub-TLV ............................ 6
4.2. Examples ................................................ 7
5. IANA Considerations .......................................... 8
6. Security Considerations ...................................... 8
7. References ................................................... 8
8. Authors' Addresses .......................................... 10
1. Introduction
[G.694.1v1] defines the Dense Wavelength Division Multiplexing (DWDM)
frequency grids for 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, i.e. the frequency spacing between two allowed nominal
central frequencies could be 12.5 GHz, 25 GHz, 50 GHz, 100 GHz and
integer multiples of 100 GHz as defined in [G.694.1v1]. All of the
wavelengths on a fiber should use different central frequencies and
occupy a fixed bandwidth of frequency.
[G.FLEXIGRID], an updated version of [G.694.1v1] will be consented
in December 2011 in support of flexible-grids. The terms "frequency
slot (The frequency range allocated to a channel and unavailable to
other channels within a flexible-grid)" and "slot width" (the full
width of a frequency slot in a flexible-grid) are introduced to
address flexible-grids. A channel is represented as a LSC (Lambda
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Switching Capable) LSP in the control plane, i.e. a LSC LSP should
occupy a frequency slot on each fiber it traverses. In the case of
flexible-grid, different LSC LSPs may have different slot width on a
fiber, i.e. the slot width is flexible on a fiber.
[WSON-OSPF] defines the OSPF-TE extensions for WSON networks, which
focuses on the fixed grids of DWDM. [GEN-OSPF] defines OSPF-TE
extensions in support of the general network element constraints
under the control of GMPLS. This document describes the additional
requirements and extensions of routing protocol brought by flexible-
grid.
This document uses the fiber link model which is shown in [FLEXIBLE-
REQ] to describe the requirement and extensions for routing. The
flexible-grid related terminologies can also refer to [FLEXIBLE-REQ].
2. Terminology
Flexible Grid: See [FLEXIBLE-REQ].
Frequency Slot Width: See [FLEXIBLE-REQ].
Frequency Range: See [FLEXIBLE-REQ].
SSON: Spectrum-Switched Optical Networks; See [FLEXIBLE-REQ].
LSC SS-LSP or flexi-LSP (Lambda Switch Capable Spectrum-Switched
Label Switched Path): a control plane construct that represents a
data plane connection in which the switching involves a frequency
slot of a variable (flexible) slot width. The mapped client signal
is transported over the slot width, using spectrum efficient
modulations such as Coherent Optical Orthogonal Frequency Division
Multiplexing (CO-OFDM).
3. Requirements for Flexible-grid Routing
As described in [FLEXIBLE-REQ], the main changes for routing brought
by flexible-grid are related to the DWDM links.
3.1. Available Frequency Ranges on the Flexible-Grid DWDM Links
In the case of flexible-grids, the central frequency steps from
193.1 THz with 6.25 GHz granularity. The central frequency is
calculated as follows:
Central Frequency = 193.1 THz + n * 0.00625 THz
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Where n is a positive or negative integer including 0.
Different LSC LSPs could occupy frequency slots with different slot
width. The frequency slot width of a LSC LSP is defined as follows:
Slot width = 0.0125 THz * m
Where m is a positive integer.
The frequency slot of a LSP can be determined by the slot width and
central frequency as follows.
Lowest frequency = (central frequency) - (slot width)/2
= (193.1 + n * 0.00625) - (0.0125 * m)/2
= (193.1 + (n - m) * 0.00625) THz;
Highest frequency = (central frequency) + (slot width)/2
= (193.1 + n * 0.00625) + (0.0125 * m)/2
= (193.1 + (n + m) * 0.00625) THz;
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.
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
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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 LSC LSPs.
Hence, the available frequency ranges should be advertised for the
flexible-grid DWDM links. A set of non-overlapping available
frequency ranges SHOULD be disseminated in order to allow efficient
resource management of Flexible-grid DWDM links and RSA procedures
which are described in section 4 of [FLEXIBLE-REQ].
3.2. Comparison with Fixed-grid DWDM Links
In case of fixed-grid DWDM links, each wavelength has a pre-defined
central frequency and all the wavelengths occupy the same frequency
range (channel spacing). Hence all the wavelengths in the DWDM links
can be identified uniquely and the status (available or not) of the
wavelengths can be advertised through routing protocol.
W(-2) | W(-1) | W(0) | W(1) | W(2) |
...---------+-----------+-----------+-----------+-----------+----...
50 GHz | 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
Figure 2 shows a link that supports fixed-grid with 50 GHz channel
spacing. The central frequencies of the wavelengths are pre-defined
by 'n' and each wavelength occupies a fixed 50 GHz frequency range
as described in [G.694.1v1].
Different from the fixed-grid DWDM links, the slot width of the
wavelengths are flexible on a flexible-grid DWDM link as described
in section 2.1, i.e., the value of m in the formula is uncertain
before a frequency slot is allocated. So, the available frequency
ranges instead of the specific "wavelengths" should be advertised
for a flexible-grid DWDM link.
4. Extensions
As described in [FLEXIBLE-REQ], the network connectivity topology
constructed by the links/nodes and node capabilities are the same as
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WSON which can be advertised by GMPLS routing protocol (refer to
section 6.2 of [RFC6163]. In case of flexible-grid, the available
frequency ranges instead of the specific ''wavelengths'' should be
advertised for the link, which is different from the fixed grid DWDM.
This section defines the GMPLS OSPF-TE extensions in support of
advertising the available frequency ranges for the flexible-grid
DWDM links.
4.1. Available Labels Set sub-TLV
As described in section 2.1, the available frequency ranges other
than the available frequency slots should be advertised for the
flexible-grid DWDM links. The Available Labels Set sub-TLV defined
in [GEN-OSPF] can be re-used to advertise the available frequency
ranges for the flexible-grid DWDM links.
To make the encoding efficiently, the inclusive/exclusive label
ranges format of Available Labels Set sub-TLV defined in [GEN-OSPF]
can be used for specifying the frequency ranges of the flexible-grid
DWDM links.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|2 or 3 | Num Labels(not used) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| End Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note that it needs multiple Available Labels Set sub-TLVs if there
are multiple discontinuous frequency ranges on a link.
The fields of Start Label and End Label specify the lowest frequency
and highest frequency of a frequency range. The label format defined
in [FLEXIBLE-SIG] shown below can be used to encode the Start Label
and End 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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In case of Grid=1 (ITU-T DWDM), a new value of C.S. is defined for
flexible 6.25 GHz grid.
If the C.S. is 6.25 GHz in an Available Labels Set sub-TLV, it means
that the corresponding link supports flexible-grid and the Start
Label/End Label specifies the frequency range of the link.
[Editors' Note: the other formats of Label set (e.g.,
Inclusive/Exclusive Label Lists and Bitmap Label Set) can also be
used to specify the frequency ranges for the flexible-grid DWDM
links.]
4.2. Examples
Figure 3 shows an example of a flexible-grid DWDM link which is
traversed by two LSC LSPs.
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 = 193.14375 THz
Slot width = 25 GHz Slot width = 37.5 GHz
Figure 3 - Two Frequency Slots on a Link
The available frequency resource of the link could be advertised as
follows:
<Available Labels> sub-TLV:
o Exclusive Range 1: [Start label = 193.1 + (-2)*0.00625,
End Label = 193.1 + 2*0.00625]
o Exclusive Range 2: [Start label = 193.1 + 4*0.00625,
End Label = 193.1 + 10*0.00625]
It is noted that the central frequency denoted by n=3 is available
for a LSC LSP with 12.5 GHz slot width request but unavailable for a
LSC LSP with a wider slot width request.
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o If a LSC LSP which requires a 12.5 GHz width frequency slot is
requested on this link, the central frequency denoted by n=3 is
available because the corresponding frequency slot [n=2, n=4] dose
not overlap the existing LSPs (the unavailable frequency ranges is
[n=-2, n=2] and [n=4, n=10]).
o If a LSC LSP which requires a 25 GHz width frequency slot is
requested on this link, the central frequency denoted by n=3 is
unavailable because the corresponding frequency slot [n=1, n=5]
overlaps the unavailable central frequencies (the unavailable
frequency ranges is [n=-2, n=2] and [n=4, n=10]).
5. IANA Considerations
TBD.
6. Security Considerations
This document does not introduce any further security issues other
than those discussed in [RFC3630], [RFC4203].
7. References
[RFC2119] S. Bradner, "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
[G.694.1v1] ITU-T Recommendation G.694.1, Spectral grids for WDM
applications: DWDM frequency grid, June 2002.
[G.FLEXIGRID] Draft revised G.694.1 version 1.3, Unpublished ITU-T
Study Group 15, Question 6.
[WSON-PCE] Y. Lee, G. Bernstein, Jonas Martensson, T. Takeda and T.
Tsuritani, "PCEP Requirements for WSON Routing and
Wavelength Assignment", draft-ietf-pce-wson-routing-
wavelength-05, July 2011.
[WSON-SIG] G. Bernstein, Sugang Xu, Y. Lee, G. Martinelli and
Hiroaki Harai, "Signaling Extensions for Wavelength
Switched Optical Networks", draft-ietf-ccamp-wson-
signaling-02, September 2011.
[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-06, September 2011.
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[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-02, September 2011.
[RFC6163] Y. Lee, G. Bernstein and W. Imajuku, "Framework for GMPLS
and Path Computation Element (PCE) Control of Wavelength
Switched Optical Networks (WSONs)t", RFC 6163, April 2011.
[RFC6205] T. Otani and D. Li, "Generalized Labels for Lambda-Switch-
Capable (LSC) Label Switching Routers", RFC 6205, March
2011.
[FLEXIBLE-REQ] F.Zhang et al, "Requirements for GMPLS Control of
Flexible-grids",draft-zhang-ccamp-flexible-grid-
requirements, in progress.
[FLEXIBLE-SIG] F.Zhang et al, " RSVP-TE Signaling Extensions in
support of Flexible-grid",draft-zhang-ccamp-flexible-grid-
rsvp-te-ext-00, in progress.
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8. Authors' Addresses
Fatai Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972912
Email: zhangfatai@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
Xiaobing Zi
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28973229
Email: zixiaobing@huawei.com
Intellectual Property
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