Network Working Group Fatai Zhang
Internet-Draft Xian Zhang
Intended status: Informational Huawei
Ramon Casellas
CTTC
O. Gonzalez de Dios
Telefoni
Expires: September 12, 2012 D. Ceccarelli
March 12, 2012 Ericsson
GMPLS OSPF-TE Extensions in support of Flexible Grid in DWDM Networks
draft-zhang-ccamp-flexible-grid-ospf-ext-01.txt
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Abstract
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This memo describes the OSPF-TE extensions in support of GMPLS
control for flexi-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 Flexi-grid Routing .......................... 3
3.1. Available Frequency Ranges .............................. 3
3.2. Application Compliance Considerations ................... 5
3.3. Comparison with Fix-grid DWDM Links ..................... 5
4. Extensions ................................................... 6
4.1. Available Labels Set sub-TLV ............................ 6
4.1.1. Inclusive/Exclusive Label Range .................... 7
4.1.2. Inclusive/Exclusive Label Lists .................... 7
4.1.3. Bitmap ............................................. 8
4.2. Extensions to Port Label Restriction sub-TLV ............ 8
4.3. Examples for Label Set .................................. 9
5. IANA Considerations ......................................... 10
6. Security Considerations ..................................... 10
7. References .................................................. 10
7.1. Normative References ................................... 10
7.2. Informative References ................................. 11
8. Authors' Addresses .......................................... 12
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.
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[G.FLEXIGRID], an updated version of [G.694.1v1] has been consented
in December 2011 in support of flexi-grids. The terms "frequency
slot (The frequency range allocated to a channel and unavailable to
other channels within a flexi-grid)" and "slot width" (the full
width of a frequency slot in a flexi-grid) are introduced to address
flexi-grids. A channel is represented as a LSC (Lambda 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 flexi-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 flexi-
grid.
This document uses the DWDM link model which is shown in [SSON-FWK]
to describe the requirement and extensions for routing. The flexi-
grid related terminologies can also refer to [SSON-FWK].
2. Terminology
Flexi-grid: See [SSON-FWK].
Slot Width: See [SSON-FWK].
Frequency Range: See [SSON-FWK].
SSON: Spectrum-Switched Optical Networks; See [SSON-FWK].
Flexi-LSP: See [SSON-FWK].
3. Requirements for Flexi-grid Routing
As described in [SSON-FWK], the main changes for routing brought by
flexible grid are related to the DWDM links.
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 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 flexi-LSPs could occupy frequency slots with different
slot width. The frequency slot width of a flexi-LSP is defined as
follows:
Slot width = 0.0125 THz * m
Where m is a positive integer.
The frequency slot of a flexi-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 flexi-LSPs.
Hence, the available frequency ranges should be advertised 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 4 of [SSON-FWK].
3.2. Application Compliance Considerations
As described in [G.FLEXIGRID], devices or applications that make use
of the flexi-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).
Hence, the following information should be advertised for a flexi-
grid DWDM link:
o Central frequency granularity: a multiple of 6.25 GHz.
o Slot width granularity: a multiple of 12.5 GHz.
o Slot width range: the minimal and maximal slot width supported by
a port.
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 Fix-grid DWDM Links
In case of fix-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.
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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
Figure 2 shows a link that supports fix-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 fix-grid DWDM links, the slot width of the
wavelengths are flexible on a flexi-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
flexi-grid DWDM link.
4. Extensions
As described in [SSON-FWK], the network connectivity topology
constructed by the links/nodes and node capabilities are the same as
WSON which can be advertised by GMPLS routing protocol (refer to
section 6.2 of [RFC6163]. In case of flexi-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 flexi-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
flexi-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 flexi-grid DWDM links.
The label format defined in [FLEXIBLE-SIG] shown below MUST be used
to encode the Label fields in Available Labels Set sub-TLV:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In case of Grid=1 (ITU-T DWDM), a new value of C.S. is defined for
flexible grid.
If the C.S. is set to "Flexible grid" in an Available Labels Set
sub-TLV, it means that the corresponding link supports flexible grid.
Note that according to the label format defined in [FLEXIBLE-SIG],
for the case where the channel spacing value is set to "Flexible
grid", a channel spacing of 6.25 GHz should be used in the central
frequency computation formula.
4.1.1. Inclusive/Exclusive Label Range
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 flexi-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.
4.1.2. Inclusive/Exclusive Label Lists
The inclusive/exclusive label lists format of Available Labels Set
sub-TLV defined in [GEN-OSPF] can be used for specifying the
available central frequencies of the flexi-grid DWDM links.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 or 1 | Num Labels (not used) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Base Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.1.3. Bitmap
The bitmap format of Available Labels Set sub-TLV defined in [GEN-
OSPF] can be used for specifying the available central frequencies
of the flexi-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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | Num Labels | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Base Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bit Map Word #1 (Lowest numerical labels) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bit Map Word #N (Highest numerical labels) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In this case, the Base Label specifies the lowest available central
frequency.
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, there are some restrictions on a port
to support flexi-grid. Port Label Restriction sub-TLV is defined in
[GEN-OSPF] that can be used to describe the label restrictions on a
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port. A new restriction type, i.e. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 Label Set
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
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:
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o Start Label = -2;
o End Label = 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 Label 1 = -1;
o Label 2 = 0;
o Label 3 = 1;
o Label 4 = 2;
o Label 5 = 3;
o Label 6 = 4;
o Label 7 = 5;
o Label 8 = 6;
o Label 9 = 7.
Bitmap:
o Base Label = -1;
o Bitmap = 111111111(padded out to a full multiple of 32 bits)
5. IANA Considerations
This document introduces a new Restriction Type for the Port Label
Restriction sub-TLV defined in [GEN-OSPF]:
Restriction Type: TBA (flexi-grid)
6. Security Considerations
This document does not introduce any further security issues other
than those discussed in [RFC3630], [RFC4203].
7. References
7.1. Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
[G.FLEXIGRID] Revised G.694.1 version 1.6, Consented in
December 2011, ITU-T Study Group 15.
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[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.
[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.
[SSON-FWK] F.Zhang et al, "Framework for GMPLS Control of Spectrum
Switched Optical Networks ", draft-zhang-ccamp-sson-
framework-00, 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.
7.2. Informative References
[G.694.1v1] ITU-T Recommendation G.694.1, Spectral grids for WDM
applications: DWDM frequency grid, June 2002.
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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
Xian Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972913
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
Xiaobing Zi
Huawei Technologies
F3-5-B R&D Center, Huawei Base
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Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28973229
Email: zixiaobing@huawei.com
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