One document matched: draft-zhang-ccamp-flexible-grid-requirements-00.txt
Network Working Group Fatai Zhang
Internet-Draft Xiaobing Zi
Intended status: Standards Track Huawei
O. Gonzalez de Dios
Telefonica
Expires: April 11, 2012 October 11, 2011
Requirements for GMPLS Control of Flexible Grids
draft-zhang-ccamp-flexible-grid-requirements-00.txt
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet-Drafts
as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 15, 2012.
Abstract
A new flexible grid of DWDM is being developed within the ITU-T
Study Group 15 to allow spectrum allocation much more efficient.
This memo describes the requirements of GMPLS control of flexible
grid DWDM network.
Zhang Expires 2012 [Page 1]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
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. Characteristics of Flexible Grid............................. 3
2.1. Central Frequency....................................... 3
2.2. Slot Width ............................................. 4
3. Impact on WSON .............................................. 4
3.1. Fiber Links ............................................ 4
3.2. Optical Transmitters and Receivers ..................... 5
4. Routing and Spectrum Assignment.............................. 5
4.1. Architecture Approaches to RSA ......................... 6
4.1.1. Combined RSA (R&SA)................................ 6
4.1.2. Separated RSA (R+SA)............................... 7
4.1.3. Routing and Distributed SA (R+DSA) ................ 7
5. Requirements of GMPLS Control................................ 7
5.1. Routing ................................................ 7
5.1.1. Available Central Frequency of DWDM Links.......... 8
5.1.2. Tunable Optical Transmitters and Receivers......... 8
5.2. Signaling .............................................. 8
5.2.1. Slot Width Requirement............................. 8
5.2.2. Frequency Slot Representation ..................... 9
5.3. PCE .................................................... 9
5.3.1. RSA Computation Type............................... 9
5.3.2. RSA path re-optimization request/reply ............ 9
5.3.3. Frequency Constraints.............................. 10
6. Security Considerations...................................... 10
7. References .................................................. 10
7.1. Normative References.................................... 10
7.2. Informative References.................................. 11
8. Authors' Addresses .......................................... 12
1. Introduction
In WDM applications, each wavelength needs to occupy a range of
frequency on a fiber. [G.694.1v1] defines the 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
Zhang Expires 2012 [Page 2]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
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]. The channel spacing of the
channels on a fiber is fixed.
The speed of the optical signal becomes higher and higher with the
advancement of the optical technology. In the near future, high-
speed signal (beyond 100 Gbps or 400Gbps) will be deployed in the
optical network. Those signals may not be accommodated in the
channel spacing specified in [G.694.1v1]. On the other hand, the
frequency bandwidth requirements of the optical signals with
different rate speed may be different. When the optical signals with
different rate speed are mixed to be transmitted on a fiber, the
frequency allocation needs to be more flexible to promote the
frequency efficiency.
[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 specific 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 define flexible grid. A channel is represented as a
wavelength LSP in the control plane, it means a wavelength LSP
should occupy a frequency slot on each fiber it traverses. In the
case of flexible grid, the different wavelength LSPs may have
different slot width on a fiber, i.e. the slot width is flexible on
a fiber.
WSON related documents are being developed currently and those
documents focus on the GMPLS control of the fixed grids. This
document describes the new characteristics of flexible grid and
analysis the requirements of GMPLS control of flexible grid.
2. Characteristics of Flexible Grid
Per [G.FLEXIGRID], flexible grid is defined for the DWDM system.
Compared with the fixed grids (i.e. traditional DWDM), flexible grid
has a smaller granularity for the central frequency and the slot
width of the wavelength LSPs is more flexible on a fiber.
2.1. Central Frequency
According to the definition of flexible DWDM grid in [G.FLEXIGRID],
the step granularity for the central frequency of flexible grid is
6.25 GHz. The allowed nominal central frequency is calculated as
such in the case of flexible grid:
Zhang Expires 2012 [Page 3]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
Central Frequency = 193.1 THz + n * 0.00625 THz
Where n is a positive or negative integer including 0.
2.2. Slot Width
A slot width defined by:
12.5 GHz * m where m is a positive integer.
On a fiber, the slot width of different wavelength LSPs may be
different.
3. Impact on WSON
Wavelength Switched Optical Networks (WSONs) are constructed from
subsystems that include Wavelength Division Multiplexing (WDM) links,
tunable transmitters and receivers, Reconfigurable Optical Add/Drop
Multiplexers (ROADMs), wavelength converters, and electro-optical
network elements. WSON framework is described in [RFC 6163]. The
introduced flexible grid brings some changes on WSON.
3.1. Fiber Links
The flexible grid has a granularity of 6.25 GHz for the central
frequency and a multiple of 12.5 GHz for the slot width. The fiber
link for flexible grid can be modeled as shown in figure 1.
-9 -8 -7 -6 -5 -4 3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
...+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
^
193.1THz
Figure 1 Fiber link model for flexible grid
The symbol '+' represents the allowed nominal central frequency. The
symbol "--" represents a 6.25 GHz frequency unit. Each frequency
slot must occupy an even multiple of the 6.25 GHz frequency units,
i.e. a multiple of 12.5 GHz frequency range. The number on the top
of the line represents the 'n' in the frequency calculation formula.
The nominal central frequency is 193.1 THz when n equals zero.
Hence, the following information is needed as parameters to perform
basic, impairment-unaware modeling of a flexible grid link:
o Available central frequencies: The set of central frequencies
which are available on this link.
Zhang Expires 2012 [Page 4]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
3.2. Optical Transmitters and Receivers
Optical transmitter is the wavelength source and optical receiver is
the wavelength sink of the WDM system. In each direction, the
wavelength used by the transmitter and receiver along a path shall
be consistent if there is no wavelength converter in the path.
In the case of flexible grids, the central frequency utilized by a
transmitter or receiver may be fixed or tunable. The slot width
needed by different transmitters or receivers may be different.
Hence, the changes introduced by flexible grid of fundamental
modeling parameters for optical transmitters and receivers from the
control plane perspective are:
o Available central frequencies: The set of central frequencies
which can be used by an optical transmitter or receiver.
o Slot width: The slot width needed by a transmitter or receiver.
4. Routing and Spectrum Assignment
A wavelength LSP should occupy a frequency slot, i.e. a range of
frequency. The route computation and frequency slot assignment could
be called RSA (Routing and Spectrum Assignment).
Similar to fixed grids network, if there is no wavelength converter
in an optical network, there is "wavelength continuity constraint"
for a flexible grid wavelength LSP which is described as section 4
of [RFC 6163].
Because of the high cost of the wavelength converters, an optical
network is generally deployed with limited or without wavelength
converters. Hence, the wavelength continuity constraint should be
considered without wavelength converters during the RSA process.
The RSA should determine a route and frequency slot for a wavelength
LSP. The frequency slot can be deduced from the two parameters which
are central frequency and slot width as follows:
Lowest frequency = (central frequency) - (slot width)/2;
Highest frequency = (central frequency) + (slot width)/2.
Hence, after a route is determined, the SA process should determine
the central frequency for a wavelength LSP based on the slot width
and available central frequency information of the links that the
route traverses.
Zhang Expires 2012 [Page 5]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
Figure 2 shows two wavelength LSPs that traverse a link.
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 2 Two Wavelength LSPs traverse a Link
The two wavelengths shown in figure 2 have the following meaning:
Wavelength LSP 1: central frequency = 193.1 THz, slot width = 25 GHz.
It means the frequency slot [193.0875 THz, 193.1125 THz] is assigned
to this wavelength LSP.
Wavelength LSP 2: central frequency = 193.14375 THz, slot width =
37.5 GHz. It means the frequency slot [193.125 THz, 193.1625 THz] is
assigned to this wavelength LSP.
Note that the frequency slots of two wavelength LSPs on a fiber
should not overlap with each other.
4.1. Architecture Approaches to RSA
Similar to RWA for fixed grids, three different ways of performing
RSA in conjunction with the control plane are considered. The
approaches are provided for reference purposes only, and other
approaches are possible.
4.1.1. Combined RSA (R&SA)
In this case, a centralized entity performs the routing and
frequency slot assignment. The centralized entity should have the
detailed network information, e.g. network topology, available
frequency resource on each link, node capability, etc.
The centralized computation entity could be placed on the following
two places:
o PCE: PCE get the detailed network information and implement the
RSA algorithm for RSA requests from the PCCs.
Zhang Expires 2012 [Page 6]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
o Ingress node: Ingress node gets the detailed network information
through routing protocol and implements the RSA algorithm when a
wavelength LSP request is received.
4.1.2. Separated RSA (R+SA)
In this case, routing computation and frequency slot assignment are
performed by different entities. The first entity computes the
routes and provides them to the second entity; the second entity
determines the route and assigns the frequency slot.
The first entity should get the network topology information to
compute the proper routes; the second entity should get the
available frequency resource information and nodes capabilities to
assign the spectrum.
4.1.3. Routing and Distributed SA (R+DSA)
In this case, one entity computes the route and the frequency slot
assignment is performed hop-by-hop in a distributed way along the
route. The available central frequencies which meet the wavelength
continuity constraint should be collected hop by hop along the route.
This procedure can be implemented by GMPLS signaling protocol.
The GMPLS signaling procedure is similar to the procedure which is
described in section 4.1.3 of [RFC 6163] except that the label set
should specify the available central frequency that meet the slot
width requirement of the wavelength LSP, i.e. the frequency slot
which is determined by the central frequency and slot width should
not overlap with the existing wavelength LSPs.
5. Requirements of GMPLS Control
According to the different architecture approaches to RSA, it brings
some additional requirements of GMPLS control.
5.1. Routing
In the case of combined RSA architecture, the computation entity
needs to get the detailed network information, i.e. network topology,
available frequency resources and node capabilities. This can be
done by the GMPLS routing protocol.
Compared with [RFC6163], except wavelength-specific availability
information, the network topology and node capabilities are the same
as WSON which can be advertised by GMPLS routing protocol (refer to
Zhang Expires 2012 [Page 7]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
section 6.2 of [RFC6163]. This section analysis the changes of link
information brought by flexible grids.
5.1.1. Available Central Frequency of DWDM Links
In the case of flexible grids, the central frequency steps from
193.1 THz towards the two sides with 6.25 GHz granularity (See
Figure 1). Different wavelength LSPs could occupy the frequency
slots with different slot width. Hence, the available central
frequency should be advertised, but the slot width is not required
to be advertised for a DWDM link.
5.1.2. Tunable Optical Transmitters and Receivers
The slot width of a wavelength LSP is determined by the transmitter
and receiver. The transmitters and receivers could be mapped to
ADD/DROP interfaces in WSON. Hence, the slot width of an ADD/DROP
interface should be advertised.
The central frequency of a transmitter or receiver could be fixed or
tunable. Hence, the available central frequencies should be
advertised.
5.2. Signaling
Compared with [RFC6163], except identifying the resource (i.e.,
fixed wavelength for WSON and frequency resource for flexible grids),
the other signaling requirements (e.g., unidirectional or
bidirectional, with or without converters) are the same as WSON
described in the section 6.1 of [RFC6163].
In the case of routing and distributed SA, GMPLS signaling can be
used to allocate the frequency slot to a wavelength LSP. This brings
the following changes to the GMPLS signaling.
5.2.1. Slot Width Requirement
In order to allocate a proper frequency slot for a wavelength LSP,
the signaling should specify the slot width requirement of a
wavelength LSP. Then the intermediate nodes can collect the
acceptable central frequencies that meet the slot width requirement
hop by hop.
The tail node also needs to know the slot width of a wavelength LSP
to assign the proper frequency resource. Hence, the slot width
requirement should be specified in the signaling message when a
wavelength LSP is being set up.
Zhang Expires 2012 [Page 8]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
5.2.2. Frequency Slot Representation
The frequency slot can be determined by the two parameters, which
are central frequency and slot width as described in section 4.
Hence, the frequency slot can be represented as a combination of
[central frequency, slot width]. The signaling messages should be
able to specify the accurate frequency slot which is assigned to a
wavelength LSP, i.e. the signaling messages should be able to
specify the central frequency and slot width of a wavelength LSP.
5.3. PCE
[WSON-PCE] describes the architecture and requirements of PCE for
WSON. In the case of flexible grid, RSA instead of RWA is used for
routing and frequency slot assignment. Hence PCE should implement
RSA for flexible grids. The architecture and requirements of PCE for
flexible grids are similar to what is described in [WSON-PCE]. This
section describes the changes brought by flexible grids.
5.3.1. RSA Computation Type
The PCReq message must be able to specify the computation type of
the request:
o Combined RSA: Both of the route and frequency slot should be
provided by PCE.
o Routing Only: Only the route is requested to be provided by PCE.
The PCRep Message must be able to specify the route, frequency slot
assigned to the route.
In the case where a valid path is not found, the PCRep Message must
be able to specify why the path is not found (e.g., no route,
spectrum not found, etc.)
5.3.2. RSA path re-optimization request/reply
For a re-optimization request, the PCReq Message must provide the
path to be re-optimized and include the following options:
o Re-optimize the path keeping the same frequency slot.
o Re-optimize spectrum keeping the same path.
o Re-optimize allowing both frequency slot and the path to change.
Zhang Expires 2012 [Page 9]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
The corresponding PCRep Message for the re-optimized request must
provide the Re-optimized path and frequency slot.
In case that the path is not found, the PCRep Message must include
why the path is not found (e.g., no route, frequency slot not found,
both route and frequency slot not found, etc.)
5.3.3. Frequency Constraints
PCE for flexible grids should consider the following constraints
brought by the transmitters and receivers:
o Available central frequencies: The set of central frequency that
can be used by an optical transmitter or receiver.
o Slot width: The slot width needed by a transmitter or receiver.
This constraint may be provided by requester (PCC) in PCReq or the
PCE's TEDB which stores the ability of the origination laser
transmitter.
PCC may also specify the frequency constraints for policy reasons.
In this case, the constraints should be specified in the PCReq
message.
PCE compute the route and assign the frequency slot to meet the
constraints specified in the PCReq message. Then return the result
to the PCC.
6. Security Considerations
This document does not introduce any further security issues other
than those described in [RFC6163] and [RFC5920].
7. References
7.1. Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
[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.
Zhang Expires 2012 [Page 10]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
[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.
[G.FLEXIGRID] Draft revised G.694.1 version 1.3, Unpublished ITU-T
Study Group 15, Question 6.
7.2. Informative References
[G.694.1v1] ITU-T Recommendation G.694.1, Spectral grids for WDM
applications: DWDM frequency grid, June 2002.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
Zhang Expires 2012 [Page 11]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
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
Oscar Gonzalez de Dios
Telefonica Investigacion y Desarrollo
Emilio Vargas 6
Madrid, 28045
Spain
Phone: +34 913374013
Email: ogondio@tid.es
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
The IETF Trust takes no position regarding the validity or scope of
any Intellectual Property Rights or other rights that might be
claimed to pertain to the implementation or use of the technology
described in any IETF Document or the extent to which any license
under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any
such rights.
Copies of Intellectual Property disclosures made to the IETF
Secretariat and any assurances of licenses to be made available, or
the result of an attempt made to obtain a general license or
Zhang Expires 2012 [Page 12]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
permission for the use of such proprietary rights by implementers or
users of this specification can be obtained from the IETF on-line
IPR repository at http://www.ietf.org/ipr
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
any standard or specification contained in an IETF Document. Please
address the information to the IETF at ietf-ipr@ietf.org.
The definitive version of an IETF Document is that published by, or
under the auspices of, the IETF. Versions of IETF Documents that are
published by third parties, including those that are translated into
other languages, should not be considered to be definitive versions
of IETF Documents. The definitive version of these Legal Provisions
is that published by, or under the auspices of, the IETF. Versions
of these Legal Provisions that are published by third parties,
including those that are translated into other languages, should
not be considered to be definitive versions of these Legal
Provisions.
For the avoidance of doubt, each Contributor to the IETF Standards
Process licenses each Contribution that he or she makes as part of
the IETF Standards Process to the IETF Trust pursuant to the
provisions of RFC 5378. No language to the contrary, or terms,
conditions or rights that differ from or are inconsistent with the
rights and licenses granted under RFC 5378, shall have any effect
and shall be null and void, whether published or posted by such
Contributor, or included with or in such Contribution.
Disclaimer of Validity
All IETF Documents and the information contained therein are
provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION
HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET
SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE
DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION THEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Full Copyright Statement
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
Zhang Expires 2012 [Page 13]
draft-zhang-ccamp-flexible-grid-requiements-00.txt October 2011
This document is subject to BCP 78 and the IETF Trust's Legal
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.
Zhang Expires 2012 [Page 14]
| PAFTECH AB 2003-2026 | 2026-04-24 12:18:10 |