Network Working Group Yuefeng Ji
Internet Draft Hongxiang Wang
Intended status: Informational Lin Guo
Expires: January 29, 2009 Univ. of Bupt.
July 29, 2008
MSWS Method to Support Shared-Mesh Restoration for Wavelength
Switched Optical Networks
draft-ji-ccamp-wson-msws-00.txt
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Copyright Notice
Copyright (C) The IETF Trust (2008).
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Abstract
This document proposes a method called Most Sharable Wavelength per
Segment (MSWS) to support shared-mesh restoration for wavelength
switched optical networks (WSON). The proposed method can perform
efficient wavelength sharing in a distributed fashion. It uses the
signaling extensions for WSON which is previously proposed in the
document "Signaling Extensions for Wavelength Switched Optical
Networks" (draft-bernstein-ccamp-wson-signaling-01) and no other
protocol extensions of Generalized Multi-Protocol Label Switching
(GMPLS) routing and signaling are needed.
Table of Contents
1. Introduction................................................2
2. Conventions used in this document............................3
3. Problem Statement and Analysis...............................3
3.1. Current GMPLS-based Shared-Mesh Restoration.............3
3.2. Wavelength Resource Sharing in WSON.....................4
4. MSWS Method.................................................6
4.1. Conveying Wavelength Sharable information...............6
4.2. Procedures.............................................7
4.2.1. With No Wavelength Converters......................7
4.2.2. With Limited Wavelength Converters.................8
5. Discussion..................................................9
6. Security Considerations......................................9
7. IANA Considerations.........................................9
8. Acknowledgments.............................................9
9. References.................................................10
9.1. Normative References...................................10
9.2. Informative References.................................10
Author's Addresses............................................11
Intellectual Property Statement................................12
Disclaimer of Validity........................................12
1. Introduction
GMPLS extends MPLS to support Time-Division Multiplex Capable (TDM),
Lambda Switch Capable (LSC) and Fiber-Switch Capable (FSC) interfaces
and switching. However optical switching technologies are
significantly different from other circuit switch technologies such
as TDM. [WSON-frame] provided a framework for applying GMPLS and Path
Computation Element (PCE) architecture to the control of WSON. In
[WSON-Info], an informational model and efficient encodings of
information needed by routing and wavelength assignment (RWA) in WSON
are provided. [WSON-Signaling] provides extensions to GMPLS signaling
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for control of WSON. [WSON-PCEP] provides requirements and protocol
enhancements for the Path Computation Element communication Protocol
(PCEP) for the support of WSON.
Through an automated common control plane, GMPLS can provide various
and flexible recovery mechanisms. Functional description, protocol
extensions, terminology and analysis of GMPLS-based recovery
mechanisms are given in [RFC4426], [RFC4427], [RFC4428], [RFC4872]
and [RFC4873]. Shared-mesh restoration defined in [RFC4427], is an
efficient approach to reduce the restoration resource requirements by
allowing multiple restoration (Label Switched Paths) LSPs to share
common resources. Until now, requirements and extensions of GMPLS to
support shared-mesh restoration for WSON are not specified.
This memo proposes MSWS method to support shared mesh restoration for
WSON. The proposed method can perform efficient wavelength sharing in
a distributed fashion. It uses the signaling extensions for WSON
which is proposed by [WSON-Signaling] and no other protocol
extensions of GMPLS routing and signaling is needed.
2. 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.
3. Problem Statement and Analysis
3.1. Current GMPLS-based Shared-Mesh Restoration
According to current GMPLS-based shared-mesh restoration mechanism,
the routing approach does not require the flooding of any per LSP
information or any detailed distribution of the bandwidth allocation
per component link or individual ports. This routing approach is
referred to as a Partial (or Aggregated) Information Routing
[RFC4428]. To be specific, the Maximum Reservable Bandwidth, the
Unreserved Bandwidth, and the Maximum LSP Bandwidth (see [RFC4202])
are the useful information during protecting path computation in
shared-mesh restoration. By using the aggregated information, source
node can perform path computation for the protecting path considering
resource sharing. Then signaling process is generated. First, the
recovery resources for the protecting LSPs are pre-reserved during
the provisioning phase. Then when a failure on the working LSP occurs,
an explicit signaling action is required to activate the protecting
LSPs[RFC 4872]. An ASSOCIATION object is defined to associate working
LSPs with their corresponding protecting LSPs. A PRIMARY_PATH_ROUTE
object is defined to inform nodes along the path of the protecting
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LSP about which resources are being used by the associated working
LSP.
3.2. Wavelength Resource Sharing in WSON
In a WSON with no wavelength converters, it is normally required that
the same wavelength be allocated on all the links along the path.
This limitation is known as the "wavelength continuity constraint",
which makes the path selection of WSON different from that of other
circuit switched networks (such as TDM). With wavelength converters,
a lightpath does not have to be on the same wavelength and can
consist of several consecutive wavelength continuous segments, with
wavelength conversion carried out at the junction nodes. Network
performance can be greatly improved by adding wavelength conversion
ability. However, since wavelength converters are still expensive,
only some of the network nodes will have capability of wavelength
conversion. In the case of limited or no wavelength converters are
implemented, route computation is known as Routing and Wavelength
Assignment (RWA) problem. Three possible RWA computation
architectures are discussed in [WSON-Frame]. They are combined RWA,
separate routing and WA and routing with distributed WA. In the first
two methods, exact network link wavelength information is required at
any entity that responsible for RWA or WA. In the third method,
routing is performed at a computational entity (PCE or NE), while
wavelength assignment is performed in a distributed fashion across
nodes along the path. In this memo, we focus on shared-mesh
restoration under routing with distributed WA architecture.
Here we discuss the shortcomings of existing GMPLS protocols in
supporting shared-mesh restoration for WSON. The current link
resource measures in GMPLS do not provide enough information needed
for RWA [WSON-frame]. If current routing methods for shared-mesh
restoration are used, the pre-reserved wavelength resource for a
protecting path may not satisfy the "Wavelength Continuity
Constraints". [WSON-Signaling] proposed a more compact Wavelength
Sets object instead of the LABEL_SET object (see [RFC3471] and
[RFC3473]) to describe the current set of available wavelengths
during the distributed WA process. On reception of Path message,
destination node gets the available wavelengths along the path, thus
it can perform certain wavelength selection algorithm such as First-
Fit, Random, Least-Loaded. (Notice that Least-Loaded algorithm needs
some supplemental information.) This method works well for the
distributed WA of working path, but not for the protecting path. Even
if Wavelength Set object is used to collect the wavelength
availability information along the protecting path, it is still hard
to perform efficient distributed WA at the destination node. An
example is given as follows.
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+--------------------------------------------------+
| +-----+ |
| | PCE1| |
| +--+--+ |
| || routing results |
| || |
| || |
| +---+ +---+ +---+ +---+ |
| | A +-----+ B +-----+ C +-----+ D | |
| +---+ +---+ +---+ +---+ |
| | ------> | |
| | Path message | |
| * | |
| working path protecting path-->| |
| * | |
| | | |
| | +---+ +---+ +-+-+ |
| +-------+ G +-----+ F +-----| E | |
| +---+ +---+ +---+ |
| wavelength selection |
| at node G |
| |
+--------------------------------------------------+
Figure 1 Example network topology
Example:
Figure 1 depicts part of a mesh topology WSON network which consists
of Wavelength Cross-Connects (WXCs) and (Dense WDM) DWDM links. A
lightpath (wavelength-based LSP) from node A to node G is to be setup.
Routing with distributed WA is used and routing for working path and
protecting path is performed at a computational entity PCE1 [WSON-
PCEP]. Node A generates Path message and starts the distributed WA
process.
Here, we use the network link configuration given in [WSON-Signaling].
A 40 channel C-Band DWDM system with 100GHz spacing with lowest
frequency 192.0THz (1561.4nm) and highest frequency 195.9THz
(1530.3nm) is used in the example network. These frequencies
correspond to n = -11, and n = 28 respectively. Now suppose the
following channels are available and five wavelengths (1, 2, 3, 4,
6) are sharable on some link. n value and bit map position are
defined for Wavelength Set object [WSON-Signaling]. The wavelength
available and sharable information is showed as follows:
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Symbol Frequency (THz) n Value bit map position sharable link
-----------------------------------------------------------------
1 192.0 -11 0 (A-B),(D-E)
2 192.3 -8 3 (F-G)
3 193.1 0 11 (B-C)
4 194.5 14 25 (D-E)
5 194.8 17 28 --
6 195.5 24 35 (B-C),(C-D),(E-F)
By checking the information in PRIMARY_PATH_ROUTE object, each node
along the protecting path can decide which wavelength on the local
links can be shared with the current protecting path. On reception of
a Path message with the available wavelengths in Wavelength Set
object, the destination selects a wavelength for the lightpath. Since
no per wavelength information on each link is known to node G. It
will be confused to choose a wavelength according to the wavelength
available information in Wavelength Set object and can not realize
efficient resource sharing. According to local information at G, the
wavelength sharing can be only performed at last hop (link F-G) by
selecting 2 (2 is the only wavelength G knows for sure that can be
shared). In fact, wavelength sharing can be performed at link (B-C),
(C-D) and (E-F) if 6 is selected.
4. MSWS Method
This section presents our MSWS method to support shared-mesh
restoration under routing with distributed WA architecture in WSON.
A lightpath can have one or more consecutive wavelength continuous
segments, with wavelength conversion carried out at the junction
nodes. In a segment, the first node (at upstream) is its head-end
node and the last node (at downstream) is its tail-end node. The
basic idea of MSWS method is to collect the wavelength sharable
information in Path message along the protecting path. And on
reception of the Resv message, the tail-end node of each segment
selects the most sharable wavelength of this segment based on the
collected information.
4.1. Conveying Wavelength Sharable information
Wavelength Set Metric TLV is defined in [WSON-Signaling] to provide
supplemental information for distributed wavelength assignment. Here
we inherit that TLV to convey information about sharable capability
of each wavelength. Info Type is set to 1 (means list). There is a
one-to-one correspondence between the value in the list of Wavelength
Set Metric and the available wavelength in Wavelength Set. Along the
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protecting path, RSVP-TE Path message will collect the wavelength
sharable information and modify Wavelength Set Metric TLV. This
process will be explained in the following sections.
4.2. Procedures
4.2.1. With No Wavelength Converters
First, a simple scenario where no wavelength converters are
implemented to the network (or no wavelength converters will be used
along the protecting path) is considered. In this case, the whole
path is a single wavelength continuous segment. As RSVP-TE Path
message travels along the path, following operations should be
performed:
1. A Wavelength Set object is used to indicate the wavelength
availability along the path. The operation for processing this
object is the same to that is described in [RFC3473] and [WSON-
signaling].
2. At the beginning, the value corresponding to each wavelength in
Wavelength Set Metric is set to 0. Source node generates Path
message with Wavelength Set object and Wavelength Set Metric. On
reception of the Path message, each node is responsible to decide
the sharable wavelengths for this hop (from itself to its
downstream node). If certain wavelength is sharable, its
corresponding value in Wavelength Set Metric is increased by 1.
3. Wavelength Set Metric is modified and passed along the protecting
path in Path message until it gets to the destination node. The
destination node is responsible to perform wavelength selection
according to Wavelength Set object and Wavelength Set Metric. The
wavelength with largest value (the most sharable wavelength) in
the list of Wavelength Set Metric value is selected.
Example: In Figure 1, the Wavelength Set object and Wavelength Set
Metric TLV received at destination node G is showed as follows:
Wavelength Set object:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Action = 4 | Reserved | Num Wavelengths = 40 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Grid | C.S. |S| Reserved | n for lowest frequency = 11 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0 0| Not used in 40 Channel system (all zeros) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Here, Grid=1, C.S.=4, S=1. (see [WSON-Signaling] and [Otani])
Wavelength Set Metric TLV:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Info Type=1 | M.Size = 0 | Num Metrics = 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 1 | 1 | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | 3 | Padded to 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Since the value corresponding to 6 is 3, 6 will be selected by
destination node G and wavelength sharing will be performed on three
links on the protecting path.
4.2.2. With Limited Wavelength Converters
In case Wavelength Converters are used each lightpath may include
several consecutive wavelength continuous segments. On reception of
the Path message, intermediate node with wavelength conversion
ability can decide whether wavelength conversion is required by
checking whether the egress available wavelengths for the available
wavelengths in Wavelength Set object is null or deemed too small.
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1. Source node generates Path message with Wavelength Set object and
Wavelength Set Metric. The operations to process Wavelength Set
object and Wavelength Set Metric inside a wavelength continuous
segment are similar to that in section 4.2.1. On reception of the
Path message, the tail-end node of a segment stores the Wavelength
Set and Wavelength Set Metric of this segment. And it generates a
new Wavelength Set Metric according to the Wavelength Set and
resets the value in the list in Wavelength Set Metric TLV to 0. If
this tail-end node is not the destination, it must be the head-end
of the next wavelength continuous segment. It will decide the
sharable wavelength of the next hop and starts a new round of
collecting Wavelength Set Metric operation.
2. The destination node is always the tail-end of the last wavelength
continuous segment and it is responsible to perform wavelength
selection for the last segment according to the Wavelength Set and
Wavelength Set Metric of its segment. On reception of the Resv
message, the tail-end of each segment is responsible to perform
wavelength selection for its own segment.
5. Discussion
Wavelength converter sharing is allowed but not deliberately
considered in our proposed method. The tail-end of a wavelength
continuous segment can optionally carry out wavelength converter
sharing during the Resv process if it is possible.
A probable way to explore wavelength converter sharing ability is to
enlarge the wavelength set at every node where wavelength sharing is
possible. However, this will potentially lead to break wavelength
continuity even though it is not necessary. Maybe the "Reserve field"
in Wavelength Set object can be used to provide more precisely
control to deal with this contradiction.
6. Security Considerations
This document introduces no new security considerations to [RFC3473].
7. IANA Considerations
This document includes no request to IANA.
8. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
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9. References
9.1. Normative References
[RFC4426] Lang, J., Ed., Rajagopalan, B., Ed., and D. Papadimitriou,
Ed., "Generalized Multi-Protocol Label Switching (GMPLS)
Recovery Functional Specification," RFC 4426, March 2006.
[RFC4427] Mannie, E., Ed., and D. Papadimitriou, Ed., "Recovery
(Protection and Restoration) Terminology for Generalized
Multi-Protocol Label Switching (GMPLS)", RFC 4427, March
2006.
[RFC4428] Papadimitriou D. and E.Mannie, Editors, "Analysis of
Generalized Multi-Protocol Label Switching (GMPLS)-based
Recovery Mechanisms (including Protection and Restoration)",
RFC 4428, March 2006.
[RFC4872] Lsang, J.P., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
Ed., "RSVP-TE Extensions in support of End-to-End
Generalized Multi-Protocol Label Switching (GMPLS)
Recovery", RFC 4872, May 2007.
[RFC4873] Berger, L., Bryskin, I., Papdimitriou, D., and A. Farrel,
"GMPLS Segment Recovery," RFC 4873, May 2007.
[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.
[RFC4202] Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4202, October 2005.
9.2. Informative References
[WSON-Frame] G. Bernstein, Y. Lee, W. Imajuku, "Framework for GMPLS
and PCE Control of Wavelength Switched Optical Networks",
work in progress: draft-ietf-ccamp-wavelength-switched-
framework-00.txt, May 2008.
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[Otani] T. Otani, H. Guo, K. Miyazaki, D. Caviglia, "Generalized
Labels of Lambda-Switching Capable Label Switching Routers
(LSR)", work in progress: draft-otani-ccamp-gmpls-lambda-
labels-01.txt, November 2007.
[WSON-Info] G. Bernstein, Y. Lee, D. Li and W. Imajuku, "Routing and
Wavelength Assignment Information for Wavelength Switched
Optical Networks", work in progress: draft-bernstein-ccamp-
wson-info-02.txt, February 2008.
[WSON-Signaling] G. Bernstein, Y. Lee, "Signaling Extensions for
Wavelength Switched Optical Networks", work in process:
draft-bernstein-ccamp-wson-signaling-01.txt, February 2008.
[WSON-PCEP] Y. Lee, G. Bernstein, "PCEP Requirements and Extensions
for WSON Routing and Wavelength Assignment", work in
process: draft-lee-pce-wson-routing-wavelength-01.txt,
February 2008.
Author's Addresses
Yuefeng Ji
Key Laboratory of Optical Communication and Lightwave Technologies
Ministry of Education
P.O. Box 128, Beijing University of Posts and Telecommunications,
P.R.China
Email: jyf@bupt.edu.cn
Hongxiang Wang
Key Laboratory of Optical Communication and Lightwave Technologies
Ministry of Education
P.O. Box 128, Beijing University of Posts and Telecommunications,
P.R.China
Email: wanghx@bupt.edu.cn
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Lin Guo
Key Laboratory of Optical Communication and Lightwave Technologies
Ministry of Education
P.O. Box 128, Beijing University of Posts and Telecommunications,
P.R.China
Email: guolintom@gmail.com
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