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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Protection Mechanisms for Optical WDM Networks
based on Wavelength Converter Multiplexing and
Backup Path Relocation Techniques
Sunil Gowda, Expedia.com, Seattle, WA
Krishna M. Sivalingam, Univ. of Maryland, Baltimore County, MD
IEEE INFOCOM 2003
Presented by: Brian V. Jarvis
Wright State University: CEG790-01
Winter 2004, 2 February 2004
[email protected]
Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
• Introduction
• Background
• Proposed Mechanisms
• Performance Analysis
• Conclusions
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
• Introduction
• Background
• Proposed Mechanisms
• Performance Analysis
• Conclusions
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Introduction
• Exponential growth in bandwidth requirements
• This paper considers routing algorithm designs for optical WDM networks
• Fault-tolerance (survivability) is an important consideration
• Survivability is introduced into an optical network
• Three different mechanisms to help improve network performance
• Conversion Free Primary Routing (CFPR)
• Converter Multiplexing Technique (CMT)
• Backup Path Relocation Scheme (BPRS)
• Results indicate that the proposed algorithms:
• Reduced the required number of wavelength converters at each node by 75%.
• Reduced the overall blocking probability from 60% to nearly 100%.
• Reduced the number of primary paths undergoing conversion.
• Reduced overall network blocking probability by up to an order of magnitude.
• Provided higher improvements for low to moderate loads.
• All with negligible additional overhead.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
• Introduction
• Background
• Proposed Mechanisms
• Performance Analysis
• Conclusions
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• Present relevant background material on wavelength
division multiplexing (WDM) networks, routing and
wavelength assignment (RWA) algorithms, protection
techniques, and wavelength router architectures that
incorporate conversion.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Background
• Routing and Wavelength Assignment (RWA) Problem
• A dynamic network model where connection requests arrive randomly.
• Determining the end-to-end route and the specific wavelength
• Static or dynamic routing scheme approaches
• Static routing scheme
• Dynamic routing scheme (this technique is used in this paper)
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Background
• Wavelength Router Architecture
• Without wavelength conversion, connections are often blocked
• With wavelength conversion, the lightpath can use different wavelengths
• High cost, lack of availability, signal degradation
• Various optical wavelength conversion techniques
• Minimize the usage of wavelength conversion
• Reduce the number of converters required
• Location of wavelength converters
• Three architectures for a wavelength convertible switch
• Dedicated
• Share-per-link
• Share-per-node
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Multiplexers
De-Multiplexers
Input Links
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WC
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Output Links
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Dedicated Wavelength Convertible Switch Architecture
• A wavelength converter is available at each output port.
• The incoming optical signal is de-multiplexed into separate wavelengths.
• The output signal may have its wavelength changed.
• The various wavelengths are multiplexed.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Multiplexers
De-Multiplexers
Input Links
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Output Links
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Share-per-node Wavelength Convertible Switch Architecture
• A wavelength converter bank (WCB) is available at the optical switch.
•
•
•
•
The incoming optical signal is de-multiplexed into separate wavelengths.
Only the wavelengths that require conversion are directed to the WCB.
Converted wavelengths are switched to the appropriate outbound fiber link.
The various wavelengths are multiplexed.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Multiplexers
De-Multiplexers
Input Links
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WCB
Output Links
WCB
Share-per-link Wavelength Convertible Switch Architecture
• A wavelength converter bank (WCB) is available at each outgoing fiber link.
•
•
•
•
The incoming optical signal is de-multiplexed into separate wavelengths.
The optical switch is configured to direct wavelengths toward a particular link.
Only the wavelengths that require conversion are directed to the WCB.
The various wavelengths are multiplexed.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Protection in Mesh-Topology WDM Networks
• Link Failures
• Node Failures
Recovery Mechanisms
• Protection (proactive)
• Backup lightpaths are identified and resources are reserved along the backup lightpaths at the
time of establishing the primary lightpath itself.
• Faster recovery
• 100 percent restoration guarantee
• Restoration (reactive)
• When an existing lightpath fails, a search is initiated to find a new lightpath which does not use the
failed components. (After the failure happens)
• Longer restoration time
• It can not guarantee successful recovery,
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Lightpath Migration
• Migration of lightpath onto new paths to accommodate other connections.
• A virtual topology reconfiguration scheme to adapt to the changing traffic patterns
– modeled as an integrated linear programming (ILP) formulation
• Lightpaths are torn down and re-established, providing better paths for the primary.
• During reconfiguration, transmission on that path is terminated.
• Other migration schemes studied. (Not presented here.)
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
• Introduction
• Background
• Proposed Mechanisms
• Performance Analysis
• Conclusions
Monday, February 02, 2004
• Presents the network architecture studied and the
details of three proposed mechanisms.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Network Architecture
• Dynamic routing; shortest path is computed between nodes based on current situation.
• Path level protection; with dedicated and shared protection schemes for backup paths.
• Wavelength router architecture is based on share-per-node wavelength converter
configuration.
– Offers the best cost to performance ratio.
• Connections are blocked only if free wavelength or wavelength converters are unavailable.
The design goals of the proposed mechanisms are to:
• Improve performance
• Increase cost effectiveness
Proposed mechanisms:
• Conversion-Free Primary Routing (CFPR)
• Converter Multiplexing Technique (CMT)
• Backup-Path Relocation (BPR)
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Conversion Free Primary Routing
(CFPR)
• The goal is to avoid wavelength conversions
while routing primary connections.
• Multi-layered graph is used, the layers
representing individual wavelength planes.
• CFPR algorithm models such a graph.
• For each wavelength plane, the nodes are
the physical nodes.
4
2
Wavelength 0
1
3
5
2
4
Backup path b
1
Wavelength 1
3
5
2
4
1
Wavelength 2
5
3
Blocked route
Unoccupied wavelengths//
Wavelengths occupied by
Backup paths
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Wavelengths occupied by
Primary paths
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Conversion Free Primary Routing (CFPR)
• An overlapping segment is defined as the part
of the backup path occupying the wavelength
assigned to the requested connection.
• Relocation schemes may be used to relocate
these overlapping segments.
• Advantages of CFPR:
• Reduces conversion delays and
degradation due to converters
• Reduces costs
• Lower computational complexity
• Computes path on each wavelength
separately; alternate paths are available
if shorted paths are blocked
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Potential primary path with some component links
overlapping existing backup paths
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Converter Multiplexing:
• Based on backup path multiplexing.
• Allows wavelength converters to be shared among multiple backup paths
• The converters are reserved during the establishment of the backup paths.
• Objective is to:
– Reduce the number of connections blocked
– Reduce the numbers of converters in use.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Converter Multiplexing:
• The node returns a CONV-RESV-ACK message if the request is accepted.
• The node returns a CONV-RESV-NACK message if the request is not accepted.
• A wavelength conversion status table (WCST) is maintained.
• When a network fails, a CONV-SETUP message is sent to the node.
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Converter Multiplexing Between Paths b1 and
b2
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Conv. ID
Conn. ID
Incoming Port Outgoing Port
Status
1
1
1 - λ0
2 – λ1
Reserved
1
2
3 - λ2
5 – λ0
Reserved
2
-
-
-
Free
3
4
1 - λ0
4 - λ1
Primary
Wavelength Converter Status Table
Converter Multiplexing:
• Node checks the WCST to select a wavelength converter.
• The appropriate entry is inserted into the WCST
• Wavelength converter identifier
• Connection (session) identifier
• Incoming port & associated wavelength
• Outgoing port & associated wavelength
• Path status (free, primary, reserved)
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Backup Path Relocation (BPR)
• Used when it becomes necessary for primary paths to accommodate certain routes which
are occupied by the backup path.
• Objective is to:
• Help in providing primary paths with fewer hops.
• Reduce blocking.
• Improve network utilization.
• Two relocation schemes are used to migrate an overlapping backup segment.
• Wavelength Relocation (WR).
• Segment Relocation (SR).
• Backup paths are relocated only if all overlapping segments can be relocated.
• If relocation fails, none of the overlapping segments are relocated.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
(Network states before relocation)
(Network states after relocation)
Examples of backup path relocation mechanisms.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
• Introduction
• Background
• Proposed Mechanisms
• Performance Analysis
• Conclusions
Monday, February 02, 2004
• Presents the performance analysis of the proposed
techniques, based on a discrete-event simulation model.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Simulation Model
• A dynamic network traffic model
• Connection requests arrive at a node
• Each connection request is assignment a wavelength
• Traffic load is defined in Erlangs.
• Share-per-node architecture is used; all nodes allocate an equal number of converters.
• Both the dedicated and shared protection schemes are studied.
Simulations are performed for two networks:
• A 24-node ARPANET-like network with 16 and 32 wavelength on each link. The results for this
network is discussed.
• Also, a random 50-node network with 32 wavelength per link.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Comparison of mechanisms
• Basic hop-count (HC) based shortest path routing algorithm,
• CFPR routing algorithm with wavelength relocation, and
• CFPR routing algorithm with segment relocation.
• The notation X-Y-Z is used to specify an algorithm, where
–X
{HC,CFPR} denotes the routing algorithm,
–Y
{NR,WR,SR} denotes no relocation, wavelength relocation and segment relocation
respectively, and
–Z
{DP,SP} denotes dedicated and shared protection, respectively.
• The performance metrics presented are the:
–
–
–
–
blocking probability (Pb),
link and converter utilization,
average hop count, and
backup path relocation statistics
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Blocking Probability
• Network blocking probability;
attempt to minimize this metric
• Architectures employing converter
multiplexing and backup path
relocation schemes perform
significantly better than the basic
scheme.
• CFPR with WR/SR has lower Pb
than that of the basic scheme.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Reduction in Number of Converters.
• Graph demonstrates the reduction in
the number of converters required
per node.
• For an offered load of 3.0 Erlangs,
the basic architecture needs a
minimum of 16 converters to offer a
blocking probability of less than10−1.
• The new techniques offer the same
performance for as few as 4
converters.
• We can also observe that having
more than 8 converters, does not
lower the blocking probability any
further.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Reasons for blocked connections
• Converter unavailability accounts for:
• 2% - 3% for the CFPR-based techniques w/dedicated protection
• 20% for the CFPR-based techniques w/shared protection
• 99% for the basic scheme w/dedicated protection
• 100% for the basic scheme w/shared protection
Scheme
Blocking Probability
%WU
%CU
HC-NR-DP
0.319
1%
99%
CFPR-WR-DP
0.114
98%
2%
CFPR-SR-DP
0.106
97%
3%
HC-NR-SP
0.262
0%
100%
CFPR-WR-SP
0.051
80%
20%
CFPR-SR-SP
0.053
80%
20%
Percentages of Connections Blocked Due to
Wavelength Unavailability and Converter Unavailability.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Average Hop Count
• Graph shows the average hop
count of the primary paths for
accepted connections.
• Basic scheme exhausts all the
converters as the network load
increases.
• In comparison, the converter
multiplexing based algorithms have
a steady hop count.
* hop = the number of links between a pair of nodes.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Revenue Metric
• Metric based on the number of hops routed.
• Defined as the shortest–hop count based on the static topology.
• For the basic scheme the revenue drops when load increases
• The proposed algorithms, show only a marginal drop in revenue.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Conversion Statistics
• One objective was to provide
wavelength-conversion free paths for
the primary paths.
• Around 30% of the basic routing
scheme connections need at least
one wavelength converter.
• The proposed algorithm eliminates
the need for wavelength conversion.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Relocation Statistics
• Performance of systems with and
without backup path relocation
schemes.
• When relocation was deployed, the
blocking probability was lower.
• More significant benefits were seen in
the context of wavelength conversion.
• Results indicate that the backup
relocation overhead is manageable,
and only a reasonable number of
relocations are necessary.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
• Introduction
• Background
• Proposed Mechanisms
• Performance Analysis
• Conclusions
Monday, February 02, 2004
• Wraps up and concludes the paper.
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Protection Mechanisms for Optical WDM Networks based on Wavelength
Converter Multiplexing and Backup Path Relocation Techniques
Conclusion
• Three different mechanisms were proposed and analyzed.
– The proposed converter multiplexing scheme reduces the number of connections blocked.
– The CFPR routing algorithm significantly reduced the number of primary connections undergoing
wavelength conversion.
• Two different backup path relocation mechanisms were presented
– Analysis showed that the combination of the mechanisms results in substantial reduction in blocking
probability.
– Also, lower number of converters were required per node to achieve a target blocking probability.
• The additional overhead of using segment relocation compared to the wavelength
relocation scheme did not result in much improvement.
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