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Dynamic Routing and Wavelength
Assignment Scheme for
Protection against Node Failure
Ying Wang1 , Tee Hiang Cheng1,2 and Biswanath Mukherjee3
1School of Electrical and Electronic Engineering, Nanyang
Technological University, Singapore
2Lightwave Department, Institute for Infocomm Research, Singapore
3 Department of Computer Science, University of California, Davis,
California 95616
Outline
There are few studies on the design of optical
networks that could survive single node failures.
We design a dynamic RWA scheme that will set up a
primary path as well as a node-disjoint shared
protection path for each connection.
We propose a novel scheme that uses three vectors
to convey incomplete information of link state.
Finally, we get the experiment results of some criteria.
Introduction
Optical network is prone to failures; hence,
network survivability is a major concern of
network operators.
․Resiliency is generally achieved by means of
Protection and Restoration.
In a typical protection scheme against node
failure, the primary and backup paths need to be
node-disjoint in any intermediate node along their
routes.
․node-disjoint requirement can also protect against a
link failure.
Introduction (contd.)
Most of the RWA problem studies related to
protection and restoration in the optical layer
focus on off-line computation.
․These problems are pertaining to network planning
or static provisioning.
DLE (Dynamic Lightpath Establishment)
․ The primary and backup paths need to
be calculated at the same time and wavelength
channels need to be allocated for both paths.
Network Information Scenarios
We consider three possible ways in which
network status information can be stored and
disseminated and the effect on capacity
efficiency.
․Full Information Scenario (FIS)
․Partial Information Scenario (PIS)
․No Sharing of Information Scenario (NSIS)
Full Information Scenario (FIS)
Having a centralized RWA server that stores
all the information about the network and
computes the primary and backup paths for
any new wavelength demand.
․scalability problem
Partial Information Scenario (PIS)
PIS is to disseminate the network information
to every node in the network such that each
ingress node can make a RWA decision based
on the network information it posses.
․Only essential network information can be disseminate.
․Uses three vectors to describe the state of each link.
- Wavelength Channel Availability Vector Wavi
- Backup Wavelength Channel Reservation Vector Wres
- Conflict Vector CN
No Sharing of Information Scenario
(NSIS)
When ingress nodes make a routing and
wavelength assignment decision, it has no
information of existing primary and backup
lightpaths , so it cannot share any wavelength
channels on the backup lightpath with others;
․It will result in the worst capacity efficiency and can be
used as a benchmark
ILP solution
Values given :
N Set of nodes in the network
E Set of unidirectional fiber links in the network
W Set of wavelengths channel on each fiber link
s Source node of a lightpath
d Destination node of a lightpath
Sijw Assume the value of 1 if wavelength channel w is
free on link ij; zero otherwise
The variables are:
Pijw Assume the value of 1 if the primary lightpath uses
wavelength channel w on link ij; zero otherwise
Bijw Assume the value of 1 if the backup lightpath uses
wavelength channel w on link ij; zero otherwise
Zijw The cost of using wavelength channel w on link ij in
the backup lightpath
ILP solution (contd.)
The ILP formulation is as follows:
ILP solution (contd.)
Experiment Result
Capacity Efficiency
Effectiveness of PIS with Different Number of
Wavelength Channels per Link
Capacity Comparison between Node Failure
and Link Failure Protection
Capacity Efficiency
The saving in the total number of wavelength
channels used between NSIS and FIS varies from
18% to 23%, the saving in total wavelength channel
usage between NSIS and PIS is from 10% to 15%.
The result seems reasonable.
Effectiveness of PIS with Different
Number of Wavelength Channels per Link
The results lead us to conclude that there exists an
optimal number of wavelengths to aggregate; beyond
which, the network will suffer a significant drop in
capacity efficiency.
# of wavelength
channels per link
Saving in total wavelength
channel usage between
NSIS and PIS
36
48
9% ~ 13%
5% ~ 10%
60
4% ~ 7%
16
10%~ 15%
Capacity Comparison between Node
Failure and Link Failure Protection
The simulation results also show that for most meshed
topologies, less than 7% extra capacity is needed to
provide node and link failure protection compared to link
failure protection.