International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 1 (2016) pp 404-410
© Research India Publications. http://www.ripublication.com
Survivable Routing with Path Length Constraint in WDM Networks
Dinesh Kumar Tyagi
Assistant Professor, Department of Computer Science and Engineering,
Malaviya National Institute of Technology Jaipur, Jaipur, Rajasthan, India.
E-mail: [email protected]
V. K. Chaubey
Professor, Department of Electrical & Electronics Engineering,
Birla Institute of Technology & Science Pilani, Pilani, Rajasthan, India.
E-mail: [email protected]
Abstract
Wavelength-routed WDM optical network has the tremendous
capability of providing overgrowing needs of higher bandwidth to
the end users. It uses preconfigured optimal lightpaths to carry the
traffic of users from one node to another node. Hence, an
intelligent RWA algorithms required to be employed to achieve
better performance of the network. In this paper, we investigate
the impact of path lengths in the RWA problem. We study the
effect of length of the path in the blocking performance of
network when working and protection paths computed for the
resiliency to an occurrence of single link failure in WDM
network. Proposed algorithms will optimize individual connection
request. In this work, we have simulated and analyzed the relative
performances of the three RWA heuristics algorithms for
survivable routing and wavelength assignment problem named as
Shortest Path Pair (SPP), Shortest Longest Path Pair (SLPP) and
Longest Shortest Path Pair (LSPP) strategy. These algorithms
have been compared based on the percentage of successful lightpaths established. The proposed heuristic strategies described here
differs from each other in the length of the path of working and
backup path. The simulation results reveal that SPP algorithm
always outperforms in terms of call blocking performance ratio.
Hence, for better network performance survivable RWA
algorithm ensure to consider a pair of the shortest path as a
working and protection path.
Keywords: RWA, WDM Network, Blocking Probability, Optical
Network, Survivable Routing
Introduction
Wavelength-routed wavelength division multiplexing optical
network has become omnipresent as it has tremendous bandwidth
capacity due to the recent advancements that happen in WDM
technology. Revolutionary WDM has the capability of
transferring the data through fiber links in several orders of
magnitude. It is capable of fulfilling the overgrowing bandwidth
requirements of the end users of Internet. Each optical fiber link
can support enormous rate of data transfer through the multi
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channels of a fiber. Optical fiber links have the transfer
capability of the order of gigabits to terabits per second. It
communicates between a pair of network nodes by
establishing an optimal lightpath and assigning a free
wavelength to the established path. This step is known as
routing and wavelength assignment problem[1]. A lightpath
uses same wavelength channel along the links of the
established path between a pair of network nodes. This
constraint ensures that no two paths can be assigned the same
wavelength if both are going through the same fiber. Traffic
on such lightpath does not undergoes any optoelectronic
conversion at any intermediate nodes. In a wavelength routed
Wavelength Division Multiplexing optical network,
lightpaths are the basic mechanism of data communication
between pairs of nodes of the network. Hence an intelligent
RWA algorithms have necessary to achieve an effective
performance and resource optimization of the network. In
RWA problem, lightpaths are not always viable to establish
between the pair of network nodes due to the confinement of
the number of usable wavelength channels of the fiber and
hardware constraints at the network nodes. Further physical
constraints such as wavelength channel spacing in fiber,
capability of optical transceivers and bandwidth granularity
limit the utilization of available bandwidth[2].
Nodes of a WDM optical network may be equipped with
wavelength converters. In the optical network when nodes
have not equipped with wavelength converters than on each
link of the light path, the same wavelength must be used.
This restriction has known as wavelength continuity
constraints. When a wavelength converter is available at
nodes, different wavelength on each link may be used to
create a lightpath. This relaxation in wavelength continuity
constraints may enhance the network performance. In a
wavelength-routed optical network to mitigate the
interference with each other, two or more light paths
traversing through the same link needs to use different
wavelengths[3]. The components of a WDM optical network
are prone to hardware failures. Various component of WDM
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 1 (2016) pp 404-410
© Research India Publications. http://www.ripublication.com
network such as the transceiver, receiver, amplifier, optical cross
connect, switch, FDL and fiber links may suffer to failures. These
failures interrupt the ongoing services of light paths that are
passing through such failed components. In general, most
prominent component failure situation is the fiber cable cut due to
the laying of longer lengths of cable as backbone networks. Such
components failure can result in an enormous amount of
information loss and financial revenue losses. Hence, the need for
highly survivable RWA algorithms is obvious, considering the
vast transport and switching capacity of networks using
wavelength division multiplexing techniques, potential data loss
as a result of a failure and the fact that probability of network
failures is not low[4]. So one of the important aspects of network
design is its potentiality of the heterogeneous type of service
delivery in the event of failures. Therefore, survivability is an
important concern in the optical network to overcome to such
failures [5]. On-line rerouting and off- line protection are two
important approaches to providing survivability. To ensure the
protection against failure, an active primary path established for
each incoming connection request. After that, another protection
path that needs to be node or link disjoint to the primary path is
pre-computed in advance before the transfer of traffic over the
primary path initiates. Hence, the reliability of the network can be
provided by assigning additional secondary paths along with each
active path to transmit the information. After a failure of an active
path, these amended additional secondary paths to be used for
switching the affected traffic over it. Further resource efficiency
and network performance can be enhanced by sharing the
wavelengths amongst the secondary backup paths. In this backup
wavelength multiplexing approach, backup resources can be
shared among many lightpaths if they fail independently.
Resources along the protection paths may be shareable, hence, the
switching nodes along the protection paths are not configured
during the connection setup. Instead, upon a failure, source nodes
of failed paths are notified, and after that source generates the
signaling message to configure the switches along the protection
path. In this paper, we suggest three heuristic strategy that
performs the routing decision based on the criteria of path length
and avoid congestions among the wavelength links of the network
through uniform distribution of traffic loads among the links of
the network. This paper evaluates the effect of length of path
constraint on blocking performance of the various network and
contributes to the selection of optimal and efficient primary and
backup light path in a survivable wavelength-routed optical
network to realize maximum utilization of network resources.
The rest of the paper has structured in six sections. Section 2,
describe background. In section 3 we present system model and
the mathematical formulation. Section 4 discuss the proposed
routing heuristic strategies. In Section 5, we evaluate the
performance and discuss the simulation results. A conclusion has
drawn in section 5.
Background
WDM Optical networks are used now a day's as a carrier of user’s
data as well as real time traffics. The vast variety of traffic such as
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voice, data, and multimedia, etc. journeying over the Internet
and other networks are growing at unpredictable rates[2]. So
the utilization of the resources requires to be intelligently
optimized, and desirable service quality of network be
ensured. Therefore, an intelligent RWA algorithms of
survivable WDM network is a major concern to the end users
for an uninterrupted data transmission over the established
light path. Due to an immense demands fulfilling capability
of wavelength routed wavelength division multiplexing
optical network, it has to ensure various performance
measurable pre-specified service attributes such as call
acceptance throughput, delay, bandwidth, reliability,
recovery time, and jitter, etc. .
In literature, there is two basic failure recovery strategy one
is on-line rerouting and another is off- line protection
switching [4]. In the on-line recovery by rerouting strategy, a
new end to end lightpath or lightpath segments is
accomplished when there has a demand for restoring affected
traffic after the occurrence of faults. In the off-line protection
switching strategy of recovery, a recovery lightpath or
segments of lightpath are pre-established in an advance for
switching the traffic, after the occurrence of a fault to restore
the affected traffic. Both of these strategies may be further
can be local-based, which protects against a fault of node or
link of an active primary path , or segment- based to protect
against a failure that may occur in a segment of path and
global strategy of recovery which protects against fault in
any link or node or segment of the protected lightpaths.
Various routing strategies are available in the literature to
compute primary path and backup path where the main goal
is to minimize the resource usages and maximize the network
performance [5]. The problem of determining an optimal
route for primary and backup paths is known to be an NPcomplete problem [6].
In wavelength routed optical network lightpaths are a
foremost important building block of RWA problem. So an
effective strategy for the establishment of lightpath becomes
significant to improve and optimize the network resources
and performance. Various schemes for optimal path selection
have proposed in the literature that differ in the aspect of
various optimality constrains considered during the lightpath
selection such as wavelength availability, common channel
availability, pattern and type of incoming traffic and various
link or node based weight age assignment approaches [7].
The RWA policies can assume the centralized or
decentralized way of controlling the network status
information in the process of selection of best optimal
lightpaths. In [8] author considered individual wavelength
usages count during the lightpath routing in WDM optical
network in dynamic traffic condition. A weight based edge
disjoint RWA algorithm in [9] suggests a criterion for route
selection based on the static and dynamic link weight that
considers in-degree and out-degree of edges. In [10] a
priority based lightpaths selection algorithm suggested which
considers the traffics to be prioritized in various distinct
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 1 (2016) pp 404-410
© Research India Publications. http://www.ripublication.com
levels. In [11] authors attempts to minimize the combined primary
and secondary path length, where author selected the path in a
way so that both paths be small and hence tried to minimize both
the chosen paths. In [12] a service specific path quality attributes
based path selection for dynamic routing and wavelength
allocation in WDM optical networks proposed which considers
physical layer impairments, reliability, policy, and traffic
conditions. Nature inspired techniques have also suggested in the
literature for routing and wavelength assignment such as Ant
Colony Optimization, Genetic algorithms and Bee Colony
Optimization which adopt the dynamic network environment in
the process of routes selection [13,14,15,16,17]. Artificial Bee
Colony algorithm is a population based stochastic optimization
algorithm that simulates the intelligent behavior of honey bee to
model an iteration based optimization problems [16]. A study of
the delay versus capacity optimization of RWA problem has
presented by author based on genetic algorithm in [17]. In [18] an
agent based routing algorithm has proposed which is based on the
ant and bee colony meta-heuristic optimization techniques for a
fault tolerant WDM network. In [19] authors suggested a bioinspired load balancing routing algorithm forever changing
network that adopts the dynamic behavior of network status.
Set of candidate lightpath requests between s, d node pair :
r Rs ,d
Input traffic of requested connections from node s to node d :
Basic cost of link l e.g. physical length of link :
Objective Formulation:
The objective is here to minimize the length of light path can
be specified as
subjected to the various constraint mentioned below:
 Same wavelength w are not assigned to the two light paths
which traverse the same fiber link l

Input traffic demand of each s, d pair to be satisfied by the
resulting light path flows
Network model
Consider a network topology represented as a graph G(V,L,W)
such that it has V nodes, L fiber links and each links has distinct
W wavelengths. We assume that nodes did not equipped with
wavelength conversion capabilities. Assume each connection
request arrives at the network orderly and dynamically and there
is only a connection request arrives at a time. Bandwidth
requirements of each connection request is assumed to be only
one wavelength channel. Various considered notations are as
follows:
: Flow value on link l ,which is expressed in terms of light
path flows traversing link l
Total flow value ( ) on link l, expressed in terms of light path
flows traversing link l as :
here, all such lightpaths, r have considered such that r traverses
link l , that is, light paths which crosses the link.
Lightpath flow cost indicator variable(
w given as
) of light path r over
=
Here various considered parameters are:
Source node : s
Destination node : d
Network nodes : s, d  V
Available wavelengths on each link : w W
Network fiber link: l  L
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 Flow indicator variable can take either value 0 or value 1
only i.e.
 Basic cost of link takes value as 1 for all link, which
specifies the hop distance of fiber i.e.
The above objective function minimize the light path length
in terms of the number of hops for each connection request .
For better network performance few lower congested links to
be preferable than a single link which may be totally
congested. First constraint is distinct wavelength assignment
constraints. Second constraint ensure incoming traffic
constraint. Remaining two constraint specifies that variable
can take either value 0 or 1.
Proposed Survivable Routing Heuristic Strategy
We investigate here three strategies for establishing an
optimal RWA of working and a link disjoint protection path
based on the length of the path. In this work, we have
simulated and analyzed the relative performances of three
heuristics algorithms for survivable routing and wavelength
assignment problem to provide protection against any single
link failure named as Shortest Path Pair (SPP), Shortest
Longest Path Pair (SLPP) and Longest Shortest Path Pair
(LSPP) strategy. The suggested heuristic strategies described
below differs from each other in respect to the path length
considered in the selection of working and backup path. In
the process of computing primary and backup path using
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 1 (2016) pp 404-410
© Research India Publications. http://www.ripublication.com
above described strategy, we prefer to select the links that have
excess available free resources to avoid unbalanced state due to
quick depletion of resources over the links. In all the three
strategies, the algorithm tries to assign an available free
wavelength to the primary path using first fit concept. However,
for the backup paths, a concept of maximizing of the usage of
shared protection wavelengths has considered in assigning the
wavelengths. There can be sharing of wavelengths between light
paths used as a backup path, which enhance the network resource
utilization. The various heuristic strategies are as follows:
C. LSPP-RWA strategy
In this strategy, longest length path use as the route for
primary path and another link disjoint shortest length path
use as the route for backup path. In this strategy, the primary
path is shortest length path and backup path is longest length
path. Algorithm descriptions are as follows:
A. SPP-RWA strategy
In this strategy minimum length path use as the route for primary
path and another link disjoint shortest length path use as the route
for backup path. Algorithm descriptions are as follows:
Effect of Path Length to Survivable RWA
B. SLPP-RWA strategy
In this strategy minimum length path use as the route for primary
path and another link disjoint longest length path use as the route
for backup path. In this strategy, primary path is shortest and
backup path is longest one. Algorithm descriptions are as follows:
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In preconfigured path protection to cope with a single link
failure, for every connection request a primary path and a
backup path has computed. Wavelengths assigned to backup
paths can be shareable to the backup path of another
incoming connection request to maximizing the network
resource utilization. In this strategy of sharing of resources,
we prefers the assignation of backup channels that has
already reserved so that idle wavelength channels can be
utilized to primary path of future incoming connection
requests. Resources along the protection paths shared.
Hence, the switching nodes along the protection paths are not
configured during the connection setup. Instead, upon a
failure of any link of a primary path, the source node of failed
primary path receives a failure intimation message from the
source node of the link that has failed. Primary paths are
always pre-provisioned with an alternate backup path. Hence
after getting the failure notification message, the source node
of the primary path initiates setup process along the backup
path to configure and enable optical cross-connect switches.
After receiving the confirmation notification from destination
node back to the source node, the interrupted traffic restored
over the backup path successfully. The process of restoration
of failed traffic over backup path involves delays. It consists
of distinct delays, such as delay of detection of failure of the
link (Df), link propagation delay (Dprop), at each node
processing delay (Dproc) and delay of the setup of optical
cross connect switches (Doxc) at every node.
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 1 (2016) pp 404-410
© Research India Publications. http://www.ripublication.com
Therefore overall cumulative delay (D), connotes in transferring
traffic to backup lightpath in situation of disruption of primary
lightpath traffic due to link failure can be expressed as follow:
D =Df +( l'p -1)* Dprop + Dproc *l'p + 2(lb * Dprop )+ 2( lb +1 )
Dproc + (lb +1 )Doxc's
here, l'p is number of node from failed link to source node of
primary lightpath path and lb is hop length of backup path. Here
queuing delay has not considered as circuit switched WDM
network assumed to have no optical buffers.
From the above equation, the total cumulative delay involves to
restore traffic upon the failure, depends significantly on the length
of the primary and backup lightpaths. For the lesser delay of
switching the traffic to restore connections affected means l'p and
lb path lengths needs to be shorter which ensures the delay in
the recovery to be smaller. Hence, faster recovery can be ensured
after an occurrence of the failure, which also affects the capacity
cost efficiency besides the recovery efficiency. Sometimes this
delay may be unacceptably high in case length of backup
lightpath path become very large. Such larger delay can be critical
in a quality of service constrained WDM networks. Therefore
shorter physical length of paths is desirable in RWA of survivable
WDM network.
Performance Results
We evaluate the performance of proposed heuristic strategies on
two sample representative network topologies shown in Fig.1. and
Fig.2. The sample US IP Backbone network topology in Fig.1.
consists of 24 nodes and 43 links and sample US network
topology of Fig.2. has 15 nodes and 26 links. Each links assumed
to have the same number of W wavelength channels. We tested
for dynamic traffic and compared the consequence of path length
on network performance of RWA of survivable routing in single
link failure scenario, where the primary path and protection path
established for each pair of connection request. Assume that each
connection requests arrive with a random source and destination
one at a time. In each simulation run a large number of requests
generated and results have averaged over many simulation runs.
When a connection request cannot be satisfied using above
described strategy that connection request dropped. Performance
has compared on the three scenarios i) changing the network
topology ii) load and iii) total wavelengths availability per link.
Figure 2: Network Topology 2
Call blocking probability has used as performance metric that
is the ratio of the number of the unsatisfied connection
request to the total number of connection request generated.
Number of Increased Accepted Calls (IAC) performance
metric will depicts how better one strategy may performs in
comparison to another which can be specified as [20]:
IAC = the number of calls accepted by SLPP - number of
calls accepted by SPP
Call Blocking Improvement(BPI) performance metric shows
the percentage improvement of SPP blocking probability
against SLPP blocking probability, which can be specified as
BPI=( BPSLPP - BPSPP ) / BPSLPP
here, BPSLPP is SLPP blocking probability and BPSPP is SPP
blocking probability.
A. Blocking Performance Analysis
We compare the blocking probability performance of all the
three strategies. We have shown in Fig.3. and Fig.4. , the
comparative blocking performance of three strategies over
the topology shown in Fig.1. and Fig.2. respectively.
Figure 3: Blocking probability in network topology 1
Figure 1: Network Topology 1
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 1 (2016) pp 404-410
© Research India Publications. http://www.ripublication.com
Figure 6: Blocking Performance for varying wavelength
in topology 2
Figure 4: Blocking probability in network topology 2
It has observed from the graph that SPP strategy has a lower
blocking probability than SLPP and LSPP strategy while LSPP
has worst network performance. SLPP strategy is better than
LSPP due to the wavelengths sharing amongst backup paths
leaving more resources for other connections. All those strategy
in which longest path has chosen either as the primary lightpath
or backup lightpath has lower network performance, which has
attributed due to the occupancy of the larger number of the
resource along these longer paths compared to shorter paths.
Hence, fewer spare wavelength channels may be available in the
network that causes the incoming traffic to be dropped out.
Fig.5. and Fig.6. shows the changes in call blocking
probability in respect to the number of wavelength per fiber
for all three strategies over sample topology. It has observed
that as the number of wavelengths per link increased, call
blocking probability ratio gets reduced for all strategies. The
result reveals that better network performance achieved when
abundant resources are available in the network.
B. Number of Increased Call Accepted Performance Analysis
Fig.7. and Fig.8. depicts IAC versus the arrival of lightpath
connection requests. The result shows that performance
improvement by SPP strategy consistently performs better
than SLPP and LSPP in all scenario. SPP strategy accepts
more connection requests than other two strategies.
C. Call Blocking Improvement Analysis
In Fig.9. and Fig.10. shown call blocking improvement of
SPP blocking probability against SLPP and LSPP over
network topology 1 and topology 2 respectively. The result
shows that SPP can improve blocking performance more
significantly. When higher the arrival rate of connection
requests, the performance benefits of SPP strategy uniform
and does not decrease comparatively to other two strategies.
Figure 5: Blocking Performance for varying wavelength
in topology 1
Figure 7: Increased Accepted call of SPP in comparison
to SLPP and LSPP in topology 1
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 1 (2016) pp 404-410
© Research India Publications. http://www.ripublication.com
shorter in length for better performance. For the desirable
QoS, shorter paths are also desirable as path length affects
the delay and reliability aspects of network quality. From the
above simulation results analysis, it is observed that the
blocking SPP strategy outperforms the other two strategies in
terms of blocking probability, IAC and BPI performance
metrics. Hence, we can conclude that SPP strategy is always
a better approach in the selection of paths in survivable
routing problem as it has higher network throughput
performance.
Conclusion
Figure 8: Increased Accepted call of SPP in comparison to
SLPP and LSPP in topology 2
Figure 9: Call blocking improvement of SPP against SLPP and
LSPP in topology 1
In wavelength routed optical networks each lightpath carries
huge traffic. So how to select the primary route and backup
route for better utilization of network resource is one of the
important challenges. Hence in this work we consider the
RWA problem in the survivable WDM networks. We have
investigated three strategies of establishing an optimal route
for working lightpath and a link disjoint protection lightpath
considering the length of paths. Longer backup paths have
more delay in restoring the affected traffic in the event of any
failures of the network components. Intensive simulation
result confirms that shortest pair of primary and backup path
strategy always has significantly lower blocking
performance. Shorter path length is one of the desirable
parameter in a QoS constrained WDM network
environments. So shorter pairs of primary and backup paths
chosen for better efficiency in terms of faster recovery and
capacity cost in a survivable wavelength routed optical
network. Hence to maintain service quality of WDM network
shorter path preferable while longer paths avoided for better
and desirable network performance.
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Figure 10: Call blocking improvement of SPP against SLPP and
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performance of routing approach in the survivable optical
network. In the path selection, always the choice of shorter path
length routes are preferable. The survival routing that requires to
keep two paths, primary path and protection path needs to be as
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