AN EFFICIENT MATHEMATICAL MODELING FOR THE COMPREHENSIVE DESIGN OF AON INCLUDING WAVELENGTH ASSIGNMENT SCHEME

Integrated Optics and Lightwave:An International Journal(OPTLJ), Vol. 1, No.1
19
“AN EFFICIENT MATHEMATICAL MODELING FOR
THE COMPREHENSIVE DESIGN OF AON
INCLUDING WAVELENGTH ASSIGNMENT SCHEME”
Tarun Gupta1
and Amit Kumar Garg2
1
Ph.D. Scholar, ECE Dept., DCRUST University, Murthal, Haryana, India
2
Professor in ECE Dept., DCRUST University, Murthal, Haryana, India
ABSTRACT
This paper recommends a systematic wavelength assignment scheme which deliberately enhance the
quality of service by minimizing the average dispersion in optical network. In this approach assignment of
the wavelength recommended that allocates the wavelength as per mathematical model based on the path
length request. Results validate that path length-based scheme improves the system performance in
comparison with the commonly used existing assignment technique which works on the principle of first fit
wavelength assignment(FFWA) and former assignment methodology should be ideal choice when the
number of connection requests extremely high.
KEYWORDS
Dispersion, RWA, WCC, lightpath.
1. INTRODUCTION
In all optical network, dispersion greatly depends upon the assigned wavelength and if the
assignment of the wavelength is not appropriate it reduces the system performance to a large
extent. By using several compensating techniques such as phase conjugation, dispersion
compensating fiber, we generally reduce the effect of dispersion but they are costly methods. In
brief dispersion means broadening or scattering of the light pulse which results the distorted
signal during transmission and the effect of dispersion largely depends on the fiber length as fiber
length goes on increasing, level of dispersion also enlarged. Thus the aim is to reduce the system
dispersion considering expense of designed network in mind. The choice of systematic WA
approach plays a comprehensive role as it directly impact the network performance. Various
assignment schemes suggested but in this scenario we consider only those techniques which not
requires any conversion of the wavelength approach. Many existing wavelength assignment
schemes mostly used are first fit (FF) wavelength, random WA, most used as well as least used
assignment schemes. The existing conclusion obtains that FFWA scheme is superior on many
aspects as compare to other above-mentioned schemes. Now a days to meet the ever-increasing
demand of traffic we make our network efficient enough to handle the traffic in any conditions.
But with the evolution of the Internet traffic, requirement for better services have been rapidly
increased. Many difficult tasks came on to the picture in order to provide services like video-
conferencing,internet telephony which requires a higher bandwidth than other applications.
Various queuing techniques suggested to perform quality of services and all the existing schemes
utilizing buffers at intermediate nodes with stipulated buffer limit.

20
For any communication networks, the measure problem relates while assigning resources as
buffers and providing bandwidth to various links. The restricted resources assigned depending
upon type of traffic flows in order to enhance the system performance. The operation of routers
can be controlled in accordance with different queuing schemes such as WFQ, FQ, Frame-based
FQ and all these existing schemes comprises buffers at intermediate nodes with stipulated buffer
limit. Now a days to meet the ever-increasing demand of traffic we make our network efficient
enough to handle the traffic in any conditions. But with the evolution of the Internet traffic,
requirement for better services have been rapidly increased. Many difficult tasks came on to the
picture in order to provide services like video-conferencing, internet telephony which requires a
higher bandwidth than other applications. The result obtains by using simulation tool OPNET
Modeler (version 14.5) [14]. The Opnet stands for Optimum Network performance. It is a
network simulation tool which consists Opnet products palette along with some additional
modules such as 3D network visualize, Application Characterization Environment (ACE) and
system in the loop modules which enables advanced simulations for both wired and wireless
networks.
In this paper new approach based on path length has been recommended that allocate the
wavelength to the requested links in accordance with the length a light travel. The outcome of
suggested scheme is distinguished with the existing FFWA terminology with respect to overall
dispersion. The rest paper is structured in different sections, section 2 emphasize on simulation
model along with mathematical formulations, section 3 reveals the outcomes of the recommended
approach and lastly section 4 gives conclusion supporting the current work describes.
2. SIMULATION MODEL ALONG WITH MATHEMATICAL FORMULATIONS
The former first fit wavelength assignment scheme works on the approach of Greedy algorithm
which hungrily finds the connection keeping in mind getting the least delay from an initial
topology designed. In this scheme numbering of wavelengths should be accomplish by allocating
smaller number or subscript to higher priority for assigning the wavelength as per user requests. In
FF, the wavelength having lowest character is allocated first to the connection requests in order to
initiate the path. In any case, if the smallest symbol wavelength is not available, then network link
makes an attempt to check the availability of second lowest subscript wavelength and so on. This
approach does not assign the wavelength according to the path length, here assignment of
wavelength should be done in accordance with highest priority given to lowest subscript as per the
availability of free wavelengths.
The brief algorithm approach as below:
a. For each request generated distinguish it by source-destination (s–d pair).
b. Find out the path to route the information using the look-up table.
c. Search a free wavelength availability and assign some specific holding time to the free
wavelength in order to establish the path request.
d. In case of unavailability of free wavelength during requested time, the said call request is
blocked.
Secondly the proposed scheme works on another emerging algorithm known as an Evolutionary
algorithm whose primary responsibility is to make the best use of network resources in such a way

21
so that it minimises the average delay of an optical network. In order to fulfil that it uses both
hybrid routing as well as WA strategy to simulate the initial topology and works on the said
approach to design the final topology. Here the allocation of wavelength should be performed
according to path length rather than to assign on the basis of first free wavelength available. In the
path length based approach, allocation of wavelengths as per accordance with the wavelengths
having higher dispersion are designated to the shortest path link requests and vice-versa. This
proposal elevates network performance like reducing the overall dispersion. So here describing
one simple approach by defining two sets of wavelengths:
In first set, there is an availability of all the available wavelengths and in second set, only few
higher subscript wavelengths are available. Let's assume that there is an availability of 6
wavelengths in WDM network then
set 1= (λj), where value of j= 1 : 6
set 2= (λk), where value of k= 5 : 6
The second set wavelengths generally used when the path requests having longer distance will
come, all the shortest distance requests will be served by set one. Now the challenge is to
categorized the requests, whether it’s come for shortest lightpath distance or for longest lightpath
distance. So we opted one threshold path length based on some mathematical analytics and all the
request with distance ≤ to Z (where Z is threshold distance) acted as shortest distance requests
and the path requests with path length > Z acted as longest distance requests. For extracting the
value of Z, specific mathematical computation performed for all possible s-d pairs including their
path length.
The brief algorithm approach as below:
a. For every request established distinct it by source destination pair.
b. Search out the exact path distance for the given request for different pair.
c. If the requested distance is ≤ to Z, then allocation of wavelength should be done based on FFW
approach from set 1 wavelengths.
(i) Then search a free wavelength availability from set 1 and assign some specific holding time to
the free wavelength in order to establish the path request.
(ii) In case of unavailability of any free wavelength during requested time, the said call request is
blocked.
d. If path length is greater than Z
(i) Then again search a free wavelength availability from set 2 and assign some specific holding
time to the free wavelength in order to establish the path request.
(ii) In case of unavailability of any free wavelength during requested time, the said call request is
blocked.

22
The proposed path length structured WA scheme deliberately enhances the quality of service by
minimizing the average dispersion in all optical network. To accomplish our aim, the link
requests allocate the wavelength in accordance with such that longer distance are allocated those
wavelengths which contains lesser dispersion and those containing higher dispersion are
allocated with shorter path distance but the conventional WA approach not works on the same
principle as mentioned above due to which the average dispersion may increase which lowers the
quality of given signal. So, if the wavelengths are allocated as per above path length-based WA
strategy, the overall total dispersion can be improved to higher extent which leads to provide
improved quality of service in accordance with average signal quality keeping in mind not to
increase the network setup expense. The brief explanation of how to assign the wavelength is
understand via the below algorithm, where K represent alternate paths and the below table
defines the notations and flags which we are going to use in this paper.
Table 1 Used notations.
TO ANALYSIZE THE COMPLEXITY OF ABOVE ALGORITHM WITH RESPECT OF TIME
To understand its complexity, flags and notations defined as above.
• The time to organize all the wavelengths as per ascending arrangement based on its dispersion
is O(WlogW.E).
• Computing K number of paths, arrange them according to their foremost path distance in the
descending order is O(((E+NlogN+K))·Z)+ZlogZ).
• The timeline for carry out allocated wavelength for Z connection request is O(L·W·K·Z).
Consequently average timeline needs is O(WlogW·E) + O(((E+NlogN+K))·Z)+ZlogZ) +
O(L·W·K·Z).

23
3. OUTCOMES OF THE PROPOSED SCHEME
The below figure 1 shows the graph between the overall dispersion and number of link requests
for the path length-based wavelength and mostly used first fit WA schemes considering the link
requests in WDM network are set-up productively. This graph shows the two types of lines, the
solid line pointing to overall dispersion for path length-based wavelength
assignment scheme (QWA) and the dotted line represent the total dispersion for first fit
wavelength assignment scheme (WAFF) respectively. Simulation result obtains that overall
dispersion increases when no. of link requests increases either in case for QWA or for WAFF
schemes but the overall growth of total dispersion in case of QWA is less than that of WAFF.
Figure 1. Overall dispersion and number of link requests (small plot inside shows the behavior
between propagation losses and no. of link requests).
where WAFF: represents the approach where wavelength assigns based on FF scheme
QWA: represents the approach where the wavelength assigns according to the path length

24
This is due to the fact that in case of path length-based assignment, link request consists larger
distance allocate those wavelengths which contains fewer dispersion and vice-versa. The small
plot inside the figure shows the behavior between the propagation loss and no. of link requests for
both the approaches. It is concluded to the above plot that propagation loss for both the approach
is nearly similar and it increases by increasing the link requests.
4. CONCLUSION
The consequence of the discussed scheme is analyzed through the above simulation and it’s
concluded that by using path length-based WA scheme, the overall dispersion of optical network
reduces remarkably in comparison with most commonly used conventional first fit wavelength
assignment scheme which in result enhance the service quality keeping in mind not to increase the
network expense. Hence, proposed scheme is an efficient and profitable approach in most of the
practical networks and the above discussed scheme would be best choice especially whenever the
requests goes high.
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