 Open Access
 Total Downloads : 365
 Authors : Namita Nag, Indu Bala
 Paper ID : IJERTV2IS100492
 Volume & Issue : Volume 02, Issue 10 (October 2013)
 Published (First Online): 15102013
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Comparative Study of Wavelength Assignment Algorithms for WDM Optical Network
Namita Nag 1 & Indu Bala 2
ECE Department, CEC Mohali
Abstract
Wavelength assignment in optical networks is a critical designing issue as it affects the overall performance of the network. In this paper, wavelength assignment algorithms have been reviewed namely random, first fit and dynamic (proposed) wavelength assignment algorithm. For given system parameters, the performance of all three algorithms is evaluated in terms of blocking probability. Results are showing that performance of dynamic algorithm is better than other two algorithms discussed.

Introduction
Communication networks are reaching more and more people every day and providing new means of information exchange. Consequently, data and traffic demand is growing rapidly (exponentially). All these bandwidth hungry applications have increased user data traffic and therefore demand for bandwidth [1]. This exponential growth has triggered the development of new technologies, and the advancement of existing one promising technology that meets the high bandwidth demand of data networks is optical networking technologies. This can be accomplished by a multiplexing technique like time division multiplexing (TDM), code division multiplexing (CDM), and wavelength (or frequency) division multiplexing (WDM) [2].
WDM network can provide endtoend optical communication channels through optical fibres and intermediate nodes with optical crossconnects, even the source and destination nodes are not connected by a fibre directly. There are issues related with optical communication system like congestion. The problem of congestion can be handled using wavelength assignment technique.
In this paper various wavelength assignment techniques have been reviewed and their performance comparison is done in terms of blocking probability. Section 2 briefly describes the routing and wavelength assignment issues and constraints. In section 3 pseudo code for Random, FirstFit and dynamic (Proposed) algorithms are given. In section 4 performance comparison for these algorithms is given for variable system parameters. In the end of this paper, conclusion is given based on simulated results.

Routing and Wavelength Assignment
RWA is the unique feature of WDM networks in which light path is implemented by selecting the path of a physical link between source and destination edge nodes and reserving a particular wavelength on each of these links for the light path. Routing deals with an optical connection and wavelength assignment policy allocate available wavelengths for the path selected for routing. Collectively it is known as routing and wavelength assignment (RWA) [3].
There are two constraints that have to be kept in mind by the approaches when trying to solve RWA.

Distinct wavelength assignment constraint: All light paths sharing a common fiber must be assigned distinct wavelengths to avoid interference. This applies not only within the all optical network but in access links as well [4].

Wavelength continuity constraint: The wavelength assigned to each light path remains the same on all the links it traverses from source endnode to destination end node [4].
Wavelength continuity constraints can be eliminated by using wavelength converter. The wavelength routed networks with this capacity is known as wavelength convertible networks.


Wavelength Assignment Algorithms
Wavelength assignment is a unique feature in which wavelength are searched before allocating to the path selected. Many algorithms have been proposed by researchers in past few years. In this section the most popular wavelength assignment algorithms have been reviewed [5]. These are:

Random wavelength assignment algorithm

Firstfit wavelength assignment algorithm

Proposed wavelength assignment algorithm

Random wavelength assignment algorithm
Step1: Initialisation of network parameters. Step2: Select any source destination pair.
Step3: Select any root out of all possible roots for selected source destination pair.
Step4: Assign any wavelength out of available wavelengths.
Step5: Is blocking probability of path is greater than threshold value?
Step6: If yes, repeat step4 and select new wavelength value if no, establish network connection.
Step7: Repeat step2.

First Fit Wavelength Assignment Algorithm
Step1: Initialisation of network parameters. Step2: Select any source destination pair.
Step3: Select any root out of all possible roots for selected source destination pair.
Step4: Arrange available wavelengths in ascending order.
Step5: Assign first/next wavelength to the selected path.
Step6: Calculate blocking probability for selected route.
Step7: Is blocking probability of path is greater than threshold value?
Step8: If yes, repeat step4 and select new wavelength value if no, establish network connection.
Step 9: Repeat step 2 for particular route.

Proposed wavelength assignment algorithm
Step1: Initialisation of network parameters. Step2: Pick a request with wavelength.
Step3: Find the first two paths.
Step4: If yes (path is returned), then make primary and secondary paths. If No, request has been discarded.
Step5: Send request for sd pair.
Step6: Check the destination frequency (frequency matching).
Step7: If yes, update path selection matching, If no, then frequency conversion is done.
Step8: Update path structure in links. Step9: Update load of the path assignment. Step10: Update bandwidth structure of path. Step11: Repeat step 2.


Performance Evaluation of algorithms The system parameters considered in simulation set up are mentioned in Table 1 below.
Table 1: System Parameters
Parameter
Value
Simulator
NS2
Simulation Time
90 mSec
No of nodes
210
Traffic Model
CBR
Packet size
2 Bytes
No. of Packets
10
Wavelength Index
1550.X nm
*X is variable
Table 2 to Table 6 are showing the performance comparison of mentioned algorithms for variable load and nodes. The load values taken in simulation are two, four, six, eight and ten only [6].
Table2: Blocking Probability with Two Erlangs
Blocking Probability with Two Erlangs load
Number of Nodes
Blocking Probability (%) x 106
Random
First Fit
Dynamic
2
100
100
100
4
110
120
100
6
160
190
100
8
190
210
130
10
230
220
150
Table3: Blocking Probability with Four Erlangs
Blocking Probability with Four Erlangs load
Number of Nodes
Blocking Probability (%) x 103
Random
First Fit
Dynamic
2
1.1
2
1.1
4
4.0
4
4.0
6
5.5
6
5.5
8
7.3
8
7.3
10
8.3
10
8.3
Table 4: Blocking Probability with Six Erlangs
Blocking Probability with Six Erlangs load
Number of Nodes
Blocking Probability (%) x 103
Random
First Fit
Dynamic
2
1.3
2
1.3
4
3.2
4
3.2
6
5.3
6
5.3
8
8.6
8
8.6
10
9.8
10
9.8
Table5: Blocking Probability with Eight Erlangs
Blocking Probability with Eight Erlangs load
Number of Nodes
Blocking Probability (%) x 103
Random
First Fit
Dynamic
2
4.1
2
4.1
4
5.9
4
5.9
6
7.9
6
7.9
8
9.2
8
9.2
10
9.9
10
9.9
Table6: Blocking Probability with Ten Erlangs
Blocking Probability with Ten Erlangs load
Number of Nodes
Blocking Probability (%) x 103
Random
First Fit
Dynamic
2
5.4
2
5.4
4
6.7
4
6.7
6
8.7
6
8.7
8
9.4
8
9.4
10
9.9
10
9.9
It is clear from the observations made in tables that dynamic wavelength assignment algorithm out performs over first fit and random algorithm. Blocking probability of dynamic algorithm is significantly less than rest two algorithms studied in this paper.

Conclusion
In this paper, three wavelength assignment algorithms have been discussed. These are Random, FirstFit and Dynamic (proposed) wavelength assignment algorithm. For given system parameters (i. e. Table 1), the performance of all three algorithms is evaluated in terms of blocking probability. Results are showing that performance of dynamic algorithm is better than other two algorithms.
References

K. Sivalingam and S. Subramanian, Emerging Optical Network Technologies, Eds. Boston, MA: SpringerVerlag, pp.46, 2004.

C. S. R. Murthy and M. Gurusamy, WDM Optical NetworksConcepts, Design, and Algorithms, Singapore: Pearson Education, pp.264, 2003.

H. Zang, J. P. Jue, and B. Mukherjee, A review of routing and wavelength assignment approaches for wavelength routed optical WDM networks, Opt. Networks Mag., vol. 1, no. 1, pp.146149, Jan. 2000.

B. P. Pal, Guided Wave Optical Components and Devices, Elsevier academic Press, 2006.

A. Wason and Dr. R. S. Kaler, Wavelength Assignment Problem in Optical WDM Networks, IJCSNS International Journal of Computer Science and Network Security, VOL.7 No.4, pp.28, April 2007.

N. Nag and I. Bala, Dynamic WDM Routing Solutions, International Journal of engineering Research and Technology, vol. 2, Sept 2013.