Evaluation Methodology

Different scenarios as described in the above section are simulation using the NS2 simulation framework in order to evaluate the performance of the proposed load balancing framework and algorithms. For each of the simulation scenario the following set of parameters are observed and analysed:

 Average throughput of mobile nodes

 Packets drop rate

 Throughput at different networks

 Average handover latencies

 Load at each network

The obtained results are individually analysed but then also cross compared to study the effect of the various algorithms across different scenarios. While some of the above parameters like packets drop rate, Average throughput at each mobile node, traffic on each network, total handover latencies observed by each mobile node and total number of handovers performed by each mobile node for the different scenarios can be easily compared, direct comparisons of parameters is not possible in some cases. The following subsection briefly introduces these issues and the methodology adopted for analysing the results

5.5.1 Comparison of network load

For the comparison of network load it is necessary to choose some time points in the simulation where the load on each network changes. Figure 5-3 shows the selected points in the simulation topology where the load of each

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network is plotted for comparison between different simulation scenarios. The seven points shown in Figure 5-3 are selected for monitoring the load as the load in different networks changes on these points. The reason for change of networks load on these points is that these points are located at the boundary of different networks coverage areas. When mobile nodes enter or leave the coverage area of any network the load aware RAT selection is triggered and it handovers mobile nodes to appropriate available networks.

UMTS WiMax WLAN Satellite P1 P2 P3 P4 P5 P6 P7 Mobile nodes trajectory

Figure 5-3: Methodology for comparison of network load

Position P1 in Figure 5-3 is the place where mobile nodes start their movement from the satellite only coverage area. Position P2 is the location where satellite coverage area overlaps the UMTS coverage area. Similarly position P3 represents the place where WiMax coverage area is begins to overlap satellite and UMTS common coverage areas. The points P4 and P5 represent the start and end of WLAN coverage area. P6 represents the place where WiMax coverage finishes on the mobile nodes trajectory. The point P7 is the final destination of all the mobile nodes and this area is the common coverage area of UMTS and satellite networks. Network load at these various

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positions will be compared to analyse the performance of the proposed algorithms.

5.5.2 Study the Effect of User speed

Two different user speeds are considered in the simulation scenarios; low speed of 2m/s to simulated walking users and high speed of 25m/s to simulate users in a vehicle. Depending on the speed of the moving users, they would reach the above described positions (P1 to P7) at different times. The total time taken to travel the trajectory is also different for different speed. Hence direct comparison using simulation time is not feasible when comparing similar scenarios with also speed changes. For these comparisons also the above mentioned positions are used. Table 5-2 shows the time in simulation; when all the mobile nodes reach these different positions for both the high speed and low speed scenarios.

Table 5- 3: Time for each point with respect to mobile node velocity

Points Times for 25m/s scenarios Times for 2m/s scenarios

P1 8 seconds 8 seconds P2 30 seconds 250 seconds P3 51 seconds 511 seconds P4 66 seconds 710 seconds P5 74seconds 810 seconds P6 90 seconds 1010 seconds P7 250 seconds 1500 seconds

5.5.3 Effect of Cost preference

The performance of algorithms has also been compared when the cost of service is a parameter of concern for the user. Networks like the satellite networks may have a higher tariff for usage as compared to the terrestrial networks like UMTS. To observe the effects of cost on load balancing, it is

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assumed in all scenarios that 70% of the mobile nodes in the scenarios do not want to pay for the satellite networks when other terrestrial networks are available to them. Hence as soon as these users come into the coverage of a cheaper terrestrial network they prefer to move away from the satellite networks. It is assumed that the remaining 30% mobile nodes are however willing to pay for these satellite networks. These users may be premium users who do not want to handover frequently or they could be on a pricing model that is uniform across networks.

5.6 Summary

In the beginning, this chapter first presents the implementation tools and software implementation of the proposed load balancing framework. It then presents the simulation topology and finally the target scenarios for

simulation. At the end in “Evaluation Methodology” section this chapter

explained the methodology of how the load at different networks is compared in different scenarios. The influence on load balancing mechanism by user speed and the cost of services offered by different wireless network access technologies are also explained on the load balancing mechanism.

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