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182 T. Abdullah et al.<br />

(except when d = n) and cannot search the resources <strong>of</strong> all participat<strong>in</strong>g nodes.<br />

Figure 3a and 3b compare the number <strong>of</strong> messages required to f<strong>in</strong>d a match <strong>in</strong><br />

the vary<strong>in</strong>g the degree <strong>of</strong> neighborhood approach with centralized and multiple<br />

adaptive matchmakers approach, respectively, <strong>in</strong> the ad hoc grid.<br />

Although the distribution <strong>of</strong> ad hoc grid nodes among two or more matchmakers<br />

vary accord<strong>in</strong>g to the workload <strong>of</strong> the matchmakers [12], we assume<br />

ni = n/m for the case <strong>of</strong> multiple adaptive matchmakers, while compar<strong>in</strong>g the<br />

message complexity for vary<strong>in</strong>g the degree <strong>of</strong> neighborhood <strong>in</strong> completely decentralized<br />

approach with other two approaches <strong>in</strong> Figure 3a and 3b. 1MM represents<br />

one matchmaker <strong>of</strong> the centralized approach, whereas 2MM, ..., 5MM<br />

represent two or multiple matchmakers <strong>of</strong> the multiple adaptive matchmakers<br />

approach <strong>in</strong> Figure 3b. The number <strong>of</strong> messages exchanged <strong>in</strong> different resource<br />

discovery approaches are summarized <strong>in</strong> Table 1.<br />

6 Experimental Setup and Results<br />

We developed our ad hoc grid experimental platform on top <strong>of</strong> Pastry [15].<br />

Although we used Pastry, <strong>in</strong> pr<strong>in</strong>ciple any other structured overlay network can<br />

be used. Pastry is a self-organiz<strong>in</strong>g and adaptive overlay network. Pastry is used<br />

for node arrival/departure, node failure handl<strong>in</strong>g, and for message rout<strong>in</strong>g <strong>in</strong><br />

this work. Node jo<strong>in</strong>/leave and Pastry message rout<strong>in</strong>g is expla<strong>in</strong>ed <strong>in</strong> [15].<br />

The experiments are executed on PlanetLab [16]. PlanetLab is a global,<br />

community-based effort and is used mostly for network related experiments. The<br />

PlanetLab nodes are connected through the Internet. Research <strong>in</strong>stitutions/ organizations<br />

contribute a m<strong>in</strong>imum <strong>of</strong> 2 comput<strong>in</strong>g mach<strong>in</strong>es. The researchers <strong>of</strong><br />

the correspond<strong>in</strong>g <strong>in</strong>stitute/organization are granted access to a pool <strong>of</strong> more<br />

than 1000 PlanetLab nodes.<br />

The experiments are executed to answer the questions discussed <strong>in</strong> Section 1.<br />

The first set <strong>of</strong> experiments are executed to analyze the effect <strong>of</strong> vary<strong>in</strong>g the degree<br />

<strong>of</strong> neighborhood. In the second set <strong>of</strong> experiments, the experimental results<br />

with vary<strong>in</strong>g the degree <strong>of</strong> neighborhood are compared with total centralized approach<br />

and with multiple adaptive matchmakers approach for resource discovery<br />

<strong>in</strong> an ad hoc grid.<br />

The number <strong>of</strong> participat<strong>in</strong>g nodes varies from 15 to 650. The number <strong>of</strong><br />

matchmakers varies from 1 to 5 <strong>in</strong> the experiments with multiple adaptive<br />

matchmakers. TTL <strong>of</strong> the request/<strong>of</strong>fer messages is set to 10000 milliseconds<br />

<strong>in</strong> order to cater the delays observed <strong>in</strong> PlanetLab. In this work, we have only<br />

considered computational power (CPU cycle) as a resource. However, other resources<br />

like memory, bandwidth and disk storage can also be <strong>in</strong>corporated <strong>in</strong> this<br />

model. The job execution time, job deadl<strong>in</strong>e, budget, and request/<strong>of</strong>fer computational<br />

resource amount are randomly generated from a predef<strong>in</strong>ed range. The<br />

request/<strong>of</strong>fer resource quantity varies for each request/<strong>of</strong>fer message. Data presented<br />

is obta<strong>in</strong>ed after the system reaches a steady state, when 1/4th <strong>of</strong> the<br />

experiment time is elapsed.

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