## 4 Performance Evaluation  
In Section 3, we proposed ASST, a new mechanism for data dissemination based on DHT and TBF. In this section, we evaluate the performance of our proposed mechanism in ns-2 simulations. Ns-2 supports detailed simulation of mobile, wireless networks. Our simulation uses an 802.11 radio with a 30 m radio range, rather than the 250 m radio range of IEEE-compliant hardware; this choice is similar to that made in the evaluation of GHT with a 40 m radio range. ASST was implemented on the basis of GPSR. 900 sensor nodes were deployed in a 600 m \(\times\) 600 m field in grid topology. The distance between sensor nodes was 20 m so that each sensor node has 8 neighboring nodes. The sensor nodes at the border line of the field were set as query nodes, frequently sending queries. The target point was set at the center of the field. Each sensor node consumes 0.5 w of power when it sends and 0.2 w of power when it receives. Table 3 provides details of the simulation parameters. RXThresh is a receive threshold, CPThresh capture threshold, and CSThresh carrier-sensing Threshold. Scalability, as a property of systems, is generally difficult to define; however, it is essential to define the specific requirements for scalability based on the dimensions that are deemed important. In telecommunications and software engineering, scalability is a desirable property of a system, a network, or a process; it indicates the ease with which the system can either handle growing amounts of work, or can be readily enlarged. For example, it can refer to the capability of a system to increase total throughput under an increased load. An algorithm, design, networking protocol, program, or other system is said to be scalable if it is suitably efficient and practical when applied to large situations (e.g., a large input data set or a large number of participating nodes in the case of a distributed system). If the design fails when the quantity increases then it does not scale. In particular, load scalability means the ability of a distributed system to expand easily and to contract its resource pool to accommodate heavier or lighter loads. Alternatively, it is the ease with which a system or component can be modified, added, or removed to accommodate a changing load. In this paper, we use load scalability as an evaluation metric. We evaluate the performance of ASST with a diverse query frequency. We compare ASST with GHT and GCLP. To evaluate the scalability of ASST, we varied the query frequency from 0.5 queries per second to 100 queries per second. To reflect query processing, each query has a query processing time of 100 ms. A replica node receiving the query packet has to wait for 100 ms before responding. To provide load scalability, each query has to maintain the response time of 100 ms. The query was uniformly distributed among sensor nodes. \begin{table}
\begin{tabular}{|l|l|l|l|l|} \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline Radio Propagation & Shadowing & Routing Protocol & GPSR \\ \hline MAC & 802.11 & \multirow{2}{*}{Energy} & Idle Power & 0.1 w \\ Queue & DropTail & & Rx Power & 0.2 w \\ \hline Antenna & OmniAntenna & \multirow{2}{*}{Consumption} & Tx Power & 0.5 w \\ \cline{1-1} \cline{5-5} Network size & 600 m \(\times\) 600 m & & 900 nodes \\ \hline \multirow{3}{*}{Radio} & CPThresh & 10.0 & Packet size & 60 bytes \\ \cline{1-1} \cline{2-5}  & CSThresh & 1.559e–11 & \multirow{3}{*}{Antenna} & X & 0 \\ \cline{1-1} \cline{5-5} Parameter & RXThresh & 3.652e–10 & & Y & 0 \\ \cline{1-1} \cline{5-5}  & Pt & 2.5872e–4 & & Z & 1.5 \\ \hline \end{tabular}
\end{table} 
Table 3: Simulation parameters. Figure 9 shows the number of repository nodes and the number of queries received per repository node given several query frequencies. GHT saves information into very few repository nodes--home nodes and neighboring nodes surrounding the target point--and GCLP uses many repository nodes forming a trajectory from end-to-end in the network.