## 5 Discussion
### Performance of Massive Deployment by the Proposed BT Solution
When \(n\) is large enough (e.g., 10), the total number of nodes in the tree that can provide data could be approximated as \(n/c\). Let \(d\) be the data size to be transmitted to a peer. \(d_{total}\) is the total data to be transmitted in the BT-based solution. \(b\) is the network bandwidth that a peer can use, and \(b_{total}\) is the total bandwidth available in the BT-based solution. Thus, the total time for all of the peers in the BT solution to complete the download can be formulated as:  
\[t_{total}=d_{total}/b_{total}=dn/(bn/c)=dc/b \tag{2}\]  
Equation (2) formulates the total time required to complete the distribution of data size \(d\) to \(n\) peers in the BT environment when the available bandwidth for each peer is \(b\). In the ideal case, which has no bottleneck or error in the hardware, and with some approximation, because the number of peers (\(n\)) will not influence the total time (\(dc/b\)) in Equation (2), the total download completion time is constant. This explains why the total time is almost constant when the number of client machines is more than 10. Furthermore, the total download completion time \(dc/b\) can be approximated from the experimental results in Section 4. The mean value of the time to deploy 10 to 32 clients (refer to Table 2) using the BT-based solution is 1072.174 s. Figure 12 demonstrates that (1) the average deployment time for each configuration obtained from the experiments as well as (2) the division of \(t_{total}\) value (1072.174 s) by the number of client machines (i.e., \((dc/b)/n\)). As shown in Figure 12, two curves match very well when the number of clients is equal to or larger than 10. These two curves also roughly match each other as the number of clients is less than 10, except for the case of one client. This result validates that Equation (2) can be used to estimate the total download completion time for the proposed BT solution. As for the mismatches between the experimental results as well as Equation (2) in Figure 12, when the client number is less than 10, the major reason is due to the insufficient clients in the BT solution that cannot form a complete or good enough tree-typed network topology to optimize the network [92; 93]. Therefore, some biases between the ideal case and the experimental results exist. Table 5 summarizes the pros and cons of the BT and multicast solutions in system deployment. For the pros, based on the experiment results, feedback from other users about using the proposed BT-based mass deployment software, and other studies [3, 58], the BT-based solution is more reliable and flexible. When the number of clients to be deployed is large (for example, equal to or more than 11 clients in this work), the deployment performance is better than that of the multicast solution as well. Although the BT-based solution has a lot of advantages, some cons exist. The quality barrier caused by the network switches and the requirement for more disk space for the image repository are significant disadvantages. For the quality barrier caused by the high loadings of the network switches, client(s) may fail to retrieve the required files for network booting, and the deployment manager, ocsmgrd, may fail to receive the signals from clients that have finished the deployment. Therefore, the quality of network switches, which have high data transmission rates and no tolerance for congestion, is required to ensure successful deployments. Another drawback of the proposed BT-based solution stems from the extra disk space that is required for the image repository. As the BT image must be prepared in the FSTB format, it will require more disk space in the repository. In terms of the pros of the multicast solution, a lower bandwidth is required compared to the BT-based solution. Furthermore, no extra disk space is required for the image repository because the image does not have to be converted to the FSBT format. The multicast solution also has better performance with a smaller number of clients (e.g., fewer than 11 clients in this work).