# Secure and Time-Aware Communication of Wireless Sensors Monitoring Overhead Transmission Lines
## 5 Results Analysis and Discussion  
In this section we study the results gathered for several different scenarios, including variation in the number of groups, direct connections to the substation, routing algorithms and security mechanisms. We compare the results of our proposed formulation and evaluate time delays of the network, including the cases of constrained cellular coverage. The simulation results of various implementation scenarios of WSNs and overhead smart grid networks aim at highlighting their performance and examining how inherent and imposed factors influence the maximum delay time of the different arrangement scenarios. The below analysis concerns only the results obtained for the transmission line, where the distance between two adjacent poles is equal to 100 m. Remaining results (for distances equal to 50, 200 and 300 m) are summarized in the Appendix section, in Tables 14-15. All the system parameters as well as their default values, that are involved in the following analysis, are reported in Table 3. These values help towards the establishment of realistic implementation scenarios. Note that all the assumptions of Section 3 are also satisfied. Table 4 contains the results gathered for the first scenario (Scenarios 1a,b). In this scenario, we consider the transmission line to be divided into two sub-lines, where each of them has only one direct link to the substation (\(\kappa=2\)). Thus, the number of hops (intermediary relay nodes), obtained data should traverse to finally reach the substation, is equal to 22 for the left sub-line, and 23 for the right sub-line (\(\eta=22\), \(\eta=23\)). The size of the measurement data gathered by each sensor at every tower is the same, and is equal to 80 bytes. It takes about 4000 ms for TelosB to transmit it to the relay node. Because there are 4 measurement sensors at each pole, the size of the data received by the relay node is 320 bytes, and the time taken for its transmission is calculated using the algorithm available in QoP-ML model. As we look at the results in Table 4, we can see that the time needed by sink to send the measurement data to the neighboring relay node increases along with the number of hops, and it is always the longest for the last node on line (sink 22 and sink 45). Furthermore, the difference between transmitting encrypted and unencrypted data grows rapidly as well. Additionally, the results in Table 4 indicate that this linear network model suffers from an imbalance of workload. The relays located closer to the substations have to handle a lot more traffic than those sitting farther away on the line. Considering the topological constraints posed by the transmission lines, the low bandwidth, low data rate wireless nodes fail to transmit huge amounts of data in a multi-hop manner. As a consequence of analyzing results gathered for Scenario 1, it was necessary to identify a more efficient way of delivering collected data to substations. In order to balance the workload of transmitting sinks, we established Scenario 2, where each relay on every pole along the transmission line has a direct connection to the substation. The size of transmitted data and transmission times are the same as in Scenario 1. Table 5 consists of the results gathered for this Scenario 2a,b. As is evident from Table 5, by dividing all nodes into \(\kappa=45\) stand-alone groups, we managed to solve the issue of imbalanced workload: the time needed by each sink is almost equal, no matter if we consider the first, or the last relay node on line. Moreover, the difference in transmission times between encrypted and unencrypted traffic is almost constant--it does not change as severely as in Scenario 1. Although this approach has many advantages (balanced workload, the constant time difference between various security options), there exist some drawbacks as well. One of them is cost--deploying cellular transceivers on each tower is a very expensive solution.