*3.6. Selection Results*

As mentioned earlier, the downloaded articles were based on the initial screening processes, which were based on inclusion criteria. The articles were screened using the initial quality assessment criteria (QAC). The main objective of using the QAC was to ensure that the primary studies selected were appropriate to address the concerns of previous studies. Nearly 300 articles were found on the above topics. After applying a duplication filter, 40 articles were discarded, leaving 260 articles that were reviewed based on the above exclusion criteria. In the next step, 60 articles were excluded based on the inclusion/exclusion criteria. A quality analysis was performed for the remaining 200 articles. After the quality analysis, only 120 articles were reviewed. Figure 6 shows the year-by-year distribution of articles reviewed that were used for the SLR study. There is no doubt that the eliminated articles contained valuable material, but they were not studied because they did not meet the screening criteria. The number of articles was initially limited to 120, after which they were stored in the citation manager software for information synthesis.

The selected papers were evaluated against the quality assessment criteria (QAC) listed in Table 6. Table 6 shows the quality assessment criteria (QAC) used to screen the articles for response grading. Studies selected for screening are described in Table 7. Studies with a score greater than or equal to 80 were selected according to the grading criteria shown in Figure 7.

**Table 6.** Selection criteria versus response graded.


**Figure 7.** Graded percentage of selected studies.


**Table 7.** Selected studies used for SLR analysis.





### *3.7. Data Extraction and Synthesis Process*

After collecting articles relevant to the research questions and objectives, we performed a SLR according to various characteristics, such as year of publication, limitations, and future work. The information or previously collected characteristics were integrated with the responses collected through questionnaires to summarize the information.

After an extensive and systematic review of the literature, the research questions are answered and described in the following sections. The contributions and types of WSN and IoT are respectively explained in the Sections 4.1–4.3. Before attacks network intrusions are briefly classified in Section 4.4. In contrast, network security attacks and WSN and IoT layer issues are discussed in Sections 4.5 and 4.6. In Section 4.7, we discuss the limitations and future work of the selected papers. Finally, we conclude the paper in Section 7.
