http://fivedots.coe.psu.ac.th/~touch/241-101/Introcom253/Lecture/Chapter6-Structure/Chapter6-Structure-253.ppt
https://apipong.weebly.com/uploads/5/3/5/8/53586393/bs113_lect11_structure.pdf
https://home.kku.ac.th/urachart/intro/structure.pdf