I have experienced HTTP communication through API calls while working on various projects, but when I actually opened the book to study network theory, it felt far removed from practice and was difficult to understand. (In particular, the part about the hierarchical structure was confusing...) Then I came across this lecture, and it was good because it explained the basic network concepts that web developers should know through real cases and practice, rather than theoretical explanations that were difficult to understand. In addition, I was able to learn more easily thanks to the instructor's clear explanations and well-organized lecture materials including various example codes. Above all, I was able to understand the overall operating principles of the network more clearly by checking how HTTP messages are exchanged in actual data transmission and request/response processing in the browser, and hearing an explanation of how these HTTP messages are divided into packets and transmitted. In addition, I was able to gain specific knowledge that can be applied immediately in practice, such as how to store state information in communication between clients and servers, so I think it will be very useful in the future. I recommend it to aspiring web developers or junior developers who are afraid to open a thick network theory book.