Backend developers are mostly interested in Spring and DB and often start learning, but the part that they actually encounter the most in practice is communication. This lecture was good because I was able to organize basic network knowledge and HTTP. This lecture is better to watch often to find the parts you forgot rather than just once. In particular, unlike other lectures, since I didn't code, I studied efficiently by looking at PDF files and imagining what Younghan said. I sincerely thank you for the great lecture!