I am trying to learn about Congestion Control in TCP and in this video (at 1:56), he says if there is no ack received, it assumes network congestion and cuts back the cwnd, no where he mentions about re transmitting the packet.
This article on the other hand mentions that if there is no ack received within the expiry of the timer, the packet is simply re transmitted and doesn't mention about cutting back the cwnd. My question is, in this case, how is congestion really detected if the packet gets successfully delivered after re transmission?