I have 2 linux machines connected over the serial port using an external wireless modem. I'm using ppp. I was trying to inject noise in to the channel and observe how tcp performs. My understanding of congestion control algorithms is that if there is packet loss tcp reduces its window size to avoid congestion. I'm using tcpdump to study packet loss and tcp headers. I can see that packets are getting lost and tcp is retransmitting. But the window sizes are not changing. Initially when I'm setting up the link the window size starts at 512 and then from the next transmission on is 32000.
So I'm not seeing either slow start or congestion control algorithms. Am i missing something. Please help me if anyone knows whats going on.