Estimating Congestion Window Sizes in Python using DPKT from pcap file

Question

I am currently completing an assignment for a Networking course related to parsing PCAP files and outputting some information about the TCP flows. I have pretty much finished but I've been stuck on one part for days. This part of the assignment requires us to estimate the first 3 congestion window sizes in a flow (estimated at the sender) and to comment on how the congestion window size grows. Currently, the congestion window has been described to me as the number of packets sent in one RTT. From this information, I attempted to count the number of transactions from sender to receiver and add it to a list whenever a response was received from the receiver. Though, I seem to be getting a ton of different values even though it seems like I should only be getting a few. Is there anything I'm missing? Any advice or information on how to estimate congestion window sizes in a flow using DPKT in Python 3 would be greatly appreciated. Thanks!