TCP – Congestion Control #2: What is a TCP Window?

In this video I describe what a TCP Window is. I’ll be describing the “Congestion Window” which I believe is the concept widely considered to be what people are referring to when they use the term “Window”. The congestion window is the range of sequence numbers that can be placed on the wire by the sending device before requiring all sequence numbers to be acknowledged. All the sequence numbers are required to be acknowledged before a new window is sent. There are a lot other videos on YouTube about the “sliding window”. The sliding window is a term used to describe the receive side buffer and often mistaken for the congestion window. The same goes for the receive window, which is the remaining capacity of receive buffer that is reported back to the sender via the ACKs. A basic understanding of sequence numbers ACKs is required. If you aren’t familiar with these concepts, please watch my previous videos.

The command I used to create the sample capture is:
tc qdisc add dev eth0 root netem delay 2000ms

This should be run only in a lab and not on a production machine.

These are my custom Wireshark profiles for analyzing TCP segments.

Windows Profile:
http://bit.ly/2oMZlnX

Linux Profile:
http://bit.ly/2F7iY13 .