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While the standalone version of tcptrace is rarely used these days, the basic approach and much of its functionality lives on as part of toolsets such as WireShark.
For a good explanation of tcptrace-style graphs and how to use them, check out Stuart Cheshire's (Apple) section of a WWDC (World Wide Developer Conference) 2015 presentation about what a difference ECN and CoDel make for the behavior of TCP bulk transfers.
Example usage
This shows the sessions in a tcpdump log:
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