As a very interesting aside, wouldn't it be wonderful if one could actually trace the flow of the sender and receiver processes as they execute? Well, Linux provides several tools to do precisely this. Among the more sophisticated ones is a software called Linux Tracing Toolkit next generation (LTTng).
LTTng is really powerful; once set up, it has the ability to trace both kernel and user space (although tracing user space involves the application developers explicitly instrumenting their code). Well, your author used LTTng to perform a trace of the system (kernel-space) while the previous processes ran; LTTng did its job, capturing trace data (in a format called CTF).
Then, the superb Trace Compass GUI application was used ...
