Great summary of SIP CANCEL messages. Thank you very much Andrew!
As I have said on a number of occasions, I occasionally teach a two and half day SIP class. While that’s hardly enough time to become a SIP expert, my students always leave with more than enough knowledge to make educated decisions in regards to SIP endpoints, applications, and trunks. Although some may never again have a compelling reason to use Wireshark to trace SIP call flows, just knowing that they can is often good enough.
Every class is different and no two students are alike, but I find commonality in the things that they absorb quickly and the things that require a little more explanation. One of those from the latter camp is the CANCEL request.
On the surface, CANCEL doesn’t sound too complicated, but there are a few aspects that are a wee bit confusing.
Before I delve into the details, let’s take a look at a basic…
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