When to use it
When you have no capture but you do have the PBX log. Most problems are visible in signalling: a private IP in SDP (no audio), a missing ACK (call drops after 32 seconds), codec mismatch (488), a wrong password (repeated 401), DTMF not negotiated (menu keys do not work). If you have a pcap, load it into the pcap analyzer: it also measures audio quality.
STIR/SHAKEN
Carriers in the US and Canada sign the caller’s number: the Identity header carries a PASSporT token with attestation A, B or C. A means the carrier knows the customer and their right to the number. Calls with C or no signature are more often flagged as spam.