This value identifies which PDU type carried the cause information element that explains this failed call, per the description, chosen from release(1), addPartyReject(2), or dropParty(3). Knowing which PDU carried the failure cause tells you whether this was a whole-call failure (release) or a multiparty-specific failure (addPartyReject or dropParty), which determines whether you should be looking at basic SVC setup logic or the multipoint call features on this port. An entry showing addPartyReject(2) points specifically at the multiparty ADD PARTY handling path rather than ordinary point-to-point call setup.