This value records which combination of forward ATM traffic descriptor parameters (peak cell rate, sustained cell rate, maximum burst size, tagging) was requested for this failed call, per the description, chosen from a defined set of PCR/SCR/MBS combinations or unknown(8). This lets an admin see whether calls requesting a particular traffic profile -- say, a specific PCR/SCR/MBS combination used by a certain application -- are the ones disproportionately failing, which would point at a QoS/CAC (call admission control) mismatch on this port rather than a general signaling problem. A cluster of failures all showing the same non-default traffic descriptor type is a strong CAC-related clue.