This value records the forward QoS class that had been requested for this failed call, per the description, an integer coding the class of service (e.g. CBR-like versus best-effort characteristics) negotiated in the forward direction. This is the field to check alongside the traffic descriptor parameters when a failure's cause code suggests a service/QoS incompatibility, since it tells you what class of service this particular call was asking for when the network couldn't grant it. A run of failed calls all requesting the same demanding QoS class would point at that class being over-provisioned or unsupported on this trunk.