traffic log would list an application as "not-applicable" if the firewall denied the traffic before the application match could be performed. This can happen if the traffic matches a security rule that is set to deny based on any parameter other than the application, such as source, destination, port, service, etc1. In this case, the firewall does not inspect the application data and discards the traffic, resulting in a "not-applicable" entry in the application field of the traffic log1.