This 16-byte octet string captures the destination and source SMDS addresses of the last PDU that triggered the 'Dst Ia Scrn Fail' violation, meaning the destination individual address failed the switch's screening check -- the destination exists but this port isn't authorized to reach it. An admin decoding this pair can identify a device attempting to send SMDS traffic to a destination it isn't permitted to reach under the current address screening policy, distinct from an address simply not existing. For example, this would fire if a customer's device tried to reach another customer's address that the network's screening rules explicitly block from this port.