This read-only counter tallies outbound frames not transmitted because they contained an unknown protocol, again only for connections using service interworking in translation mode. It's the outbound mirror of casfVcIwfCountInUnknownProts, frames this switch tried to translate for transmission but couldn't because the protocol carried on the ATM side wasn't recognized, so it climbing points to unsupported traffic originating from the ATM side rather than the frame-relay side. An ATM-attached host sending an obscure protocol toward a frame-relay-attached translation-mode peer would generate increments here instead of the frames ever reaching the frame-relay side.