The KAD/ARR/101 is designed with two Ethernet network interfaces, which monitor network traffic on dually redundant A664P7 Ethernet links.

The A664P7 redundancy remover captures frames on the two A664P7 links and performs error checking, such as Ethernet frame check sequence and the IP header checksum, on the received frames. Valid frames are buffered to facilitate filtering of redundant frames captured on the two A664P7 links. Each A664P7 frame has a Virtual Link IDentifier (VLID) in the destination field and a sequence number, which increments by one with each frame. The first A664P7 frame on a virtual link received after reset/startup is sent to the redundancy remover. That VLID and Sequence Number (SN) are stored and any subsequent frame on that virtual link, with a sequence number equal to SN+1 or SN+2, is passed to the redundancy remover, and the new sequence number is stored. For any frames received on that virtual link with a sequence number not equal to SN+1 or SN+2, the new sequence number is stored but the frame is discarded.

Redundant copies are identified by having the same VLID and SN. The first A664P7 frame with a unique VLID and SN is sent directly to the output Ethernet interfaces. If another A664P7 frame with the same VLID and SN is received less than 5 ms later, it is considered redundant and is not output. Should a redundant copy arrive in this time frame it is removed. The filtered frames are then output unchanged on two Ethernet network interfaces after a fixed latency.