TPCAT is based upon pcapdiff by the EFF. TPCAT will analyze two packet captures (taken on each side of the firewall as an example) and report any packets that were seen on the source capture but didn’t make it to the dest. See docs for info.
PcapDiff is a perl script based on Net::Pcap intented to corelate pcap files from endpoints(precise latency calculation, protocol conformance checks, firewall/router misbehaviour detection etc).