rate is a swiss-army-knife commandline traffic analysis tool, designed to help a network administrator to see what is happening at a router at the moment.
Unlike tcpdump(1), rate uses statistical and stream-oriented methods, and will never produce an output stream at a speed beyond human perception. The output is less accurate, however.
Rate features four different operating modes, designed to perform the following tasks: estimating overall traffic rates, determining nodes generating the highest traffic, determining connections and flows generating the highest traffic and extracting strings from packets.