This is a cumulative count of characters received on this port since the last node, port, or statistics reset. Since this device's ports are character-oriented (async, PAD-style) rather than purely packet-oriented, tracking characters rather than just packets or frames gives an admin a finer-grained view of exactly how much raw traffic has flowed inbound on a specific serial circuit. For example, comparing this counter's growth rate across a shift would reveal whether a particular terminal port is unusually chatty.