Flow control is used to prevent or reduce the dropping of frames due to the lack of buffer space. Overall, networks are more efficient when a sending station is asked to pause in its sending process, rather than having the transmitted frames dropped. Flow control is not as efficient when used in conjunction with a shared ports, i.e. when used with a repeater. Therefore, flow control is not recommended for a port connected to shared topologies. Flow control is most effective when the port is directly connected to an end-station, especially when connected to a server. Flow control is recommended for ports connected directly to end-stations. When the port is in half-duplex mode, back pressure is used to control the incoming flow. Back pressure essentially forces collisions for short periods of time. When the port is in full-duplex mode, IEEE 802.3 standard pause frames are used to control the incoming flow. Note that setting an ether-gigabit(4) port to enable-with-aggressive-backoff(3) results in an error.