open TCPDUMP, "tcpdump -e -i $interface ether src $dst_hw_addr|" or die "Can't open tcpdump.\n";

sub get_rssi {

	my $rssi = undef;
	while (!defined $rssi) {
		my $line = readline(TCPDUMP);
		if ( $line =~ m#(?<sig_level>-\d{1,3})dB signal.*QoS#ig ) {
			$rssi = $+{sig_level};
		}
	}
	$rssi;
}