finally, since the xoff/xon codes are sent in-band, they cannot appear in the data being transmitted without being mistaken for flow control commands. any data containing the xoff/xon codes thus must be encoded in some manner for proper transmission, with corresponding overhead. this is frequently done with some kind of escape sequence. for printing devices that directly interpret ascii codes, this is not a large problem, because the xon and xoff codes use ascii "device control" code numbers.