Controls whether the X.25 Q-bit (Qualified Data Bit) is accessible by the user. It expects an integer argument. If set to 0 (default), the Q-bit is never set for outgoing packets and the Q-bit of incoming packets is ignored. If set to 1, an additional first byte is prepended to each message read from or written to the socket. For data read from the socket, a 0 first byte indicates that the Q-bits of the corresponding incoming data packets were not set. A first byte with value 1 indicates that the Q-bit of the corresponding incoming data packets was set. If the first byte of the data written to the socket is 1 the Q-bit of the corresponding outgoing data packets will be set. If the first byte is 0 the Q-bit will not be set.