JPS6239865B

PURPOSE:To reduce the transmission delay for the frame of high urgency, by interrupting the frame of a level higher than the frame during the transmission of frame and providing an interruption display filed for transmission priority. CONSTITUTION:In a frame transmission system performing the data transmission in frame unit, a 2-bit interruption display field INT for the transmission with priority is provided to interrupt the frame at higher level than the frame during the transmission of frame with priority with a high level data link HDLC frame. From the content of 1, 0 of bits b1, b0 of the INT field, the production of interruption to the frame during the transmission or the end of transmission of the frame is displayed, and at the end of transmission of the frame, the relation of relative levels between the frame and a frame transmitted succeedingly is displayed. Thus, the frame of higher urgency can be transmitted with interruption with priority in the longer frame and the delay in transmission can be reduced.