ISDN LAPB and ISDN LAPD deflection - conversion manner and system null

摘要

PURPOSE: To perform highly reliable transformation by inspecting an LAPB frame for an address field and, when the response or command pattern in the address field is not coincident, invalidating the frame. ;CONSTITUTION: An LAPB frame is received by means of a control mechanism 28 through a bus 22. The mechanism 28 directly transmits the LAPB frame through an ISDN LAPB channel which does not require format conversion, but delivers the frame through a converter 30 and multiplexer 32 when the mechanism 28 transmits the frame through an ISDN LAPD channel. After passing through the multiplexer 32, an LAPD frame is processed by means of an HDLC chip before transmission in order to add flag field and CRC inspections to the frame. The converter 30 receives all frames and information designating the numbers of bytes in the frames from the mechanism 28 for transmission. Similarly, data are first received at a terminal as a bit stream from a transmission line, but a frame is assembled by means of a lower-order ISDN layer before the data arrive at the converter 30.;COPYRIGHT: (C)1994,JPO