backward indicator bit (SS7) (BIB)

Structure of the Message Signalling Unit (MSU)

The Backward Indicator Bit (BIB) is a 1-bit data field from the Message Transfer Part ( MTP) of the Message Signaling Unit( MSU) in SS7 signaling. This bit is used to confirm correct or incorrect reception of the character units. In case of faulty transmission, the Backward Indicator bit is inverted. The inversion of the BIB signal is maintained until the following faulty character transmission. Only then is a new inversion performed. The Backward Indicator Bit (BIB) forms an octet together with the 7-bit long data field Backward Sequence Number( BSN).