This OID stores the four receive signaling bits (ABCD) as a 4-character string of 1's and 0's, representing the bits arriving from the far end on a voice interface. Network engineers monitor this to ensure the far end is sending the expected signaling bits and to detect mismatches that indicate communication problems. For example, a value of '0101' means the received bits are A=0, B=1, C=0, and D=1.