This comprises 48 bit frames which are sent and received over the S-Bus in 250 micro seconds. The frames comprise 16 bits from the B1 channel (transmitted at a rate of 64 kbit/sec), 16 bits from the B2 channel (transmitted at a rate of 64 kbit/sec), 4 bits from the D channel, (transmitted at a rate of 16 kbits/sec) and 12 framing bits (transmitted at a rate of 48 kbit/sec). This is equivalent to a total throughput of 192 kbit/sec.