8 bits per sample x 8000 samples/sec = 64,000 bits/sec
So for data channels (23B +1D), times the 64,000 bits/sec by 24 (24 channels) = 1536k. This is the TRUE throughput, since throughput is referred to as the amount of DATA that you can cram down a pipe.
Many people think that it is 1.544Mbps, but this is technically inaccurate as this accounts for the 8k of framing that is on top of the 1536k. So the routers may talk to each other with a total of 1.544Mbps, but usable circuit size for data packets is still 1536k.