Please explain about T-carrier digital multiplexing hierarchy.

What I know about it? => It is a system/way of making digital multiplexing channels for voice signals transmission.

I got confused, at these things 1) DS-1 transmission format is the basis of TDM hierarchy in North America and Japan( William Stallings). It says that DS1 transmission format muxes 24 channels. Each frame contains 8 bits per channel plus a framing bit...i.e 193 bits.

So, we take 8000 samples/sec, and the speed becomes 1.544 Mbps.

Now, another source(some ppts) sas that T-carrier in North America means DS0 hierarchy. WTF? What about T1 carrier? Is it DS1? Or, what?