T-Carriers Hierarchy and Difference
A T1 line is equivalent to a group of 24 voice grade lines, which means its capacity is 1.544 million bits per second (mbps).
A T2 trunk has a capacity of 96 voice circuit equivalent (6.312 mbps), T3 has a 672 voice circuit equivalent (44.736 mbps) and T4 has a 4,032 voice circuit equivalent (139.264 mbps).
T-carriers are used mainly to carry analog voice signals that have been digitized, while the nomenclature of DS represents the arrival of true end-to-end digital circuits.