DSL (Broadband Connection Delivered over POTS lines (Plain-Old-Telephone-Lines).

T1 = 1.544Mbps Connection composed of 24-64Kps channels called DS0s When attached to a phone system you can attach 24 phones to each end of the DS0s for voice converstations. or they can call be used together or in groups for fractional-data/voice services.

Assuming that you are interested only in the data-communications aspect of DSL/T1/T3 A T1 = 1.544Mbps this is bi-directional.

A T3 line works just like a T1 however it has the capacity of about 28 T1 lines giving it a combined bandwidth of 43.232Mbps this is bi-directional.

Hope this helps :-)