T1 T2 Lines
T1 and T3 lines are basically leased lines, which are used in the field of telecommunications. They are an example of reserved circuit communication that works through fiber optic cables and copper wiring.
They are called ‘leased lines’ because they are leased by companies to form connections between offices for the purpose of networking offices in different locations. They are quite expensive to rent which is probably why it is mostly corporations that use them.
T1 lines are use in accordance with the T1 standard, created by AT&T. there transmission rate is that of symmetric DSL(1.5mbps). Fractional T1 lines operate at 128kbps ad are a little lower in cost, so it might not be too surprising to find them in heavily residential buildings. The cost for a full T1 line is $1000/month.
The T3 standard is an amalgamation of 28 T1 lines. Its operating bandwidth is 44.7 mbps. These are superb for long distance data transmission and are used by businesses for building up the core at headquarters. They are phenomenally expensive at $3000/month.
There are other standards too, such as T2, T4 and T5 but they are rather unpopular and generally unheard of.