T1 and T3 - technical definition

A cost-effective way of linking voice and data, both between offices and within offices. These technologies act as alternatives to high-speed modems for data transportToday, there is quite a bit of discussion about T1 Gateways and T1 trunks, primarily because the cost of these services continues to decrease. Consumers are finding that it costs them less to have a T1 trunk than to have a number of leased telephone lines in a point-to-point topology. In basic terms, T1 is a high-speed digital network (1.544 mbps) developed by American Telephone & Telegraph (AT&T) in 1957. This technology was implemented in the early 1960s to support long-haul, pulse-code modulation (PCM) voice transmission. During its inception, the main innovation of T1 was that it introduced “digitized” voice, thus creating a network that was fully capable of digitally representing what was until then a fully analog telephone system.

The AT&T Digital Carrier System CCUNET T1.5 was a two-point, dedicated, high-­capacity, digital service provided on land digital facilities and capable of transmitting 1.544 Mb/s. The interface to the customer was either a T1 carrier or a higher-order multiplexed facility—used to provide access from fiber optic and radio systems. Thus, in the basic definition of T1, there is a higher order, or hierarchy, of T1. There was T1, a network having a speed of 1.544 Mbps and designed for voice circuits or channels (24 per each T1 line or “trunk”). There was also T1-C, operating at 3.152 Mbps, and T-2, operating at 6.312 Mbps and implemented in the early 1970s to carry one Picturephone channel or 96 voice channels. Finally, T-3, operating at 44.736 Mbps, and T-4, operating at 274.176 Mbps, were known as “supergroups”; their operating speeds were generally referred to as 45 Mbps and 274 Mbps, respectively.