A T-carrier is a type of digital transmission system used to send data over telephone lines. It is commonly used in telecommunications to provide high-speed connections for voice and data services. The most well-known T-carrier system is the T1 line, which can transmit data at a rate of 1.544 megabits per second. T-carrier systems are structured in a hierarchy, with different levels such as T1, T3, and T4, each offering higher data rates. These systems use time-division multiplexing to combine multiple signals into a single transmission line, making them efficient for businesses and service providers needing reliable communication.