What is a T-1?

What is a T-1?
When telecom professionals say “T-1,” they probably mean one of the following four definitions:

- Access T-1: A connection from the customer’s premise to a long-distance carrier that provides access to the public-switched network. Access T-1s are generally provided by the local telephone company, but it is common for customers to receive a bill directly from the long-distance carrier (see Figure 1).


Figure 1: Customers use access T-1s to connect to their long-distance carriers.

- Internet T-1: A connection to an ISP. Medium to large-size companies use Internet T-1s for e-mail, Internet access, and Web hosting (see Figure 2).


Figure 2: Customers use T-1s to connect to their ISP.

Point-to-point T-1: A dedicated private line between two customer sites. Customers use these fixed connections for data and voice traffic between locations. If voice traffic is carried on the T-1, this is called a tie line, because the T-1 ties the two locations together (see Figure 3).


Figure 3: Customers use point-to-point T-1s to share data and voice traffic between locations.

- T-1 Bandwidth: Equals 1.544 Mbps, the capacity needed to carry 24 simultaneous phone calls.

T-3 service
T-3 service has 44.736 Mbps of bandwidth available. T-3s are normally only used by corporations and large universities. A T-3 has the capacity of 28 T-1s and can carry 672 simultaneous voice conversations. One T-3 usually costs the same as 8 to 10 T-1s.

All of these examples use dedicated private line technology. Circuit switching and packet switching are different technologies, but they are still measured by bandwidth.