If you are interested in having a fast internet connection, it is a good idea to have a T1 connection.  This T1 connection is also known as a DS1 connection.  If you are looking at getting a T1 connection, you should think about the details involved in a DS1 connection.  To start, DS1 signals are used to connect equipment within a facility. In this case, a low-level signal called the DSX1 is used. DSX refers to a digital signal cross connect, and it is essentially a patch panel allowing easy interconnection. When a DS1 leaves the building, it becomes a T1 and is referred to as a span.

Keep in mind that the signal is boosted to a higher level and superimposed on a DC voltage, enabling repeaters in the field to be powered from the span itself. Repeaters are placed every few thousand feet, to clean up and strengthen the signal.

It is good to know that DS3 signals are almost exclusively used within buildings, for interconnections and as an intermediate step before being onto a SONET circuit. This is because a T3 circuit can only go about 600 feet between repeaters. When a customer orders a DS3, they usually get a SONET circuit run into the building and a multiplexer mounted in a big cabinet. The DS3 is delivered in its familiar form, two coax cables with BNC connectors on the ends.

Remember that carriers price DS1 lines in many different ways. The loop price has several components built into it, including the mileage calculation and the telco piece. Hence, the price calculation has two distance steps: geomapping and the determination of local price arrangements. For voice DS1 lines, the calculation is mostly the same, except that the port is replaced by LDU.

As soon as the price of the loop is determined, only voice-related charges are added to the total. In short, the total price = loop + LDU x minutes used. The T-carrier system traditionally uses in-band signaling or bit robbing, resulting in lower transmission rates than the E-carrier system. This resulted in many US ISDN installations only having an effective data rate of 56 kbit/s over a nominal 64 kbit/s channel. See also A&B.

It is good to know that in the late 1960s and early 1970s Bell Labs developed higher rate systems. T-1C with a more sophisticated modulation scheme carried 3 MBPS, on those balanced pair cables that could support it. T-2 carried 6.2 Mbit/s, requiring a special low-capacitance cable. This was standard for Picture phone. T-4 and T-5 used coaxial cables, similar to the old L carriers used by AT&T Long Lines.

In addition, a TD microwave radio systems were also fitted with high rate modems to allow them to carry a DS1 signal in a portion of their FM spectrum that had too poor quality for voice service.