Leased Line Types

Leased Line Types

When customers require full-time access to a communication path, a dedicated, leased line serves as one option. Several levels of digital lines are available, including those detailed in the following list:

T1
T3
Fractional and multiple T1 or T3
Digital data service
Switched 56

A very popular digital line, T1, provides point-to-point connections and transmits a total of 24 channels across two wire pairs—one pair for sending and one for receiving—for a transmission rate of 1.544 Mbps. T3 is similar to T1, but T3 has an even higher capacity. In fact, a T3 line can transmit at up to 45 Mbps.

Very few private networks require the capacity of a T3 line, and many do not even need the full capacity of a T1. The channels of a T1 or T3 line thus can be subdivided or combined for fractional or multiple levels of service. For instance, one channel of a T1’s 24-channel bandwidth can transmit at 64 Kbps. This single-channel service is called DS-0. DS-1 service is a full T1 line. DS-1C is two T1 lines, DS-2 is four T1 lines, and DS-3 is a full T3 line (equivalent to 28 T1s). A level of service called T4 is equal to 168 T1 lines.

Microsoft reportedly has three T3 lines going into Redmond.

Digital Data Service (DDS) is a very basic form of digital service. DDS transmits point-to-point at 2.4, 4.8, 9.6, or 56 Kbps. In its most basic form, DDS provides a dedicated line. A special service related to DDS, Switched 56, offers a dial-up version of the 56 Kbps DDS. With Switched 56, users can dial other Switched 56 sites and pay only for the connect time.