1. Field of the Invention
This invention generally relates to telecommunications and, more particularly, to maintenance termination units for locating trouble in a telecommunications network.
2. Description of the Related Art
Maintenance termination units help locate trouble in a telecommunications network. When trouble is reported, that trouble may lie within the customer's premises and/or within the local loop serving the customer. Maintenance termination units have been used to help determine whether the trouble lies within the local loop or within the customer's premises.
U.S. Pat. No. 4,529,847 to DeBalko (issued Jul. 16, 1985) shows a maintenance termination unit. This maintenance termination unit comprises a pair of “normally open” voltage switches connected between the ring and tip of the local loop (see Column 3, lines 30–33). When this maintenance termination unit is installed at the customer's premises, the maintenance termination unit produces a distinctive, periodic DC signal (see Column 4, lines 37–50). When a fault lies within the customer's premises, this distinctive, periodic DC signal is produced regardless of polarity between the ring and the tip (see Column 4, line 63–Column 5, line 1). If trouble lies within the telecommunications network, then the maintenance termination unit produces either a steady signal (a “hard” fault) or a periodic signal (a “light” fault) (see Column 5, lines 1–7). Because this maintenance termination unit utilizes voltage switches, these switches unfortunately cycle between an open position and a closed position when indicating the presence of a fault (see Column 4, lines 46–48). This periodic signal is often confused by test technicians and leads to an inaccurate diagnosis. This constant cycling, between an open position and a closed position, also leaves little time to conduct a test of the local loop.
Other maintenance termination units have disadvantages. Many of these prior art maintenance termination units utilize custom, integrated circuitry. These integrated circuits are expensive and time-consuming to design and to fabricate. The expense of designing and fabricating these circuits, in fact, is often cost-prohibitive. Even when an integrated circuit is used, the harsh, ambient environment leads to many field failures. When the integrated circuit fails, the entire maintenance termination unit is then wastefully discarded.
There is, accordingly, a need for an improved maintenance termination unit that is easier to use, less expensive to design and to manufacture, tolerant of ambient conditions, and cheaper to repair or replace in the field.