The load source is the service object of the wire harness, usually refers to the user equipment; in a broad sense, the upper-level device is the load source of the next-level device. In telephone communication, the load source is also called the source, and the number of service devices included in the harness is called the harness capacity. FIG. 1 is a schematic diagram of the harness. The harness has a capacity of V, which serves N load sources. Any load source that makes a call can consume one of the idle service devices in the harness.