Impedance discontinuity causes energy reflection. With the presence of an impedance discontinuity in the transmission path, part of the transmitted signal reflects back to the transmitter and is not detected by the receiver. Each discontinuity reduces the amount of signal that is delivered to the receiver. In addition, multiple reflections distort the forward propagating waveform. Common sources of discontinuities include package-to-PCB interfaces, PCB vias, surface-mount device (SMD) footprints, connectors, and cable-to-connector interfaces.