zero transmission level point

In a transmission system, a point chosen as the reference level for measuring and expressing all relative transmission levels, including electronic, optical, and sound power levels. Common abbreviation OTLP. Note 1: The absolute power level at the zero transmission level point (OTLP) is measured and defined as such. Usually it is not zero dBm (0 dBm), i.e., not one milliwatt (1 mW). Note 2: The point chosen for the zero transmission level point (OTLP) usually is a conveniently accessible point, such as the input of a transmission line. For instance, if the input point to a transmission line is chosen as the zero transmission level point (OTLP) and it has a 100 mW(milliwatt) absolute power level, and a measurement at a point. A somewhere along the line has a power level of one milliwatt (1 mW), then the power level at point A is −20 dBaO or −20 dBr, i.e., 20 dB below OTLP. Note 3:The zero transmission level point may be (a) a point in an electronic circuit or an optical circuit and...