In telecommunications, a transmission level point (TLP) is a test point in an electronic circuit that is typically a transmission channel.
[1] Various parameters, such as the power of the signal, noise, voltage levels, wave forms, may be measured at the TLP.
Voice-channel transmission levels at test points are measured in decibel-milliwatts (dBm) at a frequency of ~1000 hertz.
The abbreviation dBm0 stands for the power in dBm measured at a zero transmission level point.
[3] The level at a TLP where an end instrument, such as a telephone set, is connected is usually specified as 0dBm.