Transmission level point
In telecommunication, a transmission level point (TLP) is a physical test point in an electronic circuit, typically a transmission channel, where a test signal may be inserted or measured. Typically, various parameters, such as the power of the signal, noise, or test tones inserted are specified or measured at the TLP.
Voice-channel transmission levels at test points are measured in decibel-milliwatts (dBm) at a frequency of ca. 1000 hertz. The dBm is an absolute level with respect to 1 mW. The TLP is thus characterized by the relation:
- TLP = dBm — dBm0
When the nominal signal power is 0 dBm at the TLP, the test point is called a zero transmission level point, or zero-dBm TLP. In general, the term TLP is commonly used as if it were a unit, preceded by the nominal level for the test point. For example, the expression 0 TLP refers to a 0 dBm TLP. At a −16 TLP, the measured level of 0 dBm is +16 dBm0.
- Whitham R. Reeve (1992) Subscriber Loop Signaling and Transmission Handbook—Analog, IEEE Press, p.229