Editing Transmission level point

{{Short description|Test point for signal monitoring}}

In [[telecommunications]], a '''transmission level point''' ('''TLP''') is a [[test point]] in an [[electronic circuit]] that is typically a [[transmission channel]]. At the TLP, a test [[signal]] may be introduced or measured.<ref name=reeve>Whitham D. Reeve (1992) ''Subscriber Loop Signaling and Transmission Handbook—Analog'',  IEEE Press, p.229</ref> Various parameters, such as the [[power (physics)|power]] of the signal, noise, voltage levels, wave forms, may be measured at the TLP.<ref name="tia">{{cite web
|url=https://standards.tiaonline.org/market_intelligence_/glossary/index.cfm?term=%27%234SQRB%2BHJDE%24%0A
|title=Transmission level point (TLP)
|work=Glossary of Telecommunication Terms
|publisher=Telecommunication Industry Association (TIA)
|access-date=2023-05-19
}}</ref>

The nominal transmission level at a TLP is a function of system design and is an expression of the design [[Gain (electronics)|gain]] or [[attenuation]] (loss).

[[Voice channel|Voice-channel]] transmission levels at test points are measured in [[dBm|decibel-milliwatts]] (dBm) at a [[frequency]] of ~1000 [[hertz]].

The [[dBm]] is an absolute reference level measurement (see {{Slink|Decibel|Suffixes and reference values}}) with respect to 1 mW power. When the nominal signal power is {{gaps|0|dBm}} at the TLP, the test point is called a ''zero transmission level point'', or ''zero-dBm TLP''. The abbreviation [[dBm0]] stands for the power in [[dBm]] measured at a zero transmission level point. The TLP is thus characterized by the relation:<ref name="reeve" />

:TLP = dBm — dBm0

The term ''TLP'' is commonly used as if it were a unit,<ref name="tia"/> preceded by the nominal level for the test point. For example, the expression ''{{gaps|0|TLP}}'' refers to a ''{{gaps|0|dBm|TLP}}''. If for instance a signal is specified as -13 dBm0 at a particular point and -6 dBm is measured at that point, the TLP is +7 TLP.<ref>{{Cite web |last=Reeve |first=Whitham D. |date=1996 |title=Application Note No. 8 |url=https://reeve.com/Documents/Transmission%20Level%20Point%20No8.pdf |url-status=live |archive-url=https://web.archive.org/web/20230201062929/https://reeve.com/Documents/Transmission%20Level%20Point%20No8.pdf |archive-date=2023-02-01 |access-date=2023-06-26 |website=reeve.com}}</ref>

The level at a TLP where an [[end instrument]], such as a [[telephone]] set, is connected is usually specified as {{gaps|0|dBm}}.

==See also==
* [[Alignment level]]
* [[Nominal level]]
* [[Digital milliwatt]]

==References==
{{reflist}}

==External links==
*[https://link.springer.com/referenceworkentry/10.1007/1-4020-0613-6_21341 Zero transmission level point]


[[Category:Telecommunications engineering]]