Telecommunications Industry Association
TR41.3.3-10-08-009L
Document Cover Sheet
Project Number
PN-3-4705.110-RV1
Document Title
Several telecommunication definitions pertaining to Reference Codec.
Source
Texas Instruments
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Name:
Warren Karapetian
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20450 Century Blvd.
Germantown, MD 20874
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Email:
301 407-9307
wkarapetian@ti.com
TR-41.3.3
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The document to which this cover statement is attached is submitted to a Formulating Group or
sub-element thereof of the Telecommunications Industry Association (TIA) in accordance with the
provisions of Sections 6.4.1–6.4.6 inclusive of the TIA Engineering Manual dated March 2005, all of
which provisions are hereby incorporated by reference.
Abstract
The following text was provided as a set of definitions suitable for the Appendix section of Transmission
Requirements for Wideband Digital Wireline Telephones document(s). Definitions are presented in an orderly
fashion to allow readers to comprehend subtleties involved in the definition of the dBm0, and its relationship to
signal levels present in a telecommunications network. The final section highlights dBm0 relationship for various
types of codecs and transcoding related issues. However, the last section may be omitted if deemed unnecessary.
dBm: (sometimes also called dBmW) is an abbreviation for the power ratio in decibels (dB) of the measured
power referenced to one milliwatt (mW). The logarithmic expression for power, referenced to 1 milliwatt is dBm =
10 log (power / 1 mW). For electrical power level measurements, 0 dBm can also be referred to as the power of
0.775 volts RMS Sinusoidal signal applied across a defined resistive load (often 600 Ohms in
telecommunications), which results in a reference active power level of 1 mW. Note: specifying dBm without
specifying the impedance may be misleading. For digital networks, since there is no impedance used, it should also
be defined by the corresponding Sinusoidal peak code value (dBFS, or dBov) for the given codec.
dBov/dBFS: dBov stands for dB overload. It is the rms signal level of a digital signal relative to the overload or
maximum peak level of the digital format. This is also commonly referred to as dBFS (Full Scale). For example, a
rectangular function with only the positive or negative maximum number is 0 dBov; a single frequency tone with
peak at maximum level is -3.01 dBov. Note: 0dBm0 equals (-3.17-3.01) = -6.18 dBFS
TLP-Max: Maximum Transmission Level Point is defined as the maximum dBm power measured across a defined
impedance (e.g. 600 Ohm resistive) by applying a full scale (0 dBFS or dBov) Sinusoidal signal (just below its
clipping point). Consequently, Max-TLP for A-law and μ-law codecs in a system, are defined as +3.14 dBm and
+3.17 dBm, respectively.
0-TLP: Zero Transmission Level Point is an arbitrarily established point in a system relative to which transmission
levels at all other points in the system are measured. 0-TLP for A-law and μ-law codecs in a system is defined as 3.14 dB and -3.17 dB, below TLP-Max, respectively. In digital transmissions networks, the 0-TLP is often referred
to as 0 dBm0, which is also equivalent to 0 dBm).
dBm0: Is defined as the power level in dBm relative to a reference point called the Zero Transmission Level Point,
or 0-TLP. This level for A-law and μ-law codecs is defined as -3.14 dBm0 and -3.17 dBm0 below the full scale (or
TLP-Max.), respectively. Consequently, for an A-law and μ-law codecs, the 0 dBm0 (which is also referred to as 0
digital reference point or digital milliwatt) and 0-TLP are all the same, and may be used interchangeably. Also note
that 0-TLP, sometimes is referred to as 0 dBr (or dB relative to 0 dBm) in some of the earlier telecom literature.
The following section provides further details. However, it may be omitted if deemed unnecessary:
For the purposes of this standard, 0 dBm0 (or 0-TLP) is the RMS level of a Sinusoidal wave with -3.17 dB
below L16-256 TLP-Max level, and -9 dB below G.722 codecs TLP Max level. Consequently, the 0 dBm0 digital
reference point may be defined for 0 dBm Sinusoidal test signal considering the following TLP-Max designations:
Codec Type
A-law
Defined TLP-Max in dBm
at 600 Ohm
+3.14
0 dBm0 reference point
is defined as 0 dBm at
(TLP-Max) – 3.14
μ-law
+3.17
(TLP-Max) – 3.17
L16-256
+3.17
(TLP-Max) – 3.17
G.722
+9.00
(TLP-Max) – 9.0
Note: It is the responsibility of the transcoder to correctly implement the digital full scale to dBm0 level translation
for each codec when digital signals are translated from one codec format to another, and to ensure that dBm0 levels
at one port of the transcoder are correctly translated to the same dBm0 levels at the other port of the transcoder.
This simply means that a continuity test tone (1004 Hz) entering one end of the network at 0 dBm level
(terminated with 600 Ohm impedance), should produce a 0 dBm output signal across 600 Ohm load on the other end
of the network independent of any codec types or transcoding used in between the two points.