Question 1/IV - Terminology and definitions (continuation of Question 1/IV, studied in 1985-1988; revised wording) What additions or changes are required to Study Group IV's terminology and definitions for use in the M, N and O Recommendations? Some of the terms and issues needing attention (see Annex 1) in regard to terminology and/or definitions are: -data transmission systems, data transmission circuits, data transmission links and digital blocks; -TMN Vocabulary, i.e., maintenance, operations, management, administration and the application and use of the OSI management list of applications functions; -alarms and performance monitoring terms; -logarithmic quantities and associated unit designations used in specifying and measuring signal levels (see Annex 2); -semi-permanent circuits (Virtual connections, etc.); -harmonization of terms appearing in both Recommendations M.300 and G.701; -terms for sound programme and television circuit maintenance; -terms for television distribution via satellite to television receive stations only (TVROs); -terms for videoconference systems; -international telecommunication service (see Recommendations M.10, M.93, etc.); - quiet termination. Note - Account will need to be taken of the interest of other Study Groups. ANNEX 1 (to Question 1/IV) Organization for the study of Question 1/IV Study Group IV is of the opinion that studies of maintenance terminology should be progressed under the leadership of a Special Rapporteur for Terminology appointed by the Study Group. Further, each of the Working Parties in Study Group IV should appoint a Terminology Expert who would represent the Working Party to coordinate a unified view of maintenance terminology within the Study Group. It is expected that each Working Party would propose appropriate terminology and definitions within its areas of expertise. Then the Working Party representative would bring the results of these initial studies to the Special Rapporteurs' Group working under Study Group IV to harmonize the views within the Study Group and to establish and maintain the appropriate Recommendations. ANNEX 2 (to Question 1/IV) Logarithmic quantities and special unit notations (Information submitted by the Danish Administration) 1. General concepts related to quantities and units In physics and in all the activities where knowledge of physics is applied, such as telecommunication, we find quantitative expressions and relations describing the phenomena of the physical world. This description of physical phenomena is made by means of physical quantities. Physical quantities may be defined either as base quantities or as derived quantities. Base quantities are quantities which are considered to be independent of each other. A based quantity is defined by the way in which it is measured. Derived quantities are defined through a mathematical relation describing a given physical situation. In order to be able to write equations between the quantities and to make calculations with them the quantities must have a known mathematical structure and it must be possible to express relations between different quantities. The defining method of measurement for a base quantity also serves as a basis for the definition of the sum of two elements of that quantity. Since it is also possible to define the product of a number (e.g. a real number) and an element of the quantity as a new element of that same quantity, the quantity is seen to have the mathematical structure of a linear space or vector space. Expressed very loosely, multiplication or division between two elements of the same or different quantities is possible because each quantity is defined "linearly", i.e. as a vector space. Thus, we can express relations between quantities and carry out calculations according to rules similar to those for ordinary numbers, remembering that addition is defined only between elements of the same quantity. The definition of other mathematical operations or functions is in general not possible for all quantities, but is restricted to special cases. The operation consisting in taking the logarithm of a quantity can be defined only when the quantity is a so- called dimensionless quantity, i.e. the quantity has the mathematical structure of a number field. A system of quantities is defined through a given set of base quantities and a set of rules for defining derived quantities, making it possible to decide whether or not a given quantity belongs to the system. Any element, or value as it is usually called, of a quantity is expressible as the product of a number and a specific value of the quantity chosen for reference. The number is called the numerical value of the quantity for the given choice of unit, and the reference value chosen is called the unit. Similar to a system of quantities it is possible to speak of a system of units. Most simply a system of units consists of a set of independently defined base units, each corresponding to a base quantity, and a set of derived units corresponding to the derived quantities. If each derived unit is defined from the base units as the same function as the quantity itself is defined from the base quantities, only that the numerical factor is always 1, then the system of units is called a coherent system of units with respect to a given system of quantities. The International System of Units (SI) adopted and recommended by the General Conference on Weights and Measures is a coherent system of units. The symbols used in physical equations may represent physical quantities, i.e. the product of a number and a unit. Such equations are called quantity equations. The symbols may also be taken to represent only the numerical values of the quantities for a given set of units. The equations are then called numerical value equations. Numerical value equations will depend on the choice of units, whereas quantity equations in a given system of quantities are independent of the choice of units. But the description of the same physical situation in two different quantity systems will in general lead to two different quantity equations. The subjects related to the definition of quantities and units, the use of quantity equations and also the mathematical reasoning justifying the use of quantity equations have been treated in various places in the literature. There are also international standards and vocabularies in this field [1], [2], [3], [4] and [5]. Of these [1] and [2] are known to be under revision at present in the bodies responsible for them. 2. Logarithmic quantities A logarithmic quantity is a quantity which may be expressed as the logarithm of another quantity which must be a number (e.g. the ratio of two quantities of the same kind, or the number of events, states or elements of some sort). A general definition of a logarithmic quantity L is given by b dX Xb L = _ - = ln+ _ X Xa a which expresses that the logarithmic quantity L is the limit value of the sum of relative changes when X varies from Xa to Xb. Possible mathematical difficulties, e.g. in connection with discontinuities, are left out of consideration here. This definition serves to show that a logarithmic quantity is defined in the most simple way, i.e. without arbitrary constants, if it is defined as the natural logarithm of a ratio. In telecommunication logarithmic quantities defined from a ratio of power quantities or from a ratio of field quantities are of special interest and only these logarithmic quantities are considered here. A power quantity is power or a quantity proportional to power. A field quantity is a quantity, such as voltage or sound pressure, the square of which in a linear system is proportional to power. Now, in practice and this for historical and practical reasons, not only one general logarithmic quantity definition is applied, but two of them exist, namely one for logarithmic power quantities L(p), e.g. apparent power loss AS, and another one for logarithmic field quantities L(F), e.g. voltage attenuation AU. L(P) = 0.5 ln|P1/P2| AS = 0.5 ln|S1/S2| L(F) = ln|F1/F2| AU = ln|U1/U2| These definitions are in full accordance with the definitions given by ISO in ISO 31/2 [1] and not in disagreement with what is stated in IEC 27-3 [3]. These general definitions are the basis for the definition of other logarithmic quantities. As examples, definitions of power loss, composite loss and insertion loss are given below: Power loss The power loss of a two-port network is 0.5 ln|P1/P2|, where P1 is the input power and P2 is the output power of the two-port network. Usually specific loss definitions which specify terminal impedances and other special measuring conditions will be applied. It should be specified whether the power is real or apparent. Composite loss The composite loss of a two-port network inserted between a generator impedance ZE and a load impedance ZR is 0.5 ln|S0/S2| where S0 is the apparent power that the generator with internal impedance ZE would furnish to a load of impedance ZE and S2 is the apparent power that the same generator furnishes via the two-port network to the load ZR. Composite loss with opposite sign is composite gain. Insertion loss The insertion loss of a two-port network inserted between a generator impedance ZE and a load impedance ZR is 0.5 ln|S1/S2| where S1 and S2 represent the apparent power in the load impedance ZR before and after the insertion of the two-port network concerned. The quantities as defined above may be used in quantity equations. Examples of such quantity equations are: AS = AU - 0.5 ln|Z1/Z2| 2A |S1| = e S |S2| Although the equations have been written as quantity equations they are formally equal to the numerical value equations when the neper is used as a unit for the logarithmic quantities. Thus the neper, being a special name for the number 1, is the natural unit for these logarithmic quantities. The units decibel and neper are used as units for real, or the real part of complex logarithmic power or field quantities. It is important to note that both units are defined as units of the same general quantities A(P) and A(F). Since the value of a logarithmic quantity may be uniquely identified with a number (or it may even be said to be a number), also the units will correspond to (or be equal to) a number. From the quantity definitions we may get L(P) = 0.5 ln|P1/P2| = 0.5 ln|P1/P2| 1 = 10 1g|P1/P2| (ln 10)/20 L(F) = ln|F1/F2| = ln|F1/F2| 1 = 20 1g|F1/F2| (ln 10)/20 Taking neper (symbol Np) as a special name for the number 1, and decibel (symbol dB) as a special name for the number (ln 10)/20 when used in connection with these logarithmic quantities (1 = 1 Np = 8.686 dB), we may now write: L(P) = 0.5 ln|P1/P2|Np = 10 1g|P1/P2|dB and L(F) = ln|F1/F2|Np = 20 1g|F1/F2|dB. Unfortunately the CCITT Recommendation B.12 [6] - and the similar CCIR Recommendation 574-2 [7] - are only to a very limited degree influenced by the general ideas concerning quantities, quantity definitions and quantity equations as presented especially by ISO in ISO 31/0 [1]. The two main objections that may be raised against Recommendation B.12 are the following: -a proper quantity definition (general definition of logarithmic power quantity and logarithmic field quantity) is not found. Instead several definitions of each of the two units neper and decibel are given corresponding to various situations; -in many cases no clear distinction is made between a ratio and a logarithmic quantity based on that ratio. 3. Logarithmic quantities related to a CCITT transmission system Most of the logarithmic quantities, such as power gain, voltage attenuation and power level with respect to a given reference value are defined without reference to a specific network or transmission system. There are, however, a few very important quantities defined with special reference to a CCITT transmission system. Among these quantities the relative level is fundamental. The relative power level at a given point in a transmission system is the power gain from a reference point called the transmission reference point to the point considered. In the transmission plan (Recommendation G.101) [8] the location of the reference point is given with reference to the virtual switching points, which again are points having given values of relative level. Thus, the definitions seem to be circular. In practice this circularity is broken because nominal values of the relative power level at a reference frequency have been assigned to various points in the transmission system. Another quantity describes a given signal measured at a point with a given relative level. It is defined as the power level with respect to 1 mW that would be measured at the transmission reference point or at any point of zero relative level. Unfortunately, this quantity has not been given a simple designation. It is sometimes referred to as the level with respect to 1 mW referred to a point of zero relative level, but usually is simply called level, the values being characterized by a special addition to the unit symbol (dBm0). The term load level has been used provisionally in Working Party IV/6 (Maintenance of sound-programme and TV transmissions) of Study Group IV and will also be used here in lack of an agreed term. Thus it can be said that if the power level with respect to 1 mW of a given signal at a point with relative power level Lr is Lm then the load level Lm0 is given by Lm0 = Lm - Lr. The load level of a given signal is nominally the same along a transmission line. A transmission plan is not necessarily based on power or power levels. For sound-programme circuits also a transmission plan based on voltage or voltage levels is described. The nominal relative voltage level at a given point of this transmission system is the voltage gain from the sound-programme transmission reference point to the point considered. A quantity similar to the load level may be defined, but no name has been given to such a quantity. 4. Special notations used in connection with the unit symbol dB In the ITU and elsewhere extensive use is made of special notations for indicating values of logarithmic quantities, especially in connection with the unit symbol dB. For a correct understanding and use of these symbols a few points must be clear: -a special symbol added to the unit symbol dB does not change or redefine the unit but is only an indication that the value in question is a value of a specific quantity conventionally indicated by the special symbol; -there is in principle no limit to the possible number of suffixes since each new specific quantity may require a new suffix; -the use of suffixes is in principle superfluous since the information carried in the suffix only serves to identify a specific quantity, but does not qualify or change the unit in any way. In practice, however, the use of suffixes may be found convenient. Level definitions are applicable for the measurement of sinusoidal test tones and other signals, e.g. noise signals. However, great care is needed when measuring non-sinusoidal signals. It is necessary to ascertain that the measuring instrument is compatible with the level definition for the signal to be measured. In Table 1 a list of some of the special notations used in connection with the unit symbol dB is given together with an explanation of the meaning of the special symbols. Only suffixes appended to the unit symbol dB are given in the list since the decibel is the only unit used for measurement of the quantities considered. The suffixes may, however, equally well be applied to the unit symbol Np. TABLE 1 Some special notations used in connection with the unit symbol dB + - + Special notation Quantity referred to. Remarks + - + - dBm power level with respect to 1 mW. In practice, usually the apparent power level dBu voltage level with respect to 0.775 V dBr relative power level. This quantity, which expresses a power gain, is used in connection with a CCITT transmission system for which the transmission plan is described in terms of power or power levels dBm0 power level with respect to 1 mW, referred to a point of zero relative level. The use of this quantity is restricted to a CCITT transmission system for which the transmission plan is described in terms of power or power levels dBrs the relative power level in a sound-programme transmission system. It expresses a power gain dBm0p psophometric power level (weighted for telephony) with respect to 1 mW, referred to a point of zero relative level dBm0s power level with respect to 1 mW, referred to a point of zero relative level in a sound-programme transmission system dBmOps psophometric power level (weighted for sound-programme transmission) with respect to 1 mW, referred to a point of zero relative level in a sound-programme transmission system dBq voltage level with respect to 0.775 V measured with a quasi-peak noise measuring instrument complying with CCIR Recommendation 468 [9] without a weighting network dBq0s voltage level with respect to 0.775 V measured with a quasi-peak noise measuring instrument complying with CCIR Recommendation 468 [9] without a weighting network, referred to a point of zero relative level in a sound- programme transmission system dBqp voltage level with respect to 0.775 V measured with a quasi-peak noise measuring instrument (weighted for sound- programme transmission) complying with CCIR Recommendation 468 [9] dBq0ps psophometric voltage level with respect to 0.775 V measured with a quasi-peak noise measuring instrument (weighted for sound-programme transmission) complying with CCIR Recommendation 468 [9], referred to a point of zero relative level in a sound-programme transmission system + - + Note (to Table 1) - No special notations are in use specifically related to sound-programme transmission systems in cases where the constant voltage method is applied. 5. Level measurements, measuring principles Level measurements are measurements made for the determination of the level of a signal, e.g. a test signal, at different points. The measurements are made with a high resistance voltmeter as the basic instrument. In different countries, different principles are applied for carrying out the measurements and different terms are used in their description. Three factors are involved in a level measurement, namely: 1) the quantity to be determined may be either a power level or a voltage level; 2) the nominal value of the quantity to be measured as well as the result of the measurement may be expressed in either decibels or nepers; 3) the measurement made may be either a bridging measurement (through level) or a terminated level measurement: a) bridging measurement (through level): the high input resistance instrument is bridged across a circuit in its working condition; or b) terminated level measurement: the circuit is disconnected at the point of measurement and terminated with a purely resistive impedance (usually provided within the instrument for use as required) the measurement then being made across the terminals of the terminating impedance. These various factors are independent. Bridging measurements are not particularly associated with voltage levels, nor terminated measurements with power levels. Neither should nepers be considered to be particularly associated with voltage levels nor decibels with power levels. National usage may make such an association, but a different association may occur in other countries. The usual measuring situation is the one where a nominal (apparent) power level is given while a voltage level is measured, and this has to be compared with the power level. For making this comparison possible the impedance at the point of measurement must be known. In practice, this impedance is assumed to be equal to the nominal value of the impedance at the point of measurement. For the measurement two different procedures may be applied. The reference power (usually 1 mW) is assumed to be the same in the two procedures described below: 1) The reading of the instrument is the voltage level with respect to a voltage reference Uref (usually 0.775 V) which is independent of the nominal impedance at the measuring point. From the nominal apparent power level and the absolute value of the nominal impedance the nominal value of the voltage level is calculated. The instrument reading can be directly compared with this voltage level. 2) The reading of the measuring instrument is the voltage level with respect to a voltage reference which depends on the nominal impedance at the measuring point. At a point where the absolute value of the nominal impedance is |Zn| the voltage reference U'ref is given by: Zn U'ref = Uref Zref The nominal voltage level with respect to U'ref is equal to the nominal power level so that the instrument reading can be directly compared with the nominal power level. The two measuring principles described above have two things in common: a) The measuring instrument used is a voltage level measuring instrument, even if the instrument is built and used according to the second measuring principle allowing the reading with necessary caution to be interpreted as a power level. b) When comparing a measured voltage level with a nominal power level a term equal to -10 1g|Z/Zn| dB is left out of consideration since it will usually be negligibly small. Some calculations referring to the two principles of measurement are given in the Appendix to this Annex. Appendix (to Annex 2 to Question 1/IV) Notations used Notations referring to a point of measurement: Uvoltage; S apparent power; Z impedance; LS apparent power level; LU voltage level. Note - Nominal values are indicated by an n as a subscript, e.g. Un, LS,n. Notations referring to reference values: Uref = 0.775 V, reference of voltage level; Sref = 1 mW, reference of power level; Zref = 600 _ , Zref = U2ref/Sref; U'ref alternative reference of voltage level. Nominal values at a point of measurement Comparison of a measured level with a nominal level In a measurement according to method No. 1 the two values at the right hand side of the equations are compared. In a measurement according to method No. 2 the two values at the right hand side are compared. In both cases a term with the absolute value of 10 1g|Z/Zn| dB is left out of consideration. REFERENCES [1]International Standard ISO 31-series, especially ISO 31/0 "General principles concerning quantities, units and symbols" and ISO 31/2 "Quantities and units of periodic and related phenomena." [2]International Electrotechnical Vocabulary, chapter 111, section 111- 03 "Concepts related to quantities and units." [3]IEC Publication 27-3 "Logarithmic quantities and units." [4]International vocabulary of basic and general terms in metrology, BIPM, IEC, ISO and OIML. [5]Vocabulary of legal metrology, OIML. [6]CCITT Recommendation, Use of the decibel and the neper in telecommunications, Volume I, Recommendation B.12. [7]CCIR Recommendation, Use of the decibel and the neper in telecommunications, Volume XIII, Recommendation 574. [8]CCITT Recommendation, The transmission plan, Volume III, Recommendation G.101. [9]CCIR Recommendation, Measurement of audio-frequency noise voltage level in sound broadcasting, Volume X-1, Recommendation 468.