The recommendation G.821 error performance OF on internationally digitally connection operating RK A bit guesses below the primary guesses/advises to and forming part OF at Integrated Services Digital Network of the ITU-T is an international agreement over the transmission quality of lines of the telephone network, which are used also for the transmission of digital data. Voice grade channels are independent of, whether they are shifted in the local area as Teilnehmeranschlussleitung, or whether they serve the foreign telephone service within the net, not always for the data communication suitably. Thus technical criteria had to be found and agreed upon, with which one could judge the suitability of a voice grade channel for the data communication, and in addition measuring procedures, with which one could examine these criteria. As the most important criterion one agreed on the bit error rate. An agreement was obtained that with a bit error rate by 10-4 a line for the similar speech transmission is quite still suitable, but with 10-3 a line would be completely useless. The bit error rate of 10-3 was equated a complete dropout, with which instead of the corrupt information signal AIS into the line one inserts. For the digital speech transmission in the ISDN and for the data communication the transmission quality of a line should be so good however that bit errors with a small frequency appear as 10-6. These criteria and suitable quality parameters were prepared in detail in the recommendation G.821. Multiplexers and other devices of the digital transmission technique measure these parameters constantly and seize them in one (performance) - MIB.

Historical

The original recommendation originates from the year 1980 and treated a 64-kbit-Kanal of the ISDNs. Since it was the first of a digital line, it was used also for speeds, for which it was not developed. Since 1993 the recommendation G.826 describes all speeds of 2 Mbit upward, since 2002 the G.821 everything under it.

Application

The G.821 is a theoretical paper, however world-wide practically is actually used. In the Erstfassung describes it a measurement with a check text on 27,500 km are enough for international one hypothetical reference line (Hypothetical Reference digitally Path). The measuring period is not defined (original: A by iodine OF the order OF any one month is suggested"…), the suggested time is not applicable.

In practice the conduit length is usually neglected and its own measuring period is used.

Check texts

Check texts in the synchronous data communication are bit design, which repeat themselves after a certain number of bits. Since they appear optical like an arbitrary composition, they become also as quasi-coincidence sequence (QZF) or engl: Pseudo random text designates. These test specimens are however not coincidental, them are based on mathematical formulas and can be reconstructed at any time.

There are at least ten different used check texts. Although there is a standardization, no agreement over the bit sequence, for example 2047r (r = written undertaking) or 2047i between the manufacturers of bit error measuring instruments (i = inverted) exists.

The production these bit design is relatively simple and also as IC in hardware is offered.

The G.821 does not prescribe test specimens.

• In the International Telecommunication Union T recommendation O.152 for speeds to 2 Mbit/s a check text 211-1 = to 2047 is recommended bits.
• O.151 and O.153 are further international recommendations regarding check texts at different speeds.
• Check texts for an asynchronous data communication see R.52.

Error evaluation

Since with a sufficient long measuring period (months, see above) bit error tolerates to develop to always be able, become these.

Valuation criteria:

• Disturbed second (incorrect second, engl: errored second, IT): One second of gate time, in which one or more bit errors are present.
  • Limit value: Less than 8 % of the gate time
• Strongly disturbed second (Unakzeptable second, engl: severely errored second, SES): one second with a bit error rate = 1 10-3. Example: On a 64-kbit-Leitung 63 Bitfehler/s are incorrect; 64 is considered as unakzeptabel.
  • Limit value: Less than 0.2 % of the gate time
• Impaired minute (engl: degraded minute, DM): This error evaluation gave it in the first expenditure of the G.821; it was practically hardly usable and was spareless painted. It is however present with older bit error measuring instruments still.
  • Limit value: Less than 10 % of the gate time

From these values in practice conditions are formed, for example error free to disturbed seconds; a quality profile of the measured line results on time of the measurement.

See also: Quality OF service

Literature

Karl-Heinz Schmidt (Hrgs.): To transmission of news measuring technique, volume 1 line measuring technique, R. v. Decker's publishing house, G. give GmbH, Heidelberg 1990, ISBN 3-7685-4989-1

ITU-T RECOMMENDATION G.821: ERROR PERFORMANCE OF ON INTERNATIONALLY DIGITAL CONNECTION OPERATING RK A BIT RATE BELOW THE PRIMARY RATE AND FORMING PART OF AT INTEGRATED SERVICES DIGITAL NETWORK

Articles in category "G.821"

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• ITU-T Recommendation G.821 Corrigendum 1 - AAP 12
  [G.821C1] LC - Text: ITU-T Recommendation G.821 Corrigendum 1 - Error performance of an international digital connection operating at a bit rate below the ...


• ITU-T Recommendation G.821- (1 comment received) - AAP 45
  [G.821] LC - Text: Recommendation G.821 - Error performance of an international digital connection operating at a bit rate below the primary rate and ...


• [G.821] LC - Text: Recommendation G.821 - Error performance of an ...
  [G.821] LC - Text: Recommendation G.821 - Error performance of an international digital connection operating at a bit rate below the primary rate and ...