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1994-11-03
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INTERNATIONAL TELECOMMUNICATION UNION
ITU-T RECOMMENDATION SUMMARY
Rec. No. : G.763
Title : Digital circuit multiplication equipment using 32 kbit/s ADPCM
and digital speech interpolation
Study Group : XV - Transmission Systems and Equipment
Version : Revised
Date of adoption : 1990
Notes :
Speech signals occurring on telecommunications links are generally the
product of two-way conversations. It is customary for one talker to
pause while the other speaks; thus, an active speech signal is present
on each direction of the trunk channel for only a fraction of the
available time. In addition, even when only one talker is speaking,
pauses occur between utterances, so there are times when the circuit
is idle. Measurements show that speech is present on each direction of
the trunk channel approximately 30 to 40% of the time, averaged over a
large number of busy trunks. DCME reduces the transmission capacity
needed to handle a multiplicity of telephone trunk channels by
exploiting the low average channel activity and by transmitting active
speech using ADPCM techniques.
The DCME provides a nominal 5 : 1 reduction in the transmission
capacity required to carry various mixtures of speech, voice-band data
and 64 kbit/s unrestricted channels. An overload strategy consisting
of variable bit rate encoding and dynamic load control techniques is
utilized to limit speech clipping. The DCME data detector discriminates
between voice-band data and speech in order to assign the voice-band
data signal to a bearer channel protected against the formation of
overload channels which degrade the voice-band data performance.
Recommendation G.763 is applicable to the design of digital circuit
multiplication equipment intended for, but not limited to, use in an
international digital circuit. Freedom is permitted in design details
which are not covered in Recommendation G.763.
To order the complete text of this Recommendation, please use the
Order Form for ITU-T Recommendations. An electronic version of this
form is available on ITUDOC (Winword: UPI=ITU-5265; ASCII: UPI=ITU-2488).