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.



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