Question 20/XII - Wideband telephony
(New Question)

Considering

(a) that current telephone connections generally provide a bandwidth of
about 300 to 3 400 kHz;

(b) that this bandwidth results from historical decisions regarding
efficient design of telephone set transducers and circuits, analogue
lines, signalling apparatus, and time and frequency division multiplex
carrier systems;
(c) that as the telecommunications network evolves to an end-to-end
digital transmission capability many of the elements limiting the
bandwidth to 3.1 kHz will disappear;

(d) that the CCITT has approved a Recommendation G.722 "7 kHz Audio
Coding within 64 kbit/s" by accelerated procedures;

(e) that G.722 is a unique, world-wide standard for coding 7 kHz at 64
kbit/s;

(f) that subjective tests have shown that G.722 is markedly superior to
G.711 A-law or m5 -law PCM coding at the same 64 kbit/s rate;

(g) that end-to-end digital communications using 64 kbit/s G.722 ADPCM
would utilize the same switching and transmission capacities as 64
kbit/s G.711 PCM;

(h) that the bandwidth of a voice connection in an end-to-end digital
connection will be determined by the transducers, codecs and analogue
circuitry in the telephone sets;

(i) that low cost, small, wide bandwidth, high quality receiver and
microphone transducers are available;

(j) that current handset and hands free telephone set transmission
objectives generally provide for a 300 to 3 400 Hz bandwidth;

(k) that current methods and instruments for objectively measuring
handset and hands free telephones generally may be limited to the same
bandwidth, and that;

(l) that the existing body of subjective and objective methods for
assessing the performance of telephone connections are based upon the
use of 3.1 kHz telephones,

it is proposed that the CCITT study:

1. how existing definitions of transmission parameters used to define
the performance of telephone connections, e.g., loudness ratings, echo
return loss, circuit noise, etc., should be revised to provide for an
increase in the bandwidth from 3.1 kHz to 7 kHz;

Note 1 - The transmission performance of 3.1 kHz bandwidth digital
telephones is studied under Question 10/XII, and the corresponding test
methods are studied under Question 30/XII.

2. how the existing transmission objectives for handset and hands free
telephones should be revised to accommodate wideband operation;

Note 2 - Methods for determination of loudness ratings are studied under
Question 8/XII.

3. how the existing subjective and objective methods and instruments for
measuring the transmission performance of telephone sets should be
revised to accommodate wide bandwidth;

4. how the existing subjective and objective methods for assessing the
performance of telephone connections should be revised to accommodate
wideband operation, and

Note - See Recommendation P.70 which incorporates requirements for a 7
kHz MNRU to be used when testing wideband digital processes.

5. the need for new subjective and/or objective tests designed to
establish the degree of improvement in performance of connections
employing wideband telephones as compared to connections using
conventional sets.