Question 16/XII - Impedance strategy in the local network
(continuation of Question 16/XII studied during the 1985-1988 study
period; new working)

Considering

- that a range of equipment is used to interwork with the local network
and that such equipment incorporates 2-wire to 4-wire conversion with
associated impedances and possible adaptive balancing then the following
Question should be studied.

What is the optimum impedance strategy for future customer equipment,
local lines and network digital switching and multiplex equipment?

In particular the following points should be considered:

a) the echo and stability performance of connections;

b) the sidetone performance offered to customers;

c) the effect on loudness rating specifications;

d) the specification of the levels of information tones and
announcements;

e) the use of adaptive balancing techniques in 2-wire 4-wire conversion
devices;

f) the tolerances of specified impedances.
ANNEX 1

(to Question 16/XII)

List of documents submitted to the Question

COM XII-1Que3tions allocated to Study Group XII, 1985-1988 study period

COM XII-2 (Ellemtel) Sidetone, impedance matching and permissible end-
end loss

COM XII-21 (CTNE) Optimum network for the impedance of subscriber
equipment and the hybrid transformer balance impedance in digital local
exchanges

COM XII-22 (LM Ericsson) Sidetone and nominal impedance of local
exchanges

COM XII-44 (Netherlands) Sidetone, impedances and the transmission plan

COM XII-45 (India) Comments on 2.2 of Annex 4 of COM XII-32

COM XII-75 (Sweden) Sidetone problems in PABXs

COM XII-76 (Sweden) Subjective tests on talker and listener sidetone

COM XII R 6, R 13, R 18Reports of the Working Party XII/4 meetings
ANNEX 2

(to Question 16/XII)

COM XII-215 (from Working Party XI/4), Annex 2 to Part B.3,
1984-1988 study period