Question 28/XII - Listener echo (receive end echo) in the public
switched telephone networks
(continuation of Question 28/XII studied in 1985-1988)

How should Recommendations be revised to take account of transmission
planning aspects of listener echo (receive end echo) in the public
switched telephone networks?

Note 1 - Listener echo can cause bit errors in data transmission over
telephone networks. Listener echo in voice transmission is mainly
exhibited by hollowness. The increased use of four-wire equipment, such
as digital exchanges and transmission equipment, in telephone networks
may increase the occurrence of listener echo unless proper measures are
taken. In particular, the number of 2w-4w-2w loops in a connection, and
the loss in each loop, will influence the listener echo received at the
far-end of the connection.

Note 2 - Recommendation G.122 contains information on listener echo and
the number of loops in a connection. The adequacy of this information
and any additional information or planning rules need to be studied.

Note 3 - Supplement No. 3 and Annex 2 provide useful information on
listener echo.
ANNEX 1

(to Question 28/XII)

COM XII-173, 1984-1988 study period
ANNEX 2

(to Question 28/XII)

COM XII-208, 1984-1988 study period