Canon FACSIMILE BASIC 2000 Service Manual page 335

time, such phenomenon occur. That is, one's own voice is reflected at the
other party, and is heard after 0.6 sec and 0.2 sec, respectively.
The time for the echo to return may reach 1.2 sec in the case of satellite
communications.
Fig. A-28 Transmission Lines for International Communications
7.3.2 Echo control devices on telephone line networks
(1) Echo suppressor (Standardized in
Since echo is annoying to the person making the telephone call, a device
called an "echo suppressor" is attached on international telephone lines
and domestic long-distance transmission lines where delay exceeds 45
msec. Echo suppressors are equipped with special switches for eliminating
voice signals that are reflected on the other party while the speaker is still
talking. Each suppressors are equipped on each channel. The Fig. A-29
shows the operation of switches when the voice of the speaker on the right
reaches the other party on the left.
Path of echo
2-wire
International
exchange
Submarine
coaxial cable
Long distance 4-wire
transmission line
4-wire
SW
2-wire
/4-wire
Echo
BNW
suppressor
conversion
circuit
4-wire
Fig. A-29 Echo Suppressor
Communication
satellite
ITU-T G.164)
4-wire
2-wire
/4-wire
Echo
BNW
suppressor conversion
circuit
SW
4-wire
BNW: Balancing network
1
2
3
4
5
6
A
çi
2-wire
Voice signal
A–29