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C H A P T E R
6 :
Figure 6.28:
PESQ Gain Variation diagram
6.6.5 Command Line Arguments
PESQ currently requires no algorithm specific command line switches. To use
PESQ from the commandline, OPERA must be started with the -Algorithm
Name=PESQ switch.
6.7 Echo Measurement
6.7.1 Fundamentals of the Echo Measurement Algorithm
About Echo
In the Public Switched Telephonic Network (PSTN) the transit network is built
with using four wires (see Figure 6.29). Two wires are used to transmit voice
in one direction, and the two other wires are used for the opposite direction. In
contrast, the subscriber network is built with using only two wires to transmit
voice in both directions in a full-duplex connection to be cost effective.
Figure 6.29: PSTN Transit Network [NMS99]
Because the length of the subscriber's line varies from 0 to 9 km (5.5 miles), the
impedance of the line never matches the reference impedance of the hybrid.
This non-balanced impedance generates echo on the hybrid.
When telephone set A is connected to telephone set B through the telephone
network, telephone A will receive a near-end echo from hybrid A and an far-
end echo from hybrid B.
T E L E P H O N Y
B A N D
T E S T I N G
148
V O I C E
Q U A L I T Y
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