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(2) Echo suppressor disabler (Standardized in
Problems may arise with the echo suppresor which is necessary for general
telephone calls when carrying out data communication using the full-
duplex system. For this reason, a device called a "disabler" for disabling
the echo suppressor is built into the echo suppressor.
A disabler turns of the echo suppressor by a tone (echo suppressor disable
tone) of 2100±21 Hz that lasts for 300±100msec or longer so that echo
occurs.
The echo suppressor is turned back on when a no-signal state lasts for 100
msec or more.
The CED that appears at the start of the facsimile procedure disables the
echo suppressor functions as its frequency is 2100 Hz. This causes echo to
occur as shown in the Fig. A-30. Since this causes an inconvenience in fac-
simile transmission, adopt countermeasures described in this chapter, 7.3.3
Echo countermeasures.
A–30
TX
Fig. A-30 Example of Echo Occurrence by Echo Suppressor Disabler
ITU-T
G.164)
Long-distance
transmission line
RX
CED
(2100Hz)
preamble
NSF
CSI
DIS
Time taken for echo
to return
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