Canon fax basic 2000 Manuale Di Servizio

A–30

(2) Echo suppressor disabler (Standardized in 

 G.164)

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.

Fig. A-30   Example of Echo Occurrence by Echo Suppressor Disabler

preamble

NSF

CSI

DIS

TX

RX

CED

(2100Hz)

Long-distance
transmission line

Time taken for echo
to return