Panasonic KX-FT21RS - Manual (Page 37)

5. Unit can copy, but cannot transmit/receive long distance or international communications
The following 2 causes can be considered for this.
Cause 1:
The other party is executing automatic dialling, the call has been received by this unit, and the CED or DIS signal response
time is too long. (In most cases, this unit detects the CNG signal and can respond to the CED or DIS.) (According to the ITU-
T standard, the communication procedure is stopped when there is no response from the other party within 35 sec, so that
the other party releases the line.)
(Cause and Countermeasure)
As shown in the chart above, the total handshaking time must be reduced. Long distance connection and linking of several
stations means the line connection time cannot be reduced. Accordingly, the following countermeasures should be attempted.
(A) The TEL/FAX DELAYED RING count should be 1. (User parameter: code No. 78)
(B) As the 35 sec. count starts directly after dialing or directly after the START button has been pressed for models with a
START button, the other party should be called manually, if possible.
Another possibility is entering two pauses at the end of the auto dial number on the transmission side. Then the count start time
will be delayed for 2 pauses (about 10 sec.).
Cause 2:
Erroneous detection due to an echo or echo canceler.
(Echo/Echo Canceler)
The signal from FAX1 reaches FAX2 via the stations 1 and 2, but the reflection signal at station 2 also returns via station
1(echo). As the distance between station 1 and station 2 is far, the echo returns to FAX 1 a max. of 600 msec after
transmission. There is a possibility that this signal is detected erroneously as the signal from FAX2. For a normal call, there is
a possibility that the echo of their own voice will make the call difficult to understand. For this reason, each station (station 1,
station 2) attaches echo cancellers (S1, S2) for international lines or long distance lines. For the echo canceller, the level of the
transmission signal from FAX 1 is compared with the level of the reception signal from FAX2. When the S1 is closed and S2
is open, so that the echo does not return to FAX1.
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KX-FT21RS