Dell 2135CN, Service Manual

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6 – 8
Chapter 6 Principle of Operation (Fax)
Version 1 2008.02.01
3) The switch connects lines according to the transmitted number.
4) When a connection between local switches is established, the local switch of the called party
sends a ringing signal to the telephone of the called party. The telephone that receives the ringing
signal emits its ringtone. At the same time, the called party's local switch sends a ring back tone
(RBT) to the calling party's telephone to indicate that a connection to the called party has been
established.
Gnb06025KA
697Hz
1209Hz 1336Hz 1447Hz
770Hz
852Hz
941Hz
Pulse Dialing & Tone Dialing
Pulse dialing
Tone dialing
Switch
Switch
Low
frequency
High frequency
DTMF matrix
3 5 .........
3 5 2 .........
"3, 5, ...... "
"3, 5, 2, ...... "