Tone

(A)             BUSY TONE:

                       

It is a burst 400 Hz signal with silence period in between. The burst and silence durations have the sum value of 0.755 or 0.3755. A busy tone is sent to the calling subscriber whenever the switching equipment or junction line is not available to put through the call or the called subscriber line is engaged no distinction is made between these conditions. It is not possible for a calling subscriber to conclude on the basis of the busy that the called party was actually engaged in a conversation.

                  (B)    DIAL TONE:

                       

This tone indicates that the exchange is ready to accept dialed digits from the subscribed. The subscriber should start dialing only after hearing the dial tone otherwise; initial dial pulses may be missed by the exchange. Which may result in the call landing on a wrong number Most often the dial tone is send out by the exchange even before the handset is brought near the ear. Sometimes however, a few seconds may elapse before the dial tone is heard this happens practically in common control exchange which is use shared resources for user interfaces. The dial tone is 33 Hz or 50 Hz or 400 Hz continuous tone.

                  (C)    ROUTING TONE:

                       

Routing tone or call-in-progress tone is a 400 Hz or 800 Hz intermittent pattern. It has 0.5 on/off period. In analog electronic exchanges it is a 400 Hz pattern with 0.5 on period and 2.5 off period. In digital exchanges it has 0.15 on/off periods at 400 Hz.Pride and Prejudice