Pulse dialing vs tone dialing-difference between pulse dialing and tone dialing

This page pulse dialing vs tone dialing describes basics of these dialing types and mention difference between pulse dialing and tone dialing.

As we know there are two types of methods by which we can inform telephone number to be dialed to the telephone exchange i.e. telephone company. The methods are pulse and tone dialing. Pulse method was in use which is now obsolete. The tone dialing is most popular and in wide use. Refer telephone system tutorial which describes telephone system block diagram and functions.

Pulse dialing

pulse dialing

In order to use pulse dialing, rotary dial type of telephone is needed. The dial usually generates pulses on local loop by way of opening and closing electrical switch when dial is rotated and released.

For example, dialing number '3' generates 3 pulses as shown in figure-1. It takes a total of 0.3 seconds in time to transmit all 3 pulses. (6 x 0.05 seconds = 0.3 seconds). Here each pulse is caused due to interruption in current flow on local loop for duration of 0.05 second. There will be 0.05 second pause between the pules.

tone dialing

tone dialing DTMF Keypad

In order to use tone dialing, touchtone type of telephone is needed. This type of telephone will have DTMF keypad as shown in the figure-2. Most telephones will have DTMF keypad with 12 keys which maps numbers 0 to 9 and spacial symbols such as * and #. It also accommodates 4 additional keys for such spacial applications.

Each key represent two audio frequencies which are associated row and column wise as shown. For example if key 5 is pressed then audio frequency pair (770, 1336) in Hz is generated and transmitted to the telephone exchange. These tones are recognized at the telephone central office (CO). Tolerance on these frequencies should be within +/- 1.5 percent.

The difference between pulse dialing vs tone dialing is that pulse dialing takes longer for the dialed digits compare to fast dialing used in tone dialing. For example to dial number '9' will take about 0.9 seconds ( Derivation: 0.05 seconds X 18 = 0.9 seconds).

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