Network and Telecommunications Concepts

Essay by jeppolitCollege, UndergraduateA, November 2008

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Rotary and Dual Tone Multi-frequency (DTMF)Telephone communication is designed to create a circuitous route between two callers and subsequently between two telephones. Call routing is determined using one of two methods, pulse or rotary dialing or dual tone multi-frequency (DTMF).

Macao Communications describes pulse dialing by using the following example,While Dialing a Number, for example, five, the Dial is drawn round in the Clockwise Direction to the Finger Stop Position and released. The ICT [phone] then generates the Dial Pulses by closing and opening itself to interrupt the DC Current loop. The number of interruptions is equivalent to the Dialed Digit. After finishing Dialing, the Pulses are then decoded at the Telephone Exchange that makes a connection to the Called Customer (2008).

As noted previously call routing is the goal and instead of the electronic pulses used in rotary dial telephones, DTMF uses sound tones to determine the call route.

In fact, each button on a “touch tone” telephone generates a pair of tones (hence the name dual tone). Each pairs of tones consists of a high frequency and low frequency tone as illustrated in the chart below.

The combination of the tones, along with the order they are selected is then decoded in the same way the rotary dial is and the call is routed to the appropriate receiver. DTMF is far more accurate than rotary dialing because the combination of tones and their sequence determines the opening and closing of the circuit. In contrast, rotary dial phones rely on the number of clicks or circuits passed as the rotary dial spins past. If the user does not fully reach the number “five” the number of clicks will be off. Similarly, these electronic circuits are subject to interference and ultimately misinterpretation. The efficiency of DTMF compared to rotary dialing...