Pulse dialing

The pulse dialing method was technically determined by how the rotary dial of the telephone works. When the caller picks up the receiver and operates the rotary dial, it disconnects the loop between the telephone and the exchange at a specific frequency and at defined intervals based on the number dialed. The analog exchange switch uses these disconnections to determine which telephone number the subscriber dialed and forwards these to the so-called rotary switch as current pulses. A certain pause between the individual numbers must be maintained for correct signaling. Even analog phones with push-buttons typically support the pulse method. The devices can be flexibly configured for the pulse method and multi-frequency signaling. The pulse dialing method is referred to as in-band signaling, since the telephone number is transmitted over the voice channel and can be heard by the subscriber.

Multi-frequency signaling is also a form of in-band signaling. However, here the telephone numbers are not transmitted as pulses, but consist of a mix of difference frequencies. Each number is represented by two specific frequencies. The switching center filters these frequencies out of the voice channel and determines the respective number.

Many VoIP-compatible phone systems still allow the use of telephones which support the pulse dialing method. The analog telephone ports in many phone systems automatically recognize whether a device is using the pulse dialing method or multi-frequency signaling. If a system only supports multi-frequency signaling, a pulse to tone converter can be used to connect a pulse telephone.