s is approximately 600ms to 800ms. A typical chamber to ensure good sound reproduction. dial pulse train is shown in Figure 58.12. 58.7.2 Outgoing signalling Modern telephones use integrated circuits to generate the dial pulses. The IC will be connected to a keyboard, and so will have a keyboard scanning circuit and key debouncing circuits, to ensure Each telephone in the network is assigned a unique number and each correct registration of the keys selected. The IC will also provide country has been assigned a unique number, therefore to obtain a facilities for muting the speech circuits during dialling, for much the distant telephone it is necessary to pass this number (address) to the same reason as the off normal contacts in the mechanical dial. In telephone exchange, which will then route the request through the addition to the basic dialling functions the addition of memory cells network to the distant telephone. There are two basic types of to the IC provides the user with functions such as last number redial address signalling: and stores for most frequently dialled numbers. 1. Dial pulse or loop disconnect. 2. Multifrequency. 58.7.4 Dual tone multifrequency signalling 58.7.3 Dial pulse or loop disconnect signalling Multifrequency signalling consists of a combination of two tones with frequencies within the speech band, each combination of two Dial pulse or loop disconnect signalling takes its name from the frequencies representing a single digit. The tones are presented on rotary dial method of signalling information to the exchange. The the line for approximately 100ms and then an intertone pause of rotary dial is a mechanical device which is connected across the 100ms before the next combination of tones is sent. The speed of telephone line with a pair of contacts. The user places a finger in the dialling is therefore many times faster than loop disconnect dialling. dial and turns the dial round to the finger stop and then releases the The tones are in two groups, a low band and a high band, and they di