In a country such as Iran that the expansion of the network call through a digital network looking for. the use of the technique that the capacity of the transmission network, telephone, digital PCM, increases. necessary and desirable. Span and all-consuming being a telephony network, causing an increased demand for sending non-speech information ( such as data, image and . . . ) On the phone lines.
so due to limitation of band channel, telephone the necessary signal talk as much as possible compressed, we the most common techniques to do this, use the system ADPCM. For this reason, in recent years, the recommendations of the CCITT for the conversion of the signal log-PCM, bit rate kbps 64 to signal ADPCM with a bit rate, the less is offered.