Components of a VoIP DSP

Tone generator:
Generates DTMF (Dual Tone Multi Frequency) tones and call progress
tones.

Echo canceller:
Performs echo cancellation on sampled, full-duplex voice signals.

Voice activation
detector: This module monitors the received signal for
voice activity. When no activity is detected for a pre-determined period
of time, the software informs the packet voice protocol. This prevents
the encoder output from being transmitted across the network when there
is silence, thus preventing unwanted network traffic.

Tone detector:
Detects the received DTMF tones and performs voice/fax detection.
Detected tones are relayed to the host equipment, so that the
appropriate speech or fax function can be activated.

Voice codec:
Compresses voice data for transmission over the network.