Voice over IP
The transmitting of analog voice signals over a digital network utilising packet switching. This can be contrasted with traditional telephony which uses analogue circuit switched networks such as the PSTN (Public Switched Telephone Network).
There are two types of PSTN to VoIP services: DID (Direct Inward Dialing) and access numbers. DID will connect the caller directly to the VoIP user while access numbers requires the caller to input the extension number of the VoIP user. Access numbers are usually charged as a local call to the caller and free to the VoIP user(citation/example needed) while DID usually has a monthly fee. There are also DID that are free to the VoIP user but is chargeable to the caller.
