Voice over IP technologies is used for placing and transmitting telephone calls over an IP network, such as the internet.
VoIP phones can simply be software based softphones or purpose-built hardware devices that appear much like any other ordinary telephone.
The components of a VoIP telephone consist of both software and hardware components. Software requires standard networking components such as TCP/IP network stack, client implementation for DHCP, and the Domain Name System. A VoIP signalling protocol stack is needed, such as Skype or Cisco.
For media streams, the Real-time Transport Protocol is the most used for VoIP systems. User interface software controls the operation of the hardware components, and may respond to user actions with messages to a display screen.