modem) A device that converts Internet-based voice service from the cable or telephone company to the user's telephones. Officially called an analog telephone adapter
modem) A device that converts Internet-based voice service from the cable company to the user's analog telephones. A VoIP modem combines a DOCSIS cable modem and analog telephone adapter (ATA) in one unit. Officially an "embedded-multimedia terminal adapter" (E-MTA), the modem converts the cable company signals to packets and vice versa, and the terminal adapter converts the packets to analog voice and vice versa. The adapter also delivers dial tone and manages the call setup.
If the VoIP modem supports cable access, it may be called a "VoIP cable modem," and for DSL telephone access, a "VoIP DSL modem."
PacketCable certification from CableLabs ensures that quality of service (QoS) and other critical telephony and real-time functions are supported for delivering multimedia over IP. See analog telephone adapter
, cable modem
Combined and Separate Units
A VoIP modem can stand alone for VoIP conversion only, or it can be combined with a cable or DSL modem for both voice and data over the Internet.
Connecting a VoIP Cable Modem
This wiring diagram for a Cisco VoIP cable modem shows the coaxial line (RF cable) from the cable company coming into the unit. Analog outputs go to the telephones, and digital output to the PC (or to a switch for more connectivity). (Image courtesy of Cisco Systems, Inc.)