Two key differences between VoIP and traditional telephone technology are the network over which a call is transmitted and the transmission format. In traditional telephony, a call over the public switched telephone network (PSTN) generally results in the creation of an end-to-end circuit that establishes a physical connection between the caller and the called party through the wires, cables and switches of the telephone network. The circuit exists for the duration of the call until hang-up, and is typically dedicated to the voice signals flowing between the two parties participating in the call. In contrast, in a VoIP call there is no dedicated circuit. The contents of a VoIP call flow between the caller and the called party over various networks that comprise the Internet. This happens through a router or switch operated by the VoIP provider, which matches a telephone number with an IP address. Different portions of a VoIP call may be routed over different transmission paths, with the contents of the call moving over the Internet amidst other traffic, including other VoIP calls, e-mails, miscellaneous data and video traffic.

The call format is the second feature distinguishing VoIP from traditional telephony. Voice communications on a PSTN call begin as analog signals, or electronic sound waves, which are converted into digital format (i.e., a series of ones and zeroes). The digits are transmitted in sequence over the circuit and converted back into analog format to be heard by the other party on the call. The digits move across the circuit in sequence, corresponding to the voice signals on the call. Spoken words on a VoIP call are converted from analog into digitized Internet Protocol (IP) packets. A packet is analogous to an envelope with data on the inside and sequence coding, as well as originating and destination addresses, on the outside. The VoIP user’s telephone is connected to a router. These packets enter the Internet at the router and are sent individually, though not necessarily in sequence, over the Internet. At the router closest to their destination (i.e. the other party on the call), they are reassembled in original sequence and converted back into analog format for reception by the recipient. A key point associated with VoIP is the significantly lower transmission costs of this technology.

The DVG-1120 is a VoIP Gateway equipped with two standard phone ports, one lifeline voice port for fail-over to standard phone services, one WAN Fast Ethernet 10/100BaseTX Port, and one LAN Fast Ethernet 10/100BaseTX Port.

With the integration of both voice and data, the DVG-1120 offers Small-to-Medium-Size Businesses (SMB) the ability to route data information into one end-to-end network solution. In addition to standard residential gateway data services, end-users are enabled with low-cost long-distance calling, faxing, and a host of advanced services including DVG-1120-to-Phone, Phone-to-DVG-1120, and DVG-1120-to-DVG-1120.

The DVG-1120 is compatible with xDSL and Cable-Modem Broadband service providers with built-in support for with DHCP Client, MAC Address Cloning, PPPoE, and multiple auto-provisioning methods.

The DVG-1120 has been tested with most major VoIP Softswitch vendors' Call Management systems. Devices such as the DVG-1120 require a Call Management system to function. These services are offered independently of D-Link, but are only required if user would like to use voice features of the DVG-1120.

For Internet connection sharing in your home the DVG-1120 offers support for up to 32 IP devices. Services offered to the internal home network are DHCP Server, Network Address Translation (NAT), and IPSEC pass-thru. Because the DVG-1120 shares your single ISP IP address, it masks the local users' IP addresses from the outside world, preventing intruders and hackers from gaining access to network resources, data files or personal information.

The DVG-1120 has voice support that includes hardware based Quality of Service (QoS), voice compression (popular voice CODECs G.711-G.729e), echo cancellation, dynamic latency (jitter) buffers, silence suppression, and comfort noise generation.

The DVG-1120 features can be remotely configured using the convenient and secure Web-based Interface. For diagnostics features, the DVG-1120 has management-at-a-glance LEDs on the front panel, and over 100 real-time statistics.

VoIP, in overly simplified terms, allows one to use a standard telephone to place calls over the internet, eliminating the need for a dedicated phone line (and all of the fees/tolls charged by the phone company).

“sending voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public switched telephone network”, with more information available on their site, if desired.