Softphone

A softphone is a software program for making telephone calls over the Internet using a general purpose computer, rather than using dedicated hardware. The softphone can also be installed on a piece of equipment such as a workstation, portable computer, tablet or even a cellphone and allows the user to place and receive calls without requiring an actual telephone set. Often a softphone is designed to behave like a traditional telephone, sometimes appearing as an image of a phone, with a display panel and buttons with which the user can interact. A softphone is usually used with a headset connected to the sound card of the PC, or with a USB phone.

See Comparison of VoIP software

To communicate, both end-points must support the same , and at least one common audio codec.

Many service providers use the (SIP) standardized by the Internet Engineering Task Force (IETF). Skype, a popular service, uses proprietary protocols, and Google Talk leverages the (XMPP).

Some softphones also support the Inter-Asterisk eXchange protocol (IAX), a protocol supported by the open-source software application Asterisk.

A typical softphone has all standard telephony features (DND, Mute, DTMF, Flash, Hold, Transfer etc.) and often additional features typical for online messaging, such as user presence indication, video, wide-band audio. Softphones provide a variety of audio codecs, a typical minimum set is G.711 and G.729.

To make voice calls via the Internet, a user typically requires the following:

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