1. Applications

2. Communication protocols

3. Features

4. Requirements

5. See also

6. References

A softphone is a software program for making telephone calls over the Internet using a general purpose computer rather than dedicated hardware. The softphone can be installed on a piece of equipment such as a desktop, mobile device, or other computer and allows the user to place and receive calls without requiring an actual telephone set.^[1] Often, a softphone is designed to behave like a traditional telephone, sometimes appearing as an image of a handset, 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.^[2]

Applications

See Comparison of VoIP software

Communication protocols

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

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

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

Features

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.

Requirements

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

• A modern PC with a microphone and speaker, or with a headset, or with USBphone.
• Reliable high-speed Internet connectivity like digital subscriber line (DSL), or cable service.
• Account with an Internet telephony service provider or IP PBX provider.
• Mobile or landline phone.

See also

• Auto dialer
• Chatcord
• Comparison of VoIP software
• Computer telephony integration
• H.323
• List of SIP software
• Mobile VoIP
• Videotelephony
• VoIP phone

References

• Hrádek u Rokycan
• Hríchy lásky
• Hrímþursar
• Hrísná krev
• Hrísoula Goudenoudi
• Hrøríkʀ
• Hrœrekr of Dorestad
• Hrœrikr
• Hs1
• HS-11
• HS2 line
• HS-376
• HS-393
• HS4Air
• Hs578T
• Hs 578T
• HS 578T
• HSAIL
• HSA Intermediate Language
• HS algorithm
• H. Salzwedel
• H.Samuel
• H. sancta
• H:SAND
• H. Sanford Riley