In computing, a softphone is a software program for making telephone calls over the Internet using a general purpose computer, rather than using dedicated hardware. 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.
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Softphone Applications
A typical application of a softphone is to make calls via an Internet telephony service provider to other softphone or to fixed or cell phone. Service provide may offer PC-to-PC calls for free, but PC-to-phone and phone-to-PC calls usually are not free. Other type of softphone connects to a private branch exchange (PBX) through a local area network (LAN) and is used to control and dial through an existing hardware phone. This is often used in a call center environment to make calls from a central customer directory, and to "pop-up" information on the screen about which customer is calling, instantly providing the operator with details of the relationship between the caller and the company using the call center. It's important to differentiate softphones from services based on softphones. Skype, Google Talk, and Vonage are Internet telephony service providers having their own softphones that you install on your computer. Unfortunately these three major providers are not interoperable, and you can't place a direct call between them.
Communication Protocols
To communicate, both end-points must have the same communication protocol and at least one common audio codec. Most service providers use a communication protocol called SIP (Session Initiation Protocol) by IETF, except Skype which is a totally proprietary system and Google Talk which is based on Jabber. Examples of SIP softphones can be found in the category "VoIP_software" (see below) and at Comparison of VoIP software
Softphone Features
A typical softphone has all standard telephony features (DND, Mute, DTMF, Flash, Hold, Transfer etc) and a lot of new ones like Presence, Video, Wideband Audio and more. The minimum codecs set is G.711, GSM and iLBC. Softphone vendors may offer more codecs and different feature set.
Softphone Requirements
To make voice calls over Internet, you should have
- Any modern PC with a microphone and a speaker, or with a headset, or with USBphone.
- Reliable Internet connectivity like DSL, WiFi, cable or LAN. 28.8 dial-up modem may be enough if you use a codec compressing the speech to this bandwidth.
- Account with an Internet telephony service provider.
