SOFT PHONE
A softphone is a piece of software 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.
Soft Phone 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 PC2PC calls for free, but PC2phone and phone2PC calls usually are not free. Other type of softphone connects to a private branch exchange through a Local Area Network 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.
Communication Protocols
To communicate, both end-points must have the same communication protocol and at least one common audio codec. Most service providers use communication protocol called SIP (Session Initiation Protocol) by IETF
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 microphone and speaker, or with headset, or with USBphone.
Reliable Internet connectivity like DSL, WiFi, cable or LAN. 28.8 dialup modem is good too if you use codec compressing speech to this bandwidth.
Account with an Internet telephony service provider.
