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Understanding softphones

paulcolmer's picture

[b]Understanding softphones[/b]

A softphone is a software program for making telephone calls over the Internet using a general purpose computer,(usually refered to as a softphone client) 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.

A typical application of a softphone is to make telephone calls on the network of an ISTP (Internet telephony service provider) or to connect locally to a IP PBX server as an office extension or for use with call centre agents.

To communicate, both end-points must have the same communication protocol and at least one common audio codec. Most service providers use the Session Initiation Protocol (SIP) G729, G711 ect. Some softphones also support the Inter-Asterisk eXchange protocol (IAX), a protocol supported by the popular open-source software application Asterisk.

[b]Features & Cost[/b]
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. This is where it gets messy ! There are hundreds of ‘FREE’ softphones out there and they all share one thing in common, they don’t support G729 ! They all claim to but require an upgrade to the full version and although this upgrade may give you a few extra features, in reality the upgrade price is what you have to pay to enable the G729 license

To make voice calls over the Internet, a user typically requires the following:
A modern PC, laptop or Tablet ( Windows, Mac, Linux ) with a microphone and speaker, or with a headset, or with USBphone.
Reliable high-speed Internet connectivity
Account with an Internet telephony service provider or IP PBX provider. (SIP account)

If you are going to run your softphone behind an IP PBX on your office LAN you have hundreds of free softphones to choose from for Windows, Mac and Linux. If however you want to connect direct to a provider you are going to need a G729 codec, G711 is way too hungry for bandwidth ! So download the free version, if you like it, a couple of G711 calls wont kill you, get the full version.
I will be reviewing some softphones here, especially the new ones as they are released, so watch this space !