Testing the waters of open source softphones

In our test of two Session Initiation Protocol-based freeware softphone options -- PortSIP and Phoner -- we required them to register and place calls via both freeware Asterisk 1.2 and Zultys MX 250 Enterprise Media Exchange IP PBXs.

Several other open source softphone projects are flourishing on the Internet. In general, the feature sets tend to be simplistic compared with commercial SIP-based and proprietary offerings, but if basic telephony is all that is required, and you have the expertise to support them within your organization, these might fit the bill. We selected two projects that had generally positive reviews from the Internet community and also could be used as a SIP endpoint on an IP PBX.

PortSIP is sort of a hybrid open source softphone. The softphone itself is free and can be downloaded from the project's Web site, which also offers a software development kit (SDK) and sample code for download. The catch on the SDK and code is that it will only allow three-minute voice conversations. The unrestricted SDK can be purchased along with technical support to allow for private labeling and custom user interfaces.

The PortSIP softphone runs on Microsoft Windows 98, 2000, XP and 2003 machines. Installation and registration were straightforward with both PBX systems. It can support as many as five phone-line appearances. The feature list is brief: call hold, call transfer, three-party conferencing, do not disturb, auto answer and redial. It also can record calls locally as a WAV file. The standard codecs (G.711, GSM, iLBC, G.723.1, G.729) are supported as well as video-delivery standards H.263 and H.264.

Audio quality was on par with the other softphone tested, though to use the headset we had to manually configure the audio device to be used. Latency on our test system was less than 100 msec. There were no issues placing calls to other SIP softphones or hard phones registered to the SIP-based PBX systems. Overall, PortSIP was a solid, basic softphone.

Phoner (we tested build 1.93) also is a no-frills softphone with a very simple interface, but it offers a feature set that is a little richer than PortSIP's. Developed and distributed as freeware, it provides all the basic functions of a commercial softphone. Installation was straightforward, and the phone registered to our Asterisks and Zultys SIP PBX systems without any issues.

Phoner supports a range of codecs (G.711, G.726, GSM, iLBC, Speex), as well as echo cancellation. We were surprised that it also provided support for encryption via Secure Real-time Transport Protocol, adding a level of security through the encryption of voice streams. The interface is direct and easy to understand. It provides basic phone features: call hold, call transfer, three-party conference, call forward and the ability to record calls locally.

Users can create a local phone book and import Outlook contacts to it. There also is a built-in answering machine and call log. Commercial systems usually integrate these features with a voice-mail system, whereas Phoner offers them independently. As with PortSIP there were no issues with the audio quality or placing calls to other commercial or open source SIP endpoints tested.