The VoipBlaster is a discontinued product of CreativeLabs and InnoMedia. This device, a little wider than a Nokia 8260 cellular phone, provides a POTS telephone jack, handsfree headset jack, and a USB connector.
The VoipBlaster is a true FXS device. This means it generates dialtone, decodes DTMF, and can even generate voltage to "ring" the telephone ringer. Since this is a standard POTS jack, nearly any analog telephone can be connected -- ranging from portable phones, speakerphones, to cheapo walmart flip phones.
The unit contains a DSP which encodes and decodes G.723.1 streams. This low bitrate stream (a dual rate codec that can switch from 5.3kbps to 6.3kbps -- slightly faster than a 4800 baud modem, but less than a 9600 baud modem) is sent transparently through the computer, requiring very little CPU processing time.
Two drivers exist for this unit. The "factory" drivers only function on the Windows platform. Although H.323 compatible, it is very difficult to bypass the existing "phonebook" interface and dial an IP address directly. Although a little cumbersome, the software works fine. You can make PC-to-PC calls and register with the "phonebook" for free, but to terminate a call to a real telephone (via PSTN), a monthly service must be purchased.
As wireless buffs who wish to use this technology on self-contained, non internet connected networks, the "factory" drivers are not very useful. We cannot always find an outgoing link to the internet, especially after an emergency.
Last, H.323 does not do very well when transversing firewalls. The firewall must take in account special H.323 considerations, such as dynamic port allocation, and watch the application layer very closely. Many SOHO router and firewall devices cannot do this properly. Some expensive and commercial firewall and NAT solutions can, however.
The second driver set corrects many of these problems. Not only does fobbit ( http://www.fobbit.com ) support Windows, but also FreeBSD and Linux. Fobbit also has an open-source phone book system, and the ability to directly dial IP addresses (replacing dots with the "*" key).
Fobbit drivers, however, cannot extablish sessions with VoipBlaster factory driver units and other H.323 devices. They cannot communicate with any existing service for outbound PSTN call termination.
Last, fobbit uses a standard, dedicated port for UDP (the voice "channel" or stream) and TCP for signalling. Fobbit can make outgoing calls behind *any* firewall/NAT configuration, and incoming calls can be made, assuming the firewall forwards the two specific ports/protocols to the machine with the device plugged in.
Fobbit also has been tested over a home wireless network, and no performance problems have been encountered. Assuming that a multi-hop wireless network had a good SNR and fade-margin, and packet loss / jitter / congrestion were low, this application will work flawlessly.
