Portable and Secure IP PBX

I have been trying to build a prototype of VoIP system for rural area, and I would like to integrate/link the project with my Computer and Network Security course in terms of practical and hands-on application of the materials in the course as well as developing research and team work cultures. In this short post I will try to draw the concept of this system.

The system basically comprises an IP PBX or VoIP server runs on embedded system/single-board computer, several small wireless routers, and VoIP clients. The characteristics of the system that will be implemented in rural area should be portable and resilience, hopefully, regarding devices and their interconnections to each other also connection to other networks or the Internet.

Let us narrow it down to the prototype, make sure it follows the aforestated characteristics or design considerations. First, it needs an IP PBX, we will use Raspberry Pi B+ for the hardware, Raspbian for the OS, and Asterisk for the IP PBX server software that supports SIP and RTP. Second, the network should be resilient in connecting when one or two devices move out to other areas or they shutdown for some reasons. The possible topology is mesh, and the routing protocol is OLSR/B.A.T.M.A.N/Babel. Third, we need to make sure that communications happening over the system could not be intercepted by adversaries. Hence, we need to secure the communications by employing security protocol, such as SRTP or ZRTP.