Repeaters and VoIP

Analog repeaters are connected in “Voice over IP” (VoIP). Voice is digital, and is transported between sites by computer networks using TCP/IP protocol.

We choosed Asterisk as the central element of our system. Asterisk is a free and open-source software that was originally built for enterprise telephony systems. A team of developers wrote a driver to connect an analog repeater to Asterisk. It’s called app_rpt. It’s widely used in the US, where there is a national network of Asterisk analog repeaters (AllStar). But it can also be used to build standalone systems. That’s why we choosed Asterisk / app_rpt for building a radioamateur VoIP network on our island.

The system is composed of

• A central hub (TKNet-VoIP) : This is Asterisk software, running on a virtual server in the data center. The hub is the central node of the VoIP. All remote VoIP systems (VHF/UHF repeaters) connect to the hub.
• Several VHF/UHF analog repeaters : Each repeater is composed of an receiver, a transmitter, an USB sound card, and a Raspberry Pi running Linux, Asterisk and app_rpt. Each repeater can work in standalone mode, or can be connected to the hub.
• An Echolink gateway (TK5KP-R) : Internet users can connect to the TK5KP-R Echolink entry point. If it is connected to the hub, Echolink users can be heard on any repeater also connected to the hub.

Connections between Asterisk nodes are using Asterisk native protocol (IAX2) over TCP/IP on TKNet. As it is a “closed” network, traffic is never transmitted to Internet, and no Internet user can connect to it.

There are other ways to connect to TKNet-VoIP :

• Android “IaxRPT” application : This dedicated app can connect to the hub from any Android smartphone. An OpenVPN Android client (with valid authentication) is required.
• Any VoIP application : Any VoIP application (initially designed for remote access to business telephony systems) can be used from any smartphone (Android or Apple). Some succesful tests have been made using Zoiper Android app. An OpenVPN client is also required to enter TKNet.

Thys system has the advantage of using only standard protocols (IAX2, SIP). Most of the software are also free and open-source. HAM network manager has full freedom about what he can do, and how he wants to build his network. No agreement from any third-party business or group is required.

Interconnections are also being developped between Asterisk (Analog) and pure digital systems (D-Star, DMR, etc…). More to follow…