In the former Funkrufmaster-Network the connection to the transmitter was established by the Funkrufmaster sofware. So the client was listening on its AX.25 interface for a connect from the master. Using IP as the main protocol to connect transmitters and the DAPNET-Nodes, this direction of connection establishment was inverted. Incoming connections are in some cases a problem with IP: Think of transmitters connected via UMTS or restrictive internet access point, where incoming port forwarding is not possible. So in DAPNET, the transmitter connects itself to the node. As the software of the old RPC transmitters should not be changed, DAPNET-Proxy was born.
The software can be downloaded from github https://github.com/rwth-afu/raspager-proxy. The readme on github is written very good, so we don't repeat here its content. The main idea of the proxy is to establish in both directions a connection to the DAPNET node emulating a UniPager transmitter and on the other side conneting via TCP and xinet.d towards an old AX.25 transmitter emulating a Funkrufmaster software. There is a keep-alive functions implemented towards the AX.25-transmitter. So the DAPNET-Node will be notified, if the AX.25 connection is not alive any more.