Everything I now about Doka-b is at:   https://sites.google.com/site/andythomasorg/amateur-satellites/rs-30-yubilei...   I have seen it in action, it is a combined hard wired modem interface and az/el controller at the ground station end. It is only available to Russian (diaspora?) universities and is a protected commercial secret.   Each setup is unique to the particular university research project and multiple projects at different Russian universities have their own groundstations.     I think you have to consider the satellite part as one half of a whole network with the ground station which performs the connection being the other half of the circuit. To that extent, consider the satellite as having its own tcp/ip address, and its transceiver operating in a psk variant using radio to link instead of a cable.  A lot of handshaking etc.   I don't think there is a broadcast mode in Doka-b, just the circuit, although it is understood to be possible for the transmitter to beacon images and other data.   73 de andy g0sfj