A contention-based datalink couples a receiving station and a plurality of sending stations. A first sending station has established a communication session with the receiving station. If a second one of the plurality of sending stations requests a call setup for a higher priority low-latency transmission, the receiving station sends a poll to the second sending station. The poll causes the first sending station to temporarily suspend its transmission activities and permits the second sending station to transmit a real time protocol (RTP) datagram. Upon completion of transmission from the second sending station, the suspended transmission from the first sending station resumes in a transparent fashion. The receiving station controls transmission rate by sending poll requests at intervals determined by a data value transmitted from sending station. Within the sending station, datagrams in an output queue are monitored and polling rate varied so as to maintain the number of datagrams in the output queue at an optimal level.