TFRC and RTT thresholds interdependence in a selective retransmission scheme

Retransmission based error recovery is not always applicable for multimedia applications; however it can be used if the transmission characteristics and network conditions are examined before. Retransmissions can be carried out only if there is no congestion in the network and the network delay is low enough to receive the retransmitted packet before the playout. These two attributes are depending and one can be estimated from the other. In this paper we introduce a TFRC and RTT threshold interdependence model to determinate network delay thresholds for the retransmission decision algorithm. Using the calculated sending rate of the TFRC (TCP Friendly Rate Control) to estimate the congestion level in the network, we can set up a threshold of disabling/enabling the retransmissions. Our goal was to determinate a matching RTT threshold to gain similar retransmission behavior as using the sending rate threshold. We found that using our threshold estimating model, the number of retransmitted packets was similar, using the TFRC-based sending rate threshold and the RTT retransmission threshold.