An adaptive multiple retransmission technique for continuous media streams


Retransmission can be used for loss recovery in continuous media applications but the number of retransmission attempts is bounded by the size of the playout buffer. For efficient recovery, a protocol must attempt as many retransmissions as possible but avoid late retransmissions. This typically requires that the playout buffer be sized in round-trip time (RTT) multiples plus some margin for error. RTT-based timers are then used to trigger retransmissions. However, this approach is problematic due to (i) the high variation in RTT commonly encountered in the Internet, and (ii) the coarse granularity of timers typically used in protocol implementations. We present two new retransmission-based protocols, for unicast and multicast respectively, which eliminate RTT estimation and timer-triggered events. As a result, our protocols are immune to errors due to RTT jitter and timer granularity and recover more losses, while better suppressing unnecessary retransmission requests and retransmissions than timer-based protocols. At the same time, our protocols are simpler to implement and degrade more gracefully than timer-based protocols.

Publication Title

Proceedings of the International Workshop on Network and Operating System Support for Digital Audio and Video