TCP gives you two guarantees over UDP: * All packets arrive. (Reliable transport). * All packets that arrive are in order. (Sequential transport). Unfortunate

TCP gives you two guarantees over UDP: * All packets arrive. (Reliable transport). * All packets that arrive are in order. (Sequential transport). Unfortunately, both of these aren't so necessary for real time audio (and somewhat less so, video). In fact, they get in the way. Missing packets can often be replaced in VoIP settings with various kinds of interpolation. And out of order data can be buffered and used to build the interpolated data before playback. Interestingly enough, even packets that have been damaged still often are usable to VoIP applications, since they still contain some payload that can be used to improve the signal.