distor- nities, TT is a set of length-N binary vectors TT, with one tion at the client for a given average transmission rate. such vector for each data unit l under consideration for Our discussion serves as the starting point for the transmission. In this representation, the N binary ele- extensions and variations described in the later ments of TI indicate whether, under the policy, the data sections. unit l will be transmitted at each of the next N trans- mission opportunities. The policy is understood to be 3.5.2.1 Basic RaDiO framework contingent upon future acknowledgments that might arrive from the client to indicate that the packet has been Let us assume that a media server has stored a com- received. No further transmissions of an acknowledged pressed audio or video stream that has been packetized data unit l are attempted, even if III specifies a trans- into data units. Each data unit l has a size in bytes BL and mission for a future time slot. a deadline by which it must arrive at the client in order to Each transmission policy leads to its own error prob- be useful for decoding. The importance of each data unit ability, E( TTI), defined as the probability that data unit l is captured by its distortion reduction AD1, a value arrives at the client late, or not at all. Each policy is also representing the decrease in distortion that results if the associated with an expected number of times that the data unit is decoded. Often, distortion is expressed as packet is transmitted under the policy, p(). The goal of mean-squared error, but other distortion measures might the packet scheduler is to find a transmission policy TT be used as well. with the best trade-off between expected transmission Whether a data unit can be decoded often depends on rate and expected reconstruction distortion. At any which other data units are available. In the RaDiO transmission opportunity the optimal TT minimizes the framework, these interdependencies are expressed in Lagrangian cost function a directed acyclic graph. An exam