t re- and interdependencies of the data units available at the ceives a media packet, the client sends an acknowledg- server ahead of time. The size of this hint track or rate- ment packet (ACK) to the server. If the ACK packet is distortion preamble is small relative to the media stream. lost, the server may decide to unnecessarily retransmit The receiver uses this information to compute the packet at the expense of other packets. media packet packet Client Server a) Sender-Driven request packet media packet Client Server b) Receiver-Driven Figure 3.5-3 In sender-driven streaming (a), the server computes an optimal sequence of media packet transmissions and the client acknowledges packets upon receipt. In receiver-driven streaming (b), the complexity is shifted to the client. The client computes an R-D optimized sequence of requests to send to the server and the server only needs to respond to the client's requests. Network adaptive media transport CHAPTER 3.5 A transmission policy specifies what transmission action Switch/ Packet Router will be taken as a function of what state qi is reached in the tree. Media Server Proxy Client A Markov decision tree is shown in Figure 3.5-5. The Server tree enumerates the possible sequences of observation- action pairs for the transmission of a data unit using the Backbone Network rich acknowledgment scheme. In the tree, possible ac- Last hop tions a are send or don't send. Possible observations o are (0), no relevant feedback has arrived, ACK, a feedback Figure 3.5-4 Proxy-driver RaDiO streaming. A proxy server lo- packet has acknowledged the reception of the data unit, cated between the backbone network and a last hop link uses or NACK, a feedback packet has indicated that the a hybrid of receiver- and sender-driven RaDiO streaming to jointly packet has not been received by the feedback packet's optimize requests to send to the server and media packets to send time. NACKs with different time stamps are dis- forward to the client. tinct observations. In contrast, in the con