I. INTRODUCTION
The recent development of overlay networks is quite interesting
for multimedia transmission since these networks offer
significant network diversity that can be used for improved
quality of service. The traditional streaming systems based on
ARQ or channel coding techniques often fail to efficiently exploit
this diversity, since they suffer from high computational
costs and are quite unreliable in large scale networks where
channel conditions are hard to estimate. A different paradigm
has been initiated recently with network coding [1], [2], where
some processing is requested from the network nodes in
order to improve the transmission performance. Specifically,
network coding nodes randomly combine the buffered packets
before forwarding them to next hop nodes. It is particularly
appealing in networks with diversity, as it does not impose
coordination between nodes. It allows for better adaptation to
the available bandwidth and even permits to approach maxflow
min-cut bound of the network graph. Overall, the network
coding systems show improved resiliency to dynamics, delays,
scalability and buffer capacities [3].