  Intra-session network coding has been shown to offer significant gains in
terms of achievable throughput and delay in settings where one source
multicasts data to several clients. In this paper, we consider a more general
scenario where multiple sources transmit data to sets of clients and study the
benefits of inter-session network coding, when network nodes have the
opportunity to combine packets from different sources. In particular, we
propose a novel framework for optimal rate allocation in inter-session network
coding systems. We formulate the problem as the minimization of the average
decoding delay in the client population and solve it with a gradient-based
stochastic algorithm. Our optimized inter-session network coding solution is
evaluated in different network topologies and compared with basic intra-session
network coding solutions. Our results show the benefits of proper coding
decisions and effective rate allocation for lowering the decoding delay when
the network is used by concurrent multicast sessions.
