  We consider the problem of linear network coding over communication networks,
representable by directed acyclic graphs, with multiple groupcast sessions: the
network comprises of multiple destination nodes, each desiring messages from
multiple sources. We adopt an interference alignment perspective, providing new
insights into designing practical network coding schemes as well as the impact
of network topology on the complexity of the alignment scheme. In particular,
we show that under certain (polynomial-time checkable) constraints on networks
with $K$ sources, it is possible to achieve a rate of $1/(L+d+1)$ per source
using linear network coding coupled with interference alignment, where each
destination receives messages from $L$ sources ($L < K$), and $d$ is a
parameter, solely dependent on the network topology, that satisfies $0 \leq d <
K-L$.
