  We present a process algebra aimed at describing interactions that are
multiparty, i.e. that may involve more than two processes and that are open,
i.e. the number of the processes they involve is not fixed or known a priori.
Here we focus on the theory of a core version of a process calculus, without
message passing, called Core Network Algebra (CNA). In CNA communication
actions are given not in terms of channels but in terms of chains of links that
record the source and the target ends of each hop of interactions. The
operational semantics of our calculus mildly extends the one of CCS. The
abstract semantics is given in the style of bisimulation but requires some
ingenuity. Remarkably, the abstract semantics is a congruence for all operators
of CNA and also with respect to substitutions, which is not the case for strong
bisimilarity in CCS. As a motivating and running example, we illustrate the
model of a simple software defined network infrastructure.
