  In this article we study port-Hamiltonian partial differential equations on
certain one-dimensional manifolds. We classify those boundary conditions that
give rise to contraction semigroups. As an application we study
port-Hamiltonian operators on networks whose edges can have finite or infinite
length. In particular, we discuss possibly infinite networks in which the edge
lengths can accumulate zero and port-Hamiltonian operators with Hamiltonians
that neither are bounded nor bounded away from zero. We achieve this, by first
providing a new description for maximal dissipative extensions of
skew-symmetric operators. The main technical tool used for this is the notion
of boundary systems. The latter generalizes the classical notion of boundary
triple(t)s and allows to treat skew-symmetric operators with unequal deficiency
indices. In order to deal with fairly general variable coefficients, we develop
a theory of possibly unbounded, non-negative, injective weights on an abstract
Hilbert space.
