  We study sharply localized sectors, known as sectors of DHR-type, of a net of
local observables, in arbitrary globally hyperbolic spacetimes with dimension
$\geq 3$. We show that these sectors define, has it happens in Minkowski space,
a $\mathrm{C}^*-$category in which the charge structure manifests itself by the
existence of a tensor product, a permutation symmetry and a conjugation. The
mathematical framework is that of the net-cohomology of posets according to
J.E. Roberts. The net of local observables is indexed by a poset formed by a
basis for the topology of the spacetime ordered under inclusion. The category
of sectors, is equivalent to the category of 1-cocycles of the poset with
values in the net. We succeed to analyze the structure of this category because
we show how topological properties of the spacetime are encoded in the poset
used as index set: the first homotopy group of a poset is introduced and it is
shown that the fundamental group of the poset and the one of the underlying
spacetime are isomorphic; any 1-cocycle defines a unitary representation of
these fundamental groups. Another important result is the invariance of the
net-cohomology under a suitable change of index set of the net.
