  We investigate the problem of determining the parameters that describe a
quantum channel. It is assumed that the users of the channel have at best only
partial knowledge of it and make use of a finite amount of resources to
estimate it. We discuss simple protocols for the estimation of the parameters
of several classes of channels that are studied in the current literature. We
define two different quantitative measures of the quality of the estimation
schemes, one based on the standard deviation, the other one on the fidelity.
The possibility of protocols that employ entangled particles is also
considered. It turns out that the use of entangled particles as a new kind of
nonclassical resource enhances the estimation quality of some classes of
quantum channel. Further, the investigated methods allow us to extend them to
higher dimensional quantum systems.
