  Loss tomography has received considerable attention in recent years and a
number of estimators have been proposed. Unfortunately, almost all of them are
devoted to the tree topology despite the general topology is more common in
practice. In addition, most of the works presented in the literature rely on
iterative approximation to search for the maximum of a likelihood function
formed from observations, which have been known neither scalable nor efficient.
In contrast to the tree topology, there is few paper dedicated to the general
topology because of the lack of understanding the impacts created by the probes
sent by different sources. We in this paper present the analytical results
obtained recently for the general topology that show the correlation created by
the probes sent by multiple sources to a node located in an intersection of
multiple trees. The correlation is expressed by a set of polynomials of the
pass rates of the paths connecting the sources to the node. In addition to the
expression, a closed form solution is proposed to obtain the MLE of the pass
rates of the paths connecting the sources to the node. Then, two strategies are
proposed to estimate the loss rate of a link for the general topology: one is
path-based and the other is link-based, depending on whether we need to obtain
the pass rate of a path first. The two strategies are compared in the context
of the general topology that shows each has its advantages and the link-based
one is more general. Apart from proving the estimates obtained are the MLEs, we
prove the estimator presented here has the optimal asymptotic property.
