The present invention detects a failure location of network in the
Internet. A pair of networks consists of an access network and an
Internet service provider network, and a route consists of a source pair
of networks and a destination pair of networks. The quality information
values are inputted to elements in a matrix that all pairs of networks
are put in same order as rows (or columns) of source pairs of networks
and columns (or rows) of destination pairs of networks. If inferior
quality values in the matrix line up in the row (or column), a failure is
determined in a destination (or a source) pair of networks in column side
(or row side) corresponding to a row (or a column). If inferior quality
values line up in a slanting direction, a failure is determined in a
route between the Internet service provider networks indicated to the
slanting direction.
