  The multichannel scattering problem for the stationary Schr\"{o}dinger
equation on a line with different thresholds at both infinities is
investigated. The analytical structure of the Jost solutions and of the
transition matrix relating the Jost solutions as functions of the spectral
parameter is described. Unitarity of the scattering matrix is proved in the
general case when some of the scattering channels can be closed and the
thresholds can be different at left and right infinities on the line. The
symmetry relations of the $S$-matrix are established. The condition determining
the bound states is obtained. The asymptotics of the Jost functions and of the
transition matrix are derived for a large spectral parameter.
