  Simplified model for current-voltage characteristics of weak links is
suggested. It is based on an approach considering the multiple Andreev
reflection in metallic Josephson junction. The model allows to calculate
current-voltage characteristics of the superconductor - normal metal -
superconductor junctions with different thicknesses of normal layer at
different temperatures. A hysteretic peculiarity of $V(I)$ dependence is
described as result of the negative differential resistance. The
current-voltage characteristic of high-$T_c$ composite YBCO +BaPbO${_3}$ were
computed.
