Presentation of analysis results of the instabilities of QKD systems with modelling of quantum channel as telecom optic fiber. Simulation of a real telecom transmission line of the quantum channel was archived with use of many fiber patches with FC/PC connectors, which modeled wields and connections in real telecom infrastructure. Possibilities of many configurations of transmission line (different numbers of connectors and finals line length) allowed for performance of wide range analysis of QKD systems parameters and overall performance. The dependence of QBER with decrease of quality of real quantum channel of telecom optic fiber was analyzed. The abilities of QKD implementation within telecom metropolitan infrastructure were examined. Also the sensitivity of classical-architecture (non-entanglement-based) and entanglement-based architecture of QKD systems were analyzed in terms of transmission-line defects.