Distributed fibre optic sensing is well known in defence or oil industry in use as acoustic sensing. Telecommunication networks are threatened by fibre cuts mainly caused by digging activity or theft. Many network operators seeking appropriate solution for selfprotecting infrastructure system. Most commercially available solutions of distributed sensing systems allow sensing only on dedicated fibres. Sharing the same infrastructure for data transmission and sensing is, however, more advantageous. On the other hand, it is necessary to solve the possible interaction of both services and thus the interference. We have developed our own sensing systems and we have made several measurements to evaluate the suitability of the most widely used distributed sensing techniques – interferometric, reflectometry and polarization for using in existing data infrastructures on optical fibres with active data traffic.