In this paper we consider a direct numerical simulation of transition from laminar to turbulent flow excited by wall disturbances in a cylindrical pipe. The wall disturbances are imposed by means of blowing and suction through the pipe wall. Two cases are considered: periodic suction/blowing (PSB) and random suction/blowing (RSB). The former case can be interpreted as a pipe flow in combination with a periodic roughness element of a fixed size and the latter as a pipe with randomly distributed wall roughness elements. For the PSB case the critical amplitude of the blowing/suction velocity that causes transition is obtained. The dependence of this critical amplitudes on the Reynolds number is considered. In addition the dependence of the transition time on the suction/blowing amplitudes and the Reynolds number is investigated. This latter parameter is also considered for the RSB case.