The dynamic properties of monodisperse high molecular weight model and entangled linear polymers are by now qualitatively understood to a high degree of sophistication and various processes have been taken into account to complete their full linear relaxation spectrum in both frequency and time domain. The use of scattering methods, i.e. the neutron spin echo method and lately also the small angle scattering technique is responsible for the latest developments which, after reptation, e.g. also allowed contour length fluctuations to be spatially correlated. The foregoing description bases on the tube model as an effective means to simulate the many-chain problem in a mean field approach. The situation is entirely different as soon as non-linear rheology is concerned. No consensus as to the description of start-up flow or microscopic details of the relaxation is present, not the least due to the lack of suitable experimental proof. This work aims at solving these problems and explores the whole time regime after a controlled step-strain experiment with subsequent relaxation.