  We discuss differences and similarities between jets powered by super-massive
black holes in quasars and by stellar-mass black holes in microquasars. The
comparison is based on multi-wavelength radio-to-infrared observations of the
two active galactic nuclei 3C 273 and 3C 279, as well as the two galactic
binaries GRS 1915+105 and Cyg X-3. The physical properties of the jet are
derived by fitting the parameters of a shock-in-jet model simultaneously to all
available observations. We show that the variable jet emission of galactic
sources is, at least during some epochs, very similar to that of extra-galactic
jets. As for quasars, their observed variability pattern can be well reproduced
by the emission of a series of self-similar shock waves propagating down the
jet and producing synchrotron outbursts. This suggests that the physical
properties of relativistic jets is independent of the mass of the black hole.
