  The true nature of the radio emitting material observed to be moving
relativistically in quasars and microquasars is still unclear. The microquasar
community usually interprets them as distinct clouds of plasma, while the
extragalactic community prefers a shock wave model. Here we show that the
synchrotron variability pattern of the microquasar GRS 1915+105 observed on 15
May 1997 can be reproduced by the standard shock model for extragalactic jets,
which describes well the long-term behaviour of the quasar 3C 273. This
strengthens the analogy between the two classes of objects and suggests that
the physics of relativistic jets is independent of the mass of the black hole.
The model parameters we derive for GRS 1915+105 correspond to a rather
dissipative jet flow, which is only mildly relativistic with a speed of 0.60 c.
We can also estimate that the shock waves form in the jet at a distance of
about 1 AU from the black hole.
