  The development of instabilities leading to the formation of internal shocks
is expected in the relativistic outflows of both gamma-ray bursts and blazars.
The shocks heat the expanding ejecta, generate a tangled magnetic field and
accelerate leptons to relativistic energies. While this scenario has been
largely considered for the origin of the spectrum and the fast variability in
gamma-ray bursts, here we consider it in the contest of relativistic jets of
blazars. We calculate the expected spectra, light curves and time correlations
between emission at different wavelengths. The dynamical evolution of the wind
explains the minimum distance for dissipation (~10^{17} cm) to avoid
$\gamma$--$\gamma$ collisions and the low radiative efficiency required to
transport most of the kinetic energy to the extended radio structures. The
internal shock model allows to follow the evolution of changes, both dynamical
and radiative, along the entire jet, from the inner part, where the jet becomes
radiative and emits at high energies ($\gamma$-jet), to the parsec scale, where
the emission is mostly in the radio band (radio-jet). We have produced some
animations that can be found at http://www.merate.mi.astro.it/~lazzati/3C279/,
in which the temporal and spectral informations are shown together.
