  At a distance of 249 Mpc ($z$=0.056), Cygnus A is the only powerful FR II
radio galaxy for which a detailed sub-parsec scale imaging of the base of both
jet and counter-jet can be obtained. Observing with VLBI at millimeter
wavelengths is fundamental for this object, as it uncovers those regions which
appear self-absorbed or free-free absorbed by a circumnuclear torus at longer
wavelengths. We performed 7 mm Global VLBI observations, achieving ultra-high
resolution imaging on scales down to 90 $\mu$as. This resolution corresponds to
a linear scale of only $\sim$400 Schwarzschild radii. We studied the transverse
structure of the jets through a pixel-based analysis, and kinematic properties
of the main emission features by modeling the interferometric visibilities with
two-dimensional Gaussian components. Both jets appear limb-brightened, and
their opening angles are relatively large ($\phi_\mathrm {j}\sim 10^{\circ}$).
The flow is observed to accelerate within the inner-jet up to scales of $\sim$1
pc, while lower speeds and uniform motions are measured further downstream. A
single component seen in the counter-jet appears to be stationary. These
observational properties are explained assuming the existence of transverse
gradient of the bulk Lorentz factor across the jet, consisting of a fast
central spine surrounded by a slower boundary layer.
