  We study the long-term time-scale (i.e. period comaprable to the orbital
period of the outer perturber object) transit timing variations in transiting
exoplanetary systems which contain a further, more distant (a_2>>a_1) either
planetary, or stellar companion.
  We give an analytical form of the O-C diagram (which describes such TTV-s) in
trigonometric series, valid for arbitrary mutual inclinations, up to the sixth
order in the inner eccentricity. We show that the dependence of the O-C on the
orbital and physical parameters can be separated into three parts. Two of these
are independent of the real physical parameters (i.e. masses, separations,
periods) of a concrete system, and depend only on dimensionless orbital
elements, and so, can be analyzed in general. We analyze these dimensionless
amplitudes for different arbitrary initial parameters, as well as for two
particular systems CoRoT-9b and HD 80606b. We find in general, that while the
shape of the O-C strongly varies with the angular orbital elements, the net
amplitude (departing from some specific configurations) depends only weakly on
these elements, but strongly on the eccentricities. As an application, we
illustrate how the formulae work for the weakly eccentric CoRoT-9b, and the
highly eccentric HD 80606b. We consider also the question of detection, as well
as the correct identification of such perturbations. Finally, we illustrate the
operation and effectiveness of Kozai cycles with tidal friction (KCTF) in the
case of HD 80606b.
