  We present the development of the End-to-End simulator for the SOXS
instrument at the ESO-NTT 3.5-m telescope. SOXS will be a spectroscopic
facility, made by two arms high efficiency spectrographs, able to cover the
spectral range 350-2000 nm with resolving power R=4500. The E2E model allows to
simulate the propagation of photons starting from the scientific target of
interest up to the detectors. The outputs of the simulator are synthetic
frames, which will be mainly exploited for optimizing the pipeline development
and possibly assisting for proper alignment and integration phases in
laboratory and at the telescope. In this paper, we will detail the architecture
of the simulator and the computational model, which are strongly characterized
by modularity and flexibility. Synthetic spectral formats, related to different
seeing and observing conditions, and calibration frames to be ingested by the
pipeline are also presented.
