  Blazars outburst provide an opportunity to study their spectral behaviour,
correlated variations, and structure of the jet. Such an unprecedented flaring
activity in FSRQ CTA102, during 2016 - 2017, is used for a detailed study to
understand variability mechanisms at short and long time scales, spectral
behaviour in different energy regimes and to estimate sizes and location of the
high-energy emitting region in the jet. Multiwavelength (MW) data (gamma-ray,
X-ray, UV, optical and radio) for CTA102 during its outburst period, are
obtained from Fermi-LAT, Swift-XRT/UVOT, Steward, Mt Abu Infrared Observatory
and OVRO. These are analyzed to construct MW light curves, extract the spectral
information, and to perform the correlated variability studies. Our study shows
that CTA102 attained the highest ever flux levels across the EMS while flaring
and otherwise, with rapid and prolonged activities at all the frequencies. A
number of short term (3 to 8 days) and long term (>month) variability events
are noticed across the EMS. We infer a redder when brighter trend in faint
state and a bluer when brighter trend during a few optical flares. Based on the
flux doubling timescale, the size of the gamma-ray emitting region is estimated
as 8.76x10^{15}cm, located at a distance of about 5.58x10^{16} cm from the
central engine. CTA102 was in extremely bright phase during 2016-17, due
possibly to, successive high energy particle injections into the jet, creating
shocks traveling down the jet which lead to the overall flux enhancement across
the EMS. Alternatively, a decreasing viewing angle could also lead to the
enhanced flux. The study reveals correlated variations in all the energy bands,
with lags within time bins, indicating to co-spatial origin of the emissions.
During the flaring event, a BWB color in optical and harder when brighter trend
in X-ray and gamma-ray spectra are noticed.
