  The signatures of Ultra High Energy (E >1 EeV) proton propagation through CMB
radiation are pair-production dip and GZK cutoff. The visible characteristics
of these two spectral features are ankle, which is intrinsic part of the dip,
beginning of GZK cutoff in the differential spectrum and E_{1/2} in integral
spectrum. Measured by HiRes and Telescope Array (TA) these characteristics
agree with theoretical predictions. However, directly measured mass composition
remains a puzzle. While HiRes and TA detectors observe the proton dominated
mass composition, the data of Auger detector strongly evidence for nuclei mass
composition becoming progressively heavier at energy higher than 4 EeV and
reaching Iron at energy about 35 EeV. The models based on the Auger and
HiRes/TA data are considered independently and classified using the transition
from galactic to extragalactic cosmic rays. The ankle cannot provide this
transition. since data of all three detector at energy (1 - 3) EeV agree with
pure proton composition (or at least not heavier than Helium). If produced in
Galaxy these particles result in too high anisotropy. This argument excludes or
strongly disfavours all ankle models with ankle energy E_a > 3 EeV. The
calculation of elongation curves, X_{\max}(E), for different ankle models
strengthens further this conclusion. Status of other models, the dip, mixed
composition and Auger based models are discussed.
