  We construct some admissible Banach representations of GL_2(Q_p) that
conjecturally should correspond to some 2-dimensional tamely ramified,
potentially Barsotti-Tate representations of G_{Q_p} via the p-adic local
Langlands correspondence. To achieve this, we generalize Breuil's work in the
semi-stable case and work on the first covering of Drinfel'd upper half plane.
Our main tool is an explicit semi-stable model of the first covering.
