  We relate a part of the abelian etale fundamental group of curves over local
fields to the component group of the Neron model of the jacobian. We apply the
result to the modular curve X_0(p)/Q_p to show that the unramified abelian
covering X_1(p) over X_0(p) (Shimura covering) uses up all the possible
ramification over the special fiber of X_0(p).
