  We consider a characteristic problem of the vacuum Einstein equations with
part of the initial data given on a future complete null cone with suitable
decay, and show that the solution exists uniformly around the null cone for
general such initial data. We can then define a segment of the future null
infinity. The initial data are not required to be small and the decaying
condition inherits from the works of \cite{Ch-K} and \cite{K-N}.
