In this paper we present a rapid review of known results in the context of different scenario of the erasure channel. We will also give a converse capacity bound for relay channel showing that the cut-set bound is not attainable in general by any fixed coding scheme for the single sender-single relay case. This bound shows the difference between the degraded situation where the cut-set bound is attainable and some specific case of the non-degraded situation where the cut-set bound is not attainable. The obtained reverse bound could be used for deriving tighter cut-set type bound for general multi-terminal erasure channels.