The direction of a message indicates whether the message is coming into an endpoint or going out from an endpoint. Input is incoming to the server and Output is outgoing from the server. For a basic request/response message pattern, a request is incoming to the server and the response is outgoing from the server. On callbacks from the server to client, however, a request is outgoing from the server and a response is incoming to the server.
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)