Provided is a network adapter for unidirectional transmission of a user data stream to a bidirectional network interface, the network adapter including: a first connection unit which is physically connected to a bidirectional network interface of a first device; a second connection unit which is physically connected to a bidirectional network interface of a second device; and a terminating unit which has at least one bit transmission module and which is designed to establish a bidirectional data link to the network interface of the first device, to receive the user data stream from the first device exclusively in a unidirectional fashion via the data link, and not to send a user data stream to the first device.