A method in which a media server detects a media stream from a gateway which is only capable of sending a stream from a half duplex source. Call setup, such as a floor request from the gateway or the half duplex source, is not required. The media server then blocks media streams from full duplex sources to create half duplex communication, without using a buffer. Once the stream from the gateway has ended, the server detects streams from other sources and restores full duplex communication. A communication server carries out the method and is capable of detecting whether or not the server is connected to a half duplex source, such as a Land Mobile Radio (LMR) gateway, and then altering behavior according to that source. In doing so, the server enables either half duplex or full duplex operation, depending upon whether the source data originates from the half duplex source.