A media stream is transmitted from a server device to a client device. The client device (10) transmits set-up request messages (43a), discovery messages (44b) and a play command message (45a). The server receives versions of the set-up request messages (43b), the discovery message (44b) and the play message (45b) with matching identifier in the payloads of the messages. The server device (12) receives the discovery messages (44b) on a predetermined port and stores information recording that the discovery messages (44b) have been received, at least when no corresponding set-up request message 43b has been received before. The server device (12) compares the identifiers from the received set up request message (43b) and the discovery message (44b) according to the information recording reception, at least when the discovery message (44b) has been received before the set-up request message (43b). The server device (12) selects transport parameters for transmission of the media stream responsive to detection that the first and second identifier have matching values, the selected transport parameters being based on data from said set-up request message (43b) and a port identification from a source field of the discovery message (44b). The media stream is transmitted in accordance with the selected transport parameters to the client device (10) addressed to the port determined from the source field of the discovery message (44b).