TRANSMISSION SYSTEM

PROBLEM TO BE SOLVED: To prevent a mobile unit which cannot transmit data from being selected. SOLUTION: A controller 17 of a base unit 1 periodically checks the existence (operating status) of camera mobile units 3A-3C and sub-base units 4A-4D by repetitiously sending a control signal containing check data, and receiving a control signal containing a response while sequentially polling IDs of individual camera mobile units 3A-3C and sub-base units 4A-4D at regular time intervals. When a monitor button or an extension line button is operated, the controller 17 of the base unit 1 eliminates buttons B4-B6 and B11-B14 corresponding to the camera mobile units 3A-3C and sub-base units 4A-4D assigned with the IDs which have been confirmed as absent from a video monitor selection screen G1 or an extension line selection screen G2, and does not display those buttons thereon. Consequently, the camera mobile units 3A-3C and sub-base units 4A-4D which cannot transmit data are prevented from being selected by mistake on the video monitor selection screen G1 or the extension line selection screen G2. COPYRIGHT: (C)2008,JPO&INPIT