Land mobile radio system (LMRS), also called public land mobile radio or private land mobile radio, is a term that denotes a wireless communications system intended for use by terrestrial users in vehicles (mobiles) or on foot (portables). Such systems are used by emergency first responder organizations, public works organizations, or companies with large vehicle fleets or numerous field staff. Such a system can be independent, but often can be connected to other fixed systems such as the public switched telephone network (PSTN) or cellular networks.