A network for data communication and for data exchange between communication units (1, 2), a) comprising a base network and a number of communication units (1, 2) connected to the base network, specifically - at least one control centre and - at least one mobile terminal disposed and/or arranged in a vehicle mounted on rails, b) wherein the base network is connected to a number of transmitter stations disposed along the rail section, c) via the transmitter stations, in particular exclusively, two types of communication channels (51, 52) are available via radio from the base network to the mobile terminals disposed in the vehicles, more specifically - a voice channel for transmitting speech, and - a data channel for transmitting digital data, and d) wherein the base network, upon the request of a communication unit (1, 2), creates one or more communication channels (51, 52) for data transmission between, in particular exclusively, two communication units (1, 2), wherein e) a central distribution computer for establishing, terminating and managing one or more communication channels (51, 52) for data and/or voice communication between the distribution computer and the communication units (1, 2) via the base network is connected to the base network as a further communication unit, f) the distribution computer, when a request of a communication unit (1, 2) arrives via a data channel, can be activated and creates and maintains a voice communication via a voice channel both for the requesting communication unit and one or more communication units (1, 2) specified or determinable by the particular request, and g) during the existence of the voice channels (51, 51') established in this way, when voice messages arrive at the distribution computer the distribution computer forwards said messages to the other communication units (1, 2) specified or determined by the particular request, characterised in that - the base network is a TETRA or LTE network or a GSM, but not a GSM-R network, wherein data channels are established via a signalling by means of short messages, in particular SMS or SDS, or the base network is an analogue radio network, wherein a modem is provided for the transmission of data between the base network and the mobile terminals and encodes the data to be transmitted into an analogue signal superimposed with the voice data and decodes superimposed encoded data present in the voice data and makes this data available in digital form. a) comprising a base network and a number of communication units (1, 2) connected to the base network, specifically - at least one control centre and - at least one mobile terminal disposed and/or arranged in a vehicle mounted on rails, - at least one control centre and - at least one mobile terminal disposed and/or arranged in a vehicle mounted on rails, b) wherein the base network is connected to a number of transmitter stations disposed along the rail section, c) via the transmitter stations, in particular exclusively, two types of communication channels (51, 52) are available via radio from the base network to the mobile terminals disposed in the vehicles, more specifically - a voice channel for transmitting speech, and - a data channel for transmitting digital data, and - a voice channel for transmitting speech, and - a data channel for transmitting digital data, and d) wherein the base network, upon the request of a communication unit (1, 2), creates one or more communication channels (51, 52) for data transmission between, in particular exclusively, two communication units (1, 2), wherein e) a central distribution computer for establishing, terminating and managing one or more communication channels (51, 52) for data and/or voice communication between the distribution computer and the communication units (1, 2) via the base network is connected to the base network as a further communication unit, f) the distribution computer, when a request of a communication unit (1, 2) arrives via a data channel, can be activated and creates and maintains a voice communication via a voice channel both for the requesting communication unit and one or more communication units (1, 2) specified or determinable by the particular request, and g) during the existence of the voice channels (51, 51') established in this way, when voice messages arrive at the distribution computer the distribution computer forwards said messages to the other communication units (1, 2) specified or determined by the particular request, - the base network is a TETRA or LTE network or a GSM, but not a GSM-R network, wherein data channels are established via a signalling by means of short messages, in particular SMS or SDS, or the base network is an analogue radio network, wherein a modem is provided for the transmission of data between the base network and the mobile terminals and encodes the data to be transmitted into an analogue signal superimposed with the voice data and decodes superimposed encoded data present in the voice data and makes this data available in digital form.