Terminology

	PMR		Private Mobile Radio
	TETRA		Terestrial Trunked Radio
		DMO	Direct Mode Operation (directly from Device to Device)
		TMO	Trunked Mode Operation (network based Kommunikation)
	PTT		Push to Talk  Collective term that can also be used for radio devices, but is usually only used in connection with mobile phones or special PTT devices
		PTToC	Push to Talk over Cellular  defines by name the use on mobile phones or special PTT devices
		MC-PTT	Mission Critical Push to Talk The operator of the 4G/5G data network can provide special bands to ensure communication via the network even if the network is overloaded by private users, e.g. at major events.

PMR operates in a freely available frequency range in which anyone can operate a radio. This was initially only analogue, but was later expanded to include digital channels. With PMR, a predetermined frequency range was divided into channels. The channel number defined a specific intermediate range on which the voice connection was established. Communication was possible within the range of the radio. A licence was not required here.

TETRA is a digital radio which communicates by means of data packets. Radio operation is possible here in DMO as well as TMO.

The range of DMO is limited to the range from transmitter to receiver.

The range of TMO is limited to the devices that are located within a cell around the TETRA base station. For TMO operation of a TETRA network, it is essential to operate a TETRA base station. By networking several base stations, it is possible to extend the range and enable communication between users in different cells. To operate TETRA radio, it may require to obtain licences from your Federal Agency which is responsible for Radio Communication.

PTT is realised via an application that is installed on a mobile device. Communication is not limited to the range between devices or cells. As long as there is a data connection to the Internet (4G, 5G, WLan, ....),it is possible to communicate with each other as long as the same application is used (depending on the application, group management is carried out by an administrator).

PTT (like TETRA) is based on data packets in a network, which is why we do not talk about channel selection as with PMR, but about groups.