With the request technique, a data station wishing to transmit makes sure that the transmission medium is free, e.g. by listening to the bus before transmission starts with the Ethernet or by detecting a token with the Token Ring.
With the request technique, stations willing to transmit send a request for channel allocation to the central station. This request is then taken into account according to various criteria.
Since in case of failure of a single station, depending on the protocol version, the total failure is not mandatory, decentralized techniques are preferred. They also correspond more to the idea of distributed processing of problems, which is the basis of the local area networks (LAN).