Data transmission in a radio telephone network

For bidirectional transmission of packet data, a packet data service unit (Agent) is disposed in a digital cellular system connected to be in association with a Mobile Switching Center, and connecting the cellular network to the date network. As a mobile station is connected to the packet data service unit, signalling related to connection formation characteristics of the network is first accomplished. As a result thereof, the mobile station and the data service unit are provided with a number of stored parameters relating to each other. This situation creates or is called a virtual channel. When a mobile station wants to transmit or receive data packets between the mobile station and the data service unit a packet data transfer channel is established making use of the parameters of the virtual channel and thereby using substantially less signalling than the channel establishment signalling characteristic of the network, one part thereof being a radio channel and the other part a time slot in a digital trunk line. On termination of data packet transfer, at least said radio channel is disassembled but the virtual channel is maintained until the disconnection of the mobile station from the data service.