Data transmission in a radio telephone network

For bidirectional transmission of packet data, a packet data service unit (Agent) is disposed in a digital time-division cellular network having a plurality of mobile stations and base stations, with at least one Base Transceiver Station (BTS) in each base station (BS) connected via radio communications channels with at least one mobile station (MS), and with a base station controller (BSC) connected to at least one BTS, and a Mobile Switching Center (MSC) connected to at least one BSC, which Agent connects the cellular network to a data network. As a mobile station is connected to the Agent, signalling related to connection formation characteristics of the network is first accomplished. As a result thereof, the mobile station and the Agent 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 Agent, 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 the radio channel part is disassembled but the virtual channel is maintained until the disconnection of the mobile station from the Agent.