Packet data transfer in a digital cellular radio system including at least one common organization channel for sending pages, connection requests, and channel assignments so as to establish an actual connection on another channel. User data is transferred from the mobile stations to the base station interleaved with the connection request messages on at least one random-access-type organization channel in messages which will not result in a normal connection establishment. The mobile station sends a random-access-type packet data transfer request on the random-access-type organization channel. A timing advance corresponding to the distance between the base station and the mobile station is determined on the basis of the request received at the base station. The mobile station then utilizes the timing advance for sending data packets on the random-access-type organization channel in messages longer than the transfer request by timing the transfer of the messages with respect to the operation of the base station.