140 detects the contents of fifo buffer 142 as exceeding watermark 402 and instructs clearinghouse to send less message data i e use long flags 302 during the following lag period t2 t1 the volume of data in fifo buffer continues to grow until the time t2 when clearinghouse actually starts using long flags 302 the level of message data in fifo buffer 142 then begins to reduce the transmission rate of message data leaving radio station 114 being greater than the transfer rate to radio station 114 at time t3 scag 140 detects the level of message data in fifo buffer 142 as falling below watermark 402 and instructs clearinghouse 110 to use short flags 302 to increase message data flow at a later time t4 following a lag period t4 t3 clearinghouse 110 acts on these instructions and fifo buffer 142 begins to fill with message data the cycle repeats beginning at time t5 when scag 140 detects the size of fifo buffer 142 as exceeding watermark 402 thus management of data flow to radio station 114 is achieved by avoiding overflow and underflow of fifo buffer 142 a similar use of long and short flags 308 is used to prevent underflow and overflow of buffer 164 in such case scag 140 manages directly the use of long and short flags sent to clearinghouse 110 as scag 140 can monitor directly to volume of data in buffer 164 fig4 d illustrates programming of scag 140 to manage data flow to clearinghouse.