Problems with understanding packet downlink assignment

hi, i try to unterstand downlink assignment. there are two ways to perform it: - on AGCH/PAGCH when mobile is in packet idle mode - on PACCH when mobile is in packet transfer mode (currently ongoing uplink TBF) (for establishment of uplink TBF in packet idle mode, the mobile repeats channel requests after one second timeout.) i don't see any procedure how the networks repeats a downlink assignment, if there is no response from the mobile (if downlink assignment got lost, hence it was not received by mobile). the only logical procedure i can see is that the messages from SGSN will get dropped during release of downlink TBF. (the release happens, because there is no response from mobile to polling of downlink acknowledgements.) regards, andreas