Research conclusions:According to the different resource distribution mode, different announcement mode and different group call end and releasemodes, the discussions and descriptions are made for the different time of setting up group call and the occupation ofdifferentGSM -R resources aswell as the detailed flowsof setting up group call, the callend and call release with A Interface protoco.l In real test, selection of which resource allocation to the corresponding equipment should be careful on the basis of consideration of network resource situation, network co-operating situation and the actual demands of railway dispatching operation.