On the layer 1 of the Air interface we have the parameter called RADIO-LINK-TIMEOUT. This parameter sets the threshold for the radio downlink failure on the SACCH (slow associated control channel). The channel should only be held for as long as a user could reasonably be expected to hold while experiencing loss of audio. After this, the user would assume the call had dropped, and hang up.
This parameter is set from 4 – 64 SACCH frames, corresponding to 1.92 – 30.72 seconds (1 SACCH frame = 480ms). You can increase this parameter so that the MS will hold the channel longer in case of bad RF link performance.