1.16 KBPS LAPD Links can support upto 12 SDCCH channels & a maximum of 18 channels at any time.So,if in a particular TRX if you are using 2 SDCCH & rest are TCHD,there is every possibility of TCH/SDCCH blocking & drop.
In non-BCCH TRX also,take care of this fact & keep only 1 SDCCH & at max 3 TCHD.
2.Check with the command “ZOLT;” in BSC,if TX/RX Erlang >0.2 in BH,need to add SL(if < 16 SL) or augment(64 KBPS to 128 KBPS). Yes,reducing MAXRET will help. Reducing DMAX is a cynical way of reducing SDCCH Blocking Br\\ Bijoy