Slightly OT: NanoBTS / OpenBSC question

Hi, does anybody know when the exact moment in a call is, when the NanoBTS starts forwarding audio from a MS to OpenBSC? Is it always when the "Create Connection" RSL message is sent and the TCP connection was established? (Assuming the channel was set up as traffic channel) Or could it be that the BTS waits for the "Connect" message from the MS? I started thinking about that when I saw that the NanoBTS _never_ sets the "transparent to the BTS" bit in the first byte of RSL messages... Regards, -Tobias