Basically when using mainBCCH, we see that the uplink RXLEV within the measurement reports coming from the BTS drop to 0 after 10 seconds after reception of the location update request (no reply sent from the MSC).
While when using bcchCombined, we see that the measurement reports are fine and then after 20 seconds we see a release indication for sapi 0, indicating that the MS has explicitely released layer 2.
This behaviour has been observed with all or handsets.
(We are currently testing the particular behaviour whereby the mobile doesn’t get an answer for a LU request).