Measurement reports weirdness:
- Normally, when activating a channel when establishing a call, we very soon get measurements for the new channel and send a measurement report to the BSC.
- After RSL Chan Activ and RSL Chan Activ ACK for handover, however, there are no measurements for a while.
Using a not-yet-merged patch from pmaier to log measurements in detail ("adding measurement") in osmo-bts, I see that we are not receiving any measurements from the l1.
Looking at the failing cases:
0ms Channel Activ Ack
(no measurements from l1 all this time)
700ms Handover Failure
Looking at the cases where handover succeeds:
0ms Channel Activ Ack
200ms first Handover Detection
couple more Handover Detection
250ms last Handover Detection
260ms first measurement from l1, from now on every ~15ms
400ms RSL Establish IND
550ms Handover Complete
Looks bleak in comparison to a normal TCH/F channel activation:
0ms Chan Activ ACK
2ms first measurement from l1
21ms 2nd
45ms 3rd
56ms 4th
62ms 5th
(these timings according to the packet timestamps when the gsmtap_log is received on the core host, didn't bother with the gsmtap_log timestamps themselves)
It actually looks like the l1 purposefully waits for a Handover Detection before it even considers sending measurements.
Which does make sense to me, as these are uplink measurements, and we wouldn't get any if the MS isn't telling us about them, IIUC.
So, I think examining measurements for handover, as I did now, is actually moot.