Cellular Network Infrastructure » Radio Access Network » OsmoBTS

So it seems like the SACCH in downlink is received, but the fill frames that should be sent by the related code in osmo-bts (https://gerrit.osmocom.org/c/osmo-bts/+/10415) are either not sent, or somehow lost, or not detected by the test case.

That commit has been reverted (see Ibd8c0899451ae3c17bc07d4e112e32b4897405c9). It looks like another implementation was merged.

See also https://osmocom.org/issues/1950#note-14
Updated by stsp about 2 years ago:

These changes are currently stalled because the foundations for testing DTX mode are missing from trxcon.

We're checking DTX frames on Downlink, so trxcon only needs to decode Downlink frames. I don't think anything is missing.

My DTX TTCN3 tests are currently unable to deal with frame numbers in a reliable way.
A hardware setup might serve as a workaround but AFAIK won't result in automated tests which can be run in our current jenkins setup.

I checked the test case implementation, and indeed it's not handling frame numbers correctly (especially the case where the frame number wraps). In general, the code is messy and hard to read. I think we need to clean it up first, I already have some patches.

https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/20884 BTS_Tests/DTX: get rid of f_g_chan_is_{tchf,tchh,sdcch4,sdcch8}
https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/20887 BTS_Tests/DTX: SACCH has nothing to do with fill frames
https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/20888 BTS_Tests/DTX: provide more details in failed verdict message
https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/20889 BTS_Tests/DTX: remove redundant RSL channel number check

With this patch set applied, it reveals that in TCH/F DTX mode, osmo-bts-trx does not send any fill frames at all.

Moreover, we don't cover TCH/F and TCH/H in speech mode. DTX is also allowed for the later.