ttcn3-bts-test: both TC_rsl_bs_pwr_static_ass and TC_rsl_bs_pwr_static_power_control failing
Both test cases were introduced back in 2019 without taking into account that BS power control is not allowed on C0 (except when the BTS is in the BCCH carrier power reduction mode). Until recently, osmo-bts used to accept and ACKnowledge any BS power reduction value during the CHANnel ACTIVation on C0, and then pretend like the given value is actually used by indicating it in the RSL Measurement Reports. However, since recently this is not the case anymore:
commit 30aea88c2cc09b8da4252ba7882c01eff0282790 Author: Vadim Yanitskiy <firstname.lastname@example.org> Date: Thu Jul 1 02:00:14 2021 +0200 power_control: constrain BS power reduction on BCCH carrier BS Power Control is not allowed on the BCCH/CCCH carrier, unless the BTS is operating in the BCCH carrier power reduction mode. Allow constrained BS power reduction (up to 6 dB) on active logical channels iff BCCH carrier power reduction mode is enabled. Change-Id: I3299b6cdd230d3767321c3d6c64d468b7f5e1d02 Related: SYS#4919, SYS#4918
After this change, osmo-bts does constrain the received BS power reduction value depending on whether the BCCH power reduction is enabled (up to 6 dB) or not (forced to 0 dB). So osmo-bts does not lie anymore, and this is exactly what makes the test cases fail.
How de we solve this?¶
Ideally, we should run these test cases against additional transceivers, not against the BCCH carrier. We already run the IUT in a multi-trx configuration, however none of the test cases actually make use of additional resources so far. The test suite still needs quite a lot of work to make this possible. A quick and dirty solution would be to enable BCCH carrier reduction mode in these test cases, however I don't like this idea.