tree f7fd8909901b34b8e861f4c0c2e136d5e35fff16
parent 15b2b94883519debf026ef0f04ba3783253338d0
author Vadim Yanitskiy <vyanitskiy@sysmocom.de> 1667235698 +0700
committer Vadim Yanitskiy <vyanitskiy@sysmocom.de> 1667235720 +0700

BTS_Tests: fix TC_conn_fail_crit: tune the MS back to BCCH

osmo-bts-trx declares a connection failure when the radio link counter
S reaches 0.  This counter is decreased every time the Viterbi decoder
yields a decoding error on the Uplink SACCH.  For more details, see
3GPP TS 45.008, section 5.2.

The scheduler in osmo-bts-trx expects NOPE indications to be sent by
the transceiver in the absence of valid Uplink bursts.  However, due
to the asynchronous nature of TRXD link, our virtual Um interface
implementation, fake_trx.py, does not generate NOPE indications on
it's own.  Instead, trxcon is sending empty TRXDv0 PDUs (BURST.req),
which are then translated to proper TRXDv1 NOPE.ind by fake_trx.py.

The TC_conn_fail_crit currently sends L1CTL_DM_REL_REQ in order to
simulate connection loss, what makes trxcon disable all active
timeslots and thus stop sending NOPE.req to fake_trx.py.

Let's tune trxcon back to BCCH, in order to ensure that NOPE.req
messages are still being sent, so that osmo-bts-trx will be able
to declare a connection failure over the RSL as expected.

Change-Id: I34aee95111eafea90eeeea861682f1b4547d7b03
Related: Ic292d180ba64206fb4d88adb284f9f9d058b4587