So far, sms_pending_failed() starts a new sms_queue_trigger() run. The
intention behind that might have been to fill up the queue when sending SMS has
failed, but the practical effect is actually bad:
As current ttcn3-msc-test runs show, a failed MT SMS gets triggered multiple
times in short succession, i.e. osmo-msc repeatedly sends Paging Requests for
the same subscriber.
This special case happens actually only when there are few SMS still in the DB
to be delivered. In the TTCN3 test, there is exactly one MT SMS for one
subscriber, and retriggering the queue brings up the same SMS every time.
See f_tc_lu_and_mt_sms_paging_and_nothing() and f_tc_sgsap_mt_sms_and_nothing()
which say:
"/* Expect the MSC to page exactly 10 times before giving up */"
This is bad because an MSC should send a Paging Request exactly once. Retrying
failed Paging is clearly the task of the BSC, not the MSC. The remaining code
around Paging correctly follows this paradigm, but this retrigger doesn't.
Do not immediately trigger the SMS queue on a failed MT SMS. Instead, leave it
up to the periodical SMS queue trigger to decide.
This patch will cause the MT SMS tests in ttcn3-msc-tests to fail, because the
test expectations are bogus. The patch fixing the test run is listed 'Related'
below.
Related: I7dce12942a65eaaf97f78ca69401c7f93faacb9e (osmo-ttcn3-hacks)
Change-Id: I24bf9f1c1167efe1080ae4cf47ed2ef0bd981e49
d553c085e7