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msc: fix a race condition in f_mt_call_establish()

It can happen that the MSC sends a paging request quicker than
function f_ran_register_imsi() returns (e.g. when a node executing
the testsuite is under significant load).  In this case the
BSSMAP PAGING message is dropped by the RAN_Emulation CT:

  CommonBssmapUnitdataCallback: IMSI/TMSI not found in table

This can be avoided by calling f_ran_register_imsi() *before*
sending the MNCC SETUP.req, which is triggering paging.

This patch fixes sporadic failures of:

* TC_lu_and_mt_call
* TC_lu_and_mt_call_ipv6
* TC_lu_and_mt_call_no_dlcx_resp

Change-Id: Ie8b69c3b59ea61e01adb24c71c1376335a5ddde6
---
M msc/BSC_ConnectionHandler.ttcn
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/msc/BSC_ConnectionHandler.ttcn b/msc/BSC_ConnectionHandler.ttcn
index b7d1b94..4444f37 100644
--- a/msc/BSC_ConnectionHandler.ttcn
+++ b/msc/BSC_ConnectionHandler.ttcn
@@ -1420,12 +1420,12 @@
 
 function f_mt_call_establish(inout CallParameters cpars)
 runs on BSC_ConnHdlr {
+	f_ran_register_imsi(g_pars.imsi, g_pars.tmsi);
 
 	/* Initiate the call via MNCC */
 	f_mt_call_initiate(cpars);
 
 	/* BSC <- MSC: Expect paging. FIXME: By TMSI or not? */
-	f_ran_register_imsi(g_pars.imsi, g_pars.tmsi);
 	f_expect_paging()
 
 	/* Complete the call via BSSAP */

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