diff --git a/bsc/BSC_Tests.ttcn b/bsc/BSC_Tests.ttcn
index b141a0a..9109933 100644
--- a/bsc/BSC_Tests.ttcn
+++ b/bsc/BSC_Tests.ttcn
@@ -1626,7 +1626,7 @@
 	f_init(1);
 
 	/* BTS->BSC: Send CHAN RQD and wait for allocation; acknowledge it */
-	dt.rsl_chan_nr := f_chreq_act_ack(f_rnd_octstring(1), 23);
+	dt.rsl_chan_nr := f_chreq_act_ack(f_rnd_ra_cs(), 23);
 
 	/* BTS->BSC: simulate CONN FAIL IND */
 	f_ipa_tx(0, ts_RSL_CONN_FAIL_IND(dt.rsl_chan_nr, RSL_ERR_RADIO_LINK_FAIL));