hodec2: fix intra-cell congestion balancing with source lchan on dyn TS

Related: SYS#5301
Change-Id: I332477cbddf32cf6f057007b45cda8477227f0b1

3 files changed, 34 insertions, 15 deletions

diff --git a/src/osmo-bsc/handover_decision_2.c b/src/osmo-bsc/handover_decision_2.c
index 0bfae9ba2..2cb7a54f3 100644
--- a/src/osmo-bsc/handover_decision_2.c
+++ b/src/osmo-bsc/handover_decision_2.c
@@ -682,7 +682,18 @@ static void check_requirements(struct ho_candidate *c)
 	current_overbooked = load_above_congestion(c->current.free_tch, c->current.min_free_tch);
 	if (requirement & REQUIREMENT_A_TCHF) {
 		bool ok;
-		int32_t target_overbooked = load_above_congestion(c->target.free_tchf - 1, c->target.min_free_tchf);
+		int32_t target_overbooked;
+		int target_free_tchf_after_ho;
+
+		/* To evaluate whether a handover improves or worsens congestion on TCH/F, first figure out how many
+		 * TCH/F lchans will be occupied on the target after the handover. If the target is a different cell,
+		 * then we obviously reduce by one TCH/F. If source and target cell are the same (re-assignment), then
+		 * the source lchan may also free a TCH/F at the same time. Add up all of these effects to figure out
+		 * the congestion percentages before and after handover. */
+		target_free_tchf_after_ho = c->target.free_tchf - 1;
+		if (c->current.bts == c->target.bts)
+			target_free_tchf_after_ho += c->current.lchan_frees_tchf;
+		target_overbooked = load_above_congestion(target_free_tchf_after_ho, c->target.min_free_tchf);
 		LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
 				 "current overbooked = %s%%, TCH/F target overbooked after HO = %s%%\n",
 				 osmo_int_to_float_str_c(OTC_SELECT, current_overbooked, LOAD_PRECISION - 2),
@@ -718,7 +729,18 @@ static void check_requirements(struct ho_candidate *c)
 	}
 	if (requirement & REQUIREMENT_A_TCHH) {
 		bool ok;
-		int32_t target_overbooked = load_above_congestion(c->target.free_tchh - 1, c->target.min_free_tchh);
+		int32_t target_overbooked;
+		int target_free_tchh_after_ho;
+
+		/* To evaluate whether a handover improves or worsens congestion on TCH/H, first figure out how many
+		 * TCH/H lchans will be occupied on the target after the handover. If the target is a different cell,
+		 * then we obviously reduce by one TCH/H. If source and target cell are the same (re-assignment), then
+		 * the source lchan may also free one or two TCH/H at the same time. Add up all of these effects to
+		 * figure out the congestion percentages before and after handover. */
+		target_free_tchh_after_ho = c->target.free_tchh - 1;
+		if (c->current.bts == c->target.bts)
+			target_free_tchh_after_ho += c->current.lchan_frees_tchh;
+		target_overbooked = load_above_congestion(target_free_tchh_after_ho, c->target.min_free_tchh);
 		LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
 				 "current overbooked = %s%%, TCH/H target overbooked after HO = %s%%\n",
 				 osmo_int_to_float_str_c(OTC_SELECT, current_overbooked, LOAD_PRECISION - 2),
diff --git a/tests/handover/test_dyn_ts_amr_tch_f_to_h_congestion_assignment_2.ho_vty b/tests/handover/test_dyn_ts_amr_tch_f_to_h_congestion_assignment_2.ho_vty
index 619459662..a7984572d 100644
--- a/tests/handover/test_dyn_ts_amr_tch_f_to_h_congestion_assignment_2.ho_vty
+++ b/tests/handover/test_dyn_ts_amr_tch_f_to_h_congestion_assignment_2.ho_vty
@@ -14,16 +14,15 @@ set-ts-use trx 0 0 states * TCH/F - - - * * *
 # (there must be at least one measurement report on each lchan for congestion check to work)
 meas-rep lchan * * * * rxlev 40 rxqual 0 ta 0 neighbors 30
 congestion-check
-# FAIL: after the handover from the dyn TS to TCH/H, the dyn TS has freed two TCH/H, while the static TCH/H has reduced
-# the TCH/H count by one. So the resulting free slots are 3 TCH/H, which means no congestion. A handover should occur.
-expect-no-chan
+expect-ho from lchan 0 0 1 0 to lchan 0 0 4 0
+expect-ts-use trx 0 0 states * pdch - - TCH/H- * * *
 
 # Again with one more TCH/H occupied, there will still be two free TCH/H after HO on the dyn TS
 set-ts-use trx 0 0 states * TCH/F - - TCH/H- * * *
 meas-rep lchan * * * * rxlev 40 rxqual 0 ta 0 neighbors 30
 congestion-check
-# FAIL: resulting free slots are 2 TCH/H, which means no congestion. A handover should occur.
-expect-no-chan
+expect-ho from lchan 0 0 1 0 to lchan 0 0 4 1
+expect-ts-use trx 0 0 states * pdch - - TCH/HH * * *
 
 # Again, with the target being a dyn TS
 create-bts trx-count 1 timeslots c+s4 dyn TCH/F TCH/F dyn PDCH PDCH PDCH
@@ -37,13 +36,12 @@ network
 set-ts-use trx 1 0 states * TCH/F TCH/F - pdch * * *
 meas-rep lchan 1 * * * rxlev 40 rxqual 0 ta 0 neighbors 30
 congestion-check
-# FAIL: after the handover from the dyn TS to TCH/H, the dyn TS has freed two TCH/H, while the static TCH/H has reduced
-# the TCH/H count by one. So the resulting free slots are 3 TCH/H, which means no congestion. A handover should occur.
-expect-no-chan
+expect-ho from lchan 1 0 1 0 to lchan 1 0 4 0
+expect-ts-use trx 1 0 states * pdch TCH/F - TCH/H- * * *
 
 # Again with one more TCH/H occupied, there will still be two free TCH/H after HO on the dyn TS
 set-ts-use trx 1 0 states * TCH/F TCH/F - TCH/H- * * *
 meas-rep lchan 1 * * * rxlev 40 rxqual 0 ta 0 neighbors 30
 congestion-check
-# FAIL: resulting free slots are 2 TCH/H, which means no congestion. A handover should occur.
-expect-no-chan
+expect-ho from lchan 1 0 1 0 to lchan 1 0 4 1
+expect-ts-use trx 1 0 states * pdch TCH/F - TCH/HH * * *
diff --git a/tests/handover/test_dyn_ts_amr_tch_h_to_f_congestion_assignment_2.ho_vty b/tests/handover/test_dyn_ts_amr_tch_h_to_f_congestion_assignment_2.ho_vty
index 36a981745..de9595b48 100644
--- a/tests/handover/test_dyn_ts_amr_tch_h_to_f_congestion_assignment_2.ho_vty
+++ b/tests/handover/test_dyn_ts_amr_tch_h_to_f_congestion_assignment_2.ho_vty
@@ -21,8 +21,7 @@ expect-ts-use trx 0 0 states * pdch TCH/F - - * * *
 set-ts-use trx 0 0 states * TCH/H- - - TCH/F * * *
 meas-rep lchan * * * * rxlev 40 rxqual 0 ta 0 neighbors 30
 congestion-check
-# FAIL: after the handover from the dyn TS to TCH/F, the dyn TS has freed a TCH/F, while the static TCH/F has reduced
-# the TCH/F count by one. So the resulting free slots are 2 TCH/F, which means no congestion. A handover should occur.
-expect-no-chan
+expect-ho from lchan 0 0 1 0 to lchan 0 0 2 0
+expect-ts-use trx 0 0 states * pdch TCH/F - TCH/F * * *
 
 # (TCH/H -> TCH/F onto a dyn TS will always make TCH/H congestion worse, so there is no useful test case left here)