paging: Add VTY options to calculate T3113 timeout dynamically

The idea is to have a base static value which is set like before "timer
t3113 [seconds]", but now have a part of this timeout calculated
dynamically based on BTS channel configuration and channel load.

This patch only implements initial support to calculate based on channel
configuration, but doesn't include code to calculate based on channel
load. To implement the later part, we probably need to keep track of BTS
paging queues per paging group, which we don't do nowadays.

Dynamic calculation is enabled by default, and default static base value
is decreased accordingly. This way, in a typical setup were the default
10 seconds were used, now the calculated final value is 11 seconds.
That's intended because it was observed experimentally in osmo-gsm-tester with
a similar channel setup that sometimes paging response can arrive slightly
later than 10 seconds.

Related: OS#3680
Change-Id: I4fb2969b690151415038631fb6ad059aa6835c7f

7 files changed, 86 insertions, 4 deletions

diff --git a/include/osmocom/bsc/gsm_data.h b/include/osmocom/bsc/gsm_data.h
index 0b472a47b..e57da55c0 100644
--- a/include/osmocom/bsc/gsm_data.h
+++ b/include/osmocom/bsc/gsm_data.h
@@ -1147,6 +1147,7 @@ struct gsm_bts {
 
 	/* BTS-specific overrides for timer values from struct gsm_network. */
 	uint8_t T3122;	/* ASSIGMENT REJECT wait indication */
+	bool T3113_dynamic; /* Calculate T3113 timeout dynamically based on BTS channel config and load */
 
 	/* Periodic channel load measurements are used to maintain T3122. */
 	struct load_counter chan_load_samples[7];
diff --git a/include/osmocom/bsc/gsm_timers.h b/include/osmocom/bsc/gsm_timers.h
index 78f04edd9..699c461ad 100644
--- a/include/osmocom/bsc/gsm_timers.h
+++ b/include/osmocom/bsc/gsm_timers.h
@@ -37,7 +37,7 @@ struct T_def *T_def_get_entry(struct T_def *T_defs, int T);
 
 void T_defs_vty_init(struct T_def *T_defs, int cfg_parent_node);
 void T_defs_vty_write(struct vty *vty, const char *indent);
-
+struct T_def *parse_T_arg(struct vty *vty, const char *T_str);
 
 struct state_timeout {
 	int T;
diff --git a/src/osmo-bsc/bsc_vty.c b/src/osmo-bsc/bsc_vty.c
index 983dcb9b3..8c7d8e19d 100644
--- a/src/osmo-bsc/bsc_vty.c
+++ b/src/osmo-bsc/bsc_vty.c
@@ -3951,6 +3951,56 @@ DEFUN(cfg_bts_amr_hr_hyst3, cfg_bts_amr_hr_hyst3_cmd,
 	return check_amr_config(vty);
 }
 
+#define TNUM_STR "T-number, optionally preceded by 't' or 'T'\n"
+DEFUN(cfg_bts_t3113_dynamic, cfg_bts_t3113_dynamic_cmd,
+	"timer-dynamic TNNNN",
+	"Calculate T3113 dynamically based on channel config and load\n"
+	TNUM_STR)
+{
+	struct T_def *d;
+	struct gsm_bts *bts = vty->index;
+
+	d = parse_T_arg(vty, argv[0]);
+	if (!d)
+		return CMD_WARNING;
+
+	switch (d->T) {
+	case 3113:
+		bts->T3113_dynamic = true;
+		break;
+	default:
+		vty_out(vty, "T%d cannot be set to dynamic%s", d->T, VTY_NEWLINE);
+		return CMD_WARNING;
+	}
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_bts_no_t3113_dynamic, cfg_bts_no_t3113_dynamic_cmd,
+	"no timer-dynamic TNNNN",
+	NO_STR
+	"Set given timer to non-dynamic and use the default or user provided fixed value\n"
+	TNUM_STR)
+{
+	struct T_def *d;
+	struct gsm_bts *bts = vty->index;
+
+	d = parse_T_arg(vty, argv[0]);
+	if (!d)
+		return CMD_WARNING;
+
+	switch (d->T) {
+	case 3113:
+		bts->T3113_dynamic = false;
+		break;
+	default:
+		vty_out(vty, "T%d already is non-dynamic%s", d->T, VTY_NEWLINE);
+		return CMD_WARNING;
+	}
+
+	return CMD_SUCCESS;
+}
+
 #define TRX_TEXT "Radio Transceiver\n"
 
 /* per TRX configuration */
@@ -5129,6 +5179,8 @@ int bsc_vty_init(struct gsm_network *network)
 	install_element(BTS_NODE, &cfg_bts_no_acc_ramping_cmd);
 	install_element(BTS_NODE, &cfg_bts_acc_ramping_step_interval_cmd);
 	install_element(BTS_NODE, &cfg_bts_acc_ramping_step_size_cmd);
+	install_element(BTS_NODE, &cfg_bts_t3113_dynamic_cmd);
+	install_element(BTS_NODE, &cfg_bts_no_t3113_dynamic_cmd);
 	neighbor_ident_vty_init(network, network->neighbor_bss_cells);
 	/* See also handover commands added on bts level from handover_vty.c */
 
diff --git a/src/osmo-bsc/gsm_data.c b/src/osmo-bsc/gsm_data.c
index 6d39642e2..0f76a2746 100644
--- a/src/osmo-bsc/gsm_data.c
+++ b/src/osmo-bsc/gsm_data.c
@@ -849,6 +849,7 @@ struct gsm_bts *gsm_bts_alloc(struct gsm_network *net, uint8_t bts_num)
 
 	/* timer overrides */
 	bts->T3122 = 0; /* not overriden by default */
+	bts->T3113_dynamic = true; /* dynamic by default */
 
 	bts->dtxu = GSM48_DTX_SHALL_NOT_BE_USED;
 	bts->dtxd = false;
diff --git a/src/osmo-bsc/gsm_timers_vty.c b/src/osmo-bsc/gsm_timers_vty.c
index de61e2453..e744dfac5 100644
--- a/src/osmo-bsc/gsm_timers_vty.c
+++ b/src/osmo-bsc/gsm_timers_vty.c
@@ -32,7 +32,7 @@ static struct T_def *g_vty_T_defs = NULL;
 
 /* Parse an argument like "T1234", "t1234" or "1234" and return the corresponding T_def entry from
  * g_vty_T_defs, if any. */
-static struct T_def *parse_T_arg(struct vty *vty, const char *T_str)
+struct T_def *parse_T_arg(struct vty *vty, const char *T_str)
 {
 	int T;
 	struct T_def *d;
diff --git a/src/osmo-bsc/net_init.c b/src/osmo-bsc/net_init.c
index 1199bdc82..5ea564d70 100644
--- a/src/osmo-bsc/net_init.c
+++ b/src/osmo-bsc/net_init.c
@@ -37,7 +37,7 @@ static struct T_def gsm_network_T_defs[] = {
 	{ .T=3109, .default_val=5, .desc="RSL SACCH deactivation" },
 	{ .T=3111, .default_val=2, .desc="Wait time before RSL RF Channel Release" },
 	{ .T=993111, .default_val=4, .desc="Wait time after lchan was released in error (should be T3111 + 2s)" },
-	{ .T=3113, .default_val=10, .desc="Paging"},
+	{ .T=3113, .default_val=7, .desc="Paging"},
 	{ .T=3115, .default_val=10, .desc="(unused)" },
 	{ .T=3117, .default_val=10, .desc="(unused)" },
 	{ .T=3119, .default_val=10, .desc="(unused)" },
diff --git a/src/osmo-bsc/paging.c b/src/osmo-bsc/paging.c
index afe32453e..246114f74 100644
--- a/src/osmo-bsc/paging.c
+++ b/src/osmo-bsc/paging.c
@@ -287,6 +287,32 @@ static void paging_T3113_expired(void *data)
 	paging_remove_request(&req->bts->paging, req);
 }
 
+#define GSM_FRAME_DURATION_us	4615
+#define GSM51_MFRAME_DURATION_us (51 * GSM_FRAME_DURATION_us) /* 235365 us */
+static unsigned int calculate_timer_3113(struct gsm_bts *bts)
+{
+	unsigned int to_us, to;
+	struct T_def *d = T_def_get_entry(bts->network->T_defs, 3113);
+
+	if (!bts->T3113_dynamic)
+		return d->val;
+
+	/* TODO: take into account load of paging group for req->bsub */
+
+	/* MFRMS defines repeat interval of paging messages for MSs that belong
+	 * to same paging group accross multiple 51 frame multiframes.
+	 * MAXTRANS defines maximum number of RACH retransmissions.
+	 */
+	to_us = GSM51_MFRAME_DURATION_us * (bts->si_common.chan_desc.bs_pa_mfrms + 2) *
+		bts->si_common.rach_control.max_trans;
+
+	/* ceiling in seconds + extra time */
+	to = (to_us + 999999) / 1000000 + d->val;
+	LOGP(DPAG, LOGL_DEBUG, "(bts=%d) Paging request: T3113 expires in %u seconds\n",
+	     bts->nr, to);
+	return to;
+}
+
 /*! Start paging + paging timer for given subscriber on given BTS
  * \param bts BTS on which to page
  * \param[in] bsub subscriber we want to page
@@ -298,6 +324,7 @@ static int _paging_request(struct gsm_bts *bts, struct bsc_subscr *bsub, int typ
 {
 	struct gsm_bts_paging_state *bts_entry = &bts->paging;
 	struct gsm_paging_request *req;
+	unsigned int t3113_timeout_s;
 
 	rate_ctr_inc(&bts->bts_ctrs->ctr[BTS_CTR_PAGING_ATTEMPTED]);
 
@@ -317,7 +344,8 @@ static int _paging_request(struct gsm_bts *bts, struct bsc_subscr *bsub, int typ
 	req->chan_type = type;
 	req->msc = msc;
 	osmo_timer_setup(&req->T3113, paging_T3113_expired, req);
-	osmo_timer_schedule(&req->T3113, T_def_get(bts->network->T_defs, 3113, T_S, -1), 0);
+	t3113_timeout_s = calculate_timer_3113(bts);
+	osmo_timer_schedule(&req->T3113, t3113_timeout_s, 0);
 	llist_add_tail(&req->entry, &bts_entry->pending_requests);
 	paging_schedule_if_needed(bts_entry);