bts: Allow config of RACH control parameters tx-integer & max retrans

Tweaking theses can be useful especially tx-integer that influence
both the spread of rach attemps and the delay between two attemps.

Looking up GSM 04.08 3.3.1.1.2 & 10.5.2.29 can help determine good
values. The default are choosed with a wide spacing between attemps
(tx integer = 9 -> T=12 & S=217 (non-combined CCCH/SDCCH) or 115 (for
combined CCCH/SDCCH)). This alleviates the problem of responding to
several RACH attempts by a same MS, allocating several RF channels when
only 1 is needed.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

4 files changed, 43 insertions, 5 deletions

diff --git a/openbsc/include/openbsc/gsm_utils.h b/openbsc/include/openbsc/gsm_utils.h
index 5809221a3..56a4120a5 100644
--- a/openbsc/include/openbsc/gsm_utils.h
+++ b/openbsc/include/openbsc/gsm_utils.h
@@ -37,5 +37,12 @@ int ms_pwr_dbm(enum gsm_band band, u_int8_t lvl);
 int rxlev2dbm(u_int8_t rxlev);
 u_int8_t dbm2rxlev(int dbm);
 
+/* According to GSM 04.08 Chapter 10.5.2.29 */
+static inline int rach_max_trans_val2raw(int val) { return (val >> 1) & 3; }
+static inline int rach_max_trans_raw2val(int raw) {
+	const int tbl[4] = { 1, 2, 4, 7 };
+	return tbl[raw & 3];
+}
+
 void generate_backtrace();
 #endif
diff --git a/openbsc/src/bsc_init.c b/openbsc/src/bsc_init.c
index 14a9777c1..1a70230fc 100644
--- a/openbsc/src/bsc_init.c
+++ b/openbsc/src/bsc_init.c
@@ -823,11 +823,6 @@ static int bootstrap_bts(struct gsm_bts *bts)
 	/* T3212 is set from vty/config */
 
 	/* some defaults for our system information */
-	bts->si_common.rach_control.re = 1; /* no re-establishment */
-	bts->si_common.rach_control.tx_integer = 5; /* 8 slots spread */
-	bts->si_common.rach_control.max_trans = 3; /* 7 retransmissions */
-	bts->si_common.rach_control.t2 = 4; /* no emergency calls */
-
 	bts->si_common.cell_options.radio_link_timeout = 2; /* 12 */
 	bts->si_common.cell_options.dtx = 2; /* MS shall not use upplink DTX */
 	bts->si_common.cell_options.pwrc = 0; /* PWRC not set */
diff --git a/openbsc/src/gsm_data.c b/openbsc/src/gsm_data.c
index 12f439be2..d6ebd9224 100644
--- a/openbsc/src/gsm_data.c
+++ b/openbsc/src/gsm_data.c
@@ -175,6 +175,10 @@ struct gsm_bts *gsm_bts_alloc(struct gsm_network *net, enum gsm_bts_type type,
 	bts->si_common.cell_alloc.data = bts->si_common.data.cell_alloc;
 	bts->si_common.cell_alloc.data_len =
 				sizeof(bts->si_common.data.cell_alloc);
+	bts->si_common.rach_control.re = 1; /* no re-establishment */
+	bts->si_common.rach_control.tx_integer = 9;  /* 12 slots spread - 217/115 slots delay */
+	bts->si_common.rach_control.max_trans = 3; /* 7 retransmissions */
+	bts->si_common.rach_control.t2 = 4; /* no emergency calls */
 
 	for (i = 0; i < ARRAY_SIZE(bts->gprs.nsvc); i++) {
 		bts->gprs.nsvc[i].bts = bts;
diff --git a/openbsc/src/vty_interface.c b/openbsc/src/vty_interface.c
index 077e1d03f..808db3fb0 100644
--- a/openbsc/src/vty_interface.c
+++ b/openbsc/src/vty_interface.c
@@ -168,6 +168,11 @@ static void bts_dump_vty(struct vty *vty, struct gsm_bts *bts)
 		VTY_NEWLINE);
 	vty_out(vty, "Cell Reselection Hysteresis: %u dBm%s",
 		bts->si_common.cell_sel_par.cell_resel_hyst*2, VTY_NEWLINE);
+	vty_out(vty, "RACH TX-Integer: %u%s", bts->si_common.rach_control.tx_integer,
+		VTY_NEWLINE);
+	vty_out(vty, "RACH Max transmissions: %u%s",
+		rach_max_trans_raw2val(bts->si_common.rach_control.max_trans),
+		VTY_NEWLINE);
 	if (bts->si_common.rach_control.cell_bar)
 		vty_out(vty, "  CELL IS BARRED%s", VTY_NEWLINE);
 	if (is_ipaccess_bts(bts))
@@ -290,6 +295,11 @@ static void config_write_bts_single(struct vty *vty, struct gsm_bts *bts)
 	vty_out(vty, "  channel allocator %s%s",
 		bts->chan_alloc_reverse ? "descending" : "ascending",
 		VTY_NEWLINE);
+	vty_out(vty, "  rach tx integer %u%s",
+		bts->si_common.rach_control.tx_integer, VTY_NEWLINE);
+	vty_out(vty, "  rach max transmission %u%s",
+		rach_max_trans_raw2val(bts->si_common.rach_control.max_trans),
+		VTY_NEWLINE);
 	if (bts->si_common.rach_control.cell_bar)
 		vty_out(vty, "  cell barred 1%s", VTY_NEWLINE);
 	if (is_ipaccess_bts(bts)) {
@@ -1263,6 +1273,26 @@ DEFUN(cfg_bts_challoc, cfg_bts_challoc_cmd,
 	return CMD_SUCCESS;
 }
 
+DEFUN(cfg_bts_rach_tx_integer,
+      cfg_bts_rach_tx_integer_cmd,
+      "rach tx integer <0-15>",
+      "Set the raw tx integer value in RACH Control parameters IE")
+{
+	struct gsm_bts *bts = vty->index;
+	bts->si_common.rach_control.tx_integer = atoi(argv[0]) & 0xf;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_bts_rach_max_trans,
+      cfg_bts_rach_max_trans_cmd,
+      "rach max transmission (1|2|4|7)",
+      "Set the maximum number of RACH burst transmissions")
+{
+	struct gsm_bts *bts = vty->index;
+	bts->si_common.rach_control.max_trans = rach_max_trans_val2raw(atoi(argv[0]));
+	return CMD_SUCCESS;
+}
+
 DEFUN(cfg_bts_cell_barred, cfg_bts_cell_barred_cmd,
       "cell barred (0|1)",
       "Should this cell be barred from access?")
@@ -1550,6 +1580,8 @@ int bsc_vty_init(struct gsm_network *net)
 	install_element(BTS_NODE, &cfg_bts_oml_e1_cmd);
 	install_element(BTS_NODE, &cfg_bts_oml_e1_tei_cmd);
 	install_element(BTS_NODE, &cfg_bts_challoc_cmd);
+	install_element(BTS_NODE, &cfg_bts_rach_tx_integer_cmd);
+	install_element(BTS_NODE, &cfg_bts_rach_max_trans_cmd);
 	install_element(BTS_NODE, &cfg_bts_cell_barred_cmd);
 	install_element(BTS_NODE, &cfg_bts_ms_max_power_cmd);
 	install_element(BTS_NODE, &cfg_bts_per_loc_upd_cmd);