Fix: Change T200 of LAPDm if SAPI 0 and SAPI 3 share bandwidth on SDCCH

We use 1 second on FACCH and 2 seconds on SACCH when SMS is transfered
during a call on TCH. There is no impact on bandwidth, because SAPIs use
differen channels.

In order to correctly transfer SMS during SDCCH, the T200 must be raised
from 1 (SAPI 0) to 2 (SAPI 0 and 3), so T200 will not timeout before
receiving acknowledge from BTS. This is because both SAPIs share the same
ressource on SDCCH. After release of SAPI 3, T200 is lowered back to 1.

1 files changed, 31 insertions, 0 deletions

diff --git a/src/host/layer23/src/mobile/gsm48_rr.c b/src/host/layer23/src/mobile/gsm48_rr.c
index bc244699..36488606 100644
--- a/src/host/layer23/src/mobile/gsm48_rr.c
+++ b/src/host/layer23/src/mobile/gsm48_rr.c
@@ -3284,6 +3284,11 @@ static int gsm48_rr_dl_est(struct osmocom_ms *ms)
 	gsm48_rr_activate_channel(ms, &rr->cd_now, ma, ma_len);
 #endif
 
+	/* set T200 of SAPI 0 */
+	ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_sec =
+		T200_DCCH;
+	ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_usec = 0;
+
 	/* start establishmnet */
 	return gsm48_send_rsl(ms, RSL_MT_EST_REQ, nmsg, 0);
 }
@@ -3623,6 +3628,11 @@ static int gsm48_rr_tx_ass_cpl(struct osmocom_ms *ms, uint8_t cause)
 	/* RR_CAUSE */
 	ac->rr_cause = cause;
 
+	/* set T200 of SAPI 0 */
+	ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_sec =
+		T200_DCCH;
+	ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_usec = 0;
+
 	return gsm48_send_rsl(ms, RSL_MT_RES_REQ, nmsg, 0);
 }
 
@@ -3990,6 +4000,11 @@ static int gsm48_rr_tx_hando_cpl(struct osmocom_ms *ms, uint8_t cause)
 
 	// FIXME: mobile observed time
 
+	/* set T200 of SAPI 0 */
+	ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_sec =
+		T200_DCCH;
+	ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_usec = 0;
+
 	return gsm48_send_rsl(ms, RSL_MT_RES_REQ, nmsg, 0);
 }
 
@@ -5025,6 +5040,13 @@ static int gsm48_rr_estab_ind_sapi3(struct osmocom_ms *ms, struct msgb *msg)
 
 	LOGP(DSUM, LOGL_INFO, "Radio link SAPI3 is established\n");
 
+	if ((link_id & 0xf8) == 0x00) {
+		/* raise T200 of SAPI 0 */
+		ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_sec =
+			T200_DCCH_SHARED;
+		ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_usec= 0;
+	}
+
 	/* send inication to upper layer */
 	nmsg = gsm48_rr_msgb_alloc(GSM48_RR_EST_IND);
 	if (!nmsg)
@@ -5101,6 +5123,11 @@ static int gsm48_rr_rel_ind_sapi3(struct osmocom_ms *ms, struct msgb *msg)
 
 	LOGP(DSUM, LOGL_INFO, "Radio link SAPI3 is released\n");
 
+	/* lower T200 of SAPI 0 */
+	ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_sec =
+		T200_DCCH;
+	ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_usec = 0;
+
 	/* send inication to upper layer */
 	nmsg = gsm48_rr_msgb_alloc(GSM48_RR_REL_IND);
 	if (!nmsg)
@@ -5140,6 +5167,10 @@ static int gsm48_rr_est_req_sapi3(struct osmocom_ms *ms, struct msgb *msg)
 		LOGP(DRR, LOGL_INFO, "Requesting DCCH link, because no TCH "
 			"(sapi %d)\n", sapi);
 		rr->sapi3_link_id = 0x00 | sapi; /* SAPI 3, DCCH */
+		/* raise T200 of SAPI 0 */
+		ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_sec =
+			T200_DCCH_SHARED;
+		ms->lapdm_channel.lapdm_dcch.datalink[DL_SAPI0].dl.t200_usec= 0;
 	} else {
 		LOGP(DRR, LOGL_INFO, "Requesting ACCH link, because TCH "
 			"(sapi %d)\n", sapi);