Delay ImmAss(PCH, PktDlAss) if waiting for PKT_CTRL_ACK answering UL_ACK_NACK (FinACK=1)
In that state (ul_tbf=TBF_ST_FINISHED), we are unable to reach the MS to
assign a new DL TBF.
* MS Is not available in CCCH because it's attached the PDCH.
* MS won't be able to PKT_CTRL_ACK a PktDlAss on PACCH, because next
thing it will do is to PKT_CTRL_ACK the UL_ACK_NACK(FINACK=1) we
already polled it for, and immediatelly after that it will release the
UL TBF on its side and go back to packet idle mode.
Hence, we must wait for MS to send the PKT_CTRL_ACK to us in order to be
able to assign the DL TBF in PCH (CCCH).
Related: OS#5700
Change-Id: I7a30db9cc7dae70e04054f1a4dba004bd1780d4a
diff --git a/src/gprs_ms.c b/src/gprs_ms.c
index f4da3a5..5733a7c 100644
--- a/src/gprs_ms.c
+++ b/src/gprs_ms.c
@@ -23,6 +23,7 @@
#include "gprs_codel.h"
#include "pcu_utils.h"
#include "nacc_fsm.h"
+#include "tbf_ul_ack_fsm.h"
#include <time.h>
@@ -1024,10 +1025,75 @@
}
}
+/* Can we get to send a DL TBF ass to the MS? */
+static bool ms_is_reachable_for_dl_ass(const struct GprsMs *ms)
+{
+ struct gprs_rlcmac_ul_tbf *ul_tbf = ms_ul_tbf(ms);
+
+ /* This function assumes it is called when no DL TBF is present */
+ OSMO_ASSERT(!ms_dl_tbf(ms));
+
+ /* 3GPP TS 44.060 sec 7.1.3.1 Initiation of the Packet resource request procedure:
+ * "Furthermore, the mobile station shall not respond to PACKET DOWNLINK ASSIGNMENT
+ * or MULTIPLE TBF DOWNLINK ASSIGNMENT messages before contention resolution is
+ * completed on the mobile station side." */
+ /* The possible uplink TBF is used to trigger downlink assignment:
+ * - If there is no uplink TBF the MS is potentially in packet idle mode
+ * and hence assignment will be done over CCCH (PCH)
+ * - If there's an uplink TBF but it is finished (waiting for last PKT
+ * CTRL ACK after sending last Pkt UL ACK/NACK with FINAL_ACK=1, then we
+ * have no ways to contact the MS right now. Assignment will be delayed
+ * until PKT CTRL ACK is received and the TBF is released at the MS side
+ * (then assignment goes through PCH).
+ */
+ if (!ul_tbf)
+ return true;
+ if (ul_tbf_contention_resolution_done(ul_tbf) &&
+ !tbf_ul_ack_waiting_cnf_final_ack(ul_tbf))
+ return true;
+
+ return false;
+
+}
+
+/* This should be called only when MS is reachable, see ms_is_reachable_for_dl_ass(). */
+int ms_new_dl_tbf_assignment(struct GprsMs *ms)
+{
+ bool ss;
+ int8_t use_trx;
+ struct gprs_rlcmac_ul_tbf *ul_tbf;
+ struct gprs_rlcmac_dl_tbf *dl_tbf;
+
+ ul_tbf = ms_ul_tbf(ms);
+
+ if (ul_tbf) {
+ use_trx = tbf_get_trx((struct gprs_rlcmac_tbf *)ul_tbf)->trx_no;
+ ss = false;
+ } else {
+ use_trx = -1;
+ ss = true; /* PCH assignment only allows one timeslot */
+ }
+
+ /* set number of downlink slots according to multislot class */
+ dl_tbf = dl_tbf_alloc(ms->bts, ms, use_trx, ss);
+
+ if (!dl_tbf) {
+ LOGPMS(ms, DTBF, LOGL_NOTICE, "No PDCH resource\n");
+ return -EBUSY;
+ }
+
+ LOGPTBFDL(dl_tbf, LOGL_DEBUG, "[DOWNLINK] START\n");
+
+ /* Trigger the assignment now. */
+ tbf_dl_trigger_ass(dl_tbf, ul_tbf_as_tbf(ul_tbf));
+ return 0;
+}
+
int ms_append_llc_dl_data(struct GprsMs *ms, uint16_t pdu_delay_csec, const uint8_t *data, uint16_t len)
{
struct timespec expire_time;
struct gprs_rlcmac_dl_tbf *dl_tbf;
+ int rc = 0;
LOGPMS(ms, DTBFDL, LOGL_DEBUG, "appending %u bytes to DL LLC queue\n", len);
@@ -1041,10 +1107,17 @@
ms_start_llc_timer(ms);
dl_tbf = ms_dl_tbf(ms);
- if (dl_tbf && tbf_state(dl_tbf_as_tbf_const(dl_tbf)) == TBF_ST_WAIT_RELEASE) {
- LOGPTBFDL(dl_tbf, LOGL_DEBUG, "in WAIT RELEASE state (T3193), so reuse TBF\n");
- tbf_establish_dl_tbf_on_pacch(dl_tbf_as_tbf(dl_tbf));
+ if (dl_tbf) {
+ if (tbf_state(dl_tbf_as_tbf_const(dl_tbf)) == TBF_ST_WAIT_RELEASE) {
+ LOGPTBFDL(dl_tbf, LOGL_DEBUG, "in WAIT RELEASE state (T3193), so reuse TBF\n");
+ tbf_establish_dl_tbf_on_pacch(dl_tbf_as_tbf(dl_tbf));
+ }
+ } else {
+ /* Check if we can create a DL TBF to start sending the enqueued
+ * data. Otherwise it will be triggered later when it is reachable
+ * again. */
+ if (ms_is_reachable_for_dl_ass(ms))
+ rc = ms_new_dl_tbf_assignment(ms);
}
-
- return 0;
+ return rc;
}