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Neels Hofmeyr gerrit-no-reply at lists.osmocom.org
Review at https://gerrit.osmocom.org/748
dyn TS: if PCU is not connected, allow operation as TCH
Before this patch, Osmocom style TCH/F_TCH/H_PDCH dyn TS were paralyzed if no
PCU was running. The state of the dyn TS would lock up in the PDCH activation
phase since the PCU never completed the process.
Make more robust, i.e. don't concern the BSC with PDCH activation failures.
This matches the way plain PDCH TS work: besides declaring the TS as PDCH, the
BSC is not involved and is not told about errors.
During PDCH deactivation, still wait for the PCU to tear down the PDTCH SAPIs,
but in case no PCU is connected, send a rel ack right away.
Thus, the BSC will happily switch Osmocom style dynamic timeslots to and from
PDCH mode, using the dyn TS as voice channels as needed, and not caring about
possible PDCH failures. GPRS starts working right away as soon as a PCU
connects, regardless of dyn TS having been used for voice any number of times,
and without another switchover needed.
In detail:
In rsl_rx_chan_activ(), upon receiving a PDCH activation, send an RSL chan act
ack right away, unconditionally (with an explaining comment). Do not concern
the Abis link with PDCH activation failures.
Since we're acking right away now, drop the chan act ack that would follow
after the PCU activation: as before dyn TS, only send acks and nacks for
rel_act_kind == LCHAN_REL_ACT_RSL (PDCH runs as LCHAN_REL_ACT_PCU).
In dyn_ts_pdch_release, indicate that the PCU is not connected by means of
returning 1. In rsl_rx_rf_chan_rel(), use this indicator to send a rel ack
right away if the PCU is not connected.
Change-Id: I2a0b9730197786b99ff3bc1f08c75f7d279cb1f7
---
M src/common/rsl.c
1 file changed, 29 insertions(+), 11 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-bts refs/changes/48/748/1
diff --git a/src/common/rsl.c b/src/common/rsl.c
index 37c142c..f96f0e5 100644
--- a/src/common/rsl.c
+++ b/src/common/rsl.c
@@ -606,14 +606,7 @@
/* Send an RSL Channel Activation Ack if cause is zero, a Nack otherwise. */
int rsl_tx_chan_act_acknack(struct gsm_lchan *lchan, uint8_t cause)
{
- /*
- * Normally, PDCH activation via PCU does not ack back to the BSC.
- * But for GSM_PCHAN_TCH_F_TCH_H_PDCH, send a non-standard act ack for
- * LCHAN_REL_ACT_PCU, since the act req came from RSL initially.
- */
- if (lchan->rel_act_kind != LCHAN_REL_ACT_RSL
- && !(lchan->ts->pchan == GSM_PCHAN_TCH_F_TCH_H_PDCH
- && lchan->rel_act_kind == LCHAN_REL_ACT_PCU)) {
+ if (lchan->rel_act_kind != LCHAN_REL_ACT_RSL) {
LOGP(DRSL, LOGL_NOTICE, "%s not sending CHAN ACT %s\n",
gsm_lchan_name(lchan), rc ? "NACK" : "ACK");
return 0;
@@ -931,6 +924,24 @@
if (ts->pchan == GSM_PCHAN_TCH_F_TCH_H_PDCH
&& ts->dyn.pchan_want == GSM_PCHAN_PDCH) {
/*
+ * We ack the activation to the BSC right away, regardless of
+ * the PCU succeeding or not; if a dynamic timeslot fails to go
+ * to PDCH mode for any reason, the BSC should still be able to
+ * switch it back to TCH modes. So for the BSC, it is not
+ * helpful in any way to know that a PDCH channel fails to
+ * work, e.g. if the PCU is not running. If the BSC tells us to
+ * do PDCH, we do our best, and keep the details on the BTS and
+ * PCU level. This is kind of analogous to how plain PDCH TS
+ * operate. Directly call rsl_tx_chan_act_ack() instead of
+ * rsl_tx_chan_act_acknack() because we don't want/need to
+ * decide whether to drop due to lchan->rel_act_kind.
+ */
+ rc = rsl_tx_chan_act_ack(lchan);
+ if (rc < 0)
+ LOGP(DRSL, LOGL_ERROR, "%s Cannot send act ack: %d\n",
+ gsm_ts_and_pchan_name(ts), rc);
+
+ /*
* pcu_tx_info_ind() will pick up the ts->dyn.pchan_want. If
* the PCU is not connected yet, ignore for now; the PCU will
* catch up (and send the RSL ack) once it connects.
@@ -981,7 +992,7 @@
/* PCU not connected yet. Just record the new type and done,
* the PCU will pick it up once connected. */
ts->dyn.pchan_is = GSM_PCHAN_NONE;
- return 0;
+ return 1;
}
return pcu_tx_info_ind();
@@ -990,6 +1001,8 @@
/* 8.4.14 RF CHANnel RELease is received */
static int rsl_rx_rf_chan_rel(struct gsm_lchan *lchan, uint8_t chan_nr)
{
+ int rc;
+
if (lchan->abis_ip.rtp_socket) {
rsl_tx_ipac_dlcx_ind(lchan, RSL_ERR_NORMAL_UNSPEC);
osmo_rtp_socket_free(lchan->abis_ip.rtp_socket);
@@ -1004,8 +1017,13 @@
/* Dynamic channel in PDCH mode is released via PCU */
if (lchan->ts->pchan == GSM_PCHAN_TCH_F_TCH_H_PDCH
- && lchan->ts->dyn.pchan_is == GSM_PCHAN_PDCH)
- return dyn_ts_pdch_release(lchan);
+ && lchan->ts->dyn.pchan_is == GSM_PCHAN_PDCH) {
+ rc = dyn_ts_pdch_release(lchan);
+ if (rc != 1)
+ return rc;
+ /* If the PCU is not connected, continue right away. */
+ return rsl_tx_rf_rel_ack(lchan);
+ }
l1sap_chan_rel(lchan->ts->trx, chan_nr);
--
To view, visit https://gerrit.osmocom.org/748
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Gerrit-MessageType: newchange
Gerrit-Change-Id: I2a0b9730197786b99ff3bc1f08c75f7d279cb1f7
Gerrit-PatchSet: 1
Gerrit-Project: osmo-bts
Gerrit-Branch: master
Gerrit-Owner: Neels Hofmeyr <nhofmeyr at sysmocom.de>