tbf: Implement delayed release of a downlink TBF
Currently a DL TBF is immediately closed, when the LLC queue is
drained. This will lead to a new DL assignment if data is received
afterwards. In addition, it is not possible to keep the PACCH open
to poll the MS for UL establishment requests there.
GSM 44.060, 9.3.1a suggests to delay the release of an inactive TBF
for some time (max 5s).
This commit mainly changes create_new_bsn() to send LLC dummy
commands as filler if no LLC data is available until keep_open()
returns false. The keep_open() functions returns true unless a
configurable time has passed after the LLC data store drained. By
default, that time is not set which causes keep_open() to always
return false, so that delayed release is effectively disabled.
The following VTY commands are added:
- dl-tbf-idle-time <1-5000> to set the delay in ms
- no dl-tbf-idle-time to disable delayed release
Ticket: #556
Sponsored-by: On-Waves ehf
diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index 9baa1cd..65b164e 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -27,6 +27,8 @@
#include <gprs_bssgp_pcu.h>
#include <decoding.h>
+#include "pcu_utils.h"
+
extern "C" {
#include <osmocom/core/msgb.h>
#include <osmocom/core/talloc.h>
@@ -74,6 +76,8 @@
} else if (!have_data()) {
m_llc.put_frame(data, len);
bts->llc_frame_sched();
+ /* it is no longer drained */
+ m_last_dl_drained_fn = -1;
tbf_update_ms_class(this, ms_class);
} else {
/* the TBF exists, so we must write it in the queue
@@ -354,14 +358,19 @@
* space-1 octets */
m_llc.put_dummy_frame(space - 1);
+ /* The data just drained, store the current fn */
+ if (m_last_dl_drained_fn < 0)
+ m_last_dl_drained_fn = fn;
+
/* It is not clear, when the next real data will
* arrive, so request a DL ack/nack now */
request_dl_ack();
LOGP(DRLCMACDL, LOGL_DEBUG,
"-- Empty chunk, "
- "added LLC dummy command of size %d\n",
- m_llc.frame_length());
+ "added LLC dummy command of size %d, "
+ "drained_since=%d\n",
+ m_llc.frame_length(), frames_since_last_drain(fn));
}
chunk = m_llc.chunk_size();
@@ -380,7 +389,8 @@
break;
}
/* if FINAL chunk would fit precisely in space left */
- if (chunk == space && llist_empty(&m_llc.queue)) {
+ if (chunk == space && llist_empty(&m_llc.queue) && !keep_open(fn))
+ {
LOGP(DRLCMACDL, LOGL_DEBUG, "-- Chunk with length %d "
"would exactly fit into space (%d): because "
"this is a final block, we don't add length "
@@ -424,6 +434,7 @@
/* return data block as message */
break;
}
+
LOGP(DRLCMACDL, LOGL_DEBUG, "-- Chunk with length %d is less "
"than remaining space (%d): add length header to "
"to delimit LLC frame\n", chunk, space);
@@ -456,17 +467,19 @@
m_llc.put_frame(msg->data, msg->len);
bts->llc_frame_sched();
msgb_free(msg);
+ m_last_dl_drained_fn = -1;
}
/* if we have more data and we have space left */
- if (space > 0 && m_llc.frame_length()) {
+ if (space > 0 && (m_llc.frame_length() || keep_open(fn))) {
li->m = 1; /* we indicate more frames to follow */
continue;
}
/* if we don't have more LLC frames */
- if (!m_llc.frame_length()) {
+ if (!m_llc.frame_length() && !keep_open(fn)) {
LOGP(DRLCMACDL, LOGL_DEBUG, "-- Final block, so we "
"done.\n");
li->e = 1; /* we cannot extend */
+
rh->fbi = 1; /* we indicate final block */
request_dl_ack();
set_state(GPRS_RLCMAC_FINISHED);
@@ -771,3 +784,26 @@
return wrapped - 2715648;
}
+int gprs_rlcmac_dl_tbf::frames_since_last_drain(unsigned fn) const
+{
+ unsigned wrapped;
+ if (m_last_dl_drained_fn < 0)
+ return -1;
+
+ wrapped = (fn + 2715648 - m_last_dl_drained_fn) % 2715648;
+ if (wrapped < 2715648/2)
+ return wrapped;
+ else
+ return wrapped - 2715648;
+}
+
+bool gprs_rlcmac_dl_tbf::keep_open(unsigned fn) const
+{
+ int keep_time_frames;
+
+ if (bts_data()->dl_tbf_idle_msec <= 0)
+ return false;
+
+ keep_time_frames = msecs_to_frames(bts_data()->dl_tbf_idle_msec);
+ return frames_since_last_drain(fn) <= keep_time_frames;
+}