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authorPhilipp <pmaier@sysmocom.de>2016-11-07 13:07:36 +0100
committerPhilipp Maier <pmaier@sysmocom.de>2017-01-26 11:19:21 +0100
commitd935d88a8c5dbc3bce5476545a785a7a35cfc2d3 (patch)
treec2ee72eeb88dabe18b043accd74d705fad8a936f
parente9a138e11111f509f988807bbdc5ca8cce2b3d3d (diff)
BTS: accept also relative frame numbers with rach requst
The rach request contains a relative frame number (Fn % 42432), while BTS::rcv_rach() accepts the full frame number only. Since the BTS is always aware of the full frame number this is not a problem. But for BSC co-located PCU schemes it is a problem since the rach request only contains the relative frame number as mentioned above. The pcu continusly receives frame number updates with the GSM time indication message. It is simple to re-calculate the full frame number from that information. This patch makes BTS::rcv_rach() compatible with relative frame numbers, while not breaking the compatibility for full frame numbers Change-Id: Iaa182d8d29c6a0f5fa06064c2eb48b21b1ba2775
-rw-r--r--src/bts.cpp15
-rw-r--r--tests/tbf/TbfTest.cpp5
2 files changed, 19 insertions, 1 deletions
diff --git a/src/bts.cpp b/src/bts.cpp
index 25cbc60..e1c6dcc 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -536,6 +536,21 @@ int BTS::rcv_rach(uint16_t ra, uint32_t Fn, int16_t qta, uint8_t is_11bit,
if (is_11bit)
rach_frame_11bit();
+ /* Note: If a BTS is sending in a rach request it will be fully aware
+ * of the frame number. If the PCU is used in a BSC-co-located setup.
+ * The BSC will forward the incoming RACH request. The RACH request
+ * only contains the relative frame number (Fn % 42432) in its request
+ * reference. This PCU implementation has to fit both secenarious, so
+ * we need to assume that Fn is a relative frame number. */
+
+ /* Ensure that all following calculations are performed with the
+ * relative frame number */
+ Fn = Fn % 42432;
+
+ /* Restore the full frame number
+ * (See also 3GPP TS 44.018, section 10.5.2.38) */
+ Fn = Fn + m_cur_fn - m_cur_fn % 42432;
+
LOGP(DRLCMAC, LOGL_DEBUG, "MS requests UL TBF on RACH, "
"so we provide one \n"
"ra=0x%02x Fn=%u qta=%d is_11bit=%d:\n", ra, Fn, qta, is_11bit);
diff --git a/tests/tbf/TbfTest.cpp b/tests/tbf/TbfTest.cpp
index aec6ef8..e367ce6 100644
--- a/tests/tbf/TbfTest.cpp
+++ b/tests/tbf/TbfTest.cpp
@@ -42,6 +42,8 @@ extern "C" {
#include <errno.h>
+#define DUMMY_FN 2654167
+
void *tall_pcu_ctx;
int16_t spoof_mnc = 0, spoof_mcc = 0;
@@ -166,6 +168,7 @@ static void setup_bts(BTS *the_bts, uint8_t ts_no, uint8_t cs = 1)
trx = &bts->trx[0];
trx->pdch[ts_no].enable();
+ the_bts->set_current_frame_number(DUMMY_FN);
}
static gprs_rlcmac_dl_tbf *create_dl_tbf(BTS *the_bts, uint8_t ms_class,
@@ -1692,7 +1695,7 @@ static void test_tbf_single_phase()
{
BTS the_bts;
int ts_no = 7;
- uint32_t fn = 2654167; /* 17,25,9 */
+ uint32_t fn = DUMMY_FN; /* 17,25,9 */
uint32_t tlli = 0xf1223344;
const char *imsi = "0011223344";
uint16_t qta = 31;