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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
This commit is contained in:
Philipp Maier 2016-11-07 13:07:36 +01:00 committed by Philipp Maier
parent e9a138e111
commit d935d88a8c
2 changed files with 19 additions and 1 deletions
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15
src/bts.cpp
View File

@ -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);

5
tests/tbf/TbfTest.cpp
View File

@ -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;