Osmocom Packet control Unit (PCU): Network-side GPRS (RLC/MAC); BTS- or BSC-colocated https://osmocom.org/projects/osmopcu
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osmo-pcu/src/sba.c

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/* sba.c
*
* Copyright (C) 2021 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
* Author: Pau Espin Pedrol <pespin@sysmocom.de>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
#include <sba.h>
#include <gprs_debug.h>
#include <bts.h>
#include <pcu_utils.h>
#include <pdch.h>
#include <errno.h>
#include <osmocom/core/logging.h>
#include <osmocom/core/talloc.h>
#include <osmocom/gsm/protocol/gsm_04_08.h>
#include <osmocom/gsm/gsm_utils.h>
#include "pdch.h"
#include "pdch_ul_controller.h"
/* TBF Starting Time for assigning SBA.
* See TS 44.060 12.21 "Starting Frame Number Description".
* According to spec, k=0 (offset=4) "should not be used, so as to leave time
* for the MS to analyze the message and get ready to receive or transmit".
* Hence, k=1 (offset=8-9) is theoretically the minimum offset which could be
* used.
*
* However, it was found, empirically, that it takes around 30-40 FNs time for
* the Immediate Assignment message created with this "TBF Starting Time" to
* travel from PCU->BTS and be transmitted over CCCH on the Um interface. Hence,
* we must account for this delay here, otherwise the MS would be receiving eg.
* a TBF Starting Time of FN=40 while the Imm Assigned containing it is sent in
* eg. FN=50, which would be too late for the MS to answer to it.
*
* The situation described above, can even get worse on high BTS load for AGCH,
* since the Immediate Assignment will queue in the BTS waiting to be
* transmitted one after the other, hence increasing the required delay.
*/
#define AGCH_START_OFFSET 52
struct gprs_rlcmac_sba *sba_alloc(void *ctx, struct gprs_rlcmac_pdch *pdch, uint8_t ta)
{
struct gprs_rlcmac_sba *sba;
uint32_t start_fn;
sba = talloc_zero(ctx, struct gprs_rlcmac_sba);
if (!sba)
return NULL;
/* TODO: Increase start_fn dynamically based on AGCH queue load in the BTS: */
start_fn = next_fn(pdch->last_rts_fn, AGCH_START_OFFSET);
sba->pdch = pdch;
sba->ta = ta;
sba->fn = pdch_ulc_get_next_free_fn(pdch->ulc, start_fn);
pdch_ulc_reserve_sba(pdch->ulc, sba);
return sba;
}
/* Internal use */
static void sba_free_norelease(struct gprs_rlcmac_sba *sba)
{
bts_do_rate_ctr_inc(sba->pdch->trx->bts, CTR_SBA_FREED);
talloc_free(sba);
}
void sba_free(struct gprs_rlcmac_sba *sba)
{
if (pdch_ulc_release_fn(sba->pdch->ulc, sba->fn) < 0)
LOGPDCH(sba->pdch, DRLCMAC, LOGL_NOTICE,
"Trying to release unregistered SBA (FN=%u, TA=%u)\n",
sba->fn, sba->ta);
sba_free_norelease(sba);
}
void sba_timeout(struct gprs_rlcmac_sba *sba)
{
/* Upon timeout, the UL Controller node is already released */
sba_free_norelease(sba);
}