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