diff options
| -rw-r--r-- | include/osmo-bts/lchan.h | 14 | ||||
| -rw-r--r-- | src/common/l1sap.c | 288 |
2 files changed, 284 insertions, 18 deletions
diff --git a/include/osmo-bts/lchan.h b/include/osmo-bts/lchan.h index d89aa1fd..d17bf96c 100644 --- a/include/osmo-bts/lchan.h +++ b/include/osmo-bts/lchan.h @@ -8,6 +8,7 @@ #include <osmocom/core/linuxlist.h> #include <osmocom/core/logging.h> #include <osmocom/gsm/gsm_utils.h> +#include <osmocom/codec/codec.h> #include <osmocom/codec/ecu.h> #include <osmocom/gsm/lapdm.h> #include <osmocom/gsm/sysinfo.h> @@ -265,6 +266,19 @@ struct gsm_lchan { /* last UL SPEECH resume flag */ bool is_speech_resume; } dtx; + struct { + bool last_rtp_input_was_sid; + uint8_t last_sid[GSM_FR_BYTES]; + uint8_t last_sid_len; + uint8_t last_sid_age; + /* A SID was transmitted on the DL in the period + * beginning with the last transmitted speech frame + * or the last mandatory-Tx position, whichever was + * more recent. */ + bool dl_sid_transmitted; + /* The current frame in the DL is taken up by FACCH */ + bool dl_facch_stealing; + } dtx_fr_hr_efr; uint8_t last_cmr; uint32_t last_fn; diff --git a/src/common/l1sap.c b/src/common/l1sap.c index cc775d38..75177a5a 100644 --- a/src/common/l1sap.c +++ b/src/common/l1sap.c @@ -1164,6 +1164,7 @@ static int l1sap_ph_rts_ind(struct gsm_bts_trx *trx, pp_msg = lapdm_phsap_dequeue_msg_facch(lchan, le, fn); else pp_msg = lapdm_phsap_dequeue_msg(le); + lchan->tch.dtx_fr_hr_efr.dl_facch_stealing = (pp_msg != NULL); } if (!pp_msg) { if (L1SAP_IS_LINK_SACCH(link_id)) { @@ -1217,26 +1218,259 @@ static int l1sap_ph_rts_ind(struct gsm_bts_trx *trx, return 1; } -/* This helper function for l1sap_tch_rts_ind() preens incoming RTP frames - * for FR/EFR SID: if the received frame is a valid SID per the rules of - * GSM 06.31/06.81 section 6.1.1, it needs to be rejuvenated by clearing - * all reserved bits and resetting the SID code word to error-free 95 zeros - * for FR or 95 ones for EFR, and if the received frame is an invalid SID - * per the same rules, then we need to drop it. We return false if - * l1sap_tch_rts_ind() needs to drop this frame, otherwise true. */ -static bool rtppayload_sid_preen(struct gsm_lchan *lchan, struct msgb *msg) +/* The following static functions are helpers for l1sap_tch_rts_ind(), + * used only for FR/HR/EFR speech modes. For these speech TCH modes, + * if our incoming RTP stream includes SID frames, we need to apply + * the following transformations to the downlink frame stream we actually + * transmit: + * + * - We need to cache the last received SID and retransmit it in + * SACCH-aligned frame positions, or if the SACCH-aligned frame + * position was stolen by FACCH, then right after that FACCH. + * + * - That cached SID needs to be aged and expired, in accord with + * TS 28.062 section C.3.2.1.1 paragraph 5 - the paragraph concerning + * expiration of cached downlink SID. + * + * - In all other frame positions, extraneous SID frames need to be + * dropped - we send an empty payload to the BTS model, causing it + * to transmit an induced BFI condition on the air (fake DTXd), + * or perhaps real DTXd (actually turning off Tx) in the future. + */ + +/*! \brief Check if the given FN of TCH-RTS-IND corresponds to a mandatory + * SID position for non-AMR codecs that follow SACCH alignment. + * \param[in] lchan Logical channel on which we check scheduling + * \param[in] fn Frame Number for which we check scheduling + * \returns true if this FN is a mandatory SID position, false otherwise + */ +static inline bool fr_hr_efr_sid_position(struct gsm_lchan *lchan, uint32_t fn) { + /* See GSM 05.08 section 8.3 for frame numbers - but we are + * specifically looking for FNs corresponding to the beginning + * of the complete SID frame to be transmitted, rather than all FNs + * where we have to put out a non-suppressed burst. */ + switch (lchan->type) { + case GSM_LCHAN_TCH_F: + return fn % 104 == 52; + case GSM_LCHAN_TCH_H: + switch (lchan->nr) { + case 0: + return fn % 104 == 0 || fn % 104 == 52; + case 1: + return fn % 104 == 14 || fn % 104 == 66; + default: + return false; + } + default: + return false; + } +} + +/*! \brief This helper function implements DTXd input processing for FR/HR/EFR: + * we got an RTP input frame, now we need to check if it is SID or not, + * and update our DL SID reshaper state accordingly. + * \param[in] lchan Logical channel structure of the TCH we work with + * \param[in] resp_msg The input frame from RTP + * \param[out] sid_result Output flag indicating if the received frame is SID + * \returns true if the frame in resp_msg is good, false otherwise + */ +static bool fr_hr_efr_dtxd_input(struct gsm_lchan *lchan, struct msgb *resp_msg, + bool *sid_result) +{ + enum osmo_gsm631_sid_class sidc; + bool is_sid; + switch (lchan->tch_mode) { case GSM48_CMODE_SPEECH_V1: - if (lchan->type == GSM_LCHAN_TCH_F) - return osmo_fr_sid_preen(msg->data); - else - return true; /* FIXME: see OS#6036 */ + if (lchan->type == GSM_LCHAN_TCH_F) { + sidc = osmo_fr_sid_classify(msgb_l2(resp_msg)); + switch (sidc) { + case OSMO_GSM631_SID_CLASS_SPEECH: + is_sid = false; + break; + case OSMO_GSM631_SID_CLASS_INVALID: + /* TS 28.062 section C.3.2.1.1: invalid SIDs + * from call leg A UL are treated like BFIs. + * Drop this frame and act as if we got nothing + * at all from RTP for this FN. */ + return false; + case OSMO_GSM631_SID_CLASS_VALID: + is_sid = true; + /* The SID code word may have a one bit error - + * rejuvenate it. */ + osmo_fr_sid_reset(msgb_l2(resp_msg)); + break; + default: + /* SID classification per GSM 06.31 section + * 6.1.1 has only 3 possible outcomes. */ + OSMO_ASSERT(0); + } + } else { + /* The same kind of classification as we do in + * osmo_{fr,efr}_sid_classify() is impossible for HR: + * the equivalent ternary SID classification per + * GSM 06.41 can only be done in the UL-handling BTS, + * directly coupled to the GSM 05.03 channel decoder, + * and cannot be reconstructed downstream from frame + * payload bits. The only kind of SID we can detect + * here is the perfect, error-free kind. */ + is_sid = osmo_hr_check_sid(msgb_l2(resp_msg), + msgb_l2len(resp_msg)); + } + break; case GSM48_CMODE_SPEECH_EFR: - return osmo_efr_sid_preen(msg->data); + /* same logic as for FRv1 */ + sidc = osmo_efr_sid_classify(msgb_l2(resp_msg)); + switch (sidc) { + case OSMO_GSM631_SID_CLASS_SPEECH: + is_sid = false; + break; + case OSMO_GSM631_SID_CLASS_INVALID: + return false; + case OSMO_GSM631_SID_CLASS_VALID: + is_sid = true; + osmo_efr_sid_reset(msgb_l2(resp_msg)); + break; + default: + OSMO_ASSERT(0); + } + break; default: - return true; + /* This static function should never be called except for + * V1 and EFR speech modes. */ + OSMO_ASSERT(0); + } + *sid_result = is_sid; + lchan->tch.dtx_fr_hr_efr.last_rtp_input_was_sid = is_sid; + if (is_sid) { + uint8_t copy_len; + + copy_len = OSMO_MIN(msgb_l2len(resp_msg), + ARRAY_SIZE(lchan->tch.dtx_fr_hr_efr.last_sid)); + memcpy(lchan->tch.dtx_fr_hr_efr.last_sid, + msgb_l2(resp_msg), copy_len); + lchan->tch.dtx_fr_hr_efr.last_sid_len = copy_len; + lchan->tch.dtx_fr_hr_efr.last_sid_age = 0; + } else { + /* We got a speech frame, not SID - therefore, the state flag + * of "we already transmitted a SID" needs to be cleared, + * so that the very first SID that follows this talkspurt + * will get transmitted right away, without waiting for + * the next mandatory SID position. */ + lchan->tch.dtx_fr_hr_efr.dl_sid_transmitted = false; + } + return true; +} + +/*! \brief This helper function implements DTXd output processing for FR/HR/EFR: + * here we update our state to deal with cached SID aging, mandatory-Tx + * frame positions and FACCH stealing, and we make the desired output + * transformations of either regurgitating a cached SID or vice-versa, + * dropping a SID we received from RTP. + * \param[in] lchan Logical channel structure of the TCH we work with + * \param[in] fn Frame Number for which we are preparing DL + * \param[in] current_input_is_sid Self-explanatory + * \param[in] resp_msg_p Pointer to l1sap_tch_rts_ind() internal variable + * \param[in] resp_l1sap_p ditto + * \param[in] empty_l1sap_p ditto + * + * This function gets called with pointers to l1sap_tch_rts_ind() internal + * variables and cannot be properly understood on its own, without + * understanding the parent function first. This situation is unfortunate, + * but it was the only way to factor the present logic out of + * l1sap_tch_rts_ind() main body. + */ +static void fr_hr_efr_dtxd_output(struct gsm_lchan *lchan, uint32_t fn, + bool current_input_is_sid, + struct msgb **resp_msg_p, + struct osmo_phsap_prim **resp_l1sap_p, + struct osmo_phsap_prim *empty_l1sap_p) +{ + struct msgb *resp_msg = *resp_msg_p; + bool sid_in_hand = current_input_is_sid; + + /* Are we at a mandatory-Tx frame position? If so, clear the state flag + * of "we already transmitted a SID in this window" - as of right now, + * a SID has _not_ been transmitted in the present window yet, and if + * we are in a DTX pause, we do need to transmit a SID update as soon + * as we are able to, FACCH permitting. */ + if (fr_hr_efr_sid_position(lchan, fn)) + lchan->tch.dtx_fr_hr_efr.dl_sid_transmitted = false; + + /* The next stanza implements logic that was originally meant to reside + * in the TFO block in TRAUs: if the source feeding us RTP is in a DTXu + * pause (resp_msg == NULL, meaning we got nothing from RTP) *and* the + * most recent RTP input we did get was a SID, and that SID hasn't + * expired, then we need to replicate that SID. */ + if (!resp_msg && lchan->tch.dtx_fr_hr_efr.last_rtp_input_was_sid && + lchan->tch.dtx_fr_hr_efr.last_sid_age < 47) { + /* Whatever we do further below, any time another 20 ms window + * has passed since the last SID was received in RTP, we have + * to age that cached SID. */ + lchan->tch.dtx_fr_hr_efr.last_sid_age++; + + /* The following conditional checking dl_sid_transmitted flag + * is peculiar to our sans-E1 architecture. In the original + * T1/E1 Abis architecture the TFO-enabled TRAU would repeat + * the cached SID from call leg A into *every* 20 ms frame in + * its Abis output, and then the BTS would select which ones + * it should transmit per the rules of GSM 06.31/06.81 section + * 5.1.2. But in our architecture it would be silly and + * wasteful to allocate and fill an msgb for this cached SID + * only to toss it later in the same function - hence the + * logic of section 5.1.2 is absorbed into the decision right + * here to proceed with cached SID regurgitation or not, + * in the form of the following conditional. */ + if (!lchan->tch.dtx_fr_hr_efr.dl_sid_transmitted) + resp_msg = l1sap_msgb_alloc(lchan->tch.dtx_fr_hr_efr.last_sid_len); + if (resp_msg) { + resp_msg->l2h = msgb_put(resp_msg, + lchan->tch.dtx_fr_hr_efr.last_sid_len); + memcpy(resp_msg->l2h, lchan->tch.dtx_fr_hr_efr.last_sid, + lchan->tch.dtx_fr_hr_efr.last_sid_len); + *resp_msg_p = resp_msg; + *resp_l1sap_p = msgb_l1sap_prim(resp_msg); + sid_in_hand = true; + } + } else if (resp_msg && sid_in_hand) { + /* This "else if" leg implements the logic of section 5.1.2 + * for cases when a SID is already present in the RTP input, + * as indicated by (resp_msg != NULL) and sid_in_hand being + * true. Because we are in the "else" clause of the big "if" + * above, this path executes only when the SID has come from + * RTP in _this_ frame, rather than regurgitated from cache. + * But be it fresh or cached, the rules of section 5.1.2 still + * apply, and if we've already transmitted a SID in the current + * window, then we need to suppress further SIDs and send + * an empty payload to the BTS model, causing the latter + * to transmit an induced BFI condition on the air. This + * strange-seeming behavior is needed so that the spec-compliant + * Rx DTX handler in the MS will produce the expected output, + * same as if the GSM network were the old-fashioned kind with + * Abis TRAUs and TFO. */ + if (lchan->tch.dtx_fr_hr_efr.dl_sid_transmitted) { + msgb_free(resp_msg); + resp_msg = NULL; + *resp_msg_p = NULL; + *resp_l1sap_p = empty_l1sap_p; + } } + + /* The following conditional answers this question: are we actually + * transmitting a SID frame on the air right now, at this frame number? + * If we are certain the BTS model is going to transmit this SID, + * we set the state flag so we won't be transmitting any more SIDs + * until we either hit the next mandatory-Tx position or get another + * little talkspurt followed by new SID. The check for FACCH stealing + * is included because if the BTS model is going to transmit FACCH in + * the current FN, then we are not actually transmitting SID right now, + * and we still need to transmit a SID ASAP, as soon as the TCH becomes + * becomes free from FACCH activity. GSM 06.31/06.81 section 5.1.2 + * does mention that if the mandatory-Tx frame position is taken up + * by FACCH, then we need to send SID in the following frame. */ + if (resp_msg && sid_in_hand && !lchan->tch.dtx_fr_hr_efr.dl_facch_stealing) + lchan->tch.dtx_fr_hr_efr.dl_sid_transmitted = true; } /* TCH-RTS-IND prim received from bts model */ @@ -1249,6 +1483,7 @@ static int l1sap_tch_rts_ind(struct gsm_bts_trx *trx, struct gsm_lchan *lchan; uint8_t chan_nr, marker = 0; uint32_t fn; + bool is_fr_hr_efr_sid = false; chan_nr = rts_ind->chan_nr; fn = rts_ind->fn; @@ -1278,10 +1513,6 @@ static int l1sap_tch_rts_ind(struct gsm_bts_trx *trx, if (!resp_msg) { LOGPLCGT(lchan, &g_time, DL1P, LOGL_DEBUG, "DL TCH Tx queue underrun\n"); resp_l1sap = &empty_l1sap; - } else if (!rtppayload_sid_preen(lchan, resp_msg)) { - msgb_free(resp_msg); - resp_msg = NULL; - resp_l1sap = &empty_l1sap; } else { /* Obtain RTP header Marker bit from control buffer */ marker = rtpmsg_marker_bit(resp_msg); @@ -1290,6 +1521,27 @@ static int l1sap_tch_rts_ind(struct gsm_bts_trx *trx, msgb_push(resp_msg, sizeof(*resp_l1sap)); resp_msg->l1h = resp_msg->data; resp_l1sap = msgb_l1sap_prim(resp_msg); + + /* FR/HR/EFR SID or non-SID input handling */ + if (lchan->tch_mode == GSM48_CMODE_SPEECH_V1 || + lchan->tch_mode == GSM48_CMODE_SPEECH_EFR) { + bool drop; + + drop = !fr_hr_efr_dtxd_input(lchan, resp_msg, + &is_fr_hr_efr_sid); + if (OSMO_UNLIKELY(drop)) { + msgb_free(resp_msg); + resp_msg = NULL; + resp_l1sap = &empty_l1sap; + } + } + } + + /* FR/HR/EFR DTXd output stage */ + if (lchan->tch_mode == GSM48_CMODE_SPEECH_V1 || + lchan->tch_mode == GSM48_CMODE_SPEECH_EFR) { + fr_hr_efr_dtxd_output(lchan, fn, is_fr_hr_efr_sid, &resp_msg, + &resp_l1sap, &empty_l1sap); } memset(resp_l1sap, 0, sizeof(*resp_l1sap)); |