falconia has uploaded this change for review. ( https://gerrit.osmocom.org/c/libosmocore/+/32184 ) Change subject: codec: add SID preening functions for FR & EFR ...................................................................... codec: add SID preening functions for FR & EFR Those network elements which receive a stream of codec frames that may come from the uplink of GSM call A and which are responsible for preparing the frame stream for the downlink of GSM call B (OsmoMGW feeding TRAU-DL, or OsmoBTS receiving RTP and feeding DL to its PHY) must be prepared for the possibility that their incoming frame stream may contain corrupted SID frames, presumably from bit errors on radio link A. Per the rules of section 6.1.1 of GSM 06.31 for FR and GSM 06.81 for EFR, SID frames with just one errored bit are still to be accepted as valid, whereas frames with more corrupted bits which are still recognizable as SID are classified as invalid SID. In the case of a TrFO call, the entity switching from leg A UL to leg B DL is responsible for *not* transmitting invalid SID frames on the destination leg (they should be treated like BFIs), and any deemed-valid SID frames that are forwarded should be preened, correcting that one bit error they may exhibit. The functions added here provide that functionality. Change-Id: Iec5c1f2619a82499f61cb3e5a7cd03ff0f020ad8 --- M include/osmocom/codec/codec.h M src/codec/gsm610.c M src/codec/gsm660.c 3 files changed, 110 insertions(+), 0 deletions(-) git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/84/32184/1 diff --git a/include/osmocom/codec/codec.h b/include/osmocom/codec/codec.h index ac7a8e9..b318e2f 100644 --- a/include/osmocom/codec/codec.h +++ b/include/osmocom/codec/codec.h @@ -94,6 +94,8 @@ enum etsi_sid_class osmo_fr_sid_classify(const uint8_t *rtp_payload); enum etsi_sid_class osmo_efr_sid_classify(const uint8_t *rtp_payload); +bool osmo_fr_sid_preen(uint8_t *rtp_payload); +bool osmo_efr_sid_preen(uint8_t *rtp_payload); int osmo_amr_rtp_enc(uint8_t *payload, uint8_t cmr, enum osmo_amr_type ft, enum osmo_amr_quality bfi); diff --git a/src/codec/gsm610.c b/src/codec/gsm610.c index 81876d6..e3dff17 100644 --- a/src/codec/gsm610.c +++ b/src/codec/gsm610.c @@ -388,3 +388,42 @@ else return ETSI_SID_CLASS_VALID; } + +/*! Preen potentially-SID FR codec frame in RTP format, ensuring that it is + * either a speech frame or a valid SID, and if the latter, making it a + * perfect, error-free SID frame. + * \param[in] rtp_payload Buffer with RTP payload - must be writable! + * \returns true if the frame is good, false otherwise + */ +bool osmo_fr_sid_preen(uint8_t *rtp_payload) +{ + enum etsi_sid_class sidc; + uint8_t *p, sub; + + sidc = osmo_fr_sid_classify(rtp_payload); + switch (sidc) { + case ETSI_SID_CLASS_SPEECH: + return true; + case ETSI_SID_CLASS_INVALID: + return false; + case ETSI_SID_CLASS_VALID: + /* "Rejuvenate" this SID frame, correcting any errors: + * zero out all bits that aren't LARc or Xmaxc, thereby + * clearing all SID code word bits and all unused/reserved + * bits. */ + p = rtp_payload + 5; /* skip magic+LARc */ + for (sub = 0; sub < 4; sub++) { + *p++ = 0; + *p++ &= 0x1F; + *p++ &= 0x80; + *p++ = 0; + *p++ = 0; + *p++ = 0; + *p++ = 0; + } + return true; + } + + /* should never be reached */ + return false; +} diff --git a/src/codec/gsm660.c b/src/codec/gsm660.c index def93d7..67c7731 100644 --- a/src/codec/gsm660.c +++ b/src/codec/gsm660.c @@ -350,3 +350,44 @@ else return ETSI_SID_CLASS_VALID; } + +/*! Preen potentially-SID EFR codec frame in RTP format, ensuring that it is + * either a speech frame or a valid SID, and if the latter, making it a + * perfect, error-free SID frame. + * \param[in] rtp_payload Buffer with RTP payload - must be writable! + * \returns true if the frame is good, false otherwise + */ +bool osmo_efr_sid_preen(uint8_t *rtp_payload) +{ + enum etsi_sid_class sidc; + + sidc = osmo_efr_sid_classify(rtp_payload); + switch (sidc) { + case ETSI_SID_CLASS_SPEECH: + return true; + case ETSI_SID_CLASS_INVALID: + return false; + case ETSI_SID_CLASS_VALID: + /* "Rejuvenate" this SID frame, correcting any errors: + * set all 95 SID code word bits to 1. */ + rtp_payload[6] |= 0x6F; + rtp_payload[7] = 0xFF; + rtp_payload[8] = 0xFF; + rtp_payload[9] |= 0x80; + rtp_payload[12] |= 0x3B; + rtp_payload[13] = 0xFF; + rtp_payload[14] = 0xFF; + rtp_payload[15] |= 0xE0; + rtp_payload[19] = 0xFF; + rtp_payload[20] = 0xFF; + rtp_payload[21] = 0xFF; + rtp_payload[25] = 0xFF; + rtp_payload[26] |= 0xFC; + rtp_payload[27] = 0xFF; + rtp_payload[28] |= 0xC0; + return true; + } + + /* should never be reached */ + return false; +} -- To view, visit https://gerrit.osmocom.org/c/libosmocore/+/32184 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: libosmocore Gerrit-Branch: master Gerrit-Change-Id: Iec5c1f2619a82499f61cb3e5a7cd03ff0f020ad8 Gerrit-Change-Number: 32184 Gerrit-PatchSet: 1 Gerrit-Owner: falconia &lt;falcon(a)freecalypso.org&gt; Gerrit-MessageType: newchange