Change in libosmocore[master]: coding: prevent marking FACCH frames as AMR's special DTX frames

fixeria has uploaded this change for review. ( https://gerrit.osmocom.org/c/libosmocore/+/28127 ) Change subject: coding: prevent marking FACCH frames as AMR's special DTX frames ...................................................................... coding: prevent marking FACCH frames as AMR's special DTX frames Both gsm0503_tch_a[fh]s_decode_dtx() functions accept an optional 'dtx' pointer, which is used to indicate type of a received AMR block to the caller in DTX mode of operation. If not NULL, it's expected to be updated by gsm0503_detect_a[fh]s_dtx_frame() every time one of the mentioned functions is called. However, in case of FACCH both functions return early, so the value of dtx remains unchanged and thus FACCH frames may be misinterpreted as AMR's special DTX frames. This is rather critical during the DTX silence periods, when all special DTX frames (e.g. SID_UPDATE) are being treated as SUB frames. Each unsuccessful FACCH decoding attempt will 'poison' SUB measurements, causing unexpected RxQual- SUB values in the Uplink measurement reports. Fix this by resetting *dtx to AMR_OTHER in the FACCH specific path. Change-Id: I2e6f4b748c6445725211e264ab5f3f5a2712087a Related: SYS#5853 --- M src/coding/gsm0503_coding.c 1 file changed, 13 insertions(+), 0 deletions(-) git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/27/28127/1 diff --git a/src/coding/gsm0503_coding.c b/src/coding/gsm0503_coding.c index 98439e3..e81bf02 100644 --- a/src/coding/gsm0503_coding.c +++ b/src/coding/gsm0503_coding.c @@ -2171,6 +2171,12 @@ gsm0503_tch_fr_deinterleave(cB, iB); if (steal > 0) { + /* If not NULL, dtx indicates type of previously decoded TCH/AFS frame. + * It's normally updated by gsm0503_detect_afs_dtx_frame(), which is not + * reached in case of FACCH. Reset it here to avoid FACCH/F frames being + * misinterpreted as AMR's special DTX frames. */ + if (dtx != NULL) + *dtx = AMR_OTHER; rv = _xcch_decode_cB(tch_data, cB, n_errors, n_bits_total); if (rv) { /* Error decoding FACCH frame */ @@ -2633,6 +2639,13 @@ /* if we found a stole FACCH, but only at correct alignment */ if (steal > 0) { + /* If not NULL, dtx indicates type of previously decoded TCH/AHS frame. + * It's normally updated by gsm0503_detect_ahs_dtx_frame(), which is not + * reached in case of FACCH. Reset it here to avoid FACCH/H frames being + * misinterpreted as AMR's special DTX frames. */ + if (dtx != NULL) + *dtx = AMR_OTHER; + for (i = 0; i < 6; i++) { gsm0503_tch_burst_unmap(&iB[i * 114], &bursts[i * 116], NULL, i >> 2); -- To view, visit https://gerrit.osmocom.org/c/libosmocore/+/28127 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: libosmocore Gerrit-Branch: master Gerrit-Change-Id: I2e6f4b748c6445725211e264ab5f3f5a2712087a Gerrit-Change-Number: 28127 Gerrit-PatchSet: 1 Gerrit-Owner: fixeria &lt;vyanitskiy(a)sysmocom.de&gt; Gerrit-MessageType: newchange