falconia has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-mgw/+/39478?usp=email )
Change subject: E1: replace idle_tf_fr[] with a better version ......................................................................
E1: replace idle_tf_fr[] with a better version
The only truly correct way to pass FR/HR/EFR traffic from an incoming RTP stream to TRAU-DL frames is to apply the transform of TS 28.062 section C.3.2.1.1, originally specified for TFO but also necessary in the non-3GPP-specified case of GSM TrFO as it happens here. Unlike the situation with EFR, a FOSS implementation of TFO transform for FRv1 does exist in Themyscira libgsmfr2 - however, making these Themyscira codec libraries usable from mainline Osmocom programs by way of a proposed libosmocore DSO plugin mechanism, followed by a major redesign of OsmoMGW-E1 to pass all DL traffic through this TFO transform, would be a major project, difficult to justify prior to development of a proper TFO transform for EFR to complement the one for FRv1. Hence no change is being made currently to the arguably flawed general architecture of OsmoMGW-E1, which consists of passing through unaltered all valid codec frames that are received in RTP, and inserting fixed dummy TRAU-DL frames when no RTP-derived ones are available.
The original dummy TRAU-DL frame for FRv1 exhibited the following defects:
* The payload frame transmitted to the MS consisted of all zero bits. Standard type-approved GSM MS would interpret this bit pattern as a SID frame, even though the BTS is told via C16 bit "this frame is not a SID". Passing a SID is not inherently bad in itself in this context, but a SID with all LARc parameters set to 0 is a strange/poor choice.
* The setting of C-bits (defined in TS 48.060 section 5.5.1.1.1) was a mish-mash between TRAU-UL and TRAU-DL frame formats, thereby not matching the standard TRAU-DL C-bits fill produced by osmo_rtp2trau().
The replacement fill frame introduced here differs as follows:
* The payload bit content is the silence frame of GSM 46.011 Table 1: certainly better than a SID with all LARc parameters set to 0, and arguably better than any SID at all.
* The full TRAU-DL frame (C-bits pattern, peculiar ordering of D-bits) was generated by passing said silence frame through osmo_rtp2trau(), using this ad hoc tool:
https://gitea.osmocom.org/themwi/dummy-dl-frames
Change-Id: I995824586058e4e4ed77e900d4b57e5113f9eff6 --- M src/libosmo-mgcp/mgcp_e1.c 1 file changed, 42 insertions(+), 36 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-mgw refs/changes/78/39478/1
diff --git a/src/libosmo-mgcp/mgcp_e1.c b/src/libosmo-mgcp/mgcp_e1.c index f3471fb..3a7a450 100644 --- a/src/libosmo-mgcp/mgcp_e1.c +++ b/src/libosmo-mgcp/mgcp_e1.c @@ -105,47 +105,53 @@ 1, 1, 1, 1, 1, 1, 1, 1, };
-/* FR idle frame */ +/* The following FRv1 TRAU-DL frame is a dummy to be transmitted in the absence + * of RTP-derived TRAU-DL frames. The payload bit content here is the silence + * frame of TS 46.011 Table 1 - the best we can do without integrating the + * TFO transform for FRv1 from Themyscira libgsmfr2 - while the full TRAU-DL + * frame was generated by passing said FRv1 silence frame through + * osmo_rtp2trau(). + */ static const ubit_t idle_tf_fr[] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, - 0, 0, 0, 0, 1, 0, 0, 0, + 0, 0, 0, 0, 1, 1, 1, 1, + 1, 0, 1, 0, 1, 0, 1, 1, + 1, 1, 0, 0, 1, 1, 0, 1, + 1, 0, 1, 0, 1, 0, 1, 0, + 1, 0, 0, 1, 0, 0, 1, 0, + 1, 1, 1, 0, 0, 1, 0, 0, + 0, 0, 1, 0, 1, 0, 0, 0, + 1, 1, 0, 0, 0, 0, 0, 0, + 0, 1, 1, 0, 0, 0, 1, 1, + 1, 1, 0, 0, 0, 1, 0, 0, + 1, 1, 1, 0, 1, 1, 0, 1, + 1, 1, 0, 1, 1, 0, 0, 0, + 1, 0, 0, 1, 1, 1, 0, 1, + 1, 1, 0, 0, 0, 0, 1, 0, + 1, 0, 0, 0, 1, 0, 0, 0, + 1, 0, 0, 0, 0, 1, 1, 0, + 0, 0, 1, 1, 1, 0, 0, 0, + 1, 1, 0, 0, 1, 1, 1, 0, + 1, 1, 0, 1, 1, 0, 1, 1, + 1, 0, 0, 0, 1, 0, 0, 1, + 1, 1, 0, 1, 1, 0, 0, 0, + 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 0, 0, - 0, 0, 0, 0, 0, 0, 0, 0, - 1, 0, 0, 0, 0, 0, 1, 0, + 1, 1, 1, 0, 0, 0, 1, 1, + 1, 0, 0, 0, 1, 0, 0, 1, + 1, 1, 1, 0, 1, 1, 0, 1, + 1, 0, 1, 1, 0, 0, 0, 1, + 1, 0, 0, 1, 1, 1, 0, 1, + 1, 0, 0, 0, 0, 1, 0, 1, + 1, 0, 0, 0, 1, 0, 0, 0, + 0, 0, 0, 0, 1, 1, 0, 0, + 1, 0, 1, 1, 1, 0, 0, 0, + 1, 0, 0, 1, 1, 1, 0, 1, + 1, 1, 0, 1, 1, 0, 1, 1, + 0, 0, 0, 1, 0, 0, 1, 1, + 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, };
-
falconia