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sdp, engine, imsd, media: the far end's telephone-event packets are played as the tones they stand for

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Keys pressed on the other phone reached imsd-media as RFC 4733 events and
were dropped with every packet that is not the audio's. The playout now
takes them: the gap before an event's start (a stock sender's DTX silence
often precedes a key press) is filled as before an audio frame, each
packet reports the event's duration so far from its start stamp, and what
the clock has not covered yet is synthesized as the event's Q.23
frequency pair at the packet's volume, so a retransmitted end packet adds
nothing, a lost update is caught up by the next, and a far end whose
audio resumes past the event (the stock phone's does) meets the clock
with the usual fill. An answer may renumber telephone-event from what we
offered (RFC 3264: the answerer sends with the offer's numbers, §6.1,
and the offerer with the answer's, §5.1), so the leg gets both: DTMF_PT
to send with, DTMF_RX_PT to take events at as well — our own SDP's
number: the offer's 98 or 100 on a call we placed, the offer's number we
echoed on one we answered; when the answer gave the audio our offer's
number, that number is the leg's audio and DTMF_RX_PT is the answer's
telephone-event number instead — and takes events at either number,
never at the audio's. --selftest pins the frequency table; the stats
gain rx_dtmf, tones and dtmf_rx_pt.

Tested: --selftest, tests/Sdp and tests/Engine (the eight suites pass);
the loopback's --dtmf-rx arm on a host build of this commit's tree
(journal/ims/captures/2026-10-15-dtmf-loopback-c3-rx.txt; the tx, both,
plain and collision runs beside it); the dev phone's dtmf benches ran in
builds of this series.
This commit is contained in:
Jorijn van der Graaf 2026-10-15 21:18:28 +02:00
commit e31887bf21
Signed by: jorijnvdgraaf
GPG key ID: 2937E59CDCC1BCFB
7 changed files with 244 additions and 38 deletions
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31
tests/Engine/main.cpp
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@ -270,6 +270,7 @@ int main() {
auto a200 = m.OnInviteResponse(R200Sdp(m.CallId(), std::format("{}m=audio 6004 RTP/AVP 97 98 100\r\na=rtpmap:97 AMR-WB/16000/1\r\na=rtpmap:98 telephone-event/16000\r\na=rtpmap:100 telephone-event/8000\r\n", SdpHead)));
const Action* media = Find(a200, Action::Type::StartMedia);
Check(media && media->media.dtmfPt == 98, "the leg carries the answer's telephone-event pt at the codec's clock (98, not the narrowband 100)");
Check(media && media->media.dtmfRxPt == 98, "outgoing: the far end sends at our offer's number for that clock");
Check(m.State() == CallState::Active, "active");
auto sent = m.OnDtmf("12#*a");
const Action* dt = Find(sent, Action::Type::SendDtmf);
@ -292,6 +293,35 @@ int main() {
Check(!Has(late, Action::Type::SendDtmf) && Find(late, Action::Type::Log) && Find(late, Action::Type::Log)->text.ends_with("the call is terminated"), "DTMF after the call: dropped, the line names the state");
}
// ---- DTMF, outgoing, the answer renumbered telephone-event (RFC 3264
// allows it): we send with its number, the far end with our offer's
{
imsd::util::Rng rng(44);
CallMachine m(c, rng, "ims-call-1e", "1233", 50004, false);
m.Start();
auto a200 = m.OnInviteResponse(R200Sdp(m.CallId(), std::format("{}m=audio 6004 RTP/AVP 97 101\r\na=rtpmap:97 AMR-WB/16000/1\r\na=rtpmap:101 telephone-event/16000\r\n", SdpHead)));
const Action* media = Find(a200, Action::Type::StartMedia);
Check(media && media->media.dtmfPt == 101 && media->media.dtmfRxPt == 98, "renumbered answer: send with 101, listen on our 98");
// a narrowband answer: AMR at 99 with telephone-event/8000 at 102
imsd::util::Rng rng2(45);
CallMachine n(c, rng2, "ims-call-1f", "1233", 50004, false);
n.Start();
auto b200 = n.OnInviteResponse(R200Sdp(n.CallId(), std::format("{}m=audio 6004 RTP/AVP 99 102\r\na=rtpmap:99 AMR/8000/1\r\na=rtpmap:102 telephone-event/8000\r\n", SdpHead)));
const Action* nbMedia = Find(b200, Action::Type::StartMedia);
Check(nbMedia && nbMedia->media.codec == "AMR" && nbMedia->media.dtmfPt == 102 && nbMedia->media.dtmfRxPt == 100, "narrowband answer: send with its 102, listen on our offer's 100");
// an answer numbering for itself that gives the audio our offer's
// telephone-event number: the receive number is the answer's, never
// the audio's (every downlink frame would be taken for an event)
imsd::util::Rng rng3(46);
CallMachine o(c, rng3, "ims-call-1g", "1233", 50004, false);
o.Start();
auto c200 = o.OnInviteResponse(R200Sdp(o.CallId(), std::format("{}m=audio 6004 RTP/AVP 100 101\r\na=rtpmap:100 AMR/8000/1\r\na=rtpmap:101 telephone-event/8000\r\n", SdpHead)));
const Action* colMedia = Find(c200, Action::Type::StartMedia);
Check(colMedia && colMedia->media.payloadType == 100 && colMedia->media.dtmfPt == 101 && colMedia->media.dtmfRxPt == 101, "the audio at our telephone-event number: listen on the answer's 101, not the audio's 100");
auto again = m.OnInviteResponse(R200(m.CallId()));
Check(!Find(again, Action::Type::StartMedia), "a retransmitted 200 starts no second leg");
}
// ---- remote BYE mid-call
{
imsd::util::Rng rng(7);
@ -432,6 +462,7 @@ int main() {
Check(ok && ok->text.contains("a=rtpmap:105 telephone-event/16000\r\n"), "answer keeps telephone-event");
const Action* mtMedia = Find(aa, Action::Type::StartMedia);
Check(mtMedia && mtMedia->media.dtmfPt == 105, "incoming: the leg carries the offer's telephone-event pt");
Check(mtMedia && mtMedia->media.dtmfRxPt == 105, "incoming: the far end sends at the number we echoed");
auto mtDtmf = m.OnDtmf("9");
const Action* mtDt = Find(mtDtmf, Action::Type::SendDtmf);
Check(mtDt && mtDt->text == "9", "incoming, accepted: the tones go to the leg");