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engine/sdp: CODECS override for the codecs we offer and accept

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KPN's interconnect gateway transcodes every caller up: a G.711-only
fixed-line INVITE reached the phone offering PCMA, PCMU, AMR and AMR-WB
(bench call 2026-09-08), so the AMR-WB-only build rang and the narrowband
path — the one the Telia field report hit with 488 — cannot be reached on
the air through KPN by any caller.

CODECS=<list> (comma-separated over AMR-WB, AMR/AMR-NB, PCMA, PCMU) makes
the list both the codecs offered on an outgoing call and the acceptance
preference for an inbound offer, in that order: CODECS=PCMA takes G.711
A-law out of the mixed offer above, CODECS=PCMA,PCMU sends a G.711-only
offer toward the network. Unset, nothing changes — the default offer
bytes and the AMR-WB > AMR > PCMA > PCMU preference stay pinned. The
daemon logs an active override at startup.
This commit is contained in:
Jorijn van der Graaf 2026-09-08 17:53:26 +02:00
commit 37ec8660b7
6 changed files with 270 additions and 67 deletions
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23
interfaces/Imsd-Engine.cppm
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@ -99,15 +99,20 @@ export namespace imsd::engine {
public:
// `emergency`: the shell classified the dialled string as an
// emergency number — the first attempt targets urn:service:sos.
CallMachine(const imsd::msg::Context& ctx, imsd::util::Rng& rng, std::string uni, std::string number, int rtpPort, bool precond, bool emergency = false)
// `codecs`: the daemon's CODECS override — the codecs offered on an
// outgoing call and accepted from an inbound offer, in preference
// order; empty = the sdp module's defaults.
CallMachine(const imsd::msg::Context& ctx, imsd::util::Rng& rng, std::string uni, std::string number, int rtpPort, bool precond, bool emergency = false,
std::vector<std::string> codecs = {})
: ctx_(ctx), rng_(rng), uni_(std::move(uni)), number_(std::move(number)),
rtpPort_(rtpPort), precond_(precond), attemptSos_(emergency) {
rtpPort_(rtpPort), precond_(precond), codecs_(std::move(codecs)), attemptSos_(emergency) {
ResetDialog();
}
CallMachine(const imsd::msg::Context& ctx, imsd::util::Rng& rng, std::string uni, IncomingInvite in, int rtpPort)
CallMachine(const imsd::msg::Context& ctx, imsd::util::Rng& rng, std::string uni, IncomingInvite in, int rtpPort,
std::vector<std::string> codecs = {})
: ctx_(ctx), rng_(rng), uni_(std::move(uni)), rtpPort_(rtpPort),
precond_(false), direction_(Direction::Incoming),
precond_(false), codecs_(std::move(codecs)), direction_(Direction::Incoming),
state_(CallState::Incoming), reason_("incoming"),
invite_(in.invite) {
number_ = imsd::sip::CallerId(invite_);
@ -148,6 +153,7 @@ export namespace imsd::engine {
offer.rtpPort = rtpPort_;
offer.sessionId = rng_.UInt(1000000, 9999999);
offer.precond = precond_;
offer.codecs = codecs_;
std::string sdp = imsd::sdp::BuildOffer(offer);
std::vector<Action> a;
a.push_back(Send(imsd::msg::BuildInvite(ctx_, d_, sdp, precond_)));
@ -158,8 +164,9 @@ export namespace imsd::engine {
// UAS: answer the inbound INVITE with 100 Trying + 180 Ringing (made
// reliable only when the caller Requires 100rel) and arm the ring
// timeout. An offer we cannot serve — no audio line, or none of the
// codecs imsd-media plays (AMR-WB, AMR, PCMA, PCMU) — is refused
// with 488 up front, before the UI ever rings; the log line names
// codecs imsd-media plays (AMR-WB, AMR, PCMA, PCMU; the CODECS
// override narrows that set) — is refused with 488 up front, before
// the UI ever rings; the log line names
// what WAS offered, so a field journal answers "which codec did the
// gateway want" without a raw SIP dump.
std::vector<Action> OnInvite() {
@ -318,6 +325,7 @@ export namespace imsd::engine {
offer.sessionId = rng_.UInt(1000000, 9999999);
offer.precond = precond_;
offer.currRemote = "sendrecv";
offer.codecs = codecs_;
ans = imsd::sdp::BuildOffer(offer);
}
// RFC 4028 §9: a 2xx to a refresh MUST echo Session-Expires,
@ -429,6 +437,7 @@ export namespace imsd::engine {
std::string uni_, number_;
int rtpPort_;
bool precond_;
std::vector<std::string> codecs_; // CODECS override; empty = defaults
Direction direction_ = Direction::Outgoing;
CallState state_ = CallState::Dialing;
std::string reason_ = "outgoing";
@ -532,7 +541,7 @@ export namespace imsd::engine {
}
MediaLeg ParseAnswer() const {
imsd::sdp::Answer ans = imsd::sdp::ParseAnswer(answerSdp_);
imsd::sdp::Answer ans = imsd::sdp::ParseAnswer(answerSdp_, codecs_);
MediaLeg leg;
leg.remoteIp = ans.ip;
leg.remotePort = ans.port < 0 ? 0 : ans.port;