Linux userspace IMS daemon
- C++ 93.2%
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| Filename | Latest commit message | Latest commit date |
|---|---|---|
Jorijn van der Graaf
7a3dcc8951
With the P-CSCF coming from the PDN's PCO, the configuration file has no required line left, so the apk's ConditionPathExists=/etc/imsd.env drop-in goes: the unit starts on every phone with the package, and VoLTE is on by default. Installing the package and inserting a SIM is the opt-in; the file holds overrides only, and its existence changes nothing. By the versioning rule (AGENTS §11, the first commit of this series) that is what moves the major number: the release is 1.0.0, and §11 now records it. What used to be the file's job — keeping a phone nobody configured out of a failing unit — is now a rule on facts, the same for every phone: a modem in the failed state with a SIM reason makes the script write IMSD_IDLE=no-sim to /run/imsd.env and exit 0; a profile-indexed connect series the network refuses ten times in a row — each a persistent 3GPP cause in ModemManager's typed error (not subscribed, unknown APN, barred, not authorised in the PLMN, authentication failed, the service option not supported, the wrong PDN type) with packet service at the time; counted only while the modem reads registered, connecting or connected with packet service not detached — stricter than the daemon's PacketServiceUp; any other read, a timeout or a transient cause starts the count again — writes IMSD_IDLE=no-ims-pdn; and a bring-up that ends with no P-CSCF — none configured, none discovered: no IPv6 P-CSCF read from the PCO (PCSCF_DISCOVERY=none in the hand-off, the reader's exit 2: the list absent, empty, unreadable or IPv4/FQDN only), discovery skipped (no rmnet mux id) or no hand-off at all (a manual run) — and no registration of imsd's own to resume is the daemon's own idle, decided before it takes the bus name (SaPeer and the holds' old_gone say what can be resumed; a pair the holds wrote off is taken out of the kernel there) and at the no-target bring-up, where a pair nothing can resume is written off and taken out of the kernel first. imsd reads the key, logs idle: … and exits 0, which Restart=on-failure leaves alone, so the unit stays inactive until the next boot, a systemctl start or a start of imsd-ofonod where that runs (its Wants starts an idle imsd again). What is not a fact keeps the retry: no coverage, a SIM still waiting for its PIN, a modem without an ims profile (the APN-string connect is tried), an APN-string series (the modem's own wall), a resumable pair whose attempt failed (the fatal), and a P-CSCF reader that did not answer (PCSCF_DISCOVERY=failed: the daemon exits 1 and the restart runs discovery again). A phone that never had the file keeps its stopped unit through the upgrade and starts at its next boot, registering where the rule above lets it — at the upgrade itself where imsd-ofonod runs, whose restart pulls imsd in through its Wants (systemd queues the marked unit's try-restart, collapses it to a restart and starts what the unit Wants in the same transaction: job_type_collapse, transaction_add_job_and_dependencies, 262~rc3); the opt-out is systemctl mask --now imsd, since a plain disable is undone by that Wants. imsd-ofonod.service loses its After=imsd.service: with imsd starting on every phone, GNOME Calls' backend would otherwise wait behind the ims PDN bring-up at every boot and at its marked restart at an upgrade, for the whole bring-up (up to its TimeoutStartSec=900); it starts at once and republishes when imsd's name appears (OnImsdAppeared). The configuration file's path is the IMSD_ENV seam the mock bench uses. AGENTS §6's lint figures are this tree's (109 findings in 16 of 20 files, 2026-10-13; the 72 of 2026-10-06 predate the Qmi files). Tested: crafter-build test, 8 passed; on the host build the daemon's idle exit for the script's keys and, with no pair, for every discovery verdict but failed (none, skipped, no hand-off) — exit 0 — and the exit 1 for failed; the script's arms on the mock bench; on the dev phone (KPN), in builds of this series: the daemon's idle at the no-target bring-up with the dead pair removed and before the bus name for a pair the holds had written off, the discovery-failed exit 1 and its restart, the start without the file, the pull-in by an imsd-ofonod restart and the mask holding against it and a reboot, and imsd-ofonod starting at once with imsd stopped and republishing when imsd's name appeared. |
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| .forgejo/workflows | ||
| implementations | ||
| interfaces | ||
| packaging | ||
| tests | ||
| .gitignore | ||
| AGENTS.md | ||
| LICENSE | ||
| project.cpp | ||
| README.md | ||
imsd
Userspace IMS/VoLTE daemon for mainline Linux phones.
Most Linux phones drive the modem's internal IMS engine. imsd implements the whole IMS client in userspace instead: SIP registration with USIM AKA authentication over kernel IPsec (ESP), call signalling, and the AMR-WB RTP media plane wired into PipeWire so a stock mobile dialer like Plasma Dialer or GNOME Calls under Phosh can place and receive real VoLTE calls on a commercial network.
Status
Call-capable, both directions: outgoing calls place, answer, carry full-duplex
AMR-WB audio and tear down. Incoming calls ring, answer and carry media the
same way, driven end-to-end from a stock dialer over a frozen D-Bus ABI.
Not there yet: DTMF (SendDtmf is a stub), hold/multiparty/call waiting,
USSD.
Verified by community members to be fully working:
| Device | OS | Carrier |
|---|---|---|
| The Fairphone (Gen. 6) | postmarketOS, Linux 7.1.2 | KPN NL |
| The Fairphone (Gen. 6) | postmarketOS, Linux 7.1.2 | Telekom Deutschland GER |
| The Fairphone (Gen. 6) | postmarketOS, Linux 7.1.2 | Phonero |
| The Fairphone (Gen. 6) | postmarketOS, Linux 7.1.2 | Telia Norge |
What it needs
imsd talks to the modem through ModemManager plus qmicli over QRTR, installs
its security associations with ip xfrm and plays audio through PipeWire, so
in practice: a Qualcomm modem on a mainline kernel with working
WWAN/ModemManager integration, kernel ESP, PipeWire, systemd and polkit.
Install and configure
For automatic updates add the Catcrafts Alpine repository. Note this does also pull in other packages.
Otherwise just download the latest imsd and imsd-systemd APKs and install them.
Both can be found in the packages tab:
https://forgejo.catcrafts.net/Catcrafts/-/packages/alpine/imsd
Dialers
imsd itself is desktop-agnostic: everything a dialer needs is on the system
bus as net.catcrafts.IMS1. A small translation daemon per desktop speaks
the backend protocol its dialer already consumes, so dialer, shell and the
call-history/contacts stack run unmodified.
| Desktop | Daemon | Package | Owns | Consumed by |
|---|---|---|---|---|
| Plasma Mobile | imsd-dialerd |
imsd |
org.kde.telephony.* (session bus) |
plasma-dialer + kde-telephony-daemon, replacing modem-daemon |
| Phosh / GNOME Mobile | imsd-ofonod |
imsd-ofono |
org.ofono (system bus) |
GNOME Calls' ofono provider plugin |
Plasma Mobile needs nothing beyond the imsd package: imsd-dialerd is
autostarted in the session in place of plasma-dialer's modem-daemon, whose
own autostart must be off — the package hides it for accounts created after
the install (/etc/skel); an existing account hides it itself with a
Hidden=true copy of org.kde.modem.daemon.desktop in ~/.config/autostart.
For Phosh and GNOME Mobile, apk add imsd-ofono enables imsd-ofonod and
points GNOME Calls at its ofono provider (a gschema override; the per-user
equivalent is gsettings set org.gnome.Calls autoload-plugins "['ofono']").
Do not run it alongside a real ofonod.
Call control is polkit's net.catcrafts.IMS1.Voice: the active local
session and root may place, answer and end calls; an ssh login may not.
Full config:
Configuration is environment variables in /etc/imsd.env, none are required.
| Variable | Default | Meaning |
|---|---|---|
PCSCF |
(the first of PCSCF_DISCOVERED) |
P-CSCF address (IPv6), exactly one — not a comma-separated list — in RFC 5952 §4 form (lowercase, leading zeros dropped, the longest zero run compressed, no brackets — what ip prints for a plain IPv6 address; an IPv4-mapped address only as hex, ::ffff:a00:1 — the dotted spelling RFC 5952 §5 and ip use for it is refused); upper case, leading zeros, an uncompressed run or brackets are refused at start with the spelling to use (in the packaged unit the bring-up script refuses brackets first, with the rule), a dotted-quad tail with the rule; before 1.0.0 an upper-case, zero-padded or uncompressed PCSCF= matched no SA in ip xfrm's text and registered fresh at every restart — an upgraded phone with such a setting stops at start with the spelling to use. Set, it wins over PCSCF_DISCOVERED. It is where a fresh registration goes; a registration resumed from the kernel's SAs stays on the P-CSCF it was made to until its next fresh registration. With neither this nor PCSCF_DISCOVERED there is no fresh registration: a phone with nothing to resume idles (idle: no P-CSCF …), unless a resume failed with its pair still resumable, or the reader did not answer (PCSCF_DISCOVERY=failed): those exit non-zero for systemd's restart |
PCSCF_DISCOVERED |
(from the PDN's PCO) | the IPv6 P-CSCF list the network put in the ims PDN's PCO, comma-separated in the order the modem reports it; the first entry CanonicalIp6 accepts is used when PCSCF is unset. The packaged service gets it via /run/imsd.env from ims-pdn-up.sh, which reads it from the modem with imsd-pcscf (at most eight; it routes the first; imsd routes the P-CSCF it uses — the fresh target, the resumed SA peer — itself as well); entries CanonicalIp6 does not read — an IPv4 address, a name, an IPv6 literal with a zone or a dotted-quad tail (an IPv4-mapped entry in hex only) — are ignored (logged by the engine when the daemon goes on to register); `PCSCF_DISCOVERY=found |
IMSD_PCSCF |
/usr/libexec/imsd-pcscf |
the P-CSCF reader ims-pdn-up.sh runs — a bench seam (the mock bench's fake reader; a stub through a unit drop-in on the dev phone), from the environment |
PCSCF_PORT |
5060 |
unprotected SIP port for the initial REGISTER |
DEV |
qmapmux0.0 |
ims-PDN netdev; the packaged service passes the real one via /run/imsd.env |
LOCAL |
(auto) | UE address (compared in RFC 5952 form). The packaged service gets the PDN address ModemManager assigned, via /run/imsd.env from ims-pdn-up.sh; a manual run prefers a global IPv6 on DEV that is neither temporary nor dynamic (RA-derived), then any non-temporary one, then the first (the kernel's temporary SLAAC address is listed first, and a registration bound to it is lost when the kernel retires it) |
USER_AGENT |
imsd/<version> |
REGISTER User-Agent. Some networks fingerprint UAs; setting your device's stock build string reproduces the stock modem's registration exactly. Empty omits the header |
STATE_FILE |
/var/lib/imsd/imsreg.state (root) / $XDG_STATE_HOME/imsd/imsreg.state |
persisted registration context for warm resume |
HOLDS_FILE |
/run/imsd.holds (root) / $XDG_RUNTIME_DIR/imsd.holds (/tmp/imsd.holds without a runtime dir) |
the waits the network imposed (a Retry-After, the refusal schedule), where that schedule stands whether the old registration is gone (old_gone) and the refusal count (refusals: a resume refused without a Retry-After at a start with no fresh target is one, the restart's the second), kept across a restart of imsd for the PDN they were set on — not across a reboot; /dev/null switches the file off (only a regular file is ever removed; anything else is emptied). imsd-handover.sh honours it too |
RESUME |
auto |
0 forces a fresh registration (ignores a warm SA) where there is a fresh target; with none the untried pair is removed and the bring-up ends as AGENTS §7.2 (the daemon's own bring-up) step 1 says |
REFRESH_INTERVAL |
(auto) | keepalive re-REGISTER period in s; default = half the granted expiry, clamped to [120, 1800] |
EALG |
aes-cbc |
offered ESP cipher (aes-cbc, des-ede3-cbc, null). From the 401's Security-Server list imsd selects the highest-preference ipsec-3gpp mechanism that matches this offer (RFC 3329 §2.3.1) and takes the SPIs/ports from the entry carrying them (some cores list every mechanism they support and put the SPIs on the one they applied); when no entry matches, the P-CSCF's SPI-carrying entry is installed as listed (hmac-md5-96, an absent ealg = null) and the journal says so. The line, the selection and the SA parameters are logged at every fresh registration |
SIP_TRANSPORT |
auto |
transport of the protected leg (the second REGISTER and everything after it): tcp, udp, or auto = TCP, falling back to a fresh registration over UDP when the P-CSCF leaves two TCP connects unanswered — but only on a phone that has never registered over TCP: once the state file records a TCP registration, a silent connect is treated as an outage, not a policy (delete the file or set udp to override, e.g. after a SIM change). The challenge (first REGISTER) is always UDP. Over UDP a REGISTER or INVITE larger than ~1.2 KB leaves as IPv6 fragments at the ims PDN's 1280-byte MTU (the journal says so once per flow); there are no SIP retransmission timers over UDP yet, so a lost datagram costs a timeout. The SAs, the listener and the firewall rule cover both transports |
EMERGENCY_NUMBERS |
(empty) | comma-separated additions to the builtin 112/911 emergency numbers (e.g. a private test core's short code). SIM EF_ECC is not read yet. imsd-ofonod reads it too, for the oFono EmergencyNumbers property |
RTP_PORT |
50004 |
local RTP port advertised in SDP |
PRECOND |
0 |
1 offers SDP QoS preconditions |
CODECS |
(empty — defaults) | comma-separated codec preference list over AMR-WB, AMR (or AMR-NB), PCMA, PCMU: restricts and orders both the codecs offered on an outgoing call and those accepted from an inbound offer (default: offer AMR-WB + AMR, accept all four in that order). A bench knob — a network whose gateway transcodes every caller up to AMR-WB otherwise never lets the narrowband path run |
DUMP_SIP |
0 |
1 writes raw REGISTER-200/SUBSCRIBE-200 dumps, the last refused REGISTER or SUBSCRIBE final (imsd-register-fail.raw, imsd-subscribe-fail.raw), the last inbound INVITE (imsd-invite-in.raw) and the last outgoing INVITE (imsd-invite-out.raw), mode 0600, for debugging — they contain your IMSI/MSISDN and addresses. A refused REGISTER or SUBSCRIBE is logged with its status line and any Retry-After / Warning / Reason / Server headers |
DUMP_DIR, OUT_DIR |
state dir | where dumps / per-call media stats land |
IMSD_MEDIA |
(auto) | path to imsd-media (default: next to imsd, else /usr/libexec/imsd-media) |
IMSD_ENV |
/etc/imsd.env |
the configuration file's path — a bench seam for manual runs of ims-pdn-up.sh (the packaged unit reads /etc/imsd.env through EnvironmentFile=). The file's existence changes nothing |
The protected client/server ports are fixed at 45061/45062
(imsd::util::PortUc/PortUs) — changing them in source also requires
updating the firewall rules ims-pdn-up.sh installs.
imsd-media (per-call, set through imsd's environment)
| Variable | Default | Meaning |
|---|---|---|
MIC, PLAY |
1, 1 |
uplink mic capture / downlink playout via PipeWire, as imsd passes them (imsd-media started by hand defaults both to off) |
AUDIO_USER |
(auto) | account whose PipeWire session carries call audio; imsd sets it per call from logind's seat0 session. Set in imsd's own environment it pins an account instead |
GAIN, PLAY_GAIN |
10, 1.0 |
uplink / downlink gain, as imsd passes them (imsd-media started by hand defaults GAIN to 1.0) |
AMR_MODE |
2 |
AMR encoder mode of whichever AMR codec is active, as imsd passes it (12.65 kbit/s for AMR-WB; imsd-media started by hand defaults to 2 for AMR-WB and 7 for AMR) |
DTX |
0 |
encoder discontinuous transmission |
MEDIA_TIMEOUT |
6.0 |
seconds of downlink silence before exit 3 (far-end-hangup signal) |
RTP_DUMP |
0 |
1 captures raw downlink RTP next to the stats file |
D-Bus ABI
net.catcrafts.IMS1 at /net/catcrafts/IMS1. The ABI is frozen.
| Member | Signature |
|---|---|
Dial(number) |
s → s (callUni) |
HangUp(callUni) |
s |
Accept(callUni) |
s |
SendDtmf(callUni, tones) |
ss |
GetCalls() |
→ aa{sv} |
GetStatus() |
→ a{sv} |
CallAdded |
s a{sv} |
CallStateChanged |
s s s (callUni, state, reason) |
CallDeleted |
s |
RegistrationChanged |
b |
Both imsd-dialerd and imsd-ofonod are users of this ABI.
A new desktop needs a new translation daemon, not changes here.
License
GPL-3.0-only — see LICENSE.
Copyright
Copyright (C) 2026 Catcrafts® catcrafts.net