Jorijn van der Graaf
1d28063700
With the netdev configured, the script runs imsd-pcscf against the netdev's rmnet mux id (and the ims profile index when it knows one) and hands the IPv6 addresses it prints to imsd as PCSCF_DISCOVERED= in /run/imsd.env and gives the first — the daemon's fresh target — a host route (the SA peer of a registration imsd resumes is routed by imsd itself, as the configured address's arm already left it); IPv4 addresses and names are logged and dropped (the PDN is IPv6-only), at most eight are handed over, and nothing usable is logged with its cause and is not the script's failure: imsd resumes a registration of its own when it can, else says so and exits, and the restart runs discovery again. PCSCF= still wins and skips discovery; a list in it is refused. The script does not read the variable from its environment: the unit hands it the previous run's file, and a stale discovered value must not pass for the admin's setting. The reader's path is the IMSD_PCSCF seam the mock bench uses. Tested: on the mock bench against this commit's script (the twelve 0.3.10 scenarios; this step's discovery arms S13–S17 and S19–S22, with S18 the pre-existing non-IPv6 refusal; S55, the reader's rc-0 answer without an address), and in builds of this series on the dev phone (KPN), whose PCO — two IPv6 addresses, nothing else — reaches the plain found arm; the configured skip, the bracketed refusal and, through the IMSD_PCSCF seam, the reader's failure and its exit 2 ran on the phone too; the v4/FQDN line, the eight-address cap, the IPv4-only and no-mux-id skips, the comma-list refusal and the rc-0 arm on the mock only. On a tip build of this series (daemon 2ec1a02f62831edb; bench 40, 2026-10-13) a fresh registration reached a target this script had not routed — the reader stubbed through the IMSD_PCSCF seam to find none, the address in /etc/imsd.env as PCSCF_DISCOVERED= — over imsd's own route, and a resume stood with the peer's route removed first.
12 KiB
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
The apk's imsd.service is enabled by preset and starts at boot once
/etc/imsd.env exists (touch /etc/imsd.env is enough; the condition is checked when
the unit starts, so after creating the file run systemctl start imsd). It first brings the ims PDN up through ModemManager, then registers:
resuming an existing registration when it can, registering fresh otherwise,
and waiting out whatever the network tells it to wait out. Check on it with:
journalctl -u imsd -f
busctl --system call net.catcrafts.IMS1 /net/catcrafts/IMS1 net.catcrafts.IMS1 GetStatus
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, a fresh registration fails with a clear error |
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 logged and ignored. In /etc/imsd.env it is a bench seam |
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) |
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