On 20/01/2025 20:03, Willow Liquorice wrote:
For anyone interested, you can find the 3GPP specs and reports on IMS
through their (somewhat cursed) web portal: https://portal.3gpp.org/
#/55936-specifications
I remember reading about the Osmocom project going through a lot of pain
downloading specs and extracting ASN.1 etc. from Word documents. Maybe
this will be useful:
https://github.com/osmocom/3grr/blob/master/3gpp-spec/README.md
I'd poked around in them myself, as I thought I had a USB GSM modem
knocking around here that I could try hacking on with 9front (I do not).
You'd need an LTE modem. It would be best to start with LTE and not 5G,
as I don't think there is a fully functioning open source VoNR (5G) IMS
core yet. At least with VoLTE there is a working IMS core you can test
against. The quick way to set this up is probably via docker_open5gs:
https://github.com/herlesupreeth/docker_open5gs
I think you can do this without radio hardware and have a software UE
(mobile) and software eNodeB (base station) passing samples via ZeroMQ
instead of actually transmitting via SDRs.
The little glasses icon in each search result opens a window, and the
"see all versions" link therein provides .zip downloads for the document
itself.
There are 57(!) specifications in all under "IP Multimedia Subsystem",
but I'm unsure about how many of those are relevant to what goes on in a
handset.
See also:
https://osmocom.org/projects/foss-ims-client/wiki
Seems there has been some success in using Asterisk as an IMS client for
Voice-over-WiFi. This uses the same IMS core, albeit swapping the
cellular network for WLAN and using another component, called ePDG, to
provide secure access from WiFi connected IMS clients.
Andrew
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