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'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).
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.
Be warned: the ITU publishes their specs in Microsoft Office formats,
and 3GPP 21.202 ("Technical Specifications and Technical Reports
relating to the Common IP Multimedia Subsystem (IMS)") is a link to a
part of their site that is – for me – completely borked.
- Willow
On 20/01/2025 18:34, Andrew Back wrote:
On 20/01/2025 17:09, ron minnich wrote:
I'm getting more and more bothered by the mountain of things going on
in my phones that I can never understand.
So I got curious and found this:
https://www.instructables.com/Build-Your-Own-Smartphone/ <https://
www.instructables.com/Build-Your-Own-Smartphone/>
and now I can't get a cellphone that runs plan 9 out of my head.
Am I out of my head?
The problem with 2G and 3G is that they're either gone or soon to be
gone in a lot of places. With 4G and 5G things get more complex, since
there is no circuit switched voice; you either fall back to 2G/3G for
voice and SMS, or need an IP Multimedia System (IMS) client to support
native voice and (VoLTE/VoNR a.k.a. "HD Voice") and text messaging.
IMS is a curious mix of SIP and IPsec and I don't think there is as yet
a fully working open source IMS client. Those in COTS handsets are
proprietary and for reasons to do with integration with baseband
features IIRC, are supplied by the baseband silicon vendor and then
integrated into Android and iOS etc.
I know of one LTE modem which supports VoLTE directly, Quectel EC25.
Which I believe it achieves by embedding a cut down version of Android,
complete with IMS client. So then you have the usual AT interface over
UART for dialing, plus audio input and output connections on the module.
Andrew
------------------------------------------
9fans: 9fans
Permalink:
https://9fans.topicbox.com/groups/9fans/T937367c51de50ce3-M0280be24168c07f16c06c193
Delivery options: https://9fans.topicbox.com/groups/9fans/subscription
