Current free mobile phone OS (like postmarket OS, ...) only support voice calls
for 2G and 3G on Qualcomm based devices.
Calls via 4G using VoLTE are not supported (*except CSFB, which redirects to 2G/3G)
because the modems require a lot of addional configuration and complexity.
because the modems require a lot of addional configuration and implemented VoLTE with a lot of complexity.
Our goal is to support VoLTE on Qualcomm based phones.
We will document the relevant APIs and add support to libqmi.
Further we will implement a IMS configuration daemon which will communicate with
the baseband using QMI (Qualcomm MSM interface) to configure the relevant services
to allow the usual apis to function.
We choose Qualcomm based Android phones, because they are the commonly used phones and
widely available. Also Qualcomm baseband has received a lot of reasearch (and reverse engeering)
over the years and a lot of knowledge has been collected in the open.
Our implementation will heavily use the baseband in the same way as Android is use the baseband service,
because this way it is possible to allow handover between 2G and VoLTE.
To archive our goal we plan to:
- Document the relevant ABIs and add support to libqmi
- Implement a IMS configuration daemon (OpenIMSd) which will communicate with
the baseband using QMI (Qualcomm MSM interface) to configure the relevant services
- Integrate OpenIMSD into FOSS smartphone OS (postmarket OS, ...)
Our implementation will heavily use the baseband in the same way as Android is use the baseband to allow VoLTE. By using the baseband, it should be possible to allow handover between 2G/3G and VoLTE while in a call.
We thank NLnet for funding our work (https://nlnet.nl/project/VoLTE-Qualcom/).
