VoIP support for nRF91x LTE Modules

[4HERE_Corp]

Hello, 

Is there any documentation on setting up VoIP on the nRF91x module with Zephyr?

As the nRF91x does not have a built-in VoIP app layer, I can assemble the hardware and software pieces to address this.  In order to proceed in the correct direction, I would like to know if Nordic has any documentation/ref designs that discuss; 1. audio drivers, 2. Voice Codecs, 3. VoIP protocol stack such as PJSIP.

Thanks

Gerard

[Benjamin]

Hi Gerard,
The nRF9151 SiP is not designed for VoIP. It targets lower data-rate use cases. It may be possible to make it work over LTE-M with an efficient codec, but neither Zephyr nor our SDK provides support for VoIP or audio streaming over cellular. We use the LC3 codec for BLE Audio but I guess you will find a more suitable open source codec.

Best regards,
Benjamin

[4HERE_Corp]

Hi Benjamin,

I believe the minimum data-rate for a standard VoIP call can be 100kbps, which is is within the reported 375 kbps downlink (DL) and 300 kbps uplink (UL) of the 9151. With a codec like Opus and porting the PJSIP libraries (PJLIB, PJSIP, PJMEDIA) into the Zephyr build system, would I think help cross the hurdle.

Wanted to know if there is any documentation on using a 3rd party codec like this or the integration of PJSIP into Zephyr.

Thanks

Gerard

[matt.heins]

It's not only the data rate that will matter. The carriers do not support voice on LTE-M. They tend to limit continuous transmission of data. The technology is not intended for continuous streaming. Though the data may fit within the network, I have encountered other customers who get throttled by the network when they start trying to make continuous use of it. 

[4HERE_Corp]

Thanks Matt,

I understand the issue with continuous streaming and throttling speeds based on QoS which would impact the call quality. In our discussions with AT&T, VoIP calls are currently being done on their Cat M network, and is the main reason for starting this thread. 

If there hasn't been a successful VoIP projects, we can return to using the nRF91 for non VoIP applications and look for a different VoIP solution. 

Thanks for the help. 

[EAB]

I just wanted to add a comment here. VoIP calls on LwM2M IoT have been proven successful by several operators. For example, ~1-2 years ago there was a very nice PoC by Vodafone, and they rarely do original work, so was likely based on some other projects. I don't recall on which tech it was, but could in theory be applied also to NB-IoT if the DM provider conforms to the full LwM2M v1.2 and DTLS 1.3.

Sorry, I don't have any links.