VoLTE support progress

When I call from my VoLTE-enabled Android to my non-VoLTE L5, the L5 drops to 3G. (As expected for a non-VoLTE phone.) I suppose it will drop to 2G instead, once the carrier’s 3G is fully shut down; 2G will eventually be shut down here, too.


Sometimes. Unfortunately the most of the time the incoming call goes to the voicemail. I don’t know what’s the problem with the L5 but if there isn’t 3G network you have to set the phone to use 2G only otherwise you lose most of the calls. No matter if VoLTE is enabled or not. Purism’ support didn’t help.

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It is because ModemManager it buggy for 4G Calls. I was able to do call under 4G no volte with oFono.

Test number 2: VoLTE-enabled Android to non-VoLTE Android

Non-VoLTE Android drops to 3G during call.

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It is because you are using android for. :joy:
Let is wait to @dos to explain us what is going on with VoLTE calls.

Yes but what is the other phone doing? The phone that is VoLTE-enabled calling to a non-VoLTE phone (whether Android or the Librem 5), does it stay on 4G?

In other words, if the calling phone stays on 4G then this demonstrates that VoLTE support does not have to be available end-to-end in order for VoLTE to be used at all.

I pretty much guarantee that VoLTE doesn’t have to be end-to-end, because a cell phone calling on 4G or 5G can call a POTS landline.


Yes, it stays on LTE. But the call cannot be 100% LTE for both ends, of course. It’s likely forked off en route to reach the (still existent for now) 3G/2G end.

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Or even a VOIP line.

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Yes, that is what I expected but it is good to confirm with reality.

As you and @johnk imply, that therefore could require some sophistication within the phone network to convert various aspects of the call.

The most significant thing is the codec. With a mobile phone as the source (3G or 4G), the codec is almost always going to be some sort of voice compression codec (it may not even be a customer choice not to do that). To deliver to POTS, it must decompress somewhere in the network. To deliver to VoIP it may be necessary to decompress and leave it, or it may have to decompress and then recompress with a different codec. In amongst that, it could be downsampling as well. Lots of complication.

It would be interesting to know whether the higher bandwidth codecs that are potentially available with VoLTE are suppressed when the destination isn’t going to be able to handle or benefit from the better quality.

In other words, potentially some aspects of this could be end-to-end - but the choice of “generation” is not one of them.

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Perhaps some sort of negotiation occurs when the call is connected?

Going back on topic for this thread. I found in July that calls stopped working for me when 3g got disabled by my provider (though 2g was suppose to still work to the end of the year and I could never get a 3g signal). Thus I was forced to enable VoLTE.

Using the above mentioned tool (https://source.puri.sm/Librem5/bm818-tools/-/merge_requests/2), I tried VoLTE again. I was surprised to find that all the issues I had with it before appear to have been solved.

  1. The phone rings when I call someone else (was silent until the other parts answered)
  2. No numbers seem to hang stuck on “calling” that were never recieved.

I saw no issues at all… In fact things tended to work better than before:

  1. Every call I make works… No calls opens the new call and immediately fails(was rare but really annoying).
  2. I seem to receive every call instead of sometimes the phone just didn’t register it.
  3. No more delays in the phone switching to 2g.

I know volte is not supported yet, but it seems I have little choice but to use it. However, it appears to be working very well at present. Good work Purism! I’ll confess I had wondered if we’d be hosed when VoLTE became mandatory in the states, but turns out it works!


Which company is your cellular provider?

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I’m currently using mint mobile (a t-mobile mvno)

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I use Mint also. I’m glad it’s working so well for you. I have been hesitant with enabling this setting, but will have to try it out soon with your positive report.

Interesting I’m guessing you can make calls on mint without volte still on mint?

I wonder why it stopped working for me…

2g calls worked for me on Mint. I do miss inbound calls and there is a significant delay (750ms-1000ms) in audio with the person I’m calling. I’m hopeful Volte improves some if this.

Maybe they took down some 2g towers in your area?

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So I would assume the E1 modem might not have VoLTE enabled unlike the A1 modem? I am able to install the tools, Enable VoLTE, and add the Purism user to the dialoutgroup. No VoLTE yet unfortunately testing calls. A1 modem will be arriving soon to test on.

I’m pretty sure that some users in Europe have successfully used VoLTE, so I wouldn’t assume that the E1 variant doesn’t have VoLTE support. It won’t be enabled out-of-the-box perhaps though.


FWIW, I’ve successfully used VoLTe with BASE/Telenet in Belgium, Europe. 4G stays on during the call and haven’t had any more problems than I had before since enabling it here.