The sad state of voice support in cellular modems

Nexxxeh wrote: post #2

How annoying. Especially as several of the Huawei USB dongles support voice over USB. https://stackoverflow.com/questions/8367864/how-make-use-of-...

That answer seems to be exactly what the article is describing:

> Instead, what some modem vendors have implemented as an ugly hack is the transport of 8kHz 16bit PCM samples over one of the UARTs.

Re: The sad state of voice support in cellular modems

#5

Post by mseebach » Thu, Sep 28, 2017, 1:36 PM UTC

I suspect that the reason for this is the behaviour of most OS's around USB audio devices: switch over the default inputs and outputs to the new device -- which would mean that when you plug in your modem, suddenly your Skype would configure itself to "use" that device for it's audio IO.

Also, I'm not sure how easy it would be to even configure the OS to route modem output to default sound card input (your headphones), and the same soundcard's output (your microphone) to the modem input. The assumption of most OS's seems to be that you have one active input and one active output at any given time. It's certainly not something I'd immediately know how to wire up using the default mixer in Windows.

Re: The sad state of voice support in cellular modems

#6

Post by jsjohnst » Thu, Sep 28, 2017, 2:06 PM UTC

cesarb wrote: post #3

Would VoLTE make the situation better, since voice is sent as data?

From my experience with cellular chipsets, no. The voice channel is exposed the same way on the chip, it’s just sent differently over the network. The “bad thing” about VoLTE additionally for ultra small embedded applications is that it requires two antennas.

Re: The sad state of voice support in cellular modems

#7

Post by gsich » Thu, Sep 28, 2017, 2:08 PM UTC

cesarb wrote: post #3

Would VoLTE make the situation better, since voice is sent as data?

Probably not, since the article is about the interface on how audio gets to the modem.

Re: The sad state of voice support in cellular modems

#8

Post by mixedbit » Thu, Sep 28, 2017, 2:15 PM UTC

I have recently bought Huawei USB modem and discovered that these things run Linux with Android. This is pretty off-putting. With such a modem it is no longer enough to keep your system & drivers up to date, because the device has it's own full-blown operating system. An attacker no longer needs to hack your machine to capture your traffic or make you a part of a botnet, it can hack your modem. And the modem, like Android phones, is probably not going to receive software updates for long.

Re: The sad state of voice support in cellular modems

#9

Post by TorKlingberg » Thu, Sep 28, 2017, 2:15 PM UTC

One correction: Modems in phones are not normally LGA modules, but rather components soldered directly to the main board. Sometimes the baseband processor and protocol stack are even integrated in the main processor SoC.

Systems that use the LGA or m.2 modules often don't use the audio at all, so nobody has cared to make a nice interface.

Re: The sad state of voice support in cellular modems

#10

Post by IshKebab » Thu, Sep 28, 2017, 4:31 PM UTC

mseebach wrote: post #5

I suspect that the reason for this is the behaviour of most OS's around USB audio devices: switch over the default inputs and outputs to the new device -- which would mean that when you plug in your modem, suddenly your Skype would configure itself to "use" that device for it's audio IO. Also, I'm not sure how easy it would be to even configure the OS to route modem output to default sound card input (your headphones…

You wouldn't have to wire it up using the default mixer yourself. Whatever program you were using to make calls could do that for you.

The only vaguely valid technical reason I can think to do it how they have is to reduce latency. Of course the real reason is laziness.