[asterisk-users] VoIP over 3G/4G Data

[Patrick Laimbock]

On 18-07-14 17:59, Tech Dude wrote:
> What are the recommended settings to successfully implement VoIP over
> 3G/4G data connection. Assume we are talking about using Polycom phones,
> and the 3G/4G data connection comes from a Cradlepoint router that is
> plugged in with AC power and has high gain antennas. The device will be
> stationary, so we will not have to worry about tower handoff’s breaking
> the connection. This will be for fixed wireless.
>
> I have read to use G.729 codec, and TCP for signaling to bypass
> firewalls. Besides that, what other settings are recommended?  Changes
> in MTU? Changes in voice payload ms? Is there a better codec to use?
> Header compression?

Use TLS/SRTP so the carrier can't do packet inspection/snooping and mess 
with or block your VoIP connections. They might throttle/block port 5060 
and 5061 anyway in which case you should use different ports.

I use Asterisk 11 with TLS/SRTP, G.722 and Android phones (4G, 
CSipSimple or Bria), iPhones (4G, Bria) and Polycom phones. G.722 on 
inter-office calls has been working great so no need for G.729 and 
Asterisk uses standard alaw/ulaw for regular PSTN calls. I use TCP, have 
made no MTU changes and use standard 20ms voice payload.

Packet loss, latency and jitter are the enemy. Your router might be top 
notch but if the cell tower is overloaded and experiences too much 
packet loss, delays of more than 150ms and lots of jitter than you may 
get crappy sound quality. If possible, get some prepaid 4G sim cards for 
your router from different carriers and test which carrier consistently 
provides the best signal, least delay, packet loss and jitter.

HTH,
Patrick