[App_rpt-users] Codec Negotiation

Sat Feb 10 14:00:02 UTC 2018

Will,

You are correct that the [radio*] stanzas are for incoming connections, at 
least as they are used by AllStar.

I haven't looked the iax2 driver code over, but, empirically speaking, the
CODECs listed in in the "allow=" don't seem to be used in any guaranteed
order, even though the iax2 documentation says otherwise.  I've tried 
combinations of "bandwidth=" and "codecpriority=" settings, etc...So, I 
assume this is a bug---unless I'm overlooking something obvious (anyone 
got any other ideas?).

The only 2 ways (so far!) I've found to guarantee that a certain CODEC is 
used are:

Method 1: ---Only specify a single allowed CODEC for outbound connections.

;;; On the portable node, allow only one CODEC you want:
[general]
disallow=all
allow=ilbc

;;---------------------------------------------------------------

Method 2: ---Allow multiple CODECs for outbound, but connect to a 
destination stanza that only allows a single CODEC.

;;; On the portable node, your CODEC list:
[general]   
disallow=all
allow=ilbc
allow=g729
allow=ulaw

;;; On the portable node, your defined nodes:
[nodes]
abcd = radio-g729 at my-abcd-hub.com/abcd,NONE     ; Hub stanza --- only g729
wxyz = radio-ulaw at my-wxyz-hub.com/wxyz,NONE     ; Hub stanza --- only ulaw

;;; On the abcd HUB:
[radio-g729]
type=user
disallow=all
allow=g729
context=radio-secure
transfer=no

;;; On the wxyz HUB:  
[radio-ulaw]
type=user
disallow=all
allow=ulaw
context=radio-secure
transfer=no

;;;-------------------------------------------------------

73, David KB4FXC

On Fri, 9 Feb 2018, Will Bashlor wrote:

> Fantastic, thanks David. A couple questions...

How do I specify to use a particular stanza while connecting to a certain 
node?

I thought the [radio] stanza was for incoming connections, no? Since I 
can't receive incoming connections using my cellular hotspot I didn't 
think I needed to modify [radio]. At work and home where I have ports 
forwarded I have a high speed connection, I don't really need to change 
the codecs as it works great using ulaw.

Will
KE4IAJ

-----Original Message-----
From: App_rpt-users [mailto:app_rpt-users-bounces at lists.allstarlink.org] On Behalf Of David McGough
Sent: Friday, February 9, 2018 9:39 AM
To: Users of Asterisk app_rpt <app_rpt-users at lists.allstarlink.org>
Subject: Re: [App_rpt-users] Codec Negotiation

Will,

iLBC and g729 probably sound best over highly "jittery" mobile networks.

Note that the hamvoip iLBC implementation is patched to use 20msec frames, NOT 30msec frames, which are the default in Asterisk. You *MUST* use 20msec frames with AllStar!

My patches for Asterisk to add iLBC and use 20msec frames were published years ago. If interested, here is the link: 
https://hamvoip.org/downloads/patch-kit-with-ilbc.tgz

And, here are example iax.conf stanzas, which only allow a specific CODEC:

[radio-ulaw]
type=user
disallow=all
allow=ulaw
codecpriority=host
context=radio-secure
transfer=no

[radio-g726]
type=user
disallow=all
allow=g726aal2
codecpriority=host
context=radio-secure
transfer=no

[radio-g729]
type=user
disallow=all
allow=g729
codecpriority=host
context=radio-secure
transfer=no

[radio-ilbc]
type=user
disallow=all
allow=ilbc
codecpriority=host
context=radio-secure
transfer=no

....For your setups, take a look at the CODEC definitions in the [radio] 
stanza. Also, you can have multiple stanzas (like above), and force 
various nodes to connect with a specific CODEC, etc. I run this style 
setup on all my systems.

73, David KB4FXC

On Thu, 8 Feb 2018, Will Bashlor wrote:

> Hi List,
> 
> Ok, so I have a portable node and it works great at home but on the road
> using my iPhone hotspot with Verizon it's quite jittery and doesn't sound
> very good, even when I have 2 or 3 bars. I can connect to the same node
> using echolink and it works fine even with 1 to 2 bars.
> 
> I'm using the hamvoip image without any codec changes and I notice it
> connects to our local repeater hamvoip node with g726aal2 which makes sense
> because  g726aal2 is first in [general] which I believe controls outbound
> connections.
> 
> So I wanted to see what I sounded like so I connected to 40894 so I could
> hear my own voice. It connected using ulaw for some reason. The only way I
> could get it to change was to comment out the codecs I didn't want to use
> in [general]. Apparently it doesn't negotiate how I think it does.
> 
> On ulaw and  g726aal2 it sounded pretty terrible. gsm was better but it was
> still broken up. I wanted to try ilbc but codec negotiation failed which
> I'm sure means that 40894 doesn't allow ilbc.
> 
> I then connected successfully to our local repeater node with ilbc and it
> sounded just fine, even with one bar, but I need to test more...
> 
> Is this anyone else's experience with using hotspots?
> 
> I've modified the codec under [genera] to the below, which the way I
> understand is for outgoing connections. And the codec order is the order of
> attempted negotiation. I ordered them on my portable node in order of least
> bandwidth to greatest.
> 
> So with that said, when I connect to my local node, which allows ilbc, why
> does it negotiate to g726aal2?
> 
> And how can I setup iax.conf so it always connects using the lowest
> bandwidth codec that the other side allows?
> 
> allow=ilbc
> allow=gsm
> allow=g726aal2
> allow=ulaw
> 
> 73,
> 
> Will, KE4IAJ
> 

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