[App_rpt-users] Codecs

Tue Mar 7 17:59:16 UTC 2017

Interesting to learn some of the workings of iax.conf.

I'm aware of the rest, however, I would encourage iax.conf is modified 
to have the following priorities for every connection stanza:
ulaw
g726aal2
gsm

this is to ensure audio quality is better than IRLP and echo-stink. If 
you cannot tell the difference, listen to a conversation on a local 
repeater, and the same conversation with the convenient delay over IRLP 
or echo-stink.

You may then remember in days-past of analog cellular listening to the 
person on the other end had more body and fidelity.

Regarding bandwidth, be it a DSL or mobile connection, this should be a 
non-issue. Even 1G cellular data connection will support two full-duplex 
uLaw streams.

For hub nodes, 30 ulaw streams is right around 2.25Mbits. If this is a 
concern, perhaps the owner of the hub should really consider putting the 
node elsewhere. That's like trying to put a Pinto engine in my E-350 and 
expecting it to work the same.

Considering jitter and packet loss if it is thought a higher bandwidth 
codec will cause this, such is not the case. This is the cause of little 
or no implementation of Qos/ToS in the WAN facing side of a router. 
There are other external considerations, but those are outside the scope 
of this thread.

While on that subject a brief description of an example is the node at 
my home. My connection, fortunately, has maintained +25Mbps down and 
5Mbps up, I've have zero issues with jitter and packet loss with QoS 
implemented, even while the kids are watching netflix, skyping, and 
watching something on youtube.... all at the same time.

On 03/06/2017 11:08 PM, David McGough wrote:
> Hi Benjamin,
>
> If you want to only use the G.711 CODEC, only allow that one CODEC at your
> end. But, be aware that may not be compatible with all hubs out there.
> Also, be aware that if you do NOT run the same CODEC as that which is
> preferred by a given hub, you'll likely end up with poorer audio due to
> transcoding.
>
> If you only want G.711, set your config such as:
>
> [whatever_stanza]
> disallow=all
> allow=ulaw
>
>
> ....On a side note, while I agree with you that the Asterisk GSM and speex
> CODECs presents lower quality audio, with many others (such as G.726 and
> iLBC), you would be hard pressed to tell the difference between them, with
> repeater audio. If fact, I'm not sure _I_ could tell the difference in a
> blind A/B test.
>
> Another factor to consider is the hub bandwidth used for EACH audio
> stream. This is a BIG deal for hub out-bound bandwidth. Here are results
> from actual measurements on my hub:
>
> One IAX2 half-duplex stream. All results in Kbytes-per-second:
>
> GSM     3.2
> iLBC    3.5
> G726    5.5
> ULAW    9.4
>
>
> These data rates will be in-bound or out-bound, depending of if your local
> node is listening or talking to another node across the VoIP network. If
> you have 30 nodes connected to a hub, the total bandwidth required is 31
> times the above numbers---30 out-bound listeners + 1 in-bound talker.
>
> 73, David KB4FXC
>
>
>
> On Mon, 6 Mar 2017, Benjamin L. Naber wrote:
>
>> While reading an email from another VoIP email reflector, I got to
> thinking about some of the codecs we use.
>
> Perusing through the iax.conf through a few allstar network linking
> distros, each seem to have their own preferred set of codecs.
>
> I'm rather disturbed that iLBC and speex remains in any of them, while
> I'm sure for compatibility of older installations. However, low quality
> bandwidth codes sounds no better than echo-stink. This is one of the
> reason why we use Allstarlink, for better audio quality, is it not?
>
> As I connect to different allstar nodes throughout the world, more-so in
> the US, some are using iLBC or gsm... and a majority are hub nodes. This
> to me, is unacceptable, and appears the codec being used are whatever
> the allstar box has been packaged with.
>
> So, given than I'm not a Steve Henke or Steve Zingman, but I want to
> ensure that I'm doing my part to achieve high fidelity through g711
> codec and proper URI <-> radio hardware interfacing techniques.
>
> Which stanza in the iax.conf is for out-going connections?
>
> I was under the impression [radio-proxy] was, however, when a node with:
> disallow=all
> allow=ulaw
> allow=g726aal2
> allow=gsm
>
> connects to my node which has the *same* key=value pairs under [radio]
> stanza, I got the message something along the lines of:
>
> connected: IP
> codes available: g726aal2/gsm
> host codecs available: ulaw|g726aal2|gsm|ilbc
> actual codec: g726aal
> ...
>
> bost sides do not have ilbc *anywhere*. The codec has been
> removed/deleted. Why does it still show up?
>
> What is the ultimate deciding factor of which codec is used if both side
> have codecpriority=mine?
>
> ~Benjamin, KB9LFZ
>
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