[Asterisk-Users] Voice Quality

[Sean Kennedy]

david at ccds.ca wrote:

>Hello,
>
>I have setup two * servers and they are communicating using IAX. I'm
>passing calls from SRV A (internet connection T1) to SRV B (internet
>connection: 512).
>
>For some reasons I have an issue with the quality. The voice is a bit
>scratchy. I have tried iLBC and SPEEX, but it didn't make any difference.
>
>Now, assuming that I have an issue with Bandwidth, what would be the best
>way to configure my iax.conf. (A bit confused about jitterbuffer and tos)
>
>Here is my iax.conf @ location A:
>
>[general]
>port=4569
>bandwidth=low
>disallow=all
>allow=ilbc
>;allow=ulaw
>;allow=speex
>jitterbuffer=200
>jitterbuffer=yes
>tos=lowdelay
>
>and iax.conf @ location B:
>
>[general]
>port=4569
>bandwidth=low
>disallow=all
>allow=ilbc
>;allow=ulaw
>;allow=speex
>jitterbuffer=200
>jitterbuffer=yes
>tos=lowdelay
>
>[guest]
>type=user
>context=default
>callerid="Guest IAX User"
>disallow=all
>allow=ilbc
>
>
>Thanks guys
>  
>
Have you tried ulaw yet?  With 512 and a t1, you have more than enough 
bandwidth for a few streams with that codec.  One wouldn't be a 
problem.  Also, check to make sure the entire path is a single codec, I 
have run into an issue before ( when I first started playing with * as a 
matter of fact ), where I was going from gsm, to ulaw to alaw ( long 
story ) back to gsm.  Voice quality sucked, obviously, because I was 
doing all sorts of conversions.  Keep yourself to a single codec, 
preferrably ulaw/alaw, and you should be fine.

Also check for iax timing, that could cause issues as well. 

TOS is a quality of service bit on the packets in the stream, they don't 
do anything by themselves.  Instead, any switches/routers than 
understand it will push those packets to their appropriate position in 
the queue based on the TOS value. 

I'm not entirely clear on what jitter is either, but it's never been 
important enough for me to go digging.  Anybody have any insight here?

Sean