Re: [Linphone-users] typical delay (latency) time ?

[Simon Morlat]

Hi,

Usually most part of the delay comes from the sound driver/card. Good
drivers/cards have low latency, this means that blocks of data exchanged
with the application can be short (256 or 512 bytes). Bad drivers/card
can only exchange data with a size of 8192 bytes (0.5 sec) or sometimes
16384 bytes (1 sec) for some old isa cards.
Alsa drivers usually have a better latency, that 's why I recommend
them.
Here is a formula that should give the delay for one direction:
delay=MAX(local_driver_latency,codec_latency)+jitt_comp+
    (ping_delay/2)+MAX(remote_driver_latency,codec_latency)
You can see the driver latency on the terminal when linphone is running:
you should see a message "blocksize=8192" or something like this. The
value is given in number of byte, just divide by 16000 to get it in
seconds.

So there two things to try for you to improve this delay:
-alsa drivers (but don't change anything in linphone's configuration,
and don't recompile it)
-set jitter compensation to the minimum on both (perhaps you are
already)

With two PC's connected by ethernet cards (ping=1ms), and alsa drivers
(ens1374, cs41xx), jitt_comp=60ms I have a one way delay of approx 1/4
seconds. This is very acceptable. With adsl connections, the ping time
is about 80ms, however this is still very acceptable (not very different
of a cellular phone call).

Salutations,
Simon

Le dim 04/08/2002 à 19:02, Marc-Olivier BERNARD a écrit :
> Hi there,    
>     
> I encounter important delay by using VoIP/liphone, about 1s and don't  
> understand why.  
>   
> I'm using linphone between 2 computer (see below for system infos) both  
> connected to internet with (A)DSL, with   
>   
> * ping average time is 120 ms.  
> * sound traitement at both ends are quite quick (I did not try with an ALSA  
> driver)  
> * both machines are directly connected to internet  
> * no delay due to firewall (i tried without firewall)  
> * codecs G711  
> * jitter compensation of 60 ms  
> * no proxy  
>   
> and the delay is around 1s. I don't understand the origin of such a delay ? 
>  
> What kind of delay do you have ? and do you have any idea how to get it 
> better 
> (install ALSA driver for ex.) ? 
>   
> system infos :  
> ~~~~~~~~~~~~~~  
> linphone-0.8.0-1  
> redhat 7.3  
> OSS driver  
> SoundBlaster 5.1 live (full duplex)  
>     
> --     
> Marc-Olivier BERNARD    
> 
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