This certainly explains why we get terrible audio at 10% packet loss
between Asterisk servers between 2 end points using iLBC, but if we
use 2 SPA2000s using G.729 to commincate directly with each other
(and having the same 10% packet loss), they sound pretty good. We
had been trying to figure why iLBCs loss concealment wasn't helping
much. I was never able to explain this until now:)
Thanks.
If you have 10% packet loss G.729 should sound awful. Are you really
getting 10% packet loss in the G.729 case? If not, why does iLBC give
that? Is the higher bit rate of iLBC pushing things over your
available bandwidth limit? Seems pretty odd.
Bandwidth at the mentioned test server is 256MB and usage consumption
was only 20-25kbps during the test. Packet loss is at the ISP
(confirmed by them). I attribute the bad audio on iLBC due to Steve's
explanation that Asterisk does not do any loss-concealment, but a direct
call between 2 Sipuras does (no Asterisk involved). The SPA manual
clearly states that "The SPA applies an error concealment algorithm to
alleviate the effects of packet loss". We have tested this under many
conditions of packet loss and the SPA sounds great up to about 10-12%
packet loss. Even at 20% loss you can carry a convesation that sounds
like a mediocre cellphone call.
Regards,
Steve
--
Andres
Network Admin
http://www.telesip.net
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