[asterisk-users] basic asterisk knowledge

[Craig Guy]

G729 and annex A differ in the perceived quality and cpu requirements.  The
annex A version requires less CPU at the cost of loss of quality.  The
bitstreams are compatible with each other in that a G729A codec can decode a
G729 stream and vice versa.

Craig

-----Original Message-----
From: asterisk-users-bounces at lists.digium.com
[mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Gordon
Henderson
Sent: Monday, 11 June 2007 3:54 PM
To: Asterisk Users Mailing List - Non-Commercial Discussion
Subject: Re: [asterisk-users] basic asterisk knowledge

On Sun, 10 Jun 2007, Khaled Chehab wrote:

> I have question concerns asterisk
>
> 1-What is difference between G.729 and G.729A?

The letter A.

http://en.wikipedia.org/wiki/G.729

... says that G279A uses slightly less CPU to do the compression at the 
expense of sound quality. Digium appear to supply G279 rather than G729A. 
(at least they don't mention A)

> 2-How can I know the requirement hardware for 150 extension on asterisk
> 1.4.4 making 50 simultaneous call?

Google or search the voip-wiki for asterisk scaling, etc. However these 
days you don't really have much choice - it's a 2.8-3.4GHz 
Pentium/something or a 1.8-3GHz Xeon/something, or a 3GHz AMD/something. 
(and their dual/quad processor versions)

Basically any modern "server" class box will do for your needs unless 
you're transcoding every call. A 3GHz processor and 1GB or RAM will be 
fine - but you need to be careful with other issues - like making sure 
disk IO (if doing a lot of call recording/voicemail) won't interfere with 
Ethernet/Zap/TelcoInterface traffic...

I know that 50 simulataneous calls will work fine on a 1GHz processor as 
long as you're not transcoding.

Also, see this:

http://www.digium.com/en/products/voice/g729codec.php

where they have done some tests themselves and mention the transcoding 
numbers vs. CPU speed.

> 3-Do asterisk have a codec conversion?

Asterisk will transcode between different codecs, if the codecs are 
compiled in, or licensed (g729) but transcoding comes at a big CPU cost.

Gordon
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