[Asterisk-Users] G.729? Worth it?

[Jim Van Meggelen]

asterisk-users-bounces at lists.digium.com wrote:
> Hi All,
> 
> For a small installation using ITSPs via DSL is G.729 a
> worthwhile exercise? I have G.729 capable SIP phones and my
> ITSPs cupport the codec so I could go end-to-end without
> transcoding. What's call quality like compared to G.711, GSM or iLBC?

 Low bandwidth
 Low CPU utilization
 Best audio quality

 Pick any two.


G.729 is an extremely low bandwidth codec, offering surprisingly good
quality. Unfortunately, it is also a CPU hog.

Generally speaking, you should avoid the use of compressed codecs unless
bandwidth is a concern. Especially with Asterisk, the performance
penalty due to transcoding is a high price to pay.

On the LAN, I'm not able to see any reason to use anything but G.711. In
the WAN, it depends on how much bandwidth you need for voice, versus
what you have available.

Keep in mind that the type of trunking you use plays a role.

For example, although I haven't done the math, it is entirely possible
that 20 trunked channels of IAX2/G.711 would use less bandwidth than 20
discrete SIP/G.729A connections between the same endpoints. Much of the
bandwidth used by packetized voice is overhead, so a lower bitrate codec
does not yield a linear improvement in bandwidth.

There are other considerations as well, such as how well a codec handles
a lossy link. This can be very important to the percieved quality of the
connection, which, to the user, is far more important.

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