Bottom line why/when g729a codec?

Can anyone give me the bottom line on g729a - as to when to use it and why, compared to default/common g711 a-ulaw stuff?

Besides being 8k instead of 64k per channel (nice):

  • Better/same/worse sound quality?
  • Do all/most/few handsets support it?
  • Will it cause complications talking to other SIP based systems (i.e. Vonage, FWD, etc.)?
  • It’s an issue with other Asterisk systems that haven’t purchased it, in which case what happens in this situation?
  • Can Asterisk be configured to try g729a first and auto switch down to a g711 if the receiing end doesn’t support it?

Thanks gang,

Hi Tony,

Replying in the same order as your questions:

  • Good sound quality… That’s what’s so nice about G.729… It has both low bandwidth and good quality.
  • Most handsets support it (and some, such as the Zyxel wireless handsets, actually work better with it). Quite a lot of softphones, especially free ones, don’t.
  • No. If the other SIP system can’t handle G.729, Asterisk will negotiate another codec, as long as you have other codecs enabled.
  • If the other system can’t handle it, Asterisk will negotiate a switch to a codec supported on both systems.
  • Yes. All you have to do is enable the other codecs in your sip.conf and iax.conf files.

I have been very happy with G.729 and feel it is definitely worth the $10, especially if used on a typical home DSL connection (1024k down/256k up, for example), where 64kbps connections quickly add up and saturate the upload bandwidth. As I also mentioned, it helps a lot with some handsets and alongside the latest firmware was instrumental in making our Zyxel P2000W handsets useable (if not fantastically so!)

Hope that helps.



What’s the saying “a gentleman and a scholar”? Thanks, helps indeed. It would be nice of Digium incorporated your response into their product description (for idiots such as myself) - just makes it clear what a truly good benefit & deal their g729 offering is.

We purchased four licenses with our TDM400P under the vague impression of the things you covered. Good to have them confirmed and better understood.


This seems to be an incredibly common question, If any one wishes to add to the comment feel free but I feel this should not get lost in the forum especially as it picks up speed.

One last question/confusion regarding licensing under Asterisk:

  • The Digium site suggests one per FXO channel you may be using to a PSTN (e.g. four for TDM400P w/4xFXO). However there is a wiki page at that suggests a very different and more expensive scenario (see end of article at … — which might be correct?


For most apps it is a one encoder one decoder. So I have sip phone a and fxo b going from sip g729 to fxo takes one transcoder for all of call, listening to voicemail takes a transcoder while you are listening to message or recording message. however few apps take more than one, monitor takes two do to the way the apps and channels work in asterisk. but for the most part you need a license for the max number of channels you will have up at any give time.

and for fax support?, the g729 works fine how the ulaw or alaw?


You should never, I repeat never fax in anything but ulaw or alaw. Compressing fax will destroy the fax.

If running, for example, an Asterisk@Home distro which is CentOS v3.x (RHEL3) which shows configured for i686 (even though it is a Pentium 4 machine) - which codec binary should be downloaded … i686 or Pentium 4?


always use your proccessor type, it doesnt matter what the rest is built for, but you want the version optimized for your machine.

Is it possible to change the codec during the session? Like I receive a call with g729, detect fax and switch to ulaw or receve with ulaw, not detect fax and then switch to g729…


I noticed from the order page

Should you want to place 5 licenses on one machine and 5 on
another machine, please place two orders for 5 licenses each. Do not make one order for 10 licenses. Your registration number will be keyed to unlock X amount of licenses on one machine.


Lets say you buy 5 licenses and then later find you need 5 more. Can you just buy another licsense for 5 more or do you need to buy a new license for 10? I’m assuming that you do because in the above ording instruction you would have simply purchased 10 individual licenses. If so what happens to the 5 you already have? Do you just kiss them good bye? Trade them in? Sell them on ebay?

I haven’t purchased any licenses so I’m not quite sure how Asterisk handles them. I was just curious.

where can i get the G729 codec

try here … oduct=G729

got it already ,thanks anyway

I am having trouble registering my G729 codec, I follow the instructions and get a “Segmentation fault”, could anyone shine some light on this

Instructions are fine. I have followed them and they work. The problem is on your side.


the only fault could be with the build that i have, it installs and then i try and install the codec and it just gives me the finger

I have a asterisk server up and running and am currently using IAX2 and some softphones to do some testing. I want to purchase and add the g729 codec on the test server. I do not think this will be much of a problem.

Question is:
If I purchase and install codec on this test server. If/when I want to upgrade to a Newer more powerful production server will I need to purchase licenses again for the new production server? I am presently testing on an older pIII 600 and will most likely be reinstalling on a more current server when I put this into production.

Thanks, Jeff

Digium will let you move the licenses a few times in good faith. Just check with them for their most current policy on this.