# Problems with conferencing and g729

**URL:** <https://community.asterisk.org/t/problems-with-conferencing-and-g729/20274>\
**Category:** Asterisk Support\
**Created:** [April 10, 2008, 5:59pm UTC](https://community.asterisk.org/t/problems-with-conferencing-and-g729/20274 "2008-04-10T17:59:05Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![wglass](https://sea1.discourse-cdn.com/asterisk/user_avatar/community.asterisk.org/wglass/32/835_2.png) [@wglass](https://community.asterisk.org/u/wglass)\
**Post date:** [April 10, 2008, 5:59pm UTC](https://community.asterisk.org/t/problems-with-conferencing-and-g729/20274/1 "2008-04-10T17:59:05Z")

</div>

Hi,

I’m having consistent problems making a conference call with my Grandstream GXP2000 phone and Asterisk 1.4.4.

Use Case:

- On the phone, I dial one number, put it on hold
- Dial the second number
- Push the phone “conference button”
- The call looks to be conferenced. However, I can only hear sound from one number and not the other.

(basic config details: sip, provider is Vitelity, g729 codec required for provder connection).

Apparently, this is due to problems the use of the g729 codec. When I use “sip show channels”, I see 5 lines

local extension g729  
remote number g729  
local extension g729  
other remote number g729  
local extension ulaw

Before I hit the “conference” button, I just see the first 4 lines, all g729. When i conference, I see the ulaw line. My guess is that there’s no conversion of sound between g729 and ulaw.

When I check “show g729” it tells me I have 4 licensed channels.

As an experiment, I reconfigured the Grandstream phone to only allow g729. (right now it allows g729a, PCMU, PCMA, GSM). Now, when I click the conference button, it hangs up one of the lines, and I see an error in Asterisk

chan\_sip.c: No compatible codecs, not accepting this offer!

Any suggestions? Excerpts from sip.conf below.

```auto
[general]

...

; codecs
disallow=all
allow=g729
allow=ulaw
allow=alaw
allow=ilbc
allow=gsm

[90]
mailbox=90
username=xx
secret=xx
type=friend
host=dynamic
context=internal-forio
dtmfmode=rfc2833
canreinvite=no

[vitel-outbound]
type=friend
host=outbound1.vitelity.net
context=outbound-to-vitelity
username=xx
fromuser=xx
trustrpid=yes
sendrpid=yes
secret=xx
disallow=all
allow=g729
```