Problems with SIP

[lou]

Hi everybody. I have SIP configured on avaya ip office. I can make phone calls. But the problem is when i start to speak and the other person is speaking as well. His voice dissapear.

For exemple. If i listen a phone locution, and i try to speak, the locution voice dissapears.

I did outbound nat. But it still not working.

If someone can help me.

Thanks.