Incoming Call Latency in FreePBX Systems with FXO

When someone call my Elastix box from PSTN, this guy hears ringback tone from his phone for about twice before my SIP extension rings! I have disabled the fax detection and caller ID detection,but delay remains! 

How can I enable immediate incoming call indication at the SIP phone(extension) ?

Please help!

With PSTN you’ll always be off by at least one ring to start. The card does not know the line is ringing until it trips with a ring pulse at which time it’s missed the first ring. Now if you also have it getting caller ID it might will wait until that info is transmitted between ring pulses so that when it starts ringing on your phone you have that info.