Internal Response Time

Dear friends

First of all i’d like to thank you in advance for the great support in this forum you help until now solves alot of my problems .

Now i make some fresh installs for testing and i find out that all the times when i make a call from an internal number to another it takes 2-3 sec for the destination number to response .

I try also several Grandstream devices GXP200 , GWX4008 , BT100 .
Is there something a can adjust to reduce this dead time ?

Thanks.

Sorry
the post submited twice !!!