off-net call transfer

Hi,

I do off-net calling using the following network build by cisco 1750 routers
with 12.2 series IOSs.
PBX1-->FXS--->IP--->FXO-->PBX2-->PSTN

After answering the PSTN number, it takes approximately 10 second to
transfer that call to another extension on PBX1. How can I decrease that
time ?

Any help would be appreciated.
Thanks in advance.

Ahmet

Ahmet Kaynas