i have connected 8 PSTN lines to My pbx my requirement is that the trunk line need to be siezed by rotation vise for example suppose user 1001 calls 8 times he should get all 8 lines connected to the pbx
I'm not aware that Asterisk supports this. If it does it is not AsteriskNOW installation specific, so you should ask on Asterisk Support. Normal best practice is to have the FXO hunt linearly in one direction and the FXS hunt linearly in the other direction. This minimises the number of collisions.
You could obviously synthesise the behaviour using the dialplan and global variables.