Socket

Question

Hi all,
Here are some questions, plz kindly share your ideas on that
1) Where should the socket be closed ideally? is it while closing the application or after receiving the response from the device.
2) How to know if any data has arrived on the socket? is there any in-built function triggered on receiving some data on the socket?
3) How do v know if the socket is already created?
Thanks & Regards
daff180