Enabling the Error Page while accessing EP whenever the system is down

Hi Experts,

We have a requirement in one of the projects as "Enabling the Error Page in SAP EP whenever following scenario occurs".

1. SAP EP is down then while accessing SAP EP url (including anonymous page) page should display "System under maintenance"
2. SAP ECC is down then the login page from EP will get display but it will fail to login. This is also to be displayed like "System under maintenance"
3. SAP EP and ECC is down then also "System under maintenance" message should be displayed while accessing EP url (including anonymous page)
4. SAP XI/PI is down then this case also to be handled.

Your response will be appreciated.

Regards,

Vamshi krishna.