GTM for Active / Active DC with component failure detection

Hi David

Thanks for your help... Yes, there are LTM in all three layers. as shown below...

GTM ->LTM->Web Farm->LTM->App Farm->DB, Cache Server, Payment Server etc..

Now, my worry is how the GTM would know the DB or Cache or Payment server failure..and do the failover !!!

is there any document or URL which could explain me in detail on this config? If so would you please share it..!!It would be a great help..

Thanks Mahendra