How to get host "client" initiator wwn's from FC SAN card & switch

I saw an IBM San Storage and at Host alias creation page they can show you available host (client) initiators wwn's to choose. And I wonder how they can find client initiator wwn's from storage? I think they should be using a discover method for taking this information from SAN switch via fc but how? If we simplify the question I'm the Storage System as you can see at below. And I want to discover available initiator port wwn number via FC port. Do you know anything about this?