World wide names are 64-bit identifiers that are used to uniquely identify ports on the network during discovery and network initialization. Each controller or HBA on the network has a unique WWN written at the factory and encoded in non-volatile memory in the controller/HBA. In that sense, they are persistent port identifiers. Therefore, WWNs are useful for re-establishing network connections following a site disaster such as a prolonged power outage.
Switches maintain tables that map WWNs to switch ports. However, the WWN is NOT used for addressing in the network, as addresses are either 24 bits in fabrics and public loops - or 8-bits in private loops. I have to confess that I do not know how WWNs are implemented in large multi-ported subsystems, but I assume each physical port would have its own WWN.
This was first published in May 2001