[kaze]

Without going too deep into the technical details:

An ESS network is most often under a single organization (say, the IT department of a large Hotel). The Wi-Fi credential combination required by a user to roam across the different Access Points in the ESS is the same.

But what about when you leave hotel premises and go to the airport? Manual intervention is often required by you, especially if you are going to that airport for the first time and have not yet purchased a plan there. With Passpoint, the hotels in the city, the airport etc could all be participating in a common program. Sign up once, use anywhere. With passpoint software, your device has a _standardized_ way to avail of such facilities.

The ESS architecture does not handle such possibilities - it operates at a much lower level. Higher level handshaking is required to enable this, and in a standards defined manner so that it works everywhere.