I'm writing `JSON` data with lots of data. Sometimes several thousand records.

I want to use pagination to display, for example, 20 records per page.
When the user scrolls down, I want to add next 20 records.

Im sending current page( www.exampleRequest/&pageCounter=1 ) and receive 
adequate records

pageCouter = 1 => 1\*20 = 0 to 20 records 

pageCouter = 2 => 2\*20 = 21 to 40 records

But my question is how does the *iOS-swift* `UITableView` know when to get the next page of results?