How does primetime trace net arcs

[identical]

I understand how the timing arcs (rise and fall) are stored in the .db file for cell timing arcs. How are the timing arcs for nets traced? I know the RC component is in .spef file. But, where does it get the delay through a net or time of flight from?

 

[ThisIsNotSam]

Nets are loads, they affect the timing of the standard cells they are connected to.