SAS can be connected via a direct cable between initiator and target, this would be used in a point to point configuration or for internal connectivity in a desktop PC or laptop.
SAS connectivity can also be extended by using an Expander. There are two types of Expander, Edge and Fanout.
An Edge Expander will support up to 128 SAS addresses
A Fanout Expander connects up to 128 Sets of Edge Expanders to form a SAS Domain