Please answer a question about the following article about Internet service provider:

For customers with more demanding requirements (such as medium-to-large businesses, or other ISPs) can use higher-speed DSL (such as single-pair high-speed digital subscriber line), Ethernet, metropolitan Ethernet, gigabit Ethernet, Frame Relay, ISDN Primary Rate Interface, ATM (Asynchronous Transfer Mode) and synchronous optical networking (SONET).

what is high-speed dsl used for?
customers with more demanding requirements