For customers with more demanding requirements (such as <answer>medium-to-large businesses, or other ISPs</answer>) 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 type of customers would typically have more demanding requirements? 
medium-to-large businesses, or other ISPs