1。One primary difference between a WAN and a LAN is that a company or organization must subscribe to an outside WAN service provider in order to use WAN carrier network services.

2.术语:
customer premises equipment (CPE).
central office (CO). 
local loop
data circuit-terminating equipment, or data communications equipment (DCE).
data terminal equipment (DTE)

3
 

The DCE primarily provides an interface for the DTE into the communication link on the WAN cloud