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