WAN Physical Layer Terminology
One primary difference between a WAN and a LAN is that a company or organization must subscribe to an outside WAN service provider to use WAN carrier network services. A WAN uses data links provided by carrier services to access the Internet and connect the locations of an organization to each other, to locations of other organizations, to external services, and to remote users. The WAN access physical layer describes the physical connection between the company network and the service provider network. The figure illustrates the terminology commonly used to describe physical WAN connections, including:
Customer Premises Equipment (CPE)-The devices and inside wiring located at the premises of the subscriber and connected with a telecommunication channel of a carrier. The subscriber either owns the CPE or leases the CPE from the service provider. A subscriber, in this context, is a company that arranges for WAN services from a service provider or carrier.
Data Communications Equipment (DCE)-Also called data circuit-terminating equipment, the DCE consists of devices that put data on the local loop. The DCE primarily provides an interface to connect subscribers to a communication link on the WAN cloud.
Data Terminal Equipment (DTE)-The customer devices that pass the data from a customer network or host computer for transmission over the WAN. The DTE connects to the local loop through the DCE.
Demarcation Point-A point established in a building or complex to separate customer equipment from service provider equipment. Physically, the demarcation point is the cabling junction box, located on the customer premises, that connects the CPE wiring to the local loop. It is usually placed for easy access by a technician. The demarcation point is the place where the responsibility for the connection changes from the user to the service provider. This is very important because when problems arise, it is necessary to determine whether the user or the service provider is responsible for troubleshooting or repair.
Local Loop-The copper or fiber telephone cable that connects the CPE at the subscriber site to the CO of the service provider. The local loop is also sometimes called the "last-mile."
Central Office (CO)-A local service provider facility or building where local telephone cables link to long-haul, all-digital, fiber-optic communications lines through a system of switches and other equipment.