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2.1 | WAN Service Providers |
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2.1.1 | WAN services |
A WAN is a data communications network that operates beyond a LAN's
geographic scope. One way that a WAN is different from a LAN is that you must subscribe to an outside WAN service provider, such as a regional Bell operating company (RBOC) to use WAN carrier network services.
A WAN uses data links, such as Integrated Services
Digital Network (ISDN) and Frame Relay, that are provided by carrier
services to access bandwidth over wide-area geographies. A WAN
connects the locations of an organization to each other, to locations
of other organizations, to external services (such as databases), and
to remote users. WANs generally carry a variety of traffic types, such
as voice, data, and video.
WAN technologies function at the three lowest layers of the OSI
reference model: the physical layer, the data link layer, and the
network layer. Figure Telephone and data services are the most commonly used WAN services. Telephone and data services are connected from the building point of presence (POP) to the WAN provider's central office (CO). The CO is the local telephone company office to which all local loops in a given area connect and in which circuit switching of subscriber lines occurs. An overview of the WAN cloud (see Figure
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