WANs can be categorized as follows:
• Point-to-point links—Provide a single, preestablished WAN communication path from the customer premises through a carrier network, such as the telephone company, to a remote network. A point-to-point link is also known as a leased line because its established path is permanent and fixed for each remote network reached through the carrier facilities.
• Circuit switching—A WAN switching method in which a dedicated physical circuit is established, maintained, and terminated through a carrier network for each communication session. Used extensively in telephone company networks, circuit switching operates much like a normal telephone call. Integrated Services Digital Network (ISDN) is an example of a circuit-switched WAN technology.
• Packet switching—A WAN switching method in which network devices share a single point-to-point link to transport packets from a source to a destination across a carrier network. Statistical mulitplexing is used to enable devices to share these circuits. Asynchronous Transfer Mode (ATM), Frame Relay, Switched Multimegabit Data Service (SMDS), and X.25 are examples of packet-switched WAN technologies.
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