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Wide-area networks evolved from the need to share data across vast geographical distances. The definition of WAN is a network spanning a wide geographic area. The purpose of the WAN is to connect local-area networks (LANs) and to transport data from one LAN to another. In our studies, the WAN is used much in the same way. WAN protocols have changed over time. At first, WAN protocols focused on error correction and were designed to operate on old, unreliable copper lines. WAN protocols today offer high-speed reliable transport on copper and fiber optic lines. Despite the vast evolution of the WAN, it still proves to be the slowest and most expensive part of any modern internetwork. WAN protocols function at the lower three layers of the OSI model. X.25 PLP is one of the protocols that operates at Layer 3, but most WAN protocols operate at Layer 2. Table 3-1 displays some common WAN protocols and their corresponding layers in the OSI reference model. Table 3-1. WAN Protocols and Their Corresponding OSI Layers
In the lab, using Cisco 2500 and 2600 series routers, you can readily model HDLC, PPP, Frame Relay, and X.25. Our studies start with these protocols and end with ISDN and ATM. Modeling ISDN and ATM requires the use of specialized routers and switches. |
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