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Wide area networks (WANs) can be formed by integrating different LANs together. The need for WANs becomes essential as LANs are separated by a wide distance. Organizations can have their own LAN infrastructure but normally they have to lease WANs from the carrier network like telephone companies. Four types of connections or circuits are used in WAN: circuit-switched, cell-switched, packet-switched, and dedicated connections.
There are a large number of WAN services present like analog dialup, ATM, dedicated circuits, cable, DSL (digital subscriber line) Frame Relay, ISDN, Switched Multi-megabit Data Services (SMDS), and X.25. These services can be grouped in different categories: Analog dialup and ISDN falls in circuit switched services, ATM and SMDS are cell-switched services and Frame Relay and X.25 are examples of packet-switched services.
Circuit-switched services: It provides a temporary connection through phone lines. A circuit-switched service helps backing-up the primary circuits. The bandwidth is dedicated among the two sites connected through permanent dedicated connection. Cell-switched services: These services can provide the similar facilities as dedicated circuits. They have a plus point over the dedicated circuits that a single device can connect to multiple devices on the same interface. Also there are some disadvantages of cell-switched services like they are not accessible at all locations, their equipment is expensive and they are hard to setup and troubleshoot. Packet-switched services: Packet-switched services are having some features in common with cell-switched services. Packet-switched services switch the variable length packet while the cell-switched services switch fixed-length packet, this capability makes them better specifically for data services but can’t provide some of the Quality of service features that cell-switched services provide. Today Cable and DSL WAN services are very popular in the US. DSL is much more efficient and cost effective as compared to a typical WAN. It supports both voice and video and doesn’t require a dialup connection. Coaxial cable is used for connections, its data rates are greater than DSL and like DSL it provides full-time connection. Its main disadvantage is that it is a shared service and functions in a logical bus topology, the number of user increases in an area results a low bandwidth distribution across all the users connected. Here are some useful network devices normally used to construct a WAN Cable and DSL modems, Carrier switches, CSU/DSUs, firewalls, modems, NT1s, and routers. |
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