Wide area network
Wide Area Network (WAN) is a computer network that covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries [1]). Or, less formally, a network that uses routers and public communications links [1]. Contrast with personal area networks (PANs), local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs) which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively. The largest and most well-known example of a WAN is the Internet.
WANs are used to connect (LANs) and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations. Many WANs are built for one particular organization and are private. Others, built by Internet service providers, provide connections from an organization's LAN to the Internet. WANs are often built using leased lines. At each end of the leased line, a router connects to the LAN on one side and a hub within the WAN on the other. Leased lines can be very expensive. Instead of using leased lines, WANs can also be built using less costly circuit switching or packet switching methods. Network protocols including TCP/IP deliver transport and addressing functions. Protocols including Packet over SONET/SDH, MPLS, ATM and Frame relay are often used by service providers to deliver the links that are used in WANs. X.25 was an important early WAN protocol, and is often considered to be the "grandfather" of Frame Relay as many of the underlying protocols and functions of X.25 are still in use today (with upgrades) by Frame Relay.
Academic research into wide area networks can be broken down into three areas: Mathematical models, network emulation and network simulation.
Performance improvements are sometimes delivered via WAFS or WAN Optimization.
WAN connectivity options
Several options are available for WAN connectivity: [2]
| Option: | Description | Advantages | Disadvantages | Bandwidth range | Sample protocols used |
|---|---|---|---|---|---|
| Leased line | Point-to-Point connection between two computers or Local Area Networks (LANs) | Most secure | Expensive | PPP, HDLC, SDLC, HNAS | |
| Circuit switching | A dedicated circuit path is created between end points. Best example is dialup connections | Little Expense | Call Setup | 28 Kb/s - 144 Kb/s | PPP, ISDN |
| Packet switching | Devices transport packets via a shared single point-to-point or point-to-multipoint link across a carrier internetwork also known as a CIN. Variable length packets are transmitted over Permanent Virtual Circuits (PVC) or Switched Virtual Circuits (SVC) | Shared media across link | X.25 Frame-Relay | ||
| Cell relay | Similar to packet switching, but uses fixed length cells instead of variable length packets. Data is divided into fixed-length cells and then transported across virtual circuits | best for simultaneous use of Voice and data | Overhead can be considerable | ATM |
Transmission rate usually range from 1200 bits/second to 6 Mbit/s, although some connections such as ATM and Leased lines can reach speeds greater then 156 Mbit/s . Typical communication links used in WANs are telephone lines, microwave links & satellite channels.
References
- ^ a b
Groth, David (2005). 'Network+ Study Guide, Fourth Edition'. Sybex, Inc. ISBN 0-7821-4406-3.
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McQuerry, Steve (November 19 2003). 'CCNA Self-Study: Interconnecting Cisco Network Devices (ICND), Second Edition'. Cisco Press. ISBN 1-58705-142-7.
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