Senin, 15 Oktober 2012

Wide area network


Wide Area Network (WAN) is a network that covers a broad area (i.e., anytelecommunications network that links across metropolitan, regional, or national boundaries) using private or public network transports. Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations. In essence, this mode of telecommunication allows a business to effectively carry out its daily function regardless of location. The Internet can be considered a WAN as well, and is used by businesses, governments, organizations, and individuals for almost any purpose imaginable.[1]
Related terms for other types of networks are 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.

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[edit]Design options

The textbook definition of a WAN is a computer network spanning regions, countries, or even the world. However, in terms of the application of computer networking protocols and concepts, it may be best to view WANs as computer networking technologies used to transmit data over long distances, and between different LANs, MANs and other localised computer networking architectures. This distinction stems from the fact that common LAN technologies operating at Layer 1/2 (such as the forms of Ethernet or Wifi) are often geared towards physically localised networks, and thus cannot transmit data over tens, hundreds or even thousands of miles or kilometres.
WANs necessarily do not just connect physically disparate LANs. A CAN, for example, may have a localised backbone of a WAN technology, which connects different LANs within a campus. This could be to facilitate higher bandwidth applications, or provide better functionality for users in the CAN.
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 byInternet 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 the LAN on one side with a second router within the LAN 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 switchingmethods. Network protocols including TCP/IP deliver transport and addressing functions. Protocols including Packet over SONET/SDH,MPLSATM 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.25are still in use today (with upgrades) by Frame Relay.
Academic research into wide area networks can be broken down into three areas: mathematical modelsnetwork emulation andnetwork simulation.
Performance improvements are sometimes delivered via wide area file services or WAN optimization.

[edit]Connection technology options

Several options are available for WAN connectivity:[2]
Option:DescriptionAdvantagesDisadvantagesBandwidth rangeSample protocols used
Leased linePoint-to-Point connection between two computers or Local Area Networks (LANs)Most secureExpensivePPP,HDLC,SDLC,HNAS
Circuit switchingA dedicated circuit path is created between end points. Best example is dialup connectionsLess ExpensiveCall Setup28 - 144 kbit/sPPP,ISDN
Packet switchingDevices transport packets via a shared single point-to-point or point-to-multipoint link across a carrier internetwork. Variable length packets are transmitted over Permanent Virtual Circuits (PVC) or Switched Virtual Circuits (SVC)Shared media across linkX.25Frame-Relay
Cell relaySimilar 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 circuitsBest for simultaneous use of voice and dataOverhead can be considerableATM
Transmission rates usually range from 1200 bit/s to 24 Mbit/s, although some connections such as ATM and Leased lines can reach speeds greater than 156 Mbit/s. Typical communication links used in WANs are telephone lines, microwave links & satellite channels.
Recently with the proliferation of low cost of Internet connectivity many companies and organizations have turned to VPN to interconnect their networks, creating a WAN in that way. Companies such as CitrixCisco, New Edge Networks and Check Point offer solutions to create VPN networks.

[edit]National area network

Some countries have nationwide computer networks, such as Kwangmyong in North Korea.

[edit]See also

[edit]References

  1. ^ Groth, David and Skandler, Toby (2009). Network+ Study Guide, Fourth Edition. Sybex, Inc. ISBN 0-7821-4406-3.
  2. ^ 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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