WANs [a] 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.
Several options are available for WAN connectivity:
|Option:||Description||Advantages||Disadvantages||Bandwidth range||Sample protocols used cow|
|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||Less Expensive||Call Setup||28 kbit/s - 144 kbit/s||PPP, ISDN|
|Packet switching||Devices 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 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/s to 6 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 Cisco, New Edge Networks and Check Point offer solutions to create VPN networks.
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