Wide area network
|Computer network types
by spatial scope
A wide area network (WAN) is a network that covers a broad area (i.e., any telecommunications network that links across metropolitan, regional, national or international boundaries) using leased telecommunication lines. 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.
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.
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 do not just necessarily 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 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 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 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.
Connection technology options
Several options are available for WAN connectivity:
|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||Less Expensive||Call Setup||28 - 144 kbit/s||PPP, ISDN|
|Packet switching (Connection oriented)||Devices transport packets via a shared single point-to-point or point-to-multipoint link across a carrier internetwork. Before information can be exchanged between two endpoints, they first establish a Virtual Circuit. Variable length packets are transmitted over Permanent Virtual Circuits (PVC) or Switched Virtual Circuits (SVC)||Shared media across link||X.25, Frame-Relay|
|Packet switching (Connectionless)||Devices transport packets via a shared single point-to-point or point-to-multipoint link across a carrier internetwork. Variable length packets are transmitted. Between endpoints no connection is build; endpoints can just offer packets to the network, addressed to any other endpoint and the network will try to deliver the packet. As an example: the Internet works this way.||Very robust and low overhead||Shared media across link||IPv4, IPv6|
|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||Before 2000 this was seen as the best option for simultaneous use of voice and data. With the much higher link speeds in modern networks, this advantage is effectively meaningless.||Overhead can be considerable||ATM|
Transmission rates have increased over time and will continue to increase. Around 1960 a 110 bit/s (bits per second) line was normal on the edge of the WAN, while core links of 56 kbit/s to 64 kbit/s were considered "fast". At this moment (2014) households are connected to the Internet with ADSL or cable at speeds ranging from 1 Mbit/s to 100 Mbit/s and the connections in the core of a WAN can range from 1 Gbit/s to 100 Gbit/s.
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 Citrix, Cisco, New Edge Networks and Check Point offer solutions to create VPN networks.