WAN

·       Wide Area Network

·       Is a computer network that covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries).

·       Contrast with personal area network (PANs), local area network (LANs), campus area network (CANs), or metropolitan area network (MANs) which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively.

Design options

o  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.

o  Many WANs are built for one particular organization and are private.

o  Built by, Internet Service Providers, provide connections from an organization's LAN to the Internet.

o  Built using leased lines.

o  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.

o  Leased lines can be very expensive.

o  Can also built using less costly circuit switching or packet switching methods.

o  Network protocol including TCP/IP deliver transport and addressing functions.

o  Protocol 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.

o  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.

o  Academic research into wide area networks can be broken down into three areas: Mathematical models, network emulation and network simulation.

o  Performance improvements are sometimes delivered via WAFS or WAN optimization.

Connection technology options

·       Several ways to connect NonStop S-series servers to WANs, including via the ServerNet Wide Area Network (SWAN) or SWAN 2, 3, 4, 5, 6, 7, 8, 9, 10 concentrators, which provides WAN client connectivity to servers that have Ethernet ports and appropriate communications software.

·       You can also use the Asynchronous Wide Area Network (AWAN) access server, which offers economical asynchronous-only WAN access.

·       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	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 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 Cisco, New Edge Networks and Check Point offer solutions to create VPN networks.

WAN Technology

o  A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies.

o  WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.

o  The following articles provide information about the various protocols and technologies used in WAN environments:

§  Frame Relay

§  High-Speed Serial Interface

§  Intergrated Service Digital Network

§  Point-to-Point Protocol

§  Switched Multimegabit Data Service

§  Synchronous Data Link Control and Derivatives

§  X.25

§  Digital Subscriber Line

Reference from:

http://en.wikipedia.org/wiki/Wide_area_network

http://docwiki.cisco.com/wiki/Internetworking_Technology_Handbook#WAN_Technologies