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A Wide Area Network (WAN) is a type of computer network that covers a broad area and connects multiple other networks in order to make communications and data exchanges between users and machines at various geographically dispersed locations possible.

Introducing Wide Area Networks (WANs)

A Wide Area Network (WAN) is generally considered to be a type of computer network that covers a broad area where communications links cross regional, metropolitan or national boundaries. Today, it is probably better to think of a WAN as a network that uses routers and publicly accessible communications links. Without doubt the largest and most well-known WAN is the Internet.

Wide Area Networks (WANs) are used to connect Local Area Networks (LANs) and other types of networks, including Metropolitan Area Networks (MANs), Local Area Networks (LANs), wireless and private networks. The purpose of a WAN is to enable users and computers in one location to communicate with users and computers in other, often very geographically dispersed and separated locations.

Typically a WAN will consist of a number of interconnected switching nodes that allows transmissions from any one device to be routed through these interconnected nodes to the specified destination device(s). These nodes are not concerned with the contents of data rather their interest is focused on the provision of a switching facility to move the data from node-to-node until they arrive at their intended destination.

Wide Area Network (WAN) Models

In essence there are two basic design models upon which all WAN connectivity structures and organization are based. They are:

The Centralized WAN Model – Consists of a server or group of servers in a central location and client computers or dumb terminals that connect to the server(s) which provide the bulk of the network’s functionality. Figure 1 above is a logical construct of a typical centralized WAN. Note that all points lead to the centrally located servers.

Today’s typical physical Point of Sale (POS) functionality such as that implemented by chain organizations such as banks and supermarkets etc is a classic example of a centralized WAN. Software-as-a-Service (SaaS) and web based applications are other examples of a centralized WAN computing model.

The Distributed WAN Model – Consists of client and server computers distributed throughout the network (see Fig.2 below). The Internet is a distributed WAN.

The three tiered network design hierarchy consisting of a core layer, a distribution layer and an access layer is implemented on top of which ever WAN connectivity and organizational structures are chosen. For more about the three tiered network design hierarchy check this article out Network Design: Hierarchies.

Building Wide Area Networks (WANs)

In order to facilitate the efficient and effective transfer of information between a WAN’s end systems a number of protocols (rules that govern the transmission and reception of information between computers and network end-points) needed to be developed and implemented.

Generically speaking; a networking protocol is the formal description of a set of rules that describe, enable, govern and regulate the various characteristics, aspects, attributes and properties of an internetwork. One of the more important early WAN protocols was X.25. Although it is not used today, many of X.25’s underlying protocols and functions (with modifications and improvements) are still in use by current iterations of Frame Relay.

Initially, most WANs were built using expensive leased lines. The most common production implementations of leased line based WANs involved the use of a router at each end of the leased line to connect to the LAN on one side to a hub within the WAN on the other.

Wide Area Networks (WANs) Reducing Implementation Costs

If ever the use of Wide Area Networks (WANs), including the Internet was to become widespread and accessible to the bulk of humanity (be it as individuals or collectives) something needed to be done to reduce the startup and running costs of planning, implementing and maintaining WANs. Fortunately solutions did exist.

Less costly alternatives to using expensive leased lines when building a WAN include the use of circuit switching or packet switching technologies. Here, network protocols including TCP/IP serve to deliver transport and addressing functions. While protocols such as Packet over SONET/SDH, Multiprotocol Layer Switching (MPLS), Asynchronous Transfer Mode (ATM) and Frame Relay are commonly used by Internet Service Providers (ISPs) to deliver the links that are used in WANs.

Wide Area Network (WAN) Connectivity Options

Leased Line – Provide secure but comparatively expensive Point-to-Point connectivity between two computers or Local Area Networks (LANs) using protocols such as Point-to-Point Protocol (PPP), High-Level Data Link Control (HDLC) and Synchronous Data Link Control (SDLC).

Circuit Switching – A less expensive dedicated circuit path offering bandwidth data transfer rates ranging from 28K-bit/sec to 144K-bit/sec is created between end points. On the downside call setup and connection establishment needs to be renegotiated every time access is desired because the link is not necessarily permanent. The most well known example of circuit switching WAN connectivity is dial-up connections. Point-to-Point Protocol (PPP) and Integrated Service Digital Network (ISDN) are two of the most widely used protocols for circuit switching WAN connectivity.

Packet Switching – Variable length packets are transported over a shared single point-to-point or point-to-multipoint link across a carrier internetwork using Permanent Virtual Circuits (PVC) or Switched Virtual Circuits (SVC). X.25 and Frame Relayare two examples of packet switching protocols used for WAN connectivity.

Cell Relay – Cell Relay is very 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. Unfortunately the overhead can constitute a significant proportion of the total bandwidth. Cell relay protocols such as Asynchronous Transfer Mode (ATM) (up to 155M-bit/sec) are best for simultaneous use of Voice and data.

Virtual Private Network (VPN) – With the recent reductions in Internet connectivity and concurrent increases in bandwidth and transmission rates now offered by ISPs many organizations have opted to use VPN technologies such as those on offer from the likes of Cisco Systems, New Edge Networks, Juniper, Check Point and Vyatta to interconnect their networks. One of VPN’s strong points is encryption and considering the prevalence of cyber-crime today it is no surprise to find that this form of WAN is currently very popular.

Wide Area Network (WAN) Transmission Media and Links

Any given WAN may use one, more or even all of the following technologies for the transmission and transport of information:

Copper-Based Media – Telephone lines, coaxial cable, CAT cable etc

Fiber Optic-Based Cables – Single-Mode and Multi-Mode (see Fiber Optic Cableand Optical Networkingfor more).

Wireless – Radio frequency channels, microwave links, satellite channels and publically accessible wireless “hot spots”

Wide Area Network (WAN) Transmission Rates

Typically, WAN transmission rates usually have ranged from 1.2K-bits/sec to 6 M-bit/sec, although some connections such as ATM and Leased lines can reach speeds greater than 156 M-bit/sec. The advent of ADSL 2+ has upped the ante even further.

Now with transmission rates up to 30 Mbps, DSL and cable modem are two high data-transmission rate consumer Internet connections that transmit considerably faster than a dial-up modem (56 kbps). Add to this the fact that they are also generally cheaper than both ISDN and dial-up and you get a very cost-effective solution.

Wide Area Network (WAN) Access

Wide Area Networks (WANs) may be public (usually built by Internet Service Providers (ISPs) to provide Internet connectivity) while others are private (built for a specific organization). That is to say that public access to an organization’s “private” network component is regulated by that organization. In contrast, access to public networks and user privileges remains largely unregulated beyond the criteria as defined by the agreement between the consumer and your Internet Service Provider (ISP).

Hence, the general public, anonymous and guest visitors, colleagues, business partners, and associates etcetera may be permitted limited privilege access to various sectors of an organization’s private network but not to all of it. Functionalities, services, assets and user capabilities will vary greatly on a case-by-case network-by-network basis.

Demilitarized Zones (DMZs)

A classic example of this regulated limited access is commonly implemented in the form of Demilitarized Zones (DMZs) that allow public access to a very restricted and confined portion of an organization’s private network. Here they may be able to access a web server for e-commerce, technical support or even just for casual browsing. You cannot make a sale if you cannot communicate with your customers. Even auto responders and automated shopping carts require some degree of two-way participation from both the customer and your software.

Metropolitan Area Network (MAN)

Another increasingly more common type of WAN is the Metropolitan Area Network (MAN) which is basically the same as a WAN except that its boundaries are contained within a single metropolitan area (city).

In Australia, a MAN can be viewed as a network for which standard landline telephone communications are charged at the local call rate (not STD) as all endpoints have the same area code. With broadband configured as a permanently connected service the customer only pays the local call fee for the initial setup connection or reconnection if the service is interrupted for any reason.

Examples of private Metropolitan Area Networks (MANs) would be the corporate links between various branches of the same organization (chain stores, banks) in the Perth metropolitan area. The key here is that regardless of the protocols or other technologies being used, part of the transit will be via publically accessible networks such as the Internet. The remainder will of course be contained within the boundaries of their “private LAN”.

WANs, MANs and Interoperability

Internetworking and interoperability are key factors critical to the realization of effective and readily available e-commerce portals as well as other external network resources and services. Regulatory and other compliance issues also need to be taken into consideration.

The seamless, secure interoperability of multiple systems and networks is essential in order for the general public to have free and ready access to those components of the enterprise LAN/MAN/WAN deemed desirable by that organization/enterprise.

For example; it is usually deemed to be highly desirable that the general public have rapid seamless access and interactivity with an organization’s e-commerce facilities such as the shopping cart, support services if appropriate and resources such as online documentation.

The expansion of Web 2.0 functionality and the upsurge of social networking applications all rely heavily on the effective and efficient seamless integration of internetworking and interoperability technologies at all levels.