Wide Area Networks (WANs)

A Wide Area Network (WAN) is generally considered to be a type of computer network that covers a geographically 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.

WAN Functions and Functionalities

Wide Area Networking (WANs) functions and functionalities are used to interconnect other types of smaller less geographically dispersed networks, including Metropolitan Area Networks (MANs), Local Area Networks (LANs), wireless and private networks as well as individual machines. 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 or routing facility to move the data from node-to-node until they arrive at their intended destination.

Two Types of WANs

Fundamentally there are two types of WANs: the Centralized WAN and the Distributed WAN.

• The Centralized WAN Model - Consists of a server or group of servers in a central location which provide the bulk of the network’s functionality and client computers or dumb terminals that connect to the server(s).
• The Distributed WAN Model - Consists of client and server computers distributed throughout the network. The Internet is a distributed WAN.

Network Hierarchies

Other networking design structures and hierarchies may be superimposed on top of the underlying WAN structure. For example the three tiered network design hierarchy consisting of a core layer, a distribution layer and an access layer may be implemented on top of which ever WAN connectivity and organizational structures is chosen.

Dial-up or leased line, ATM or some DSL variant or any other WAN connectivity protocol or standard it makes no difference they are simply implemented upon the underlying centralized or distributed WAN model chosen. Note however; that some protocols and standards work better together than others.

Building Early 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 and to a hub within the WAN on the other.

Reducing Implementation Costs

It was recognized very early on that 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) Access

Wide Area Networks (WANs) may be public (usually built by Internet Service Providers (ISPs) to provide Internet connectivity) while others are private. That is they may be built for a specific organization for the sole and exclusive use in whole or in part by the members of that organization (e.g. the military). This means that public access to an organization’s “private” network component is regulated by that organization and may even be totally prohibited (no publically accessible component which makes for much smoother network administration).

In contrast, access to public networks and their user privileges remains largely unregulated beyond the criteria as defined by the agreement between the consumer and their Internet Service Provider (ISP). In between these extremes we find the vast majority of today's networks which allow the general public, anonymous and guest visitors, colleagues, business partners, and associates etcetera some degree of 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.

Regulating Access and 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 active two-way participation from both the customer and the 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 in nearly every aspect except that its boundaries are contained within a single metropolitan area (city). For example, 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 same metropolitan area (in the same city or local call rate area). The key here is that regardless of the protocols or other technologies being used, part of the transit may be via publically accessible networks such as the Internet. The remainder will of course be contained within the boundaries of the organization's local "branch" private LANs.

Currently large passenger air carriers conduct their bookings facilities using this type of expanded state-wide or national WAN. The customer wishing to book a flight calls a number and may be connected with an operator not necessarily located in the same city or even state. I have even had the experience on numerous occassions of connecting to and processing my flight ticketing with operators on the other side of the country which in Australia means over 2,000 kilometers and two time zones away. In this way the aircraft carrier can optimize their staffing arrangements while preserving the continuity of their service availability to the general public.

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 functionalities, user interactivity and contribution along with the upsurge of social networking applications all rely heavily on the effective and efficient seamless integration of internetworking and technology interoperability at all levels.