To explain what a metropolitan area network (MAN) is, it would first be helpful to address the nature of computer networks in general.
Computers interact with each other by forming connections, either through a direct hard line connection or via wireless capacity. Some of these connections are semi-permanent, while others can be dropped by a particular computer and rejoined later on. Whenever two computers communicate with each other, what results is a “network,” which is simply a term (in computer parlance) for multiple computers sharing data. The internet, for all its many complexities and layers of existence, is in a certain sense simply the world’s biggest computer network.
It is not the only large-scale network on Earth, however.
Computer Networks, Privacy, and You
Since the earliest days when we first began connecting computers to each other across vast distances, long before the advent of the modern internet, people have advanced the simultaneous need for greater convenience and more data security. As a result, for as long as the internet has existed in any recognizable sense, we have had other, smaller networks going by a variety of names—and filling a variety of functions.
Many institutions, such as businesses and universities, maintain local area networks. These LANs require that all computers be connected to their network directly, whether wirelessly or by hard line. The network does not connect directly to the public internet, and may be difficult to access via that route without specialized training and equipment (including software designed for the purpose). In some cases, a completely isolated LAN might be completely inaccessible—requiring access to one of a particular group of terminals connected only by a hard line.
From LAN to MAN
A MAN is a more recent development, but it works on the same principles as a LAN—it simply operates on a larger scale. As such, it can serve as a “hub” for other, smaller networks as well.
A metropolitan area network connects all of the subscribers of a given metropolitan region. Typically, this exists as a way to provide affordable, high-speed internet service to the population of a city. The easiest way to do that is to connect subscribers to the internet through a MAN, rather than directly. There is a layer of networking there, which may be invisible to most who use it—or, it may offer access to exclusive features.
During the days of America OnLine, dialup subscribers to AOL had access to sites, chatrooms, and other resources which other internet users could not conveniently access. This kind of functionality can be provided in a MAN, exclusive to those who connected to the internet within the MAN’s service area. More commonly, it serves to provide a central hub for local area networks.
Businesses, government agencies, and other large organizations may create private networks which, while not quite as secure as a completely isolated network, are easier and more affordable to set up and maintain.
There are other, even larger networks than MANs, which go back to the early days of the internet. Prior to the development of the world-wide web, the “internet” was fundamentally an isolated computer network connecting government and academic institutions separated by vast distances. Modern-day WANs serve a similar functionality.