Lesson 1 - Network Classifications and Topologies
Networks are classified according to the area over which they extend. The smallest networks consist of two nodes connected by a cable in the same room. The largest networks include millions of nodes around the world. The size and extension of a network depend on the number of nodes that need to communicate, and where these nodes are in relation to each other.
A LAN can consist of a few nodes, as depicted on the LAN Diagram, or up to several hundred nodes. However, a LAN is typically confined to a single building.
A segment is a portion of a LAN in which all nodes are directly connected. For example, all nodes may be connected by a single bus cable, or, as shown on the LAN Diagram, connected to a central hub. A LAN can consist of many segments linked together in certain ways to form a larger, but still local, network.
When computers are connected across multiple buildings, the entire collection of computers is often referred to as a campus network. A campus network consists of several LANs tied together in some way to form a larger network.
Campus networks are built by connecting LANs to other LANs with an organization's networking infrastructure. In other words, the networking equipment used to connect LANs to form a campus network is owned and operated by the people within the organization. When all of the networking equipment and transmission systems belong to the organization that uses them, that infrastructure is called private facilities. The Campus Network Diagram illustrates a typical campus network.
A metropolitan area network (MAN) interconnects two or more LANs across a city-wide area. The MAN Diagram illustrates a typical MAN. For example, a business might interconnect several branch offices.
One of the primary differences between a MAN and campus network is that a campus network uses private facilities for interconnecting individual LANs, and a MAN uses public or shared facilities leased from a local telephone company. These leased services include point-to-point lines such as T-carriers (fractional T1, T1, or T3), or switched services such as Integrated Services Digital Network (ISDN), frame relay, or Asynchronous Transfer Mode (ATM).
Wide area networks (WANs) are formed by connecting LANs across a region or the world. As you can see on the WAN Diagram, both local and long-distance public facilities are typically used to connect LANs across multiple cities. WANs can be built using the same transmission technologies as MANs.
Within each city, we may have LAN, campus, and MAN connectivity. The WAN portions of the network are the connections that provide communication between cities. Information travels across the WAN portion of the network only when it is destined for another computer in another city.