16.1 Network Infrastructure Concepts 
16.1.1 Local Area Networks (LANs)
Networks can be divided into two basic categories: Local Area Networks (LANs) and Wide Area Networks (WANs). LANs are made up of groups of computers (nodes) that have simultaneous access to common high bandwidth media. Media can be copper wire, fiber optic cable or even air as with wireless LANs. Bandwidth is the data carrying capacity of the media and LAN technology being used. Each node or computer (in most cases) gains access to the network media through a Network Interface Card (NIC), which is installed in the computer.

These nodes are connected in a relatively confined geographical location where the distance between nodes is normally less than 500 feet or approximately 150 meters. Most LANs cover a small area, usually less than 10,000 square feet or approximately 1000 square meters. Distances between nodes can be greater than a mile and still be considered a LAN, but this is uncommon. A node is an endpoint on the network and can be a workstation, a server or a printer. LANs can have as few as two computers or as many as thousands. They can occupy a single room or span multiple buildings, as with a campus environment.

LANs provide high-speed communications between all interconnected nodes or devices. This allows users to share network resources such as documents, databases, applications, printers, and Internet connections. High-speed communication is defined here as 10 Mbps (10 million bits per second) or faster. Current LAN technologies support speeds of over 1Gbps (Gigabits per second or 1,000 million bits per second).

LANs are usually interconnected by physical cabling such as copper or fiber optic, however in recent years, wireless LANs have become more common. All cabling, conduit, and interconnected network equipment, such as hubs and switches are typically owned by the organization that uses the LAN. Examples of LAN technologies or architectures include Ethernet, Token Ring and FDDI (Fiber Distributed Data Interface).

Figure summarizes the characteristics of a LAN and Figure shows a LAN with nodes interconnected by a multi-port switch in a star topology, which is very common in today's LAN network designs. Topologies will be covered later in this chapter. Multi-port switches can be interconnected which allow a large number of workstations to be on the same LAN. While routers can be used to divide the LAN into multiple segments for improved performance and security.