The concept of PC-based network can essentially be traced back to when mainframes and minicomputers were accessed by stand-alone or dumb terminals. However, with the advancements in data storage, security, communication speeds, the need to link microcomputers and networks became crucial.

The local area network or LAN is a group of computers running a specialized communications software and connected via an external data path to network nodes. A LAN can consist of workstations with network interface cards (NICs), hubs, gateways, bridges, switches, routers and servers. The physical media is consisted of Category 5 and fiber optic cabling. Category 5 cables are horizontal cables that are installed from point-to-point between the workstations and the electronics, such as hubs or switches, that make up the network. The cat5 cables terminate to the IDF, intermediate distribution facility, and must not exceed more than 100 meters from the workstations. Fiber optic cables connect all electronic devices throughout the campus to an MDF, main distribution facility. This houses the enterprise category network equipment, which are switches that are capable of switching packages at a rate of 10 or more gigabytes per second and routers with multiple ports that are capable of connecting the enterprise together.

Characteristics of LANs

The basic characteristics of LANs are that:

• LANs are typically initiated in a relatively small geographic no larger than a single building.

• LANs provide a direct high-speed connection between all workstations and servers.

• LANs provide centralized management of resources and network security.

Benefits of LANs

The benefits of LANs are:

• Resource sharing capability allows storage space and network peripherals, such as printers, to be shared by workstations, reducing hardware requirement, expenses and improving productivity.

• Standard PC hardware is used for network workstations and servers, which provide a great deal of design flexibility, easy maintenance and cost efficiency.

• Common applications are network aware, which significantly help in user transition time when relocating to different network environments. Additionally, network licensing is substantially less expensive than that of stand-alone licensing.

• Through file sharing, users can easily transfer files to one another, in order to improve productivity. Shared file access allows multi-user access to user applications.

• With centralized data storage, LANs offer the ability to place shared data on a single server within a central location. Network backups are easier and more reliable because all data resides on one physical location. This reduces the cost incurred by loss of any data during system failure.

• LANs support a number of fault tolerance features, such as disk mirroring, disk-duplexing, disk striping with parity (RAID5) and UPS (Uninterrupted Power Supply). This improves reliability and minimizes network downtime.

• LANs offer centralized security, which allows control over access to the network and its resources. Depending on an organization's requirements, this functionality is customizable to help protect sensitive data from loss, destruction, theft, or unauthorized disclosure.

• Communication to other users is also provided through a messaging system. It is the basis for implementing sophisticated systems.

Types of LAN Configurations

There are two types of LANs configurations: client/server and peer-to-peer
Client/Server Configuration
In a client/server configuration, there are two separate types of systems: Those that provide resources (servers) and those that access resources (clients). Resources and security management is totally centralized. The software running on the servers is called a network operating system or NOS, which provides a network environment for server and client. Some servers work as dedicated servers, such as Novell's NetWare. Then, there are others that function as servers that run applications with its server function in the background, such as Windows NT Server.

Peer-to-Peer Configuration
In a peer-to-peer configuration, also known as a workgroup solution, systems both provide and receive services. Each workstation within the groups acts as a server. Resources and security management are maintained and handled at the individual system level. The software that provides services runs as a separate application or is integrated in the operating system.

LAN Software and Hardware

LAN components consist of software and hardware.

LAN Software
The LAN software includes the network operating system and all applications and data files.

• Network Operating System (NOS)

Runs on the server in a client/server configuration.

Turns the PC into a server.

• Client Software

Each workstation runs software that allows it to access the network and use its shared resources.

Core portion of the workstation's operating system.

• Application and Data Files

Central storage for data files that allow users to share data

LAN Hardware
The LAN hardware includes servers, workstations, shared peripherals, connection hardware, such as network adapters, cable plant and support hardware, such as bridges, switches, routers, and gateways. But, they also vary slightly by network operating system.

• Servers and Workstations

Optimized to run a network operating system, meaning multiple processors, redundant power supplies, heavy-duty cooling systems and more RAM and disk drive space.

Some configurations support RISC-based systems, minicomputers, and even mainframes as network systems.

• Shared Peripherals

Servers contain shared disk storage and peripherals, such as printers, modems and CD-ROMs.

• Connection Hardware

Each server and workstation has at least one network adapter called a network interface card (NIC).

Provides a physical connection between PC and the cable plant.

• Cable Plant

A communication path between servers and workstations.

• Support Hardware

Depending on network configuration, additional connection devices, such as bridges, routers, and gateways may be needed.

Connecting LANs As companies become more global and the desire to access remote information strengthens, the pressure to develop ways of connecting two or more LANs increases. The pressure results from the physical limitations of LANs, the common need for users in different locations to access resources, and the need to improve resource management and troubleshooting efforts. When linking networks, the decision criteria should be based on the organizational structure, the network management style, the flexibility and scalability requirements and a consistent interface. Keep in mind that the common definition of a LAN is a network that is contained within a building that consists of small, departmental LANs connected via some sort of backbone facility, a primary connectivity mechanism of a hierarchical distributed system. Within the building, multiple LAN segments can be required to support distance limitations, heavy traffic requirements and diverse computing platforms.