What is a Network?

A network consists of two or more computers that are linked in order to share resources (such as printers and CDs), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, wireless connection, satellites, or infrared light beams.

Computer networks have been around for a long time, and several technologies have been developed to enable computers to communicate. One of the most successful is a technology called Ethernet, invented at the Xerox Palo Alto Research Center (PARC) by Bob Metcalfe in 1973 and and the company patented it in 1975. Metcalfe and others then finalized an open Ethernet standard in 1980, and by 1985 it had become an IEEE standard. An industry was born, and Ethernet was ready for its meteoric rise. IEEE’s 802.3 committee produced the first Ethernet standard. Xerox never produced Ethernet commercially but other companies did.

Ethernet lets computers on a Local Area Network (LAN), such as in an office building, connect to one another and to other network resources, such as servers.

There are many types of computer networks, including the following:

• local-area networks (LANs): The computers are geographically close together (that is, in the same building).
  
• wide-area networks (WANs): The computers are farther apart and are connected by telephone lines or radio waves.
  
• campus-area networks (CANs): The computers are within a limited geographic area, such as a campus or military base.
  
• metropolitan-area networks (MANs): A data network designed for a town or city.
  
• home-area networks (HANs): A network contained within a user's home that connects a person's digital devices.
  

Network Characteristics

In addition to these types, the following characteristics are also used to categorize different types of networks:

• Topology : The geometric arrangement of a computer system. Common topologies include a bus, star, and ring.
  
  
• Protocol : The protocol defines a common set of rules and signals that computers on the network use to communicate. One of the most popular protocols for LANs is called Ethernet. Another popular LAN protocol for PCs is the IBM token-ring network .
  
  
• Architecture : Networks can be broadly classified as using either a peer-to-peer or client/server architecture.
  

_{Network Topology diagram.}






Local Area Network

A Local Area Network (LAN) is a network that is confined to a relatively small area. It is generally limited to a geographic area such as a writing lab, school, or building. LANs can include network connection devices, such as switches and routers, and are also characterized by their relatively high data transmission rates and their ability to function without the need for outside service providers.


_{A typical small LAN.}

In the early 1980s, the three major local area networks were Ethernet (IEEE standard 802.3), Token Ring (802.5 and used extensively by IBM), and Token Bus (802.4, intended for manufacturing plants). However, over the years, Ethernet  has become the most popular wired local area network standard. While maintaining a low cost, it has gone through six versions, most ten times faster than the previous version (10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps, 40 Gbps, 100 Gbps, and in the works 400 Gbps).

Virtually all of the wired LANs installed today use a technology known as Ethernet or, more precisely, IEEE 802.3. There are several other antiquated LAN technologies, including Token ring and FDDI, that are no longer are no longer available on the market, but that you might conceivably encounter in older installations.

Computers connected to a network are broadly categorized as servers or workstations. Servers are generally not used by humans directly, but rather run continuously to provide "services" to the other computers (and their human users) on the network. Services provided can include printing and faxing, software hosting, file storage and sharing, messaging, data storage and retrieval, complete access control (security) for the network's resources, and many others.

Workstations are called such because they typically do have a human user which interacts with the network through them. Workstations were traditionally considered a desktop, consisting of a computer, keyboard, display, and mouse, or a laptop, with with integrated keyboard, display, and touchpad. With the advent of the tablet computer, and the touch screen devices such as iPad and iPhone, our definition of workstation is quickly evolving to include those devices, because of their ability to interact with the network and utilize network services.

Servers tend to be more powerful than workstations, although configurations are guided by needs. The size and speed of the server's processor(s), hard drive, and main memory might add dramatically to the cost of the system. On the other hand, a workstation might not need as much storage or working memory, but might require an expensive display to accommodate the needs of its user.

Devices connected to a LAN, such as computers or printers, are generically referred to as nodes. Computers and devices that allocate resources for a network are called servers.

On a single LAN, computers and servers may be connected by cables or wirelessly. Wireless access to a wired network is made possible by wireless access points (WAPs). These WAP devices provide a bridge between computers and networks. A typical WAP might have the theoretical capacity to connect hundreds or even thousands of wireless users to a network, although practical capacity might be far less.

Nearly always servers will be connected by cables to the network, because the cable connections remain the fastest. Workstations which are stationary (desktops) are also usually connected by a cable to the network, although the cost of wireless adapters has dropped to the point that, when installing workstations in an existing facility with inadequate wiring, it can be easier and less expensive to use wireless for a desktop.






Wide Area Network

A wide area network (WAN) is a geographically distributed private telecommunications network that interconnects multiple local area networks (LANs). WAN can be private to connect parts of a business or they can be more public to connect smaller networks together.

Wide Area Networks (WANs) connect networks in larger geographic areas, such as Florida, the United States, or the world. Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of global network.

Typically, a router or other multifunction device is used to connect a LAN to a WAN.



Using a WAN, schools in Florida can communicate with places like Tokyo in a matter of seconds, without paying enormous phone bills. Two users a half-world apart with workstations equipped with microphones and a webcams might teleconference in real time. A WAN is complicated. It uses multiplexers, bridges, and routers to connect local and metropolitan networks to global communications networks like the Internet. To users, however, a WAN will not appear to be much different than a LAN.

The easiest way to understand what a WAN is to think of the internet as a whole, which is the world's largest WAN. The internet is a WAN because, through the use of ISPs, it connects lots of smaller local area networks (LANs) or metro area networks (MANs).

No matter what the WAN joins together or how far apart the networks are, the end result is always intended to allow different smaller networks from different locations to communicate with one another.




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