What is a Network?
A network is a group or system that interconnects components together. A network of retail stores, for example, implies some sort of relationship between the stores. A railroad network suggests that the tracks interconnect at different points. And a computer network interconnects computers.
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By far the most famous computer network in the world is the Internet. The Internet is, in fact, a collection of smaller networks that are interconnected together – a network of networks if you can imagine that.
But computer networks don’t necessarily have to be large or complex. By definition, the smallest possible computer network would include just two interconnected computers. The interconnection can be achieved using a cable or by wireless technology. Whatever the medium, as long as the computers can communicate together they are part of a network.
Local Area Networks (LAN)
Surprisingly, the Information Technology industry doesn’t define networks by size, rather, by location. Computers that are interconnected in a small geographical location such as a home or an office are said to be in a LAN (Local Area Network). A LAN can have two computers or two thousand computers.
Wide Area Networks (WAN)
Conversely, computers that are connected across a wide geographical area such as between cities or countries are said to be in a WAN (Wide Area Network). Strictly speaking a WAN actually interconnects LANs. Five computers in a New York office are in a LAN, however, the New York office also connects to an Office in Chicago who hosts ten other computers. All together, that network is said to be a WAN spanning New York to Chicago. But individually each office is a LAN in its own right. One LAN in New York and one LAN in Chicago. This is why we say that strictly speaking a WAN interconnects LANs.
Network Topologies
A description of how the network is wired together can be provided using a physical network topology. Network topologies are used to describe the different ways to connect computers together. A bus topology, for example, describes computers connected across a common wire in a linear fashion. A star topology describes computers connected to a common central device such as a switch. Other types of common topologies include ring topology as well as mesh and partial mesh topology.
Figure 1. A Computer Network
Common Network Equipment Vendors
Today, there are a number of network equipment vendors including Cisco Systems, Alcatel, Juniper, Netgear, 3Com and HP
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Network Protocols
But possibly the most important critical functions of a computer network are the protocols. A protocol is a set of rules. In order to communicate correctly, computers must talk the same protocol so that they understand what is being received and know how to send information in return. The IT industry has successfully established TCP/IP as the dominant network protocol across the world. The standardization of TCP/IP in computers has allowed the internet to thrive because is provides a common language that computers can use to communicate with each other.
The following network diagram is an example of an OSPF (network protocol) design.
