19.03.2009

Networks 101: What is a Network?

Written on: 
April 22, 2003
Written by: 
Tom Jelen

You have probably heard of a computer network. Maybe you even have one (perhaps you've heard people say, "No e-mail today -- the network's down" or "No Internet today - the router isn't working"). Maybe you need one (you often hear people say, "Can you turn the printer switch to letter 'D'" or, "Can you pass me that disk"). Whatever your needs, you may be wondering, "What exactly is a network?"

In the simplest terms, a network consists of two or more computers that are connected together to share information. All networking, no matter how complex, builds off this simple system. Though this may seem like a basic idea, the concept was a major achievement in communications.

What Makes Up a Network?

A network typically includes four things (besides the computers themselves):

Protocol:
a set of communication rules to make sure that everyone speaks the same language
Network interface cards (NICs):
cards that plugs into the back (or side) of your computers and lets them send and receive messages from other computers
Cable:
the medium to connect all of the computers together
Hub:
hardware to perform traffic control

Note: The key word is "typically." Wireless networks obviously don't use cables and NICs aren't necessary for small networks that use parallel/serial ports. Some networks use switches, rather than hubs, to control the network. But the basics still apply.)

How Does a Network Work?

How does one computer send information to another? It is rather simple. The diagram below shows a simple network:

Simple Network Diagram

If Computer A wants to send a file to Computer B, the following would take place:

  1. Based on a protocol that both computers use, the NIC in Computer A translates the file (which consists of binary data -- 1's and 0's) into pulses of electricity.
  2. The pulses of electricity pass through the cable with a minimum (hopefully) of resistance.
  3. The hub takes in the electric pulses and shoots them out to all of the other cables.
  4. Computer B's NIC interprets the pulses and decides if the message is for it or not. In this case, it is, so Computer B's NIC translates the pulses back into the 1's and 0's that make up the file.

Sounds easy. However, if anything untoward happens along the way, you have a problem, not a network. So, if Computer A sends the message to the network using NetBEUI, a Microsoft protocol, but Computer B only understands the TCP/ IP protocol, it will not understand the message, no matter how many times Computer A sends it. Computer B also won't get the message if the cable is getting interference from the fluorescent lights, or if the network card has decided not to turn on today, etc.

Network Classification

Like snowflakes, no two networks are alike. So for the sake of discussion, it helps to classify them by some general characteristics. A given network can be characterized by its:

Size:
the geographic size of the network
Security and access:
who can access the network and how access is controlled
Protocol:
the rules of communication in use on it (for example, TCP/IP, NetBEUI, or AppleTalk)
Hardware:
the types of physical links and hardware that connect the network

Size (LANs and WANs): regarding size, networks are generally lumped into two categories, local area networks (LANs) and wide area networks (WANs)

A LAN is primarily defined by geography, and is typically housed in one building or campus. A WAN, on the other hand, is a network that joins many LANs together using super special, highly secret, WAN technologies, but we will delve into that arena some other day. Hopefully you're still reading. Because they are so common, LANs are usually further divided into two major types:

Peer-to-peer:
A peer-to-peer network doesn't have any dedicated servers or hierarchy among the computers. All of the computers on the network handle security and administration for themselves. The users must make the decisions about who gets access to what. For more information, see article Networking 101: Peer-to-Peer Networks .
Client-server:
A client-server network works the same way as a peer-to-peer network except that there is at least one computer that is dedicated as a server. The server stores files for sharing, controls access to the printer, and generally acts as the dictator of the network. For more information, see article Networking 101: Client-Server Networks .

Protocol

As stated above, the protocol of a network is the set of guidelines for inter-computer communication. Two computers with different protocols won't be able to communicate with one another (imagine Ralph Nader and Pat Buchanan in the same room). While many computers have the ability to interpret multiple protocols, it is important to understand the different protocols available before deciding on one that is appropriate for your network.

Hardware

While some theoretically-minded people would claim that the hardware involved in a network isn't extremely important, they probably haven't ever actually dealt with setting one up. Hardware is important. While in theory, every hub or switch should send and receive signals perfectly, that isn't always the case. And the problem is that if you ask two network administrators what hub they recommend, you will probably get two entirely different, yet passionate answers. From picking the cable (optical fiber, coaxial, or copper), to choosing a server, you should find the most suitable hardware for your needs.