Networking Basics
Network Defined
According to the Security Portal Glossary, a network is "two or more machines, interconnected for the purpose of data transfer".
Note that what is transferred is "data." So something as simple as jump-starting your car can't count as networking. Nonetheless, you probably have a network in your home. If you have a printer, a scanner, or any other external computing device, you are the proud owner of a very rudimentary network.
In the security industry, however, the word network usually refers to a larger group of machines, composed of anywhere from five computers to a hundred computers - or countless computers, in the case of the Internet.
So, why have a network to begin with?
The Purpose of a Network
Networking is more than one-way data transfer between a couple of machines. Networking is all about sharing data and information resources. It's about communicating quickly and efficiently. It's about cooperation and collaboration. It's about safe distribution of sensitive data.
Essentially, networking is about getting all the bang for your buck out of the computing resources available to you and your work group.
The fact that you are reading this page means that you are connected to a network. When an Internet access subscriber dials up with a modem and connects to their ISP (Internet Service Provider), they are connecting to a network -- the Internet. The same goes for DSL and Cable modems.
Types of Networks
There are several ways to classify networks. Here's a brief overview of three important distinguishing methods.
Wiring Structure
At a very basic level, the purpose of a network affects how it is wired. We won't go into that too much here, but for what it's worth, here are the three basic wiring configurations. Skip this section if you figure you won't ever need to know about network wiring structures. You're probably right.
Bus Structure
Picture a network wire acting like a two-way city bus route. Packets of information (the passengers) get on at one computer, and get off at some stop down the road. The cable isn't routed through each computer -- it's routed past it, but all the computers connect to the same route to share their information. Unlike most real bus routes, however, a bus network doesn't go in a circle. The network terminates on each end.
Star Structure
Picture a star with a hub at the center, like a wheel. The hub connects all the points of the star (the computers). In networking language, the official term for that hub is just that: a hub. If one computer wants to send information to another computer, it communicates through the hub.
Ring Structure
This is probably the simplest network structure to imagine. Picture a ring of computers holding hands (how cute). Their arms are the wires. Information going from one computer to another passes through all the computers in between. But the information only travels in one direction around the ring.
Hybrid
A hybrid network is a combination of two or more other types of networks. For example, the Internet is a hybrid network. It is composed of small (and not so small) networks connected by high-capacity wires and satellites.
Proximity
We may also classify a network as a WAN or a LAN. WAN stands for Wide Area Network. LAN stands for Local Area Network.
A Wide Area Network is just a network spread over a wide area. The Internet is the mother of all Wide Area Networks.
A Local Area Network is smaller and more proximate. A network in an office is a perfect example of a Local Area Network.
Relationship
The two basic network relationships are client/server and peer-to-peer.
In a client/server network relationship, a server computer serves one or more client computers. Typically, a server serves programs and other files. Technically speaking, though, any computer that serves can be called a server.
In a peer-to-peer network, a server is not needed. The networked computers share resources as peers.
In reality, few networks are one or the other. Most networks (and especially the Internet) combine peer-to-peer flexibility with client/server efficiency.
Network Hardware
So what hardware makes a network a network? Here's a quick rundown:
Clients
The client is the computer being served. Most any computer connected to a network is a client.
Servers
The main differences you'll notice immediately between a client computer and a server computer will probably be the size of the boxes and the software they are running. A server is usually bigger than a desktop computer because it is upgraded more, and upgrades take room. Also, servers run special software.
Storage Devices
Because sharing information is the work of networking, storage of information is important. Internet servers store large amounts of data on their storage devices -- usually hard disks, but in some cases laser-discs, tape drives, or other media.
External Devices
Printers are the classic example of external devices. Office networks also often make use of scanners, and, depending on the business behind the network, many other devices as well. In the manufacturing industries, networks are used extensively to remotely control amazingly complex machines.
Network Interface Cards
The network interface card (NIC) is where the wires from the network plug into your machine. It governs how data is communicated to and from the network.
Mediums of Transmission (wires)
The size and type of a network cable affects its capacity for data. As a general rule, the bigger the cable, the greater the bandwidth. Data can be transmitted by satellite and radio waves as well, but think of bandwidth as how much information a network can push through a wire during a given period of time. Here are a few common bandwidth terms you'll hear floating around:
bps
Bits per second (a bit is the smallest chunk of data stored on a computer).
Kbps
Kilobits per second (kilo=1000, but a KBit is actually 1024 bits, or 2 to the 10th power, because computers operate on a base 2 number system instead of base ten, the system people use.)
Mbps
Megabits per second (Kilobits squared per second)
T1
Up to 1.5 Mbps
T3
Up to 44.7 Mbps
OC3
Up to 155.5 Mbps (Fiber Optics, Internet Backbone)
Hubs
A hub, as mentioned earlier, is a central point where all the computers in a network connect. Most networks have a hub of some sort.
Repeaters
A repeater sits on a line, takes data, and retransmits it. This keeps the signal strong the whole length of the wire. The weakening of a signal over a long distance is called attenuation.
Bridges
A bridge connects two networks. It allows similar networks to communicate.
Routers
A router acts like a traffic cop standing in an intersection -- it routes information to where it needs to go. Some routers are more intelligent than others. A good router can even make detours on the fly.
Gateways
A gateway is used to link dissimilar networks together. A Mac network and a PC network must be linked by a gateway computer. An ISP links its modem users to the Internet via a gateway.
Modems
A modem translates data to and from a network, using a format that enables transmission over telephone lines.
Network Software
There are countless software packages designed for use on networks. Here are a few very general categories of software:
Operating Systems
An operating system runs on every computer. Common operating systems for client computers are Linux, Microsoft Windows, and MacOS. Common operating systems for servers are UNIX, Linux, Windows, and to some degree MacOS.
Server Software
Each of the above-mentioned operating systems offers special software for servers. This software controls exactly how and with whom the network's resources are shared. A server might have Web server software or email server software, for example.
Client Software
Web Browsers and E-mail programs are examples of client software.
Security Software
Firewalls are the most common security software. They protect a network or part of a network from unwanted intrusion. Firewalls are crucial for large networks.
Even home users, especially those with DSL or cable modems, should consider purchasing a firewall to protect their data and to prevent their computers from being used for illegal purposes without their knowledge.
Other types of security measures include data encryption and user authentication. All of these solutions require special software.
How Networks Communicate
Imagine traffic in downtown Seattle, New York, or LA. Now imagine no street signs. Imagine no lines on the roads, and no traffic signals of any kind. Imagine no traffic laws. Absolute chaos. That's how networks would be if they didn't have protocols.
The word protocol has been around a lot longer than computers have. When networking was born, protocol became a household word. According to Webster, one non-technical definition of a protocol is "a code prescribing strict adherence to correct etiquette and precedence."
And that's exactly what a protocol does for networking as well. It is a set of rules and standards that governs the transmission of data. Here are a few common protocols:
TCP (Transmission Control Protocol)
The information packet-level protocol of the Internet
IP (Internet Protocol)
The address-level protocol of the Internet.
HTTP (Hypertext Transfer Protocol)
The protocol used to serve web pages.
FTP (File Transfer Protocol)
The protocol used on Internet file servers.
The Internet as a Network
History
The Internet began as a research project of the United States military. In the late 60s, a network was designed that could withstand nuclear attack.
Imagine if all the sensitive data belonging to the military were stored in one location. One nuclear missile could knock it all out.
But what if that information were spread out across the entire country, and mirrored at various locations? If one site were knocked out, the data would still be available.
Although it was purely governmental to begin with (.gov), the Internet gradually expanded to include educational institutions (.edu), and then exploded across the corporate world (.com, .net) and around the globe (.ca, .es, .uk, etc.).
Standards
Various organizations have taken it upon themselves to establish Internet standards. Here are a few:
World Wide Web Consortium
Internet Engineering Task Force
European Computer Manufacturers Association
These groups define the specifications for protocols, markup languages, and security measures on the Web. The specifications themselves are by no means easy reading, but it's good to be aware that somewhere, someone is writing traffic laws for the information superhighway.
[ Comment, Edit or Article Submission ]
