Introduction to Network Types

Sunday, June 28, 2009

One way to categorize the different types of computer network designs is by their scope or scale. For historical reasons, the networking industry refers to nearly every type of design as some kind of area network. Common examples of area network types are:

* LAN - Local Area Network
* WLAN - Wireless Local Area Network
* WAN - Wide Area Network
* MAN - Metropolitan Area Network
* SAN - Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network
* CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
* PAN - Personal Area Network
* DAN - Desk Area Network

LAN and WAN were the original categories of area networks, while the others have gradually emerged over many years of technology evolution.

Note that these network types are a separate concept from network topologies such as bus, ring and star.

LAN - Local Area Network

A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.

In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization. They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.

WAN - Wide Area Network

As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth.

A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.

A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.

LAN, WAN and Home Networking

Residences typically employ one LAN and connect to the Internet WAN via an Internet Service Provider (ISP) using a broadband modem. The ISP provides a WAN IP address to the modem, and all of the computers on the home network use LAN (so-called private) IP addresses. All computers on the home LAN can communicate directly with each other but must go through a central gateway, typically a broadband router, to reach the ISP.

Other Types of Area Networks

While LAN and WAN are by far the most popular network types mentioned, you may also commonly see references to these others:

* Wireless Local Area Network - a LAN based on WiFi wireless network technology
* Metropolitan Area Network - a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation.

* Campus Area Network - a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus.
* Storage Area Network - connects servers to data storage devices through a technology like Fibre Channel.
* System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network.


Free Computer Networking Books

Thursday, June 25, 2009

Numerous published books are available for free download on the Internet. However, relatively few quality free books exist that cover general computer networking topics. Follow the links below to browse the best free computer networking books online.

1. TCP/IP Tutorial and Technical Overview (2004)

At over 900 pages, this book is truly a comprehensive reference to the TCP/IP network protocol. It covers in detail the basics of IP addressing and subnets, ARP, DCHP and routing protocols. IBM has also refreshed this book in 2006 to keep current on the more recent developments in TCP/IP technology including IPv6, QoS and mobile IP. IBM provides this book for free in both HTML and PDF formats.

2. Introduction to Data Communications (1999-2000)

Author Eugene Blanchard completed this book based on his experience with the Linux operating system. The topics covered in this book are generally applicable across environments: OSI model, area networks, modems, and wired and wireless connections. This 500 page book (PDF, HTML) should satisfy the basic needs of anyone looking to get familiar with a wide range of network technologies.

3. Internetworking Technologies - An Engineering Perspective (2002)

This 165-page PDF book written by Dr. Rahul Banerjee is available online as a read-only (non-printable) document. It is designed for networking students, covering video, data compression, TCP/IP, routing, network management and security, and some Internet network programming topics.


Introduction to Peer to Peer Networks

Wednesday, June 24, 2009

Peer to peer is an approach to computer networking where all computers share equivalent responsibility for processing data. Peer-to-peer networking (also known simply as peer networking) differs from client-server networking, where certain devices have responsibility for providing or "serving" data and other devices consume or otherwise act as "clients" of those servers.

Characteristics of a Peer Network

Peer to peer networking is common on small local area networks (LANs), particularly home networks. Both wired and wireless home networks can be configured as peer to peer environments.

Computers in a peer to peer network run the same networking protocols and software. Peer networks are also often situated physically near to each other, typically in homes, small businesses or schools. Some peer networks, however, utilize the Internet and are geographically dispersed worldwide.

Home networks that utilize broadband routers are hybrid peer to peer and client-server environments. The router provides centralized Internet connection sharing, but file, printer and other resource sharing is managed directly between the local computers involved.

Peer to Peer and P2P Networks

Internet-based peer to peer networks emerged in the 1990s due to the development of P2P file sharing networks like Napster. Technically, many P2P networks (including the original Napster) are not pure peer networks but rather hybrid designs as they utilize central servers for some functions such as search.

Peer to Peer and Ad Hoc Wi-Fi Networks

Wi-Fi wireless networks support so-called ad hoc connections between devices. Ad hoc Wi-Fi networks are pure peer to peer compared to those utilizing wireless routers as an intermediate device.

Benefits of a Peer to Peer Network

You can configure computers in peer to peer workgroups to allow sharing of files, printers and other resources across all of the devices. Peer networks allow data to be shared easily in both directions, whether for downloads to your computer or uploads from your computer.

On the Internet, peer to peer networks handle a very high volume of file sharing traffic by distributing the load across many computers. Because they do not rely exclusively on central servers, P2P networks both scale better and are more resilient than client-server networks in case of failures or traffic bottlenecks.


Basic Computer Network Information

Monday, June 22, 2009


A network is a group of things that are connected together. In a computer network, the things that are connected are computers, of course. A computer network can be as small as two computers but there is no maximum size, and many networks have hundreds or thousands of computers.

There are three main reasons for connecting computers in a network:

1. Share information. This can be messages such as e-mail, or it can be files that are stored on one computer and used by someone at a different computer.

2. Share resources. A printer that can be accessed from different computer systems is a shared resource. So is an Internet connection used by more than one computer.

3. Centralized control. In most offices, the management determines what the computers may be used for and what kind of resources and support they need. This is much easier to deal with if the computers are connected.

Types of Networks

Just as there is no limit to the number of systems in a network, there is also no limit to the geographical size of a network. As a practical matter though, there are some structural differences between a network of computers all in the same room, and a network connecting computers in Los Angeles to ones in Sydney Australia.

The most common network includes computers that are close together, usually in the same building or office. This is called a Local Area Network, abbreviated LAN.

The computers in a LAN are usually connected with cable made up of pairs of wires, but faster (and more expensive) cables are made from glass fibers, called fiber optic cable. A network may even use radio waves, in which case it is a wireless LAN.

When the computers being connected are far apart, typically in different cities, it is called a WAN or Wide Area Network. The connection is usually done with special high-speed lines leased from the phone company, but it is also possible to connect over an ordinary phone line using a device called a modem. It’s slow, but possible. Accessing a network through a phone line and modem is called a dial-up connection.

The biggest of all networks is the Internet. The backbone of the Internet consists of powerful computers all over the world with high-speed connections between them. Individual computers such as yours then connect to this backbone through an Internet Service Provider or ISP.


Most LANs in existence today use a technology called Ethernet. In an Ethernet network, every piece of information put on the network is seen by every other computer on the network, and each computer must determine if that information is meant for itself.

To make this work, before the information goes out on the network it is first broken up into small pieces called packets, and each packet has added to it the address of the computer that should receive it. The part of the packet containing the address is called the header.


Packet diagram

Then, each computer looks at the address on each packet that comes by on the network cable, and copies the ones that have the right address. The computer that sent the packet is called the source, and the one that is supposed to receive it is called the destination.
Network Connections
When a packet comes out of the computer that originated it, that packet must have a complete electrical path to every other computer. The simplest way to do this is to have a cable that goes from one computer to the next until it has connected to each one. This is called a bus network.

Bus Network

A bus network is the simplest to explain and draw, but it’s not often the simplest one to use, especially if computers are distributed around various offices in a building, and then get added, taken away, moved around and so forth.

A much more practical way to connect more than a couple of systems is to connect each one to a device called a hub. Each system has a cable that goes from it to the hub, and inside the hub an electrical connection is made between all of the cables. Each place where a cable plugs into the hub is called a port.

5-port hub ports

To create larger networks, hubs can use one or more of their connections to connect to other hubs. This is called a star network, but as far as the electrical signals are concerned, they go from one computer to every other computer, no different than the bus network.

3-hub star network

When networks get really big, with 100s of systems or more, it’s no longer such a good idea to have each computer look at every packet, because almost none of the packets will be for that computer. The large network can be broken up into smaller groups called subnets, and these are connected with a device called a data switch, or just a switch.

Within each subnet, all of the computers still see every packet, and so does the switch. Normally the switch won’t pass those packets on to the other subnets, but if the packet has an address for a destination in another subnet, the switch will pass the packet to the port for that subnet. All of the systems in that subnet will then see the packet, including the system it is actually addressed to. In order to know where to send a packet, the switch must have a table of addresses for each subnet.

Switch with 4 subnets

The simplest form of a switch is called a bridge, and it connects just two subnets. A bridge only needs two ports then, one for each of the subnets.

Sometimes a network will be so big and complex that one switch isn’t enough to connect all of the subnets. In that case the subnet receiving a packet might be connected to a different switch than the subnet where the packet started. This is a more complicated problem, because the switch would need to know not only the packet’s destination, but also where to send it next to make sure it got there.

For this, a smarter device is needed, called a router. The router needs to know not only the subnet addresses, but also the best path, or route, to get from one to another.

Route path diagram

One place where routers are used in a big way is the Internet. If you send a message on the Internet, it might go through many routers before it reaches its destination. And when you surf to a website, all of the graphics and text showing up on your screen had to go through routers to find their way from the web site to your computer.

By the way, every LAN that connects to the Internet becomes a subnet of the Internet, even if it has its own internal subnets.

Clients and Servers

In addition to the various ways networked systems can be physically connected, there are two basic ways that network activities can be arranged. In one, all of the computers have equal status. This is called peer-to-peer, because a peer means someone (or something) that is the equal of another. Peer-to-peer is used mostly in very small networks of less than a dozen systems.

The more common arrangement is called client-server. One system, called the server, is responsible for a particular activity or resource. The other systems are called clients, and they go through the server when they want to use the function or resource that the server is responsible for.

Some of the things servers are commonly used for include network administration, e-mail, printers, file storage, and Internet access. Often several of these functions will be combined into one machine. There is no rule that says a network server and a print server can’t be the same system.
Clients Server

print server

There is also no rule that says a server must serve the entire network. It is usually convenient to have a separate network server for each subnet. There are other divisions that can occur even within a subnet. Computers that need to share the same resources can be organized into workgroups. With the Windows NT operating system, the LAN can be divided into sections called domains, and each domain needs its own server called a domain controller.


A protocol is an agreed-upon standard for how something will be done. When your mother taught you to chew with your mouth closed and keep your elbows off the table, that was a protocol for proper dining. Computer protocols are the rules for connecting with other computers and exchanging information with them.

Ethernet is a protocol. Earlier we called it a technology, but it is also a set of rules for how that technology is used. If each piece of hardware and software complies with the rules, then information can be correctly transferred from one from one system to another in a LAN.

There are many protocols used in networking. There are some protocols that are used together with other protocols, where each one takes care of different aspects of networking. Sometimes two protocols do the same thing in different ways, and it is necessary to choose one or the other. The important thing is that both systems trying to communicate with each other have matching protocols that they can use.


One very important set of protocols is called TCP/IP. It is important because it is what the creators of the Internet decided would be used for that particular network, which means that any computer that wants to connect to the Internet must also use TCP/IP. TCP/IP stands for Transmission Control Protocol / Internet Protocol.

TCP/IP is actually in two parts. The TCP portion covers the agreements between systems about how they will carry on their ‘conversation’, and the IP portion deals with addressing the packets and routing them.

The TCP part all happens in the background and we don’t really need to concern ourselves with it under normal circumstances. However, in a network that uses TCP/IP, every system must have a unique IP address, and that is something that requires human intervention in one way or another.

IP Addresses

An IP address is made up of four sets of numbers separated by periods. An example is:

Each of these sets of numbers is called an octet, because they started out as 8-digit binary numbers. By changing them into 3-digit decimal numbers, the whole address is shorter and easier to remember. The highest value for any octet is 255, because the highest number you can make with eight binary digits is equal to 255 in decimal.

In most networks, the first three octets are the same for all systems, and the last octet is different for every machine. If there are more than 255 computers in a network, it is usually divided into smaller subnets.

Static or Dynamic?

There are two ways to associate a unique IP address to a specific computer. One way is for the administrator to assign a number, which stays the same unless somebody decides to change it some day. That number is then a static IP address.

The other way is to assign a group of addresses to a server, and let the server hand them out as needed to any system that wants to communicate on the network. This produces a dynamic IP address. It is sometimes important to know which method is in use on a network, because with dynamic addressing, the IP address of a machine may be different each time you try to communicate with it.

Computer Names

The example address is only one digit longer than a phone number with area code, but that’s plenty long enough to give most of us a hard time. It’s much easier for people to remember a name instead of a number, and for this reason computers in a network are also given a unique name. It may be something mundane like Sales14, but at least it’s a name and not a number.

This is not only easier to remember, but it solves the problem of a dynamic address that changes all the time, because the computer name doesn’t normally change. It does create another problem though, because the computers use only the addresses and not the names to keep track of each other. Fortunately there is a part of the TCP/IP protocol called address resolution, and it matches up the names and addresses so things keep rolling smoothly along.


The problem with connecting computers to the Internet is that they are then sharing a network with many other computers from all over the world, and the users of some of those other computers are not such nice folks. Protecting the network and the information on it is one of the most important parts of a network administrator’s job.


One way to protect information is to scramble it so that it appears to be gibberish unless someone has the right ‘key’ to unscramble it. Scrambling it is called encryption, and unscrambling it is called decryption. There are many ways to encrypt information, and of course just as many keys to decrypt it.

Encrypting and decrypting information slows things down a bit, so a decision must be made about when to use it. For packets going around the LAN, it depends on how likely it is that someone will gain unauthorized access to the LAN, called hacking. It also depends on how much damage would be done if that happened. If the threat is severe, encryption can be done not only on the transmitted packets but also to information stored on the disk drive.

For information going over the Internet, encryption is much more important unless it’s all right for the whole world to see the information. If you send your credit card number to a vendor, you must trust that vendor to encrypt and safeguard the information.

Virus Software

A computer virus is a little program that makes copies of itself to send to other computers. It’s very similar in some ways to contagious germs spreading a disease from one person to the next. And like diseases, some of these computer viruses have some really nasty side effects, like wiping out important files in the operating system or filling up the hard drive with garbage data.

As we will discuss a little later, there are ways to keep these virus programs from getting to your computer, but they are not foolproof. A lot of viruses come in attached to e-mail, and then they will mail copies of themselves to everyone in your e-mail address folder. You can’t completely block them without blocking e-mail, and most of us like to get e-mail from our friends and coworkers.

The most important prevention for viruses is to have a good anti-virus program installed on your computer. Norton, McCaffey and Panda are probably the most popular. The next most important thing is to keep the anti-virus software up-to-date, because the delinquents who write virus software are always coming up with new tricks, and the anti-virus companies are just as quickly coming up with new versions to stop them.

Access Control

If you have ever had a computer that was connected to a local area network, you almost certainly had to type in a user name and password to get network access. It’s two forms of ID, just like when you cash a check at department store.

The network administrator used that identification information to determine what you could and couldn’t do on the network. And there may have been additional passwords to access the company’ customer database, employee payroll records, or files stored on someone else’s computer.

Here are a few tips about passwords:

1. First, if you share files on your computer, use password protection for them even if they are available to everyone in the network. That way they can’t be tampered with if a hacker breaks in.

2. In choosing a password, never use your name, your birthday or other obvious personal information. The best is a random combination of letters and numbers.

3. Commit the password to memory, and if you must write it down, hide it. A password written on a post-it note stuck to your monitor is probably worse than no password at all.

4. Don’t give your password to someone you don’t know personally just because they claim to be tech support, the phone company, the police or your long-lost Aunt Matilda. Refer them to the network administrator, or better yet, get their phone number and have the network administrator call them back.


In a building, a firewall is a wall to keep fire from spreading from one area to another. In a computer network, a firewall is a boundary that can block unwanted data packets. The firewall may be program running on the server or router, or it may be a separate piece of hardware or even a complete computer system just for that purpose. In any case, its purpose is to look at all of the packets coming through, and decide which ones can pass and which ones get blocked.

Ports – Several pages ago, we defined a port as the place in a hub that a cable plugs into. There is another completely different kind of thing called a port, and that is a location in a computer’s memory that is used by a device or application to send and receive data. Each application will have one (or more) of these locations for its own use.

For instance, there is a common e-mail program that has port # 110, which means that the program exchanges information with the rest of the system at memory location 110. The popular game called Doom uses port # 666.

When a packet is sent over a network, it will contain not only the destination address, but also the port number of the application that will use it at that destination. One of the ways a firewall controls the packets is by looking at the port number, and only passing packets with ports that are appropriate for the destination. If nobody should be playing Doom on the network’s computers, then it would make sense to block port 666.

Another way a firewall can control traffic is to look at the source of the packet. It can have a ‘prohibited’ list that keeps out packets from certain IP addresses, or it can have an ‘allowed’ list and block everyone who isn’t on it. Ports can be done the same way, with a ‘prohibited’ or ‘allowed’ list of ports.


There is much more to know about security, and about networks in general, if one is to be involved in managing them. The purpose of this paper is to present just enough information to enable you talk with network administrators and to understand their concerns when presenting network products to them. For additional training in this subject, we recommend the Micro2000 A+ and Network+ courses.


WWW - World Wide Web

Definition: The term WWW refers to the World Wide Web or simply the Web. The World Wide Web consists of all the public Web sites connected to the Internet worldwide, including the client devices (such as computers and cell phones) that access Web content. The WWW is just one of many applications of the Internet and computer networks.

The World Web is based on these technologies:

* HTML - Hypertext Markup Language
* HTTP - Hypertext Transfer Protocol
* Web servers and Web browsers

Researcher Tim Berners-Lee led the development of the original World Wide Web in the late 1980s and early 1990s. He helped build prototypes of the above Web technologies and coined the term WWW. Web sites and Web browsing exploded in popularity during the mid-1990s.
Also Known As: World Wide Web, The Web


Fundamental Computer Networks Concepts

In the world of computers, networking is the practice of linking two or more computing devices together for the purpose of sharing data. Networks are built with a combination of computer hardware and computer software. Some explanations of networking found in books and tutorials are highly technical, designed for students and professionals, while others are geared more to home and business uses of computer networks.

* What Is Computer Networking?
* What Is Wireless Networking?
* World Wide Web (WWW)

* Client-Server Networks
* Peer-to-Peer Networks
* Free Computer Networking Books for Students


Computer and Wireless Networking Basics

These pages review the types of designs, equipment, protocols and other technologies essential to building computer networks. You will learn how home and other private networks, public hotspots and the Internet function.

1. Fundamental Computer Networks Concepts
2. Types of Computer Networks
3. Types of Network Equipment
4. Ethernet

5. Wireless Local Area Networks
6. Internet Service
7. TCP/IP and Other Internet Protocols
8. Network Routing, Switching and Bridging


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