Introduction to Networking

Introduction to Networking

In this day and age, networks are everywhere. The Internet has also revolutionized not only the computer world, but the lives of millions in a variety of ways even in the "real world". We tend to take for granted that computers should be connected together. In fact, these days, whenever I have two computers in the same room, I have a difficult time not connecting them together!

it's hard to believe that the field is still a relatively young one, especially when it comes to hooking up small computers like PCs. In approaching any discussion of networking, it is very useful to take a step back and look at networking from a high level. What is it, exactly, and why is it now considered so important that it is assumed that most PCs

and other devices should be networked?

In this section, I provide a quick introduction to networking, discussing what it is all about in general terms. I begin by defining networking in the most general terms. I then place networking in an overall context by describing some of its advantages and benefits, as well as some of its disadvantages and costs.

The Advantages (Benefits) of Networking

You have undoubtedly heard the "the whole is greater than the sum of its parts". This phrase describes networking very well, and explains why it has become so popular. A network isn't just a bunch of computers with wires running between them. Properly implemented, a network is a system that provides its users with unique capabilities, above and beyond what the individual machines and their software applications can provide.

Most of the benefits of networking can be divided into two generic categories: connectivity and sharing. Networks allow computers, and hence their users, to be connected together. They also allow for the easy sharing of information and resources, and cooperation between the devices in other ways. Since modern business depends so much on the intelligent flow and management of information, this tells you a lot about why networking is so valuable.

Here, in no particular order, are some of the specific advantages generally associated with networking:

• Connectivity and Communication: Networks connect computers and the users of those computers. Individuals within a building or work group can be connected into local area networks (LANs); LANs in distant locations can be interconnected into larger wide area networks (WANs). Once connected, it is possible for network users to communicate with each other using technologies such as electronic mail. This makes the transmission of business (or non-business) information easier, more efficient and less expensive than it would be without the network.
  
• Data Sharing: One of the most important uses of networking is to allow the sharing of data. Before networking was common, an accounting employee who wanted to prepare a report for her manager would have to produce it on his PC, put it on a floppy disk, and then walk it over to the manager, who would transfer the data to her PC's hard disk. (This sort of "shoe-based network" was sometimes sarcastically called a "sneakernet".)
  
  True networking allows thousands of employees to share data much more easily and quickly than this. More so, it makes possible applications that rely on the ability of many people to access and share the same data, such as databases, group software development, and much more. Intranets and extranets can be used to distribute corporate information between sites and to business partners.
  
• Hardware Sharing: Networks facilitate the sharing of hardware devices. For example, instead of giving each of 10 employees in a department an expensive color printer (or resorting to the "sneakernet" again), one printer can be placed on the network for everyone to share.
  
• Internet Access: The Internet is itself an enormous network, so whenever you access the Internet, you are using a network. The significance of the Internet on modern society is hard to exaggerate, especially for those of us in technical fields.
  
• Internet Access Sharing: Small computer networks allow multiple users to share a single Internet connection. Special hardware devices allow the bandwidth of the connection to be easily allocated to various individuals as they need it, and permit an organization to purchase one high-speed connection instead of many slower ones.
  
• Data Security and Management: In a business environment, a network allows the administrators to much better manage the company's critical data. Instead of having this data spread over dozens or even hundreds of small computers in a haphazard fashion as their users create it, data can be centralized on shared servers. This makes it easy for everyone to find the data, makes it possible for the administrators to ensure that the data is regularly backed up, and also allows for the implementation of security measures to control who can read or change various pieces of critical information.
  
• Performance Enhancement and Balancing: Under some circumstances, a network can be used to enhance the overall performance of some applications by distributing the computation tasks to various computers on the network.
  
• Entertainment: Networks facilitate many types of games and entertainment. The Internet itself offers many sources of entertainment, of course. In addition, many multi-player games exist that operate over a local area network. Many home networks are set up for this reason, and gaming across wide area networks (including the Internet) has also become quite popular. Of course, if you are running a business and have easily-amused employees, you might insist that this is really a disadvantage of networking and not an advantage!
  

The Disadvantages (Costs) of Networking

Now that I have portrayed the great value and many useful benefits of networking, I must bring you crashing back to earth with that old nemesis of the realistic: TANSTAAFL. For those who are not Heinlein fans, this acronym stands for "There Ain't No Such Thing As A Free Lunch". Even though networking really does represent a "whole that is greater than the sum of its parts", it does have some real and significant costs and drawbacks associated with it.

Here are a few of the items that balance against the advantages of networking.

• Network Hardware, Software and Setup Costs: Computers don't just magically network themselves, of course. Setting up a network requires an investment in hardware and software, as well as funds for planning, designing and implementing the network. For a home with a small network of two or three PCs, this is relatively inexpensive, possibly amounting to less than a hundred dollars with today's low prices for network hardware, and operating systems already designed for networks. For a large company, cost can easily run into tens of thousands of dollars—or more.
  
• Hardware and Software Management and Administration Costs: In all but the smallest of implementations, ongoing maintenance and management of the network requires the care and attention of an IT professional. In a smaller organization that already has a system administrator, a network may fall within this person's job responsibilities, but it will take time away from other tasks. In more substantial organizations, a network administrator may need to be hired, and in large companies an entire department may be necessary.
  
• Undesirable Sharing: With the good comes the bad; while networking allows the easy sharing of useful information, it also allows the sharing of undesirable data. One significant "sharing problem" in this regard has to do with viruses, which are easily spread over networks and the Internet. Mitigating these effects costs more time, money and administrative effort.
  
• Illegal or Undesirable Behavior: Similar to the point above, networking facilitates useful connectivity and communication, but also brings difficulties with it. Typical problems include abuse of company resources, distractions that reduce productivity, downloading of illegal or illicit materials, and even software piracy. In larger organizations, these issues must be managed through explicit policies and monitoring, which again, further increases management costs.
  
• Data Security Concerns: If a network is implemented properly, it is possible to greatly improve the security of important data. In contrast, a poorly-secured network puts critical data at risk, exposing it to the potential problems associated with hackers, unauthorized access and even sabotage.
  

Most of these costs and potential problems can be managed; that's a big part of the job of those who set up and run networks. In the end, as with any other decision, whether to network or not is a matter of weighing the advantages against the disadvantages. Of course today, nearly everyone decides that networking is worthwhile.

 

Fundamental Network Characteristics

There are many different kinds of networks, and network technologies used to create them. The proliferation of networking methods has generally occurred for a very good reason: different needs require different solutions. The drawback of this is that there are so many different types of protocols and technologies for the networking student to understand! Before you can really compare these approaches, you need to understand some of the basic characteristics that make networks what they are. While network types may be quite dissimilar, they are often described and even contrasted on the basis of a number of common attributes.

In this section, I introduce and discuss a number of key networking concepts that describe and differentiate different types of networks and networking technologies. I also introduce and define a number of terms and "buzzwords" that you cannot avoid if you are going to learn about networks. The topics here include explanations of protocols, switching methods, types of network messages, message formatting, and ways of addressing messages. I also discuss the differences between client-server and peer-to-peer networking.

 

Networking Layers, Models and Architectures

One of the reasons why many people find networking difficult to learn is that it can be a very complicated subject. One of the chief reasons for this complexity is that networks consist of so many hardware and software elements. While a network user may only perceive that he or she is using one computer program (like a Web browser) and one piece of hardware (like a PC), these are only parts of a much larger puzzle. In order for even the simplest task to be accomplished on a network, dozens of different components must cooperate, passing control information and data to accomplish the overall goal of network communication.

The best way to understand any complex system is to break it down into pieces and then analyze what they do and how they interact. The most logical approach for this is to divide the overall set of functions into modular components, each of which is responsible for a particular function. At the same time, we also need to define interfaces between these components, which describe how they fit together. This enables us to simplify the complexity of networking by approaching it in digestible chunks.

Networking Layers

Networking technologies are most often compartmentalized in this manner by dividing their functions into layers, each of which contains hardware and/or software elements. Each layer is responsible for performing a particular type of task, as well as interacting with the layers above it and below it. Layers are conceptually arranged into a vertical stack. Lower layers are charged with more concrete tasks such as hardware signaling and low-level communication; they provide services to the higher layers. The higher layers in turn use these services to implement more abstract functions such as implementing user applications.

Dividing networks into layers this way is somewhat like the division of labor in a manufacturing facility, and yields similar benefits. Each hardware device or software program can be specialized to perform the function needed by that layer, like a well-trained specialist on an assembly line. The different modules can be combined in different ways as needed. Understanding how a network functions overall is also made much easier this way.

 

Networking Models

One other important benefit of layering is that it makes it possible for technologies defined by different groups to interoperate. For this to be possible, it is necessary for everyone to agree on how layers will be defined and used. The most common tool for this purpose is a networking model. The model describes what the different layers are in the network, what each is responsible for doing, and how they interact. A universally-accepted model ensures that everyone is on the same page when creating hardware and software.

The most common general model in use today is the Open Systems Interconnection (OSI) Reference Model, which concepts of seven stacked layers. These range from the Physical Layer (layer one) at the bottom, which is responsible for low-level signaling, to the Application Layer (layer seven) at the top, where application software is implemented. Understanding the OSI model is essential to understanding networking as a whole. I explain models and layers in more detail, as well as providing a complete description of the OSI Reference Model, in its own dedicated section.

 

Networking Architectures

Closely related to the concept of a model is that of an architecture. An architecture is essentially a set of rules that describes the function of some portion of the hardware and software that constitute a stack of layers. Such a rule-set usually takes the form of a specification or standard that describes how equipment and programs using the technology must behave. A networking architecture is designed to implement the functions associated with a particular contiguous set of layers of the OSI Reference Model, either formally or informally.

In this Guide we are, of course, interested in the TCP/IP protocol suite, which runs the Internet, and a complex set of technologies that spans many layers of the OSI model. It is by examining the various components of TCP/IP and how they implement different OSI model layers that we will really learn how TCP/IP works. For starters, the name of the suite, TCP/IP, comes from the Transmission Control Protocol (TCP), which operates at layer four of the OSI model, and the Internet Protocol (IP) that runs at OSI model layer three. IP provides services to layer four and uses services of layer two below it. TCP uses IP's functions and provides functions to the layers above it. The complete examination of TCP/IP starts by looking at its architecture and a second, special model that was developed specifically to make sense of TCP/IP.