part0005

Introduction

In addition to a connection between two or more devices to share resources and exchange of information, a computer network enables the interaction of people, reduction of transportation costs, and the realization of distributed processing. To perform these activities, a computer network works with different complexities, because for each objective to be achieved, a network may have different equipment and ways of working. To help you understand these structures, in this chapter, you will study the first concepts about what makes up a computer network and how it works.

In this chapter, you will learn about conceptualizing protocol, Rate networks as its scope, recognize the different topologies of computer networks, and Compare the components as well as physical means used in a network.

With the evolution and the emergence of minicomputers in the 1960s, users had available terminals connected to these central computers, creating the first idea of computer networks. In the mid-1970s, the United States Department of Defense (DoD) has expanded its network used in research and military operations for universities. With this network, it was possible to share the physical environment and using multiple ways to connect two points without the need to use a telephone line connection, starting the ARPAnet.

The Beginning of Data Sharing

However, it was in the 1980s that was a great expansion of information technology and computer networks for home users because, with the advent of personal computers (PCs), home users have access to information technologies, which led to the need for connection between these importers computed. At that time, they originated the Bulletin boards (BBS), where users shared messages and files from your computer to other computers via telephone lines.

Then, in the 1990s, it was the union of these two ideas, the possibility of sharing data and information for users and companies using the physical environment, thus resulting in the internet.

The Internet Today

We are currently experiencing the second generation of the Internet, where certain information is not available in one physical location in the world. Today, information is available on the concept of clouds, i.e., the same information can be in several places in the world and still be changed location without users noticing this movement.

This book will help you to contribute to the evolution of the Internet, understanding and performing the deployment of such services.

Server Architecture and Peer

If you need to connect home computers or business, the way simpler to deploy a computer network is each component looks user folders from their computers to be accessed by others. These mannerisms, you are using the point to point architecture in which all computers on the network share and access data from other computers.

In architecture servers, there is a computer responsible for maintaining and provide information, called a server; computers accessing this information are called stations.

This architecture is widely used in enterprises and institutions that need to ensure the security and availability of information. Therefore, the centered data, it is much easier to perform backups (backup) or ensure the security of information against possible attacks.

The point to point architecture can be expanded to the internet where, through specific programs, you can share files with other users on the internet. Research peer to peer client.

Internet, Intranet, and Extranet

The intranet is where a company can use the same systems and servers that provide information to the internet, only back for the internal public, that is, a place that allows its employees to access restricted information from within the company, but with the same interface a site.

As we have seen, the Internet is a framework that enables information sharing among all global way. However, some information is not de- be public, especially in the business area.

Imagine companies having access to the purchase price of products from its current con-, or your personal data are available for all to access? To protect this information, it created the concept of the intranet.

Already the extranet is an evolution of the intranet; It is to share restricted information from a company with its customers or suppliers, making use of any means of protection as cryptographic cards or passwords. Thus, an undertaking client can access the system from a supplier, for example, ordering products online form.

Structure of Information Sharing

Internet	It is a framework that enables the sharing of data worldwide.
Intranet	It is a network that uses the same systems and servers internet; however, with the internal operation, usually on an enterprise level.
Extranet	It is a resource based on the intranet, typically used in enterprise-level, which allows data sharing restricted between company and customers.

Protocols of Communication

In our relationships in society, daily, use the protocol of good manners, how to respond "OK" or "more or less" when someone asks us "as you are?". This is the concept of protocol, preset messages, and responses that can be used both by individuals or computers to conduct communication.

In a computer network, we use communication protocols to define how the data will be transmitted.

We may use various protocols to establish a single communication:

one for the definitions of which physical medium is used;
another for what types of information to be exchanged;
another to define how they will be dealt with communication errors.

In just one simple connection between two computers, they can be used multiple protocols as needed.

Classification of Networks

Computer networks are physically classified according to their type and scope. When we connect only two computers or devices, we have a link point-to-point, such as used during a telephone connection between two people.

Now, when we have more than two computers, we have a link type multipoint, as used in telephone meetings between several people. Regarding its geographical coverage, networks are classified in three ways:

LAN (Local Area Network) - Known as local networks are limited to the same continuous physical space such as a room, a building, a company, a condo, or even an industrial complex.
MAN (Metropolitan Area Network) - These are networks that span one or more nearby cities and share the same physical medium. Making a strategy with the telephone system, area code (DDD) represents a MAN network, and it has a metropolitan scope.
WAN (Wide Area Network) - are networks of scattered connections over large geographical distances, such as the interconnection of the array of em- arrested in the capital with its subsidiaries inside or interconnection from one country to another.

These interconnections form the WAN may be the most varied possible connections between LAN and MAN networks.

Now it's your turn!

Noting the concepts of the intranet, extranet, and Internet, which companies use to structure the sharing sensitive information with its internal public?
Cite examples of the links multipoint type.

Physical Topologies

The physical topology of a network is how your devices or computers and a network are physically connected, with three possible structures (See the below Table):

Summary of Physical Topologies

bus	Ring	Star
Computers are connected to a single cable linearly.	The signal circulates between the computers connected in only one direction.	The signal is distributed to computers through a hub device.

Bus

In the bus topology, all computers are connected to a single cable. In this way, the network can be expanded easily as it is only necessary to extend the cable to insert a new computer on the network.

However, there is a big problem that virtually withdrew this topology strategy of use: if you have a break problem in any part of the cable, all computers will be without the network.

Ring

In the ring topology, the signal circulating between the computers in one direction (Figure below). This enables the network to be deterministic, i.e., after the computers know how long it takes to pass the signal from its neighbors, it is possible to know the total time a signal takes to go through all computers in the ring. However, if there are many stations in the network, it will be slower.

Star

The star networks require hub equipment (explained in more detail below) which distributes the signal between computers. Its disadvantage is the need for a unique cable for each computer, which increases the costs of deployment, but at the same time brings a great advantage in case of rupture of a cable, only one prospect computed will be out of network, not all as occurs in topologies and backslash ring. As a result, the star topology networks are the majority among the existing local networks today, using the Ethernet standard in its structure.

To Know More

The Ethernet standard refers to the physical and data-link connections to a network, such as electrical signals, access protocols in half and speed. These characteristics influence the definition of physical devices and cabling. The definition of this and other standards used in computer networks comes from the Institute of Electrical and Electronics Engineers - IEEE (Institute of Engineers Electrical and Electronics).

Media

A computer network requires necessarily a means of communication for the establishment of a connection. The means defining the communication to be used is the distance desired connection speed and whether or not mobility (Table below).

Communication for the Connection

wire rope	Mainly used in local area networks (LAN), as they are easy to handle. They have high costs and have good rates of speed. This medium is also used for wide area networks, using the existing structure of the telephone companies.
Radiofrequency	Also known by wireless (wireless), allows a point to point or multipoint connection of mobile devices in local networks through computers, phones, tablets, etc.
Optical fiber	means of communication that does not suffer electromagnetic interference extender, since it uses light as a means of transport. Optical fibers are used in networks that require high speeds and/or large distances because, with a single optical fiber, it is possible to pass a continuum net to another.

The use of means of communication for wireless multipoint networks is not restricted to local networks (LAN). They may have a metropolitan scope (MAN), making use of WiMAX or cellular technology.

The RF communication in computer networks is already used for decades, but only to peer connections, in which there is the need for an antenna, has a direct view to another. This medium is employed principally in regions where there is no infrastructure metal cables or optical fibers.

Now it's your turn!

Find out what is the physical topology of the network used in the institution where you study.
Knife a survey in your town of internet providers that provide a connection by radiofrequency.

Communication Components of a Computer Network

Data communication between distant points has two basic components, called DTE (Data Terminal Equipment) and DCE (Data Communications equipment).

The DTE or terminal transmission equipment is responsible for receiving and transmitting data. In a home network, the DTE would be our computer.

The DCE, or data communications equipment, is responsible for control communication. In a home network, the DCE would be our modem; their responsibility is to receive data from the DTE and DCE transmit to another.

This type of communication using modems is always necessary that the information to be transmitted/received must pass a digital means to an analog medium such as occurs in the use of elements of the public telephone network. Thus, in many WAN connections, the modem is still used.

The modem is the acronym of the modulator and demodulator words. It modulates (turns) and demodulates the analog signal to digital and digital to analog.

For communication in local area networks, the most commonly used components are:

Network Adapter

Also known as NIC (Network Interface Card), device pre- feel today on every computer to transmit and receive data from other computers.

This device has an identification number called a MAC address (Media Access Control), which is different on all network adapters and serves to computers on a network to identify who they are exchanging information.

Concentrator

In a multipoint network with bus star, the concentrator is responsible for gathering all the cables coming from the computers in a single device. There are several types of concentrators, among them the recognized are:

HUB: when you receive a message from a computer, it forwards this same message to every other computer networks.
Switch: It has a table with all MAC addresses of the devices connected to it. Thus, upon receiving a message from a computer, it verifies the destination MAC address and forwards it to the port where this computer is connected.
Router: This equipment makes it possible for computers or other devices operating with different physical media and different protocols to communicate through him. For this, when receiving a message from a computer, the router examines its contents and forwards it to the next rewriting device seeing the message so that the device according to understand.

Normally, the router is used to connect LAN to WAN networks using different physical media. The router is also able to choose which way a message should follow when there is more than one alternative.

IMPORTANT

The HUB is a device that allows only one active communication on the network, regardless of the number of computers. Already the Switch allows multiple communications are established at the same time, provided they are between different computers.