part0006

As computers began to be used in businesses, schools, homes, etc., there was a need to connect them to each other to share information or data through a more secure and adequate method than soft floppy disks. Due to the above, it is essential to know the management of the networks, from the sharing of programs, printers, hard drives, scanners, servers, and so on.

After studying this chapter, you will be able to identify the types of networks that we can place on a computer, through its structure and characteristics, for the diagnosis and choice of the most convenient type of network, according to the user's needs.

When the software component in a network is referred to, reference is made to the programs necessary to manage the devices that are interconnected by physical means (hardware). But it is important to emphasize that first, the physical components are required so that software or logic ones are installed on them. Software

Components, they are the programs or controllers required to establish communications between physical components, and enable interoperability between devices through communication protocols (see Communication protocols). An excellent example of these components is the network operating systems and the controllers of each of the physical components.

The main functions performed by a network operating system are to create, share, store and retrieve files from the network, as well as transmit data through the network and its multiple connected computers.

As for the hardware, it is the necessary equipment and primary basis for the creation of a network. Within these teams, the most representative is the following:

• Work stations: Computers connected to the network that allows users to access all the resources of the network (database, printer, scanner, etc.).

• Servers: Servers are responsible for providing services to workstations connected to the network. Within these services are email, printers, and databases.

• Repeaters: Repeaters are devices that amplify the signal emitted by a segment from one network to another, to increase the reach of the same networks.

• Bridges: Bridges interconnect two different network segments. One of its main functions is to restrict the sending of information to equipment belonging to the same segment, allowing the passage of those that are directed to different segments and whose MAC address is within the bridge registration table.

• Routers: Routers enable the routing of information packets in a network and consist mainly of a routing table, where the routes to the different devices connected in the network are registered.

• Brouters: Brouters combine the functionality of a router and a bridge by increasing it. René Montesano Brand, Development of web applications, write SUA, Plan 2005, School of Accounting and Administration.

• Hubs: Hubs are electronic devices whose purpose is to increase the reach of a network and serve as a signal distribution point, by concentrating in them a link input cable to the network or main server with several output cables that link to the stations of work. There are several types of concentrators, from the simplest ones, which function as a common and current electrical extension, to the intelligent ones, which have a microprocessor and memory integrated and work with the SNMP communication protocol (simple network management protocol), which gives them the ability to detect collisions and control and diagnose the state of the network.

• Switching hub or Ethernet switch: They divide the network into several segments, limiting traffic to one or more of them, instead of allowing packets to be broadcast across all ports. Within the switches, there is a circuit that works like a traffic light: it creates a series of address tables where each packet is examined and identifies to which segment of the network an address belongs and allows it to pass through it.

It is important to emphasize that, apparently, the previous devices seem the same, but it is not so; each one does and offers very specific functions; In addition, some devices include several of the functions of the hubs, such as router (router) and bridge ( bridge ) in the same device, for example.

In addition, for the correct installation of a network, inputs such as cables, RJ-45 connectors, jacks, punching pliers, gutters, covers, belts, cable testers, etc. are needed.

So, to choose the hardware components of a network, it is necessary to consider the needs that said network must cover. In this order, the questions to be answered are: what network topology? What is the scope of the network? What the number of machines and other peripherals that will connect to the network? What level of security should the network have? Will it be wired or wireless? What is the transmission speed? And so on.

Topologies refer to the way a network is physically structured; that is, how each component of a network connects with the others. There are several topologies, each with decisive advantages and disadvantages for network performance.

It may be that a network is formed by the union of more than one topology, which is known as hybrid topology, and requires software and hardware, as the central device (hub), bridges (bridges), routers (routers) or doors link (gateways).

The bus or channel topology is distinguished by having the main cable to which all the devices that are going to integrate the network physically connect. The cable or channel propagates the signals in both directions so that all devices can see all the signals of the other devices. This feature can be advantageous if all devices are required to obtain that information, but it would also represent a disadvantage due to traffic: there is a possibility of collisions that would affect the network.

It is characterized by sequentially connecting all devices (computers, printer, scanner, etc.) in a cable, forming a closed ring, in which each device or node is connected only to the two adjacent devices or nodes.

It is possible to establish a network with double ring topology, consisting of two concentric rings, where each device in the network is connected to both rings, although these do not appear directly connected.

This topology is analogous to that of the ring, with the difference that, to increase the reliability and flexibility of the network, there is a second redundant ring that connects the same devices.

In a network with this topology, each device or node examines the information sent through the ring. If the information is not directed to that node, it is delivered to the next node in the ring, and the process is repeated until the signal reaches the destination node.

• Advantage: the main advantage in networks with ring topology is the stability with respect to the time it takes for the signals to reach their destination, without collisions.

The main advantage in networks with ring topology is the stability with respect to the time it takes for the signals to reach their destination without collisions, with the disadvantage that the break in the connection of a device throws the entire network.

It comprises a central device called a hub or hub, from which all the links to the other devices or nodes radiate. Through the hub, pass all the signals that circulate in the network, so its main function is to speed up the transmission of signals and avoid collisions.

The star-channel hybrid topology is a channel or bus that is physically wired like a star through hubs; that is to say, it results from the union of two or more networks with a star topology, connected by a central linear cable that uses the channel topology.

In this topology, the signal generated by one device is sent to the hub, which transmits it to the other hub connected in the channel, and from this hub, it reaches the destination device.

The architecture of a network is the standard that defines how the transmission of electrical signals is carried out. These architectures were created by the manufacturers of the network cards and the means or wiring required.

The most common architectures are Ethernet and token ring. Token Ring Architecture is applied in networks with ring-star topology; the wiring is arranged in the form of a star, but the signals travel in the form of a ring. When a computer transmits data to another, it must wait for permission called a token (witness).

This permit passes from device to device until it reaches one that requires a transmission. When this happens, the address of the sending device, the address of the receiving device, and the data to be sent are incorporated into the token, and so it goes from device to device until it reaches its destination.

The Ethernet architecture can be used in networks with channel, star, and star-channel topologies. This architecture is based on the following premises:

There are several ways to establish a network; these depend on the selected topology and architecture, the possibility of growth or expansion and updating, and the speed that is required to make transmissions.

Each access point can serve 20 teams or more. The amount is limited for the use made of the band act; that is, the more devices are running simultaneously, the slower the transmission will be.

For data transmission to be successful, the sender and receiver must follow certain communication rules for the exchange of information, known as line protocols.

When different types of microcomputers are connected in a network, the protocol can become extremely complex. So, for the connections to work, the network protocols must conform to certain standards.

Originally, the protocols were relatively simple; for example, on which simple computer-terminal networks were supported, and that was contained in other computer application programs, such that, in addition to its main processing function, the computer would be controlling the line transmission between it and the associated terminals, and other peripheral equipment.

IBM put into circulation the first set of business standards, which he called Systems Network Architecture(SNA, systems network architecture), but only operated with IBM's own team. As the networks became sophisticated, many computer accessories (equipment from different manufacturers) were incompatible.

To stop this situation, the concept of layer protocols was developed to separate all telecommunications functions to form a set of sub-functions by layers. In a short time, the International Standards Organization (ISO) defined a series of communications protocols called Open Systems Interconnection (OSI, open systems interconnection), whose purpose is to identify the functions provided by any network, taking up the concept of working in layers, with the idea of establishing global design standards for all telecommunications data protocols, so that all the equipment produced is compatible.

In this protocol scheme, each layer would develop a different and self-sufficient task but would be dependent on the sub-layers. Thus, complex tasks would comprise several layers, while simple ones only some. The simple function of each layer would imply simple implementation of circuitry and logistics and would be independent of the functions of other layers so that they could be changed, either the functions or the realization of a functional layer, with minimal impact on logistics and circuitry of the other layers.

Currently, most commonly used data transfer protocols employ an array of layer protocols. It is important to study this arrangement to get an accurate idea of the full range of functions necessary for successful data transfer. In this order, it is essential to consider the functions of each protocol layer established in the OSI model (in Spanish, ISA), which is not in itself a set of protocols but rather fulfills the function of carefully defining the division of the functional layers, with which it is expected to integrate all modern protocols.

The principle of the open systems interconnection model states that as long as the layers interact in a “paired” manner and the interface between the function of a layer and its immediate upper and lower layer is not affected, how the function of that individual layer is carried out is not important.

Send the data about the medium. It is a combination of material and logistics that converts the data bits required by the data link layer into electrical pulses, modem tones, optical signals, or any other entity that will transmit the data. It ensures that the data is sent over the link and presented at both ends of the data link layer in the standard form.

Regarding the format that the data must have to be handled by the protocols, the key is to use headers. Each protocol layer adds a header that contains information for its own use; thus, the entire message is longer than the one received from the highest layer (layer 7)

The datalink layer operates only within the individual links of a connection, handling the transmission of data so that the individual bits are sent over those links without error.

It establishes the end-to-end connection through a real network and determines what permutation of individual links is used (routing functions).

The transport service is responsible for the end-to-end data relay in the communication session; In addition, it establishes the network connection that best suits the session requirements in terms of quality of service, data unit size, flow control, and data mail needs. You must also supply the network addresses to the network layer for the correct delivery of the message.

The session protocol includes commands, for example, start, interrupt, resume, and end, to manage a communication (conversation) session between devices in an appropriate and orderly manner.

Your task is to negotiate a mutually consistent technique for coding and scoring data (data syntax) and takes care of any necessary conversations between different code formats or data arrays so that the application layer receives the type it recognizes.

In reality, most OSI protocol layers exist only in software and can’t be identified as physical elements; however, not all protocol layers demand to be instrumented within the same computer program or carried out by the same part of the team.

Another aspect of the ISO model is that it provides great possibilities and guarantees the development of very sophisticated networks. It may be that very complex functions are not needed; in this case, the model allows the use of null protocols.

For example, in a network that uses similar terminal devices, the syntax conversion possibilities of the presentation layer are unnecessary. In this way, it is avoided to implement functions that could increase the cost and volume of the administration.

Today, the network that connects thousands of networks and millions of users around the world is the Internet, a huge cooperative community without central ownership. In itself, the Internet is the conduit for transporting data between computers. Whoever has access to the Internet can exchange text, data files, and programs with any other user.

But this would not be possible if each computer connected to the Internet did not use the same set of rules and procedures (protocols) to control the synchronization and format of the data. In this order, the set of commands and synchronization specifications used by the Internet is called the transmission control protocol / Internet protocol or TCP / IP.

This protocol allows linking any type of computer regardless of the operating system used or the manufacturer, and the IP system allows networks to send an email, transfer files and interact with other computers, no matter where they are located, as long as they have access to the Internet.

TCP / IP protocols include specifications that identify individual computers and exchange data between computers. They also include rules for various categories of application programs. In this way, programs that run on different types of computers can communicate with each other.

To understand the operation of TCP / IP protocols, the architecture they propose to communicate networks must be taken into account. Such architecture considers all networks to be the same when connected, regardless of their size, whether local or wide coverage.

Likewise, although TCP / IP software may appear different on different types of computers, it always looks the same to the network; however, all networks that exchange information must be connected to the same computer or processing equipment (equipped with communication devices); that is, routers or bridges. Based on this, Internet activity is understood as an activity of computers that communicate with other computers through the use of TCP / IP.

In addition, so that in a network two computers communicate with each other, both will be accurately identified, since the computer that originates a transaction will identify with a unique address the destination to which it is directed; Therefore, on the Internet, each computer has a numerical address consisting of four parts, known as the Internet protocol address or IP address. This address identifies both the network to which a computer belongs and itself within that network because it has routing information.

Remote access (telnet): It allows a user's direct access to another computer on the network. To establish telnet, you must set the address or name of the computer to which you want to connect. When accessed by this type of protocol, the remote computer generally asks for a username (user name, login, etc.) and a password (password). When you want to end the session, just close the protocol with the logout, logoff, exit, etc. commands.

Network File Systems (NFS): It causes a system to incorporate files to another computer in a more appropriate way than through an FTP. The NFS gives the impression that the hard drives of the remote computer are directly connected to the local computer. This creates a virtual disk in the local system. The above, apart from the economic benefits, allows users to work on several computers and share common files.

Remote printing: It allows access to printers connected to the network, for which print queues are created; the use of printers can be restricted, either by a password or to certain users. The benefit is to be able to share these resources.

Remote execution: It makes it run some specific program on some computers. It is useful when you have a large job that is not possible to run in a small system.

Most computers on the Internet (except those used exclusively for internal routing and switching) also have an address called a domain name system (DNS) address, which uses words instead of numbers to make them easier to handle directions to humans. DNS addresses consist of two parts: an individual name and a domain, which generally identifies the type of institution that occupies the address (for example, .com refers to commercial business).

Sometimes, this domain is divided into subdomains to specify more the address (even a domain can also identify the country in which the system is located; for example, .us refers to the USA).

When a computer is at the service of many users, each of them must also identify with a single account within the domain. The standard format includes the user name, separated from the DNS address by the @ symbol (at), which means “in”; for example, jhondoe@gmail.com.

Since the creation of the World Wide Web, the Web or www, in 1989, and the web examiners that developed from it, a world of possibilities has been opened for people to carry out activities through a PC since your home or office, thanks to the Internet.

Next, the different types of real networks used for sending data will be reviewed, starting with simple point-to-point technology to WAN networks.

The point to point networks, involving nothing more interconnecting two teams, are relatively simple to establish and may employ either digital lines or analog modem lines. Whenever the protocols at both ends of the link match, the data terminal equipment (DTE) easily dialogue.

In its simplest form, a point-to-point network can be worked in asynchronous mode, character by character. This is a common method of connecting remote terminals to a computer. This technique considerably reduces the complexity and cost of the material and logistics needed at remote computer terminals.

This kind of connection does not match the ISO ideal since only computer terminals of this type, and a few manufacturers can be used with third-party computers, but a disadvantage of the ISO model is the volume of equipment and logistics indispensable in each transmission and reception device.

LAN networks (Local Area Network) are small, usually tens of meters; for example, those constituted by the PCs that we find in offices and homes. These types of networks connect a limited number of equipment (printers, PCs, scanners, faxes, etc.), and the connectivity between the elements is ensured through the same wiring. The most used protocol in these networks is the 10/100/1000 Mbit / s Ethernet.

MAN (Metropolitan Area Network) networks are produced as an extension of LAN to the most geographically extensive areas and generally cover several kilometers. For example, a company with several branches in the same city would have several LANs in its buildings, and if it were connected through rented lines and equipment that would manage the exchange of information between the networks, it would together form a MAN.

The protocols and network equipment used in the MAN are adapted to work with several devices and a transmission capacity for equipment far superior to local area networks. The most used protocols in this type of networks are FDDI (fo), token ring (Fo), X25, and frame relay.

WAN networks (Wide Area Network) or distributed networks are the extensions of the concept of MAN or several regions or geographically remote areas. The most used protocols for these networks are TCP / IP. ATM and frame relay.

It is important to mention that the main functions of computer networks are very accessible in this computing medium, to share necessary and detailed information among users; On the other hand, in the structure of the topologies, it is necessary to know the type and its characteristics, to select the type of network that is most suitable for daily use.