When deciding which type of network to use, the main question is whether the organization can afford a file server, a network operating system, and a network administrator. If yes, then you can use a server network environment. If not, it's a peer-to-peer network.

You can organize a peer-to-peer network similar to a server one, using one powerful peer-to-peer computer to store files and serve shared resources (for example, printers). This will allow you to centrally administer resources and perform backup on one machine. Meanwhile, such a computer will experience a heavy load, so you need to make sure that a limited number of PCs work with it. Computers used in this way are called non-dedicated servers.

Based on the design conditions set (a large number of workstations, the need for expansion, a high level of security, a large number of resources, etc.), the correct solution would be to design a network based on a dedicated server, which will allow the requirements to be met.

Topology selection.

Network topology is its physical diagram, showing the location of nodes and their connection by cable. Each topology has its own strengths and weaknesses. There are four main network topologies:

• star-shaped;

  ring;

  cellular (cellular).

Bus topology.

Bus topology is often used in small, simple or temporary network installations.

In a typical bus topology network, a cable contains one or more pairs of conductors, and there is no active circuitry to amplify the signal or transmit it from one computer to another. Thus, the bus topology is passive. When one machine sends a signal along a cable, all other nodes receive this information, but only one of them (whose address matches the address encoded in the message) receives it. The others discard the message.

Only one computer can send a message at a time, so the number of machines connected to the network significantly affects its performance. The computer must wait for the bus to become free before transmitting data. These factors also apply in ring and star networks.

One more important factor is . Since the bus topology is passive, the electrical signal from the transmitting computer travels freely along the entire length of the cable. Without termination, the signal reaches the end of the cable, is reflected and travels in the opposite direction. This echoing and signal traveling back and forth along the cable is called looping (ringing). To prevent this phenomenon, connect to both ends of the cable segment (terminators) . Terminators absorb the electrical signal and prevent its reflection. In networks with a bus topology, cables must not be left unterminated.

Advantages of the bus topology:

it works reliably in small networks, is easy to use and understandable;

the bus requires less cable to connect computers and is therefore cheaper than other cable connection schemes;

The bus topology is easy to expand. Two cable segments can be joined into one long cable using a BNC barrel connector. This allows you to connect additional computers to the network;

A repeater can be used to expand a network with a bus topology. A repeater amplifies the signal and allows it to be transmitted over long distances.

Disadvantages of bus topology:

Intensive network traffic significantly reduces the performance of such a network. Since any computer can transmit data at any time, and in most networks they do not coordinate transmission times with each other, in a network with a bus topology with a large number Station computers often interrupt each other, and a considerable part of the bandwidth (information transmission power) is wasted. As you add computers to the network, the problem becomes even worse;

each cylindrical connector weakens the electrical signal, and a large number of them will prevent the correct transmission of information along the bus;

A network with a bus topology is difficult to diagnose. A broken cable or malfunction of one of the computers can result in other nodes being unable to communicate with each other. As a result, the entire network becomes inoperable.

What are network topologies? Why are they necessary? Where are they used and for what purpose? What types and types exist? Is it possible to somehow neutralize the negative aspects of network topologies and enhance the positive ones? Here is a short list of questions that will be answered in this article.

General information

Many people know about network devices. Topologies for the majority are a dark forest. So let's imagine a small model. We have computers that operate within one They are connected through communication lines. Depending on how their interaction is structured, the following types of networks are distinguished:

1. Ring.
2. Star.
3. Tire.
4. Hierarchical.
5. Free.

All of the above refers to the physical topology. But there are also logical ones. They are independent of one another. So, the first one refers to the geometry of the network construction. Logical topology deals with the fact that it directs data flows between different network nodes and selects the method of data transfer. Each of the types of relationship building discussed below has its own characteristics, advantages and disadvantages. Now let's look at the main network topologies.

Tire typology

It is used in cases where a linear mono channel is used for data transmission. Terminators are installed at its ends. Each computer is then connected to a linear mono channel using a T-connector. Data is transmitted on both sides and reflected from the terminal terminators. As you can understand from this, information in this case is sent to all available nodes. But it can only be accepted by those for whom it is intended. The data transmission medium in this case is used by all personal computers that are connected to the network. And the signal that comes from one PC spreads across all devices. Popularity this technology found using Ethernet architecture. What advantages does this network equipment provide us? First, it is necessary to note the ease of setup and configuration of the network. Also, if one node fails, it will be able to continue its work as a whole. Thanks to this, we can say that networks built using the bus typology have significant resistance to faults. But there are also disadvantages. First of all, it is necessary to note the limitations regarding the cable length, as well as the number of workstations. In addition, a break in the linear mono channel negatively affects the performance of the entire network. As a result, it is often difficult to determine the location of the defect, especially if it is hidden by insulation.

Star network topology

In this case, a twisted pair each workstation connected to a hub or hub. Thanks to them it is ensured parallel connection all personal computers. Through a hub or concentrator, PCs communicate with each other. The sent data arrives at all workstations. But only the one for whom they were intended can accept them. Regarding the advantages, it is worth noting that it is easy to connect a new personal computer to the network. It is also resistant to failures of individual nodes and disconnections. And all this is complemented by the possibility of centralized management. True, there are certain disadvantages. Thus, there is significant cable consumption. In addition, the failure of a hub or hub will negatively affect the operation of the entire network.

Using a central hub

This network typology is based on the previous type of network creation. The main role in this case is played by the central concentrator. It is an intelligent device that provides different stations according to the “output-input” principle, that is, thanks to it, each computer is connected to two more workstations. For stable operation there are main and backup rings. Thanks to this, it is possible to maintain the functionality of the network even in the presence of significant damage. The problem point is simply turned off. A special token is used to transmit data. It contains the address of the sender and recipient of the information. It should be noted that, in addition to high reliability, this typology also provides equal access to the network to all workstations. But you have to pay for everything. In this case, this refers to high cable consumption and expensive wiring of communication lines.

Tree

This network typology is considered as a combination of several stars. The tree can be in the following states:

1. Active.
2. Passive.
3. True.

Depending on the required condition, the responsible personnel selects what needs to be used: central computers or hubs (concentrators). Each choice has its own advantages and disadvantages. In the first case, we can talk about building a more centralized system with better controllability and the like. But the use of hubs or concentrators, as a rule, is much more profitable in terms of resources and finances.

Ring topology

In this case, a connection is provided into one unbroken chain. However, it does not have to resemble a circle. In this case, it is envisaged that the output of one personal computer, which is connected to the input of another computer. Therefore, when information starts moving from one specific point, it will ultimately end up there, having completed one circle. Data in such rings always moves in one direction. Only the workstation to which it was addressed can recognize and process the received message. When the topology operates, token access is used. It provides for the right to use the ring in the prescribed manner. A logical ring is used during data transfer. It is very easy to create and configure this network. But due to the fact that damage in one place can disable it, pure form it is almost never used due to its unreliability. To work in practice, various modifications of this typology can be used.

Combinations

They are used to reduce or eliminate negative aspects when creating a relationship between different computers. The most common combined types of network topologies are based on star, bus and ring technologies. To understand the situation, several examples can be given. Let's take the star-bus topology for the first one. The main thing in it is the concentrator. But not only can they connect to it individual computers, but also entire bus segments of the network. Of course, not one concentrator can be used, but many. A backbone (backbone) bus architecture can also be used. The advantage of this combination is that system administrator can take advantage of both typologies and easily influence the number of computers that are connected to the network. Let's look at another example. The star-ring topology will be considered. It does not connect computers, but hubs, to which the computers are directly connected. Thus, a closed loop is created in which the advantages of these two topologies are combined, and a number of other conveniences also appear. An example of this is that all concentrators can be collected in one place. This means that the cable connection points will be located together, and working with them will be significantly simplified.

Conclusion

So we looked at the main types of network topology. The possibilities presented in the article for building relationships between different computers are the most popular due to their practicality. But in some cases, more specialized network topologies may be needed. Their development or use of already created technologies is carried out taking into account all necessary for correct operation features, nuances and aspects. Typically, something like this is used only for scientific and military facilities, while for civilian life the most common approaches are more than enough. After all, the network topologies considered are the developments of decades!

2.1 Selecting network type and topologies

Network topology - geometric shape and physical location computers in relation to each other. There are physical and logical topologies. Logical and physical network topologies are independent of each other. Physical topology is a way physical connection computers using certain data transmission media, for example, sections of network cable. The logical topology defines the data transmission routes in the network. The choice of topology depends on the user's needs. Choice of topologies influences selection and performance network equipment, how to manage the system and whether it is possible to expand the network in the future.

There are 3 main local topologies computer network:

- “Star” - if you use this topology, then each computer will connect to the router separately, so computers connected to the network will be able to communicate with each other. This topology is used in local networks with 10Base-T Ethernet architecture.

- “Ring” - In a network with a given topology. all nodes will be connected by communication channels into an unbreakable ring (not necessarily a circle). A ring topology is characterized by the absence of connection endpoints. This network is very easy to create and configure. One end of the cable is connected to the socket network adapter, the other is connected to central device, called a hub. Today, the “ring” topology is not used in its pure form due to its unreliability, so modifications of this topology are used in practice.

- “Bus” - When using a bus topology, computers are connected into one line, at the ends of which computers are installed. This topology is used in local networks with Ethernet architecture.

This enterprise implements the “Star” technology.

Tree topology is a network topology in which each node is connected in a star fashion, forming a combination of stars. The tree topology is also called a hierarchical star. A node that is more high level, is usually called the parent, and the two downstream nodes connected to it are called the children. The choice of star or tree depends only on personal preference. The only differences are that in a “tree” topology, as a rule, the scheme is more strict and hierarchical; it is easier to track network connections, and this circuit often uses elements of a "bus" architecture.

This topology was chosen because of most of its advantages and minor disadvantages. In particular, the implementation of the network topology is easy to connect and configure, which greatly simplifies the scalability of the enterprise network, which is important with constant growth computer technology, its replacement. It is also convenient that in this topology it is very easy to monitor the performance of the entire network. This network is very easy to upgrade. The star topology is good because in this topology computers are connected in parallel, and control is centralized.

It has minor drawbacks that will not affect the performance of the network in any way.

Unlike the “star”, other topologies are significantly worse, for example, the “ring” - this topology is significantly inferior in many advantages to the “star” topology, since its implementation is more expensive, and the local computer network implemented according to this topology does not have the greatest speed, which greatly affects the speed of work of employees in the enterprise.

The “bus” topology has a number of advantages, for example, if one of the computers fails, this network will not change its operation, the computer network is easy to set up, there are no problems when laying network cables, as well as a large number of shortcomings that will affect the performance of the local computer network, for example, in this topology it is difficult to find a breakdown, therefore, it will not be possible to quickly fix it. If the cables are damaged, such a breakdown will significantly affect the performance of the entire local area network; also, this topology has a small throughput and limits the number of computers connected to the local area network.

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There are many factors to consider when choosing the most appropriate topology for a given situation. This table 2.2 will help you do right choice.

Table 2.2

Factors needed when choosing a topology

Topology	Advantages	Flaws
	Economical cable consumption. Relatively inexpensive and easy to use transmission medium. Simplicity. Reliability. Easy to expand	With significant volumes of transmitted information, network throughput decreases. It is difficult to localize problems. Cable failure stops many users from working
	All computers have equal access. The number of users does not have any significant impact on performance	The failure of one computer impedes the operation of the entire network. It is difficult to localize problems. Changing the network configuration requires stopping the entire network
	It is easy to modify the network by adding new computers. Centralized control and management. The failure of one computer does not affect the functionality of the network	Failure of the central node disables the entire network

To consolidate the material presented, let’s consider the solution to the problem.

An independent insurance company consisting of a president, manager, administrator and 5 agents decided to establish a network. The company occupies half of a small building. Recently, there has been an increase in clientele and in order to cope with the increasing volume of work, it is planned to hire two more agents.

Every employee of the company has a computer. If you need to exchange business information, you have to do it orally or using floppy disks. All agents deal only with the affairs of their clients, and information about these clients is strictly confidential. An eight-year-old laser printer is in the possession of the office administrator. Each agent has its own dot matrix printer.

Simultaneously with the installation of the network, it was decided to purchase a high-speed laser printer.

You are tasked with setting up a network for this small company. To make the problem easier, answer the following questions.

1. What type of network would you recommend this company install?

Peer-to-peer ______

Server based ______

2. Which topology is appropriate in this situation?

Ring ______

Star ______

Star-tire ______

Ring star ______

Possible solution

There is no clear solution to this problem. Possible solutions and their justifications are merely recommendations.

1. Server based.

It would seem that since there are only 8 people in the company, a peer-to-peer network could be a suitable network. But we already know that the company is starting to grow. In addition, some of the information is confidential. Therefore, the conclusion is: it is better to install a server-based network, which provides opportunities for company growth and centralization of data protection, while a peer-to-peer network may exhaust its potential in a year or two.

2. There is no single correct answer. Today, the most popular topologies are star-bus and bus.

The first seems more attractive because it makes it easier to solve network problems and reconfigure the network.

You can also choose a network with a “bus” topology - it is cheaper and easier to install, but at the same time we will lose the advantages that the hub gives in administration and decision network problems.

The ring topology is too complex for such a network.

First of all, decide on the type of carrier.
The fact is that the use of coaxial cable or twisted pair implies fundamentally different architectures local network.

In the first case, the network will be built on the principle of a “common bus” - all computers included in it are sequentially connected to each other in a chain using cable segments, forming a single backbone.

This is quite convenient if all users of your network live on the same landing or in apartments located one below the other.
However, if computers are scattered throughout the entrance (or house), the coaxial cable will loop, which is inconvenient even at the stage of initial network installation.

If you need to connect several more new users to it, the problems will increase exponentially.
In addition, the “common bus” is dangerous: if a section of the network between two computers is damaged, the entire network is disconnected.

Fine transfer speed coaxial cable(in its structure it is similar to that used in television antennas - only the resistance in it is 50 Ohms) is limited.
It is no more than 10 Mbit/s.

Twisted pair allows you to create a completely different network architecture.
A twisted pair cable is similar to a regular telephone cable, but instead of 2 (or 4) wires, it uses 8 wires divided into 4 pairs.

Twisted pair cable is a more flexible and practical cable, easy to install and well protected from external influences.
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Using twisted pair, you can create networks with a throughput of 10 Mbit/s, 100 Mbit/s (Fast Ethernet) and 1000 Mbit/s (Gigabit Ethernet).

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