Network topology structure. Computer network topology

The term topology describes the physical arrangement of computers, cables, and other network components.

Topology is a standard term used by professionals to describe the basic layout of a network.

In addition to the term “topology”, the following is also used to describe the physical layout:

Physical location;

Layout;

Diagram;

The network topology determines its characteristics. In particular, the choice of a particular topology affects:

composition of the necessary network equipment;

characteristics of network equipment;

network expansion possibilities;

network management method.

To share resources or perform other network tasks, computers must be connected to each other. For this purpose, in most cases, a cable is used (less commonly, wireless networks - infrared equipment). However, simply connecting your computer to a cable that connects other computers is not enough. Different types of cables, combined with different network cards, network operating systems, and other components, require different computer layouts.

Each network topology imposes a number of conditions. For example, it can dictate not only the type of cable, but also the way it is laid.

Basic topologies

• star

  ring

If computers are connected along a single cable, the topology is called a bus. When computers are connected to cable segments originating from a single point, or hub, the topology is called a star topology. If the cable to which the computers are connected is closed in a ring, this topology is called a ring.

Tire.

The bus topology is often called a “linear bus”. This topology is one of the simplest and most widespread topologies. It uses a single cable, called a backbone or segment, along which all computers on the network are connected.

In a network with a bus topology, computers address data to a specific computer by transmitting it along a cable in the form of electrical signals.

Data in the form of electrical signals is transmitted to all computers on the network; however, the information is received by the one whose address matches the recipient address encrypted in these signals. Moreover, at any given time, only one computer can transmit.

Since data is transmitted to the network by only one computer, its performance depends on the number of computers connected to the bus. The more there are, the slower the network works. The bus is a passive topology. This means that computers only “listen” to data transmitted over the network, but do not move it from sender to recipient. Therefore, if one of the computers fails, it will not affect the operation of the others. In this topology, data is distributed throughout the network - from one end of the cable to the other. If no action is taken, the signals reaching the end of the cable will be reflected and this will not allow other computers to transmit. Therefore, after the data reaches the destination, the electrical signals must be extinguished. To do this, terminators (also called plugs) are installed at each end of the cable in a network with a bus topology to absorb electrical signals.

Advantages: the absence of additional active equipment (for example repeaters) makes such networks simple and inexpensive.

Linear local network topology diagram

However, the disadvantage of a linear topology is the limitations on network size, functionality and expandability.

Ring

In a ring topology, each workstation is connected to its two closest neighbors. This relationship forms a local network in the form of a loop or ring. Data is transmitted in a circle in one direction, and each station plays the role of a repeater, which receives and responds to packets addressed to it and transmits other packets to the next workstation “down”. In the original ring network, all objects were connected to each other. This connection had to be closed. Unlike the passive bus topology, here each computer acts as a repeater, amplifying the signals and passing them on to the next computer. The advantage of this topology was the predictable response time of the network. The more devices were in the ring, the longer the network took to respond to requests. Its most significant drawback is that if at least one device fails, the entire network refuses to function.

One of the principles of data transmission over a ring is called passing the token. The gist of it is this. The token is transmitted sequentially, from one computer to another, until the one that wants to transfer the data receives it. The sending computer modifies the token, places the email address in the data, and sends it around the ring.

This topology can be improved by connecting all network devices via hub(Hub device connecting other devices). Visually, a “tweaked” ring is no longer physically a ring, but in such a network data is still transmitted in a circle.

In the figure, solid lines indicate physical connections, and dotted lines indicate data transfer directions. Thus, such a network has a logical ring topology, while physically it is a star.

Star

In a star topology, all computers are connected via cable segments to a central component that has a hub. Signals from the transmitting computer travel through the hub to everyone else. In star networks, cabling and network configuration management are centralized. But there is also a disadvantage: since all computers are connected to a central point, cable consumption increases significantly for large networks. In addition, if the central component fails, the entire network will be disrupted.

Advantage: If one computer breaks down or the cable connecting one computer fails, then only that computer will not be able to receive and transmit signals. This will not affect other computers on the network. The overall network speed is limited only throughput hub.

The star topology is dominant in modern local networks. Such networks are quite flexible, easily expandable and relatively inexpensive compared to more complex networks in which the methods of device access to the network are strictly fixed. Thus, “stars” have replaced outdated and rarely used linear and ring topologies. Moreover, they became a transitional link to the last type of topology - dialed stars e.

A switch is a multiport active network device. The switch “remembers” the hardware (or MAC–MediaAccessControl) addresses of devices connected to it and creates temporary paths from the sender to the recipient, along which data is transmitted. In a typical local network with a switched topology, there are several connections to a switch. Each port and the device that is connected to it has its own bandwidth (data transfer rate).

Switches can significantly improve network performance. First, they increase the total bandwidth that is available for a given network. For example, an 8-wire switch can have 8 separate connections, supporting speeds of up to 10 Mbit/s each. Accordingly, the throughput of such a device is 80 Mbit/s. First of all, switches increase network performance by reducing the number of devices that can fill the entire bandwidth of a single segment. One such segment contains only two devices: the workstation network device and the switch port. Thus, only two devices can “compete” for a bandwidth of 10 Mbit/s, and not eight (when using an ordinary 8-port hub, which does not provide for such division of bandwidth into segments).

In conclusion, it should be said that topology is distinguished physical connections (physical structure networks) and the topology of logical connections (logical network structure)

Configuration physical connections is determined by the electrical connections of computers and can be represented as a graph, the nodes of which are computers and communications equipment, and the edges correspond to cable segments connecting pairs of nodes.

Logical connections represent the paths of information flows through the network; they are formed by appropriately configuring communication equipment.

In some cases, the physical and logical topologies are the same, and sometimes they are not.

The network shown in the figure is an example of a mismatch between the physical and logical topology. Physically, computers are connected using a common bus topology. Access to the bus occurs not according to a random access algorithm, but by transferring a token (token) in a ring pattern: from computer A to computer B, from computer B to computer C, etc. Here, the order of token transfer no longer follows physical connections, but is determined by the logical configuration of network adapters. Nothing prevents you from setting it up network adapters and their drivers so that the computers form a ring in a different order, for example B, A, C... However, the physical structure does not change.

Wireless network.

The phrase “wireless environment” can be misleading because it means that there are no wires on the network at all. In reality, wireless components typically interact with a network that uses cable as the transmission medium. Such a network with mixed components is called hybrid.

Depending on the technology, wireless networks can be divided into three types:

local area networks;

extended local area networks;

mobile networks (laptop computers).

Transfer methods:

infrared radiation;

• radio transmission in a narrow spectrum (single-frequency transmission);

  radio transmission in the scattered spectrum.

In addition to these methods of transmitting and receiving data, you can use mobile networks, packet radio connections, cellular networks and microwave data transmission systems.

Currently office network- This is not just connecting computers to each other. It is difficult to imagine a modern office without databases that store both the financial statements of the enterprise and personnel information. In large networks, as a rule, for the security of databases and to increase the speed of access to them, separate servers are used to store databases. Also, now it is difficult to imagine a modern office without access to the Internet. Scheme option wireless network office is shown in the picture

So let's conclude: the future network must be carefully planned. To do this, you should answer the following questions:

Why do you need a network?

How many users will there be on your network?

How quickly will the network expand?

Does this network require Internet access?

Is centralized management of network users necessary?

After this, draw a rough diagram of the network on paper. You should not forget about the cost of the network.

As we have established, topology is the most important factor in improving overall network performance. Basic topologies can be used in any combination. It is important to understand that the strong and weak sides Each topology affects the desired network performance and is dependent on existing technologies. It is necessary to strike a balance between the actual location of the network (for example, in several buildings), the possibilities of using the cable, the path of its installation and even its type.

Topology of local networks.

The composition and configuration of network equipment depending on the network topology.

1. Concept of network topology

The general scheme for connecting computers into local networks is called network topology

Topology is the physical configuration of the network combined with its logical characteristics. Topology is a standard term used to describe the basic layout of a network. By understanding how different topologies are used, you can determine what capabilities they have. Various types networks.

There are two main types of topologies:

• physical
• logical

Logical topology describes the rules for interaction between network stations when transmitting data.

Physical topology defines the method of connecting storage media.

The term "network topology" describes the physical arrangement of computers, cables, and other network components. The topology of physical connections can take on different “geometric” forms, and what is important is not the geometric location of the cable, but only the presence of connections between the nodes (closed/open, presence of a center, etc.).

The network topology determines its characteristics.

The choice of a particular topology affects:

• composition of the necessary network equipment
• network equipment characteristics
• network expansion possibilities
• network management method

The network configuration can be either decentralized (when the cable “runs around” each station in the network) or centralized (when each station is physically connected to some central device that distributes frames and packets between stations). An example of a centralized configuration is a star with workstations located at the ends of its arms. A decentralized configuration is similar to a chain of climbers, where everyone has their own position in the chain, and everyone is connected together by one rope. The logical characteristics of a network's topology determine the route a packet takes as it travels across the network.

When selecting a topology, you need to take into account that it ensures reliable and efficient operation of the network and convenient management of network data flows. It is also desirable that the network should be inexpensive in terms of the cost of creation and maintenance, but at the same time there would remain opportunities for its further expansion and, preferably, for the transition to higher-speed communication technologies. This is not an easy task! To solve it, you need to know what network topologies there are.

According to the topology of connections there are:

• networks with a “common bus (bus)” topology;
• networks with star topology;
• networks with a “ring” topology”;
• networks with tree topology;
• networks with mixed topology

2. Basic network topologies

There are three basic topologies on which most networks are built.

• bus
• star
• ring

A “bus” is a topology in which computers are connected along a single cable.

A "star" is a topology in which computers are connected to cable segments originating from a single point, or hub.

A topology is called “ring” if the cable to which the computers are connected is closed in a ring.

Although the basic topologies themselves are simple, in reality there are often quite complex combinations that combine the properties of several topologies.

2.1 Bus network topology

In this topology, all computers are connected to each other with one cable. Each computer is connected to a common cable, at the ends of which terminators are installed. The signal passes through the network through all computers, reflecting from the end terminators.

Network topology diagram "bus" type

The "bus" topology is generated by a linear structure of connections between nodes. This topology can be implemented in hardware, for example, by installing on central computers two network adapters. In order to prevent signal reflection, terminators that absorb the signal must be installed at the ends of the cable.

In a network with a bus topology, computers address data to a specific computer, transmitting it along the cable in the form of electrical signals - hardware MAC addresses. To understand the process of computer interaction via a bus, you need to understand the following concepts:

• signal transmission
• signal reflection
• Terminator

1. Signal transmission

Data in the form of electrical signals is transmitted to all computers on the network; however, only the one whose address matches the recipient address encrypted in these signals receives information. Moreover, at any given time, only one computer can transmit. Since data is transmitted to the network by only one computer, its performance depends on the number of computers connected to the bus. The more there are, i.e. The more computers waiting to transfer data, the slower the network. However, it is impossible to derive a direct relationship between network bandwidth and the number of computers in it. Because, in addition to the number of computers, network performance is influenced by many factors, including:

• characteristics hardware computers on the network
• the frequency with which computers transmit data
• type of network applications running
• type network cable
• distance between computers on the network

The bus is a passive topology. This means that computers only “listen” to data transmitted over the network, but do not move it from sender to recipient. Therefore, if one of the computers fails, it will not affect the operation of the others. In active topologies, computers regenerate signals and transmit them across the network.

2. Signal reflection

Data, or electrical signals, travel throughout the network - from one end of the cable to the other. If no special action is taken, the signal reaching the end of the cable will be reflected and will not allow other computers to transmit. Therefore, after the data reaches the destination, the electrical signals must be extinguished.

3. Terminator

To prevent electrical signals from being reflected, plugs (terminators) are installed at each end of the cable to absorb these signals. All ends of the network cable must be connected to something, such as a computer or a barrel connector - to increase the cable length. A terminator must be connected to any free (not connected to anything) end of the cable to prevent electrical signals from being reflected.

Terminator installation

Network integrity can be compromised if a network cable breaks when it is physically severed or one of its ends is disconnected. It is also possible that there are no terminators at one or more ends of the cable, which leads to reflection of electrical signals in the cable and termination of the network. The network "falls". The computers themselves on the network remain fully functional, but as long as the segment is broken, they cannot communicate with each other.

This network topology has advantages and disadvantages.

D advantages bus topologies:

• short network setup time
• low cost (less cable required and network devices)
• ease of setup
• Failure of a workstation does not affect network operation

Flaws bus topologies:

• such networks are difficult to expand (increase the number of computers in the network and the number of segments - individual sections of cable connecting them).
• Because the bus is shared, only one of the computers can transmit at a time.
• The “bus” is a passive topology - computers only “listen” to the cable and cannot restore signals that are attenuated during transmission over the network.
• The reliability of a network with a bus topology is low. When the electrical signal reaches the end of the cable, it (unless special measures are taken) is reflected, disrupting the operation of the entire network segment.

The problems inherent in the bus topology have led to the fact that these networks are now practically not used.

The bus network topology is known as 10 Mbps Ethernet logical topology.

2.2 Basic star network topology

In a star topology, all computers are connected to a central component called a hub. Each computer is connected to the network using a separate connecting cable. Signals from the transmitting computer travel through the hub to everyone else.

There is always a center in the “star” through which any signal in the network passes. The functions of the central link are performed by special network devices, and signal transmission to them can occur in different ways: in some cases, the device sends data to all nodes except the sending node, in others, the device analyzes which node the data is intended for and sends it only to it.

This topology originated in the early days of computing, when computers were connected to a central, main computer.

Star network topology diagram

Advantages"star" typologies:

• the failure of one workstation does not affect the operation of the entire network as a whole
• good network scalability
• easy troubleshooting and network breaks
• high network performance (subject to proper design)
• flexible administration options

Flaws"star" typologies:

• failure of the central hub will result in the inoperability of the network (or network segment) as a whole
• networking often requires more cable than most other topologies
• the finite number of workstations in a network (or network segment) is limited by the number of ports in the central hub.

One of the most common topologies because it is easy to maintain. Mainly used in networks where the carrier is twisted pair cable. UTP category 3 or 5. (Twisted pair cable categories, which are numbered from 1 to 7 and determine the effective transmission frequency range. A higher category cable usually contains more pairs of wires and each pair has more turns per unit length).

The star topology is reflected in Fast technologies Ethernet6.

2.3 Basic ring network topology

In a ring topology, computers are connected to a cable that forms a ring. Therefore, the cable simply cannot have a free end to which a terminator must be connected. Signals are transmitted along the ring in one direction and pass through each computer. Unlike the passive bus topology, here each computer acts as a repeater (repeater), amplifying the signals and passing them on to the next computer. Therefore, if one computer fails, the entire network stops functioning.

Ring network diagram

The functioning of a closed ring topology is based on token passing.

A token is a data packet that allows a computer to transmit data to the network.

The token is transmitted sequentially, from one computer to another, until the one that “wants” to transfer the data receives it. A computer wanting to start a transmission "captures" the token, modifies it, puts the recipient's address in the data, and sends it around the ring to the recipient.

The data passes through each computer until it reaches the one whose address matches the recipient address specified in the data. After this, the receiving computer sends a message to the transmitting one, confirming that the data has been received. Having received confirmation, the sending computer creates a new token and returns it to the network.

At first glance, it seems that transferring the marker takes a lot of time, but in fact the marker moves almost at the speed of light. In a ring with a diameter of 200 meters, the marker can circulate at a frequency of 10,000 revolutions per second.

Advantages ring topology:

• ease of installation
• almost complete absence of additional equipment
• the possibility of stable operation without a significant drop in data transfer speed under heavy network load, since the use of a token eliminates the possibility of collisions.

Flaws ring topology:

• failure of one workstation and other problems (cable break) affect the performance of the entire network
• complexity of configuration and setup
• difficulty in troubleshooting

It is most widely used in fiber optic networks. Used in FDDI8, Token ring9 standards.

3. Other possible network topologies

Real computer networks are constantly expanding and modernizing. Therefore, such a network is almost always hybrid, i.e. its topology is a combination of several basic topologies. It is easy to imagine hybrid topologies that are a combination of star and bus, or ring and star.

3.1 Tree network topology

The tree topology can be considered as a union of several “stars”. It is this topology that is most popular today when building local networks.

Tree network topology diagram

In a tree topology, there is a root of the tree from which branches and leaves grow.

A tree can be active or true and passive. With an active tree, central computers are located at the centers of combining several communication lines, and with a passive tree, there are concentrators (hubs).

Figure 6 - Active tree network topology diagram

Figure 7 - Passive tree network topology diagram

3.2 Combined network topologies

Combined topologies are quite often used, among them the most common are star-bus and star-ring.

A star-bus topology uses a combination of a bus and a passive star.

Scheme of a combined star-bus network topology

Both individual computers and entire bus segments are connected to the hub. In fact, a physical bus topology is implemented that includes all computers on the network. In this topology, several hubs can be used, interconnected and forming the so-called backbone, support bus. Separate computers or bus segments are connected to each of the hubs. The result is a star-tire tree. Thus, the user can flexibly combine the advantages of bus and star topologies, and also easily change the number of computers connected to the network. From the point of view of information distribution, this topology is equivalent to a classic bus.

In the case of a star-ring topology, it is not the computers themselves that are united into a ring, but special hubs, to which the computers in turn are connected using star-shaped double communication lines.

Scheme of a combined star-ring network topology

In reality, all computers on the network are included in a closed ring, since within the hubs the communication lines form a closed loop (as shown in Figure 9). This topology makes it possible to combine the advantages of star and ring topologies. For example, hubs allow you to collect all network cable connection points in one place. If we talk about information dissemination, this topology is equivalent to a classic ring.

3.3 "Grid" network topology

Finally, mention should be made of a mesh or mesh topology, in which all or many computers and other devices are directly connected to each other (Figure 10).

Figure 10 - Network mesh topology diagram

This topology is extremely reliable - if any channel is broken, data transfer does not stop, since several routes for information delivery are possible. Mesh topologies (most often not complete, but partial) are used where it is necessary to ensure maximum network fault tolerance, for example, when connecting several sections of a large enterprise network or when connecting to the Internet, although, of course, you have to pay for this: cable consumption increases significantly, Network equipment and its configuration become more complicated.

Currently, the vast majority of modern networks use a star topology or a hybrid topology, which is an amalgamation of several stars (for example, a tree topology), and a CSMA/CD (carrier sense multiple access) transmission method. collision detection).

Fragment computer network

A fragment of a computer network includes the main types of communication equipment used today to form local networks and connect them through global connections to each other. To build local connections between computers, they are used different kinds cable systems, network adapters, repeater hubs, bridges, switches and routers. To connect local networks to global connections, special outputs (WAN ports) of bridges and routers are used, as well as data transmission equipment over long lines - modems (when working over analog lines) or devices connecting to digital channels(TA – terminal adapters ISDN networks, servicing devices for digital dedicated channels such as CSU/DSU, etc.).

The term “topology” has many meanings, one of which is used in computer world to describe networks. What topology is will be discussed further. But, looking ahead a little, in the simplest case this concept can be considered as a description of the configuration (location) of computers connected to the network. In other words, it all comes down to understanding not even the connections themselves, but the geometric shapes that correspond to each type of terminal arrangement.

What is meant by local network topology?

As is already clear, computers combined into unified networks, connect to them not chaotically, but in a strictly defined order. To describe this circuit, the understanding of topology was introduced.

Essentially, what is topology? Map, diagram, chart, map. The descriptive process, as is already clear, is somewhat akin to elementary knowledge of geometry. However, this term cannot be considered only from a purely geometric point of view. Since we are talking not only about connections, but also about the transfer of information, this factor should also be taken into account.

Main types of networks and their topologies

In general, there is no single concept of computer topology. It is generally accepted that there may be several types of topologies that collectively describe a particular network organization. Actually, networks can be completely different.

For example, the simplest form of organizing the connection of several computer terminals into a single whole can be called a local network. There are also intermediate types of networks (city, regional, etc.).

Finally, the biggest ones are global networks, which affect large geographic regions and include all other types of networks, as well as computers and telecommunications equipment.

But what is meant by local network topology, as one of the most simple shapes organizing the connection of several computers with each other, in this case?

Based on the processes and structures described, they are divided into several types:

• physical - a description of the actual structure of the location of computers and network nodes, taking into account the connections between them;
• logical - description of the signal passage through the network;
• informational - description of the movement, direction and redirection of data within the network;
• exchange control - a description of the principle of using or transferring rights to use the network.

Network topology: types

Now a few words about the generally accepted classification of topology types by connections. In the context of what a topology is, it is worth separately noting another type of classification, which describes exclusively the way a computer connects to the network or the principle of its interaction with other terminals or main nodes. In this case, the concepts of fully connected and incompletely connected topologies become relevant.

A fully connected structure (and this is recognized throughout the world) is extremely cumbersome due to the fact that each single terminal included in a single network structure is connected to all the others. The inconvenience in this case is that additional communication equipment must be installed for each computer, and the terminal itself must be equipped with a sufficiently large number of communication ports. And as a rule, such structures, if used, are extremely rare.

An incompletely connected topology in this regard looks much more preferable, since each individual terminal is not connected to all other computers, but receives or transmits information through certain network nodes or accesses directly a central hub or hub. A striking example of this is the star network topology.

Since we are talking about the main methods of combining terminals into a single whole (network), we should dwell on the basic topologies of all the main types, among which the main ones are “bus”, “star” and “ring”, although there are some mixed types.

Bus network topology

This type of networking of terminals is quite popular, although it has very serious disadvantages.

You can see what a “bus” topology is at simple example. Imagine a cable with several branches on both sides. At the end of each such branch there is a computer terminal. They are not directly connected to each other, but information is received and transmitted through a single highway, at both ends of which special terminators are installed that prevent signal reflection. This is a standard linear network topology.

The advantage of such a connection is that the length of the main line is significantly reduced, and the failure of a single terminal does not have any impact on the operation of the network as a whole. The main disadvantage is that if there is a disruption in the operation of the highway itself, the entire network becomes inoperative. In addition, the “bus” topology is limited in the number of connected workstations and has rather low performance due to the distribution of resources between all terminals in the network. The distribution may be uniform or uneven.

Star topology

The topology of the “star” network in some sense resembles a “bus”, with the only difference being that all terminals are connected not to a single backbone, but to a central switchgear(hub, hub).

It is through the hub that all computers can communicate with each other. Information is transmitted from the hub to all devices, but is received only by those for which it is intended. The advantages of such a connection include the ability to connect to all network terminals, as well as the connection of new ones. However, as in the case of the “bus,” the failure of the central switching device has consequences for the entire network.

Ring topology

Finally, we have another type of connection - a ring network topology. As is probably already clear from the name, computers are connected sequentially from one to another through intermediate nodes, as a result of which a vicious circle is formed (of course, a circle in this case is a relative concept).

During transmission, information from the starting point passes through all terminals that are in front of the final recipient. But recognition of the final beneficiary is based on token access. That is, only those tagged in receive information. information flow terminal. This scheme is almost never used due to the fact that the failure of one computer automatically entails a disruption in the operation of the entire network.

Mesh and mixed topology

This type of connection can be obtained by removing some connections from the above connections or adding them additionally. In most cases, this scheme is used in large networks.

In this regard, several main derivatives can be defined. The most common are considered to be schemes such as “double ring”, “tree”, “lattice”, “snowflake”, “Clos network”, etc. As can be seen even from the names, all these are variations on the theme of the main types of connections, which are taken as a basis.

There is also a mixed type of topology, which can combine several others (subnetworks), grouped according to some characteristic characteristics.

Conclusion

Now it’s probably clear what topology is. If we make a general conclusion, this concept is a description of how computers are connected on a network and how they interact. How this is done depends solely on the method of combining the terminals into one. And it is impossible to say that today it is possible to single out one universal connection option. In each specific case and depending on the needs, one or another type of connection can be used. But in local networks, if we talk specifically about them, the most common is the “star” circuit, although the “bus” is still used quite widely.

It remains to add that you can also find the concepts of centralization and decentralization, but they are mostly associated not with connections, but with the system for managing network terminals and exercising control over them. Centralization is clearly expressed in star-type connections, but decentralization is also applicable for this type, ensuring the introduction of additional elements in order to increase the reliability of the network when the central switch fails. A fairly effective development in this regard is the “hypercube” scheme, but it is very difficult to develop.

Network topology refers to the physical or electrical configuration of the network's cabling and connections.

In describing the topology of networks, several specialized terms are used: network node - a computer or network switching device; network branch - a path connecting two adjacent nodes; terminal node - a node located at the end of only one branch; intermediate node - a node located at the ends of more than one branch; adjacent nodes are nodes connected by at least one path that does not contain any other nodes.

There are only 5 main types of network topologies:

1. “Shared Bus” topology. In this case, the connection and exchange of data is made through a common communication channel called a common bus: A common bus is a very common topology for local networks. The transmitted information can be distributed in both directions. The use of a common bus reduces wiring costs and unifies the connection of various modules. The main advantages of this scheme are the low cost and ease of cable distribution throughout the premises. The most serious disadvantage of the common bus is its low reliability: any defect in the cable or any of the numerous connectors completely paralyzes the entire network. Another disadvantage of the shared bus is its low performance, since with this connection method only one computer at a time can transmit data to the network. Therefore, the communication channel bandwidth is always divided here between all network nodes.

2. Star topology. In this case, each computer is connected by a separate cable to a common device called a hub, which is located in the center of the network:

The function of a hub is to direct information transmitted by a computer to one or all other computers on the network. The main advantage of this topology over a common bus is greater reliability. Any problems with the cable affect only the computer to which this cable is connected, and only a malfunction of the hub can bring down the entire network. In addition, the hub can play the role of an intelligent filter of information coming from nodes on the network and, if necessary, block transmissions prohibited by the administrator. The disadvantages of a star topology include the higher cost of network equipment due to the need to purchase a hub. In addition, the ability to increase the number of nodes in the network is limited by the number of hub ports. Currently, a hierarchical star is the most common type of connection topology in both local and global networks.

3. “Ring” topology. In networks with a ring topology, data in the network is transmitted sequentially from one station to another along the ring, usually in one direction:

If the computer recognizes the data as intended for it, then it copies it to its internal buffer. In a network with a ring topology, it is necessary to take special measures so that in the event of a failure or disconnection of any station, the communication channel between the remaining stations is not interrupted. The advantage of this topology is ease of management, the disadvantage is the possibility of failure of the entire network if there is a failure in the channel between two nodes.

4. Mesh topology. The mesh topology is characterized by a computer connection scheme in which physical communication lines are established with all adjacent computers:

In a network with a mesh topology, only those computers between which intensive data exchange occurs are directly connected, and for data exchange between computers that are not directly connected, transit transmissions through intermediate nodes are used. The mesh topology allows the connection of a large number of computers and is typically characteristic of global networks. The advantages of this topology are its resistance to failures and overloads, because There are several ways to bypass individual nodes.

5. Mixed topology. While small networks typically have a typical star, ring, or bus topology, large networks typically have random connections between computers. In such networks, individual subnetworks with a typical topology can be identified, which is why they are called networks with mixed topology.

is a way of describing a network configuration, a diagram of the location and connection of network devices. The network topology allows you to see its entire structure, the network devices included in the network, and their connections with each other.

There are several types of topologies: physical, logical, informational and exchange control topology. In this article we will talk about the physical topology of the network, which describes the actual location and connections between the nodes of the local network.

There are several main types of physical network topologies:

1. Bus network topology- a topology in which all computers on the network are connected to one cable, which is shared by all workstations. With this topology, the failure of one machine does not affect the operation of the entire network as a whole. The disadvantage is that if the bus fails or breaks, the operation of the entire network is disrupted.
2. Zvezda network topology— a topology in which all workstations have a direct connection to the server, which is the center of the “star”. With this connection scheme, a request from any network device is sent directly to the server, where it is processed at different speeds, depending on the hardware capabilities of the central machine. Failure of the central machine leads to the shutdown of the entire network. The failure of any other machine does not affect the operation of the network.
3. Ring network topology- a scheme in which all nodes are connected by communication channels into an unbroken ring (not necessarily a circle) through which data is transmitted. The output of one PC is connected to the input of another. Having started the movement from one point, the data ultimately ends up at its beginning. Data in a ring always moves in the same direction. This network topology does not require the installation of additional equipment (server or hub), but if one computer fails, the operation of the entire network stops.
4. Mesh network topology- a topology in which each workstation is connected to all other workstations on the same network. Each computer has many possible ways to connect to other computers. Therefore, a cable break will not result in loss of connection between the two computers. This network topology allows the connection of a large number of computers and is typically typical for large networks.
5. At mixed topology Several types of connections between computers are used. It occurs quite rarely in particularly large companies and organizations.

Why do you need to know the types of topologies and all their pros and cons? The composition of the equipment and software. The topology is chosen based on the needs of the enterprise. In addition, knowledge of the network topology allows you to evaluate its weak points, as well as the dependence of the stability of its operation on individual components, and more carefully plan subsequent connections of new network equipment and PCs. In case of any failure, lack of connection with any computer on the network, you can always see on the map where this device located, on which floor, in which office or room, what, first of all, you need to pay attention to and where to go first to troubleshoot the problem.

And here we come to one of the key questions of interest to all system administrators, namely: how to draw a network diagram with minimal time, effort and money? If the network is large and consists of dozens of servers, hundreds of computers and many other network devices (printers, switches, etc.), even an experienced system administrator(not to mention for a beginner) it is very difficult to quickly understand all the connections between network equipment. Creating a network topology manually is out of the question here. Fortunately, the modern software market offers special programs for automatic exploration and construction of a network diagram. This allows the system administrator to know where and what equipment is located without having to manually examine the wires.

Thus, even if you are new to the company, and the previous system administrator was not very eager to “hand over” the network to you according to all the rules, programs for drawing network topology will allow you to quickly get involved in the work and start with building a diagram of your network.