General network topology. Basic LAN topologies

15.04.2019 Windows Phone

The term "topology" has many meanings, one of which is used in computer world to describe networks. What is the topology further and will be discussed. But, running a little ahead, in the very simple 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 geometric shapes that correspond to each type of terminal arrangement.

What is meant by a local network topology?

As it is already clear, computers united into single networks are connected to them not chaotically, but in a strictly defined order. To describe this circuit, an understanding of topology was introduced.

Essentially, what is topology? Map, diagram, diagram, 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, in this regard, this factor should also be taken into account.

The main types of networks and their topologies

In general, there is no single concept of computer topology. It is generally accepted that there can be several types of topologies, collectively describing one or another network organization. Actually, the 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 (urban, regional, etc.).

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

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

On the basis of the described processes and structures, they are divided into several types:

physical - a description of the actually existing structure of the location of computers and network nodes, taking into account the connections between them;
logical - a description of the signal flow through the network;
informational - a 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 generally accepted classification types of link topologies. In the context of what topology is, one more type of classification should be separately noted, describing exclusively the way a computer is connected to a network or the principle of its interaction with other terminals or main nodes. In this case, the concepts of fully connected and not fully connected topologies become relevant.

A fully connected structure (and this is recognized all over the world) is extremely cumbersome due to the fact that each single terminal in a single network structure is connected to all others. The inconvenience in this case is that for each computer it is necessary to install optional equipment communication, and the terminal itself must be equipped with sufficient big amount communication ports. And as a rule, such structures, if used, are extremely rare.

In this regard, a loosely coupled topology looks much preferable, since each individual terminal does not connect to all other computers, but receives or transmits information through certain network nodes or addresses directly to a central hub or hub. A striking example of this is the "star" network topology.

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

Bus network topology

This type of connecting terminals into a network is quite popular, although it has very serious disadvantages.

Consider what the "bus" topology is, you can on simple example... Imagine a cable with multiple branches on either side. At the end of each such branch 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 to prevent signal reflection. This is the standard line topology networks.

The advantage of such a connection is that the length of the main backbone is significantly reduced, and the failure of a single terminal has no effect on the operation of the network as a whole. The main disadvantage is that in case of violations in the operation of the highway itself, the entire network turns out to be inoperative. In addition, the "bus" topology is limited in the number of connected workstations and has a rather low performance due to the distribution of resources between all terminals in the network. The distribution can be uniform or uneven.

Star topology

The topology of the "star" network in a sense resembles a "bus", with the only difference that all terminals are connected not to a single backbone, but to a central one. 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 to whom it is intended. The advantages of such a connection include the ability centralized management all terminals of the network, as well as connecting new ones. However, as with the "bus", failure of the central switching device has consequences for the entire network.

Ring topology

Finally, we have before us another type of connection - a ring network topology. As, probably, it is 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 (naturally, a circle in this case is a conditional concept).

During transmission, information from the starting point passes through all the terminals that face the final recipient. But the recognition of the ultimate beneficiary is based on token access. That is, the information is received only by the terminal marked in the information stream. Such a scheme is practically not used anywhere 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 connections can be obtained by removing some connections from the above connections or adding them additionally. In most cases, such a scheme is used in large networks.

In this regard, several basic derivatives can be defined. The most common schemes are considered " double ring"," Tree "," lattice "," snowflake "," Clos net ", etc. As you can see even from the names, all these are variations on the theme of the main types of compounds, which are taken as a basis.

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

Conclusion

Now, perhaps, it is already clear what topology is. If we make a certain grand total, this concept is a description of how computers connect on a network and how they interact. How this is done depends solely on the method of combining the terminals into one whole. And say that today one can single out universal option connection, it is impossible. 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 scheme is the "star", although the "bus" is still used quite widely.

It remains to add that in you can also find the concepts of centralization and decentralization, but they are mostly related not to connections, but to the control system. network terminals and exercising control over them. Centralization is clearly expressed in star connections, but decentralization is also applicable for this type, providing the introduction of additional elements in order to increase the reliability of the network upon exit central switch out of service. A fairly effective development in this regard is the "hypercube" scheme, but it is very difficult to develop.

Network topology (from the Greek. τόπος, - place) - a way of describing the network configuration, layout and connection network devices.
(Wikimedia)

Topology - This is a diagram of the connection by communication channels of computers or network nodes to each other.
The network topology can be

physical - describes the actual location and connections between network nodes.
logical - describes the path of the signal within the physical topology.
information - describes the direction of information flows transmitted over the network.
exchange management is the principle of transferring the right to use the network.

There are many ways to connect network devices. The following topologies are distinguished:

fully connected
cellular
common bus
star
ring
Snowflake

Let's consider each of them in more detail.

1) Fully connectedtopology- topology computer network in which each workstation is connected to everyone else. This option is cumbersome and ineffective, despite its logical simplicity. An independent line must be allocated for each pair, each computer must have as many communication ports as there are computers in the network. For these reasons, the network

can only have relatively small final dimensions. Most often this topology is used in multi-machine complexes or global networks with a small number of workstations.

The access technology in networks of this topology is implemented by the token transfer method. A marker is a packet with a special sequence of bits (it can be compared to an envelope for a letter). It is sequentially transferred around the ring from computer to computer in one direction. Each node relays the transmitted token. The computer can transmit its data if it received a blank token. The packet token is passed until the target computer is found. In this computer, data is received, but the token moves on and returns to the sender.
After the sending computer verifies that the packet has been delivered to the addressee, the token is released.

Disadvantage: g A cumbersome and ineffective option, i.e. To . each computer must have a large number of communication ports.

2) Mesh topology - basic fully-mesh topology of a computer network, in which each workstation on a network is connected to several other workstations on the same network. It is characterized by high fault tolerance, configuration complexity and excessive cable consumption. Each computer has many possible ways connections with other computers. Broken cable will not result in loss of connection between the two computers.

It is obtained from fully connected by removing some possible connections. This topology allows the connection of a large number of computers and is typical, as a rule, for large networks.

3) Common bus, is a common cable (called a bus or backbone) to which all workstations are connected. There are terminators at the ends of the cable to prevent signal reflection.

Advantages:

Disadvantages:

Network problems, such as cable breaks and terminator failure, completely block the entire network from working;
Complex localization of faults;
With the addition of new workstations, network performance decreases.

A bus topology is a topology in which all devices in a local area network are connected to a linear network data transmission medium. This linear environment is often referred to as a channel, bus, or trace. Each device, such as a workstation or server, is independently connected to the common bus cable using a special connector. The bus cable must have a terminating resistor, or terminator, at the end that absorbs the electrical signal, preventing it from reflecting and moving in the opposite direction along the bus.

4) Star - basic topology of a computer network, in which all computers on the network are connected to a central site (usually a switch), forming a physical segment of the network. Such a network segment can function both separately and as part of a complex network topology (usually a “tree”). All information exchange is carried out exclusively through the central computer, on which a very large load is imposed in this way, therefore it cannot be engaged in anything other than the network. As a rule, it is the central computer that is the most powerful, and it is on it that all the functions of managing the exchange are entrusted. In principle, no conflicts in a network with a star topology are possible, because the management is completely centralized.

The access method is implemented using Arcnet technology. This accessor also uses a token to pass data. The token is transmitted from computer to computer in ascending order of address. As with a ring topology, each computer regenerates a token.

Comparison with other topologies.

Advantages:

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 correct design);
flexible administration options.

Disadvantages:

failure of the central hub will result in the inoperability of the network (or network segment) as a whole;
more cable is often required to lay the network than for most other topologies;
the finite number of workstations on the network (or network segment) is limited by the number of ports in the central hub.

5) Ring - this is the topology , in which each computer is connected by communication lines with only two others: from one it only receives information, and to the other only transmits. On each communication line, as in the case stars , only one transmitter and one receiver works. This allows you to abandon the use of external terminators.

The operation in the ring network is that each computer repeats (resumes) the signal, that is, acts as a repeater, so the signal attenuation in the entire ring does not matter, only the attenuation between neighboring computers in the ring is important. In this case, there is no clearly designated center; all computers can be the same. However, quite often a special subscriber is allocated in the ring, which manages the exchange or controls the exchange. It is clear that the presence of such a control subscriber reduces the reliability of the network, because its failure immediately paralyzes the entire exchange.

The computers in the ring are not completely peer-to-peer (unlike, for example, a bus topology). Some of them necessarily receive information from the computer, which is transmitting at this moment, earlier, while others - later. It is on this feature of the topology that the methods of controlling the exchange over the network, specially designed for the "ring", are built. In these methods, the right to the next transfer (or, as they say, to capture the network) is sequentially transferred to the next computer in the circle.

Connecting new subscribers to the "ring" is usually completely painless, although it requires a mandatory shutdown of the entire network for the duration of the connection. As with the bus topology, maximum amount the number of subscribers in the ring can be quite large (1000 and more). Ring topology Usually it is the most resistant to congestion, it provides confident work with the largest flows of information transmitted over the network, because, as a rule, there are no conflicts (unlike a bus), and there is also no central subscriber (unlike a star).

In the ring, unlike other topologies (star, bus), a concurrent method of sending data is not used, a computer in the network receives data from the previous one in the list of addressees and redirects them further if they are not addressed to him. The mailing list is generated by the token generator computer. Network module generates a token signal (usually about 2-10 bytes to avoid fading) and passes it on to the next system (sometimes in ascending MAC address). Next system having received the signal, it does not analyze it, but simply transfers it further. This is the so-called zero cycle.

The subsequent work algorithm is as follows - the GRE data packet transmitted by the sender to the addressee begins to follow the path laid by the marker. The packet is transmitted until it reaches the recipient.

Comparison with other topologies.

Advantages:

Easy to install;
Practically complete absence additional equipment;
Possibility of stable operation without a significant drop in the data transfer rate under intensive network load, since the use of the token eliminates the possibility of collisions.

Disadvantages:

Failure of one workstation, and other problems (broken cable), affect the performance of the entire network;
Complexity of configuration and configuration;
Complexity of troubleshooting.
The need to have two network cards, at each workstation.

6) Cnezhinka ( Hierarchical Star or tree topology) -star topology, but several concentrates are used, hierarchically interconnected by star links.A snowflake topology requires less cable length than a star, but more elements.

Most common the way of communication as in local networks, and the site lyceum1.perm.ru

Term network topology refers to a way of connecting computers to a network. You may also hear other names - network structure or network configuration (This is the same). In addition, the concept of topology includes many rules that determine the location of computers, how cables are laid, how to place communication equipment, and much more. To date, several basic topologies have been formed and established. Of these, it can be noted “ tire”, “ring" and " a star”.

Bus topology

Topology tire (or, as it is often called common bus or highway ) assumes the use of one cable to which all workstations are connected. A common cable is used by all stations in turn. All messages sent by individual workstations are received and listened to by all other computers connected to the network. From this stream, each workstation selects messages addressed only to it.

Advantages of the bus topology:

ease of customization;
relative ease of installation and low cost if all workstations are located nearby;
failure of one or more workstations does not affect the operation of the entire network in any way.

Disadvantages of bus topology:

bus malfunctions anywhere (cable break, failure of the network connector) lead to the inoperability of the network;
the complexity of troubleshooting;
low performance - at a time, only one computer can transmit data to the network; with an increase in the number of workstations, the network performance decreases;
poor scalability - to add new workstations, it is necessary to replace sections of the existing bus.

It was on the “bus” topology that local networks were built on coaxial cable... In this case, pieces of coaxial cable connected by T-connectors were used as a bus. The bus was laid through all rooms and went to every computer. The side terminal of the T-connector was inserted into a slot on the network card. This is how it looked: Now such networks are hopelessly outdated and have been replaced everywhere with a "star" on twisted pair, but equipment for coaxial cable can still be seen in some enterprises.

Ring topology

Ring Is a local network topology in which workstations are connected in series to each other, forming a closed ring. Data is transferred from one workstation to another in one direction (in a circle). Each PC acts as a repeater, relaying messages to the next PC, i.e. data is transferred from one computer to another as if by relay race. If a computer receives data intended for another computer, it transfers them further along the ring, otherwise they will not be transferred further.

Ring topology benefits:

ease of installation;
almost complete absence of additional equipment;
the possibility of stable operation without a significant drop in the data transfer rate with an intensive network load.

However, the “ring” also has significant disadvantages:

each workstation must actively participate in the transfer of information; in case of failure of at least one of them or a cable break, the operation of the entire network stops;
connecting a new workstation requires a short-term shutdown of the network, since during the installation of a new PC the ring must be open;
the complexity of configuring and setting;
the complexity of troubleshooting.

Ring network topology is rarely used. She found the main application in fiber optic networks Token Ring standard.

Star topology

Star Is a local network topology where each workstation is attached to a central device (switch or router). A central device controls the movement of packets on the network. Every computer through network card connected to the switch with a separate cable. Multiple star networks can be linked together if required, resulting in a network configuration with tree-like topology. Tree topology is common in large companies... We will not consider it in detail in this article.

The "star" topology today has become the main one in the construction of local networks. This happened due to its many advantages:

failure of one workstation or damage to its cable does not affect the operation of the entire network as a whole;
excellent scalability: to connect a new workstation, it is enough to lay a separate cable from the switch;
easy troubleshooting and network interruptions;
high performance;
ease of setup and administration;
additional equipment can be easily integrated into the network.

However, like any topology, the star is not without its drawbacks:

failure of the central switch will result in the inoperability of the entire network;
additional costs for network hardware- a device to which all computers on the network will be connected (switch);
the number of workstations is limited by the number of ports in the central switch.

Star Is the most common topology for wired and wireless networks... An example of a star topology is a cabled network. twisted pair, and the switch as central unit... These are the networks found in most organizations.

Under the topology(layout, configuration, structure) of a computer network is usually understood physical location network computers are one relative to one and the way they are connected by communication lines. It is important to note that the concept of topology refers primarily to local networks, in which the structure of links can be easily traced. In global networks, the structure of connections is usually hidden from users, which is not very important, because each communication session can be performed along its own path.
The topology determines the requirements for the equipment, the type of cable used, the possible and most convenient methods of exchange control, the reliability of operation, and the possibility of expanding the network.

There are three main network topologies:

1. Bus network topology(bus), in which all computers are connected in parallel to one communication line and information from each computer is simultaneously transmitted to all other computers (Fig. 1);

2. Star network topology(star), in which other peripheral computers are connected to one central computer, and each of them uses its own separate communication line (Fig. 2);

3. Network topology ring(ring), in which each computer always transmits information to only one computer, the next in the chain, and receives information only from previous computer in a chain, and this chain is closed in a "ring" (Fig. 3).

Rice. 1. Network topology "bus"

Rice. 2. Star network topology

Rice. 3. Network topology "ring"

In practice, combinations of basic topologies are often used, but most networks are focused on these three. Let us now briefly consider the features of the listed network topology.

Bus topology(or, as it is also called, "common bus") by its very structure allows the identity of the network equipment of computers, as well as the equality of all subscribers. With such a connection, computers can only transmit in turn, because the communication line is the only one. Otherwise, the transmitted information will be distorted as a result of overlap (conflict, collision). Thus, the bus implements the half duplex exchange mode (in both directions, but in turn, and not simultaneously).
In the bus topology, there is no central subscriber through which all information is transmitted that increases its reliability (after all, if any center fails, the entire system controlled by this center ceases to function). Adding new subscribers to the bus is quite simple and is usually possible even while the network is running. In most cases, using the bus requires a minimum amount of connecting cable compared to other topologies. True, you need to take into account that two cables are suitable for each computer (except for the two extreme ones), which is not always convenient.
Because the resolution of possible conflicts in this case falls on the network equipment of each individual subscriber, the equipment network adapter the bus topology is more complicated than the other topology. However, due to the widespread distribution of networks with a "bus" topology (Ethernet, Arcnet), the cost of network equipment is not too high.
The tire is not a terrible failure individual computers because all other computers on the network can continue to exchange normally. It may seem that the bus is not terrible and dug off the cable, since in this case we are obsessed with two fully functional tires. However, through the distribution features electrical signals over long communication lines, it is necessary to provide for the inclusion of special devices at the ends of the bus - terminators shown in Fig. 1 as rectangles. Without the terminators turned on, the signal is reflected from the end of the line and distorted so that communication over the network becomes impossible. So if the cable breaks or is damaged, the communication line is disrupted, and the exchange even between those computers that remain connected to each other stops. A short circuit at any point in the bus cable will destroy the entire network. Any failure of network equipment in the bus is very difficult to localize, because all adapters are connected in parallel, and it is not so easy to understand which one has failed.
When passing through the communication line of a network with a "bus" topology information signals are weakened and not renewed in any way, which imposes strict restrictions on the total length of communication lines, in addition, each subscriber can receive signals of different levels from the network, depending on the distance to the transmitting subscriber. This puts forward additional requirements for the receiving nodes of network equipment. To increase the length of a network with a bus topology, several segments (each of which is a bus) are often used, interconnected with the help of special signal updates - repeaters.
However, such an increase in the length of the network cannot last indefinitely, because there are also limitations associated with the finite speed of propagation of signals over communication lines.

Star topology is a topology with an explicitly dedicated center to which all other subscribers are connected. All information exchange is carried out exclusively through the central computer, which in this way bears a very heavy load, therefore it cannot be engaged in anything other than the network. It is clear that the network equipment of the central subscriber must be significantly more complex than the equipment of the peripheral subscribers. In this case, there is no need to talk about the equality of subscribers. As a rule, it is the central computer that is the most powerful, and it is on it that all the functions of managing the exchange are entrusted. In principle, no conflicts in a network with a star topology are possible, because the management is completely centralized, there is no conflict why.
If we talk about the resistance of a star to computer failures, then failure peripheral computer does not in any way affect the functioning of the part of the network that remains, but any failure of the central computer makes the network completely inoperative. Therefore, should be taken special events to improve the reliability of the central computer and its network equipment. Dropped any cable or short circuit in it, in a star topology, it disrupts communication with only one computer, while all other computers can continue to work normally.
On the declination from the bus, in the star on each communication line there are only two subscribers: the central one and one of the peripheral ones. Most often, two communication lines are used to connect them, each of which transmits information in only one direction. Thus, there is only one receiver and one transmitter on each link. All this greatly simplifies the network installation in comparison with the bus and saves the use of additional external terminators from the need. The problem of signal attenuation in the communication line is also solved in the "star" more easily than in the "bus", because each receiver always receives a signal of the same level. A serious disadvantage of the "star" topology is the severe limitation of the number of subscribers. Typically, a central subscriber can serve no more than 8-16 peripheral subscribers. If within these limits it is quite simple to connect new subscribers, then if they are exceeded, it is simply impossible. True, sometimes a star provides for the possibility of building up, that is, connecting another central subscriber instead of one of the peripheral subscribers (as a result, a topology of several interconnected stars comes out).
The star shown in Fig. 2, is called an active, or real star. There is also a topology called a passive star, which is only superficially similar to a star (Fig. 4). At this time, it is much more common than an active star. Suffice it to say that it is used in today's most popular Ethernet network.

Rice. 4. Topology "passive star"

In the center of a network with this topology, there is not a computer, but a hub, or hub, which performs the same function as a repeater. It resumes signals that come in and forwards them to other communication lines. Although the cabling scheme is similar to a real or active star, in fact we are dealing with a bus topology, because information from each computer is simultaneously transmitted to all other computers, and there is no central station. Naturally, a passive star is more expensive than a conventional bus, because in this case, you also need a hub. However, it provides a number of additional features associated with the benefits of a star. That is why in recent times a passive star is increasingly displacing a real star, which is considered an unpromising topology.
It is also possible to distinguish an intermediate type of topology between an active and a passive star. In this case, the concentrator not only retransmits the signals, but also controls the exchange, but does not take part in the exchange itself.
Big star advantage(both active and passive) is that all connection points are collected in one place. This allows you to easily monitor the operation of the network, localize network faults by simple shutdown from the center of certain subscribers (which is impossible, for example, in the case of a bus), as well as to restrict access outsiders to vital network connection points. In the case of a star, each peripheral subscriber can be approached by either one cable (through which there is transmission in both directions), or two cables (each of them transmits in one direction), and the second situation is more common. A common disadvantage for the entire star topology is significantly greater than for other topologies, the cost of the cable. For example, if computers are located in one line (as in Fig. 1), then choosing a star topology will require several times more cable than a bus topology. This can significantly affect the cost of the entire network as a whole.

Ring topology- this is a topology in which each computer is connected by communication lines with only two others: from one it only receives information, and to the other only transmits. On each communication line, as in the case of a star, only one transmitter and one receiver works. This eliminates the need for external terminators. An important feature of the ring is that each computer repeats (resumes) the signal, that is, acts as a repeater, therefore the signal attenuation in the entire ring does not matter, only the attenuation between neighboring computers in the ring is important. In this case, there is no clearly designated center; all computers can be the same. However, quite often a special subscriber is allocated in the sprat, who manages the exchange or controls the exchange. It is clear that the presence of such a control subscriber reduces the reliability of the network, because its failure immediately paralyzes the entire exchange.
Strictly speaking, computers in a sprat are not completely equal in rights (unlike, for example, a bus topology). Some of them necessarily receive information from the computer, which is transmitting at this moment, earlier, while others - later. It is on this feature of the topology that the methods of controlling the exchange over the network, specially designed for the "ring", are built. In these methods, the right to the next transfer (or, as they say, to capture the network) is sequentially transferred to the next computer in the circle.
Connecting new subscribers to the "ring" is usually completely painless, although it requires a mandatory shutdown of the entire network for the duration of the connection. As in the case of the "bus" topology, the maximum number of subscribers in a sprat can be quite large (up to a thousand or more). The ring topology is usually the most resistant to congestion, it ensures reliable operation with the largest flows of information transmitted over the network, because, as a rule, there are no conflicts in it (unlike a bus), and there is also no central subscriber (unlike a star) ...
Because the signal in the sprat passes through all the computers on the network, the failure of at least one of them (or its network connection) disrupts the robot of the entire network as a whole. Likewise, any open or short circuit in each of the cables in the ring makes the entire network impossible. The ring is most vulnerable to cable damage, therefore, in this topology, it is usually provided for the laying of two (or more) parallel communication lines, one of which is in reserve.
In the same time great advantage ring is that the retransmission of signals by each subscriber can significantly increase the size of the entire network as a whole (sometimes up to several tens of kilometers). The ring is relatively superior to any other topology.

Disadvantage rings (in comparison with a star), we can assume that two cables must be connected to each computer on the network.

Sometimes a ring topology is performed on the basis of two circular communication lines that transmit information to opposite directions... The purpose of this solution is to increase (ideally twice) the speed of information transfer. In addition, if one of the cables is damaged, the network can work with another cable (although top speed decrease).
In addition to the three considered basic, basic topologies, the network topology is also often used " tree "(tree), which can be seen as a combination of several stars. As in the case of a star, a tree can be active, or real (Fig. 5), and passive (Fig. 6). With an active tree, central computers are located in the centers of combining several communication lines, and with a passive tree, hubs (hubs).

Rice. 5. Topology "active tree"

Rice. 6. Topology " passive tree". K - concentrators

A combined topology is also used quite often, for example, star bus, star ring.

Significance of the concept of topology.

The topology of a network determines not only the physical location of computers, but, which is much more important, the nature of the connections between them, the features of the propagation of signals over the network. It is the nature of the connections that determines the degree of network fault tolerance, the required complexity of the network equipment, the most suitable exchange control method, the types of transmission media (communication channels), the permissible network size (length of communication lines and the number of subscribers), the need for electrical coordination, and much more are possible.
When the literature recalls the topology of a network, they can mean four completely different concepts that relate to different levels network architecture:

1. Physical topology (that is, the layout of computers and cabling). In this content, for example, a passive star is no different from an active star, therefore it is often called simply a "star".

2. Logical topology (that is, the structure of connections, the nature of the propagation of signals over the network). This is probably the most correct definition of topology.

3. Exchange control topology (that is, the principle and sequence of transferring the right to delight the network between individual computers).

4. Information topology (that is, the direction of the flows of information transmitted over the network).

For example, a network with a physical and logical topology "bus" can use the handover of the network capture right as a control method (that is, be a ring in this content) and simultaneously transmit all information through one dedicated computer (be a star in this content).

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INTRODUCTION

Primary communication networks are a collection of network nodes, stations and transmission lines (more precisely, linear paths) that connect them to each other and form a network of typical channels and paths. The ramified and multi-level nature of this network forces all work related to design, installation, adjustment, commissioning, reconstruction, modernization, etc. individual sites primary network. In relation to the intercity (zonal or trunk) primary network, such sections are called highways. The backbone includes two or more network nodes (stations) on which the terminal and / or transit equipment of several transmission systems (SP) is located, as well as one or more physical lines communications on which the line paths of these joint ventures are organized. In turn, the linear paths contain serviced or unattended amplifying (or regeneration) points, correction points, branches, etc. Thus, the highway is a rather complex and expensive device, which is of great economic importance for a relatively large region of the country.

The aim of the course project is to optimize the network topology according to the criterion of minimum length using the branch and bound method.

1 COMPARATIVE ANALYSIS OF TOPOLOGIES OF TELECOMMUNICATIONS NETWORKS

1.1 Stages of network development

telecommunication network length topology

Various types of telecommunications have evolved independently of each other for a long period of time. Each type of telecommunication focused on the creation of its own channels, transmission systems (TS) and networks. The structure of the network was chosen in accordance with the peculiarities of the distribution of message flows, typical for a particular type of telecommunication. Several industries and transportation have begun building networks to meet the industry's messaging needs. Disunity technical means not only did it not allow increasing the efficiency of the aggregate of networks on a national scale, but also hindered the development of isolated networks. Therefore, already in the early 1960s. it became clear that a promising direction for the development of networks was to be the interconnection of networks. It was decided to create EASC (Unified Automated Communication Network). EASC was based on the unification of disparate and numerous small networks into the nationwide networks of each type of telecommunication, and then into single network with the aim of sharing certain technical means, and, first of all, transmission systems and switching systems.

When creating the EASC, it was taken into account that certain technical means are involved in the transmission process regardless of the type of messages, that is, they are common. In this regard, the entire network of the country began to be subdivided into two interrelated components:

1) primary network - a set of network stations, network nodes (to be defined in the appendix) and transmission lines connecting them, which allows you to organize a network of transmission channels and group paths.

The structure of the primary network takes into account the administrative division of the territory of the country. The entire territory is divided into zones, which, as a rule, coincide with the territory of regions, territories. Accordingly, the primary network also consists of the following parts:

* local primary networks - a part of the network bounded by the territory of a city or rural area;

* zonal primary networks - a part of a network that covers the territory of a zone (oblast, territory, republic), providing interconnection of channels of different local networks within one zone;

* backbone primary network - a part of the network that connects channels of different zonal networks throughout the country.

The structure of the primary network is shown in Figure 1.1.

Figure 1.1 - The structure of the primary network

2) secondary network - a set of technical means that ensure the transmission of messages of a certain type, which includes: terminal devices, subscriber and connecting lines, switching stations, as well as channels allocated from the primary network to form a secondary one.

Secondary networks are divided into the following types:

* telephone;

* telegraph;

* data transmission;

* facsimile;

* television broadcasting;

* sound broadcasting.

1.2 The main methods of building telecommunication communication networks

One of the main requirements for networks for the transmission of individual messages (telephone, telegraph, facsimile, data transmission) is that the network must provide each user with the ability to communicate with another user. To fulfill this requirement, the communication network is built according to a certain principle, depending on the operating conditions. Therefore, communication networks can have different structure, that is, differ in the number and location of nodal and terminal points (stations), as well as the nature of their relationship. Figure 1.2 shows how to build communication networks.

With a fully connected construction method (the principle of "each with each"), there is a direct connection between the nodes. It is used with a small number of nodes on the network (Figure 1.2 a).

With a radial method of building a network, communication between nodes is carried out through a central node (Figure 1.2 b). It is used when building a network in a relatively small area.

Over a large area, the communication network is built according to the radial-nodal method (Figure 1.2 c).

The circular method of building a network provides for the possibility of communication both clockwise and counterclockwise (Fig. 1.2 d). In this case, in case of damage in a certain area, the network retains its operability.

With the combined method of building a network, the nodes at the upper hierarchical level are connected according to a fully connected scheme, Figure 1.2 e). In this case, the exit of one of the nodes does not disrupt the operation of the entire network.

Figure 1.2 - Methods of building communication networks

2 BUILDING A MODEL OF THE TOPOLOGY OF THE DEVELOPED TELECOMMUNICATIONS NETWORK

Data are presented in the form of table 2.1

Table 2.1- Distances between the nodes of the projected network

Smorgon

Ostrovets

Mites

Deep

Sharkovshchina

Molodechno

Radoshkovichi

Zaslavl

Traveling Salesman Problem.

Let's take as an arbitrary route:

X 0 = (1.2); (2.3); (3.4); (4.5); (5.6); (6.7); (7.8); (8.9) ; (9.10); (10.11); (11.12); (12.13); (13.14); (14.15); (15.1);

Then F (X 0) = 56 + 31 + 32 + 80 + 27 + 77 + 80 + 29 + 155 + 87 + 66 + 21 + 43 + 17 = 801

3 DEVELOPMENT OF A CALCULATING PROCEDURE FOR OPTIMIZING THE TOPOLOGY OF THE DEVELOPED NETWORK

Method essence dynamic programming consists in the approach to solving the problem in stages, each of which is associated with one controlled variable. A set of recurrent computational procedures connecting different stages, ensures that the admissible optimal solution tasks as a whole upon reaching the last stage.

Smorgon

Ostrovets

Mites

Deep

Sharkovshchina

Molodechno

Radoshkovichi

Zaslavl

When solving the problem of finding the optimal path, the task is divided into processes (by the number of nodes), in this case by 15. The process starts from node No. 1. In fact, it does not matter where to start it, the route is still circular and covers all nodes.

At the first stage, the computational procedure will be the distance from node 1 to each of the remaining nodes.

Process no.	Meaning

At the next stage, the value of the computational procedure takes on the value of the minimum distance to the next (any node).

Process no.	Stage 1 value	Phase 2 value

The minimum of the function is selected and the transition to the next stage is carried out. It should be noted that from the values of functions, you can immediately remove the knowingly wrong values... Also, one should not take into account the values leading in the "opposite direction".

4 DEVELOPMENT OF THE BLOCK-DIAGRAM OF THE PROGRAM-SHELL AND BLOCK-DIAGRAM OF THE BASIC PROGRAMS-PROCEDURES FOR OPTIMIZING THE NETWORK TOPOLOGY

In view of the fact that the main procedures are a recurrent expression, it was inappropriate to output them into separate procedures with the compilation of algorithms.

5 DEVELOPMENT AND DEBUGGING OF THE PROGRAM OF OPTIMIZATION OF THE TOPOLOGY OF THE TELECOMMUNICATIONS NETWORK BY THE CRITERION OF ITS MINIMUM LENGTH

The program is developed in the language Java programming... Java is an object-oriented programming language developed by Sun Microsystems since 1991 and officially released on May 23, 1995. Initially new language programming was called Oak (James Gosling) and was developed for consumer electronics but was later renamed Java and used to write applets, applications, and server software

A distinctive feature of Java in comparison with other programming languages general purpose is to provide high programming productivity, rather than the performance of the application or the efficiency of its use of memory.

Java uses almost identical conventions for declaring variables, passing parameters, operators, and controlling the flow of code. All the good features of C ++ have been added to Java.

Three key elements teamed up in Java language technologies

Java provides its applets for wide use - small, reliable, dynamic, platform independent active network applications embedded in Web pages. Java Applets can be customized and distributed to consumers as easily as any HTML documents

Java unleashes the power of object-oriented application development by combining simple and familiar syntax with a robust and easy-to-use development environment. This allows a wide range of programmers to quickly create new programs and new applets.

Java provides the programmer with a rich set of object classes to clearly abstract many system functions used for working with windows, networking and for I / O. The key to these classes is that they provide platform-independent abstractions for wide range system interfaces

The huge advantage of Java is that you can create applications in this language that can run on different platforms... Most computers are connected to the Internet. different types- Pentium PC, Macintosh, Sun workstations, and so on. Even within the framework of computers created on the basis of Intel processors, there are several platforms, for example Microsoft Windows version 3.1, Windows 95, Windows NT, OS / 2, Solaris, different varieties operating room UNIX systems with graphical shell XWindows. Meanwhile, creating web server on the Internet, I would like it to be used as much as possible more of people. In this case, they will help out Java applications designed to work on various platforms and do not depend on the specific type of processor and operating system.

The program takes initial data from text file which is a table. The path to the file is written in the body of the program. By default, the value is "D: \\ cites.txt". The number of cities matters, if their number changes, you need to change the value of the variable n.

For the convenience of displaying the results, the name of the cities is indicated in the program; to change them, it is also necessary to change the program code. If the names are not changed, the program works correctly and the city numbers can be taken as a basis.

The optimization results are displayed on the screen, indicating the total length of the route.

6 CALCULATION OF THE OPTIMAL TOPOLOGY OF THE DEVELOPED TELECOMMUNICATIONS NETWORK AND ANALYSIS OF THE NETWORK TOPOLOGY MODEL FOR SENSITIVITY TO CHANGES IN PARAMETERS

The result of the program is shown in Figure 5.2. In this case, the result is checked in other algorithms.

The route scheme with reference to the map of the Republic of Belarus is shown in Figure 6.1.

CONCLUSION

As a result of the accomplished term paper gained invaluable skills in the design and optimization of telecommunication networks. An algorithm was developed for the optimization program, the program was implemented and an optimization procedure was carried out for a given network configuration. The results were verified by manual calculation. The branch-and-bound method was used as a method for optimizing the network structure according to the criterion of minimum length.

LIST OF SOURCES USED

1. Taha H. Introduction to operations research / per. from English -M .: Williams, 2005.

2. Bundy B. Optimization methods. Introductory course. -M .: Radio and communication, 1988.

3. Vasiliev F.V. Numerical methods for solving extreme problems. -M .: Nauka, 1980.

APPENDIX A

PROGRAM TEXT

import java.io. *;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

import java.util.StringTokenizer;

public class ShortestPathDynamicMethods (

public static int readDistancesFromFile () throws FileNotFoundException (

File f1 = new File ("D: \\ Cities2.txt");

BufferedReader input = new BufferedReader (new FileReader (f1));

BufferedReader input1 = new BufferedReader (new FileReader (f1));

int NUMBER_CITIES = 0;

String line = null;

while ((line = input1.readLine ())! = null) (

NUMBER_CITIES ++;

) catch (IOException e) (

e.printStackTrace ();

int array = new int;

String line = null;

while ((line = input.readLine ())! = null) (

StringTokenizer st = new StringTokenizer (line);

while (st.hasMoreTokens ()) (

String tkn = st.nextToken ();

//System.out.println(tkn);

array [i] [j] = Integer.parseInt (tkn);

) catch (IOException e) (

e.printStackTrace ();

public static int getShortestDistance (int dist) (

List cityList = new ArrayList ();

cityList.add ("Ivye");

cityList.add ("Ashmyany");

cityList.add ("Smorgon");

cityList.add ("Ostrovets");

cityList.add ("Postavy");

cityList.add ("Myadel");

cityList.add ("Pincers");

cityList.add ("Deep");

cityList.add ("Sharkovshchina");

cityList.add ("Volozhin");

cityList.add ("Logoisk");

cityList.add ("Molodechno");

cityList.add ("Vileika");

cityList.add ("Radoshkovichi");

cityList.add ("Zaslavl");

int n = dist.length;

int dp = new int [n];

for (int d: dp)

Arrays.fill (d, Integer.MAX_VALUE / 2);

for (int mask = 1; mask< 1 << n; mask += 2) {

for (int i = 1; i< n; i++) {

if ((mask & 1<< i) != 0) {

for (int j = 0; j< n; j++) {

if ((mask & 1<< j) != 0) {

dp [i] = Math.min (dp [i], dp [j] + dist [j] [i]);

int res = Integer.MAX_VALUE;

for (int i = 1; i< n; i++) {

res = Math.min (res, dp [(1<< n) - 1][i] + dist[i]);

int cur = (1<< n) - 1;

int order = new int [n];

for (int i = n - 1; i> = 1; i--) (

for (int j = 1; j< n; j++) {

if ((cur & 1<< j) != 0 && (bj == -1 || dp + dist >dp [j] + dist [j])) (

cur ^ = 1<< bj;

System.out.println ("City traversal order:");

for (int i = 0; i< order.length; i++)

System.out.println ((i + 1) + "" + cityList.get (order [i]));

public static void main (String args) (

System.out.println ("Minimum distance:" + getShortestDistance (ShortestPathDynamicMethods.readDistancesFromFile ()));

) catch (Exception e) (

e.printStackTrace ();

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