Ring water supply network. Ring topology

Network topology

(from the Greek. τόπος, - place) - a way of describing the network configuration, a diagram of the location and connection of network devices. The term topology, or network topology, refers to the physical location of computers, cables, and other components of a network. Topology is a standard term used by professionals to describe the basic layout of a network. If you understand how different topologies are used, you will be able to understand what capabilities different types of networks have. To share resources or perform other network tasks, computers must be connected to each other. Most networks use a cable for this purpose. However, simply plugging your computer into a cable that connects other computers is not enough. Different types of cables, combined with different network cards, network operating systems, and other components, also require different positioning of computers. 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. Topology can also determine the way computers interact on a network. Different types of topologies correspond to different communication methods, and these methods have a large impact on the network.

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 control is the principle of transferring the right to use the network.

There are many ways to connect network devices, of which eight basic topologies can be distinguished:

B. Lattice

C. Star

D. Ring

E. Tire

ü Double ring

ü Mesh topology

A - line; B - lattice;

C - star; D - ring;

E - tire; F is a tree.

The rest of the methods are combinations of the basic ones. These topologies are generally referred to as mixed or hybrid topologies, but some of them have their own names, such as Tree.

Basic topologies

All networks are built on the basis of three basic topologies:

ü bus (bus) - (computers are connected along one cable)

ü star (star) - (computers are connected to cable segments originating from one point, or hub)

ü ring (ring) - (the cable to which computers are connected is closed in a ring)

Although the basic topologies themselves are not complex, in reality there are often quite complex combinations that combine the properties of several topologies.

Tire

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

Computer interaction

In a bus topology, computers address data to a specific computer by transmitting it over a cable in the form of electrical signals. To understand the process of communication between computers on the bus, you must understand the following concepts:

• signal transmission;
• signal reflection;
• Terminator.

Signal transmission

The data is transmitted in the form of electrical signals to all computers on the network; however, only the one whose address matches the recipient's address "encrypted in these

signals. Moreover, at a 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 for data transfer, the slower the network. However, it is impossible to deduce a direct relationship between the network bandwidth and the number of computers in it. For, in addition to the number of computers, many factors affect network performance, including:

ü characteristics of the hardware of computers in the network;

ü the frequency with which computers transmit data;

ü type of running network applications;

ü type of network cable;

ü distance between computers in the network.

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

Signal reflection

Data, or electrical signals, travels throughout the network, from one end of the cable to the other. If no special action is taken, the signal will be reflected upon reaching the end of the cable and prevent other computers from transmitting. Therefore, after the data reaches the destination, the electrical signals must be extinguished.

Terminator

To prevent the reflection of electrical signals, 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 extend the cable length. Any free - unconnected - end of the cable must be terminated to prevent reflections of electrical signals.

Violation of the integrity of the network

A break in a network cable occurs when it is physically broken 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 the reflection of electrical signals in the cable and the termination of the network functioning. The network "crashes". By themselves, computers on the network remain fully functional, but as long as the segment is broken, they cannot communicate with each other.

Star

In a star topology, all computers use cable segments to connect to a central component called a hub. Signals from the transmitting computer go through the hub to everyone else. This topology arose at the dawn of computing, when computers were connected to a central, master computer.

Here, cable connection and network configuration management are centralized.

Flaws:

• since all computers are connected to a central point, for large networks it is significantly cable consumption increases.
• if the central component fails, the entire network will be disrupted.

Advantages:

• If only one computer fails (or the cable connecting it to the hub), then only this computer will not be able to transmit or receive data over the network. This will not affect other computers on the network.
• The bandwidth of such local computing is guaranteed for each workstation on the network and depends only on the computing power of the node. Collisions in a network of this topology are impossible.
• Star networks have maximum possible performance, since data between workstations is transmitted through the central node on separate lines, which are used exclusively by these stations. The frequency of requests for transmission of information between stations is relatively low.

LAN performance is in direct proportion to the capacity of the file server. If the central node goes down, the network also shuts down.

Cable installation is straightforward as each workstation is only connected to the host, but the total cost of the cable can be quite high and increase when the host is not in the center of the network.

To expand the network, it is necessary to install a separate cable from the new workstation to the host machine.

The network is managed from its center, while the information protection mechanism is implemented in the center.

Ring

In a ring topology, computers are connected to a cable that is closed in a ring. Therefore, the cable simply cannot have a free end to which a terminator must be connected. Signals travel around the ring in one direction and pass through each computer. In contrast to the passive bus topology, here each computer acts as a repeater, amplifying the signals and transmitting them to the next computer. Therefore, if one computer fails, the entire network stops functioning.

Passing a token

One of the principles of data transmission in a ring network is called transfer token... Its essence is as follows. The token is sequentially transmitted from one computer to another until the one that "wants" to transmit the data receives it. The sending computer changes the token, puts the email address in the data, and sends it around the ring.

The data goes through each computer until it reaches the one whose address matches the recipient's address specified in the data. After that, the receiving computer sends a message to the transmitting one, where it confirms the fact of receiving data. We receive confirmation, the transmitting computer creates a new token and returns it to the network. At first glance, it seems that the transfer of the marker is time-consuming, but in fact, the marker moves at almost the speed of light. In a ring with a diameter of 200 m, the marker can circulate at a frequency of 10,000 revolutions per second.

Dignity:

Flaw:

• if at least one workstation fails, the entire network becomes inoperative. Any malfunction of the cable connection on such a network is not difficult to detect.
• To connect a new station to the local network, it is necessary to temporarily disconnect the network.
• The information transfer time increases with the number of stations on the LAN.

The length of such a network can be unlimited.

Logical ring local area network

A logical ring local area network is a special form of LAN topology. It is a connection of several networks, organized in a star topology. To connect individual "stars" to the network, special hubs are used, which are often called hubs. Hubs can be active or passive. The difference between active concentrators is the presence of an additional amplifier, which is used to connect 4 - 16 workstations. The passive hub is designed for three workstations and is essentially just a branching device. Management of each specific station in the network is carried out in the same way as in a ring LAN. Each workstation on the network receives its own address, at which the transfer of control is carried out. Failure of one of the machines can affect only the downstream stations; failure of the entire network is unlikely.

MVV capabilities allow you to organize self-healing ring nets.

There are two options for building them: unidirectional and bidirectional ring.

In the first variant, each input stream is directed around the ring in both directions, and on the receiving side, as in the case of the 1 + 1 scheme, the best signal is selected. Two fibers are used to build the ring. Transmission along all main paths occurs in one direction (for example, clockwise), and along all backup paths - in the opposite direction (the division into the main and backup paths here is conditional, since they are both equal). Therefore, such a ring is called unidirectional, with path switching or with a fixed reserve.

The signal flow diagram of both transmission directions for one connection along the main and backup paths in such a ring is shown in Fig. 5.2.

Rice. 5.2. Unidirectional ring

When bidirectional double-fiber rings do not double the signal. In normal operation, each input stream is directed along the ring along the shortest path in any direction (hence the name "bidirectional"). In the event of a failure by means of the MBV at both ends of the failed section, the entire flow of information entering this section is switched in the opposite direction. Such a ring is also said to have section switching or shared redundancy protection.

An example of a bidirectional ring is shown in Fig. 5.3 and fig. 5.4. They show the signal flow diagrams of both transmission directions for one connection during normal operation (Fig. 5.3) and in emergency mode in case of failure of one of the sections of the ring crossed out with a cross (Fig. 5.4).

Rice. 5.3. Bidirectional ring in normal mode

Rice. 5.4. Bi-directional ring in emergency mode

A bi-directional four-fiber ring is also possible. It provides a higher level of fault tolerance than rings with two fibers, but its construction costs are significantly higher, so this option is used less often.

A bi-directional ring is more economical in most cases, requiring less bandwidth. This is due to the fact that signals transmitted in different non-intersecting sections of such a ring can use the same capacities (both in the main and in emergency modes of operation). At the same time, a unidirectional ring is easier to implement. Analysis of typical situations shows that each of the two types of ring architecture has its own area of ​​preferred application.

Unidirectional rings are more suitable for centripetal traffic situations. This is typical of access networks designed to connect users to the nearest site. Bidirectional rings are more beneficial when the traffic is distributed fairly evenly so that their bandwidth advantage becomes noticeable. Therefore, their use is advisable for connecting networks.

With both options, it is possible to maintain full network performance in case of any single failure.

Did you know, what is the falsity of the concept of "physical vacuum"?

Physical vacuum - the concept of relativistic quantum physics, under which they mean the lowest (ground) energy state of the quantized field, which has zero momentum, angular momentum and other quantum numbers. Relativistic theorists call a physical vacuum a space completely devoid of matter, filled with an unmeasurable, and therefore only an imaginary field. Such a state, according to relativists, is not an absolute emptiness, but a space filled with some phantom (virtual) particles. Relativistic quantum field theory asserts that, in accordance with the Heisenberg uncertainty principle, virtual, that is, apparent (to whom?), Particles are constantly born and disappear in the physical vacuum: so-called zero-point field oscillations occur. Virtual particles of the physical vacuum, and therefore, itself, by definition, do not have a frame of reference, since otherwise Einstein's principle of relativity, on which the theory of relativity is based, would be violated (that is, an absolute system of measurement would become possible with reference from particles of a physical vacuum, which, in turn, would unequivocally refute the principle of relativity, on which the SRT is built). Thus, the physical vacuum and its particles are not elements of the physical world, but only elements of the theory of relativity, which exist not in the real world, but only in relativistic formulas, violating the principle of causality (arise and disappear for no reason), the principle of objectivity (virtual particles can be considered, depending on the desire of the theoretician, either existing or not existing), the principle of actual measurability (not observable, do not have their own IRS).

When this or that physicist uses the concept of "physical vacuum", he either does not understand the absurdity of this term, or is disingenuous, being a hidden or explicit adherent of relativistic ideology.

The easiest way to understand the absurdity of this concept is to refer to the origins of its origin. It was born by Paul Dirac in the 1930s, when it became clear that the denial of the ether in its pure form, as the great mathematician, but the mediocre physicist did, was no longer possible. Too many facts contradict this.

To defend relativism, Paul Dirac introduced the aphysical and illogical concept of negative energy, and then the existence of a "sea" of two energies compensating each other in a vacuum - positive and negative, as well as a "sea" of particles compensating each other - virtual (that is, apparent) electrons and positrons in a vacuum.

If we talk about the stability of the star to computer failures, then the failure of a peripheral computer or its network equipment does not affect the functioning of the rest of the network in any way, but any failure of the central computer makes the network completely inoperative. In this regard, special measures should be taken to improve the reliability of the central computer and its network equipment.

A break in the cable or a short circuit in it with a star topology disrupts communication with only one computer, and all other computers can continue to work normally.

In contrast to the bus, in a 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 one direction, that is, there is only one receiver and one transmitter on each communication line. This is the so-called transmission point to point... All this greatly simplifies the network equipment in comparison with the bus and eliminates the need to use additional, external terminators.

The problem of signal attenuation in the communication line is also solved in a star more easily than in the case of a bus, because each receiver always receives a signal of the same level. The maximum length of a network with a star topology can be twice as long as in the bus (that is, 2 L pr), since each of the cables connecting the center with a peripheral subscriber can have a length L pr.

A serious disadvantage of star topology is the severe limitation of the number of subscribers. Typically, a central subscriber can serve no more than 8-16 peripheral subscribers. Within these limits, the connection of new subscribers is quite simple, but beyond them it is simply impossible. In a star, it is permissible to connect another central subscriber instead of a peripheral one (as a result, a topology of several interconnected stars is obtained).

The star shown in Fig. 1.6, is called an active or true star. There is also a topology called a passive star, which only looks like a star (Figure 1.11). It is now much more widespread than the active star. Suffice it to say that it is used on the most popular Ethernet network today.

In the center of the network with this topology, not a computer is placed, but a special device - a hub or, as it is also called, a hub, which performs the same function as a repeater, that is, it restores incoming signals and sends them to all other communication lines ...

Rice. 1.11.

It turns out that although the cabling scheme is similar to a true or active star, in fact, we are talking about a bus topology, since information from each computer is simultaneously transmitted to all other computers, and there is no central subscriber. Of course, a passive star is more expensive than a conventional bus, since in this case a hub is also required. However, it provides a number of additional features associated with the benefits of the star, in particular, simplifies network maintenance and repair. That is why, in recent years, a passive star is increasingly displacing a true 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 incoming signals, but also controls the exchange, but does not participate in the exchange itself (this is done in the 100VG-AnyLAN network).

A great advantage of a star (both active and passive) is that all connection points are collected in one place. This makes it easy to monitor the operation of the network, localize faults by simply disconnecting certain subscribers from the center (which is impossible, for example, in the case of a bus topology), and also restrict access of unauthorized persons to connection points vital for the network. In the case of a star, a peripheral subscriber can be approached by either one cable (through which there is transmission in both directions), or two (each cable transmits in one of two opposite directions), and the latter is much more common.

A common disadvantage for all star topologies (both active and passive) is that the cable consumption is significantly higher than with other topologies. For example, if the computers are located in one line (as in Fig. 1.5), then when choosing a star topology, you will need several times more cable than with a bus topology. This significantly affects the cost of the network as a whole and significantly complicates the cabling.

Ring topology

A ring is a topology in which each computer is connected by communication lines with two others: from one it receives information, and transfers to the other. On each communication line, as in the case of a star, only one transmitter and one receiver (point-to-point communication) operates. This eliminates the need for external terminators.

An important feature of the ring is that each computer retransmits (restores, amplifies) the signal coming to it, that is, it acts as a repeater. Signal attenuation in the entire ring is irrelevant, only the attenuation between adjacent computers in the ring is important. If the maximum cable length, limited by attenuation, is L pr, then the total ring length can reach NL pr, where N is the number of computers in the ring. The total size of the network in the limit will be NL pr / 2, since the ring will have to be folded in half. In practice, the size of the ring networks reaches tens of kilometers (for example, in the FDDI network). The ring in this respect is significantly superior to any other topology.

There is no clearly defined center in a ring topology, all computers can be the same and equal. However, quite often a special subscriber is allocated in the ring, which manages the exchange or controls it. It is clear that the presence of such a single control subscriber reduces the reliability of the network, since its failure immediately paralyzes the entire exchange.

Ring water supply network

Ring water supply networks are a system of adjacent closed rings (circuits). In terms of reliability and uninterrupted operation, ring networks have a very significant advantage over branched ones. In the event of an accident (pipeline rupture) in one of the sections of the branched network, the water supply to the nodal points located behind the section will not be provided. For the ring network, the water supply does not stop, since the damaged section of the network is turned off, and water is supplied to the nodal points through other areas adjacent to them. In the event of a change in water consumption at the nodal points during the day, it is possible to carry out a crossflow of water from another ring. In a ring network, when a water hammer occurs, the pressure increase in the pipeline will be much less than in a branched network. However, the length of the ring network is significantly greater than the branched one and, therefore, its cost is also greater. The ring network provides guaranteed water consumption at the network nodes, which is very important for fire extinguishing.

A diagram of the ring water supply network is shown in Fig. 5.12.

Rice. 5.12. Ring network diagram

In ring networks, in contrast to branched networks, unknown quantities are the diameters of the sections, the costs in the sections and their directions.

Diameter and flow rate are unknown at each site. The number of unknowns corresponds to the number of sections of the ring network. To determine the diameters and costs in each section of the network, it is necessary to compose the appropriate number of equations and solve this system of equations. The hydraulic calculation in this case is rather complicated.

The sequence of hydraulic calculation of the ring water supply network is as follows.

1. Determined travel costs on the sections of the ring network. Travel costs are referred to as nodal costs. Travel costs for network sections:

; ; etc.

2. Preliminarily, the optimal direction of water flows is outlined with unknown pipe diameters along individual sections of the network based on the condition that water is supplied to the most distant points along the shortest path of flow.

3. The total flow rate of water arriving at the nodal point must be equal to the sum of the flow rates of the sections connected to the point, plus the nodal flow,.

For example, for point 3 we will have

4. The diameters of pipelines in the sections are determined according to the estimated travel costs based on the condition of the most advantageous economic diameters using the appropriate tables.

5. The sum of hydraulic losses in each closed ring with a sufficiently correct choice of pipe diameters of the sections should be equal to zero. Taking the condition that the pressure losses in the sections in which the water moves clockwise are equal to the pressure losses when it moves counterclockwise,.

For example, for a ring V(see fig. 5.12)

It should be noted that if this condition is met, the sum of losses in any ring will be equal to zero, and hydraulic losses in the sections will be minimal.

If the preliminary determination of travel costs and pipeline diameters of the network sections does not allow obtaining a condition, then the network is linked. Linkage consists in a possible redistribution of the direction of movement of the calculated water flows, directing slightly higher flows to areas where hydraulic losses are less, or vice versa. As a result of the redistribution of costs, the amount of hydraulic losses should be close to zero.