In the modern world, local networks have become not just necessary - they are actually necessary to achieve good level labor productivity. However, before you start using such a network, you should create and configure it. Both of these processes are quite difficult and require maximum concentration, especially the first of them. A poorly designed and configured LAN will not work at all, or it will not function at all as it should, so creating a local network should be the focus of the person doing it.
As a rule, the creation of such communication systems is caused by the need to share data by users who work on remote computers. A LAN not only enables near-instantaneous exchange of information and simultaneous file sharing, but also allows remote use of network printers and other devices.
A local network is a complete set of software and hardware resources aimed at creating a single information space. In fact, this is a number of computers located at a distance from each other and connected by a communication line - a cable. The main difference between a LAN and other types of networks is the short distance at which workstations are located.
Before you create a local network, you must first design it, that is, plan the process of its creation. This stage is one of the most significant, since the LAN includes a huge number of components and nodes.
Initially, the terms of reference are drawn up on the basis of primary data, defining several points:
Once you have these points in mind, you can start designing. The project itself should contain LAN schemes, network equipment placement points, a list of required software and hardware.
A local area network is a complex mechanism, but if it is designed correctly and the equipment is selected in accordance with the requirements, then the likelihood of problems in the operation of the communication mechanism becomes minimal.
There is a list of equipment without which no LAN can function. It includes:
No LAN is complete without software. Required LAN programs include:
Installation and commissioning work takes the most time, since it is necessary to create a local network in several stages:
Installation of cable and equipment has a number of features, therefore, if there are difficulties with how to connect a local network, better solution entrust this issue to specialists.
In some cases, it may be necessary to combine two computers into one network, for example, to create a common information space. This is not very difficult to do if you follow a certain algorithm of actions:
In most cases, you may want to give each host a unique IP address:
Work nodes connected in a LAN can be connected to the Internet. A local network, to which the Internet can be connected in two ways, will work at a speed divided in two.
The first way to connect is to use a router, which is assigned an identifying IP address. And in the second case, you can use a wireless connection.
IN this case a local network is the interaction of two computers, a master and a slave, so the IP address is registered in the gateway of the main one, previously connected to the worldwide network.
If the LAN is based on the use of a server, each workstation must have an individual IP address, and a proxy server is specified in the browser settings through which the Internet is accessed.
A wireless local area network is a type of LAN that uses high-frequency radio waves to transmit information. WLAN is an excellent alternative to the conventional cable communication system, having a number of advantages:
WLAN has a certain range, which depends on the characteristics of the network devices and the noise immunity of the building. As a rule, the range of radio waves reaches 160 m.
An access point is used to connect other workstations to the network. This device is equipped with a special antenna that controls duplex data transmission (sending and transmitting) using radio signals. Such a point can transmit a signal at a distance of up to 100 m indoors and up to 50 km in an open area.
Access points significantly expand the computing power of the entire communication system, allowing users to freely move between each of them without losing connection to the LAN or the Internet. In fact, these radio points act as hubs, providing a connection to the network.
Using access points allows you to scale up your entire wireless LAN by simply adding new devices. The number of subscribers that one radio point can withstand generally depends on the network load, since the traffic is divided equally between each of the users.
First you need to prepare an ADSL modem with WiFi technology, as well as client points with connected to them wireless adapters. After that, you can start building a wireless LAN:
Access point setup:
To create an optimal information space, you can combine types of networks - cable and wireless, allowing you to use the advantages of each of them for the benefit of the enterprise. However, it is important to remember that in our time, it is WLANs that are increasingly being used, which have all the advantages of cable networks and are devoid of their disadvantages.
After completing the creation and configuration of the local network, it is important to provide for its administration and the possibility of maintenance. Even if the LAN installation is perfect, during its operation various hardware or software malfunctions are almost inevitable, which is why maintenance should be regular.
The very name Local Area Network already contains the purpose, functions and limitations of the system. Let's break down the name into parts. Local, derived from English local - local, that is, the network is tied to a specific geographical location and has restrictions on the territory, computing, associated with the composition of the network (computing equipment, software) and its purpose, net- implies association computing equipment and software in a certain area (local) to the network (via cables).
Thus, we can formulate the definition of a Local Area Network (LAN) - a system of interconnected computing resources (computers, servers, routers, software, etc.) and processing of information of various kinds.
Different local area networks can function separately or be interconnected using communication tools, for example, at enterprises with a branch network in different cities. Through this connection, the user can interact with other workstations connected to this local area network. There are local networks whose nodes are geographically separated at distances of more than 12,500 km (space stations and orbital centers), but they are still classified as local.
The purpose of the LAN is to provide joint and simultaneous access of a certain group of persons to data, programs and equipment (computers, printers, plotters, storage and processing devices for files and databases) and data transmission (electronic graphics, word processing, e-mail, access to remote databases). data, digital speech transmission).
For example: a manager accepts an order and enters it into a computer, then the order goes to the accounting department and an invoice is generated there, at the same time information can be sent to the legal service to create an agreement.
LAN characteristics:
The main functions of the LAN are:
As a result of the use of a LAN, personal computers located at many remote workplaces are combined. Workplaces of employees are no longer isolated and are combined into a single system, which has its own special features. advantages:
Application area local networks is very wide, at present there are such systems in almost every office (for example, one printer is installed on several computers, or several computers use the same software, for example, 1C: Accounting, etc.). Every day the flow of information is becoming more used software more complex and functional, the geography of organizations is expanding. The use of LAN means is becoming not only desirable, but necessary for the successful operation and development of business, science, education of students, schoolchildren, training and retraining of specialists, implementation of state programs and functions, etc.
The structure of the network functioning.
The structure of the local network is determined by the principle of management and the type of communication, often it is based on the structure of the service organization. Types of topology are used: bus, ring, radial, tree. The first two types are the most common, due to the effective use of communication channels, ease of management, flexible expansion and change.
Bus topology- all computers are connected in a chain by connecting to the main cable segment (trunk), "terminators" are placed at its ends to dampen the signal propagating in both directions. The computers on the network are connected by a coaxial cable with a tee connector. The network bandwidth is 10 Mbps, which is not enough for modern applications that actively use video and multimedia data. The advantage of this topology lies in the low cost of wiring and the unification of connections.
The bus topology is passive. The failure of a single computer does not affect network performance. Damage to the main cable (bus) leads to signal reflection and the entire network as a whole becomes inoperable. Turning off and especially connecting to such a network requires a bus break, which causes a disruption in the circulating flow of information and a system hang.
Tree topology– a more advanced “tire” type configuration. Several simple buses are connected to the common trunk bus through active repeaters or passive multipliers.
Star topology(star) - is the fastest of all topologies, information between peripheral workstations passes through the central node of the computer network. Central control node - file server can implement an optimal protection mechanism against unauthorized access to information. The entire computer network can be controlled from its center.
The cable connection is quite simple, since each workstation is connected only to the central node. Cabling costs are high, especially when the central site is not geographically located in the center of the topology. When expanding computer networks previously made cable connections cannot be used: a separate cable must be laid to the new workplace from the center of the network.
In the case of a serial LAN configuration, each device connecting to the physical medium transmits information to only one device. This reduces the requirements for transmitters and receivers, since all stations actively participate in the transmission.
Topology "ring"(ring) - computers are connected by segments of a ring-shaped cable, fundamentally identical to a bus cable, except for the need to use "terminators". If one of the network segments fails, the entire network fails.
Signals are only transmitted in one direction. Each station is directly connected to two neighbors, but listens to the transmission of any station. The ring consists of several transceivers and the physical medium connecting them. All stations may have equal access rights to the physical medium. In this case, one of the stations can act as an active monitor serving the exchange of information. Laying cables from one workstation to another can be quite complex and expensive, especially if the workstations are geographically located far from the ring (for example, in a line).
The main problem with a ring topology is that each workstation must actively participate in the transfer of information, and if at least one of them fails, the entire network is paralyzed. Faults in cable connections are easily localized. Connecting a new workstation requires turning off the network, since the ring must be open during installation. There is no limit on the extent of the computer network, since it is ultimately determined solely by the distance between two workstations.
Computers can be connected to each other using various access media: copper conductors (twisted pair), optical conductors (optical cables) and through a radio channel ( wireless technologies). Wired, optical connections are established via Ethernet, wireless - via Wi-Fi, Bluetooth, GPRS and other means. Most often, local networks are built on Ethernet or Wi-Fi technologies. It should be noted that the Frame Relay, Token ring protocols were previously used, which are becoming less common today, they can only be seen in specialized laboratories, educational institutions and services.
Components of building a simple local network are used:
Installation of Local Area Network (LAN)
The choice of the type of topology, access environment and composition of the Local Computing System depends on the requirements and needs of the Customer. Modern technologies allow us to develop an individual version that meets all the requirements and tasks.
Laying LAN cables, like other types of cable networks, can be done in different ways. When choosing an installation method, they are guided by the individual architectural and design features of the building, its technical specifications, the presence of operating networks and other equipment, the order of interaction of low-voltage systems with other systems. Basically, two methods can be distinguished - open and hidden. For concealed wiring of LAN cables, the construction of walls, floors, ceilings is used; it looks more aesthetically pleasing, the routes are protected from extraneous influences, access to them is limited, they are laid immediately in special prepared places, and better conditions for subsequent maintenance are provided. Unfortunately the opportunity to do the work in a hidden way it is rare, more often it is necessary to carry out work in an open way using plastic boxes, vertical columns and trays. Do not forget that there is another way of laying cables over the air, most often it is used for building communication when it is not possible to lay the cable into channels or if it is too expensive.
LAN installation is a complex and responsible job. , the stability and correctness of the functioning of the system as a whole, the degree of execution of the tasks assigned to it, the speed of data transmission and processing, the number of errors, and other factors depend on the quality of its implementation. This should be taken very thoroughly and seriously, since any network is the basis (skeleton and circulatory system) of the whole organism from low-current systems responsible for a large number of functions (from Email to the safety of the object). Each subsequent intervention operating system(expansion, repair, etc.), requires time and money, and their number directly depends on the parameters initially included in the system, the quality of the work performed, the qualifications of developers and performers. Cost savings at the stage of designing and installing a LAN can turn into much larger expenses at the stage of operation and upgrade
Usually covering a relatively small area or a small group of buildings (house, office, company, institute). There are also local networks, the nodes of which are geographically separated at distances of more than 12,500 km (space stations and orbital centers). Despite such distances, such networks are still classified as local.
Here it is necessary to mention such important concepts as subscriber, server, client.
Subscriber (node, host, station)- a device connected to the network and actively participating in the information exchange. Most often, the subscriber (node) of the network is a computer, but the subscriber can also be, for example, network printer or other peripheral device that has the ability to connect directly to the network. Further in the course, instead of the term "subscriber", for simplicity, the term "computer" will be used.
server called a subscriber (node) of the network, which provides its resources to other subscribers, but does not use their resources. Thus, it serves the network. There can be several servers in the network, and it is not at all necessary that the server is the most powerful computer. Dedicated server is a server dealing only with network tasks. Non-dedicated server can perform other tasks in addition to maintaining the network. A specific type of server is a network printer.
Client is called a network subscriber who only uses network resources, but does not give his own resources to the network, that is, the network serves him, and he only uses it. The client computer is also often referred to as the workstation. In principle, each computer can be both a client and a server at the same time. The server and client are also often understood not as the computers themselves, but as those working on them. software applications. In this case, the application that only sends the resource to the network is the server, and the application that only uses network resources- a client.
Local area networks allow individual users to easily and quickly interact with each other. Here are just some of the tasks that LS allows you to perform:
The basic components and technologies associated with LAN architecture may include:
Hardware:
Software:
Communication on short distances in computer technology existed long before the appearance of the first personal computers.
Large computers (mainframes) were joined by numerous terminals (or "intelligent displays"). True, there was very little intelligence in these terminals, they did practically no information processing, and the main goal of organizing communication was to separate the intelligence ("computer time") of a large powerful and expensive computer between users working at these terminals. This was called time-sharing, because the large computer solved the problems of many users sequentially over time. In this case, the joint use of the most expensive resources at that time was achieved - computing (Fig. 1.1).
Rice. 1.1. Connecting terminals to a central computer
Then microprocessors and the first microcomputers were created. It became possible to place a computer on the table of each user, as computing, intellectual resources fell in price. But all other resources were still quite expensive. And what does naked intellect mean without means of storing information and documenting it? You will not re-type the program being executed every time after turning on the power or store it in a small-capacity permanent memory. Once again, communications came to the rescue. By combining several microcomputers, it was possible to organize the sharing of computer peripherals (magnetic disks, magnetic tape, printers). At the same time, all information processing was carried out on the spot, but its results were transferred to centralized resources. Here again, the most expensive thing in the system was shared, but in a completely new way. This mode is called the inverse time division mode (Fig. 1.2). As in the first case, communications reduced the cost computer system generally.
Rice. 1.2. Networking of the first microcomputers
Then personal computers appeared, which differed from the first microcomputers in that they had a complete set sufficiently developed to fully battery life peripherals: magnetic disks, printers, not to mention more advanced user interface tools (monitors, keyboards, mice, etc.). Peripherals have fallen in price and have become comparable in price to a computer. It would seem, why now connect personal computers (Fig. 1.3)? What should they share when everything is already divided and is on the table of each user? There is enough intelligence on the spot, the periphery too. What can the network give in this case?
Rice. 1.3. Networking of personal computers
The most important thing is again the sharing of the resource. The same reverse division of time, but on a fundamentally different level. Here it is already used not to reduce the cost of the system, but to more efficiently use the resources available to computers. For example, the network allows you to combine the disk space of all computers, providing each of them with access to the disks of all the others as if they were their own.
But most clearly, the advantages of the network are manifested when all users actively work with a single database, requesting information from it and entering new information into it (for example, in a bank, in a store, in a warehouse). You won't get by with any floppy disks here: you would have to transfer data from each computer to all the others all day long, maintain a whole staff of couriers. And with the network, everything is very simple: any data changes made from any computer immediately become visible and available to everyone. In this case, special on-site processing is usually not required, and cheaper terminals could in principle be dispensed with (return to the first situation considered), but personal computers have an incomparably more convenient user interface that facilitates the work of personnel. In addition, the ability to process complex information in situ can often significantly reduce the amount of data transferred.
Rice. 1.4. Using a local network for an organization joint work computers
It is also impossible to do without a network when it is necessary to ensure the coordinated operation of several computers. This situation most often occurs when these computers are used not for calculations and working with databases, but in tasks of management, measurement, control, where the computer is interfaced with one or another external devices(Fig. 1.4). Examples are various industrial technological systems, as well as control systems for scientific installations and complexes. Here, the network allows you to synchronize the actions of computers, parallelize and, accordingly, speed up the process of processing data, that is, add up not only peripheral resources, but also intellectual power.
It is these advantages of local networks that ensure their popularity and more and more wide application despite all the inconveniences associated with their installation and operation.
Under topology (layout, configuration, structure) computer network usually refers to the physical location of network computers relative to each other 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 connections can be easily traced. In global networks, the structure of communications is usually hidden from users and is not very important, since each communication session can be carried out along its own path.
The topology determines the requirements for the equipment, the type of cable used, the acceptable and most convenient methods of managing the exchange, the reliability of operation, and the possibility of expanding the network. And although a network user rarely has to choose a topology, it is necessary to know about the features of the main topologies, their advantages and disadvantages.
Factors that affect the physical performance of the network and are directly related to the concept of topology.
1)Serviceability of computers (subscribers) connected to the network. In some cases, a failure of a subscriber can block the operation of the entire network. Sometimes a subscriber's failure does not affect the operation of the network as a whole, does not prevent other subscribers from exchanging information.
2)Health of network equipment, that is technical means directly connected to the network (adapters, transceivers, connectors, etc.). The failure of the network equipment of one of the subscribers may affect the entire network, but may disrupt the exchange with only one subscriber.
3)Network cable integrity. If the network cable breaks (for example, due to mechanical influences), the exchange of information in the entire network or in one of its parts may be disrupted. Equally critical for electrical cables short circuit in the cable.
4)Cable length limitation associated with the attenuation of the signal propagating through it. As you know, in any medium, the signal is attenuated (attenuated) during propagation. And than greater distance passes the signal, the more it decays (Fig. 1.8). It is necessary to ensure that the length of the network cable does not exceed the limit length Lpr, above which the attenuation becomes unacceptable (the receiving subscriber does not recognize the weakened signal).
Rice. 1.8. Signal attenuation during propagation over the network
There are three basic topologies networks:
Bus- all computers are connected in parallel to one communication line. Information from each computer is simultaneously transmitted to all other computers (Fig. 1.5).
Rice. 1.5. Bus network topology
Bus topology(or, as it is also called, a common bus) by its very structure implies the identity of the network equipment of computers, as well as the equality of all subscribers in accessing the network. Computers on the bus can only transmit information in turn, since the communication line in this case is the only one. If several computers transmit information at the same time, it will be distorted as a result of overlap (conflict, collision). The bus always implements the mode of the so-called half-duplex (half duplex) exchange (in both directions, but in turn, and not simultaneously).
In the bus topology, there is no explicit central subscriber through which all information is transmitted, this increases its reliability (after all, if the center fails, the entire system controlled by it 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, when using a bus, a minimum amount of connecting cable is required compared to other topologies.
Since there is no central subscriber, the resolution of possible conflicts in this case falls on the network equipment of each individual subscriber. In this regard, network equipment with a bus topology is more complicated than with other topologies. However, due to the widespread use of bus topology networks (primarily the most popular network Ethernet) the cost of network equipment is not too high.
Rice. 1.9. Cable break in a network with a bus topology
An important advantage of the bus is that if any of the computers on the network fails, the healthy machines will be able to continue the exchange normally.
It would seem that when the cable breaks, two fully functional tires are obtained (Fig. 1.9). However, it must be taken into account that due to the nature of the distribution electrical signals for long communication lines, it is necessary to provide for the inclusion of special matching devices, terminators, shown in fig. 1.5 and 1.9 as rectangles. Without terminators enabled, the signal is reflected from the end of the line and distorted so that communication over the network becomes impossible. In the event of a break or damage to the cable, the coordination of the communication line is violated, and the exchange stops even between those computers that remain connected to each other. A short circuit at any point in the bus cable disables the entire network.
Failure of the network equipment of any subscriber in the bus can disable the entire network. In addition, such a failure is quite difficult to localize, since all subscribers are connected in parallel, and it is impossible to understand which one has failed.
When passing through a communication line of a network with a bus topology, information signals are attenuated and cannot be restored in any way, which imposes severe restrictions on the total length of communication lines. Moreover, each subscriber can receive signals of different levels from the network depending on the distance to the transmitting subscriber. This imposes additional requirements on the receiving nodes of the network equipment.
If we accept that the signal in the network cable is attenuated to the limit acceptable level on the length Lpr, then the total length of the tire cannot exceed the value Lpr. In this sense, the bus provides the shortest length compared to other basic topologies.
To increase the length of a network with a bus topology, several segments are often used (network parts, each of which is a bus), interconnected using special amplifiers and signal restorers - repeaters or repeaters (Fig. 1.10 shows the connection of two segments, the maximum length of the network in this case increases to 2 Lpr, since each of the segments can be Lpr). However, such an increase in the length of the network cannot continue indefinitely. Length restrictions are associated with the finite speed of signal propagation along communication lines.
Rice. 1.10. Connecting segments of a bus type network using a repeater
Star (star)- other peripheral computers are connected to one central computer, and each of them uses a separate communication line (Fig. 1.6). Information from the peripheral computer is transmitted only to the central computer, from the central one - to one or more peripheral ones.
Rice. 1.6. Network topology star
Star- this is the only network topology with a clearly defined center to which all other subscribers are connected. The exchange of information takes place exclusively through the central computer, which bears a heavy load, therefore, as a rule, it cannot do 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 peripheral subscribers. In this case, there is no need to talk about the equality of all subscribers (as in a bus). Usually the central computer is the most powerful, it is on it that all the functions of managing the exchange are assigned. In principle, no conflicts in a network with a star topology are possible, since management is completely centralized.
If we talk about the resistance of a 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, but any failure of the central computer makes the network completely inoperable. 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 the exchange with only one computer, and all other computers can continue to work normally.
Unlike a bus, there are only two subscribers in a star on each communication line: 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 point-to-point transmission. All this greatly simplifies network equipment in comparison with the bus and eliminates the need for additional, external terminators.
The problem of attenuation of signals in the communication line is also solved in a star easier 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 Lpr), since each of the cables connecting the center to the peripheral subscriber can have a length of Lpr.
A serious disadvantage of the star topology is the strict limitation of the number of subscribers. Typically, the central subscriber can serve no more than 8-16 peripheral subscribers. Within these limits, connecting new subscribers is quite simple, but beyond them it is simply impossible. In a star, it is possible 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). At present, it is much more widespread than an active star. Suffice it to say that it is used in the most popular Ethernet network today.
In the center of a network with this topology, not a computer is placed, but a special device - a hub or, as it is also called, a hub (hub), which performs the same function as a repeater, that is, restores incoming signals and forwards them to all other communication lines .
Rice. 1.11. Topology passive star and its equivalent circuit
It turns out that although the cabling pattern is similar to a true or active star, in fact we are talking about the 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 range additional features associated with the benefits of the star, in particular, simplifies the maintenance and repair of the network. That is why recently the passive star is increasingly replacing the true star, which is considered an unpromising topology.
It is also possible to single out an intermediate type of topology between an active and a passive star. In this case, the concentrator not only retransmits the signals arriving at it, but also controls the exchange, but does not participate in the exchange itself (this is done in the 100VG-AnyLAN network).
The 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 network operation, localize faults by simple shutdown from the center of certain subscribers (which is impossible, for example, in the case of a bus topology), as well as restricting access by unauthorized persons to vital connection points for the network. In the case of a star, a peripheral subscriber can be approached by either one cable (which transmits in both directions) or two (each cable transmits in one of the two opposite directions), the latter being much more common.
A common disadvantage for all star topologies (both active and passive) is the significantly higher cable consumption than with other topologies. For example, if computers are located in one line (as in Figure 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 laying of the cable.
ring- computers are connected in series in a ring. The transmission of information in a ring is always carried out in only one direction. Each of the computers transmits information to only one computer following it in the chain, and receives information only from the previous computer in the chain (Fig. 1.7).
Rice. 1.7. Network topology ring
Ring is a topology in which each computer is connected by communication lines to two others: it receives information from one and transmits information to the other. On each communication line, as in the case of a star, there is only one transmitter and one receiver (point-to-point communication). 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. The attenuation of the signal in the entire ring does not matter, only the attenuation between neighboring computers in the ring matters. If the maximum cable length limited by attenuation is Lpr, then the total length of the ring can reach NLpr, where N is the number of computers in the ring. The total size of the network in the limit will be NLpr / 2, since the ring will have to be folded in half. In practice, the size of ring networks reaches tens of kilometers (for example, in FDDI networks). 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 identical 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.
Strictly speaking, computers in a ring are not completely equal (unlike, for example, a bus topology). After all, one of them necessarily receives information from a computer that transmits to this moment earlier and others later. It is on this feature of the topology that the network exchange control methods are built, specially designed for the ring. In such methods, the right to the next transfer (or, as they say, to capture the network) passes sequentially to the next computer in a circle. Connecting new subscribers to the ring is quite simple, although it requires the obligatory shutdown of the entire network for the duration of the connection. As in the case of the bus, the maximum number of subscribers in the ring can be quite large (up to a thousand or more). The ring topology is usually highly resistant to overloads, ensures reliable operation with large flows of information transmitted over the network, since, as a rule, there are no conflicts in it (unlike a bus), and there is also no central subscriber (unlike a star), which can be overloaded with large amounts of information.
Rice. 1.12. Network with two rings
The signal in the ring passes sequentially through all the computers on the network, so the failure of at least one of them (or its network equipment) disrupts the network as a whole. This is a significant disadvantage of the ring.
Similarly, an open or short circuit in any of the cables in the ring renders the entire network unusable. Of the three topologies considered, the ring is the most vulnerable to cable damage, therefore, in the case of a ring topology, two (or more) parallel communication lines are usually provided, one of which is in reserve.
Sometimes a network with a ring topology is based on two parallel ring links that transmit information in opposite directions (Fig. 1.12). The purpose of such a solution is to increase (ideally - twice) the speed of information transfer over the network. In addition, if one of the cables is damaged, the network can work with another cable (however, the maximum speed will decrease).
In the case of a star-ring (star-ring) topology, not the computers themselves are combined into a ring, but special hubs (shown in Fig. 1.16 as rectangles), to which computers are in turn connected using star-shaped double communication lines. In reality, all computers on the network are included in a closed ring, since inside the hubs the communication lines form a closed loop (as shown in Fig. 1.16). This topology makes it possible to combine the advantages of star and ring topologies. For example, hubs allow you to collect all the connection points for network cables in one place. If we talk about the propagation of information, this topology is equivalent to a classical ring.
In conclusion, we must also say about the mesh topology (mesh), in which computers are interconnected not by one, but by many communication lines that form a grid (Fig. 1.17).
Rice. 1.17. Grid topology: full (a) and partial (b)
In a complete mesh topology, each computer is directly connected to all other computers. In this case, with an increase in the number of computers, the number of communication lines increases sharply. In addition, any change in the network configuration requires changes to the network hardware of all computers, so the full mesh topology is not widely used.
Partial mesh topology assumes direct connections only for the most active computers transmitting the maximum amount of information. The remaining computers are connected through intermediate nodes. Grid topology allows you to choose a route for the delivery of information from subscriber to subscriber, bypassing faulty sections. On the one hand, this increases the reliability of the network, on the other hand, it requires a significant complication of the network equipment, which must choose the route.
To understand the relationship between LAN SCS (local area networks and structured cable networks), you should know about such a type of network as FOCL. A fiber-optic transmission line or fiber-optic communication line, traditionally referred to as the abbreviation FOCL, is a communication channel (line) that transmits information via optical fiber, a special material that differs from others by an extremely low degree of signal attenuation over a distance. This property of fiber optics allows it to be used in backbone networks for data transmission over long distances.
SCS stands for Structured Cabling System. How well the SCS is organized is how effective information structure the entire company. SCS as a complex of numerous elements includes such elements
A local area network (LAN) as part of the SCS is used to transfer, process and store data within a certain space (enterprise, division, office). A properly prepared LAN project within the SCS, properly implemented, provides high network throughput in conjunction with the ability to control data, control access to the network and centralized remote control of connected equipment.
So, if you arrange the above types of networks in order of their scale, you get the following picture - an extended and large-scale fiber optic link is connected to the SCS of the enterprise, which, in turn, includes a LAN.
That FOCL, that SCS, that LAN are designed and created on the basis of uniform principles. The process of building each type of networks can be divided into two major stages - design and installation of SCS, LAN or FOCL. Let's consider them in order.
An explanatory note drawn up during the design of a fiber optic, SCS or LAN contains a general description and characteristics of the object as a whole, determines its purpose, establishes general technical requirements related to network installation.
The cable log, which contains a numbered inventory list of all cables, ports, and sockets that make up the network, is the main working document.
The technical part is primarily equipment specifications, and the graphic part is various schemes, floor plans.
Then the installation and installation of cables, technical devices takes place, and configuration is carried out. Commissioning is underway.
Evidence and documentary confirmation of the qualitatively and fully carried out process of creating a FOCL, SCS or LAN network is a protocol signed by the parties of the customer and the contractor. Only experienced and highly qualified specialists in the field of design and installation of SCS and other cable networks can guarantee a high level of network construction quality, stable and efficient operation.
LAN classification
Distance between nodes
territorial
regional And global
local
corporate
intranets
By topology
tire
ring
stellar
hierarchical
Mixed topology subnets
By way of management
"client/server"
peer-to-peer
ethernet
fast ethernet
gigabit ethernet
Gigabit Ethernet networks are compatible with Ethernet and Fast Ethernet network infrastructure, but operate at 1000 Mbps - 10 times faster than Fast Ethernet. Gigabit Ethernet is a powerful solution that eliminates bottlenecks in the main network (where network segments connect and where servers are located). Bottlenecks arise from the emergence of bandwidth-demanding applications, the increasing growth of unpredictable intranet traffic flows, and multimedia applications. Gigabit Ethernet provides a way to seamlessly migrate Ethernet and Fast Ethernet workgroups to the new technology. Such a transition has a minimal impact on their operations and allows them to achieve higher productivity.
PRACTICAL PART
Type selection network cable
Based on the complex structure of the projected local network, it was decided to use a twisted pair cable in the main room, where the group of managers, accounting, technical department and server room are located. It was decided to connect remote buildings located at a distance of 500-800 meters from the main building (wholesale trade department and car park) to the local network through a single-mode stepped optical fiber. The out-of-town warehouse base, located at a distance of 1500 meters from the main building, must be connected via Wi-Fi.
Data protection
To ensure the safe operation of the server, complexes of organizational, technological, software and hardware (technical) measures and means are used.
Antivirus programs are a class of programs designed to combat computer viruses and their effects. Depending on the purpose and principle of operation, there are antivirus programs:
- "watchmen" or "detectors" - designed to detect files infected with known viruses, or signs indicating the possibility of infection;
- "phages" ("polyphages") or "doctors" - designed to detect and eliminate viruses known to them;
- "auditors" - controlling vulnerable and, accordingly, the most frequently attacked by viruses components of computer memory and capable of returning them to their original state in case of detection of changes in files and system areas of disks;
- "resident monitors" or "filters" - resident in random access memory and intercepting calls to operating system, which are used by viruses to reproduce and cause harm, in order to provide the user with the opportunity to make a decision to prohibit or perform appropriate operations;
- "complex" - performing the functions of several anti-virus programs listed above.
Program from unauthorized access - Check Point Firewall -1
Product set network security, called Check Point FireWall-1, provides Internet, Intranet, Extranet, and Remote Access Control with advanced authorization and user authentication features. FireWall -1 allows you to translate network addresses (NAT) and scan data streams for invalid information and viruses. A wide range of basic and service functions makes it possible to implement an integrated solution for providing network and information security, which fully meets the modern requirements of any organization, both large and small.
Fire Wall -1 allows an organization to create a single, integrated security policy that spans multiple firewalls and is managed from anywhere in the enterprise network. The product also has a lot of additional features, such as managing access lists of hardware routers, balancing network load on servers, as well as elements for building high-reliability systems, which are also fully integrated into the global security policy. Check Point FireWall-1 is transparent to users and delivers record-breaking performance for virtually any IP protocol and high-speed data transfer technology
Figure 3 - Fire Wall Architecture -1
FireWall-1 is based on the Stateful Inspection architecture, which provides the best level of protection. Figure 3 illustrates the main components of the FireWall-1 user authentication architecture.
CONCLUSION
As a result of the calculation and graphic work done, a local computer network was organized in each of the offices. The choice of the main topology was justified, based on standard varieties and technologies that correspond to all modern standards of information transmission.
The parameters of the workstation and server, the composition of the necessary network equipment, the characteristics of network equipment, and the method of network management were determined. Basic standards were studied wireless transmission data, and security levels are described, the most optimal for our case is selected.
The choice of data transmission technology and the physical transmission medium were substantiated. We also determined the main connection devices and their characteristics. Finally, a summary list of equipment and programs was determined, which determined the required volume of personal computers and network equipment. Also, the average access time to the network station was calculated, as well as the costs of developing a local computing system.
REFERENCES
1. Lecture notes on the discipline "Computer networks and telecommunications"
2. Aliyev T.I. "Networks and telecommunications"
APPLICATION
ANNEX 1
The concept of a local area network (LAN)
A local area network (LAN) is a communication system that allows you to share the resources of computers connected to a network, such as printers, plotters, disks, modems, CD-ROM drives and other peripheral devices. A local area network is usually geographically limited to one or more closely spaced buildings.
LAN classification
Computing networks are classified according to a number of criteria.
Distance between nodes
Depending on the distances between connected nodes, computer networks are distinguished:
territorial- covering a significant geographical area;
among territorial networks, one can distinguish networks regional And global having, respectively, regional or global scales;
regional networks are sometimes called MAN (Metropolitan Area Network) networks, and the common English name for territorial networks is WAN (Wide Area Network);
local(LAN) - covering a limited area (usually within the remoteness of stations no more than a few tens or hundreds of meters from each other, less often 1 ... 2 km);
local networks stand for LAN (Local Area Network);
corporate(enterprise scale) - a set of interconnected LANs covering the territory where one enterprise or institution is located in one or more closely spaced buildings. Local and corporate computer networks are the main type of computer networks used in computer-aided design (CAD) systems.
Highlights the one-of-a-kind global Internet(the information service implemented in it world wide Web (WWW) is translated into Russian as The World Wide Web);
it is a network of networks with its own technology. On the Internet there is a concept intranets(Intranet) - corporate networks within the Internet.
By topology
Network topology is the geometric shape of a network. Depending on the topology of node connections, there are networks of bus (backbone), ring, star, hierarchical, arbitrary structure (Figure 1).
tire(bus) - a local network in which communication between any two stations is established through one common path and the data transmitted by any station simultaneously becomes available to all other stations connected to the same data transmission medium (the latter property is called broadcasting);
ring(ring) - nodes are connected by a ring data transmission line (only two lines are connected to each node); data, passing through the ring, in turn become available to all network nodes;
stellar(star) - there is a central node from which data transmission lines diverge to each of the other nodes;
hierarchical- each device provides direct control of devices below in the hierarchy.
Mixed topology- the topology prevailing in large networks with arbitrary connections between computers. In such networks, separate arbitrarily connected fragments can be distinguished ( subnets), which have a typical topology, so they are called networks with a mixed topology.
Figure 1 Network topologies a) bus; b) ring; c) a star; d) hierarchical; e) mixed.
By way of management
Depending on the control method, networks are distinguished:
"client/server"- one or more nodes are allocated in them (their name is servers) that perform control or special service functions on the network, and the remaining nodes (clients) are terminal, users work in them. Client/server networks differ in the nature of the distribution of functions between servers, in other words, the types of servers (eg, file servers, database servers). With the specialization of servers for certain applications, we have a network of distributed computing. Such networks are also distinguished from centralized systems built on mainframes;
peer-to-peer- in them all nodes are equal; Since, in general, a client is an object (device or program) that requests some services, and a server is an object that provides these services, each node in peer-to-peer networks can perform the functions of both a client and a server.
Technologies for building local networks.\
ethernet
Ethernet is the most popular technology for building local area networks. Based on the IEEE 802.3 standard, Ethernet transmits data at 10 Mbps. In an Ethernet network, devices check for the presence of a signal on the network channel ("listen" to it). If no other device is using the channel, then the Ethernet device transmits data. Each workstation on this LAN segment analyzes the data and determines if it is intended for it. Such a scheme is most effective with a small number of users or a small number of messages transmitted in a segment. With an increase in the number of users, the network will not work as efficiently. In this case, the optimal solution is to increase the number of segments to serve groups with fewer users. In the meantime, there has been a recent trend to provide dedicated 10 Mbps lines to every desktop system. This trend is driven by the availability of inexpensive Ethernet switches. Packets transmitted over an Ethernet network can be of variable length.
fast ethernet
Fast Ethernet uses the same basic technology as Ethernet - Carrier Sense Multiple Access with Collision Detection (CSMA/CD). Both technologies are based on the IEEE 802.3 standard. As a result, both types of networks can use (in most cases) the same type of cable, the same network devices and applications. Fast Ethernet networks allow you to transfer data at a speed of 100 Mbps, that is, ten times faster than Ethernet. As applications become more complex and the number of users accessing the network increases, this increased throughput can help to get rid of the "bottlenecks" that cause an increase in network response time.
