Open Systems Interconnection Model

Network topology

When two or more computers are physically connected, computer network... In the general case, to create computer networks, you need special hardware - network equipment and special software - network software.

Already now there are spheres of human activity that, in principle, cannot exist without networks (for example, the work of banks, large libraries, etc. Networks are also used in the management of large automated industries, gas pipelines, power plants, etc. For data transmission, computers use a wide variety of physical channels commonly called transmission medium.

The purpose of all types of computer networks is determined by two functions:

· Ensuring the joint use of hardware and software network resources;

· Ensuring shared access to data resources.

For example, all participants local network can share one common printing device - a network printer or, for example, the resources of hard drives of one dedicated computer - a file server. Similarly, software can be shared. If the network has a special computer dedicated for sharing by network participants, it is called file server.

Groups of employees working on one project within a local network are called working groups... Several working groups can work within one local network. Team members can have different rights to access shared network resources. The set of techniques for dividing and limiting the rights of participants in a computer network is called network policy... Network Policy Management is called network administration... The person managing the organization of the work of the participants of the local computer network is called system administrator

1.1. Basic characteristics and classification of computer networks

By territorial prevalence networks can be local, global, and regional.

The local network (LAN - Local Area Network) - a network within an enterprise, institution, one organization.

Regional network (MAN - Metropolitan Area Network) - a network within a city or region.

Global network (WAN - Wide Area Network) - a network on the territory of a state or a group of states.

By data transfer rate computer networks are divided into low, medium and high speed:

· low speed networks - up to 10 Mbit / s;

· medium speed networks - up to 100 Mbit / s;

· high-speed networks - over 100 Mbit / s.

By the type of transmission medium, networks are divided into:

· wired (on coaxial cable, twisted pair, fiber optic);

· wireless with the transmission of information over radio channels or in the infrared range.

According to the method of organizing the interaction of computers, networks are divided into peer-to-peer and with dedicated server (hierarchicalnetwork).

All computers in a peer-to-peer network are equal. Anyone on the network can access data stored on any computer.

The main advantage of peer-to-peer networks is ease of installation and operation. The main disadvantage is that in the conditions of peer-to-peer networks, it is difficult to solve information security issues. Therefore, this method of networking is used for networks with a small number of computers and where the issue of data protection is not critical.

In a hierarchical network, when installing the network, one or more servers - computers that manage network communication and resource allocation. Any computer that has access to the server's services is called client of the network or workstation.

A server in hierarchical networks is a persistent repository of shared resources. The server itself can only be a client of a higher-level server. Servers are usually high-performance computers, possibly with multiple parallel processors, high-capacity hard drives and a high-speed network card.

The hierarchical network model is the most preferable, since it allows you to create the most stable network structure and more rationally allocate resources. Another advantage of a hierarchical network is a higher level of data protection. The disadvantages of a hierarchical network, compared to peer-to-peer networks, include:

1. The need for an additional OS for the server.

2. Higher complexity of network installation and modernization.

3. The need to allocate a separate computer as a server

Server technology distinguish networks with architecture file-server and networks with architecture customer-server... The first model uses a file server where most programs and data are stored. At the user's request, they are sent required program and data. Information processing is performed at the workstation.

In systems with a client-server architecture, data is exchanged between the client application and the server application. Data storage and processing are performed on a powerful server, which also controls access to resources and data. Workstation receives only query results.

The main characteristics of networks are:

Bandwidth - the maximum amount of data transmitted by the network per unit of time. Bandwidth is measured in Mbps.

Network response time - time spent software and network devices to prepare for the transmission of information on this channel. Network response time is measured in milliseconds.

1.2. Network topology

Network topology refers to the physical or electrical configuration of the cabling system and network connections. Several specialized terms are used in network topology:

· Network node - a computer or a network switching device;

· Network branch - a path connecting two adjacent nodes;

· End node - a node located at the end of only one branch;

· Intermediate node - a node located at the ends of more than one branch;

· Adjacent nodes - nodes connected by at least one path that does not contain any other nodes.

There are only 5 main types of network topology:

1. Topology "Common Bus". In this case, connection and data exchange is carried out through a common communication channel, called a common bus:

A shared bus is a very common topology for local area networks. The transmitted information can be spread in both directions. The use of a common bus reduces wiring costs and unifies the connection of various modules. The main advantages of such a scheme are the low cost and simplicity of cabling in rooms. The most serious drawback of the common bus is its low reliability: any defect in the cable or any of the numerous connectors completely paralyzes the entire network. Another disadvantage of the common bus is its low performance, since with this method of connection, only one computer at a time can transmit data to the network. therefore throughput the communication channel is always divided here between all network nodes.

2. Topology "Star". In this case, each computer is connected with a separate cable to common devicecalled hub, which is at the center of the network:

The function of the hub is to direct the information transmitted by the computer to one or all other computers on the network. The main advantage of this topology over the common bus is that it is significantly more reliable. Any troubles with the cable concern only the computer to which this cable is connected, and only a malfunction of the hub can damage the entire network. In addition, the hub can act as an intelligent filter for information coming from nodes to the network and, if necessary, block transmissions prohibited by the administrator.

The disadvantages of a star topology include the higher cost of network equipment due to the need to purchase a hub. In addition, the ability to grow the number of nodes in the network is limited by the number of hub ports. Currently, the hierarchical star is the most common type of link topology in both LANs and WANs.

3. Topology "Ring". In networks with a ring topology, data in the network is transmitted sequentially from one station to another along the ring, as a rule, in one direction:

If the computer recognizes the data as intended for it, then it copies it to itself into an internal buffer. In a network with a ring topology, special measures must be taken so that in the event of failure or disconnection of a station, the communication channel between the other stations is not interrupted. The advantage of this topology is ease of management, the disadvantage is the possibility of failure of the entire network in case of a failure in the link between two nodes.

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

In a network with a mesh topology, only those computers between which there is an intensive exchange of data are directly connected, and for the exchange of data between computers that are not connected by direct links, transit transmissions through intermediate nodes are used. A mesh topology allows the connection of a large number of computers and is typical, as a rule, for global networks... The advantages of this topology are its resistance to failures and overloads. there are several ways to bypass individual nodes.

5. Mixed topology. While small networks tend to have a typical topology - star, ring, or shared bus, large networks tend to have arbitrary connections between computers. In such networks, it is possible to separate arbitrarily separate subnets with a typical topology, therefore they are called networks with a mixed topology:

1.3. Open Systems Interconnection Model

The main task solved in the creation of computer networks is to ensure the compatibility of equipment in terms of electrical and mechanical characteristics and to ensure the compatibility of information support (programs and data) in terms of the coding system and data format. The solution to this problem belongs to the field of standardization and is based on the so-called oSI models (model of interaction of open systems - Model of Open System Interconnections). The OSI model was created based on the technical proposals of the International Standards Organization (ISO).

According to the OSI model, the architecture of computer networks should be considered at different levels (the total number of levels is up to seven). The topmost level is applied. At this level, the user interacts with the computing system. The lowest level is physical. It provides signal exchange between devices. The exchange of data in communication systems occurs by moving them from the upper level to the lower one, then transportation and, finally, reverse playback on the client's computer as a result of moving from the lower level to the upper one.

To ensure the necessary compatibility at each of the seven possible levels of computer network architecture, there are special standards called protocols... They determine the nature of the hardware interaction of network components ( hardware protocols) and the nature of the interaction of programs and data ( software protocols). Physically, the protocol support functions are performed by hardware devices ( interfaces) and software (protocol support programs). The programs that support the protocols are also called protocols.

Each level of architecture is subdivided into two parts:

Service specification;

Protocol specification.

A service specification defines what a layer does and a protocol specification defines how it does it, with each particular layer having more than one protocol.

Consider the functions performed by each layer of software:

1. Physical layer performs connections to a physical channel, so, disconnects from a channel, channel management. The baud rate and network topology are determined.

2. Link layer adds auxiliary characters to the transmitted information arrays and controls the correctness of the transmitted data. Here, the transmitted information is split into several packets or frames. Each packet contains source and destination addresses and error detection tools.

3. Network layer defines the route of information transfer between networks, provides error handling, as well as data flow control. The main task of the network layer is data routing (data transfer between networks).

4. Transport layer connects the lower layers (physical, channel, network) with the upper layers, which are implemented by software. This layer separates the means of forming data in the network from the means of their transmission. Here the information is divided according to a certain length and the destination address is specified.

5. Session level manages communication sessions between two interacting users, determines the beginning and end of a communication session, time, duration and mode of the communication session, synchronization points for intermediate control and recovery during data transmission; restores connection after errors during a communication session without data loss.

6. Representative - manages the presentation of data in the form necessary for the user program, performs compression and decompression of data. The task of this level is to convert data when transmitting information into a format that is used in information system... When receiving data this level data representation performs the inverse transformation.

7. Applied the layer interacts with network applications serving files, and also performs computational, information retrieval, logical information transformations, transmission of mail messages, etc. The main task of this level is to provide a user-friendly interface.

At different levels, the exchange takes place with different units of information: bits, frames, packets, session messages, user messages.

1.4. network hardware

The main components of the network are workstations, servers, transmission media (cables) and network hardware.

Workstations network computers on which network users implement application tasks are called.

Network servers are hardware and software systems that perform the functions of managing the distribution of shared network resources. The server can be any computer connected to the network that contains resources used by other devices on the local network. Quite powerful computers are used as the server hardware.

Networks can be created with any of the cable types.

1. Twisted pair (TP - Twisted Pair) is a cable made in the form of a twisted pair of wires. It can be shielded or unshielded. A shielded cable is more resistant to electromagnetic interference. Twisted pair is best suited for small institutions. The disadvantages of this cable are a high signal attenuation coefficient and high sensitivity to electromagnetic interference, so the maximum distance between active devices in a LAN when using a twisted pair should be no more than 100 meters.

2. Coaxial cable consists of one solid or stranded center conductor surrounded by a dielectric layer. A conductive layer of aluminum foil, metal braid or a combination of these surrounds the dielectric and simultaneously serves as a shield against interference. A common insulating layer forms the outer sheath of the cable.

Coaxial cable can be used in two different data transmission systems: without signal modulation and with modulation. In the first case, the digital signal is used in the form in which it comes from the PC and is immediately transmitted through the cable to the receiving station. It has one transmission channel with a speed of up to 10 Mbit / s and a maximum range of 4000 m. In the second case, the digital signal is converted into analog and sent to a receiving station, where it is again converted into digital. The signal conversion operation is performed by the modem; each station must have its own modem. This transmission method is multichannel (it provides transmission over dozens of channels using just one cable). In this way, sounds, video signals and other data can be transmitted. The cable length can be up to 50 km.

3. Fiber optic cable is more new technologyused in networks. The information carrier is a light beam that is modulated by the network and takes the form of a signal. Such a system is immune to external electrical interference and thus very fast, secret and error-free data transmission at speeds up to 2 Gbit / s is possible. The number of channels in such cables is enormous. Data transmission is carried out only in simplex mode, therefore, to organize data exchange, devices must be connected with two optical fibers (in practice, a fiber-optic cable always has an even, paired number of fibers). The disadvantages of fiber optic cable include high cost, as well as the complexity of the connection.

4. Radio waves in the microwave range are used as a transmission medium in wireless LANs, or between bridges or gateways for communication between LANs. In the first case, the maximum distance between stations is 200 - 300 m, in the second, this is the line-of-sight distance. The data transfer rate is up to 2 Mbps.

Wireless local area networks are considered a promising area of \u200b\u200bLAN development. Their advantage is simplicity and mobility. The problems associated with laying and installing cable connections also disappear - it is enough to install interface cards on workstations, and the network is ready to work.

The following types of network equipment are distinguished.

1. Network cards Are controllers plugged into expansion slots motherboard computers designed to transmit signals to the network and receive signals from the network.

2. Terminators - These are 50 ohm resistors that produce signal attenuation at the ends of the network segment.

3. Hubs (Hub) Are the central devices of the cable system or network of physical topology "star", which, when receiving a packet on one of its ports, forwards it to all the others. The result is a network with a logical structure of a common bus. Distinguish between active and passive hubs. Active hubs amplify the received signals and transmit them. Passive hubs allow the signal to pass through without amplifying or restoring it.

4. Repeaters (Repeater) - network devices, amplifies and re-forms the shape of the incoming analog signal of the network at the distance of another segment. The repeater operates at the electrical level to connect two segments. Repeaters recognize nothing on network addresses and therefore cannot be used to reduce traffic.

5. Switches (Switch) - software-controlled central devices of the cable system, which reduce network traffic due to the fact that the incoming packet is analyzed to find out the address of its recipient and, accordingly, is transmitted only to him.

Using switches is a more expensive but also more efficient solution. A switch is usually a much more complex device and can serve multiple requests simultaneously. If, for some reason, the required port is busy at a given time, then the packet is placed in the buffer memory of the switch, where it waits for its turn. Networks built with switches can span several hundred machines and extend several kilometers.

6. Routers (Router) - standard network devices operating at the network level and allowing you to forward and route packets from one network to another, as well as filter broadcast messages.

7. Bridges (Bridge) is a network device that connects two separate segments, limited by their physical length, and carries traffic between them. Bridges also amplify and convert signals for other cable types. This allows you to expand the maximum network size without violating the restrictions on the maximum cable length, the number of connected devices, or the number of repeaters per network segment.

8. Gateways (Gateway) - software and hardware systems that connect heterogeneous networks or network devices. Gateways allow you to solve the problem of differences in protocols or addressing systems. They operate at the session, presentation, and application layers of the OSI model.

9. Multiplexers Are central office devices that support several hundred digital subscriber lines... Multiplexers send and receive subscriber data over telephone linesby concentrating all traffic on one high-speed channel for transmission to the Internet or company network.

10. Firewalls (firewall, firewalls) - these are network devices that implement control over the information entering and leaving the local network and ensuring the protection of the local network by filtering information. Most firewalls are built on classical models of access control, according to which a subject (user, program, process or network packet) is allowed or denied access to an object (file or network node) upon presentation of some unique element inherent only to this subject. In most cases, this element is a password. In other cases, such a unique element is microprocessor cards, biometric characteristics of the user, etc. For a network packet, such an element is addresses or flags in the packet header, as well as some other parameters. Thus, a firewall is a software and / or hardware barrier between two networks, allowing only authorized interconnections to be established. Typically, firewalls protect the corporate network connected to the Internet from outside intrusion and prevent access to confidential information.

Depending on the place and purpose of creating a local network, a variety of network equipment may be required. At the same time, the modern market for equipment for local area networks amazes novice administrators with a variety of prices and models, so here we will consider what is required to combine computers within the framework of one knowledge.

Typical composition of local network equipment

Network cables

There are several types of network cables for installing a local network:

1. 1. Twisted pair is the most common (at the moment) type of cable used to connect computers to a local area network. The cable consists of eight copper wires that are connected in strict sequence through an RJ-45 connector.

There are many varieties of this cable, depending on the brand and conductivity. Cat 6 cable is very popular, which, in addition to good cable protection, also has high conductivity values. The main disadvantage of creating a local network using a twisted pair is the relatively small distance between connection points (it should not exceed more than one hundred meters).

1. 2. Fiber optic cable.

The main advantage of this cable is its good data transfer speed. There are no distance restrictions for such a connection, but the cost of fiber is much higher than the "classic" twisted pair.

In addition, this cable requires special soldering at the joints, which can only be done by a specialist with special equipment.

Network cards

Typically, each computer is equipped with a network card. It is a device that allows you to send and receive data through network protocols.

There are two types of network cards:

1. 1. The built-in network card looks like a card that is inserted into a special connector on a personal computer. It includes an RJ 45 connector and a data processor. Unlike desktop computers, laptops and netbooks are already equipped with a network card built into the motherboard.
2. 2. The external network card is mainly supplied as a USB-RJ45 adapter. It is used on many personal computers and laptops, which for some reason do not have the ability to install internal network cards.

Network switches

Special equipment that filters and amplifies the network signal. The main advantage of switches is bandwidth savings because the switch only sends a signal to computers on the network, ignoring turned off equipment.

Switches are divided into several types depending on the following characteristics:

1. 1. The baud rate of the switch - ie. at what speed network packets will be sent: 10, 100 or 1000 mb per second.
2. 2. The number of ports on the switch. Depending on the number of connected workstations in your local network, you can use a switch with 8.16 and 24 ports.

Routers (routers)

This equipment is mainly applied to interconnect networks (such as Ethernet and Wan). It also filters routes for sending data using a built-in algorithm.

Network equipment required for network operation is divided into two types: active and passive equipment. Active equipment includes switches, hubs, network adapters, routers, print servers, etc., passive equipment includes sockets, cables and cable channels, patchcords, connectors, and other similar equipment.

Active equipment is designed to perform all the necessary actions related to data transmission. IN modern networks packet data transmission is organized, where each packet is endowed with information about its location, the integrity of the transmitted information and other data, allowing it to be delivered to its destination.

Active network equipment contains special algorithms in its memory, with the help of which it not only picks up the signal, but also measures the path along which the packet is transmitted. Since there can be several options for data transmission in the network, which is associated with the load on the network and the number of busy and free devices, active equipment also performs the function of creating transmission channels and is responsible for distributing the load on the transmitting devices.

Network adapters are used to connect a device to a local network, switches and hubs allow computers to be connected to each other, routers decide to forward packets between network segments, etc.

Thus, ensuring the construction of a distributed information structure, active network equipment makes it possible to transfer significant amounts of data over long distances.

Passive equipment differs from active equipment primarily in that it is not powered directly from the mains and transmits a signal without amplifying it. Passive network equipment is conventionally divided into two groups. The first group includes equipment that is a route for cables: brackets, cable channels and accessories for them, metal trays, embedded pipes, clips, corrugated hoses and switch cabinets. The second group includes equipment that serves as a data transmission path. This includes sockets, cables, and patch panels.

Patch panels provide connections between active equipment ports and cables. Typically, two types of cables are used: shielded and unshielded twisted pair (STP and UTP). Depending on the type of network, telephone or computer sockets can be used.

Metal trays, cable ducts, brackets and corrugated hoses are used, as a rule, to lead the cable and protect it, and clips are used to fasten corrugated hoses. Accessories for cable ducts are used for aesthetic reasons. These include: inner and outer corners, plugs, T-bends, and a connecting bracket. In the case when it is necessary to tighten the bundle of cables, ties are used.

Definition 1

network hardware - devices necessary for the functioning of a computer network.

Network equipment is divided into active and passive equipment.

Active network equipment

Active equipmente contains electronic circuits that are powered from an electrical network or other sources and perform the functions of amplification, signal conversion, etc. Active equipment processes the signal using special algorithms. Data transmission in networks occurs in data packets, each of which also contains additional technical information (information about its source, purpose, information integrity, etc.), which allows the packet to be delivered to its destination. The task of active network equipment is not only to capture and transmit the signal, but also to process this technical information, as a result of which to redirect and distribute incoming streams in accordance with the algorithms built into the device's memory. It is this feature and mains power that is a sign of active equipment.

Remark 1

Active equipment includes the following types of devices:

Network card, network card, network adapter, Ethernet adapter - an additional device that is installed in a PC and ensures its interaction with other network devices.

In modern PCs and laptops, the controller and components that perform the functions network cardare mostly already integrated into mainboards. There are also:

• internal network cards - separate boards that are connected via the $ ISA $, $ PCI $ or $ PCI-E $ slot;
• external network cards that connect through the $ LPT $, $ USB $ or $ PCMCIA $ interface (mostly used in laptops).

Figure 1. Internal NIC

Figure 2. External network card

Definition 2

Concentrator (active hub, multiport repeater) - a network device with $ 4- $ 48 ports, which is used to connect a PC to a network using a twisted pair cable.

The hubs also have connectors for connecting to coaxial cable networks. Currently supplanted by network switches.

Figure 3.

Definition 3

Repeater, repeater - network equipment designed to increase the length of a network connection by repeating a signal at the physical layer.

There are single-port and multiport repeaters.

It differs from the hub in that the repeater has much less delay time, because it usually has two connectors for connecting a cable. He does not need to concentrate the signal somewhere and distribute it to other outputs. Multiport twisted pair repeaters are commonly called network hubs (hubs), and coaxial repeaters are called repeaters.

Figure 4.

Definition 4

Bridge - a network device with $ 2 $ ports, which is designed to combine several segments of a computer network into a single network, filters network traffic by parsing network (MAC) addresses.

Figure 5.

Definition 5

Switch (switch) - a network device that is designed to connect several nodes of a computer network.

Switches are designed using bridging technology, which is why they are often called multiport bridges. It differs from a hub, which distributes traffic from one connected device to all others, in that it only transmits data directly to the recipient. This eliminates the need to process the data segments for which the data was not intended, which certainly leads to improved network performance and security. An exception would be broadcast traffic for all hosts on the network and traffic for devices whose switch outbound port is unknown.

Figure 6.

Definition 6

Router (router) - a specialized network computer that has a $ 2 or more network interface and forwards data packets between different network segments.

The router allows you to filter network traffic by parsing network ($ IP $) addresses. It is mainly used to combine networks of different types, which are often incompatible in architecture and protocols. For example, to combine local Ethernet and WAN connections. Often a router is used to provide access from a local network to the Internet. Home routers are usually small port and connect the PC's home network to the ISP's link.

Figure 7.

Definition 7

Media converter (media converter) - a network device that converts a signal propagation medium from one type to another. Typically, the signal propagation medium is copper wires and optical cables.

Typically, a media converter has $ 2 $ ports.

Figure 8.

Definition 8

Network transceiver - a device that is intended to convert the data transfer interface $ (RS232-V35 $, $ AUI-UTP) $. Usually has $ 2 $ ports.

Figure 9.

According to some experts, a repeater (repeater) and a hub (hub) do not belong to active network equipment, because they simply repeat the signal, and do not process it according to certain algorithms. But managed hubs are still considered active network equipment even with this approach.

Passive network equipment

Definition 9

Passive network equipment - network equipment, which is not supplied from the mains or other sources, and is designed to perform functions of distribution or signal reduction.

Passive network equipment is:

A structured cabling system (SCS) consists of a set of cables and switching equipment, includes a technique for their sharing, which allows you to create regular expandable communication structures in local networks for various purposes. SCS is the physical basis of the infrastructure of the building, which allows you to combine many network information services for various purposes into a single system: local computer networks and telephone networks, security systems, video surveillance, etc.

Figure 10.

Patch panel (cross-panel, patch-panel) - an integral part of the SCS, made in the form of a panel with many connectors, which are located on the front side of the panel. On its back side there are contacts that are intended for fixed connection with cables and are electrically connected to the connectors.

Figure 11.

Plug / socket ($ RG58 $, $ RJ45 $, $ RJ11 $, $ GG45 $) Balun for coaxial cables ($ RG-58 $), etc.

Introduction

Chapter I Theoretical Foundations of Networking

Computer network topology

A ring 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 it only transfers. The topology of the ring is shown in Figure 1.

Figure 1 - Ring topology

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. The operation in the ring network 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 ring, which controls 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.

A star is the basic topology of a computer network (Figure 2), in which all computers on the network are connected to a central node (usually a switch), forming a physical network segment.

Figure 2 - Star topology

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 for managing the exchange are entrusted. In principle, no conflicts in a network with a star topology are possible, because the management is completely centralized.

Bus - This 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. The bus topology is shown in Figure 3.

Figure 3 - Bus topology

Network equipment

Network equipment - devices necessary for the operation of a computer network, for example: a router, switch, hub, patch panel, etc. Active and passive network equipment can be distinguished.

Active network equipment

This name refers to equipment followed by some “smart” feature. That is, a router, switch (switch), flexible multiplexer, etc. are active network equipment. On the contrary, the repeater (repeater)] and the hub (hub) are not ASO, since they simply repeat the electrical signal to increase the connection distance or topological branching and do not represent anything "smart". But managed hubs belong to active network equipment, since they can be endowed with some kind of "intellectual feature"

Passive network equipment

Passive equipment differs from active equipment primarily in that it is not powered directly from the mains and transmits a signal without amplifying it. Passive network equipment refers to equipment that is not endowed with "smart" features. For example cabling system: cable (coaxial and twisted pair), plug / socket (RG58, RJ45, RJ11, GG45), repeater, patch panel, hub, coax balun (RG-58), etc. Also, Passive equipment includes enclosures and racks, telecommunication cabinets. Mounting cabinets are divided into standard, specialized and vandal-proof. By type of installation: wall, floor and others.

Basic network equipment

The main network equipment includes:

Server is a dedicated computer. A server is a computer allocated from a group of personal computers (or workstations) to perform any service task without direct human participation. The server and workstation can have the same hardware configuration, since they differ only in the participation of the person at the console in their work.

Some service tasks can be performed on a workstation in parallel with the user's work. Such a workstation is conventionally called a non-dedicated server.

The console (usually a monitor / keyboard / mouse) and human participation are necessary for servers only at the stage of initial configuration, during hardware maintenance and management in emergency situations (normally, most servers are controlled remotely). For emergencies, servers are typically provided with one console kit per server group (with or without a switch, such as a KVM switch).

As a result of specialization (see below), a server solution can receive a console in a simplified form (for example, a communication port), or lose it altogether (in this case, initial configuration and abnormal management can be performed only through the network, and the network settings can be reset to default state). The server is shown in Figure 4.

Figure 4 - Server

Modem (an acronym made up of the words modulator and demodulator) is a device used in communication systems to physically interface an information signal with its propagation medium, where it cannot exist without adaptation.

The modulator in the modem modulates the carrier signal during data transmission, that is, changes its characteristics in accordance with changes in the input information signal, the demodulator performs the reverse process when receiving data from the communication channel. The modem performs the function of the terminal equipment of the communication line. The very formation of data for transmission and processing of received data is carried out by the so-called. terminal equipment (a personal computer can also act in its role).

Modems are widely used to connect computers via telephone network (telephone modem), cable network (cable modem), radio waves (en: Packet_radio, radio relay). Previously, modems were also used in cell phones (until they were superseded by digital methods of data transmission). The modem is shown in Figure 5.

Figure 5 - Modem

A twisted pair is a type of communication cable, which is one or more pairs of insulated conductors twisted together (with a small number of turns per unit length), covered with a plastic sheath.

Conductors are twisted in order to increase the degree of communication between the conductors of one pair (electromagnetic interference equally affects both wires of the pair) and then reduce electromagnetic interference from external sources, as well as mutual interference during transmission of differential signals. To reduce the connection of individual cable pairs (periodic convergence of conductors of different pairs) in UTP category 5 and higher cables, the wires of the pair are twisted with different pitch. Twisted pair is one of the components of modern structured cabling systems. Used in telecommunications and in computer networks as a physical medium for signal transmission in many technologies such as Ethernet, Arcnet and Token ring. Currently, due to its low cost and ease of installation, it is the most common solution for building wired (cable) local area networks.

The cable connects to network devices using the 8P8C connector (which is mistakenly called RJ45). The twisted pair is shown in Figure 6.

Figure 6 - Twisted pair

Coaxial cable (from Latin co - together and axis - axis, that is, "coaxial"), also known as coaxial (from English coaxial), is an electrical cable consisting of a central conductor and screen located coaxially. Typically used to transmit high frequency signals. Invented and patented in 1880 by British physicist Oliver Heaviside. The coaxial cable is shown in Figure 7.

Figure 7 - Coaxial cable

Optical fiber - a filament made of optically transparent material (glass, plastic), used to transfer light inside itself through total internal reflection.

Fiber optics is a branch of applied science and mechanical engineering that describes such fibers. Optical fiber cables are used in fiber-optic communication, which allows information to be transmitted over greater distances at a higher data rate than electronic communications. In some cases, they are also used to create sensors. Optical fiber is shown in Figure 8.