Network components. Network connections and network components

Good afternoon, Friends! I am very glad to welcome you to our educational Internet portal With a Computer on “YOU”. In the previous article, we started a conversation about doing it yourself at home.

To connect several computers or gadgets together, you need to understand what communication interfaces they already have (for example, built-in wireless modules or expansion cards), and what devices need to be purchased (access points or router).

Today I propose to consider the main network components and devices that may be useful to us when laying out a home local network.

The optimal set of components required to create a small local network:

• Network card (wired or wireless);
• Network cable (if you select a wired network);
• Modem or router.

Selecting a network cable

1. . Externally, it is very similar to a television cable, only it has different technical specifications. The maximum theoretical data transfer rate is 10 Mbit/s. Today it is practically not used.

2. . The most common type of cable today. Provides high data transfer speeds (up to 1 Gbit/s) and higher connection reliability. It has become widespread due to its low cost. The perfect solution For home network.

Usually supplied with network equipment. When purchasing a patch cord, pay attention to the presence of a factory cable crimp. If you cannot find factory cables of the required length, you can buy a cable and connectors separately, give the fiber optic cable to specialists in the store, they will do the crimping (the work costs approximately 50 rubles). Maximum length twisted pair cable – 115 meters.

3. . Most reliable connection, allowing you to achieve high speed characteristics (hundreds and thousands of Gbit/s) with a significant increase in the distance between network components (hundreds of kilometers). Expensive equipment and cable.

Selecting a network card

• 1. Wired options. Typically they are built-in elements. modern computers. They have a low cost (about 150 rubles). They differ in exchange speed (100-megabit or gigabit network adapters).

If your device does not have built-in network card, you can choose one of the following options:

Network expansion card for PCI bus;

USB Ethernet adapter.

• 2. Wireless options. Today, almost all mobile devices, laptops, tablet computers are equipped with built-in Wi-Fi adapters. If your device does not have one, you can purchase external wireless adapters.

USB option. No bigger than a flash drive. Inexpensive.

PCI version of an expansion card for PCs.

Selecting network components for device switching

• 1. Concentrator (hub)– a network device that combines several network devices into single network. The principle of operation of such a device is simple: it copies all received data to all ports. Hence there are two big disadvantages:

If data arrives on several ports at once, a collision (failure) occurs. Data is lost.
The hub transmits data to all devices, regardless of destination. That. the device loads the entire network.

Under high load during data exchange, the network may stop functioning. Currently practically not used.

• 2. Switch (switch)- looks like a concentrator, but has intellectual filling. Analyzing data during transmission, it sends it only to the device for which the data is intended. A more reliable and secure device, inexpensive, and (in a simple version) does not require settings.

• 3. Access point– a network device for organizing a wireless network. Simple device, no additional functions(see below about wireless routers): consisting of a wireless module and network connectors for connecting to an Ethernet network.

• 4. Print server is a device that provides network access to a printer that is not equipped with network interfaces. Very convenient if you need to use the printer on all computers on the network.

Let us note right away that not all printers are suitable. Because some inkjet printers Some of their tasks for processing a printed document are “shifted onto the shoulders” of the operating system. That. these so-called GDI printers will not work under the control of a print server.

• 5. Router (router)– a network device designed to combine two networks: the local home one, which we are building, and the external Internet network to which the house or apartment is connected. The hub and switch do not have such functions.

In addition, the router has additional functions external protection network using the built-in firewall (firewall). Sometimes a bonus is the presence of an additional USB port for connecting USB devices to a shared network.

• 6. Wireless routers(Internet centers)– these are devices designed to create a network of any architecture and represent an association wireless point access, router, network switch on several Ethernet ports and a firewall.

As a rule, these devices are purchased by users today to set up a home network. They have become more accessible. As a rule, one device is cheaper, more reliable and takes up less space in the apartment than a set of devices. Anyone can handle the setup. But we will talk about this in more detail in a separate article.

So, Friends, we have become acquainted with the main components of the network and now we know for sure what can be useful to us. Ahead of us are still questions about setting up network devices and some additional points of network education.

Open architecture information systems . The modern trend in the development of information systems, within which or the resources of which management systems can be used, is essentially that the structure of the system must satisfy the following requirements to ensure its survivability, ability to develop and improve:

The system must have an open architecture;

The system must be distributed.

Only with the development of microprocessor technology and network technologies has it become possible and economically justifiable to build automation systems that truly meet these requirements. It has become expedient to allocate general structure systems separate local tasks, the solution of which is entrusted to local controllers. The network allows controllers to use variables of other controllers as arguments for calculating the control vector, ensuring the connectivity of the control system as a whole. This architecture significantly increases the performance, reliability and scalability of systems. International Organization for Standardization (ISO) in 1984. formulated a model of interaction open systems(OSI), identifying seven levels of such interaction.

The reference model for the interaction of open systems declares not only the interaction, but also the architecture of such systems. Any open system is hierarchically constructed, and the internal architecture of the system is similar to the global architecture, which includes many subsystems. This means that software for systems of any level is created on general principles and is quite versatile. It is assumed that the direct connection between physically various systems or subsystems is carried out at the physical level. Ideally, each level should interact directly with only two adjacent levels.

The levels of the open systems interaction model (from bottom to top) mean the following:

1. Physical layer (lower). Responsible for the physical transmission medium: cables, connectors, coordination of communication lines, electrical signal conversion.

2. Data link level. The main task is logical control of the transmission line, network access control, detection of transmission errors and their correction.

3. Network layer. Responsible for addressing data packets, connecting physical network addresses and logical names, selects the data delivery route.

4. Transport layer. This is where data packets are created and these packets are delivered. When it is extremely important, procedures are used to recover lost data.

5. Session level. A communication session means that a logical connection has been established between network subscribers, logical names are defined, and access rights are controlled.

6. Executive level. At this level, working information is converted into a logical and physical form suitable for transmission over the network (compression, encryption, conversion of data formats, etc.).

7. Application layer(application level). User program level. The top level that directly interacts with the user.

The structure of the levels is such that replacing the hardware affects only levels 1 and 2; higher levels should not notice this replacement.

Local managers computer networks . To transmit information in automation systems, not traditional communication channels (multi-core cables, telephone channels, etc.) are increasingly being used, but local networks. The significant difference lies not so much in the form of the physical medium for transmitting information, but in the much more complex and effective ways coding and compression of information. Unfortunately, modern solutions for building local and global information networks are not always acceptable due to non-guaranteed information delivery time, which is of little use for real-time systems, and the complexity of hardware solutions, especially for high-speed networks.

Automation systems often use segments of conventional local and global networks. Most local networks have access to global network, but the nature of the transmitted information, principles of organizing exchange, modes of access to resources within the local network, as a rule, are very different from those accepted in the global network. A variety of digital information can be transmitted over a local network: data, images, telephone conversations, emails, etc. The task of transmitting full-color dynamic images places the highest demands on network speed. Most often, local networks are used for sharing resources such as disk space, printers and access to the global network, but this is only part of the capabilities of local networks. For example, they allow the exchange of information between computers of different types. Network subscribers (nodes) are not only computers, but also other devices (printers, plotters, scanners). Local networks make it possible to organize a system of parallel computing on all computers on the network, which allows you to significantly speed up the solution of complex problems. mathematical problems. With their help, you can also control the operation of a complex technological system or research facility from several computers simultaneously.

Let us mention such important concepts of network theory as server and client. A server is usually called a network subscriber (node) that provides its resources to other subscribers, but does not itself use the resources of other subscribers. There should be several servers on the network, and the server is not necessarily the most powerful computer.
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A dedicated server is a server that deals only with network tasks. A non-dedicated server can perform other tasks in addition to network maintenance. A client (workstation) is usually called a network subscriber who only uses network resources, but does not give its resources to the network. In principle, each computer should be both a client and a server at the same time. The term server and client often refers not to the computers themselves, but to the software applications running on them.

Local network topologies . The topology (layout, configuration, structure) of a computer network is usually understood as the physical location of computers on the network relative to each other and the way they are connected by communication lines. The topology determines the equipment requirements, the type of cable used, communication control methods, operational reliability, and network expansion capabilities. At different levels of network architecture there are also:

Physical topology, layout of computers and cable routing.

Logical topology, structure of logical connections and signal transmission methods.

Information topology, ways of distributing information over the network.

There are three basic network topologies:

‣‣‣ bus, in which all computers are connected in parallel to one communication line and information from each computer is simultaneously transmitted to all other computers.

‣‣‣ star (star), in which other peripheral computers are connected to one central computer, each of them using its own separate communication line.

‣‣‣ ring, in which each computer always transmits information to only one computer next in the chain, and receives information only from the previous computer in the chain, and this chain is closed in a “ring”.

In practice, any combination of basic topologies is used, but most networks are focused on these three.

Bus topology (or “common bus”) assumes the identity of the network equipment of computers and the equality of all subscribers. With this connection, there is only one communication line and the bus implements a half-duplex exchange mode in both directions, but in turn. There is no central subscriber through which all information is transmitted, which increases its reliability (if the center fails, the entire system stops functioning).

Since resolving possible conflicts in in this case falls on the network equipment of each subscriber, the network adapter equipment is more complex than with other topologies. The bus is not afraid of failures of individual computers. At the ends of the bus, it is extremely important to include matching devices - terminators, to eliminate reflections from the ends of the line. A failure of network equipment on the bus is difficult to localize, since all adapters are connected in parallel. When passing through the buses, information signals are weakened, which imposes restrictions on the total length of communication lines. Each subscriber can receive signals of different levels from the network based on the distance to the transmitting subscriber. This places additional demands on receiving nodes of network equipment. To increase the length of the network, bus segmentation is used, with the segments connected through special signal restorers - repeaters.

Star topology - this is a topology with a clearly designated center to which all other subscribers are connected. Information is exchanged through a central computer, which is usually the most powerful in the network. In principle, no conflicts are possible in the network. Failure peripheral computer does not affect the functioning of the network, but any failure of the central computer makes the network inoperable.

In a star, there are only two subscribers on each communication line: the central one and one of the peripheral ones. Each peripheral subscriber can be connected to either one cable (transmission in both directions) or two cables (transmission in one direction). The problem of signal attenuation in a communication line is solved more simply; each receiver receives a signal of the same level.

The disadvantage of the star topology is the limitation of the number of subscribers. Typically, the central subscriber can serve no more than 8-16 peripheral subscribers. Sometimes a star provides the ability to connect another central subscriber instead of a peripheral subscriber, resulting in a topology of several interconnected stars.

The great advantage of the star is that all connection points are collected in one place, which makes it easy to control the operation of the network, as well as limit access unauthorized persons to vital connection points for the network.

There is a topology called passive star, which is only superficially similar to a star. In the center of a network with this topology, there is not a computer, but a hub, which performs the same function as a repeater.
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It recovers incoming signals and forwards them to other communication lines. In fact, we are dealing with a bus topology, since information from each computer is simultaneously transmitted to all other computers, and there is no central subscriber.

Ring topology is a topology in which each computer is connected by communication lines to only two others: from one it only receives information, and to the other it only transmits. An important feature of the ring is that each computer relays (restores) the signal coming to it, that is, it acts as a repeater. There is no clearly designated center in the network, but often a special subscriber is allocated in the ring who manages the exchange or controls the exchange. The presence of a control subscriber reduces the reliability of the network.

The maximum number of subscribers in the ring should be up to a thousand or more. The ring topology is usually the most resistant to overloads; it ensures reliable operation with the largest flows of information transmitted over the network. As a rule, there are no conflicts in it. Since the signal in the ring passes through all the computers, the failure of at least one of them or its network equipment disrupts the operation of the entire network. This topology usually involves laying two (or more) parallel communication lines, one of which is in reserve. At the same time, the major advantage of the ring is that relaying signals by each subscriber allows you to significantly increase the size of the entire network as a whole (sometimes up to several tens of kilometers).

Sometimes the “ring” topology is based on two ring communication lines that transmit information in opposite directions, which allows you to increase the speed of information transfer, and if one of the cables is damaged, you can work with one cable.

literature

1. Miroshnik I.V. Theory automatic control. Linear systems: Tutorial for universities. - St. Petersburg: Peter, 2005. - 336 p.

10. Tumanov M.P. Technical means automation and control: Textbook. – M.: MGIEM, 2005, 71 p. URL: http://rs16tl.rapidshare.com/files/21651582/2889232/ Tehnicheskie_sredstva_avtomatizatsii_i_upravleniya.rar

11. Mikhailov V.S. Control theory. – K.: Vyshcha School, 1988.

12. Zaitsev G.F. Theory of automatic control and regulation. – K.: Vyshcha School, 1989.

About noticed typos, errors and suggestions for additions: [email protected].

4) Data transmission media

The most common media for transferring data between computers are three main groups of cables:

coaxial cable;

twisted pair (unshielded and shielded);

fiber optic cable.

Coaxial cable is inexpensive, lightweight, flexible, convenient, safe and easy to install. There are two types coaxial cables: thin (10 Base2 specification) and thick (10 Base5 specification). Slim - Flexible, 0.64 cm (0.25") diameter. Easy to use and suitable for almost any type of network.

twisted pair- these are two intertwined insulated copper wires. Several twisted pairs of wires are often contained within a single protective sheath. Intertwining wires allows you to get rid of electrical interference induced by neighboring wires and other external sources. The advantages of twisted pair cable are low cost and ease of connection. Disadvantages - cannot be used when transferring data to long distances at high speed.

In a fiber optic cable, digital data travels along optical fibers in the form of light pulses. This reliable way transmission, since electrical signals however, they are not transmitted. Therefore, the fiber optic cable cannot be opened and the data cannot be intercepted. Fiber optic lines designed to move large amounts of data over very high speeds. The distance is many kilometers. A significant disadvantage of this technology is the high cost and complexity of installation and connection.

To transmit encoded signals via cable, two technologies are used - unmodulated and modulated transmission.

Unmodulated systems transmit data in the form digital signals, which are discrete electrical or light pulses.

Modulated systems transmit data in the form analog signal(electrical or light), occupying a certain frequency band.

A wireless environment does not mean a completely wire-free network. The wireless environment provides a temporary connection to the existing cable network, guarantees a certain level of mobility and reduces restrictions on network length.

There are following types wireless networks: LAN, extended LAN and mobile networks (laptop computers). The main differences between them are the transmission parameters.

The operation of wireless LANs is based on four methods of data transmission: infrared radiation, laser, radio transmission in a narrow range (single frequency transmission), radio transmission in a scattered spectrum.

5) Network adapter cards

Network adapter (CA) cards act as physical interface or a connector between a computer and a network cable.

The CA board performs:

preparing data coming from a computer for transmission via a network cable;

transferring data to another computer;

control the flow of data between the computer and the cable system;

receiving data from the cable and translating it into a form understandable by the computer.

The work of a network is to transfer data from one computer to another. The following tasks can be identified in this process:

data recognition;

splitting data into manageable blocks;

adding information to each block about the location of the data and the recipient;

adding information for synchronization and error checking;

moving data to the network and sending it to a given address.

The sequence of these tasks is strictly regulated in order to transfer data between network adapters different manufacturers, when they are carried out, certain rules - protocols - are strictly followed. There are two main sets of standard protocols: reference OSI model and its modification Project 802.

6) Network equipment

Except minimally necessary equipment: transmission media and network adapter cards; when building networks, additional equipment can be used, the composition of which is determined by the specific network topology.

Terminators are 50 ohm resistors that cause signal attenuation at the ends of a network segment.

Hubs are central devices cable system or a star physical topology network, which, when receiving a packet on one of its ports, forwards it to all the others.

Repeaters are network devices that amplifies and re-forms the shape of the incoming analog network signal over a distance of another segment.

Switches are software-controlled central devices in a cabling system that reduce network traffic due to the fact that the incoming packet is analyzed to determine the address of its recipient and, accordingly, is transmitted only to him.

Routers – standard devices networks that operate at the network layer and allow you to forward and route packets from one network to another, as well as filter broadcast messages.

Bridges are network devices that connect two separate segments, limited by their physical length, and transmit traffic between them.

Gateways are software and hardware systems that connect heterogeneous networks or network devices. Gateways allow you to distinguish between protocols or addressing systems.

Multiplexers are central office devices that support several hundred digital subscriber lines.

Between firewalls(firewall, firewalls) are network devices that exercise control over information entering and exiting the network and providing protection to the local network by filtering information.

Network interaction model

Currently, interaction in computer networks is described using the Open Systems Interconnection (OSI) model. The model was developed by the International Standard Organization (ISO) in 1984 and is an international standard for network communications design.

The OSI model assumes a layered approach to building networks. Each level of the model serves different stages of the interaction process. The OSI model is supported by various services, each at its own level. Services operate according to certain rules - protocols. Accordingly, each level has its own protocol. All together, these services perform one general work- data transmission over the network, adhering to general rule(general protocol). An example of such a protocol would be network protocol TCP/IP, consisting of various protocols and services.
When we talk about the TCP/IP protocol, we always mean a set of network and transport layer protocols. The TCP/IP protocol suite is also called a protocol stack, which consists of two main protocols: TCP (Transmission Control Protocol) - a transport layer protocol and IP (Internet Protocol) - a network layer protocol.
Dividing into levels simplifies working together equipment and software. Below is the OSI model separating network functions into seven levels:

• Physical layer(Physical layer) defines the way computers on the network are physically connected. The functions of the tools belonging to this level are bit-by-bit conversion of digital data into signals transmitted via physical environment(for example, via cable), as well as the actual transmission of signals.
• Data Link Layer(Data Link layer) is responsible for organizing data transfer between subscribers through the physical layer, therefore, at this level, addressing means are provided that make it possible to uniquely determine the sender and recipient in the entire set of subscribers connected to a common communication line. In function this level also includes ordering of transmission for the purpose of parallel use of one communication line by several pairs of subscribers. In addition, link layer tools provide error checking that may occur during data transmission by the physical layer.
• Network layer(Network layer) ensures the delivery of data between computers in a network, which is an association of different physical networks. This level assumes the presence of logical addressing tools that allow you to uniquely identify a computer in an interconnected network. One of the main functions performed by the means of this level is routing - targeted transmission of data to a specific recipient, regardless of its location relative to the sender.
• Transport layer(Transport layer) implements data transfer between two programs operating on different computers, while ensuring the absence of losses and duplication of information that may arise as a result of transmission errors of lower layers. If data transmitted through the transport layer is fragmented, then the means of this layer ensure that the fragments are assembled in the correct order.
• Session (or session) level The Session layer allows two programs to maintain long-term communication over a network, called a session or session. This layer manages session establishment, information exchange, and session termination. It is also responsible for identification, thereby allowing only certain subscribers to participate in the session, and provides security services to regulate access to session information.
• Presentation layer(Presentation layer) performs intermediate data transformation outgoing message into a general format, which is provided by the means of lower levels, as well as reverse conversion of incoming data from a general format into a format understandable to the receiving program.
• Application layer(Application layer) provides high-level network communication functions, such as file transfer, sending messages over email etc.

When organizing the interaction process at a level, the following requirements must be met:

• Components at one level of one system can only interact with components at the same level in another system. A set of rules that determine the order of interaction between tools belonging to the same level and operating in different systems is called protocol(protocol).
• within one system, components of any level can only interact with components of adjacent (overlying and underlying) levels. The rules for interaction between tools belonging to adjacent levels and operating in the same system are called interface(interface).

Although various components belonging to different levels of the network model should formally be functionally independent of each other, when practical development protocols, such independence is not always maintained. This is because trying to achieve an exact match reference model may lead to ineffective operation of the software and hardware that implements the protocol. Therefore, the practical implementation of interaction methods, as a rule, involves the development not of individual protocols, but of entire sets of protocols - stacks, including protocols of adjacent layers of the OSI model that are dependent on each other.

Windows Networking Architecture

Windows networking has a layered architecture that corresponds to the layers of the OSI model.

At the lowest level physical devices- network adapters (Network Interface Card, NIC) and modems (modem), which provide the ability to connect computers to communication lines. As a rule, these devices implement functions of the physical and partly of the data link layer.

The second level is software components, providing link-layer functions that are not implemented in hardware. These include:

• device drivers;
• protocol drivers remote access;
• software that implements interaction using IrDA and ATM technologies;

The third level consists of transport protocol drivers, which are implementations of the main modern network and transport layer stacks of the OSI model. To standardize the interaction of transport protocols with lower-level tools, the NDIS (Network Driver Interface Specification) interface is designed.

The top-level features of the Windows networking software architecture include various services. The main ones are:

• service workstation, which provides the client computer with access to files and folders located on remote computer;
• server service that provides access to other computers local files and folders.

In the Windows executive system, these services are represented by separate components implemented as file system drivers - a redirector and a server. The redirector and server interact with the transport layer through standard interface transport drivers (Transport Driver Interface, TDI), which allows you to use Windows networks any transport protocol.

Additionally, Windows allows you to install customer services to access resources on networks managed by other operating systems, such as Nowell NetWare or MAC OS.

Undocumented and little known Windows features XP Klimenko Roman Alexandrovich

Network and network components

Network and network components