Principles of operation of a local network. Design and calculation of local computer networks Schemes for constructing local computer networks

Useful tips

Local area network is a concept that is familiar to many firsthand. Almost every enterprise uses this technology, so it can be said that every person has come across it in one way or another. Local networks have significantly accelerated production processes, thereby giving a sharp boost to their further use throughout the globe. All this allows us to predict the further growth and development of such a data transmission system, up to the introduction of a LAN in every, even the smallest enterprise.

The concept of a local network

A local area network is a number of computers connected to each other by special equipment that allows for the full exchange of information between them. An important feature of this type of data transmission is the relatively small area where communication nodes, that is, the computers themselves, are located.

Local networks not only greatly facilitate interaction between users, but also perform some other functions:

Simplify work with documentation. Employees can edit and view files at their workplace. At the same time, there is no need for collective meetings and meetings, which saves valuable time.
They allow you to work on documents together with colleagues, when everyone is at their own computer.
They allow access to applications installed on the server, which allows you to save free space on the installed hard drive.
Save hard drive space by allowing you to save documents on your host computer.

Types of networks

A local area network can be represented by two models: a peer-to-peer network and a hierarchical one. They differ in the ways communication nodes interact.

A peer-to-peer network is based on the equality of all machines, and data is distributed between each of them. Essentially, a user of one computer can access the resources and information of another. The efficiency of the peer-to-peer model directly depends on the number of worker nodes, and its level of security is unsatisfactory, which, coupled with a rather complex management process, makes such networks not very reliable and convenient.

The hierarchical model includes one (or more) main server, where all data is stored and processed, and several client nodes. This type of network is used much more often than the first, having the advantage of speed, reliability and security. However, the speed of such a LAN largely depends on the server, which under certain conditions can be considered a disadvantage.

Drawing up technical requirements

Designing a local area network is a rather complex process. It begins with the development of a technical specification, which should be carefully considered, since shortcomings in it threaten subsequent difficulties in building a network and additional financial costs. Primary design can be done using special configurators that will allow you to select the optimal network equipment. Such programs are especially convenient in that you can correct various values and parameters directly during operation, as well as generate a report at the end of the process. Only after these steps can you proceed to the next stage.

Schematic design

This stage consists of collecting data about the enterprise where it is planned to install a local area network, and analyzing the information received. The quantity is determined:

Users.
Workstations.
Server rooms.
Connection ports.

An important point is the availability of data on the routes for laying highways and the planning of a specific topology. In general, it is necessary to adhere to a number of requirements imposed by the IEEE 802.3 standard. However, despite these rules, sometimes it may be necessary to make calculations of signal propagation delays or consult with network equipment manufacturers.

Basic LAN characteristics

When choosing a method for placing communication nodes, you must remember the basic requirements for local networks:

Performance, which combines several concepts: throughput, response time, transmission delay.
Compatibility, i.e. ability to connect various local area network equipment and software.
Safety, reliability, i.e. capabilities to prevent unauthorized access and complete data protection.
Scalability - the ability to increase the number of workstations without degrading network performance.
Manageability - the ability to control the main elements of the network, prevent and eliminate problems.
Network transparency, which consists of presenting a single computing device to users.

Basic local area network topologies: advantages and disadvantages

The topology of a network represents its physical layout, significantly affecting its basic characteristics. In modern enterprises, three types of topologies are mainly used: “Star”, “Bus” and “Ring”.

The “Star” topology is the most common and has many advantages over others. This installation method is highly reliable; If any computer fails (except the server), this will not affect the operation of the others.

The “Bus” topology is a single backbone cable with connected computers. Such an organization of a local area network saves money, but is not suitable for connecting a large number of computers.

The “Ring” topology is characterized by low reliability due to the special arrangement of nodes - each of them is connected to two others using network cards. The failure of one computer leads to the shutdown of the entire network, so this type of topology is used less and less.

Detailed network design

An enterprise local area network also includes various technologies, equipment and cables. Therefore, the next step will be the selection of all these elements. Making a decision in favor of one or another software or hardware is determined by the purpose of creating the network, the number of users, the list of programs used, the size of the network, and its location. Currently, fiber optic highways are most often used, which are distinguished by their high reliability, speed and availability.

About cable types

Cables are used in networks to transmit signals between workstations; each of them has its own characteristics, which must be taken into account when designing a LAN.

A twisted pair consists of several pairs of conductors covered with insulation and twisted together. Low price and ease of installation are beneficial advantages, which makes this cable the most popular for installing local networks.
A coaxial cable consists of two conductors inserted one inside the other. A local area network using coax is no longer so common - it was replaced by twisted pair, but it is still found in some places.
Optical fiber is a glass thread that can carry light by reflecting it off walls. A cable made from this material transmits data over long distances and is fast compared to twisted pair and coaxial cables, but it is not cheap.

Necessary equipment

Network equipment of local area networks includes many elements, the most commonly used of which are:

Hub or hub. It connects a number of devices into one segment using a cable.
Switch. Uses special processors for each port, processing packets separately from other ports, due to which they have high performance.
Router. This is a device that makes decisions about sending packets based on data about routing tables and some rules.
Modem. Widely used in communication systems, providing contact with other workstations via a cable or telephone network.

End network equipment

The local area network hardware necessarily includes server and client parts.

A server is a powerful computer with high network significance. Its functions include storing information, databases, serving users and processing program codes. The servers are located in special rooms with a controlled constant air temperature - server rooms, and their housing is equipped with additional protection from dust, accidental shutdown, as well as a powerful cooling system. As a rule, only system administrators or company managers have access to the server.

A workstation is a regular computer connected to a network, that is, it is any computer that requests services from the main server. To ensure communication at such nodes, a modem and a network card are used. Since workstations usually use server resources, the client part is equipped with weak memory sticks and small hard drives.

Software

Local area network equipment will not be able to fully perform its functions without suitable software. The software part includes:

Network operating systems on servers that form the basis of any network. It is the OS that controls access to all network resources, coordinates packet routing, and resolves device conflicts. Such systems have built-in support for the TCP/IP, NetBEUI, IPX/SPX protocols.
Autonomous operating systems that manage the client side. They are common operating systems, for example, Windows XP, Windows 7.
Network services and applications. These software elements allow you to perform various actions: viewing remote documentation, printing on a network printer, sending email messages. Traditional services HTTP, POP-3, SMTP, FTP and Telnet are the basis of this category and are implemented using software.

Nuances of designing local networks

Designing a local area network requires a long and leisurely analysis, as well as taking into account all the subtleties. It is important to provide for the possibility of enterprise growth, which will entail an increase in the scale of the local network. The project must be drawn up in such a way that the LAN is ready at any time to connect a new workstation or other device, as well as upgrade any of its nodes and components.

Security issues are no less important. The cables used to build the network must be reliably protected from unauthorized access, and the lines must be located away from potentially dangerous places where they can be damaged - accidentally or intentionally. LAN components located outside the premises must be grounded and securely secured.

Developing a local area network is a fairly labor-intensive process, but with the right approach and due responsibility, the LAN will operate reliably and stably, ensuring uninterrupted user experience.

Introduction

The purpose of this course project is to build a local area network. LAN is a computer network that usually covers a relatively small area or a small group of buildings (home, office, company, institute). There are also local networks, the nodes of which are geographically separated over distances of more than 12,500 km (space stations and orbital centers). Despite such distances, such networks are still classified as local.

Computers can connect to each other using various access media: copper conductors (twisted pair), optical conductors (fiber optic cables) and through a radio channel (wireless technologies). Wired connections are established via Ethernet, wireless connections are established via Wi-Fi, Bluetooth, GPRS and other means. A separate local area network may have gateways to other local area networks, and may also be part of or connected to a global area network (such as the Internet).

Most often, local networks are built on Ethernet or Wi-Fi technologies. To build a simple local network, routers, switches, wireless access points, wireless routers, modems and network adapters are used. Less commonly used are media converters, signal amplifiers (various types of repeaters) and special antennas.

In this work, a LAN will be designed using Ethernet technology, with horizontal and vertical cables of the fifth UTP category, capable of transmitting 100 Mbit/s.

1. Technical requirements for LAN

1.1 Network model of Master LLC

user computer network local

At the initial stage of network development, the organization had its own standards for connecting computers together. These standards described the mechanisms needed to move data from one computer to another. However, these early standards were not compatible with each other.

In subsequent years, the International Standards Organization (ISO) and the Institute of Electrical and Electronic Engineers (IEEE) developed models that became generally accepted industry standards for the development of computer networks. Both models describe network technologies in terms of functional layers.

ISO developed a model called the Open System Interconnection (OSI) model. This model is used to describe the flow of data between a user's application and the physical connection to the network.

The OSI model divides communication functions into 7 layers:

· Application layer.

· Presentation level.

· Session level.

· Transport layer.

· Network layer.

· Data link level.

· Physical level.

The concept of the model is that each level provides a service to the next higher level. This allows each layer to communicate with the same layer on another computer. The concept of the seven-level model is depicted in Figure 1.

Figure 1 - ISO OSI seven-layer model

Functional purpose of levels:

The physical layer routes an unstructured stream of data bits through a physical transmission medium (cable).

1. The physical layer acts as a carrier for all signals transmitting data generated by all higher layers. This layer is responsible for the hardware. The physical layer defines the physical, mechanical and electrical characteristics of communication lines (cable type, number of connector connectors, purpose of each connector, etc.). The physical layer describes the network topology and determines the method of data transmission over the cable (electrical, optical).

2. The data link layer packages unstructured data bits from the physical layer into structured packets (data frames).

3. The data link layer is responsible for ensuring error-free transmission of packets. The packets contain a source address and a destination address, allowing the computer to retrieve data intended only for it.

4. The network layer is responsible for addressing messages and translating logical addresses and names into physical link layer addresses. The network layer determines the path (route) for data to pass from the transmitting to the receiving computer. The network layer restructures data packets (frames) of the data link layer (breaks large ones into a set of small ones or combines small ones).

5. The transport layer monitors transmission quality and is responsible for error recognition and correction. Transport layer

6. Guarantees delivery of messages created at the application level.

7. The session layer allows two applications on different computers to establish, use, and terminate a connection called a session. The session layer coordinates communication between two application programs running on different workstations. The session layer ensures task synchronization and implements dialogue control between interacting processes (determines which side transmits, when, for how long, etc.).

8. The presentation layer serves to transform data received from the application layer into a universally recognizable intermediate format. The presentation layer can be called a network translator. The presentation layer allows you to combine different types of computers (IBM PC, Macintosh, DEC, etc.) into a single network, converting their data into a single format. The presentation layer manages network security and encrypts data (if necessary). Provides data compression to reduce the number of bits of data that need to be transmitted.

9. The application layer (application layer) allows application programs to access a network service. The application layer directly supports user applications (file transfer software, database access, email). The Open Systems Interoperability Standard model is considered the best known model and is most often used to describe network environments.

A local area network is the main part of a corporate network that ensures the functioning and interaction of various distributed applications that may be part of an information system (IS). A modern LAN should have the following basic characteristics:

· performance adequate to the requirements of modern ICs;

· scalability;

· fault tolerance;

· support for all major communication standards and protocols;

· compatibility with equipment of adjacent subsystems;

· the ability to change the logical configuration of the LAN without changing the physical one;

· controllability.

When developing a LAN architecture, modern methods, technologies and devices are used to best achieve a balance between the basic requirements for a LAN and the capabilities of the network. The requirements for modern business and the need to support business applications determine a number of parameters, among which the most important are:

· high network availability at a level of at least 99.99%;

· high-speed packet switching;

· quality of user and application service;

· rules-based management;

· integration with directory services.

As a basis for building a LAN, a strategy should be used that allows you to create and maintain network complexes of any scale, integrate newly emerging technologies and standards, maximally preserving the investments already made and ensuring a minimum level of network support costs.

2. Basic network requirements

One of the most important requirements for a modern LAN is to ensure the safety and security of processes occurring on the LAN, since a network open to outside access is vulnerable. The implementation of a management, statistics and identification system in the LAN allows for control and increased security of the LAN.

To manage the network and the ability to prevent undesirable situations in the operation of the LAN, devices throughout the network must have system tools for monitoring quality of service and security policies, network planning and services that provide the ability to:

· collecting statistics to analyze network performance at all levels;

· redirecting traffic of individual ports, groups of ports and virtual ports to a protocol analyzer for detailed analysis;

· real-time event monitoring to expand diagnostic capabilities beyond external analyzers.

· collecting and storing information about significant network events, including changes in device configurations, topology changes, software and hardware errors

LAN must have a system solution that allows the problem to be solved comprehensively, which implies the implementation of identification of network resources and users, protection of information and resources from unauthorized access, and dynamic active control over the network.

The LAN must provide all departments of the enterprise with:

· ability to process texts;

· access to the Internet;

· ability to use email;

· work with databases;

· access to shared printers;

· Possibility of data transfer.

The TCP/IP protocol stack is shown in Figure 2.

Figure 2 - TCP/IP protocol stack

The TCP/IP protocol stack is divided into 4 levels: application, transport, internet and network access. The terms used to designate a block of transmitted data are different when using different transport layer protocols - TCP and UDP, therefore in Fig. 2 shows two stacks.

The relationship between the OSI and TCP/IP stack levels is shown in Figure 3

Figure 3 - Relationship between OSI and TCP/IP stack levels

3. Selection of the necessary material and equipment

Design a local computer network for an organization using Ethernet technology, located in two buildings (Fig.).

Local area network of the organization

The project must meet the following requirements:

1. Each department of the enterprise must have access to the resources of all other departments;

2. Traffic created by employees of one department should not affect the local networks of other departments, except when accessing resources of the local networks of other departments;

3. One file - the service can support no more than 30 users;

4. File servers cannot be shared by multiple departments;

5. All repeaters, bridges and communicators must be located in wiring closets (WS);

6. The distance between computers on a mono channel should not be less than one meter;

7. Switching equipment and file servers must be protected against loss of mains voltage;

8. The designed network must operate stably. In cases of network instability, the project must be reworked;

9. The following cable combinations are allowed: twisted pair and optical fiber;

10. The project must have a minimum cost;

11. Data transfer speed should not be lower than 10 Mbit/s;

12. Type of network technology used - Ethernet;

13. Only the equipment from the table can be used in the project. 1.

Table 1 List of equipment used

Name	Notional value (y.e.)
Thin coaxial cable (per meter)
Unshielded twisted pair (per meter)
Two-core fiber optic cable (per meter)
Network adapter with BNC connector
Network adapter with RJ - 45 connector
Two-port repeater (HUB) with BNC connectors
8-Port BNC Switch
Switch with 6 optical ports
Two-port bridge with any combination of ports for coaxial cables, UTP, and fiber optic cables
Switch with 6 optical ports and 24 ports with RJ - 45 connector
Switch for 8 ports with RJ-45 connector
Switch for 36 ports with RJ - 45 connector
800 VA uninterruptible power supply
File server based on Pentium processor with pre-installed operating system (maximum 30 users)

The company has 4 departments. Of which three are located in building 1, and the fourth, in building two, 300 meters away from the first. Each department is equipped with a personal computer (PC) in the amount of:

In the marketing department - 7 pieces.

In the ACS department - 10 pieces.

In the production department - 42 pcs.

In the design department - 30 pieces.

PC connections within departments will be made using coaxial cable. The first task is to place a PC in each department, i.e. PCs should not be located in a random order or crowded together, but at an acceptable distance from each other. Figure 8 shows the PC placement diagrams, with the indicated distances between them.

To optimize operation, the entire local network (LAN) is divided into segments. Each department has its own segment. All segments will be connected to the head switch. We select from table 1 switch with 8 optical ports with a BNC connector, which will be the head one. The switch is protected from mains voltage drop by an 800 VA uninterruptible power supply. This switch will automatically detect the speed of each segment and maintain it. This will allow you to obtain the required data transfer speed, not lower than 10 Mbit/s. The head switch is located in the WS3 wiring closet of the production department.

Marketing department.

The department has 7 PCs and a WC1 switching cabinet. For stable operation of the network, we divide the department into 2 segments of 3 and 4 PCs. The distance between the last PC in the first segment and the head switch for the segment, which allows it to be used as a single unit, because the length of the segment will not exceed 185 meters.

The WC1 wiring closet contains the department's file server (a file server based on a Pentium processor with a pre-installed operating system), an uninterruptible power supply, and an 8-port switch with BNC connectors. All PCs and file servers are equipped with network adapters with BNC connectors and are connected to each other by a thin coaxial cable using BNC T-connectors.

Communication between computers and file server

A “plug” - a terminator (Figure) is inserted into the free connector of the last T-connector. To ensure that the thin coaxial cable is not under tension, we leave a margin of one meter between computers in each section.

Terminator

ACS department.

The department contains 10 computers and a WC2 switching cabinet. The WC2 cabinet contains a switch and an uninterruptible power supply, which is connected to the file server. A file server based on a Pentium processor with a pre-installed operating system is located directly in the department. All PCs and file servers are equipped with network adapters with BNC connectors. Personal computers and the file server are connected to each other by a thin coaxial cable using BNC T-connectors. A “plug” - a terminator - is inserted into the free connector of the last T-connector. For more stable operation, the LS2 segment was divided into 2 segments of 5 PCs each. The switch is connected to the head switch in cabinet WC3 in the production department. To ensure that the thin coaxial cable is not under tension, we leave a margin of one meter between computers in each section. The length of the LS2-a segment from the last PC to the head switch and taking into account the cable reserve between the PCs is, for the LS2-b segment, which does not exceed the permissible 185 meters.

Production Department.

The department has 42 computers and a WC3 wiring closet. Due to the large number of computers, it is advisable to separate them. Thus, we get 7 segments LS3-a, LS3-b, LS3-c, etc., each of which has 6 PCs. The segments are interconnected by 8-port switches with BNC connectors (3 pcs.). Using a switch allows you to bypass the “5-4-3” rule without loss of speed; in addition, using a switch provides greater protection against collisions than following the above-mentioned rule. This department will use two file servers.

The wiring closet of the WC3 department will contain an uninterruptible power supply, which is connected to the file server; switches of a given department connecting individual segments; the head switch of the entire network.

All PCs and file servers are equipped with network adapters with BNC connectors and are connected to each other by a thin coaxial cable using BNC T-connectors. To ensure that the thin coaxial cable is not under tension, we leave a margin of one meter between computers in each section. A “plug” - a terminator - is inserted into the free connector of the last T-connector.

The total length of the LS3 segment from the last PC to the switch is. The total length of the LS3-b segment from the last PC to the switch is. The total length of the LS3-in segment from the last PC to the switch is. The total length of the LS3-g segment from the last PC to the switch is. The total length of the LS3-d segment from the last PC to the switch is. The total length of the LS3 segment from the last PC to the switch is. The total length of the LS3-zh segment from the last PC to the switch is. The length of none of the segments exceeds the permissible length of 185 m.

Project department

The department has 30 PCs and a WC4 switching cabinet. For more stable operation, the S4 segment was divided into 5 segments. In the wiring closet we install an uninterruptible power supply that protects the file servers from a drop in network voltage, and an 8-port switch with BNC connectors that connects the segments. All PCs and file servers are equipped with network adapters with BNC connectors and are connected to each other by a thin coaxial cable using BNC T-connectors. A “plug” - a terminator - is inserted into the free connector of the last T-connector. To ensure that the thin coaxial cable is not under tension, we leave a margin of one meter between computers in each section. The length of the LS4 segment from the last PC to the WC4 switching cabinet is. The length of the LS4-b segment from the last PC to the WC4 wiring closet is. The length of the LS4-in segment from the last PC to the WC4 wiring closet is. The length of the LS4-g segment from the last PC to the WC4 wiring closet is. The length of the LS4-d segment from the last PC to the WC4 wiring closet is. The length of none of the segments exceeds the permissible length of 185 m.

Connecting departments with each other

Building 2 is 300 meters away from building 1. The buildings are connected to each other by a pipeline. In order to connect the WC4 segment with the head switch, we lay a two-core fiber optic cable in the pipeline (Table 1). The cable length is 320 meters. On each side we leave a reserve of 10 meters, two of which are required for cutting the cable, the remaining eight are laid in rings in the cabinet due to technological requirements. In order to move from one data transmission medium to another, we select from Table 1 a two-port bridge with a combination of ports “coaxial cable - fiber optic cable”, which is installed in the WC4 cabinet, and “fiber optic cable - coaxial cable”, which is installed in the WC3 cabinet. Both bridges are protected from voltage drop by an uninterruptible power supply. The fiber-optic cable - coaxial cable bridge in the WC3 cabinet is in turn connected using a thin coaxial cable directly to the head switch.

Thus, we have obtained a network connecting two buildings, which has a minimum cost, but at the same time there is no broadcast traffic and the data transfer speed reaches at least 10 Mbit/s. Figures 8 and 9 show, respectively, the layout of personal computers that are part of the local computer network and the connection diagram of personal computers with a diagram of cable laying and the lengths of cable segments.

WS1: File - department server

Marketing department switch for 8 ports with BNC connectors.

WS2: File - department server

Uninterruptable power source;

ACS department switch for 8 ports with BNC connectors.

WS3: 2 uninterruptible power supplies;

2 file - department servers;

2 switches for 8 ports with BNC connectors;

Head switch for 8 ports with BNC connectors;

Double-port bridge "coaxial cable - optical fiber".

WS4: File - department server

Uninterruptable power source;

Project department switch for 8 ports with BNC connectors;

Bridge "coaxial cable - fiber optic cable"

Figure 12 shows a diagram of the placement of equipment in cable cabinets and the switching lines of this equipment.

In order for the network to operate stably, that is, there is no distortion of the transmitted information or its loss, the following conditions must be met:

1. The length of the segment should not exceed the permissible value:

thin coaxial - 185 m;

optics - 2000 m (we have a maximum of 320 m).

2. The total length of the network should not exceed 2.5 km.

3. The number of computers on the network should not exceed 90. (we have 89 computers + 5 departmental file servers).

4. One file server can support no more than 30 users (we have a maximum of 30 users).

5. File servers cannot be shared among multiple departments.

6. All repeaters, bridges and switches must be located in wiring closets.

7. The “5-4-3” rule must be followed (fulfilled).

There is no exceeding of the required parameters. Therefore, there is no need to perform robustness checks using PDV (double interval time - should not exceed 575 bit intervals) and PVV (inter-frame interval reduction should not exceed 49 bit intervals). Compliance with these requirements ensures stable operation of the network even in cases where the above conditions are violated. This check will be performed to fully ensure that the network is operational.

To simplify calculations, IEEE reference data is used that contains data on signal propagation delays in repeaters, transceivers, and various physical environments.

Table 4 Data for calculating PDV

To calculate stability, draw a section with the most distant stations.

The left segment is the segment from which the signal begins.

The right segment is the segment where the signal arrives.

Intermediate segment - a segment between the left and right segments.

The calculation must be carried out twice, when the signal propagates in both directions, because the result may be different in the case of an asymmetric network. If PDV fails in at least one case, the network will lose frames due to missed collisions.

We will carry out the calculation for the two computers most distant from each other from the marketing department and from the design department. A schematic representation is shown in Figure 13.

Let's calculate network stability using PDV and PVV

4. Economic calculation of the project

The practical use of LAN models in many cases presupposes the availability of information about the real characteristics of the computing process. Such information can be obtained by empirical methods, on the basis of which tools are currently being created for studying the hardware and software components of a LAN. The necessary information is collected using special means,

which provide measurement of parameters characterizing the dynamics of LAN functioning in test and normal operation modes. Such tools include network analyzers, protocol analyzers, etc. The creation of tools for measuring LAN operating parameters, including LAN operating systems, is one of the new tasks in computing. Experimental methods make it possible to create a basis for quantitative assessment of the effectiveness of LANs to achieve the following practical goals: analysis of existing LANs, selection of the best one and synthesis of a new LANs. Assessing the characteristics of hardware and software involves conducting experiments and measurements, which from a practical point of view can be considered as a process of obtaining useful information. Measurement data is presented in a form suitable for subsequent analysis. This is done with the help of special processing tools, the creation of which is associated with the development of analyzers. This relationship concerns, for example, the choice of uniform data formats that are convenient not only for measurements, but also for processing their results. In general, the measurement stage precedes the processing stage, and processing tools must be designed for effective application to large amounts of information, since measurements on a LAN are typically characterized by large volumes and high density of recorded data. At the final stage of experimental research, an analysis of the measurement results is carried out, which consists of obtaining meaningful conclusions about the LAN under study. An important condition for the formation of such conclusions is the successful presentation of measurement results. The effectiveness of experimental methods largely depends on the quality of experimental design and the correct choice of load type. An experiment consists of a set of tests performed during research, and a test in turn consists of a number of sessions or “runs.” The term "session" is more often used for measurements, and "run" is usually used for simulation. Over the course of a session or run, information about system behavior and possibly workload is accumulated. As the workload varies, the number of observations required for each quantity of interest must be such that the distributions for those quantities and their moments can be estimated with the required accuracy. Thus, the duration of the session depends on the required number of observations.

A single session experiment is sufficient to evaluate, if necessary, consider only one system configuration and one type of workload. For example, if measurements are made to determine whether a given LAN provides satisfactory performance for a given workload (traffic), i.e. does it meet certain requirements? Experiments lasting several sessions are necessary if the influence of certain factors on system performance is to be determined or if the system is being optimized in successive iterations.

5. Configuring network equipment and end users

Setting up equipment is the most difficult stage in network installation. The more complex the network, the more heterogeneous technically complex equipment is used in it, the more in-depth knowledge and experience is required from the engineer to configure this equipment. The final configuration and debugging of equipment to meet the customer’s goals sometimes takes much longer than installation. The performance of the future network depends on optimizing a large number of parameters for each network device. This means that the productivity of the company’s personnel depends on this.

Equipment setup may include, at the customer’s request, the following steps and work:

1. setting up switches, routers and firewalls. Setup usually includes dividing the network into virtual local networks, developing and configuring routing rules, ensuring quality of service, ensuring security, ensuring encryption of critical data, and organizing remote secure access to corporate network data. The list of configurable equipment includes active devices of the network environment, such as multiplexers, switches, routers, firewalls, service servers (DNS, DHCP, HTTP, MAIL), and very often backbone copper and optical multiplexers.

2. Currently, with the development of wireless technologies, not a single corporate data network can do without a WI-FI network. Therefore, wireless access points are also included in the configuration. Organizing a convenient, scalable network managed from a single point requires knowledge of modern technologies. A properly configured network provides high reliability, centralized management, as well as additional services such as authorization, handover, and others.

3. In addition to network equipment, network printers, multifunctional printing devices, and copiers also require configuration. Currently, they are stand-alone network devices and, like computer equipment, require professional configuration. It is better to entrust the input of settings to specialists, because... Unprofessional handling of high-tech equipment can damage it. In addition, unauthorized installations are not welcomed by manufacturers, and setting up and installing equipment yourself, without involving an authorized service center, risks losing the warranty on expensive equipment.

4. Data transmission technologies are improving, and today the list of equipment often used by corporate customers traditionally includes video conferencing systems. Correct configuration of the system allows you to obtain high-quality images, save on bandwidth, and fully use all the functionality of the system for the end user. The video conferencing system includes not only video conference servers, but also end terminal devices - IP video phones, video terminals, collective video communication systems. Correct configuration of the entire class of devices, together with the central system, will ensure the implementation of high-quality services for the user.

A modern broadband wireless router is a multifunctional device that combines:

· router;

· Fast Ethernet network switch (10/100 Mbit/s);

· wireless access point;

· firewall;

· NAT device.

The main task assigned to wireless routers is to unite all computers on a home network into a single local network with the ability to exchange data between them and organize a high-speed, secure connection to the Internet for all home computers.

Using a wireless router to connect

Currently, the most popular methods are connecting to the Internet via a telephone line using an ADSL modem and via a dedicated Ethernet line. Based on this, all wireless routers can be divided into two types:

· for connection via a dedicated Ethernet line;

· for connection via telephone line.

In the latter case, the router also has an ADSL modem built into it.

According to statistics, the method of connecting via a dedicated Ethernet line is becoming increasingly popular among providers. At the same time, routers designed for this can also be used to connect to the Internet via a telephone line, but for this you will have to additionally purchase an ADSL modem.

In what follows, we will only consider routers designed to connect to the Internet via a dedicated Ethernet line.

So, routers are network devices installed on the border of the internal local home network and the Internet, and therefore acting as a network gateway. From a design point of view, routers must have at least two ports, one of which is connected to the local network (this port is called the internal LAN port), and the second is connected to the external network, that is, the Internet (this port is called the external WAN port). Home routers have one WAN port and four internal LAN ports, which are combined into a switch (Fig. 2). Both WAN and LAN ports have a 10/100Base-TX interface, and you can connect an Ethernet network cable to them.

LAN and WAN - router ports

The wireless access point integrated into the router allows you to organize a wireless network segment, which for the router belongs to the internal network. In this sense, computers connected to the router wirelessly are no different from those connected to the LAN port.

The purpose of the firewall integrated into the router is to ensure the security of the internal network. To do this, firewalls must be able to mask the protected network, block known types of hacker attacks and information leakage from the internal network, and control applications that access the external network.

In order to implement these functions, firewalls analyze all traffic between external and internal networks for compliance with certain established criteria or rules that determine the conditions for the passage of traffic from one network to another. If the traffic meets the specified criteria, the firewall allows it to pass through. Otherwise, that is, if the established criteria are not met, the traffic is blocked. Firewalls filter both incoming and outgoing traffic and also allow you to control access to certain network resources or applications.

By their purpose, firewalls resemble a checkpoint of a protected facility, where the documents of everyone entering the territory of the facility and everyone leaving it are checked. If the pass is in order, access to the territory is allowed. Firewalls operate similarly, only the role of people passing through the checkpoint is network packets, and the pass is the compliance of the headers of these packets with a given set of rules.

All modern routers with built-in firewalls are NAT devices, that is, they support the NAT (Network Address Translation) protocol. This protocol is not part of a firewall, but helps improve network security. Its main task is to solve the problem of the shortage of IP addresses, which is becoming more and more urgent as the number of computers grows.

The NAT protocol defines how network address translation occurs. A NAT device converts IP addresses reserved for private use on local networks into public IP addresses. Private addresses include the following IP ranges: 10.0.0.0-10.255.255.255, 172.16.0.0-172.31.255.255, 192.168.0.0-192.168.255.255. Private IP addresses cannot be used on the World Wide Web, so they can be freely used for internal purposes only.

In addition to the listed functionality, some models of wireless routers have a number of additional ones. For example, they can be equipped with USB 2.0 ports, to which you can connect external devices with the ability to organize shared network access to them. So, when connecting to a printer router via the USB 2.0 interface, we also get a print server, and when connecting an external hard drive, we get a NAS (Network Attached Storage) type network storage device. In addition, in the latter case, the software used in the routers even allows you to organize an FTP server.

There are router models that have not only USB ports, but also a built-in hard drive, and therefore can be used for network data storage, as FTP servers for access both from outside and from the internal network, and even serve as multimedia centers.

Despite the apparent similarity in functionality of broadband wireless routers, there are significant differences between them, which ultimately determine whether a particular router is suitable for your purposes or not. The fact is that different Internet providers use different types of Internet connections. If we are talking about connecting one computer (without using a router), then there are no problems, since user operating systems (for example, Windows XP/Vista) contain software that supports all connection types used by providers. If you use a router to connect your home network to the Internet, then it is necessary that it fully supports the connection type used by the provider (we will look at connection types in the section on setting up the WAN interface).

Almost all routers aimed at home users have built-in quick setup software (setup wizards) or auto-configuration tools - for example, Quick Setup, Smart Setup, NetFriend, etc. However, you need to keep in mind that there may always be a provider that does not will support the automatic configuration function of a specific router. In addition, the presence of such functions does not mean that by pressing one “magic” button you will immediately cope with all problems and configure your router. After all, even in order to get to this “magic” button, you will have to make some network interface settings on your computer.

For the reasons stated above, we will not rely on the automatic configuration capabilities of the router and will consider the most universal way to manually configure it step by step.

It is advisable to configure the router in the following sequence:

· Gaining access to the router’s web interface.

· Configuring the LAN interface and built-in DHCP server.

· Configuring a WAN interface with organizing an Internet connection for all computers on the local network.

· Setting up a wireless network (if there are wireless clients).

· Setting up a firewall.

· Configuring the NAT protocol (if required).

The first step in setting up the router is to gain network access to its settings via the web interface (all routers have a built-in web server).

Let's take a closer look at the steps of setting up the LAN interface and the built-in DHCP server, as well as setting up the WAN interface. We will not talk about setting up a wireless network, firewall and NAT protocol in this article - separate publications will be devoted to these issues.

Gaining access to the web- Androuter interface

To access the router's web interface, you must connect a computer (laptop) to the LAN port. The first thing you need to find out is the IP address of the router’s LAN port, the default login and password. Any router, being a network device, has its own network address (IP address). In order to find out the IP address of the router's LAN port and password, you will have to look through the user manual.

If the router has not been used before, its settings coincide with the default (factory) settings. In most cases, the IP address of the router's LAN port is 192.168.1.254 or 192.168.1.1 with a subnet mask of 255.255.255.0, and the password and login are admin. If the router has already been in use and its default settings have been changed, but you do not know the IP address of the LAN port, or the login and password, then the first thing you will have to do is reset all settings (return to factory settings). To do this, all routers have a special recessed reset button. If you press it (with the router's power on) and hold it for a few seconds, the router will reboot and restore its factory settings.

In addition to the ability to quickly return to factory settings, most routers have a built-in DHCP server that is activated by default. This allows you to easily connect to the router, since a computer connected to the router's LAN port will automatically be assigned an IP address of the same subnet as the router's LAN port itself, and the IP address of the default gateway will be used. router LAN port address. But in order to take advantage of this opportunity, you need to make sure that the dynamic assignment of an IP address (Obtain IP address automatically) function is set in the properties of the network connection of the computer used to connect to the LAN port of the router. It is activated by default for all network interfaces, and if, after installing the operating system, network connections on the computer were not specially configured, then most likely you will be able to access the router settings immediately after connecting to its LAN port on the computer.

If you cannot connect to the router in this way, you will have to first configure the network interface of the computer connected to the router. The point of the setup is that the network interface of the computer that connects to the LAN port of the router and the LAN port of the router have IP addresses belonging to the same subnet. Let's assume the router's LAN port has an IP address of 192.168.1.1. Then the network interface of the connected computer must be assigned a static IP address 192.168.1.x (for example, 192.168.1.100) with a subnet mask of 255.255.255.0. In addition, you must specify the IP address of the router's LAN port (in our case, 192.168.1.1) as the default gateway IP address.

Setting up your computer's network interface depends on the operating system you are using.

Conclusion

This work examined the main components of a LAN, as well as the process of data transmission in the network at all levels (logical and hardware). A local computer network of a trading enterprise was modeled taking into account the requirements for the future structure. Based on the size of the room, the cable length connecting all network components was found and optimized as much as possible.

Today, the development and implementation of LAN is one of the most interesting and important tasks in the field of information technology. The need to control information in real time is increasingly increasing, and the traffic of networks at all levels is constantly growing. In this regard, new technologies for transmitting information to a LAN are emerging.

For example, among the latest discoveries, it should be noted the possibility of transmitting data using conventional power lines, and this method allows increasing not only the speed, but also the reliability of transmission.

Network technologies are developing very quickly, and therefore they are beginning to become a separate information industry. Scientists predict that the next achievement of this industry will be the complete displacement of other means of information transmission (television, radio, print, telephone, etc.). These “outdated” technologies will be replaced by a computer, it will be connected to some kind of global information flow, perhaps even the Internet, and from this flow it will be possible to obtain any information in any presentation.

Bibliography

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2. McCullough D., “Secrets of wireless technologies” / - M.: NT-Press, 2010.

3. Maufer T., “WLAN: a practical guide for administrators and professional users” / - M.: KUDITS-Obraz, 2011.

4. Novikov Yu.V., Kondratenko S.V. Basics of local networks. Lecture course. - M.: Internet University of Information Technologies, 2010.

5. Kuznetsov M.A., “Modern technologies and standards of mobile communications” - St. Petersburg: Link, 2006.

6. Kuznetsov M.A., “Modern technologies and standards of mobile communications” / Ryzhkov A.E. - St. Petersburg: Link, 2009.

7. McCullough D., “Secrets of wireless technologies” / - M.: NT-Press, 2010.

8. Maufer T., “WLAN: a practical guide for administrators and professional users” / - M.: KUDITS-Obraz, 2011.

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13. Pejman R., “Basics of building wireless local networks of the 802.11 standard. A Practical Guide to Understanding, Designing, and Using 802.11 Wireless LANs by Jonathan Leary. - M.: Cisco Press Translation from English Williams Publishing House, 2009.

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1. INTRODUCTION

The purpose of undergoing practical training in the specialty profile was to consolidate, deepen and systematize knowledge based on the activities of the company RadioZavod OJSC in the direction of “Management in Technical Systems”. During the internship period, the student’s theoretical and practical training plan was completed in full.

During the period from July 1 to July 29, I reviewed and studied the following: principles of building local computer networks; structure and operation of LAN; studying network protocols; basics of administration.

2. LOCAL COMPUTER NETWORKS

2.1 Local network topologies

LAN (English LAN - Local Area Network) is understood as the joint connection of several separate computer workstations (workstations) to a single data transmission channel.

The topology of a computer network is understood as the configuration of a graph, the vertices of which correspond to computers on the network, and the edges correspond to physical connections between them. Computers connected to a network are often called stations or network nodes. Logical connections are data transmission routes between network nodes and are formed by appropriately configuring communication equipment.

The choice of electrical connection topology significantly affects many network characteristics. For example, the presence of redundant links increases network reliability and makes it possible to balance the load on individual links. The ease of connecting new nodes, inherent in some topologies, makes the network easily expandable. Economic considerations often lead to the selection of topologies characterized by the minimum total length of communication lines.

A fully connected topology (Figure 2.1, a) corresponds to a network in which each computer on the network is connected to all the others. Despite its logical simplicity, this option turns out to be cumbersome and ineffective. Indeed, each computer on the network must have a large number of communication ports, sufficient to communicate with each of the other computers on the network. A separate electrical communication line must be allocated for each pair of computers. Fully connected topologies are rarely used.

A cellular topology is obtained from a fully connected one by removing some possible connections (Figure 2.1, b). In a network with a mesh topology, only those computers between which intensive data exchange occurs are directly connected, and for data exchange between computers that are not directly connected, transit transmissions through intermediate nodes are used.

The common bus (Figure 2.1, c) is a very common topology for local networks. In this case, computers are connected to a single coaxial cable. The transmitted information can be distributed in both directions. The use of a common bus reduces wiring costs, unifies the connection of various modules, and provides the possibility of almost instantaneous broadcast access to all network stations. Thus, the main advantages of such a scheme are the low cost and ease of cable distribution throughout the premises. The most serious disadvantage of a common bus is its low reliability: any defect in the cable or connectors completely paralyzes the entire network. Another disadvantage of the shared bus is its low performance, since with this connection method only one computer at a time can transmit data to the network. Therefore, the communication channel bandwidth is always divided here between all network nodes.

Star topology (Figure 2.1, d). In this case, each computer is connected by a separate cable to a common device, called a hub, which is located at the center of the network. The function of a hub is to direct information transmitted by a computer to one or all other computers on the network. The main advantage of this topology is that any troubles with the cable affect only the computer to which this cable is connected, and only a malfunction of the hub can bring down the entire network. The disadvantages of a star topology include the higher cost of network equipment. In addition, the ability to increase the number of nodes in the network is limited by the number of hub ports. Sometimes it makes sense to build a network using several hubs, hierarchically connected to each other by star-type connections (Figure 2.1, e).

In networks with a ring configuration (Figure 2.1, e), data is transmitted along the ring from one computer to another, usually in one direction. If the computer recognizes the data as “its own,” then it copies it to its internal buffer. In a network with a ring topology, it is necessary to take special measures so that in the event of a failure or disconnection of any station, the communication channel between the remaining stations is not interrupted. The ring is a very convenient configuration for organizing feedback - the data, having made a full revolution, returns to the source node. Therefore, this node can control the process of delivering data to the recipient. Often this ring property is used to test network connectivity and find a node that is not working correctly.

Figure 2.1 Typical network topologies

2.2 Data transmission medium

A communication line (Figure 2.2) generally consists of a physical medium through which electrical information signals, data transmission equipment and intermediate equipment are transmitted.

Figure 2.2 Communication line composition

Physical environment data transmission can be a cable, that is, a set of wires, insulating and protective sheaths and connecting connectors, as well as the earth's atmosphere or outer space through which electromagnetic waves propagate. Depending on the data transmission medium, communication lines are divided into:

Wired (overhead) communication lines are wires without any insulating or shielding braiding, laid between poles and hanging in the air. Such communication lines traditionally carry telephone or telegraph signals, but in the absence of other options, these lines are also used to transmit computer data.

Cable lines are a rather complex structure. The cable consists of conductors enclosed in several layers of insulation: electrical, electromagnetic, mechanical. In addition, the cable can be equipped with connectors that allow you to quickly connect various equipment to it. There are three main types of cable used in computer networks: twisted pair copper cables, copper coaxial cables, and fiber optic cables.

Radio channels for terrestrial and satellite communications are formed using a radio wave transmitter and receiver. There are a large number of different types of radio channels, differing both in the frequency range used and in the channel range.

The main characteristics of communication lines include:

· amplitude-frequency response;

· bandwidth;

· attenuation;

· noise immunity;

· crosstalk at the near end of the line;

· throughput;

· reliability of data transmission;

· unit cost.

Factors affecting the physical performance of the network:

1) Serviceability of computers connected to the network.

2) Serviceability of network equipment (adapters, transceivers, connectors, etc.).

3) Integrity of the network cable.

4) Limitation of cable length associated with the attenuation of the signal propagating along it.

2.3 Types of local networks

There are several types of computer networks:

· Global networks,

· Regional networks,

· City networks.

Based on the speed of information transfer, computer networks are divided into:

· low-speed (up to 10 Mbit/s),

· medium-speed (up to 100 Mbit/s),

· high-speed (over 100 Mbit/s);

The term baud is widely used to define the speed of data transfer on a network. Baud is a unit of signal transmission rate measured by the number of discrete transitions or events per second. If each event represents one bit, baud is equivalent to bps.

From the point of view of organizing the interaction of computers, networks are divided into peer-to-peer (Peer-to-Peer Network) and with a dedicated server (Dedicated Server Network).

Peer-to-peer networks. All computers in a peer-to-peer network have equal rights. Any network user can access data stored on any computer. The advantage of peer-to-peer networks is that there is no need to copy all the files used by several users at once to the server. In principle, any network user has the ability to use all data stored on other computers on the network and devices connected to them. The main disadvantage of a peer-to-peer network is the significant increase in the time it takes to solve applied problems. This is due to the fact that each computer on the network processes all requests coming to it from other users.

In a network with a dedicated server, one of the computers performs the functions of storing data intended for use by all workstations, managing interaction between workstations, and a number of service functions. Interaction between workstations on a network is usually carried out through a server. The logical organization of such a network can be represented by a star topology. The role of the central device is performed by the server. Advantages of a network with a dedicated server: reliable information security system; high performance; no restrictions on the number of workstations; Ease of Management. Disadvantages of the network: high cost due to the allocation of one computer for the server; dependence of network speed and reliability on the server; less flexibility compared to a peer-to-peer network.

Modem connection. The most common and well-known method of connecting to the Internet in Russia is modem communication using a telephone line.

A modem is connected to the computer - a device for receiving and transmitting data, which is connected to a regular telephone line. When it is necessary to establish a connection, a modem is used to dial a telephone number, which is answered by another modem installed at the Internet provider. A connection is established between the modems and data is transferred.

The main advantage of modem communication is its prevalence and low price. If a high-quality telephone line is available, modem communication is also available - there is no need to organize a special channel. The initial cost of connecting to a modem provider is low. However, modem communication also has major disadvantages, a significant part of which is associated with the deplorable state of the bulk of Russian telephone lines. A well-known problem with modem communication is low speed. Theoretically, modern modems are capable of transmitting data at speeds of up to 56 Kbps from the provider to the user and up to 40 Kbps from the user to the provider.

TechnologyEthernet

Ethernet is the most widespread local network standard today. When people say Ethernet, they usually mean any of the variants of this technology. In a narrower sense, Ethernet is a network standard based on the experimental Ethernet Network.

Ethernet standards define wire connections and electrical signals at the physical layer, frame formats and media access control protocols at the data link layer of the OSI model.

Depending on the type of physical medium, the IEEE 802.3 standard has various modifications - l0Base-5, l0Base-2, l0Base-T, l0Base-FL, l0Base-FB.

Ethernet networks use a medium access method called carrier-sense-multiply-access with collision detection (CSMA/CD).

This method is used exclusively in networks with a logical common bus. All computers on such a network have direct access to a common bus, so it can be used to transfer data between any two network nodes. At the same time, all computers on the network have the opportunity to immediately (taking into account the delay in signal propagation through the physical medium) receive data that any of the computers has begun to transmit to the common bus.

All data transmitted over the network is placed in frames of a certain structure and provided with a unique address of the destination station. The frame is then transmitted over the cable. All stations connected to the cable can recognize the fact of frame transmission, and the station that recognizes its own address in the frame headers writes its contents to its internal buffer, processes the received data and sends a response frame along the cable. The source station's address is also included in the original frame, so the destination station knows who to send the response to.

With the described approach, it is possible that two stations simultaneously try to transmit a data frame over a common cable. To reduce the likelihood of this situation, immediately before sending a frame, the transmitting station analyzes the occurrence of electrical signals on it to detect whether a data frame from another station is already being transmitted along the cable. If a carrier-sense (CS) is recognized, then the station delays transmitting its frame until the end of someone else's transmission, and only then tries to transmit it again.

To correctly handle a collision, all stations simultaneously monitor the signals appearing on the cable. If the transmitted and observed signals differ, then collision detection (CD) is detected.

Token Ring is a local area network (LAN) ring technology with “token access”.

Token Ring technology is a more complex technology than Ethernet. It has fault tolerance properties. The Token Ring network defines network operation control procedures that use feedback of a ring-shaped structure - the sent frame always returns to the sending station. In some cases, detected errors in the network operation are eliminated automatically, for example, a lost token can be restored.

In the Token Ring network, a ring is formed by sections of cable connecting neighboring stations. Thus, each station is connected to its predecessor and successor station and can only communicate directly with them. To provide stations with access to the physical environment, a frame of a special format and purpose - a token - circulates around the ring.

Having received the marker, the station analyzes it and, if it does not have data to transmit, ensures its advancement to the next station. A station that has data to transmit, upon receiving the token, removes it from the ring, which gives it the right to access the physical medium and transmit its data. This station then sends a data frame of the established format into the ring bit by bit. The transmitted data always passes along the ring in one direction from one station to another. The frame is provided with a destination address and a source address.

All stations on the ring relay the frame bit by bit, like repeaters. If the frame passes through the destination station, then, having recognized its address, this station copies the frame to its internal buffer and inserts an acknowledgment sign into the frame. The station that issued the data frame to the ring, upon receiving it back with confirmation of receipt, removes this frame from the ring and transmits a new token to the network to enable other network stations to transmit data.

2.4 High-speed fiber optic networks

Because fiber optic cable uses light (photons) instead of electricity, almost all of the problems inherent in copper cable, such as electromagnetic interference, crosstalk (crosstalk) and the need for grounding, are completely eliminated. It also provides increased secrecy of transmitted data compared to copper, since it does not emit electromagnetic radiation, and it is almost impossible to connect to it without destroying the integrity.

The disadvantages of optical fiber are mainly related to its installation and operating costs, which are usually much higher than for copper data transmission media.

Today, fiber is positioned as a high-speed networking technology, and virtually all link-layer protocols in use use it in one form or another. Here are some of them:

Fast Ethernet (100BaseFX);

Gigabit Ethernet (1000BaseFX);

Fiber Distributed Data Interface (FDDI);

Asynchronous Transfer Mode;

This method provides the highest speeds to date, which provides a good reason for the development of data transmission technologies over optical fiber. Bandwidth can reach the order of Terabits (1000 gigabits) per second. When compared with other methods of information transmission, the order of magnitude Tbit/s is simply unattainable.

2.5 Wireless network technologies

Wireless technologies are a subclass of information technologies that serve to transmit information over a distance between two or more points without requiring them to be connected by wires. Infrared radiation, radio waves, optical or laser radiation can be used to transmit information.

Currently, there are many wireless technologies, most often known to users by their marketing names, such as Wi-Fi, WiMAX, Bluetooth. Each technology has certain characteristics that determine its scope of application.

WiFi. Typically, a Wi-Fi network diagram contains at least one access point and at least one client. It is also possible to connect two clients in point-to-point mode, when the access point is not used, and the clients are connected via network adapters “directly”. The access point transmits its network identifier (SSID) using special signaling packets at a speed of 0.1 Mbit/s every 100 ms. Therefore, 0.1 Mbit/s is the lowest data transfer speed for Wi-Fi. Knowing the network's SSID, the client can determine whether a connection to a given access point is possible. When two access points with identical SSIDs are within range, the receiver can choose between them based on signal strength data.

WiMAX is a telecommunications technology designed to provide universal wireless communications over long distances to a wide range of devices.

In general, WiMAX networks consist of the following main parts: base and subscriber stations, as well as equipment connecting the base stations with each other, with the service provider and with the Internet.

To connect the base station to the subscriber station, a high-frequency radio wave range from 1.5 to 11 GHz is used. Under ideal conditions, data exchange rates can reach 70 Mbit/s without requiring line-of-sight between the base station and the receiver. Line-of-sight connections are established between base stations using the frequency range from 10 to 66 GHz, data exchange speeds can reach 140 Mbit/s. In this case, at least one base station is connected to the provider's network using classic wired connections.

Bluetooth is a low-power radio technology designed to replace existing cable connections between office and home appliances and a wide range of portable devices (mobile phones, digital cameras, record players, etc.).

The technology uses small, short-range transceivers, either directly built into the device or connected through a free port or PC card. Adapters operate within a radius of up to 10 m.

Devices using the Bluetooth standard operate in the 2.4 GHz ISM (Industrial, Scientific, Medical - industrial, scientific and medical band) band and are capable of transmitting data at speeds up to 720 Kbps. Such performance is achieved using a transmission power of 1 MW and using a frequency switching mechanism to prevent interference.

3. NETWORK PROTOCOLS

3.1 MAC addresses

A MAC address (Media Access Control) is a unique identifier assigned to each piece of computer network equipment.

On broadcast networks (such as Ethernet-based networks), the MAC address allows each node on the network to be uniquely identified and data can be delivered only to that node. Thus, MAC addresses form the basis of networks at the data link layer, which is used by higher-layer protocols. To convert MAC addresses to network layer addresses and vice versa, special protocols are used (for example, ARP and RARP in TCP/IP networks).

MAC address structure

· The first bit of the destination MAC address is called the I/G (broadcast) bit. In the source address it is called the Source Route Indicator.

The second bit determines how the address is assigned

· The three most significant bytes of the address are called the Burned In Address (BIA) or Organizationally Unique Identifier (OUI)

· The manufacturer himself is responsible for the uniqueness of the lower three bytes of the address.

Figure 3.1 MAC Address Structure

3.2 OSI model

Just because a protocol is an agreement adopted by two interacting entities, in this case two computers operating on a network, does not mean that it is necessarily standard. But in practice, when implementing networks, standard protocols are usually used. These may be proprietary, national or international standards.

In the early 80s, a number of international standardization organizations - ISO, ITU-T and some others - developed a model that played a significant role in the development of networks. This model is called the ISO/OSI model.

The Open System Interconnection (OSI) model defines the different layers of interconnection between systems in packet-switched networks, gives them standard names, and specifies what functions each layer should perform.

In the OSI model (Figure 3.2), communication means are divided into seven layers: application, presentation, session, transport, network, link and physical. Each layer deals with a specific aspect of network device interaction.

Figure 3.2 OSI Model

The physical layer receives data packets from the upper link layer and converts them into optical or electrical signals corresponding to 0 and 1 of the binary stream. These signals are sent through the transmission medium to the receiving node. The mechanical and electrical/optical properties of the transmission medium are determined at the physical layer and include: the type of cables and connectors, the pinout of the connectors, the signal coding scheme for the values 0 and 1.

Physical layer protocols: IRDA, USB, EIA RS-232, RS-485, Ethernet (including 10BASE-T, 10BASE2, 10BASE5, 100BASE-TX, 100BASE-FX, 100BASE-T, 1000BASE-T, 1000BASE-SX and others) , 802.11Wi-Fi, DSL, ISDN, IEEE 802.15, Firewire.

The data link layer ensures the transmission of data packets coming from upper-layer protocols to the destination node, whose address is also indicated by the upper-layer protocol. One of the tasks of the link layer is to check the availability of the transmission medium. Another task of the link layer is the implementation of error detection and correction mechanisms.

The IEEE 802.x specifications divide the link layer into two sublayers: logical link control (LLC) and media access control (MAC). The LLC provides network layer services, and the MAC sublayer regulates access to the shared physical medium.

Protocols: ATM, Fiber Distributed Data Interface (FDDI), IEEE 802.11 wireless LAN, Link Access Procedures, Point-to-Point Protocol (PPP), Serial Line Internet Protocol (SLIP) (obsolete), Unidirectional Link Detection (UDLD), x .25.

The network layer is designed to determine the path for data transmission. Responsible for translating logical addresses and names into physical ones, determining the shortest routes, switching and routing, and monitoring network problems.

Example: IP/IPv4/IPv6 (Internet Protocol), IPX (Internetwork Packet Exchange), X.25 (partially implemented at Layer 2), CLNP (Connectionless Network Protocol), IPsec (Internet Protocol Security) , ICMP (Internet Control Message Protocol), RIP (Routing Information Protocol), ARP (Address Resolution Protocol).

The transport layer is designed to deliver data without errors, loss or duplication in the sequence in which it was transmitted. It does not matter what data is transmitted, from where and where, that is, it provides the transmission mechanism itself. It divides data blocks into fragments (UDP datagram, TCP segment), the size of which depends on the protocol; short ones are combined into one, and long ones are split.

Example: ATP (AppleTalk Transaction Protocol), FCP (Fiber Channel Protocol), NBF (NetBIOS Frames protocol), NCP (NetWare Core Protocol), SPX (Sequenced Packet Exchange), TCP (Transmission Control Protocol), UDP (User Datagram Protocol) .

The session layer of the model is responsible for maintaining a communication session, allowing applications to interact with each other for a long time. The layer manages session creation/termination, information exchange, task synchronization, data transfer eligibility determination, and session maintenance during periods of application inactivity.

Example: ISO-SP (OSI Session Layer Protocol (X.225, ISO 8327)), L2F (Layer 2 Forwarding Protocol), NetBIOS (Network Basic Input Output System), PPTP (Point-to-Point Tunneling Protocol), RPC ( Remote Procedure Call Protocol), SMPP (Short Message Peer-to-Peer), ZIP (Zone Information Protocol), SDP (Sockets Direct Protocol).

The representative level deals with the form of presentation of information transmitted over the network, without changing its content. Presentation layer - coordinates the presentation (syntax) of data during the interaction of two application processes: converting data from an external format to an internal one. At this level, data encryption and decryption can be performed, thanks to which the secrecy of data exchange is ensured for all application services at once.

The application layer is really just a collection of various protocols that enable network users to access shared resources, such as files, printers, or hypertext Web pages, and to collaborate, such as through the email protocol.

Example: HTTP, POP3, SMTP, FTP, XMPP, OSCAR, Modbus, SIP, TELNET.

The IPX protocol is designed for the transmission of datagrams in connectionless systems, it provides communication between NetWare servers and end stations. IPX packets can be broadcast.

The SPX protocol is a serial packet exchange protocol. It is a connection-based transport layer protocol. Works on top of the IPX network protocol. It is assumed that a connection is established between the workstations before the message is sent. At the SPX protocol level, the reliability (reliability) of information transmission increases dramatically. If the packet is transmitted incorrectly, it is retransmitted.

The NetBEUI protocol, due to its primitiveness, requires the least resources and provides the highest speed, but due to a number of inherent disadvantages, such as the impossibility of routing and strong noise in a large network, NetBEUI can only be effectively used in small local networks (IBM developed the NetBEUI protocol for local networks containing about 20 - 200 workstations).

TCP is a connection-oriented protocol located at the transport layer of the TCP/IP stack, between the IP protocol and its own application. The IP protocol deals with sending datagrams over the network without guaranteeing delivery, integrity, the order of arrival of information and the readiness of the recipient to receive data; all these tasks are assigned to the TCP protocol.

SMTP is a network protocol designed for transmitting email over TCP/IP networks. Work with SMTP occurs directly on the recipient's server. Supports functions: connection establishment, authentication, data transfer. Currently, SMTP is the standard protocol for email and is used by all clients and servers.

POP3 (Post Office Protocol Version 3) is used by the email client to receive email messages from the server. Typically used in conjunction with the SMTP protocol. Mail messages are received by the mail server and stored there until the POP3 application is launched on the client workstation. This application establishes a connection to the server and retrieves messages from there.

IMAP is an application layer protocol for accessing email. Similar to POP3, it is used to work with incoming letters, but provides additional functions, in particular, the ability to search by keyword without saving mail in local memory.

SMB/CIFS is an application-level network protocol for remote access to files, printers and other network resources, as well as for inter-process communication.

HTTP -- "Hypertext Transfer Protocol", an application layer protocol for data transfer. HTTP is now widely used on the World Wide Web to retrieve information from websites.

HTTPS is an extension of the HTTP protocol that supports encryption. It provides protection against attacks based on network eavesdropping.

FTP is a protocol designed for transferring files over computer networks. FTP allows you to connect to FTP servers, view directory contents, and download files from or to a server. The FTP protocol is an application layer protocol and uses the TCP transport protocol to transfer data.

4. ROUTING BASICS

4.1 Network equipment

Network cards are controllers that are plugged into expansion slots on a computer's motherboard and are designed to transmit signals to the network and receive signals from the network.

Hubs are the central devices of a cable system or a star physical topology network, which, when receiving a packet on one of its ports, forwards it to all the others. The result is a network with a logical common bus structure.

Repeaters are network devices that amplifies and re-forms the shape of the incoming analog network signal over a distance of another segment. A repeater operates at an electrical level to connect two segments. Repeaters do not recognize network addresses and therefore cannot be used to reduce traffic.

Switches are software-controlled central devices of the cable 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 are standard network devices that operate at the network level and allow you to forward and route packets from one network to another, as well as filter broadcast messages.

4.2 Routing

topology network communication routing

Routing is the process of determining the route for information in communication networks.

Routes can be specified administratively (static routes) or calculated using routing algorithms based on information about the topology and state of the network obtained using routing protocols (dynamic routes).

A routing table is a spreadsheet or database stored on a router that describes the mapping between destination addresses and the interfaces through which a data packet should be sent to the next router.

The routing table usually contains: the address of the destination network or node; destination network mask; gateway, indicating the address of the router on the network to which the packet must be sent to the specified destination address; metric -- a numeric indicator that specifies the route preference. The lower the number, the more preferred the route (intuitively represented as distance).

Static routing is a type of routing in which routes are specified explicitly when configuring the router. All routing occurs without the participation of any routing protocols.

Dynamic routing is when table entries are updated automatically using one or more routing protocols.

IP address is a unique network address of a node in a computer network built using the IP protocol. The address consists of two parts - the network number and the node number in the network

Automatic distribution. With this method, each computer is allocated an arbitrary free IP address from a range defined by the administrator for permanent use.

Dynamic distribution. This method is similar to automatic distribution, except that the address is issued to the computer not for permanent use, but for a certain period.

Figure 4.1 Routing in TCP/IP networks

DNS is a distributed computer system for obtaining information about domains. Most often used to obtain an IP address by host name (computer or device), obtain information about mail routing, serving hosts for protocols in a domain.

ARP is a low-level protocol used in computer networks, designed to determine the link layer address from a known network layer address.

A node that needs to map an IP address to a local address generates an ARP request, inserts it into a link-layer protocol frame, indicating a known IP address in it, and broadcasts the request. All hosts on the local network receive an ARP request and compare the IP address specified there with their own. If they match, the node generates an ARP response, in which it indicates its IP address and its local address and sends it already directed, since in the ARP request the sender indicates its local address.

Address translation is performed by searching the table. This table, called the ARP table, is stored in memory and contains rows for each host on the network. Two columns contain IP and Ethernet addresses. If you need to convert an IP address to an Ethernet address, the entry with the corresponding IP address is searched.

Figure 4.2. ARP table

The ARP table is necessary because IP addresses and Ethernet addresses are chosen independently, and there is no algorithm for converting one to the other. The IP address is selected by the network manager taking into account the machine’s position on the Internet. If a machine is moved to another part of the internet, its IP address must be changed. The Ethernet address is selected by the manufacturer of the network interface equipment from the address space allocated for it under the license. When a machine's network adapter card is replaced, its Ethernet address also changes.

5. CONCLUSION

During the period of practical training in the specialty profile, the following were considered:

1) principles of constructing a LAN;

2) factors affecting network performance;

3) OSI network model;

Posted on Allbest.ru

Principles of operation of a local network. Design and calculation of local computer networks Schemes for constructing local computer networks

The concept of a local network

Types of networks

Drawing up technical requirements

Schematic design

Basic LAN characteristics

Basic local area network topologies: advantages and disadvantages

Detailed network design

About cable types

Necessary equipment

End network equipment

Software

Nuances of designing local networks

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